practical wireless 1957 february - the-eye.eu archive... · tv•valves•radio 6j5 6.17 6vfi 6k7...

BUILDING THE MINI-SET

-FEBRUARY1957

EDITOR-FJCAMM

MSM,®mmmmm

Hft^BSi '!"'. £l'

\ mm

PRACTICAL WIRELESS February, 1957

Shpteme, Ut, Gewtces

ICROMITEDRY ELECTROLYTIC CONDENSERS

These small but high quality electrolytics have proved so popular that the

range has been greatly extended. The use of high-gain etched foil

electrodes keeps size and weight down, making the condensers suitable for

suspension wiring. Conservatively rated; long shelf life ensured: green

plastic insulating sleeving prevents short-circuits.

CapacityPeak

Surge

Volts

Dimns. in Ins.Type

No.

List

Price

Eachta «*

!Volts Length Diam.

5025

1

816

32481632

12

50350350350350450450450450

15

60400400400400550550550550

IfIdl|

Hi2£

Ifl

•il

If

ifJ!

i

g><v841

14l*

CE87BCE88DECE86LCE99LECE9ILECE93LECE99PECE90PECE92PECE94PE

ii3/3«/-

«/-

3/33/65/-

7/6

I

THE TELEGRAPH CONDENSER CO. LTDRADIO DIVISION : NORTH ACTON LONDON • W.3 Telephone : ACOrn 0061

i VHF/FM TUNER

Built tii the usual Wll standard of craftsmanship, this gives outstandingperformance, due to specialised design incorporating advanced circuitsto take full advantage of the VHF/FM transmissions.

Permeability tuning, automatic frequency control, and temperature-controlled circuits give rock-steady tuning with no drift. Foster Seelcydiscriminator and cathode follower circuit. The wide frequency range

—

87. 5-108 Mc/s.— covers all proposed British stations, and also those onthe Continent and in U.S.A. Latest type tuning indicator.

The hign sensitivity enables this Tuner to be used in areas whereFM transmissions are normally regarded as out of range.No interference with television, due to negligibleradiation figure. Price £25 (inc. P.T.)

<9

See and hear this endall other Stentorian HighFidelity equipment at

our London office (109

Kingsway, W.C.2) anySaturday between 9 a.m.and 12 noon. Leaflets onall the outstanding W.B.products on request.fjfgh Rdkfity atrea/ntfc cost

WHITELEY ELECTRICAL RADIO CO. LTD . MANSFIELD • NOTTS

February.. 1957 PRACTICAL WIRELESS 793

i-boiid a cheap ta-nm m

iiuiiii this exceptionally seh-Sftlve double triodC radio.Uses unique assembly systemand nan be built by anyonewithout any radio know-ledge whatever in 4r> minutes.

Handsome black-crackle steel case withspecially made black and gold dial withstations printed. Size of radio only BiilJ. :.

Sin. x ;tln. Covers all Medium and Longwaves—uses one only all-dry battery. H.T.consumption only 1 to 1.5 mA. Uses personalphone. Ideal for Bedroom. Garden, Holiday,etc. Many unsolicited testimonials.Mr. Norton of Oxteil. writes : Yesterdimeveninq on the Medium -waveband. I counted32 separata stations : i am very pleased withtin-*", which (s well worth the money, ill ILDi hi: • SKYitOMA - now ! Total build-ing cost—Everything down In last nutand boll -17 '6 (Pontage, etc.. 2 -j—withfull set of clear, easy-to-follow plans.(Parts sold separately. Prided Parts Lists,etc. 16.)

AT last : in response to many requestswe DOW present Ihe DOI'ltLL TRIODE'• SKYPOCKET," a beautirully designedprecision POCKET RADIO. No radioknowledge needed :—EVERY SINGLEPART TESTED BEFORE DESPATCH :

our simple, pictorial plans take you slep-by-atop. This set has a remarkable sensi-tivity due to painstaking design. Cover- allmedian] waves 200 to 550 Metres. Size only5jin. x flin. x 2in. in strong. Transparentcase with panel, cover and ivorino dial. Areally personal-phone, porkei.-radio WITHDETACHABLE ROD AERIAL. Self.contained all-dry battery operation. Aver-age building time 1 hour. Total BuildingCost—Including Case, Double TriodeValves, etc., in fact, everything down lothe last mil and bolt—ONLY 37 6. Williplans. Postage, etc.. 2 .-. C.O.D. 1 6 extra.(Parts sold separately. Priced Pari

etc., 1'6. 1 Demand is certain 10 lie bcavj—so SEND TOD.W :

Total building cost includingchoice ol beautiful walnutveneered cabinet or ivory orbrown bakelite. This i- in,.levies! possible price con-sistent Willi high Quality. No radio know -

ledge whatever needed . . . can be built l>>anyone in 2-3 hours, using our very simple

allow diagrams. The terricircuit of the "OCEAN-HOPPER "

covers all medium and long waves wftnoptional negative feedback, has razor-edge selectivity, and exceptional!lone. Price also includes ready drilled andpunched chassis, set of simple easy-to-follow plans—in fact, everything ! Allparts sparkling brand new—no iiml;

I

Everj single nan letted before des-Salcluiig. Uses standard 0( lal-base valves :

(Tre high-frequency pentode reeding into6JSG anode-bend deteotoi triode, coupledI<| (AGO powerful Output beam-powertetrode, led by robust rectiller. For A.CMains. 200-250 Volts How running costs- -

approximately 18 Watts !>. Size I2it> '.

6in. x Bin. Hiiiid lids long range power -

fill midgel NOW. All parts anil set orplan-, £5.7.6. fPost and packing 36.1 Partssold separately. Priced Parts U

CAN BEBUILTFOR

5716

WE'VE DONE IT AGAIN 1

. . . our design department. Inresponse to a great manyrequests have designed this

• SKYPIXJE " Vest-PoekelTRANSISTOR RADIO whichgives a superb performance,1l is powerful and highlysensitive. Size only Kin. X 3;in. X 5in.

the weight under 1 ozs. I—yet It fea TWO-STAGE receiver' covering all medium-waves, working entirely oil a tiny "pen-light " battery, .which costs (id.— fits insidethe east- -and lusts many months. Usespersona! plume and has push-buttonI.I'MINOl S On Oil Switch, Every parttested before despatch ! SPECIAL STEP-BY-STEP PLANS for ABSOLUTE BE-GINNERS. Total building com! includingease, transistors, etc., everything down inHie las! mil and boll—ONIA 57 6 Williplans. Postage, etc.. 2-. C.O.D.. 1/6 extra,(Parts sold separately. Priced parts list

etc., 1/6.1 As thejbuilding cost Is absolutely'• rockbottom " (it mightIncrease Inlet . DEMANDWILL BE VERY III.A\ \

-SO SEND TODAY :

BUILD THIS

FRYING-PAN'

SET FOR

BUILD THE'MINI ATOM'FOR

111 II.D Villi!MOTHER ii

WIFE tl1" i' y i 11 g - P aradio ! Sights

I vrc i p C ti i f

co v e r I n gall Med-ium andi. D n g -

W a v e s .

11 a e

nor in a 1

S i I e .

s p e a ice p

and givesexcel lenttone due1 w a 1

1

" baffle"

effect. Costs only Id. for about 76 boms use.ideal for the kitchen, bedroom, etc. Hobustdesign. For &.C. mains 1 200-250 volts.TOTAL BCTLDING COST includingnili'i'or-linisli frj tag-pan, doiible-lriodevalves, step-by-step beginner's plans,nuts, iiuits, etc.. only 77 6. Postage, ete.2.6. C.O.D. t/6 extra. (Parts soldseparately.Priced parts list, etc., 1 (i.

1 PRICES M \Y<(> IP : -SEND NOW.

W~ J Vs 69. PRESTON STREET

INTRODUCING TnE MIVIMlm—to till a big need ! Anpowerful all mains one valver. size onlytijin. X 4!in. X 2Sin. .NO AERIAL OREARTH NEEDED ! Costs appro:Id. for 860 hours use. Uses latest contai 1

OOOled rectiller and works head]completelyhum -free- forpersonal ti

hear all the Continental progranbed without disturbing othersLUMINOUS push-button 0110:1and station printed dial. For A.C. main-200.250 volts. Covers all Medium-Wave.(provision for including Long-Waves)REALLY LOW III ILIUM. COST OlONLY 596. including ( a-e. Valve, Nuts.Bolts. Step-liy-Slep ISeginnei - Plan-.etc.—EVERYTHING ! -Postage, etc., mC.O.D. 1 6 exl ra 1 Pari - sold seiPriced parts list. etc.. 1 ii.

1 Tills WILLBE A WINNER so SEND NOW I

Dept.

BRIGHTONPWF

Orders dispatched Ixi return or post. Checnes accepted. Cash on delivery lit ,-

Government and Research EsMltshmnts. Complete range or component- anWELCOME : Shop

794 PRACTICAL WIRELESS February, 1957

RADIORECORD PLAYERSGarrard RCI20/H. 3-spd. auto andmanual changer (List £12/15/-), £7/19/6.

Post 3/6.

Collaro RC3/554. 3-spd. single player.

£6,10 - Post free.

B.S.R. TU8. 3-spd. single player, 92/6.

Post 3/6.

DECCA PICK-UP with t.o. crystal headHl/G. I. p. and standard, brown, with rest,

32/6. Post 2/6.

Ditto, B.S.R. , cream finish, 35/-. Post 2/6.

BRAND NEW AND PERFECT16 METAL CONE C. R. TUBESBrief Specification : 6.3 v. htr,, ion trap,

14 kV. E.H.T., wide angle 70 degrees,

standard 38 mm. neck, duodecal base,

mag. focus and deflection. LengthI7-Ill6in. Circular shape. Guaranteedby us for 3 months. List £23/9/10.

LASKY'SPRICE £8.9.6

Carr. & Insur.

22/6 extra.

LASKY'S BATTERY PORTABLE

FOR HOME CONSTRUCTION

ON PRINTED CIRCUIT

COMPLETE PARCEL contains printedcircuit, all components, valves, case,

diagram, and all instructions for building

this latest design 4-valve superhet port-able, rned. and long waves.

All components available separately.

CIRCUIT DIAGRAM, data, instructions,

and shopping list, 1/6 post free.

POWER UNIT for above, also suitablefor other battery portables. CompleteKit including printed circuit, 45/-.

TRANSISTORS, SPECIAL OFFER.Junction type suitable for use in local

station receivers, amplifiers, pre-ampli-fiers, etc. Each, 10/-. Post free.

LAIWKW'S IIIUIH1IW IIOAI») II lb.

42, TOTTENHAM COURT ROAD, W.I. Te/ephone : MUSei/,-n 2605.

370, HARROW ROAD, PADDINGTON, W.9. LAD 4075 andCUN I979.

Open all day SATURDAY. Half day Thursday.

PLEASE ADDRESS ALL MAIL ORDERS TO HARROW ROAD.

A REALLY FIRST CLASS

F.M. TUNERFOR HOME CONSTRUCTION ON A

PRINTED CIRCUIT

Note these star features :

—

ic High Sensitivity.

• All Brand New T.C.C. Condensers.* Aerial Coil and R.F. Coupling Coil

Printed on circuit.

jlr 5 Valves & 2 Germanium Diodes.

By the use of a printed circuit the I.F.

and R.F. amplifiers are extremely stable

at maximum gain and results are con-sistent on all tuners.

Valve line-up—R.F. Amplifier, Z7I9 or EF80.Mixer and Osc. B7I9 or ECC85.1st I.F. amp., W7l9or EF85.

2nd I.F. amp. W7l9or EF85.

2 Germanium Diodes GEX.34.Driver Limiter, Z7I9 or EF80.

CAN BE BUILTFOR 8 GAS. appro*.

Full instructions, data, 'and illustrations'

2/6 post free.

All parts available separately.

TV • VALVES • RADIO

6J56.17

6Vfi6K76K.86SN76SL71.SK76S.I7

PY80PY8I6AL56.16

6646X56X46AG7PL81PL82PL836AC76H66A76B46Y66U461 .6

7H77Y4 8/6

si- 7C5 8/6

lt* 5Z4 8/6X 6 5U4G 8/6

6 - 80 91-

11/- VU39 8/68 6 5Y3 8/6

8/6 PCF80 9 64 6 I2A6 7

76 I2AH711) 6 12/-

10 6 I2AT77/6 10 6

7;6 12AU7

6/- 10,6

7/6 12AX77/6 106*/- I2SH7

12 6 7/6

1 1 - 12Q7 9/12 6 I2K7 7/6

5,6 35Z4 8/6

2/6 IT4 7/-

11/6 3S4 8 66, 807 7/-

86 832 22 6

15/6 954 4-12, .955 5/-

8/6 EF36 4/-

8/6 EF39 7/6HF42 12/6

I- F50 4 -

EF54 5/-

EF91 8/6

EF37A 9,-

ECH4210 6

EL91 56EY51 1.3 6

KZ80 8/6HL23DD

8,6ECC81

10 6

ECC8210 6

ECC8310/6

ECC8412/6

ECC8510,6

ECL8010/6

PCC8410/6

PCF8212/6

Pen46 6/6U25 15/6

IR5 8/6

R1155 RECEIVEREX R.A.F.

NICECONDITION £6 AIR-

TESTED10/- Carriage.

POWER UNITFor above RX, with 6V6 outpuistage. Input 200-250 A.C.

£4 Ca5)!

a8e

BENDIX TA 12G TX

£4.10.0New condition. With 3 807, 4I2SK7 Valves. A Bargain whilethey last.

TELEPHONE HANDSETSSound-powered, no batteries re-

quired.

£» 1 Per*»* Pair.

DYNAMOTORSEx U.S.A. Surplus new comlition.

Input 28 v. DC. 1.6 amp. £1Output 230 v. D.C. 100 mA. **Input 27 v. D.C. 1.4 amp. OO/COutput 285 v. D.C. 60 mA. LL V

CONDENSERS100 Assorted .1 mfd. 5 pF. 15/-.

RESISTORS100 Assorted \, i, 1, 2 watts, 12/6.

MEIERS8 Assorted m/i, m c, T.C.

£1.2.6

30, 50, 100, 200, 300, 500 mA.Meters, 5,6 each. 1.5 kV. Electro-

static, 12/6. 250-0-250 micro-amp.,£1. 0-500 micro-amp. Meter, 15,-.

TELESCOPIC AERIALSExtend from I2in. to 14l"t., 8/-.

CONDENSERS.— Electrolytic.

450 volt working, 8 ml'd.. 2/6; 16mid., 3/3 : 8 t-8 mid.. 3/9 : 20 mfd..

3/- ; 8 |16 mfd., 4/6 ; 16+ 16 mfd..

4/6; 32 -I- 32 mfd., 6/-. Bias,

25/25, 50/50, 2/- each.

POTS.—W/W or Carbon to 2meg., 2/6 each, with Switch, 100 K.,

|, i, I, 2 meg., 4/- each.

SP41, SP61, RK342/6 each.

VINERS(MIDDLESBROUGH)

26, East St., Middlesbrough

TEL. : 3418.

Feoruary, 1957 PRACTICAL WIRELESS 795

ilt to the highest standard !

CAT. No. CAB/02. \ ..,

Bureau-type cabinet In .. roe-dhim :...i '"i in n highly liunr-<4 Waloill

uuf-id. dimnn-kii.-.. I emit h L'SiJii... .i-i-n,

Ifiln. I leighl XSMd. Sloping ...limh panelon right-hand side approx, I3l)>. IOj nRemovable baseboard on right-band «Mi .

approx. I3{1n. .\ I Sin. Large record cmn-finriraoil InsWo the cabinet, locatedthe top on leri-haud elite.

/'(-A/

left-hand vide. . rt „CASH ONLY 12 GnS.

•„,„ 20'-.

CHASSIS

CAT. NO. CAB/03. 1

Boat ;!-•> ]• I ibiuel of (hi vers blgheelqtiaHtylnBpecially electe VVnlnut.veneer-

ior. I.lghl Bj • ••r .

.-

ECextue lining Out rti dlmeu-piouc, length Win. depth ITJin., height:

-:'-"- Klopini i. i panel ™ right-hand

•M- appmx. I Bin. \ K'JIn. Removablebaseboard or right side approx, iri.Hn. .\

Km.. 'i'\... .-.in-. it ri

M..1.I- ill |||,- III- ,

CASH

16 j Gns.?,:

Miperhcl i h.i--;- ... Uttexl Hr«ign andTechnique. General 3peeiftaation» apj ltcab|iIn all model*. \ 1

1, 200 SAD ...l'. SOonly. (Suitably Hi multi-coloured -I uw din •

ibr horizontal type, Slow- t ; . ->, tnU injr

drive. Pnl i IrI i Automat lc VolumeControl. Negative tecd-baok rrom outputtranstormei secondary. Sucketapi ivldod ft*lerlal, garth, Oram, Pick-up and Bxtauaimirtpeaktr. nonneeti ™ ptoi idcd to Oram.Dlotor .-.,!, u-..ii...| i. v Ohawii OtiKM fnritoh.All Indiictai oet h.-in an exceptional]; hlgh-gvalue. Tii- Ami;.. section l> designeBret-rate reprodnFttau on Radio and'•r.i!,n-ii!i,.ii.-. Tho i mi controls have I pgiven an extrn alii nibi mk allI vl-.-- : .... .-•

1 .

AM/FM (Four Waveband) aijrjilren yup.-ri.i-i with permeabUlt] timeiKM viif band. Magic Bye tuning. PJI

- - JenalUvltj ,9 vale I;

in. in .woillator radiation Lew Hi.- n »kilocycles drift. Slanal-to-nbetter than 28 db. -iwliiu. long •

Biln. high .-,- 7*iii. deep. ftaatamrIS months tor i-h.i-.--i- I :: monl-ln

CASH

22 Gns.FIYI TUNERS

-.. tth -..i-iiiiihIi-.i

grid i:.l<\ r-i.-u,',- followed b] additiv.-..'Mir using ii FCCSfl twin triodt...iii-i ptnneabilitj tuned unit. i\.

f.P. ataget ensure maximum gam wliliHKTS double ilo le at u.i.t.j ,:

Frequency coverage n( 63-101 menue) -i, - -..'l...-,- adeqi ate overlap. Verynn«i .-

i out.

CAT NO. CAB/04, ffiminuin-., cabinet nl the rerj hlghrel qualitywith Bveaoi we b Intei - o iui I puU-owhue on the right-hand side rani

- an >Uty iwi! beariogi, i.

a

.-.-v.-ivii baffle board with speafeei em .-i

no right-hand xide belov ohan -

panel. Ovrral /• iSfn. Ion« -

. [Bin, deep.CASH

edit Term£13.10.0

CAT. N0.CR/AFM49/PPVMfVBV Bim.l i I »'«

i utpul Iwli-' lond ipi - i,r,

or on t'redi I - ii

."-i, -. •'.-,, and Carriage lii -

CAT. No. CR/AFM47.with I'M VHP Band. i fotvebandel

' '>.-ii;i T.-.

Patl '.-'.; «'../ Varrlagi 15 -.

CAT. No. CR/A. ..-.:,:

Siipeiii.-i.

:: .. .

Patbtng ,n„i •;.,:,„,, 12 «.

26

23 i

12

11

.'. Pn-li-

Gns.

Gns.

Gns.

* LOUDSPEAKERS, GRAM

CAT. No. FMT/A. tv,

l.-l. :.- ..,;!: rtj n |;.,,,

ISin. Ions i:;i-. overall depthTjiu. high (appnu.l. CASHor on I'ldlil Turin.. -|C| *»_„/,.. /;.,.,.;.,,/ i',;,,-.'u./.. 12. «. lOo UllS.

CAT. No. FMT/B.<r,U,c Magic-eye. 1 nbexe 1. 11 ;).,. Ions\ 5?in. overall depth \ -! in. high.

PatHnymdraniam 12 ii. *13.1 5.0

AMPLIFIERS, TAPE-RECORDER equipment, etc., available atkeenest prices. Send for large illustrated Catalogue.

ALL FULLY GUARANTEED. Generous extended credit terms on orders exceeding £15.Dealers supplied at full discounts.

DOMESTIC DIRECT SALES LTD90 JUDD STREET, LONDON, W.C.I. Telephone : TERmfnus 9876


IN FRAY LAMPMeans real comfort in bed as It emitsInfra H(;cl Rays which warm andkeep you healthy.• Economical.• Costs only Id. per hour telec yat Id. per unit).• Absolutory safe, no health or lire

risk.

• Meal lor many other uses— overpet's basket, rearing pup, (Slicks,

OVeff desk, work bench, etc, '

• All -complete and ready to work.

Price 36/-I'ost & Pocking 2/-

.if 11**.-

i

F.M.. TUNERThis tuner is based upon the verysuccessful circuit published byData Publications. We have madeup models at all branches and will

gladly demonstrate. Stability Is

extremely good and making andaligning most simple. Cost or all

parts including valves, preparedmetal chassis, wound coils and stoveenamelled scale, slow-motion drive,

pointer, tuning knob. In fact, every-thing needed is £6:12,6. Data is

included free with the parts or is

ile separately, price 2.'-. Extrafor fringe area model. 20'-.

SOMWEAVEThis reallylovely loud-speaker fabric

a we oflV.r a t

Si approximately a

H i bird of to-day'sPcost. It Is 42in.

wide and ourprice is 12,'- peryard, or panelsI2in. X 12m.. 1:8each. This is

also very suit-able for coveringplain woodencase, for port-able radio ampli-fiers, etc.

Ths " ESTRONIC " Band III -Converter

£

i<B To-day's best value in Hand III con-

tR vorters suitable for your 'J. v. oriu money refunded. Complete ready to

operate. 49 6 r.o:: •;ia:'iv- or 69<6

?H mams, post and insurance 3/6

CABINETS FOR ALLThe CONTINAAnother addition toour range of cabinets.This IS Of new revolu-

tionary design, styledafter the best of con-tinental mdios. Ex-ternally, it is finishedin highly polished dark.valnut veneer, withpanelling picked outin gold. Interior is ol

same very high stan-

dard. Its veneer being

,ighl. mahogany which contoaats nicely with the dark

walnut and generally gives a very pleasing appear-

ance. The doors slide on metal runners and are. iii.u-u

with gold insert linger plates. A rcaily excellent

cabinet for any home- size :ti'i. I'm. long, i it. sin.,

deep. 2ft. lHn. high, including legs which are 10m.

from floor. Motor board 12!. X ITin.. ee.uipment apei-

ture 171 x Hj.in. gives ample space, lor 8m. speakei

.

Ample storage space for recordings. Plica il»:l».->

carriage and insurance 20,'-.

TRANSISTORSRed spot, replaces Mal-

lard OC71. etc.. 10'-.

Blue spot suitable R.F.

up to 1.6 Mc.s. 15/- each.

POCKETTRANSISTORRECEIVER

All the parts to buildcigarette box ;-v<i'-:, \

.

£2.17.61 includes l-'errlte

aerials but not the ear-piece, battery or case,

The " CRISPIAN

Portable Radio

" A 4-valve trulyportable batteryset with verymany good fea-tures as follows:Feri'ite rod aeri-als, low con-sumption valves.superhet cireuitwith A.V.C.ready - built endaligned chassisif required, beau-tiful two tonecabinet coveredwithl.C.l. rexineand Tygan.Guaranteed re-sults on longand mediumwaves anywhere.All parts, in-cluding speaker

and cabinet, are available separately or if all

ordered together the Brioe is £715;- complete.post and ins. 3/8, ready-built chassis 30:- extra.Instruction booklet free with parts or aw I le

separately price 1.6.

INSTANTUS HEATER

Tractica! Convector heater 1 ..w. -ifi. lonr. maigauge sheet steel (galvanised)-. Can be used lor

e house, up to three heaters can be controlledby one thermostat.Trice £2.10.0 or with thermostat £4.5.0. oarriaa

Wrap our lieateipipes in your loft to prevew g irei

:e

up. 21 yards with l'u I;

I

- ruotiiMinor pack .1-1 yards. £1,'- -.

Major pack £1 yards, £1 10 .-'-.

COMPONENT BARGAINSTabular Ceramics 2.000pr., 1,000 pf,.

S00 pf. all 5 - per dozen,

.1 nifd. 360-VOlt metal cased •m-denscrs by Dubiliefr—small size 3:6doz. or 36,'- gross.

Philips Trimmers (i-iso pf, 1 - each or11,'- doz.

Moulded Mica Condensers, wellmixed assortment 3 - doz., 30 - gross.

Silver Mica, well mixed assortment,3/- doz.. 30'- gross.

50 nifii. 50 v. Bias FdfldensersT.C.C. 1,'6 each, ID- per doz.

Ceramic Trimmers, 5 to 30 pr.. 6d.each. 5.- doz. 20 to 60 pf. fi<l. , ach,8.'- doz. 20 to lift pf.. 13 each, 12.-

doz.

l-:ari>ieei'-nii<-ropIione. Amei-lean

midget type 3'6 each. 36- doz.

NEW CIRCUITOCCASIONAL 56. We have evolveda new T.R.F. circuit and have hadreally good results, equal in fact to

many superhets. You really shouldtry this circuit. All parts includingvalves (6K7. 6J7. BF8 and 6X53 andbakelite case with back cost only£fi 10 -. plus 2/6 post and Insurance.Data included with I he parts is alsoavailable separately, price 2-.

DON'T STUMBLE INTHE DARK

install 2-way switches.Our outfit comprises : :«) yds. Multi-core cable, two 2-way switches, twowoodblocks. Pull instructions. 19;3

post and insurance 2/6),

ELECTRIC BLAN ICETWIRE

Waterproof P.V <:'. so..... ; .

I

foot—1 per yard. 1

ket, fil post free.

m mains postal P»ce £2.10.0 or with thei osts ——__—_ „__»_=,

^ffiBBEfEfflffiBBBEE*S»RBffiBB»»BfflEfflEEE5EESeE-EeE'EE«ffEHaaBEffffffff.ffffEPTESEIBe:-E'WEEEBff

February, 1957reoruary, ivj/ pkaciICAL WIRELESS 797

B'-sfisssssaQ9asam9s»>ssi«i««»ssa«a!Qaiai^saassais»ssaas9ai»aassaa9»a9aaBfiaaBaTHE SKYSEARCHER I TUC iib.ii t \r n(ii><**i* - n*Ar» n . » ttTHE SKYSEARCHERAn all mains set for 19 S

THE UNI—T.

'i Mir Is 1 2-valve plus-metal reetineiset useful as an educational set torbeginners, also makes a Bne secondset 'ov the bedroom, workshop, etcAll nails, less cabinet, chassis andSpeaker, 19 6. Post & ins. 2(1. DataCree with parts or available sepe16. 3-vaivo battery version at*oavailable at the same price,

FLUORESCENT LIGHTS

CHASSIS 'ASSEMBLYiIgii

Superhet Chassis. 3-wavebamL col- a,ourecl scale, scale pan, pulleys, mdriving head, springs, drum, etc. EHScale si7.o 14Ho. x 3}in. Chassis size S!Bin. x loin, x 2in, Price 15.- plus 16 ffipost. Note : Wo can supply cabinet £td

for tws. Price 396 plus"

an! Insura a- carr.

'iideubtrdlv the most up-to-date televisor lor theborne constructor, Sou w«i build an or onto earl and'

; «.

]• *wJU be equal to a factony madeJent. What other constructor r.v. has aU these

* Made up units if required.

* aii miniature valves,*- Metal rectifier^

* No expensive transformers.* lS-channel circuitry.

* Multi-vibrator time bases.A- Perrujconhe, E.H.T. and scan colls+ liltffi Mrs T.F.

*- Suitable foi RMS modern 12, 11 or 17in. tube.ft Modern contemporary cabinet if required.

MULLARD AMPLIFIER "510"A Quality Amplifier desigMilliard. Power output rir?i',\. \i\

watte, Frequency response almostHat from 10 to 20,000 c.P.S. Pot usewith the Aoos • Hi G " and othei goodpi! k-UPS. Made un and ready to Worliis £12-10- or 85- deposit, plus t" -

carriage and insurance.

19/6 AMPLIRER.

Tht i| are a complete fluorescentlighting- fitting. Built-in ballast andstarters—stove enamelled white andready to work. Ideal for the kitchenover the workbench and in similarlocations.•Singh- 40. -iff.. 3in. Ions. USflS B 40

, „..,ube. Price 39 6 complete with J™.building-cost (leas tube) is only £31'10 Dins in -tube. Carriage and ins. 5/6. carriage and insurance. AH SggSKS U«»ln 20. Uses 2 20-watl standard .

momB?; *WJ information and data free w Ui nans ortubes. Price 29, 6 less tubes. Carriage i

available separately, price 3.6. ' C1

and Ins. 1.6. ——______________

T.V. CommercialisingOutfit

Do It yourself—it's reallyquite easy.

i'ou will manaue il in anevening and we guaranteeSl.'CTRSSFl „ REStT.TSOK MONEY BACKOur parcel contains :—/. /'..'.. Aerial. 88R. /./..;.Uavm Lead, i.t.a. con-

/./.!.. BBC litter-ference Eliminator,A special bargain pi

all the above items •(

bought together Is £8 10 -

Or £1 10 - down and H paymeats or £i. (Post andInsurance- 1 6). Full detailswith Illustrations 16.

Construct a powerful fchrei r .i

mains amplifier. Ideal for die,. -e-,parties, etc. Complete, less chassis,cabinet and speaker 'available If

required). Data 1,6 '.free with parts),

OFFICEINTERCOM.

This i- a 2-station" mast '-I " unit com-prising an A.C. mains

d push-pullwlib built-in

P.M. speaker whichacts as microphone orloudspeaker dependingon whether switch isvet to -' talk " or• listen. 1

' Complete inpolished cabinet readydo work, rricc com-plete with on* sub and loon, twin wire, S6.'19ij. plus

lageand Insurant a. Substations lw0 each.

Uses high-efficiency coils, ooverslong and medium wavebands and _fits into the neat white or b-own H3bakelite cabinet—limited quantity tnonly. All the parts, including cabinet. _valves, in fact, everything. £4-10-0. 3?plus 3/fl post. Constructional data rafree with the parts, or available Sseparately 16. fp

HUGE MINISTRY PURCHASE 1R.I 1 55—yours for £2 down _

Frequency 75 kc's to is mc/s- 10 (Umetal case- -robust receiver m

£60 tomake ---

willg i v eyears ofs e l'vlce.

verylittle used. Pricemeats of £2.Carr. & tramit case 15- ex.

CAR STARTER CHARGER KIT w<All parts to build 6- and 12-volt racharger which can bo connected to a RK•'flat battery and will enable f£the ear to be started Instantly. Kit n?comprising the following :— _Mains transformer S_8 m5-amp. rectifier 17 6 mResruiator Stud .Switch ae S?Resistance wire g . ffi

Resistance Former 2 6 S*Mains on oil Switch 2 6 _0-5 amp. Moving Coil Meter 12 6 ?SConstructional Data i fj rfeor if hrmcrh!. -.ill i ,«rQn,n, .-...,. i.. ho (i Q?

B3

1imiI_I

Useful for the control of appliances Ssuch as converters, gluepots, vulcani- ™sers, hot platss, etc. Adjustable, to atope'-ate over the temperature range i-8rJ> ~. r

.C\ Hate W II .,**-..- <\.rt . - . . . . —

9P if bought, all togeflll f in i t jsplus 2,- post and packing.

THERMOSTATS

-_V^^___

50-550 deg. F. 11 amp. _g.'6 ; 2 amp., QMB, 5 6CJMU. 15-.

5 amp.,15 amp.

ELECTRONIC PRECISION EQUIPMENT, LTD.Post orders should be addressed to E.P.E... LTD., Dept. 7, Sutton Road, Eastbourne.

Pi I shoppj of these editresses please.

r.oiidon itoiut.

Croydon.

day, Wednesday.

42-46. Windmill Milt.ICuislij.. MldUtX.

Pbone : [SLIP 578 I

Hail daj Wed

152-3, street, gSSlroud Green Kd,,liii,liui> Park. \.4.Phone : ARChway 1049Half day, Thursdav

243, Kilhiirn lliuli SJ.

K«.a<t. Killjiirn. Si

MAIda Vale 4921. §


/elecikical/ EEi^rii'GliiTiiiifiii

A dependably accurate inslrument for lestiag

and fault location is indispensable to the

amateur who builds or services his own set.

The UNIVERSAL AVOMlNOR(as illustrated) is a highly accurate moving-coil instrument,conveniently compact, lor measuring A.C. and D.C. voltag's.

MODEL I

D.C. VOLTAGE : to 500 volts.

A.C. VOLTAGE : to 500 volts.

D.C. CURRENT : to 500 mA.RESISTANCE : to 20,000 U.Tocal resistance of meter : 200,000 42.

SENSITIVITY : 400 fl/Y.

MODEL 2

D.C. VOLTAGE : to 1,000 volts.

A.C. VOLTAGE : to 1,000 volts.

D.C. CURRENT : to 500 mA.RESISTANCE : to 200,000 U.

Total resistance of meter : 4 M.'-',

SENSITIVITY : 4,000 QN.

D.C. current, and also resistance3-inch scale.

Size : 4\ins. x Hins. x I litis,

Neil weight : 18 ozs.

I.isi Price : £12 :0 :0

22 ranges of readings on a

Complete with lends. Inter-changeable prods and croco-dile clips, and instructionbook.

Write for a fre

hensive Guide

copy of the latest Compre-to " Avo " Instruments.

The D.C. AVOMlNORis a 21-Inch moving coil meter providing 14 ranges of readings

of D.C. voltage, current and resistance up to 600 volts, 120

milliamps. and 3 megohms respectively. Total resistance

100,000 ohms.Size : 4Jfaf. x llins. x \ litis. Complete as aboveA el i weight : 12 ozs. LM Price : £5:5:0

Sole Proprietors and Manufacturers :

—

AUTOMATIC COIL WINDER & ELECTRICAL EQUIPMENT CO., LTD.Avocet House, 92/96, Vauxhall Bridge Rd., London, S.W.I. Victoria 3434 (9 lines)

KIC\A/ LEARN THE| iSHVV PRACTICAL WAY I

With many of our courses we I

' supply actual equipment. Courses|

I include: Radio, Television,|

I Electronics, Draughtsmanship,j

I Carpentry, Photography, and|

! Commercial Art, etc.

POST THE COUPON TODAY FOR OURBROCHURE ON THE LATEST METHODSOF HOME TRAINING FOR OVER

150 CAREERS & HOBBIES

PRIVATE AND INDIVIDUAL TUITION IN YOUR OWN HOME

Cily and Guilds Grouped Certificates In Telecommunications: A.M. Brit. I.R.E.

Examination, Radio Amateur's Licence, Radio and Television Servicing Certificates,

General Radio and Television Courses, Ratlar, Sound Recording, etc. Also Courses in

all other branches of Engineering and Commerce.

The advantages Of E.M.I, training ir The teaching methods are

planned to meet modern industrial requirements, -jr We offer training in

all subjects which provide lucrative jobs or interesting hobbies. -Ar A tutor is

personally allotted by name to ensure private and individual tuition, -fc Free

advice covering all aspects of training is given to students before and after

enrolling with us.

Courses from

15/- per month

rPOST THIS COUPOK JO DAY

| MB^^M- II I

| Send without obligation your FREE book.E.M.I. INSTITUTES, Dept. 32K

. 43 -Grove Park Road, London, W.4.I Phone: Chiswick 44I7/8.

TheonlyPostalCollegewhichispart-ofl _ _.1 FEB.

a world-wide Industrial Organisation subject(S) of interestj

February, 1957 PRACTICAL WIRELESS 799

FOR^ VALVESGUARANTEED ALL

TE8TEDBEFORE PI5PATCH

7 - KCP82 15 -

ecr:« ii 6E('H« 10'6

KOHH H-BCLKtl 10 6EF'i 9-

11/6

10/06.6

6/66/6

OPtlM6S3S«f:«WISCC.6«cuei;.l..<:

6J5GTtur.MBjaiiJTC;

BK6G6K7GBK7M<;ksutilt .set'

m.'ii,

6L7r;i.l

ILV7

tWUTGK7 9'-

6&A7UT 8,-6909 7 6B8H7 II -

ii>J7 8-(isKV 6-(iHL7 «

-

6H.N7

6SQ76S87OUitiT, 15,.inr.i; 8.6IrUfi 8 6WJTO 81

10.611-11/8

95S986101.-2

IIIIH

10F9ISAfl

I2AH5 11,612AT7 9/-12AC7 9/612AX7 10/-12BAI) 9'.

12IJF.il 10/-

1208 7/-ianu 3'-

10'-

8/611-8-

1.2 n

1J5-0

8/812 67 66610H1187 611-10-11-11 6m-6-10-10-?.-

7,61167.'-

9-

B>'3

7/613,612/6

11/6

I2J512J7I2K712Q7U8071380712SH712SJ7I2SK71981,7I2SQ712SR720F22011201V.

B5L6GT 96ares 9/625YoG 9925Z4G 9,'-

2SZ5 9/-26Z6GT 9/63SL0GT 9/63SW4 9'-

35Z4GT 8/635Z5 9-50I,6GT 8,8ACB/PKN8/8ATP4 3/8CBT.l 12/6DAP9U 10 6DFOtj 10/61>H73M 10/-OK96 10,611L96 10i'6

DM7U 8/6EABCsU

10.-EAC91 6/-EAF42 12/6Kliil 9/-

EB041 10/-EBPS0 11,-8081 7.8EC'91 8,6HCCiu 12,6B00»4 126 VH?iSBD83 10,'-

! VRfilECFSO 14,8 1 CEP

!'V ki\CI AMJPO.STAc;:. Hd. p

BFBOKF22urnBF85BFRfiKIW9KF99i:i."

Kl,:;i

iKL33

:i.;i.n

[KL42ELo'l

!HI, -I

BH.M i

i:\iki-.

BY61

KY9IBZ4UEzsnB1148l'\V i

.-.»•

.

10-Q /.::: 12H30 fi -

HI, I'

III .132

IiP-lloi 5 :

.

IfR-il" 4'6

KL8J1 8/8KT24 4,8KT2 6.-

KT33C 10 -

K'rwi i5/-KTW63 .".6

KTZII 0-I

I.P220 5 -

MEIU 10/-i

MIT4 7*6MSIPKN 5 -

N'78 12/6j

put 39 i

1-3215 3 11PBNas 5 •'-

FBH48 7 -

PBH220A4.'- i

pco84 io.- I

pcfso u -

,

K.'RSa 126PCL8S 12/8

;

PL81 12 8:

I HEADPHONES MICROPHONESpair

I I'l.li l..,v :;..., ...,

, .. :.. |...

Ujm..,,! UJeruphuiHW, Americanurj'hB, i wupljBte with strap,

l«ul and plug lype T30B 3 -setMicli UciifiliHif.: Phones. 4,OTOI

<hir,-. Rumplete wit* forkl*W 18'6

H Ii: Be i- i.in.T l if. it Phonos-., 16 •

TELEDICTOR TRANSFORMERSTYPE TE8

MTAI.L MAINS TRANSFORMERSSol table tor

ti:i,k\ \*IQX CONVERTER*, Etc.SPECIFICATION OVERALL SIZEI'r

5(1

•: 230 ... Chunp Cazutra«

I.F. TRANSFORMERS

Radlornrfl l.h'.s. 163 K.~«iili comprantoo trliuuwnt,boliil cimrftntulii'li. a n::il

qualits lob. Bias I 81U|. vi-7 nun

; ig,..\- above, IIW/127 Ke.'a 12/surplus Type, 406 Kc/a e'/9.Mininhirc [F'8- -Jiir. K..... g

VIBRATORSI 1'r.i l/.\. Types. AfvalfoMe

fur 12 or ii v..lt s rqr 0»k.Mftllory, Plessey, etc. Price

«•»-»• 8'fl

MAINS DROPPING RESISTORSach

CONTROLSWITH DOUBLE POLE SWITCH2.1K ohms. 50K ohms,

i inOBohiu«.Zmegohmft.

SWITCHlegohiOH.

beoondai1. I" Ml \.

-:•.

.0 \.

CABINETSLOUDSPEAKER CABINETS

>.!•,(.( io,,. ,, Mint. Hnlahcd oabimt»™H .• tor Bjia. M .-in. ipaakerinin, Beta! opcakei fret, i pletu

;

.

''.-

' Slid ruliU^r feet.

5'-

4/-

h ii, ij ,- • Heasun - ,-]iu. xSJlp. < i tin, al base 17 8

-•". lype : Heosurea lo^ln. i

lohn. \ :.in. :.( bate 21/85iu. type • Very sizajfatr design 16 6Postage any type 2,- eaoh.

TSL ELECTROSTATIC LOUD-SPEAKERS TYPE LSH100&•» ' ' ill. s ;;::. i tpaeltri I. Ionpi'. D.C. rohs tin max. Audio volts'•" in»\. aftsctiye. T,o poltage440».W 'iv-. Price 14/-.

TYPE LSH75il.xS a.x|lu, Gapaoltj BOOpFe

!>.<•. volts .'ino max, Audio v., it.<'

'•• eBeetive. Test voltage -i W i

.

o. ,•-. price bV-,

TYPE LSH5182}u. x Jin. Wide angle

v<".-,..,. of I.XH7,-,. RectaDguIar inform. Prive 12/6.

CHASSISMuniinlum uudrHied with retaforoadComer. Available in the following

in.-* ohms ZenitWUh lag

o'.:Mn'~"v • lin! "-• "'""s ,;ric "M' " ,!"" "tans

2in. (Jv.-r V Ind- '''" "'""'; ''MM ^1 87S ohms 500\,„.l ;

ohms D ohms 3(1 ohmsFirfng" t"imtre Dagole Mains Dropper .:i.\.

3 sTn Price IS - cement coated with 2 sliders1 .2 amp. as above 1,200 ohms

.

1 1 en Vitreous Mains Dropper1,328 ohms, 2 laps, MldgelType

Zenith Mains Dropper 910 ohmsDtibllier Type BY, tapped200-210. 220-2.1". 280-240ohms

Erie Two section Dropper, IWiohms and 1,840 ohms "iih2 taps 1/9

THE TELETRON BAND IH CON-VERTOR COLL SET

FOR USE WITH TRF AND SUPER

-

HET RECEIVERSThe complete eonvertor can be

built lor about 60/The complete Coil Set with

cin-uit, practical viiitur ,ii:..

grams and parts list : per est 15,. •

TELETRON BAND m Mark I!

oil .Set. A- above

B/8

1 3

1'9

PL88PL83PP22.1i'V-0l'Vfl

PYWQWJH],.,,,.

10-12.-

a.u10-10-8-763 1110-8-

13.611-12-8-

116l'AI'42 11 8UB4I 9 6L 111 1 1 10 -

UBCJ2 11 -

UCfl42 12 8I'M! 10 -

Thy 9 -

eaoh6iW. I

In,. v-2Jin 4,«sin. . oin. -. 2}io 6/9llliii, a 7in. \ 2.;in 7/hI2in. , iiin. x 2iiu gig1'•

1 Bin. -. 2iin 6/912ir.. '. "i„. x -jji,, g,.I lii -ii'--

1 2Un a,.I«h • -. too. -: -.Mil ib','-l«ln. , Bio. -, 2Jln a/gISln, . loin. \ 21P. 14';..

1 no -sided -ideal (or radio' tlvcrs amplrhers power packsVIC.

V.ID I

O403CJ0.1

II, Uvim1:Y4

1

11-

6.8 1

V/R3J•EH. 1 2 -

n»53.KVC::::.7 6\lioli

• i:r:.-. r-\ B67Kk.-V. S-

\ R03.spni 3.

\ l!ii„ \

spii a-VR.;,;

I Pfl 1 3 9Vltiu

:;!. -1

-

V PCI-i I \ IM V

i i;o2

r.A.en 1 6t RJOO iio8 6

\ KH.i 4-|VKl-iti 6.- I

VB137 5 6Vlil.m »0

8-\'S7o 3,-v:io2

(BL32J 8.6VTfiOl 5'-VI ::;

Ml 12 II,

\ nit.1 12)

\ I III

WW» 77\.i.-.

.\oi,

K79N ti:i

hut ide lifi^r

POC84 and PCF80With circuit 17,6

CHASSISBeady drilled tlnpUle chajasla IoTeletron sneorflcattoir. si/,. 1

71a.x8tn.x I 'in. Wilh underKiile sereen. Bhitable for lioth

M,«rk I and Murk 11 Coils... 3/9Mark II for the above coil sct.-

but with evtra space forpower puck transformer andrectlffer 6'-

cmcuiTSTeletron Circuit.s also available.Mark I and Mark II each 34,

B7G MINIATURE VALVE PINSTRAIOHTENER

This ib anAm-ric 0110 1

1

price everyone can afford. 2 6 each.

COLLARO PICK-UP. HIGHFIDELITY/HIGH IMPEDANCE

For standard records 78 r.p.in. only.Listed at 40,0. Our price. 35'.post 1/6.

ROTARY SWITCH•1 position 30 amp

Our 1957 44-page cata-logue is now available.

Please send I/- in stamps.

i1 megohms, _

I

All 4'ti eaoh.I WITH SINGLE POLE' tOK Ohms. I00K ohms, i

: nieaohms. 1 niegohms. ..

AH 3/9 cocii.

M.I, THESE CONTROLS Alii: itvU 101, 1,-KNOWN MAKER? : fill.\ CPN, DITBILIEB. MOBGAKITE,liRlli. \M1'|.H)N, etc.. etcCONTROLS LESS SWITCH eacht megohm, 1 megohm nil 2,

a

EX-GOVERNMENT AND SURPLUSCONTROLS

This popular ninge is suitable lor allrelevi.-ioi, constructors, etc-. Keepyour costs down when Pudding the• *rg«8 " or - -iiuplo. - reAvailable :

.-,00 ohms. 600 ohms,1,800 ohms double t\ pe, SK ofaus,5K ohms, ink" i.hius. 20K ohnv23K oho,... ..oK 1. ion... 2U0K ohms.IOOK ohm-,

i iiicKohio.j megohm

1 megohm. 2 iriepohnw, flOK ohm<double type ,.,p 1 o .,.

COLVERN P3E-SET CONTROLS

Tyre CMS lPJll/7.1 2» „- 1«I'llll 1,11,1 ,.| 2 I, |, n,;.^. ( ,„,.

tro!>. banked wiin separateepindlea 6/9

G.E.C. LOUDSPEAKER CABINETSType BCT033 tilted with Sin. unit,low impci.-i-i,.,-, own romnie control.Very attractive cabinet. Offered atwell below cost. 52 6 each, post 3 -.

10 WATT WIRE WOUND RE-SISTORS BY DAGOLE

Special purchase nj following siw-.i'i 1 - each :

250 Ohms, 700 ohm--. 660 ohm.-. 22:,.ohms. 7.in ohms, 000 ohms. 300 ohms1.000 ohms, ITS ohms, liin ohms, 200oSm«, ii.ni ohms, -loo ohms.

TV SLLDER PANELWelwyn panel of :: ,v..i .:

1 megohms, l.iuK ohm-. 200K ohms,with Maok screen lyne tockfag Imobs,Total size iiin. x :ii„. Price lS eaoh.LOUDSPEAKER EXTENSION

SOCKET AND PLUGH.ikelile 2-hole fixing socket panel.2-pin plug when pushed halt way !:.

operates both internal and extension :

fully home cuts one a., rrouiied.Price 6d. each.ALL DRY BATTERY PLUOS AND

SOCKETSAll lypea .ivuihil.le.

Two nopnTar lypca of plusr, 2-pl', aid:j-pin, 4d. each,

INDICATOR LAMPS eachSpring fixingtype 93."' Aerovox " Condenser Clip"

. 14Pencil Rectifiers, Type Jin g

'

Aniplinii Volume Controls, 2meg, s.p.s 3 ,-6

Extemoon speaker VoluraControls 1 3

vibrator OUps (Standard) 5d.Double Pusehnlders. Pan-.Mounting, for two 1 i.in. ft-.s3s 8,'8

10-Al fi

1167/615 -

IRON ELEMENTSh.m.v. Replacement Element 3Standard Elements, will at mo.-i make* 18ARMOUR PLATED GLASSaixelSui.x Hi tin., rounded corners 3 0t

1/6

12

POTENTIOMETER PANELFour Potentiometers on Panel, aoh ohm;MPS 1 750 ohms W/w ; 29K ohm. Carbon :

Z7.vi 15- BK ohms W/W. AH with long spindle, with'•-•> - ol Oinereul coloara terminating in an

SASIi DAI SHKVB . 11 .

:.

. ?6 Bs

JUNCTION BOXESType .) \ ,22i!4. 2fi-wav

RECORDING- TAPE, 1,200 it" Puretone"NEEDLE CUP8For Oram. Needles fBaJtolHcj Id.CRYSTAL DIODESWire Ends, Plaetlc case 1/

AMERICAN RELAY4."> ohms Impedance with leads.No. AZllf.l.'i 10

IRON LEADSBlade and white Hat -iron leads,honded ends 1 3

2 RANGE POCKET VOLTMETEREx-Ministry, brand new, 0-15

coil 848 ohms per volt, complcte with lead.-. jg .

ALPHARADIO SUPPLY CO;

-II AWV II

\

5/6VINCES CHAMBERS

VICTORIA SQUARE

LEEDS I

TERMS : Cash with order orC.O.D. Postage and Packingcharges extra, as follows :

Orders value) 10/- add I'- •

20/- add 1/6 ; 40/- add 2/- ; «add 3/- unless otherwise stated.Minimum C.O.D. fee andpostage 3/-. All single valves

postage 6d.

MAIL ORDER ONLY


R.S.C. BATTERY CHARGING EQUIPMENTASSEMBLED CHARGERS

6 v. lamp 19/96 v. or 12 v. 1 amp 2596 v. 2 amps 29/9(i v. or 12 v. 2.amps 38/96 v. or 12 v. 4 amps 56/9Above ready for use. Carr. 2'9.

With mains and output leads.

HEAVY DUTY KIT12 v. 30 amp. Suitable for Garageor firm with a number of vehicles.Mains Input 200 250 v. 50 e..s.

Outputs 12 v. 15 amp. twice.Consists or Mains Trans. 2 MetalRectifiers, 2 Meters. 4 Fuses.4 Terminals. 2 Rheostats andcircuit. Only 9 Kns., carr. to?-.

BATTERY CHARGER KITSConsisting- or Mains Trans-former, F.W. Bridge. MetalRectifier, well ventilated steelease. Fuses, Fuse - holders,Grommets. panels and circuit,Carr. 2/6 extra.6 v. or 12 v. 1 amp 22 96 v. 2 amps 25 96 v. or 12 v. 2 amps 31 66 v. or 12 v. 4 amps 49/9

BATTERY CHARGER KITConsisting of F.W. UridineReel i Her 6/12 v. 5 a. Mains Trans.

,

0-945 v. 6 a. output and variablecharge rheostat with knob.Only 45 9.

ASSEMBLEDCHARGER

6 v. or 12 v.

2 amps.Fitted Ammeterand s eXep t o r

plug for v. or12 v. Louvredmetal case, fin-

ished attractivehammer blue.Ready for use.With main sa n d outputleads. DoubleFused.

CarS 46/9

All for A.C. MAINS 200-250 v., SO c/cs.

Guaranteed 12 months.

Assembled 6 v.

lie 12 \. 4 ani|»s.

Fitted Ammeter andvariable charge sel-

ector. Also selector

plug lor 6 v. or 12

v. Charging". DoubleTused. Well ven-tilated steel casewith blue hammerfinish. 6ty9Ready Tor use. withmains and outputleads. Chit. 8/6.

R.S.C. MAINS TRANSFORMERS G^^vvri,,.)Interleaved and impregnated. Prim-aries 200-230-250 \. 50 e/cs Screened.TOP S1IKOI DEI) DHOP THROUGH250-0-250 v. 70 mA. 6.3 v. 2.5a 13/8250-0-260 v. 70 mA. 6.3 v. 2 a, 5 v. 2a ... 16/9300-0-300 v. 70 mA, 6.3 v. 2.5 a 16/9350-0-350 v. 80 mA, 6.3 v. 2 a, 5 v. 2 a ... 18/9250-0-250 v. 100 mA. 6.3 v. 4 a, 5 v. 3 a. 229300-0-300 v. 100 mA. 6.3 v. 4 a. 5 v. 3 a. 22'9350-0-350 v. 100 mA, 6.3 v. 4 a. 5 v. 3 a. 22'9300-0-350 V. 100 mA, 6.3 v. 4 a. C.T.

0-4-5 v. 3 a 239350-0-350 v . 150 m A. 6.3 v. 4 a, 5 v. 3 a. ... 299FILM SIIKOl DED ri'KKiHT250-0-250 v. 60 mA. 6.3 v. 2 a, 5 v. 2 a.Midget type 21 -3-3in 17 6

360-0-350 v. 70 mA, 6.3 v. 2 a. 5 v. 2 a 19/9250-0-250 v. 100 mA, G.3 v. -4 v. 4 a,

C.T. 0-4-5 v. 3 a. 26 9250-0-250 v. 100. mA. 6.3 v. 6 K 5 v. 3 a,

for R1355 conversion 31-300-0-300 v. 100 mA. 6.3 v. -4 v. 4 a.

C.T. 0-4-5 v. 3 a. 26/9350-0-350 v. 100 mA. 6.3 v. 4 a, 5 v. 3 a. 23/9350-0-350 v. 100 mA. 6.3 v. -4 v. 4 a.

C.T. 0-4-5 v. 3 a. 27/9300-0-300 v. 130 mA, 6.8 v. 4 a. 6.3 v. 1 a. "

for Milliard 510 Amplifier 353350-0-350 v. 150 mA. 6.3 v. 4 a. 5 V, 3 a. 33/9350-0-350 v. 150 m A, 6.3 v. 2 a. 6.3 v. 2 a.

5v.3a 35 9425-0-425 v. 200 mA. 6.3 v. 4 a. C.T.

6.3 v. 4 a. C.T.. 5 v. 3 a. SuitableWilliamson Amplifier, etc: 499

450-0-450 v. 250 mA, 6.3 v, 6 a, 6.3 v. 6 a.

5v, 3 a 69.)

FILAMENT TRANSFORMERSAll with 200-250 v. so c s primaries 6.3 v.

1.5a. 59 : 6.3v.2a.76 : 0-4-6.3 v. 2a. 7 9 :

12 v. 1 a, 7/11 : 6.3 v. 3 a. 811 : 6. 3 v. 6 a.

17/6 : 12 v. 3 a or 24 v. 1.5 a, 17.6.

E.H.T. TRANSFORMERS2,500 v. 5 mA. 2-0-2 v. 1.1 a. 2-0-2 v.

1.1 a for VCR97. VCR517, etc. ... 36/6

ELIMINATOR TRANSFORMERSPrimaries 200-250 v. 50 cs 14/9120 v. 40 mA, 5-0-5 v. 1 a 15 9i)0 v. 15 mA, 4-0-4 v. 500 mA 9/9

CHARGER TRANSFORMERSAil with 200-230-250 v. 50 c s Primaries :

0-9-15 v. 1 1 a. 11 9 :0-9-15 v. 3 a. 16/9 :

0-3.5-9-17 v. 3 a. 17 9 : 0-3.5-9-17.5 v. 4 H.

18 9 : 0-9-15 v. 5 a, 19 9 :0-9-15 v. 6a, 229.

SMOOTHING CHOKES250 mA 5 H HKI ohms 12/9150 mA 7-10-250 ohms 11.9100 mA 100 H 200 ohms 8/980 mA 10 H 350 otims 5/660 mA 10 H 100 ohms 4/11

SMALLPOTTEDMAINSTRANSF.Removed from New Ex-Govt. units.Primary 0-200-230-250 v. Sees.250-0-250 v. 60 mA. 6.3 v. 2 a. 11/05v. 2a. Size 3i x4i x3in '/*»

R.S.C. BATTERY TO MAINS CON VERSION UN ITS

III II'IT TRANSFORMERSMidget Battery Pentode 66 : 1 for

3S4. etc 3/9Small Pentode. 5.000 n to 3fl yji.Small Pentode i il,000n to 3il ... 3/9Standard Pentode. 5.000 £1 to Si; ... 4/9Standard Pentode. 7 8.OOOtl to 3n ... 4.9Multi-raLio 40 mA. 30:1. 45:1. 60:1,

90:1. Class 13 Push-Pull 5/3Push-Pull 10-12 watts 6V6 to :in or

15(1 15/9Push-Pull 10-12 watts to match 0V6

to 3-5-8 or Infl 16/9Push-Pull 15-18 watts. M.'J. KT68 ... 22/9Push-Pull 20 wnrts, sectionallywound 6L6, KT66, etc., to 3 or ISO 47/6

Williamson type exact to spec. ... 85/-

SPECIAI. OFFEKS32-32-32 mid. 250 v. Dubilier smallcan electrolytic:-. 2 9 ea. Small.0005 mid. 2-gam;. 4 9 ea. WestiBg-house Rectifiers 260 v. 250 mA.. 7 9.

TypoBMl. An all-drybattery eliminator.Size 55 x 4J x 2in.approx. Completelyreplaces batteries sup-plying 1.4 v. and 90 v.

where A.C. mains ZOO-ISO v. 50 cs. Is avail-able. Suitalile for allliattoiy portablereceivers requiring1.4 v. and 90 V. Thisincludes latest lowconsumption types.

Complete kit with diagrams, 39/9, or•ready for use, 46:9.

Type BM2. Size 8x5.; x1-tin. Supplies 120 v.

90 v.. and 60 v.. 40 inAand 2 v. 0.4 a to 1 amp.foilysmoothed.There-by completely re-placing Imth II.T.batteries and I..T.

2 v. neciiimilalor-i.When connected toA.C. mains supply200-250 v. 50 e.'cs.

SUITABLE foe ALLBATTERY RECEI-

VERS normally using 2 v. AccumulatorComplete kit of parts with diagrams andinstructions 49 9. or ready for use 59/6.

Il.T. ELIMINATOR AND IRK IvI.E

CHARGER KIT. Input 200-250 v. A.C.Output 120 v. 40 mA. Fully smoothed andrectified supply to charge 2 v. accumulator.Price with louvred metal case and circuit,

29/6. Or ready for use. 8 9 extra.

T.V. CABINETS. Leading manufacturerssurplus. Attractive designs. Walnutveneered, with doors for 15, 16, or ITin.

Tube. £3-19-6. Carr. 7.6.

MINIATURE MOTORS. 24i28 v. DC. orA.C. made by Hoover Ltd., Canada. Sizeonly 2£ x llin. Spindle Kin. long, Jin.

dinm. Brand New, 9/9.

EXTENSIONSPEAKERS

Ready for use in

wal nut veneeredcabinet.6i in. 2-3 ohms, 29 3-

Bin. 2-3 ohms. 35 3.

Very limited number.

VOLUME CONTROLS with long (Jin.

diam.) spindle all value" less switch.2/9 : with S.P. .-.wiL.'.i. 3 9 : with D.P.switch, 4.6.

MANIFACIT'RERS' S I It P I. I SMAINS TRANSFORMERS. Primaries250-250 v. 50 c cs. Fully shrouded uprightmounting 425-0-425 v. 150 mA. 6.3 v. 3 a,

5 v. 3 a. 29/11, post 2 9. Wearite 325-0-325 v.

100 mA, 6.3 v. 2.5 a. 5 v. 2 a.. 19 9. DropThrough Chassis type 250-0-250 v. 70 rnA.6.3 v. 2.5 a. 10/9.

EX-GOVT. lit ANSIS. .230 250 n . 50 e/es.460 v. 200 mA, 6.3 v. 5 a, 25 9 : :«X)-'J-:J0() v.

150 mA. 4 v. 3 a. 9 9.

EX-GOVT. SMOOTHING CHOKES250 mA. 5 IT .50 ohms 12/9150 mA. 10 H 100 ohms 119150 mA, 6-10 H 150 ohms Ti op. ... 6/9100 mA. 5 H 100 ohms . 311L.T. type 1 amp. 2 ohms 2/9

EX-GOVT. E.H.T. SMOOTHING CON-DENSERS. .02 mid. 5.000 v. Cans. 2/9;.1 mid. 2.500 v. Bakelite Tubulars. 3 3.

KX.-GOY l. METAL BLOCK (PAPER)CONDENSERS

4 iiild. 500 v.. 29 : 4 mfd. 1,000 v.. 4 9 :

4 mfd. 1,500 v.. 5/9 : 8-8 mfd. 500 v., 6/9 :

8 mfd. 500 v., 4'9 : 10 mfd. 500 v.. 4/9 ;

4 mfd. 400 v. plus 2 mfd. 250 v.. 1.11.

EX-GOVT. ELECTROLYTICS. Removedfrom unused equipment. 8-16 mid. 550 v..

1/3 ; 1.000 mfd. 6 v., 1 9 ; 50 mid. 50 v.,

with dip. 9d.

EX-GOVT. DOUBLE WOUND STEPIIP/STEP DOYVX TRANSFORMER1.0-0- 100-200-220-240 v. to 5-0-75-115-135 V.

or REVERSE. 80 100 watts. Only 119.plus 29 post.

EX-GOVT. CASE. Well ventilated blackcrackle finished, undrilled cover. Size 14

x 10 x 81in. high. IDEAL FOR BATTERYCHARGER OR INSTRUMENT CASE.OR COVER COULD RE USED FORAMPLIFIER. Only 9 9. plus 29 postage.

EX-GOVT. VALVES1T41S53S45Y3G5U4G5Z4G6K7G0K8GUSJ7GT6SLGT6SN7GT6AT6

5 it

8/96 98.9897 9

EF396V6G6X4IIX5GT6L6G80712A615D225i24GMH4ECC83

(SEW)5 9 I EFB36 9 EB9189 i

FF367,9 I EIJ2

11 9 EI .91

7 9 KT4479 ! EZ904 9 EZ809/9 ' EL844 9 ! SP619 9 85Z4

7/98 94/93.95; 9898.99'6106238 9

EX-GOVT. UNIT ItDl'l. Brand new.cartoned. Complete with 14 Ives,including 5Z1. E.H.T. rectifier.

Trans. Choke, etc. Only 293. carr. 7/6.

ELECTROLYTICS (current production)NOT EX-Govt.Tuhiilar Type!8p.F4.50v. ... ]

8 mfd. 500 v. £

HiuF. 350 v. ... S

16|iF450v. ... J

16uF500v. ... 5

32|lF350v. ... i

32 mfd. 500 v. S

25uF25v. ... ]

50uF12v. ... ]

5(1 in I'd. 25 v.... ]

50 pF SO V. ... 3

100 mfd. 12 v. ]

100 mfd. 25 v. 5

41,000 mfd. 6 v.

Can Types16 mfd. 500 v. 2/916 mfd. 350 v. 1.1111uF450v. ... 2932p.F3.50 v. ... 2 1132 mfd, 450 v. 4 9100 mfd. 450 v. 4 98-8 uF 450 v. ... 2 98-16uF450v.... 3/1116-16uF 4.50 v. 3,1132-32 uF 350 v. 4/932-32uF 450 v. 5/9S4-120mfd.350v.7j9100-200 mfd.275 v. ... 6:9

Many others in stock.

HINTS MOLDSEAL CONDENSERS..005 mid. 400 v., ,01 mrd, 400 v.. .04 mfd. 50)v.. 5/6 doz. tone type ): .1 mfd. 350 v.. 8d.ea. :

.5 mfd. 500 v.. 1/8 ea.

February, 1957 PRACTICAL WIRELESS 80?

R.S.C. A8 ULTRA LINEAR 12 WATT AMPLIFIERNEW 1956 Model High-Fldellt; PushI'ull Amplifier with "Built-in ' ToneControl, Pre-atnp stafces, Htehsens ivitIncludes 5 valves t807 outputs*. HighQuality sectionally wound onto'., ranformer, specially deafened for UltraLinear operation," mid reliable nocondensers oi current manufacture,INDIVIDUAL CONTROLS FOR. U.vssAND THTCBLE "Lift-" and "Cut"Frequency response * 3 db. 30-30,000 Cc-Six negative feedback loops. Hum leve71 db. down. ONLY 70 millivolts INPUTrequired tor Kl'l.l. OUTPUT. Suitablefor use with all makes and types of ui'-l-: -

»!>•• and practically all microphones.Comparable with the very beat designs.for STANDARD orLONG-PL AY INC.B EC <) R DS, ForMUSICAL INSTRU-VI l \is such as STRING It vss.GUITARS, etc. OUTPUT SOCKE'Jwith plug provides 300 v. 20 niA. and 8.8 \.1 .6 a. Tor supply of a It ADIO FEEDER• Ml'. Size appro:-:. 12-9-7in, For A.C.mains 200-230-250 v. SO c'ck. Outputs lor ";

and IS ohm speakers. Kit is complete '

lust nut. Chassis la fully punched, PullInstructions and point-to-point wiringdiagrams supplied. Unapproachable valueat £715-. or factory imili 45- extra,Carriage 10-.If required louvred metal cover with 2

.. ,»*. .7.- iJV.Iif, (I -.

£7-15-0 carrying handles can be supplied for17 6. Additional input socket with asso-ciate Vol. Control so that two differentInputs such as Cram and "Mike" 01*Tape and Radio can be mixed, can beprovided for 13- extra. Guaranteed 12months.TERMS on assembled two input model.DEPOSIT 256 and nine monthly pay-ments 23 4.HIGH - FIDELITY MICROPHONESand SPEAKERS in stock. Keen cashprices or h.p. terms if supplied withamplifier.

SUPERSET FEEDER I NITDesign of a high quality Radio Tut(specially suitable for use. with any or ourAmplifiers.!. Delayed A.V.C. Vers UghPercentage modulation of the Transmitr.ur can he handled without distortion,The w.Ch. Sw. incorporates Oram,position. Controls are Tuning-, w .

Ch. and Vol. Only 250 v. 15 mA. u ,T .,

and L.T. of 6.3 v. 1 amp. required fromamplifier. .Size of unit appro:. 9-8-7inhigh. Simple alignment procedure.Point-to-point wiring diagrams,stria Mop and priced parts list withillustration, 2/6. Total building cost,£4 15'-. Fordescriptive leaflet SendS.A.E,

GARRARD 3--SPEED MTXER At IO-(U INGER HCiio. For Standard A.C.mains 300-250 V. 50 C/CS. CurrentModel. Brand new, cartoned. IVc-vision for taking 10 records. FittedHigh-Fidclity turnover pick-up headWilli dual sapphire point stylus forStandard or Long-playing records.Very limited number at only £7.19.6.Carr. 3 6.

LINEAR 1.45 MINIATURE 4 5 WAT!OI AI.1TY AMPLIFIER. .Suitable fol

086 with Garrard B.S.R. or anj Otherrecord-playing unit, and mosl microphones. Total negative feed-back 12 db.Separate Bass and Treble Controls. Forconvenience when mounted in cabinetmains switch is incorporated In control,For A.C. mains input of 200-250 V. 61

1

Output for 2/3 ohm speaker. Three ministuro Milliard valves used. Size of unitonly <>-5-5Jin. high. Chassis is full!isolated from mains. Onemonths. Only £5/19 6-

ELLIPTICALP.M. SPEAKER. 7 i:i

Goodmans. Suitable for above, 19 6 ;

LINEAR 'DIATONIC 10 WATTHIGH FIDELITY. Pl'SII PI 1. 1..

ULTRA LINEAR AMPLIFIER, FOi200-2:10-250 v, 50 Cos. A.C. Mains, Vahrline-up ECC83, ECC88, EL84. RUM. EZ81miniature Milliard. The unit has sell' contallied Pre-a.mpliflor.Tone Conirol .-.i:or.--

and separate Bass and Treble Controls.Independent ' Mike ' and GramSOOkets are provided. Total harmonic '

distortion only 0.26% at 6 watts. Due touse of latest miniature com —proved reliability sue Is only 10-6output Matohings for 3 and 15 •

speakers. Finished in, uluacti', i

Gold Bronze hammer. Only 12 c;>S.or Deposit 26,9 plus 10/i'carr, and !l

monthly payment:-- of:26'9. Send 8 \.i:.

for I'ur details.

Terms: C.H.O. or r.O.D.Open 9 to 5.30 : Sal-, mil

USB, U.>l.l

1 GNS.

R.S.C. 4-5 WATT ASHIGH-GAIN AMPLIFIER

A highly sen-sitive 4-vahciiualily amplifter forI h I- h o in e .

small club,etc. Only 50millivolts in-l>ii( is re-quired forfull outputso I hat il is

suitable foruse with the latest high-fidelity piek-UBheads, in addition lo all oilier types ofpick-ups and practically all mikes.Separate Bass and Treble Controls areprovided. These give full long-playingrecord equalisation. Hum level isnegligible being 71 db. down. 15 db.of negative feedback is used. II.T. of300 V. 25 in A. and L.T. or 6.3 v. 1.5 a.is available for the supply of a RadioFeeder Unit, or Tape Deck prc-ampli-1ier. For A.C. mains input of 200-230-250 v. 50 e.cs. Chassis is not alive. Kilis complete in cv cry detail and includesfull] punched chassis (with baseplate)with Blue hammer Unish and pointto-point wiring diagrams and in-structions. Exceptional value atonij £415-. or assembled ready foruse 25,- extra, plus 3/6 carr.

PLEsSET lOin. P.M. 3 OHM SPEAKERwith High Flux Density Magnet Recom-mended for use with above A5. A7. orLinear L45 Amplifiers. Price 289.B.S.C. TAi llK.il QUALITY TAPEDECK AMPLIFIER. For ALL TapeDecks with High Impedance, Playbackand Erase Heads, such as Lane,T'ruvox. etc. (Unit can now Ready forbe supplied Cor use with latest Use, O.maCollaro Tape Traiisrriptor :

refer to TAlC'i. For A.C.Mains 230-250 v. BO

|OS.

Positive compensated identification forrecording level by Magic Eye. Recordingfacilities for 15. 7i or 3}in. per sec. Auto-matic equalisation at the turn of a knob.Linear fre<iuene> response of - 3 db..50-11.000 a C8. Negative feed-back equal-isation. Minimum microphony and hum.High output with completely effectiveerasure and distortionless reproduction.

iitivity is 15 millivolts so thai, anykind ol crystal microphone is suitable.Only '.: millivolts minimum output re-quired from Recording head. Provision is• •: id< '

i-':>?;[ intra F -i iimpliii'.r. I nit can

also be used as a gram-amplifier requiringinput oi 0.75 v. R.M.S. Carriage 7/6. Illus-trated leaflet t>d.

SiO (.O.I), under £1. Post 1 9 extra under1 1 p.m. Catalogue 6d., Trade List 5d. S

R.S.C 30 WATT ULTRA LINEARHIGH-FIDELITY AMPLIFIER A6A highly sensitive Push-Pull, high outputunit with self-contained Pre-amp. ToneControl Stages. Certified performancefigures compare equally with mipensive amplifiers available. Hum level.', , ™;Ji£,wn - Frequency response 3 db30-30.000 c

.cs. A specially designed

.sectionally wound ultra linear out pertransformer is used with (107 outputvalves. All components are chosen forreliability. Six valves are used, andseparate Bass and Treble control- MSnJmum input required for full output isonly 30 millivolts so that ANY KIND OFMICROPHONE OR PICK-UP IS SUIT-ABLE, The unit is designed for CLUBSSCHOOLS, THEATRES, DANCEHALLS or OI TDOOR FUNCTIONS.fzSiwJrPS, usc' wlcn Electronic ORGAN,GUITAR, STRING it.ASS, etc. Forstandard or long-playing records. OUT-PUT SOCKET PROVIDES L.T. andH.T. lor a RADIO FEEDER I'NITAmplifier operates on 200-250 v. 50 CCSA.C. Mains and has outputs for 3 and ISohm speakers. Complete kit of parts witlfully punched chassis and point-to-point,wiring diagrams and instructionsII required cover as for AfJ ONI Ycan be supplied for 17'6.'An extra input with asso-ciated vol. control so thattwo separate inputs suchas Gram, and Mike can be Carr. 10 -

mixed, can be provided for 13- extra.The amplifier can be supplied, factorybuilt with 12 months' guarantee, for 50-extra. TERMS for assembled two Inputmode! : DEPOSIT 28 9 and 8 monthly-payments of 28/9.

O:\J.t

96NS

B.C.A. 20 WATT RE-ENTR VNTSPEAKERS, 15 ohm or 100 ohm matchtng. For Outdoor work. Only 8 GNS,P.M. SPEAKERS. All 23 ohm: HGoodmans. 17 9. 6iln. Flessey, 16,9.Bin. H"la. 19,9. lOin. Elao, 26 9. 12in.Plcssey. 29T1. 10Jn. W.B. " Stentorian "

3 or 15 ohms typo HF1012 10 watts, high-iidehtv type. Highly recommeniuse with oar AH amplifier, £4 10 9. 12in.Plessey 15 ohm 10 watts. 59/6.

PI.KSSI.Y DIAL CONCENTRIC 12in.15 ohm HIGH FIDELITY SPEAKERwith built-in tweetertcompletely separateelliptical speaker with choke, conden-sers, etc.) providing extraordinarilyrealistic reproduction when used withour A8 or similar amplifier. K

i

watts. Price complete, only £5 17 6.

M.F. SPEAKERS 2-3 ohms, 8in. R '\

Field, 600 ohms, lis,

COAXIAL CABLE 75 ohms. ;in 8dyard. Twin Screened Feeder, lid. yard.

SELENIUM RECTIFIERS6/12 v. 1 a.6/12 v. 2 a.612 v. 4 a.6/12 v. 4 a,6-12 v. 6 a.6.12 V. 10 a.

4118/911914/919'9359

8-12 v. I a. ILW„J};9I Li. Types HAY.150 v. 40 mA. 3'9250 v, 50 mA. 5-9250 v. 30 mA. 7 9250 v. 150 mA. 9 '9300 v. 250 mA. 13 9i.i. Types hay.

R.S.C. 3-4 WATT~A7HIGH-GAIN AMPLIFIER

For 230-250 v. 50 c cs. Mains input

.

Appearance and Specification, withexception of output wattage, as AS,Complete Kii with diagrams, £3'15 -.Assembled 22 6 extra. Carr. 3.6.

RADIO SUPPLY CO.

THE SKYFOl R T.R.F. RECEIVERa design of a 3- valve 230-250 v. A.C. Mainsreceiver with selenium rectifier. It con-sists of a variable-Mu high-gain H.F.stage followed by a low distortion anodebend detector. Power pentode output isused. Valve line up bcliix 6KV. 'si'in.6F6G. Selectivity and quality are well upto standard, and simplicity of construe-

a special feature. Point-to-pointWiring diagrams, instructions and part.,list, 1 9. This receiver can be built for amaximum of £4196 including attractiveBrows or Cream Bakelite or Walnutveneered wood cabinet 12 i

£2 : 29 extra under £5.. WE. w llli all enquiries.

(LEEDS) LTD.32, THE CALLS, LEEDS, 2


ae© X500 1*

REPLACEABLE STYLI, AS FITTED

CRYSTAL AND CERAMIC PICK-

HAVE PERFECT SHAPE, SIZE

TO ALL ACOSCARTRIDGES

ND FINISH

1* ACOS Styli have to pass a quality inspection at x 500

magnification. Only in this way can some faults, which may

have important effects on reproduction or record or stylus wear,

be reliably detected. The standards we set ourselves are high

but practical. They are reflected not only in ACOS products

but also in the record reproducing equipment in which ACOSpick-ups or cartridges are fitted.

/'U<"/'4£&&

C0SM0C0RD LIMITED. Eleanor Cross Road,

Waltham Cross, Herts. Waltham Cross 5206

ml

February, 1957 PRACTICAL WIRELESS 833bmbkwwmEVERY MONTH

VOL. XXX II, No. €02, FEB., 1957

COMMENTS OF THE MONTH

EDITOR • F.J. CAMM 24th YEAROF ISSUE

BY THE EDITOREditorial and Advertisement Offices :

'Practical Wireless," Georee Newnes, Ltd.. Tower House, Southampton Street. Strand, W.C.2. 'Phone : Temple Bar 4363Tolenrtims : Newnes, Rand. London.

Recistered at the. G.P.O. lor transmission by Canadian Hasazine Post.

The P.W. Film ShowA REMINDER that you still have time to

apply for a free ticket for the PracticalWireless Film Show which takes place

at the Caxton Hall (Great Hall Site) on Thursday,February 21st, at 8 p.m. The films run for wellover an hour and there is an interval for refresh-ments. The films have been produced by Mullard.Ltd.. one of the leading manufacturers of valvesand TV tubes, and I am grateful to them for their

co-operation in providing the film for what is

bound to be a most interesting evening. I shall

be in the chair. The films deal with the manu-facture of valves and transistors and when theywere shown to the trade I made the suggestionthat members of the public and especially myreaders should be afforded the opportunity ofseeing these excellent films, which are highlyinteresting and educational.

Readers wishing to attend should s^nd in their

requests for tickets to " Film Show," PracticalWireless, address as on this page. The hall

accommodates 500 people and tickets will bedespatched to the first applicants, so send yourapplication in now, as there is bound to be alarge demand for the 500 seats which areavailable.

BINDERS FOR P.W.

WILL readers please state when ordering self-

binders -for Practical Wireless (details

were given on page 689 of our issue datedDecember, 1956) the volume number theyrequire blocked on the spine. Some readers areordering more than one binder with the obviousintention of binding past volumes. In such casesthe number of every volume must be stated.

Even if ordering a single binder, however, please

state the volume number.

^AMPLIFIERS: DESIGN ANDCONSTRUCTION"

WE have just issued at 17s. 6d., or 18s. 3d. bypost, " Amplifiers : Design and Construc-

tion," which contains designs for radio, gramo-phone, tape deck and P.A. amplifiers with a

special chapter on D.C. amplifiers. The earlychapters deal with amplifier design from basicprinciples. All of the designs have beenexhaustively tested and perfected in the PracticalWireless laboratory and, of course, include thebest of the designs dealt with in articles in this

journal. Send orders to the Book Department,address as on this page.

A reminder that readers may have free ofcharge a complete catalogue of all our tech-nical publications covering engineering, radio,television, electricity, electronics, building, etc.,

by applying on a postcard to the same address.

QUERISTS PLEASE NOTEYV7TLL querists please note that we only replyW to those who have enclosed a stamped andaddressed envelope and a coupon cut from thecurrent issue. Our query service is not open to all

and sundry. It is a free service to readers of this

paper only and we must insist, therefore, uponthe coupon and a stamped and addressedenvelope being enclosed as evidence of readership.We receive a large number of queries every daywith neither coupon nor stamped and addressedenvelope, and in view of the volume of corres-pondence we are receiving we must confine theservice to our readers only.One other point : we are receiving a large

number of questions relating to commercialreceivers, and we would prefer that readerswrote direct to the firms concerned. Equally wemust decline to answer questions relating toreceivers and apparatus described in our con-temporaries, most of whom do not have afree advisory service.

CONTRIBUTIONSVV7E welcome contributions of a practicalW nature, especially constructional articles.These should be about 1.500 words in lengthand be accompanied by rough sketches, photo-graphs and sources of supply. Preference is

given to those articles not designed aroundex-Government equipment- F, J. C.

OUR NEXT ISSUE, DATED MARCH. Hit I Ol-PURUfSnED OH FEBRUARY 7th


Broadcast Receiving Licences

'"THE following statement showsthe approximate number of

Broadcast Receiving Licences in

force at the end of October, 1956,

in respect of wireless receiving

stations situated within the various

Postal Regions of England, Wales,

Scotland and Northern Ireland.

The numbers include Licences

issued to blind persons without

payment.

Region Total

London Postal . 1,260.908. 1,254,527

Midland 975,909

North Eastern ... . 1,274,265

North Western 962,208South Western 794,947

Wales and Border < 01 nues .

les

501,660

Total England and W . 7,024,424Scotland .. . 901,589Northern Ireland ... 202,656

Grand Total ... . 8,128,669

Police V.H.F.

T-HE Metropolitan Police have

placed an order withMarconi's Wireless Telegraph Com-pany Ltd. for the supply of 50

of the new Marconi 10-watt F.M.mobile transmitter/receivers type

HP81B.The Marconi type HP8IB is the

latest of the HP80 series of 10-watt

mobile V.H.F. radio-telephones.

Its compact and rugged construc-

tion makes it eminently suitable

for use in cars, harbour craft, naval

vessels or for general point-to-

point communication links.

The standard type HP8IB equip-

ment comprises a frequency-

modulated transmitter/receiver with

a control unit and a loudspeaker,

all of which are separate entities,

thus permitting the maximumamount of flexibility in installation.

Either a telephone handset or a

hand microphone may be used,

press-switches being incorporated

in these instruments for instan-

taneous changeover from " trans-

mit '*to " receive." Facilities

exist for the provision of a loud-

hailer.

Up to seven crystal-controlled

channels with independent adjust-

ment of each spot frequency are

available within any £ Mc/ssection of the frequency range

(70-100 Mc/s). The channels are

selected by a rotary switch mountedon the control unit. Provision is

By "QUESTOR"

made for operating with 50 kc/.s

channel separation ; alternatively,

operation with 25 kc./s channel

separation can be effected. Themode of operation can be commonfrequency (simplex) or dual

frequency (simplex or duplex).

Opening of the BBC's V.H.F.Sound Broadcasting Station at

Holme Moss, near Huddersfield

THE BBC's Very High Fre-

quency (V.H.F.) sound broad-

casting station at Holme Moss,

near Huddersfield, was brought

into service on December 10. This

new station, which is on the samesite as the BBC's Holme MossTelevision Station, transmits the

North of England Home Service

on 93.7 Mc/s, the Light Programmeon 89.3 Mc/s and the Third Pro-

gramme on 91.5 Mc/s, each with

an effective radiated power of120 kW. As at other BBC V.H.F.

sound broadcasting stations, the

transmissions are horizontally

polarised which means that receiv-

ing aerials will need to be fixed

horizontally.

The area in which satisfactory

reception is expected has a popula-

tion of approximately 14 million

people. It includes Yorkshire,

with the exception of the northern

and extreme eastern parts of the

North Riding : Lancashire as far

north as Morecambe Bay ;

Lincolnshire with the exception of

the extreme eastern and southern

parts ; Cheshire ;Derbyshire ;

Nottinghamshire ; north Leicester-

shire ; north Shropshire : most of

Staffordshire ; the northern part

of Anglesey ; Flintshire, and mostof Denbighshire.

Mr. E. K. Cole to Visit the Far East

A/TR. E. K. COLE. Chairman**•*- and Managing Director of

E. K. Cole, Ltd., left Britain onSaturday, December 1, bound for

Australia, where he will see for

himself the progress being madeby his associate company in

Sydney— Ediswan-Ekco (Ausi.)Ptd. Ltd.—which is jointly ownedwith Associated Electrical

Industries Ltd.

A remote control device, operated from a tanker moored at the end of

submarine cargo loading lines three and a half miles out at sea, which

is capable of stopping the cargo-loading pumps on shore, has recently

been installed at a cost of110,000 at Lutong Refinery in Sarawak, British

Borneo. This equipment, now in service, was developed jointly by

Shell and the General Electric Company, Limited, London.

February.. 1957

Television receivers are comingoff Ihe Sydney production lines

at an increasing rate to meet ihc

demand arising from the openingOf the Australian television service.

First porl-of-call before Australiawill be U.S.A.. where already Ekcoradio receivers and heating andelectronic equipment are wellknown.

PRACTICAL WIRELESS

serve them, and those who visit

the new premises will find completetechnical and information servicesavailable. In addition there

-

will

be extensive showrooms, ademonstration centre and cinema.

Mullard House, as this newbuilding will be called, has beenbuilt by Capital and CountiesProperty Co. Ltd., and will be

occupied by Mul-lard Limited on along lease. Themain contractorswere Lavender.MacMillan (Con-tractors) Ltd. andt h e a r c h i l e c t s

for this projectwere Robert Sharp& Son.The move will

take place in the

near future andeventually all headoffice staff will beaccommodated inthis new building.

Unique RecordingExperiment

•TWO youngBritish ex-

plorers, Mr. andMrs. G. Durrell, ofBournemouth, will

soon be in thejungles of theBritish Cameroons,where they intend

onduct a uniqueexperiment—record-

the family life

A novel installation from Fiance. It is not statedof

.|,ne„ g°n"a -

whether the installation is for the benefit of the, Wei known to a

baby or its mother. *W '«stcning and

805

Ekco have considerable interests

in New Zealand and India, andduring his forthcoming overseastour Mr. Cole plans to visit TheNational Ekco Radio and Engineer-ing Co. Ltd., Bombay, and TheUltimate-Ekco (N.Z.)' Co. Ltd.,Auckland.

Mullard HouseMULLARD LIMITED will

shortly be moving into their

new headquarters at TorringtonPlace, W.C. I . For some years nowseveral departments of the organisa-tion have been temporarily accom-modated in a number of separatepremises and the move will .

eventually bring all departmentsunder one roof.

Customers of the company will

viewing public, Mr.and Mrs. Durrell will spend eightmonths in the northern part ofthe Cameroons. It is their thirdexpedition there.

Although they will also becollecting fauna for zoos inBritain, America and the Continent,recording the mating and familylife of the gorilla will be the majoritem in their programme.When Mr. and Mrs. Durrell

decided on the experiment theysought the help of MinnesotaMining and ManufacturingCompany recording experts.

As a result of exhaustive tests.

14.000ft. of Scotch Boy tape ofspecial strength and high fidelity

will be used. This tape is particu-larly suitable for regions wheretemperatures and humidity are

benefit from the centralisation of high, as its water absorptionthe various departments which practically nil because of the super-

strong polyester base. It is un-affected over a range of 1 50 deg. C.

Two New Radio-telephone Services

QABLE AND WIRELESS LTD.announce that a radio-tele-

phone service was opened onDecember 1st between the UnitedKingdom and Fiji by linking theU.K.-Sydney and Sydney-Suvaservices. The cost of a three-minute call is £3 15s.. with a reportcharge of 4s.

A direct radio-telephone servicehas also been opened betweenAmman (Jordan) and Djeddah(Saudi Arabia). The charge for athree-minute call is the equivalentof £1 10s., and the service is

available on Mondays, Wednesdayand Saturdays between 13.00 and14.00 hours G.M.T.

Radio and Electronic ComponentShow

"DECOGNISED as one of themost important technical

displays or the year in GreatBritain, the 14th annual exhibitionorganised by the Radio and Elec-tronic Component Manufacturers*Federation is to be held at Gros-venor House and Park Lane House,Park Lane. London. W.l, fromMonday, April 8, to Thursday,April II. 1957.

Formerly known as the RadioComponent Show, the title hasnow been changed to Radio andElectronic Component Show to bemore descriptive of its scope,covering as it does componentsfor the radio, television, tele-

communications and electronicindustries in their widest aspects.The exhibition has grown from

year to year- next year 160 manu-facturers are expected to exhibitand this has necessitated holdingit in two sections which, however,arc close together and will beorganised and operated as a singleexhibition.

For overseas visitors and otherspecial guests a preview is beingheld from 10 a.m. to 2 p.m. on thefirst day. April X. Admission is

by ticket obtainable from theSecretary. R.E.C.M.F.. 21, TothillStreet. Westminster. London,S.W.I.

Radio ShowA REMTNDER that the 24th

National Radio Show will beheld at Earls Court, London, frontWednesday. August 28, to Satur-day, September 7. 1957. There willbe a preview on Tuesday, August


ANACORNACALL WAVESIGNAL GENERATOR

A NOVEL UNIT FOP THE EXPERIMENTER

AND SERVICEMAN

By F. G. Rayer

THE circuit described here has the particular

advantage or low cost, as only a single valve is

used and relatively few components. Despite

this, it will produce an R.F. signal, on the fundamental,

between J 6 and 2,200 meiies, modulated or un-

modulated at will. For lower wavelengths than 16

metres harmonics may be used, as with most com-mercial signal generators of the less cosily type. Thegenerator will also produce an A.F. note of adjustable

frequency, and this is useful for checking A.F.

circuits. As tuning is continuous in four bands,

operation is also possible upon the intermediate

frequency of any standard receiver, for I.F. circuit

alignment.

The circuit is shewn in Fig. 1, and employs a 954

Acorn, which is of small size and easily obtainable at

low cost from many sources. Oscillation is obtained

by means of cathode tappings on the four coils.

The grid condenser is relatively large (.001 fzF) so

that at high grid leak values grid blocking arises, the

valve going in and out of oscillation at audio fre-

quency. The frequency of grid blocking rises as the

.5 megohm control is moved towards minimum value,

until the effect ceases, mi an unmodulated R.F.

signal is then obtained. The R.F. signal is taken from

Output

CI. Which is of very low value. When an A.F. signal

is required this is taken from the A.F. output terminal,

the note being adjusted by the .5 megohm control.

Valves other than the 954, of H.F. pentode type, will

operate in the same manncr,with these values.

A small eliminator type transformer is used for

heater supply and H.T. Only a low H.T. voltage is

necessary, around 45 volts being most suitable. TheD.C. obtained from the metal rectifier is smoothedby two 2 /.iF condensers, and a 2K resistor. These

values are in no way critical. If the H.T. secondary

delivers a higher voltage the 2 K and 5 K resistors

can be of higher value to compensate for this.

Coil Details

Four coils are required with cathode tappings at

approximately the centre. The actual position of the

Fig. 1 —Theowtical circuit of the signal generator.


tapping is by no means critical. If loo low down the

coil oscillation may be top weak for A.F. modulation;

if too high up the coil oscillation will be excessively

fierce. A position about one-third to half up the eoilis thus most suitable.

The smallest coil "A" seen in Fig. 3 has 16 turn-, of26 s.w.g. enamelled wire on a Jin. diameter former,centre-tapped, turns closely side by side. This tunesfrom 1 6 to 65 metres.

Coil4i B " is a lin. diameter lube mounted with a

long bush and boll, as shown in Fig. 2, and lias 32mens of 26 s.w.g. enamelled wire side by side. It is

Grid

Details of the rails.

also centre-tapped and tunes from 60 to 200 metres.The larger coils could also be wound, but in view

of the large number of turns ready-made coils aremost suitable. Coil " C " consists of a standardmedium-wave dust-cored coil, with the addition of 45i urns of 42 s.w.g. silk covered wire. The junctionof this winding and the existing winding forms thecathode tap, and both sections must be close together.This coil covers 200 to 700 metres.The final coil, for 700 to 2,200 metres, consists of

a slandard long-wave dust-cored coil, with a lappingmade al a point roughly one-third to half from theearthed end. This tapping is obtained by carefullyprising up a lurn, scraping away the covering andsoldering on a length of thinconnecting wire. Prior to

soldering a small piece ofcard can be slipped underthe joint to prevent sojderflowing upon ihe olhcr turnsof the coil.

The two largest coils aremounted on a bracket, asin Fig. 2, and the actualwavebands covered can beadjusted initially by modi-fying the positions of thecores. Before calibration

the cores should becemenledin position. To secure thebands given it is importantto use a tuning condenser o\'

The full .0005 /J.F capacity.The wide coverage is due tothis, and a low minimumcapacity, bolh in condenserancl valve, etc.

Constructional Details

The parts may be accom-modated in a case 5.1 in. by!in. by 3in. and this should,be of metal to avoid Straj

radiation. The case actually

employed was a screening box from the TRt)sei. but no great difficulty should arise in makingsomething suitable or employing a case lo hand.Provided the parts can be fitted in. dimensions areunimportant.

Fig. 5 indicates the positions of the controls. Forband selection a four-way iwo-pole switch is used.Most of the wiring will be clear from Fig. 3, and all

connections must be stout and direct,if accurate cali-bration is to be maintained. To avoid possible errorsit is best to wire one coil at a time, or even to try theunit with a single coil only and the switch at thisposition. All centre taps go to the cathode circuit andall grid ends to the grid circuit via the switch in bothcases. All the earthed ends are taken to convenienttags bolted to the metal frame of the condenser or topoints marked M.C.

Special care is required when soldering in the valveor the glass seal may be fractured due to heating.To avoid this, thin tinned-copper wire of about 24s.w.g. can be used for the pin leads. A length of thewire is twisted to each pin and a really hot iron appliedto the extreme end of the pin only, together withcored solder. The joint should form at once, and theiron must be removed immediately. Anode and gridconnections are shown in Fig. 3. Other connectionsarc given in Fig. 4, the valve being viewed from theanode. or larger end. •

R.F. and A.F. terminals require insulated bushes.Condenser CI must be of extremely small value andis made by making one turn o\' connecting wire-

round the insulated connection going to the lixedplates lag of the tuning condenser? The .001 /.F and.01 //F condensers are bolted to the frame of thiscondenser. The valve is supported by the w iring andparticularly by a short lead from suppressor grid pinlo tuning condenser frame.

For mains switching a lead-through type ofswitch- is included in the mains leads. The latter areanchored to a twin tag strip, seen in Fig. 3, but this

To HX Secondarywinding ="<^. 76 AC.

Fig, 5. Back layout of Sfg+Ht/ generator.

'/tains


will not be necessary if the transformer has tags for

primary connections.

For ease of operation directly-calibrated tuning

scales arc used, as shown in Fig. 5. These are drawn

on stout card, together with markings for the band

switch, etc. This card is bolted to the front of the

containing, case. After wavelength calibration a

piece of celluloid or Pcrspex of the same size may be

bolted on top of the card to preserve markings.

954 Acorn

Swiich

To 6'3v.

Anode end

Fis. 4.— Valve connections.

receiver with reaction is much better. If reaction is

advanced until the receiver is on the point of oscilla-

tion, tuning can be for zero beat, and this will be more

accurate than is possible with a superhet. Thecalibrated generator is set to some definite tuning

point and the signal tuned in on the receiver. Thehome-built generator is then tuned until its note is

also accurately in tune on the receiver. The wave-

length (or frequency) reading on the calibrated unit

may then be marked upon the appropriate scale on

the home-built generator.

If no ready-calibrated generator is to hand per-

fectly satisfactory calibration of the home-built

generator is by no means difficult, but will take

longer. BBC stations will furnish many tuning points

for the receiver. The generator is then tuned until

its note is at maximum volume, and the wavelength

is marked on the scale. At ihe same time the degree

reading is noted as exactly as possible upon a wave-

length graph. Several M.W. stations will allow ihe

M.W. graph to be completed, and the wavelengths

A large ex-service tuning knob with celluloid

cursor is used, and no reduction drive is necessary.

Such a cursor may readily be made and screwed to a

knob of instrument type, about 2in. in diameter. Asan aid to initial calibration a degree scale, marked

to 180. is also provided in the position shown.

An initial lest should be made to see that the

generator oscillates on all bands and that modulation

may be obtained at will by operating the .5 megohmcontrol. Lack of oscillation on any band may indicate

switch or coil wiring is incorrect. Since the A.F. note

is produced in the way explained the presence of this

at all positions of the band switch will show that the

generator is operating properly.

The back must be fixed firmly in position before

calibrating the tuning scales.

Methods of Calibration

]f a ready-calibrated signal generator can be used

calibration is very easy. In each method a receiver

tunable over long, medium and short waves will be

required. A superhet can be used, but a T.R.F.

Figs 6.— View of ihe interior. Compare with Fig. 3.

Fig. 5.

—

Panel layout.

falling within this can then be transferred to the

scale on the generator by reference to the degree

readings. ,.„ • ,,

Harmonics can then be used to fill in other scales

and points where no stations are available. For this

purpose the receiver will always be

tuned to some multiple of frequencies

on the generator. For example, if

the generator were tuned to 500 kc/'s

(600 metres) its note would be heard

also on 1,000 kc/s (300 metres),

1,500 kc/s (200 metres) and so on.

But it would not be heard on 250 kc/s

( 1,200 metres), etc.. because these

are not multiples of the fundamental

(500 kc/s). With a T.R.F. receiver

it is possible to hear up to the sixth

or eighth harmonic. It is also

possible to obtain tuning points onhigher wavelengths by adjusting both

generator and receiver. For example,

the generator may be tuned to 350

metres, and the receiver tuned to this

signal. The receiver is then left un-

touched, and the generator tuned to

higher wavelengths until its note is

heard, It will then be on half the

frequency of thereceiver, or twice

the wavelength—700 metres.

Repeat the procedure with other

wavelengths.

February, 1957 PRACTICAL WIRELESS

LAST month we finished with the essential detailsof a suitable prc-amplifier and at (he footof this page we now show the theoretical

circuit of this section. This shows, on the right,(he frequency-correction circuit for various recordings.It will be remembered that the tone-control circuitwas described in the first section of this article andit is built as a portion of the main amplifier. Thistone-control arrangement is. however, a bone ofcontention among many amateurs. Some say it

should not be used at all, and that the amplifier andreproducing chain should be as straight as possible,and that the music or speech should be reproducedjust as it comes over either on the radio, from a tapeor from records. They hold that the control engineersat these various recording channels make the necessaryadjustments, and that it is often difficult to knowwhether your own adjustment of the tone controls is

not, in fact, introducing a wrong balance. However,the tone-control section docs enable one to make acut in top or emphasise bass if, for some reason, onefeels that the balance is not correct or is not to one's

A USEFUL AMPLIFIER. WITH TONECONTROL AND PRE-AMPLIFIER

By J, S Kendall

{Continued from pagi 758 Janitor) issue)

own particular liking. It would, however, be difficultto adjust these controls when changing records, andeach disc would then have to contain on the label thesettings of the various controls which had been foundby previous playings to be most suitable. This meansthat when a disc is changed, or on changing over fromstandard to L.P., the settings would have to bechanged, and it is obviously preferable if a fixedcorrector circuit can be incorporated so that a switchmay be marked with the indications for StandardL.P., 45 or 33, etc., and this would enable a fixedcorrection to be applied to all records in each class,leaving the tone controls at " level " or makingindividual adjustments as required. It will beappreciated that, owing to the method used in

recordings each type of disc does have to have soukform of correction applied, and if a L.P. disc is

played on an uncorrected circuit it will be foundhigh-pitched, whilst if this is corrected by somenetwork and without alteration when a Standard is

played it will be found lacking in top.The frequency correcting network is, therefore,

Fig. 1.— Theoretical circuit of the prc-amplifier.


part of (he pre-amplifier and it will be seen to consist

of the usual fixed resistors and capacitors, and the

control is effected by means of a two-pole four-wayrotary switch. In addition to carrying out the functionof changing the correction network, it also makesthe necessary modification to the input circuit

for radio or records, a single position with correction

being provided for the radio input, and the threeremaining positions being strapped on the input

side for records. Two standard sockets

are provided for the input, and these

should be preferably the small Bulgintypes with suitable plugs, the latter

being provided with screened cable fromthe pick-up or radio set.

Wiring

Fig. 8 shows the wiring of the pre-amplifier andthe illustration on the right shows the inside view

of the actual unit. The layout is simple and nodifficulty should be experienced in wiring.

Valve Substitution

Readers often write and ask whether such andsuch a valve may be used in place of one specified

in our published circuits. Valves that are shown

in the manufacturers' lists as direct substitutes

will work in orthodox types of circuit, but notnecessarily in direct-coupled amplifiers. Theuse of the N709 in place of the specified EL84

Orange6*3'V.u'Red

m

Underside view of the pre-amp.

valves presents no trouble, and in fact it is quitepossible to use one of each in this amplifier, in a20 watt version, however, details of which will begiven later, the specified output valve is an EL34,and although the KT66 is a rated equivalent it cannot

be used in the direct-coupledcircuit. This will be explainedlater. The Z729, however, appearsto have the same characteristics asthe EF86 used in the first stage ofthis amplifier, but it is not, in

COMPONENTS LIST FOR I

PRE-AMPLIFIER1 chassis, Kendall and Mousley I

Ltd. f

I B8A valveholder,' McMurdo. '

1 EBC41, Mullard Ltd. i

2 J6 Bulgin Plugs.1 100 pF Ceramicap1 200 pF Ceramicap1 680 pF Ceramicap

Lab." i

Lab."{

Lab." i

'Lab." !1 3,000 pF Ceramicap1 .05 /iF paper.I 50 «F 12 volt.

1 16 tiF 500 volt, can type.

1 switch, Kendall and MouselyLtd.

Screws, tags, wires, screenedcable and octal plug.

1 " T " 2.2 M ohm, " Lab."2 " T " 220 K ohm, " Lab."2 " T " 150 K ohm, " Lab."1 " T " 2.2 K ohm, " Lab."2 " T " 68 K ohm, " Lab."4 " T " 100 K ohm, " Lab."1 "T"1M ohm, " Lab."

Screened leads

Red

Orange Orange

Fig. 8.— Wiring diagram of the pre-amp.

Loop screen to here

Fig. 9.— Wiring of the plugmentioned last month.


practice, quite the same. However, it may be foundwith some specimens that a balance can be found at

the extreme end of the balance control. A DH77,whilst it has the same characteristics as the EBC4Iused in the pre-amplifier, has a different base, andtherefore is not interchangeable, but if it is desiredto use it the base may be changed to suit and it will

work satisfactorily.

Fig. 10.

—

Details of the chassis for the pie-amp.

Speaker

Whilst the amplifier may be used in a small hall,

the question of using a high-note or tweeter speakermay arise.

The output impedance of the normal amplifier is amatter of 4 ohms. That is not the actual resistance

of the speaker coil but its apparent resistance to afrequency of 1 ,000 cycles. For higher power amplifierswhere several speakers are to be used, the line or leadloss for a 4 ohms impedance is high, so an output of15 ohms is used. It will be appreciated that with anamplifier one requires to have the maximum amountof the output transferred into usable sound and notlost in the wiring. It will be seen that if the leads to

the speaker are of any length they will have a com-parable resistance wilh that of the impedance of thespeaker. For example, if the leads are of 1 ohm andthe speaker of 4 ohms, 20 per cent, of the total powerwill be lost in the lines as well as there being a 20 percent, miss-malch applied to the amplifier. This latter,

with amplifiers with heavy feedback, is not nearly soimportant as those without. Using the same leadsand speaker of 15 ohms impedance, the loss wouldonly be 1/1 6th and the miss-match 6 per cent.

If the speakers are to be a permanent fixture, thenthe ends of the leads can be soldered direct to the tagsof the speakers. However, it is not always possibleto leave the speakers in situ. In this case, it is a goodplan to terminate the wires on a socket. There areon the market a series of different types, some usingflat pins made especially for the job. Jack plugs andsockets are very useful, and the P38P plug made byBulgin is ideal as it is certainly not easy to damage.The insulation of the cover is of the soft plastic type

and not the usual hard and brittle material so often

met with.

Where very long lines are met with, such as wouldbe the case in factories and places with a long distancefrom the amplifier to the speakers, it is best to matchthe amplifier to a "600'* ohm line. At the otherend the line can be matched down to the speaker.

This system is also of use where a large number ofspeakers are to be used, as one does not get the large-

variation in volume between speakers at different

points along the line. Whilst on the matter of differ-

ing volume levels wilh speakers, where several roomsare to be fed, il is a good plan lo use the StentorianSenior speaker made by W.B. as it is a first-class

reproducer and has its own volume control. (Afeature of the range of all Stentorian speakers.)One of the features of negative feedback with

amplifiers is as mentioned before, that il makes thematching of the speakers to the amplifiers less critical

and allows a far wider scope for switching in andout of loads. However, it is always desirable, if

possible, to match correctly to the amplifier. Withmulti-speaker systems this can be done with a parallel

or series combination, or both together. For example,an amplifier of J 5 ohms output impedance is to beused in a hall and the speakers chosen are all of4 ohms, then it is quite in order to join them all in

series making a total of 16 ohms for the load. Here apoint comes in: one must be very careful just how the

speakers are joined in series, as if incorrectly doneone or more of the speakers will be cancelling out theoutput of the others. In the case of two speakersworking against the other two, a very large proportionof the sound would be lost. The effect of this can-cellation also gives odd tonal effects at certain parts

LPH65

Norms!

Fig. \\.—Multiple speaker Fig. 12.

—

A cross-overconnections. arrangementfor a tweeter.

of a hall, as il will completely eliminate certain bandsof frequencies. The easiest method of ensuring thatthey are correctly joined up is to use coloured wirefor the job. and make sure that if, say, the tags are atthe bottom of the speaker, you start at the right fromthe amplifier, then the left tag to right on the next,and so on. On the last speaker the return wire to theamplifier will go on the left-hand tag. Of course, thespeakers may be mounted in any manner, and insome cases in differing tag positions, one can then,to avoid confusion, work clockwise with the wiringas it were, in at the one tag and out clockwise from it.

Parallel connection of speakers is met wilh at timeswhere, say, four 15 ohm speakers are to be joined to a4 ohm amplifier. Here the matter of connecting thespeakers is again of equally great importance. Thefour speakers can be joined in parallel to give justslightly under 4 ohms impedance.

(7b be continued)


The Effects of Screening on CoilsMATERIALS AND TEMPERATURE AFFECT THE " Q " OF A COIL AS EXPLAINED HERE

By R. H. Mapplebeck

N the early days of radio the tuning coils weremounted in the open for easy access, but with

the evolution of the multi-electrode valve

increasing sensitivity and circuit complexity it wassoon found essential substantially to confine all

electromagnetic and electrostatic flux by screening

coils from each other and from neighbouring com-ponents to prevent instability from feedback due

to stray coupling.

Today the screening of coils is inclined to be

taken for granted, but it is both useful and inter-

esting to know just why this has to be done and what

is the effect of placing a coil inside a screening can,

not only on the coil but on the circuit in which it is

functioning.

In general, coils may be divided into two main

categories, high frequency and low frequency, but

as may be expected the material for shielding an

L.I", coil would not be suitable for an H.F. coil.

Electromagnetic Screening

Screening cans of high permeability are used whenthe magnetic flux is unidirectional or from a low-

frequency source. The magnetic flux lines arc pre-

vented from extending beyond the container by such

materials which act as a virtual magnetic short

circuit, giving an effect analogous to that which a

Faraday cage has on electrostatic flux. Fig. 1 (a)

and (b) illustrates the disposition of magnetic flux

when a solenoid is placed inside a container made of

magnetic material of high permeability at low flux

densities such as mu-metal.

In general, electromagnetic shielding extends over

lire audio frequency range up to about 10 Ke/s,

though depending upon requirements it may be

found necessary to use a combination of both

electromagnetic and electrostatic shielding. Such

circumstances may occur in a screened and balanced

transformer where, to preserve balance, the different

sections of the windings may need to be shielded

from capacity effects as well as inductive. Such

transformers usually employ electrostatic shielding

between primary and secondary consisting of metal

foil arranged so that its surface is approximately

parallel with the magnetic field, but provided with an

insulated gap to prevent it becoming a short cir-

cuited turn. This method of screening is used ontransformers which range from mains frequencies

up to radio frequencies in Band M.|

Electrostatic Shielding

This form of shielding extends from the frequency

where the electromagnetic ceases, that is from about

10 Kc/s upwards.The distribution of electrostatic flux for a coil

both outside and inside an aluminium can is shown

at Fig. 2 (a) and (b).

It is difficult to assign a transitional point where

the shielding ceases to be efficient as magnetic

shielding and becomes more efficient as electrostatic

shielding, because as the frequency of a magnetic

field becomes higher, more satisfactory shielding is

obtained by the use of shielding material having

high electrical conductivity, as already mentioned.The magnetic flux in attempting to pass through

such a shield induces voltages that set up eddycurrents which assist in blocking the magnetic flux andprevent it penetrating the shield. This eddy current

effect increases with frequency and with the con-ductivity of the material. Therefore the best metals

are found to be silver, copper, aluminium, etc., andeffectively form a Farady cage by screening the parts

external to the shield from electrostatic effects within.

The exact nature of the shielding material is notimportant, but aluminium is popular on account ofits lightness, ease of working and high conductivity.

Its relative resistivity to copper is 1.64 to 1, andalthough copper has largely been superseded by the

latter metal, it is still used occasionally with silver

plating for high efficiency standard coils associated

with special test gear such as Q-meters.

The eddy currents just referred to do not penetrate

the screen material deeply so the thickness of the

can is determined more by mechanical considerations.

For instance, the minimum thickness for adequateshielding at 100 Kc/s is 0.0325in. Coil cans are

invariably not thinner than 20 s.w.g. or 0.036in.,

which is greater than that required for minimumshielding. At higher frequencies, of course, the

required thickness decreases.

T^ooomc^j^o^y^-

s(*;

Fig. 1.—- Disposition of electromagnetic

side and (b) inside a screening

flux (u) out-

can.


UADIO fOMPOM\TS-RETllR\-OF-POST SERVICEDetails of some of the items from our extensive stoclj of Radio and Television components are given below.

All items are usual.lv held in stock and all orders are"normally dealt with on the day they are received.

OSRAM 912 PLUS AMPI.rrfF.ilINSTRl CTION MANUAL, 4 -. PRICE T.IST Free.

RESISTORS. Lab. Kits. Main Amplifier, only 38/4. inctnoiihree potentiometers. Passive Unit. 6 9. Pre-amplifier, 14.3.

TCC CONDENSERS. Main Amplifier, 55-. Passive Unit, 12.9.Pre-Amplffler, I8..9.

All resistors and condensers are availabl [details: list.

OUTPUT TRANSFORMERS. Partridge P3591A, 99.'-. OilsoBWO710, 526. Whiteley. 32 .-.

.MAINS TRANSFORMERS. PartrKlfrt H300.1 10 CP3391B>. 75-.Elstone MT912, 40/6. Whiteley. 78,-.

SMOOTHING CHOKES. Partridge CM) 135. S3 (>. Whiteley, IS'9.

SWITCHES. Specialist Switches. Main Amplifier. 11 - tba pair.

Passive Unit, 11 6. Pre-AmpHfler, 1C 6.

CHASSIS. DrilleO. Whiteley, Steel, gold finish, 34 3.;

'

plain aluminium 14'6.

PANELS. Main Amplifier only. Tele-Radio. 14/8. Denco, 3.

Drilled for Passive or Pro-Amp., Denco, 7 8.

VALVES. Z720. Osram. 24.4 : alternative. 15-. B339. Osram. 19 6 :

alternative. 10 -. n709, Osram, 18/- each ; alternative, 18,-each.0709, Osratn, 1110.COMPONENTS by BuK'in. Belling i.'-e and all other items arealways in stock. i'Ull details are given tn out free price list.

COMPLETE KITS. Main Amplifier only.

Kit A. Complete Kit with Partridge Transformers an 1 Choke,Whiteley Chassis and new Osram Valves. £35.5.0.

Kit it. Complete Kit with Partridge Transformers and Ch ifca

.

Denco Chassis and alternative valves. £21.17.0-

Kil C. Cheaper Kit with FJstonc Mains Transformer, GtUsonoutout. Transformer, Whiteley Choice, Denco Chassis and alterna-tive valves,£19.17.0.Remember that I hesa kits are really complete.

PASSIVE UNIT if required with the above kits. £2.13.0 extra.

I'RE-amim.ikiek if required With the above. £4.15.0 1 strawith Osram Valve or £4.6.0 extra with alternative, valve.

G.E.C, METAL CONE SPEAKER, always in stock at £9.5.0.

CREDIT TERMS. Complete or pun kits can he supplied onCredit Terms. Please since exact requirements and we Will send

a quotation.

MULI.ARI) 510 AMPLIFIERINSTRUCTION MAXl AI.. 3 8. PRICE LIST Free.RESISTORS. Lab. Kits. MAIO'SG. All resistors and potcntio-raeters lor the Main Amplifier only. H1-K39. 39 -. MA10/PA/B.All resistors and potentiometers for Main Amplifiers end Pre-Ampliflor Version B. R2-I122, K27-H29. R31-R54. 57 6. MAIO'PA.'Afor Prc-Amplilier Version A only, R31-R4K. 16 10.CONDENSERS. TCC Kits. Main Amplifier. 45 -. Our alternativekit for Main Amplifier, 30.-. TCC Kits for Pre-Amplifiers, VersionA, 16/-. Version B. 24'3.CHASSIS. Denco. Aluminium ready drilled. Main Amplifierwith base plate. 19,6. Pre-Amplifiers, Version A, 8:6. Version 11.

126.PRINTED PANELS. Denco. Main Amplifier, 6 6. Pre-Ampli-fiers. Version A. 1,6. Version B. 2 6.OCTPL'T TRANSFORMERS. Partridge F3667 (tapped for 6 kand 8 k load). 526. Elstone OTli la k.i. 45'-. Elstone 0T8 (8 k>.45 .-. Ellison OP67 (II kl. 40'-. OPG7A (6 k) 40.'-. Gilson W06C6A(8 k). 47 6. W0898B (6 k). 47.8.MAINS TRANSFORMERS. Elstone MT/510 Main Amplil'oronly. 36.-. Elstone MT ML' for amplifier when Pre-Amplificr orI'M 'rimer are used, 42/6.VALVES. EF86, Milliard. 24 4 :

alternative. 15-. BCC83 Mullard19/6: alternative, 10'-. EE81 Mullard. 16.-; alternative, 12-.EZ80 Mullard, 1110. EZB1 Mullard. 11/10.COMPONENTS by BaJlingr. Bulgin and all other items always Instock. Full details are given in our true list.

COMPLETE KITS, Main Amplifier only. Note—Those kitsinclude the MT510 Mains Transformer. If the pre-ampllfier orI'M Tuner are to he used the MT.MtJ Transformer is required.Elconi Plugsand Sockets will also he required and the price 1

and the difference on the transformer must be added to the kit.

Kit A. Complete kit with TCC Condensers, Mullard ValvePartridge output Transformer, £16.6.0.Kit It. As Kit A. but. with alternative valves mid Condi£13.16-0.Kit C. As Kit B, but with Ellison Output Transformer. £13.4. ".

••RE-AMPLIFIER KITS. Version A with Mullard Valve, £5.4.

T

With Alternative valve. £4.15.0. Version B with Mullard Ve ire,

£6.19.0 : with alternative valve. £3.10.0.PRINTEn CIRCUIT ITEMS. All in stock.Chassis. Special TCC Printed Circuit Pane!. 22 6.Frame to support the TCC panel with small chassis forUnit, 15.-.Condensers. TCC Special Kit, 45-. Vftlve Holders. Spe4 al

Printed Circuit type. 1- each.

GRAMOPHONE EQUIPMENTBSR UA8 MONARCH RECORD CHANCER. -The latest 4-spccd model. Acos turn-over cartridge. Price £9.15.9. Credit

Terms Deposit £1.13.0 and seven monthly payments of £1.6.0.

BSR TU8 MOTOR AND PICK-UP. Three speed motor arid separate pick-up. The pick-up is fitted with the Aeos turn-Over

crystal cartridge. £4.17.6.

COLI.A.RO TRANSCRIPTION MOTOR. Complete with the Transcription pick-up and insert. £19.10.0. Can be supplied

less pick-up at £14.18.0.

TV PATTERN REMOVAL I NITSpencer West Type 54. These units win give considerable assistancein removing patterning on the ITA picture. Complete with in-

struction leaflet, 25'-. __„ , , . ,, ,

I lamor Band 1 Filter. For removing BBC signal when it :s entering1 he converter via the ITA aerial. 10'-.

TRANSISTORSMULLARD.—OC70, 21/-: OC71. 24-: OC72, 30'-. MatchedPairs 60-. stc, TJl oiXMOiiNi. 40- ; TJ2 (3203018), 45'- ', TJ3l3X'302N). 50/- : TS1. 18- : TS2. 21- : TS3, 24'-

; TP1, 40- :

TP2 af)'-

CRVSTAI. SET COMPONENTScoils.- Teletron hax 3-- SpecteJls made for use with Or:

Diodes. Suitable diodes 2'6.

TUNING CONDENSER.—.0005 mfd.. 3/lfl ....CHASSIS.—Small metal chassis with tunaerial, earth and phones. 2/9.

TUNING KNOB.—IKCONDENSERS AND RESISTORS

We carry a wide range of these and fun.', detailed lists are .'•

&M ° r ,3Smge- VIEW MASTER CONVERTER

INSTRUCTION MANUALS are now available. Thea reprtnl of the articles in "Practical Television."' Price 2 G.

"TELEVISION ATTIMMORS

Belling Lee Co-Axial plug-in Type. Available In Bdo, izdb. 1Mb.24do ana S3 rib. 4.6 each.

CO-AX I AT, (ABLEThe vary best quality seml-airspa- ed. Emir.-- >

;-:.' : >ie rut Band 111

and EM. 10(1. per yard : 82:6 per l |l(l yard drum.

WHITEEEY CABINET.*AU these Cabinets are packed flat for easy home assembly.new Junior Bass Keflex Corner Console, £9.9.0. Bairn Keflex Console, £10.10.0. Senior Bass Keflex Corner Console. £11.11.0. Allthe other Whiteley types are available. Illustrated leaflet avail -

able free. Credit terms on these cabinets with a speaker if required.

WHITEEE Y SI'EA K ERSThe Whiteley Hi-Fi ran?e of sneakers. lOin. 11F1012, 99/9. 9In.HF913, 83 8. 8in.IlF812." £4.3.6*. Bin. T316. the new Treble speaker.£6.10.0. Whiteley Cross Over Unit CX1500 for the T3I6. 38/6.Bin. HF816, £6.17.0. TiO Tweeter. 84.'-. Crossover Ontt CX309>n, r tins tweeter, 30/-. Detailed leaflet on ail w.B. Speakersavailable..

TEST INSTB I MENTSA\'0 Meter Model 8, £23.10.0. AVO Miter Model 7. £19.10.1.1: \ DAB Kllovolter for e.h.t. Measurements, 3 to 3) lev., £3.17.3.

TSL TWEETER SPEAKERSThe new Moving Coil LSHU3. 39 3. Cross-over efcofces, .8'! mil..9 mli. .': mil, 1.75 mil. All 3 6 each. Electrostatic, L-SH7S. 12 S.1,311513. 17/6. LSH100, 21.-. 65 mil cross-over chokes, 7:3 each.

1'APEIt BLOCK CONDENSERSVery hiijh grade 2 mfd. 250 v. Paper Blocls Condensers. Ideal lormaking: up (he capacity required for cross-over networks. 2 - each.Brand new. Not ex-Government.

CREDIT TERMS.—Anything we sell can he supplied cm Credit Terms. The deposit is 3- in the £ and the balance payable over7 months. Send details oi your exact requirements and we will submit a quotation.

TERMS OF BUSINESS.- Cash with order or C.O.D. Please add postage tinder £3. We charge C.O.D. fees on C.O.D. ordersunder £5.

W%TTS ItAmo 8, APPLE MARKETKINGSTON-ON-THAMES, SURREY

Telephone : KINgston 4099Shop Hours: Monday, Tuesday, Tlinrsdaj —9 a.m. to 5.39 p.m. Wednesday -9 a.m. to 1 p.m. Friday, Saturday -') a.m. to


fot-9 tegufah

smooth response cam

You need a PHI LI PS

dual-cone

loudspeakerMade iu Hull.'tnd

The Philips dual-cone loudspeaker comes in two sizes:

8" and 12", price Oil gns. (tax paid) and 10 gns. respec-

tively. There is also a-single-cane loudspeaker, available

in the same twe Sites: price £6. 2s. 6d. (tax paid) and

£10.0s. Od. respectively.

A special dual-cone design

distinguishes Philips high

lidelily speakers, resulting in

energy transmissions almost

independent of frequency.

This ensures that, in an

ordinary room, sound pres-

sure within an angle of 90degrees varies by not morethan six decibels; while the excellent spatial

distribution of acoustic energy — even a', the

highest frequencies — is obtained by Philips

choice of coupling factor between high-range

and low-range cones.

The small cone acts as a high note

radiator for frequencies above 10,000

Cycles and as a dilTuser for frequencies

below 10,000 cycles from the large cone.

The large cone itself acts as a low note

radiator below 10,000 cycles, and as areflector for the high notes above ihis

frequency. The distribution of sound over

the entire frequency range is thus muchwider than on a normal loudspeaker.

These loudspeakers have a very smoothresponse curve combined with a lowi esonance frequency'

N.B. Any of these speakers may bo used on

their own or with another suitable loud-

speaker using a crossover unit.

For lull details write to:

ssi PHILIPS ELECTRICAL LTDMusical Equipment Dept. • Century Houss

Shaftesbury Avenue • London • WC2(PR435)

OPEN tii.i,C P.M. SATURDAYS

E PREMIER RADIO COMPANY =B. H. MORRIS & CO. (RADIO) LTD.

(Dept. P.W.) 207, EDGWARE ROAD, LONDON, W.2Telephone :

AMRASSADOIt 4033l'Al)I)l\<il()\ 32". 1-2

BUILD THESE NEW PREMIER DESIGNS

2-BAND T.R.F. RECEIVERMAY BE *» (

-f C ft Plus 3 '" Pk -

BUILT FOR 3uD» I O.U & Po>t.

3-iiaiui Super-set Bocwvermay be builtfor £7.19-6plus pk.& carr.3/-. These tworeceivers usethe latest typecircuitry andare fitted intoattractive cabinets 12in. x 6.jin. x 5;in. Ineither walnut or ivory bakeiite or wood.Individual instruction books 1,- each.post free.

MULLARD AMPLIFIER KIT

\Y fiy A11 I he components lor

model 510. PLUS preamplifier

on one chassis (total six

valves) may bo purchasedfor £12.12.0. Plus pkjr. & post

7/6, or preamplifier and tonecontrol in a separate unit,

HeSt ' £14.14.0 plus pkg. & post 7/3.

IVOW SUPPLIED WITHULTRALINEA It OITI'II

THAXSFOBJH 111

not

makethe

Send for the Premier WIDE ANGLETELEVISOR booklet. a/6 post free.

ALL-DRY BATTERYPORTABLE RADIO RECEIVERMAY BEBUILT FOR

£7.8.0Plus 3- Pktr.& Postage

4 Miniaturevalves in asuperhet cir-cuit covering:medium andIon? waves. Rpx-ine covered cabinets11 Sin. x lOin. x 5jin.. in contrastingcolours, wine with grey panel. Instructionhook 16 post free, which includes fullconstructional details and list of pricedcomponents.

COMPACT GRAM AMPLIFIERSuitable for anytype or Pick-up.Volume and tonecontrol fitted withknobs. Overallsize 7i in. Ion? xKlin, wide x 2Un.Iiiirh. Completeand ready for use.

£2.19.6Plus packing & postage 2:6.

GRAM

UNITS

H.s.it. 4-SpeedAutochaiigor.

£9.15.0 plus 5- pk?. & post.

B.8.R. Tl'8 3-Six-cd£4.12.6 plus 2,6 pkg. & post.

MAY BEBUILT FOR

4-WATT AMPLIFIER

£4.10.0Plus 2/6 Pkrr-

& Cair.

Valve line-upbSL7. BVB and6X5, FOR A.C.MAINS 200 250VOLTS. Suit-able for either3-ohm or 15-ohm Speakers.Negative feed-back. Anytype of pick-upmay be used.Overall size 9in. x Tin. x Sin. Price ofAmplifier complete, tested and ready foruse, £5.5.0 plus 3 6 pkg:. and carr.

A STEEL CASE IS NOW AVAILABLE.COMPLETE WITH ENGRAVED PANEL,

15/6 EXTRA.

A NEW TAPE RECORDERCREDIT TERMS DEPOSIT £5and 8 monthly payments of £4.18.6

H.P. TERMS 1 DEPOSIT £20and 12 monthly payments of £1.17.1

Cash price £40 plus paclcin? and carriage21/-. Case finished in Brown and AntiqueFawn. Size 15in. x 12!in. x 7}in. with thevery latest type Continental fittings. ForA.C. mains 200-250 volts, 50 cycles.

SEND KOK LKAl'LKTSEND 2id. STAMP FOR

CATALOGUEOUR 1937


/i?\ /V\/7 / I/

Seen-ae-Eye !

IKNEW it would happen ! As soon as ourBBC announcers have to announce a foreignplace which is in the news they go into solemn

conclave to arrive at some obscure and totallyincorrect way of pronouncing It, When Sinai cameinto the news I expected the announcers to mispro-nounce it and 1 was not disappointed. It's so fruit-fully BBC to pronounce a word or a name differentfrom the accepted standard. It makes Ihem appear sovery superior and the listeners so uneducated,especially those who presume that if the BBC saysit it must be right. During the war. in the days ofAl Varleydell (whom you will remember I look totask for mispronouncing his own name, which is

Alvar Lidell), there was the announcer who indulgedin that monstrosity "the Ukryne" for Ukraine.Now we have Seen-ee-eye, for Sinai, which it correctivis. You and I and everyone else have been taught topronounce it that way (Syn-ay-eyc). Could not some-one at the the BBC check up with various Embassieson English pronounciations of foreign place-namesbefore putting these absurdities on the air?

American Midgets

T J-IAVE, in past issues, written quite a lot aboutx midgets, and invited readers to submit details ofany they have made. Nothing really midget, however,came along. They were mostly of the all-dry typeand designed round a fairly large battery' thereceiver itself was small enough, but there is noadvantage in making a tiny receiver unless it makesuse of equally midget batteries. In America thereare many commercial really midget receivers yieldinggood volume and having reasonable long-life batteries,and they sell in large numbers. They are not intended,of course, for domestic purposes, but for the oddoccasion when you arc out and want to listen to thenews. They can be toned down so that only theowner hears the transmission. Such receivers' havenever attracted manufacturers over here and I amquite certain there would be a large demand for themif some manufacturer took his courage into hishands and put such a set on the market. Midgetbatteries having quite long life are available (indeed.one is incorporated in a pocket lighter in this country)and with transistors, printed circuits, midget resistors.

condensers and loudspeakers I see no reason whythey should not be produced. I handled one the otherday which was smaller than a cigar box in area andonly fin. thick. It easily slid into the side pocket andreproduction was of good quality . No one, of course,would expect such a receiver to be a quality receiver,nor would they expect it to be a globe trotter. It

would be a truly personal receiver.

Last year the sales of television receivers exceededthe sales of radio receivers. Manufacturers should,therefore, be seeking new markets and I suggest thatthe really midget portable, now that the ingredientsare there for making it, would provide them.

Guineas for Photographs

TJEADERS are always interested in how otherreaders conduct their hobbies and 1 therefore

oiler prizes of a guinea each to the sender of everyphotograph of a wireless den selected for publication.The photograph should be accompanied by a briefdescription of the den and the name and address ofthe sender. Address your photographs to Den,Practical Wireless, address as on the editorial page.

Decline in Amateur Transmissions ?

CEVERAL of my friends, who were keen amateurtransmitters, have dispersed their gear and gone

in for building sound receivers and TV receiving setsor S.W. receivers. 1 wonder if there is a general declinein interest in this subject ? This journal has regularly-encouraged amateur transmitters and the bookpublished by the proprietors of this journal, entitled"Wireless Transmission," continues to sell a con-siderable number of copies every year. I am informed,however, that the number of queries received by thisjournal has dropped over the years. The R.S.G.B.,of course, could confirm or deny that there is anygeneral decline, but their membership figures alonewould not be a reliable guide because amateurtransmitters continue their membership long afterthey have ceased active transmission. In fact, thefriends to whom I have referred still retain theirmembership out of loyalty to the R.S.G.B. which hasdone so much to foster interest in amateur trans-mission. I enjoy listening in to these transmissions.

Legion of Honour De Forest

AJ[ Y congratulations to Dr. Lee de Forest on beingmade an officer of the Legion of Honour. The

Cross of the Legion was presented to him in Parisby the French Minister of Industry and Commerceon the occasion of the 50th anniversary of de Forest'sinvention of the triode. High tribute was paid to thevaluable contributions of Dr. de Forest to the scienceof electronics.

Building a Car Radio Set

QUR companion monthly, Practical Motoristand Motor Cyclist, contains a very detailed

article on building a compact and sensitive car radioreceiver. The R.F. and J.F. stages make use of6 BA6's, because those valves combine vari-mucharacteristics with a relatively high mutual con-ductance. A 6BE6 is employed for the frequencychanger, although it is here adapted for use as aself-excited mixer. This means that the oscillator coilis tapped to the cathode. The article includes details ofcoil construction, although the standard type ofsingle-windjng oscillator coils can easily be modifiedby unwinding the requisite number of turns, makingthe taps and carefully rewinding. This puts the tapat the finish of the winding. A car radio has tocontend with noise, and in the receiver describedthe signal-to-noise ratio has been given specialconsideration.


MANY readers may well have come up against

the question of removing effectively andquickly all traces of recorded matter from

spools of recorded tapes.

In the author's case the matter arose mainly owing

to the fact that a small battery-cum-spring-driven

portable, self-contained, personal tape recorder had

been acquired, and whilst found very useful and

amusing, no " erase head " was included in the work-

ing mechanism. Once a spool of tape had been

recorded it was necessary to borrow the local record-

ing gear and have the spooi run through and "erased"'

before the tape could be used again. This, with its

attendant inconveniences, caused the author to find

some other method of carrying this out so as to re-use

the tapes on the portable recorder as required and to

save waste and expense.

Whilst no originality is claimed for the piece of

apparatus about to be described the construction will

be found interesting and, so long as the basic principles

Frame

A USEFUL DEVICE TO ERASE TAPES

QUICKLY WITHOUT WAITINGWHILST THEY ARE RUN THROUGH

THE TAPE DECK

By Edward Davis, Assoc.I.E.E.

of the design are adhered to, the possibilities of modi-fications and variations from the original are manifoldand leave plenty of scope for individual ingenuity,

having in mind, of course, what suitable componentsand/or material and constructional facilities mightwell be available in each constructor's workshop.

Design

The present equipment was constructed to operate

for short periods on standard electrical supply,

230/250 volts 501? A.C. current only, but no doubt

Drill and tap 2BA at centre

^ 3-wire Mains Plug 230 V. AC.

Fig. 1.— Internal wiring of the eraser.

Drill 4 holes 2BA clearance

«"W»fta 4 off 2BA steel studs % S*usreM-S;-* / *—^j each with 2 washers and nuts

Fig. 3.— Details of magnet fixings.

readers could work out necessary modifications

required in the coil formation and windings for

alternative voltages and current supplies, and whilst

D.C. supplies are now fast becoming obsolete, where

such exist a somewhat different coil technique would

be required.

In its final form the present " eraser " is designed

round the coils forming the magnetic field. After

much trial and error a pair of coils complete with

laminated pole pieces were taken from two surplus

2 overall length of-N°. 2 gauge plastic

knitting needle asspool spindle

Drill 6BAclearance

Drill lor

Spool brackets..^ off stringcut from tfo Acrylic sheet

TapCBA

(.<

Fig. 5.—Details of the spool bracket.

February, 1957 PRACTICAL WIRElESS 819

24/28 volts D.C. aircraft relays—all unnecessary partshaving been discarded and the pair of coils and polepieces so left were mounted opposite each oilier on ashort length of .]in. square M.S. bar, all as shown on

The whole assembly heldtogether with* 6 rivets

M.S. pistes approx.^thick 6«

of the pair of coils and laminations used in theauthor's set-up which may be helpful should anyreader wish to start construction from scratch.

WiringOther than two suitable coils

being found or made up to givea suitable " magnetic flux " nospecial components are needed.As will be seen by the internalwiring diagram the author in-

cluded a standard three-pin mainsoutlet— a D.P.S.T. mains voltagetoggle switch, an S.P. mainscartridge fuse, and a miniatureArcolectric neon indicator lamp ;

these latter being connected in the'ive lead.

Bolt holes on MS platesslotted to allow final

2BA steel stud, withsteel nuts and washers

1%'.

2 offRH. and L.H required

Dciuil <>/ the Umrinated core

adjustment

a square M.S. bar

the accompanying drawings. This forms (he heart othe " eraser."

Although the design of the " eraser" constructedby the author was primarily intended for use of the5in. tape spools as a maximum it was. nevertheless, soconstructed that up to 7in. spools can be accommo-dated into the " field," some tolerance beina allowedon the bearings for carrying the removal spindle asrequired, as will be observed from the .

sketches of this part of the apparatus. Thev J&&are cut from lin. acrylic sheet. jf"

It was, however, later observed that uh<>» ethe 7in. spools of recorded tape were in?

for erasure there might possibly rem;portion of the tape near the

hub and, particularly if the

spool contained its maxi-mum quantity of tape, a

similar portion of tapenear the perimeter still

containing audible signs ofnon-erasure.

This fault can, however,be overcome in the eventof an " eraser " beingrequired for definite use of7in. spools ; this will beseen from the sketch show-ing the eoij cotes formingpart of the laminationsbeing slightly offset and soto broaden the magneticfield.

It may well be worthwhile to mention at this

stage that the apparatusmay equally well be con-structed to take the spoolsinserted in a horizontal a vie* ofthe InstrumentP

' \n c

;

m hh the panel lifted, andFull technical and dimen- on the right a " ehse*

sional details are given m"" of one of the coils.

The author has made everyattempt to give the completed'' eraser " a very professionalinstrument finish. The cabinet,constructed of jj in. Obeche, beingsprayed three coats of coach-finishblack cellulose and mounted onrubber feet. The thin white" escutcheon " over the spoolinsertion slot was fret-cut from

W3-::-J,m


white opal acetate sheet, the top being,

;

; ;in. black

acrylic sheet with polished edges. Any colours may,

All holes 6BA clearance il£-~\I offin Brass C.P crAcetate sheet, thickness

I ?-, maximum

Ik This slot

6ii-cut out i

7%

Fig. 4.

—

Detail of the overlay escutcheon.

of course, be used to choice. All screws visible are

chrome-plated. The positioning of the components

is not important and may well suit the reader's choice.

The photograph of the completed article well illus-

trates a suitable layout. An improvement might well

be added in the form of a small engraved tablet

reading: "TO ERASE. Switch on before inserting

spool of recorded tape ; revolve spool slowly by

hand, whilst fully inserted with spindle in position,

for, say, half a dozen complete revolutions. Do not,

Neon PilotLampV

* — Rubber feet

Fig. 6. — End view of the cabinet.

switch off before removing spool after rotating. Donot switch on unless a spool of taps is in the spool

carrier." The above, giving an outline of operating

procedure, can, of course, be considerably condensed

for engraving. Should a metal cabinet be preferred,

a ferrous metal should not be used, aluminium being

the most suitable.

When carrying out final wiring a good heavy powerflex or 3.029 wire should be used, either rubber or

P.V.C., and as far as possible all wires kept apart andconnections soldered either direct or via suitable solder

tags. It is important to remember that the pair of coil

windings should be connected in parallel, and that

the coils must be so connected that they " pull"

together and not repel. In order to make sure of this

before finally mounting both magnetic coils oneshould be left free to move on the connecting bar,

when upon switching on the current by temporary

connections, if necessary, it will be easily ascertained

if the two magnetic coils are correctly connected so

as to be pulling towards each other.

The Cabinet

In case any reader wishes to

reproduce a cabinet similar to

that shown, the base was Si'in.

by 6{in. with the two short

sides 5gin. by 3Ain, and the

two long sides 8|in. by 3 A i n

.

The lop was made from acrylic

sheet (black) and measures8Jin. by 5^in. The inside

measure was 7Jin. by 4'in.,

and small pieces of quadrantwere fitted in each corner to

which the top panel wasscrewed. As a refinement, four small rubber feet werescrewed to the base, and the upper edges of this wererounded off. If coils cannot be obtained, a bobbinshould be made to fit the laminations shown in Fig. 2

and these should be wound full with 22 D.C.C. wire.

The resistance of the originals was 170.C; .

h s'J-

-/£-

• fDrill to suit- Switch

J(o • o'; :

i

° This slot cut out O !

:

fe el !

- ''z~^' Drill to suit/TV Lamp

, _J

s%

Dotted lines show position of overlayto escutcheon a/so spool bearing brackets

Fig. 9.

—

Detail of top panel.

Spool Bearings

lT>y

Air space

^ O"2BA tapped into M.S. bar

Fit

MS. bar'

7.

—

Sketch showing spool in position.


The Suppression of InterferencePOINTS TO BE CONSIDERED WHEN INSTALLING CAR RADIO RECEIVERS

Petrol pumpO

RECENTLY, a well-known radio manufacturerintroduced a car radio to be installed by the

purchaser himself. Suppression equipmentis provided with the radio, and in practice it will befound that a very large proportion of cars will require

little in the way of special precautions and it will

only be necessary to fix the receiver and aerial to the

vehicle, connect up the battery supply to the receiver,

fitting a suppressor in the main distributor lead, to

achieve completely satisfactory results.

In some casev however, it may not be quite so

straightforward, and it is the writer's aim to illustrate

all the suppression problems that could possibly be

met with, and their various remedies, it is earnestly

hoped that the following discourse will not convey the

impression that the installation

of a wireless receiver in a vehicle ignition

is a big undertaking only capable Coil

of being carried out by an expert.Dynamo

i

Ignition Interference via Aerial orLead-in

If interference is picked up Cut~out

only when the aerial is connected,it is reasonable to assume that

the aerial, or the lead-in, isp/u9s

transferring interference into the

receiver. First, disconnect theaerial from its lead-in and ascer-

tain whether interference is still

present. If this is the case, the

trouble lies in lack of bondingof the outer screen of the lead-in

to the vehicle. Eliminating thelead-in as the offender, inter-

ference may still be present andbeing picked up by the aerial

itself. The suggested treatmentfor the different types of aerials is

as follows :

on the side of the car nearest to the receiver so that

the lead-in is as short as possible.

(c) Under-car Type of Aerials

Re-radiated interference from various sources such

as exhaust pipe, brake cables or rods, tail lampwiring, etc., is liable to be picked up by this type of

aerial. Bond exhaust pipe, brake rods, etc., to chassis

with heavy copper braid, allowing sufficient slack in

the braid to allow for movement. Tail light leads

and/or other wires should be treated by fitting

filters as previously described. Keep the under-car

type of aerial as far away from the exhaust pipe as

possible and on the side remote from the ignition

coil. The best signal-to-noise ratio is obtained by

Voltage Regulator Loose metallic parts in car body

, Staticfin motion)

trafficator

Most commonsource ofinterference

RECEIVERCHASSIS O Other sources

ofinterference

Under—chassisAerial

(a) Roof Aerial

Interference is usually caused byre-radiation from the car wiringto the roof light, trafficators orother accessories which are in

close proximity to the aerial.

The remedy is to by-pass these

leads at the fusebox or insert a

filter in the lead at the fuseboxend. A useful filter should con-sist of a closely-wound coil oin

in diameter made up of 14/16s.w.g. D.C.C. copper wire, with

two .25 to .5 //F condensers on pipes,

connected, one between each Throttle

end of the coil and earth. c^X°Jtc

(b) Telescopic (Whip) Type Aerial

This tvpc of aerial should be . .,

mounted as far away as possibleAen*

f/anfmfss^n

ReceiverCase

Control,cables

Pilot lamp leadand

+ battery lead

Re-radiationIgnition noise

Static(Car in motion)

from the ignition coil, distributor

and sparking plugs and preferably

Exhaust pipe

Brake rods

Miscellaneous LTwiring near aerial

Wheel l

bearingsTransmission

Loose metallic parts

A chart showing interference sources.


fitting this aerial as low as practicable, consistent withthe ground clearance of the vehicle.

Ignition Interference

This type of interference is identified by a staccato" clicking "' sound at tick-over speeds, increasing in

periodicity as the engine speed increases.

First ascertain whether or not the ignition inter-

ference is present with the aerial disconnected.Assuming that disconnecting the aerial does stop the

noise, it is safe to assume that the interference is beingpicked up by the aerial or lead-in ; either directly

From the points of the sparking plugs, or due to the

ignition wiring being too close to the aerial. Fitting

a* resistance suppressor (approximately 10,000 Q)in the lead between the coil and the distributor head,as closely as possible to the distributor, should effect acure. In extreme cases the fitting of suppressors at

both ends of the lead and possibly additional sup-pressors to each sparking plug may be required.

If the hitter are fitted they should be as close as

possible to the sparking plug, but plug suppressorsare seldom required with the modern well-designedreceiver. Odd cases have been known where it wasnecessary to alter the position of the ignition coil, oreven screen this component in a metal box. Otherdifficult cases have been cured by screening the

sparking plug and distributor leads in flexible copperbraid tubes. Generally, however, the only remedyneeded is the fitting of a distributor suppressor,

provided the aerial has been mounted in a carefully

selected position.

It is a good idea to connect the aerial to its lead-in

and to move the aerial about in relationship to the

vehicle until a point most free from interference is

obtained, when the aerial can then be secured. Makesure that the screening of the lead-in from the aerial

to the set is bonded to the vehicle in a sufficient

number of places. It is essential that it is bonded at

least once, and this should be as close to the aerial as

possible, using a short length of copper braid. Mostof the modern aerials bond themselves automatically

on fixing (ensure that the metal is thoroughly cleanedat the fixing point). Make sure also that the set itself

is making a first class electrical connection with the

bulkhead, dashboard or place of mounting.In the case of engines which are rubber mounted

it is worth while to bond engine to chassis with heavyflexible copper braid in several places. Bondingtogether the silencer, exhaust and tail-pipes is also

advantageous.The roor aerial is the type most free from inter-

ference pick-up troubles, but where interference is

experienced check on the bonding of the lead-in andsuspecT wires which run near to the aerial, e.g., leads

to roof light, spotlights, petrol gauge, etc. By a

simple process of elimination, using a by-pass con-denser, the faulty lead can be found and very often

only the one condenser is required.

Any interference from electric screen wipers,

electrically operated pumps, trafficators, etc., can beeliminated by using these condensers. (See chart.)

As previously mentioned, it is of the utmostimportance that the receiver case is making goodelectrical contact with the car body, and also that anybolts, fixing screws, control cables, etc., on or entering

the case are well earthed.

The battery supply leads may also have R.F. inter-

ference induced in them. Also, if the receiver battery

lead is connected to the ammeter it must be remem-

bered that this instrument is connected directly to theignition system. A condenser of .5 //F to 2 //F placedbetween this point and earth will eliminate thetrouble. A 1 />F condenser placed between the" S.W." terminal on the coil and chassis earth will

sometimes cure interference via the L.T. supply.If R.F. interference is being picked up by control

cables, oil pipes, etc., which run from the engine com-partment through the bulkhead and are near to thereceiver and/or its external connections, this can beremoved by bonding these to chassis earth.

Static Interference

This is experienced usually only when the vehicle

is in motion and can be intermittent or continuous.In the case of intermittent noises, the trouble

is often to be found where movement is taking placebetween two parts of the vehicle which are notelectrically connected, and the cure is to bond the twoparts together with copper braid.

Continuous interference is often associated withbrake shoes, wheel bearings or fan belt. Static

generated by rubbing brake shoes can often beremoved by adjustment 'of the shoes to give clearance,and, failing this, by bonding.

Front wheels offend the most, and sometimespacking the hubs with a good quality graphite greaseafter removing the old grease will ensure success.

Brake static can generally be cured by connectingthe brake shoes with copper braid to the axle.

(Leave sufficient slack for free movement.) Inter-

ference from the dynamo which can best be describedas a whine can be easily cured by fitting a .1 //Fcondenser between the " field

'* terminal of thedynamo and earth.

Static discharge from fan belt or pulley can becured by smearing with a light coating of graphite

—

soft lead pencil will often do this job most satis-

factorily.

General Hints

1. Bonding. As a general rule bonding wires thatare up to 4in. long should be made with jiin. widebraid, 4in.-8in. long with fin. wide braid, and above8in. with Uin. wide braid. Of course, jjin. braid canbe used in single, double or treble strands andperhaps this is the cheapest way to buy it.

Always use the shortest possible length of bondingand try several strips of braid if each in turn is

reducing the interference. Good electrical connec-tions are absolutely essential for good results cannotbe obtained without them.

2. Ensure that all leads which have been screenedand isolated and which are carrying HX haveadequate insulation.

3. Make a thorough check of those H.T. leads fornoises may result from defective ignition wiringcausing intermittent arcs to earth. Do this checkingin the dark by increasing the engine revolutions andinspecting the wiring for visible arcing, particularlyin the region of the H.T. terminal on the ignition coil.

Replace any defective wires immediately.4. By-pass condensers and suppressor resistors

should always be installed as close to the source ofnterference as is practicable and any external leadson these components should be kept as short aspossible.

5. When testing keep one's body away from theignition system and ensure that the engine bonnetwhen closed is effectively earthed to the chassis.


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!

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iS*u


Uuilnmn mMINI -SETThe use of a transformer over-

comes Ihe drawback of a live chassis,and with the valves used, reduces theheat generated in the set to a verysmall amount. Finally, the use ofexternal aerials or trailing wires hasbeen overcome by the use of a"• Ferrite rod " internal aerial.

Circuit Description

The Ferrile rod aerial is tuned byone section of a midget 500 pi-' tuning condenser (C3)with trimmer (CI) connected across LI for medium-wave operation, and trimmer (C2j connected across1.2 for long-wave operation.

Valve J is an Osram X78 triodc hexode frequencyan

_ .... , t ..changer with the cathode

. .

.

'

'

'.""' "''"". "i

connected internally toA miniature A.C.. Mams-operated receiverusing B7G Base valves and a Ferrite Rod Aerial

andA miniature Battery-operated receiver using thenew low-consumption valves and a Ferrite Rod

Aerial.

THE writer has for some years been interested inthe construction of midget radio receivers formains operation, but with each design pub-

lished there has always been the usual drawbacks suchas "

I ive chassis," excessive heal and the inconvenienceol a trailing wire for

aerial. In the design aboutto be described, it is hopedthat the drawbacks men-tioned above have beenovercome.With the introduction of

television preamplifiers andBand 111 convenors there

became available to thehome constructor a smallmains transformer with an output of 6.3 volt I ampand 200 volt 25 mA. The Mini-set has been designedto operate from one of these transformers, and withcareful selection of valves and components it hasbeen found possible to produce a set giving a verygood performance and at the same time to keepwithin the current limitations of the small mainstransformer.

The internal con-is made at pin 3,

By S. E. Addis

healer.

nectionand therefore this pin mustbe connected to chassis

Osmor Q08 and Q09 arcmedium- and long-waveoscillator coils tuning b>C7 second section of ihe

500 pF midget tuning con-denser and medium-wave trimming by C6.

Valve 2 is a Brimar 6BJ6 R.F. pentode with aheater rating of 6.3 volt .15 amp. and operates as anI.F. amplifier in conjunction with I.F. I and I.F. 2.Wcarite f.F. transformers type M800.

Valve 3 is a Brimar 6AT6 double diode triode andis connected as signal diode, A.V.C. diode and L.I .

amplifier.

Ftg. I.— Theoretical circuit of the Mains, version.


Valve 4 iya Brimar 6AK6 output pentode with aheater current rating of .15 amp. and together withthe olher three valves makes a total heater consump-tion of .9 amp.

Power Supply

Wiih an input of 230 volt A.C. the mains trans-

former gave an H.T. output voltage of 180 volt half-

wave which is fed to a small contact cooled rectifier,

the smoothing being carried out by CI 7 and CISand RIO. Final H.T. voltage is about 170 volt andthe consumption 23 mA.

Construction

As will be seen from the illustrations, the receiver is

constructed on a small chassis and front panel, thechassis being 8in. x 2]in. x I in. and the panel 8in. x

6J in. In practice it was found that if the sides of thepanel were bent up, this gave added strength.

After all holes have been drilled and the cut-out

made for the loudspeaker, the tuning condenser,volume control, wavechange switch and trimmers maybe mounted on the front panel. The mains trans-

former should be mounted on the panel as near aspossible to the volume control in order to give plentyof clearance from the output transformer which is

mounted on the chassis.

The Ferrite rod aerial is mounted on two brackets

which may be of an insulating material such asPaxolin.They should consist of two strips 2;?in. x 2>n. witha oin. hole drilled at one end to carry a rubbergrommet. After the rubber grommel has been in-

serted in the hole, the Ferrite rod should be pushedinto the grommet. Jt has been found possible to

mount the Ferrite rod aerial on aluminium brackets

and this method has been used very successfully in

the prototype. If metal brackets are used it is veryimportant to note that the fixing holes should be

made at the end of the strip to form a slot and not acomplete round hole.

It would appear that if a complete hole in a metalbracket is used it has the effect of a " shorted turn

"

and spoils performance.When mounting the Ferrite rod aerial care should

be taken as the Ferrite material is very brittle and will

break if dropped. The aerial should be mounted withthe long-wave coil nearest to the wave-change switch.

This will keep the long-wave coil clear of any metalparts which might otherwise tend to make a noisybackground. Jf either of the coils are removed fromthe rod, care should be taken to see that they are

©X7BChassis

8 "x 2M' x I "deep

l.fl

6BJ6

IF2

replaced the right way round and with the turnsrunning in the right direction, otherwise performancewill be impaired.

After the valveholders, I.F. transformers, smooth-ing condenser and output transformer have been fixed

to the chassis, the panel and chassis may be fixed

together by means of the two lower bolts whichsecure the loudspeaker.The oscillator coils should now be fixed to the

panel and wiring can be commenced.It* was felt that with this type of design, the leads

from the wavechange switch to the frequency changervalve would berather long, butin practice it wasfound that theywere very little

longer than whenusing a coil packand that perform-ance was in no wayimpaired.

The contactcooled rectifier is

mounted on the

front panel behindthe output trans-

former and al-

though no heat

could be detected

from this com-ponent it is as weil

to mount the recti-

fier as far awayfrom the edge ofthe panel as pos-sible as the sur-

rounding metalis used to conductaway any heatwhich may begenerated.

It has beenfound that the

receiver will feed

a tape recorder,

and for those con-structors requiring

this feature, outlet

sockets can be

4

LIST OF PARTSResistors

Rl—1 meg. .] watt.

R2—27 K } watt.

R3—22 K I wart.

R4—47 K £ watt.

R5— I meg. Volume Control.R6— 10 meg. \ watt.

R7—270 K | watt.

R8—2.2 meg. 1 watt.

R9—330 K | watt.

R10—2.2 K \ watt.

Rl 1—470 ohm. V watt.

R12—2.2 mc;'. J watt.

CondensersCI—50 pF Trimmer.C2— 100 pF TrimmerC3—500 pF Tuner.C4—150 pF Silver Mica.C5—.01 /t¥ Tubular 150 VW.Co—500 pF Osc. Tuner.C7—50 pF Trimmer.C8—150 pF Silver Mica.C9—470 pF Silver Mica.C10—150 pF Silver Mica.Cll—.01 mV Tubular 150 VW.CI2—100 pF Silver Mica.C13— 100 pF Silver Mica.C14—.01 ,tF Tubular 350 VW.

Fig. 2.—Layout of Mains and battery mpanel vie

K»

February, 1957 PRACTICAL WIRELESS 82?

(3\

77

Output Transformer

mounted on the chassis permanently. One socketis connected to chassis and the other socket is

connected to the junction of R4 and R5. Jt is agood idea to mount a short tag strip under thechassis to provide an anchoring point for some of thewiring.

When connecting the output transformer it shouldbe noted that the H.T. connection is made to thejunction of the rectifier and CIS. This provides maxi-mum voltage for the output valve with no noticeableincrease in hum and also permits RIO to be of snlallrating.

When workingthe set will befound to be verycool running andwith only a slight

amount of heatgenerated. Dueto the method ofconnection thereshould be no heatfrom RIO smooth-ing resistor, themidget mainstransformershould be onlyslightly warm, andthe bulb tempera-lure of the valvesis the only otherheat present in set.

Forconstructorswishing to try

substitute valvesor components it

should be pointedout that every care

should be takennot to exceed the

rating of thetransformer in use.

The valves in theset have been care-fully chosen so asnot to go beyondthe limitations ofa small preampli-fier on either theH.T. or the L.T.windings.

As a safeguard against damage to th^rectifier ormains transformer, which can be caused by acci-dentally short circuiting the H.T. line, a 60 mA fusemay be connected between the rectifier and the outputtransformer. The fuse may conveniently be mountedon the mains transformer.When carrying out the wiring of the volume

control the leads should be carried out with screenedwire and C12 should be mounted across the tags onthe volume control. This will avoid the possibilityof any grid hum.

It will be noted from the circuit diagram that thelong waveband oscillator coil has no trimmer con-nected across it. This component was found to beunnecessary but a 4-way trimmer strip was used sothe top trimmer was left unconnected.

Alignment

After the wiring has been completed and checkedthe receiver should be connected to the mains andswitched on. A slight hum should be heard if theear is placed close to the loudspeaker. If no hum is

present a check should be made for H.T. voltage andexamination of the fuse if fitted.

If the l.F. transformers, oscillator coils and Ferriterod aerial are new and as received from the manu-facturers, it should be possible to tune in a signalwithout any adjustment. Should no signal be hearda short length of wire may be connected to the gridof the frequency changer. Once a signal has beenlocated the cores of the l.F. transformers should becarefully adjusted for maximum volume. Switch theset to medium waveband and tune in a station at (heH.F. or low wavelength end of the dial, as near aspossible to 200 metres, and adjust the mediumwaveband trimmer for maximum volume. Tune in astation as near as possible to 500 metres, and care-fully slide the medium-wave coil on the Ferrite rodfirst towards the end of the rod and then backtowards the centre of the rod. It will be found thatthe station will peak. Having got the feel of theseoperations the receiver alignment can be completedby first identifying a station at each end of thewaveband. If the position of these stations does notmatch up with the dial readings, adjustment may bemade with the oscillator trimmer for the stationnearest 200 metres afid the oscillator core for thestation nearest to 500 metres. Having got the stationto match up with the dial readings the aerial trimmerand coil and then trimmer again, in that order,should be peaked for maximum signal strength. It is

LTST OF PARTS — continued

Space for BatteryType B 126

and, in the centre, the rear of

CIS—20 pF Silver Mica.C16—.01 pF Tubular 350 VW.C17—32 /iF 350 VW. Electrolytic.CI8—32 /iF 350 VW. Electroivlic.

C19—25 ,<F 25 VW. Electrolytic.

C20—.01 /.F Tubular 350 VW.Ferrite Rod Aerial Osc : Coils tvpe

and Q08 and Q09 (Osmor).465 Kc/s l.F. Transformers TypeM800 (Wearite).

Portable type Tuning Scale.Tl Output Transformer 80-1.T2 Midget Mains Transformer.Mains input. 6.3 v. 1 amp and200 v\ 25 mA output.

Contact Cooled Midget Rectifier 250 v.

30mA.3-poIe 2-way wave change switch.C3 & C6 500 pF Midget Twin Gang Tuner.R5 Midget \ meg. Volume Control with

Switch.4 B7G Valveholders.2 Round Knobs.1 Pointer Knob.

ValvesVI—X78 Osram. V2—6BJ6 Brimar.V3—6AT6 Brimar.V4—6AK6 Brimar.ELAC 5in. Loudspeaker (Type 5/56).


most important that final adjustment should alwaysbe made on the trimmer and not on the Ferrite rodcoil. This is because slight alterations to the mediumwaveband trimmer does not affect performance ai

the high wavelength end of the band, whereas slight

movement of the medium waveband coil on the

Ferrite rod will greatly affect performance at the lowwavelength end of the band.The receiver should now be switched to the long

waves, and the Light Programme on 1,500 metrestuned in. Slight adjustment of the long-wave oscil-

lator core will bring the station into its properposition on the dial. Move the long waveband coil

Bracket. 2 off

i/z hole

&

h I H M& h#42 - c-2 -i ,-->

fig. 3. — Details of the Ferrite rod mottni,

on the Ferrite rod to a position about lin. from the

end of the rod then peak the station with the longua\eband trimmer.

After all alignment operations have been carried

out the coils should be sealed to the Ferrite rod andslight readjustment of the medium waveband trimmermade for maximum performance. It will be foundthai the receiver is directional and may be rotated

for maximum signal strength from a given station.This property has been found vers useful in over-coming interference on certain wavelengths.

Cabinet

This type of receiver is usually housed in a portablestyle cabinet and so one of this type was made andcan be seen in the photograph. The top. bottomand sides are of 6 mm. 5-ply and the front and backare of 3 mm. 3-ply. The front is first drilled for the

controls and a cut-out made for the speaker opening.Next, the plywood is built up into the form of a boxwith glue and panel pins and put aside to dry.

The top and bottom edges are rounded off with afile or sander and the whole box finally smoothed off.

Two pencil lines should be drawn round the box.one |in. from the front edge of the box and one Jin,from the back edge. A saw cut should now be maderound the front edge about I I6in. deep, taking careto keep to the line so that it forms a neat grooveright round the box.The back may now be sawn off and cleaned up and

the whole is ready for covering with leathercloth.This material is obtainable from furnishers andhardware stores and the constructor should obtainthe thin type of leathercloth as this is easiest to workwith.

The cabinet is designed to be covered in twocolours, the front and back in a light shade with a

contrasting colour round the centre.

The leathercloth is stuck to the plywood with glueand carefully pressed down into the sawcut wherethe two colours meet. If only one colour is requiredthe sawcut round the front of the cabinet should beomitted. The back of the cabinet should be coveredas a separate operation and fixed with two hingesand a small case clip used for keeping the back closed.

Finally, a plastic cabinet handle is secured to the

top for carrying and the receiver is complete.

(To he continued.)

TUNING CONDENSER REPAIRS(Continuedfrom page 81.4)

Next we feed the drive cord over the second pulley

and down to the spindle, securing the cord on pulley

with tape to prevent it "floating" as the necessary

fiddling of the succeeding action takes place.

Direction of rotation of cord around spindle

depends upon the disposition of drum, pulleys andspindle. Points to be watched for are cords that cross

and loops that run along the shank. Study of the

layout will usually show that there is a " natural"

angle for the cord to follow.

Approximately two turns of cord around spindle

will be needed. In the case of the layout in Fig. 1.

two and a half turns are used, the extra half turn

taking the cord back in the direction of the drum.There is no advantage in adding extra turns to the

drive spindle. The extra friction obtained in this wayis more than offset by the possibility of the cord riding

• mi itself and jamming.Having lapped the spindle shank we feed the re-

maining end o\' cord up and over the drum andaround its rim to the aperture. If tape is used onceagain to secure the cord just prior to the aperture the

next action will be considerably easier.

The spring is fitted into place, the end of drive cordpassing through its loop, and tension taken up on the

k:o\\\. There should be no slack at any noint—but no

overstrain cither. Check that the cord is following its

route correctly before finally securing to the spring.

Lastly, remove the securing adhesive tapes, fit

pointer and. adjust. Check that the pointer slide doesnot '* ride up " at the ends, or jam due to friction

and that the pointer itself does not foul backplate.

dial or—when reassembled—cabinet interior.

Condensers

Before leaving the subject, a few remarks on gangedcondensers may be appropriate.

A common fault is that of " noisy tuning."' usuallythe result of metallic dtist particles having foundtheir way between the vanes. If blowing out with abicycle pump does not clear them they can often beburned off by application of H.T. to the slator con-nection

—

Hiking care to disconnect the existing lead

first !

Where a definite short-circuit exists this will oftenbe due to the outer, split segments having becomedisplayed. Care should be taken in straighteningthese. It needs only one false move to distort a wholesection of rotor. It is seldom necessary to touch thelockout on the rotor bush.

The position of the short-circuit can be found byconnecting a meter or lest lamp across the con-denser (puce again, disconnect the existing lead.),

and rotating the spindle.


G.R.T. ISOLATION TRANSFORMERType A. Low leakagegiving a 25*

i boost on2 v., 10/8 ; 1 v., 10,810/6 ; 18.8 v., 10 6.Ditto with mains prli

ladings. Ratio I : LBSrsOottdary.ii. ;i v., 10/6 ; 10,8 v.,

rits. 12/6 each.Type B. Main-' input -Jjn.-_MH v.. Us. MultiOutput 2. 4, 6.8, 7.::. I" and 13 volt* Inputhas two taps which Increase output volts by28% and 50*0 respectively, Low capacity,mitable tor most cathode Ray Tube*. WithTag Panel. 81/- each-Type C. Low capacity wound transformer roi

use wiili 2 roll Tubes with (ailing emission.Input 280/240 volte. Outnul 2-S*-24-2*-3volts at -J amps. With Tag Panel. 1" 6 each.NOTE.- ft i? essential lo we mains primarytypes witli T.V. receivers having series-

connected heaters.

TRIMMERS. Ceramic 80, 30, 70 pi'.. 9d. 100 pi.,

150 pf., 1/8 : 230 pi., 1RESISTORS. All valuesi w..4d. : i w..6d. ; I wHIGH STABILITY. I .v.,

in" ohms i" i" meg,B will

) WIRE-WOUND RESISTORS10 watt } 25 ohms 10,000 ohms

.-mmi pf.. 7311 pf., 1.9.

lo ..inn-' i,, in meg.,8d. : 2 w., 1/-.

',„ 2.-. Preferred valnes

;l/S

.i.-i i

15,000 ohms— ,10,000 olin w., 10 : 10

12/6 PURZTONE RECORDING TAPE

1,200 ft. on standard, fitting 7' Plastic

reels. Brand new, boxed, 12/6.

Spools 5" metal, 1.6, 7" plastic, 4/3.

Ferrovoice 1200ft. Plastic Tape 25/-.

O/P TRANSFORMERS, Heavy Duty 50 iiiA., 4/d.

Muitimtio. push-pull 6'6. Tapped small pentode, 3 9.

L.F. CHOKES 13/18 H. 80/65 mA., 5.-; In II.

1-20 mA, 10'6 : 15 II. 150 inA.. 120.MAINS TRANS. 850-0-330, HO mA.. 0.3 v. tapped4 v. -I a.. 5 v. tapped -I v. 2 a., ditto 250-6-280, 21/-.

HEATER TRANS. Tapped prim., 200/250 v., U.:l v.

1 ! amp., 7/6 ; lapped see. 2, 4. ll.a v., I } amp., 8/8;

prim. 230 v. Bee. 6.3 v. 3 amp., 10/6.

VCR97 TESTED FULL PICTURE, £2.

COPPER PLATED AERIAL RODS, i x T-'in. pushlining, 3.'- do*., p. .V p. 1/-.

ALADDIN FORMERS and oo re, jin.,81 : Siii-.lOd.

3in. FORMERS 5937 8 and Cans TV1 2. ?in. sq. x

2Jiii.and Jin.sq.x 1 iiu., 2/- eu. with cores.TYANA. —Midget Soldering Iron. 200/340 v. Oi

2:111/2.1(1 v.. 1619. Solon Instrument Iron, 24/-.

MIKETRANSF. Hal in .HI : I. 3/9 ea. : 100:1.10 8.

MAINS DROPPERS. 3ln. ,* Jtto. Ad]. Sliders, .3

amp. ".HI ohm-, 4:3. .-' amp., 1,000 ohms, 4/3.

LINE CORD. .:: amp., 60 ohms per tool . .2 amp.. Hi"

ohms per loot, 2-w.iv.6d. per toot, 8-way. W. perfoot,LOUDSPEAKERS P.M. 3 OHM. 2!" 17/6.Bin. Woodman*. 17/6. 7in. x tin. Goodmaos, 21'-.

Silo, aware, Blao., 21/-. 8to. Bloc., 22 6.

'53 in- Goodmans, 18/6. lOin. H. A A., 30/-.

T8L Tweeter. L8H75, 88. I2IO. Plessey, 30.-.

Sin. M.E. 2.8k. field, tappi-.l O.I', transi., 24 6.

CRYSTAL DIODE, O.B.O., 2-. GEX34, 4/-.

HIGH RESISTANCE PHONES. 4,000 ohms, 16/6 pr.

CRYSTAL MIKE INSERT by Ac

So tr reiiui »1.

SWITCH CLEANER Fluid, squirt spout. 4.3 til

TWIN GANG TUNING CONDENSERS. .0803 luMmidget, less trimmers, 6/6 : .0005 Standard ••I/

with trimmers, 9-: less trimmers, 8/-; dittt

soiled, 2/6 ; .0005 mfd. ::-gang. 7/6.

SPEAKER FRET. Expanded Metal silver, I7;ir

Z "jin., 2.'- ea. ; 111 in. x 12 in.. 3/- ea.

GOLD CLOTH. 18in. x 2iin.. 5.-: 35io. \ 3»ln., 10/-

8/6IBS1T4IBS3843V40U4BAM68AT66J7BK8OS 1.7

6BN76V06TEBC33EPB0

Hylv. tied

saroiEZS0

V A

5/6

BBS!il>2

BF50Ktpiip.

SPB1SP41BFB2PBS 46

7'6

0BB66BW66D6BFB

I.K7I.T

i:Y.i i

L V E SNew & Guaranteed

EA50034

3/6

HAL.

7

IIJ3

HKli

BK7GBBS]II V 82(near);tuii , i"v,wi

IIIIliM 0SK7

7/6 7/6

12BE0"1X4 EL326X8 11 V If.'

A

Ml7 i'i:.S2.i

BF39 VI-2.-1

11/6V2.7 PL81

10/6.7Z4

12AT712AIJ7EBC41BBF80ECLSOECH42BF41BB8010 1-4

1

EL84BZ40KT33CMl' 14

PYHI12K 7

35Z4W7

Ws$ssmS&£mlM$

ilil HHHP4. . .... . .

1957 RADIOGRAM CHASSISTHREE WAVEBANDS FIVE VALVES8.W. Hi m. 00 ill. LATEST MULLARD..11. \v. 200 in. B50 in. ECH42, EF41, EBC41,L.W. 800 in.- -2,000 m. ELIi, EZ40.

12 month guarantee.A.C. 200/2.711 v. 4-way Swtton : ahort-Medlura-Long-firara. A.V.C. and Negative feedback-1.2 uatls. Chassis 1:1 J x .71 x 2!hi. QhtSS Dialn> \ -l!in. Imri/oiitiil or vertical avalli di

3 Pilot Lamps. Four Knobs, Walnut or rvory..

Aligned and calibrated. Chassis Isolated frommains, T.S.L. Tweeler Supplied Free:

10 gns. QuT- * '""•• '"'

TERMS: Deposit £5.5,0 and six monthlypayments uf £1,

AMFM RADIOGRAM CHASSISKlin, x 6 n. high. Dial

lly Hi; in. x2!in. 7 valvegram, socket, piano heycontrol, m,ii.. loi

Valve line-up ; EO 85,Ki.4i. rot A.c.

Measurement. "t-oui required i

pim metal red.,

wavechange, Lonev.ii.r wavehandiKCH81, BF89, BABC80,mains 100-260 v.

PRICE *l0.1".0 Carrtoge 10/0

MATCHED SPEAKERS FOR BOTH CHASSIS•Sic, 19/6 ; lliin.. 25/- ; 12in., 30/-.

Collaro Anlo-ehanEer RC531 lor 7S r.p.m. lOin. andlain, reuords. Brand new In maker's boxes! HighImpedi e lightweight Pick-up with sapphire uecdin,

«;n match any Ampiiiier or Radio. Less than half

price. C c_- I'arr. and Bw., 5/6,3 gnS. Borry—No f.O.D.

£7-19-6Brand new Plessey 3-speed Autochanser Mixer.

Xtol Heed with Duopoint sapphire stylus.

Board required 151 x 12in. Height 51in.

Walnut Veneered Playing Desk 10/6 extra.

ALLDRY UNIT POWER PACK. Replaces

Battery 111 14, eU-.. 69 V. plus I! V. Size -I Jin. x

Sfrn. x llin. 4-pln Soeket. A.C. 200/250 v.

FAMOUS. MAKE. LIST PRICE, 05/-. Ob'

R

I'lil'i:. 39/6. Ready for QBe.

B.S.R. MONARCH. 3-speed Motor and Turn-table with selecting switch for 33, 45 and 78r.p.m. records. 100-120 v. and 200-B50 v. A.O.

50 cps, Also B.S.R. MONARCH Li«litweight

I'ick-upwilh Aeos Xtal turnoverhead, separate

Sapphire stvlr.s for t.P. and Standard records.

SPECIAL OFFER, THE TWO ! £4.12.6 post 2/6.

T.V. PRE-AMP (McMICHAEL). TunableChannels 1 to 8. (Will Amplify Output of yourHand .1 Converter.) Midget size. High UainBead] tor use. i.H.t. 800 v., L.T. 6.8 v., .:)

amp." minimi.) BRAND MOW, 25/- each.

MAINS POWER PACK for above, 25:- extra.

SBPERHET COIL PACK. 27/6. Miniature•ize 21iB. x 2;in. x Uin. Illlill "Q" Dost,

cored Coils, Hhori, Mediimr Txing, GramSwltohing. BlngJe bole fixing wiili .onr.ee-

lion diagram, and circuit. 4«5 Ko/s IF.

TELETRON BAND III CONVERTERFor London, Midland and Northern I.T.A.

MARK I

Suitable all T.V. makes. T.R.F. or Superhet.Beady wound coils, two BB80 valve-, all

components, puuehed chassis, circuit diagram,wiring plans. COMPLETE KIT for mainsqperation 200-250 v. A.C. £3.10.0.

As ABOVE less POWER PACK. Requires200 v. 2(1 m.V. ll.T. Ii.3 v. .(i a, L.T.. £2.5.0.

Mark ir ca code tl extra eacli Kit.Halns Transformers to above Spec. ... 10/6Bin. Contact Rent. 250 v. 50 mA. ... 8/6I'-.ti.i'./l.T.A. aerial crossover unit ... 7/6Punched and drilled chassia 3 9Larger chassis for Mains Model .,. 8/-Tfektron Colleet «iih pi.ms 15/-Full plans and circuit details 6d.

Volume Controls 80 COAXBeml-alr spaced Poly-thene insulated. Jin.di.l,

Stranded core, qjsut 50% 'yd.

STANDARD QJlin. Coax. OU.

v j.

Long sptndles. Gaanm-teed l year. Mtdoet.in. oi'" ohms to 3 lug.N» Sw. S.P.SW. IU'.sk.

3/- 4/- 4 9l.in or Log Tracks.

COAX PLUGS... 1/- DOUBLE SOCKET ... 13SOCKETS ... 1/- OUTLET BOXES ... 4SBALANCED TWIN FEEDER, yd. 6d. 80 "r 300 ohms.DITTO SCREENED per yd. 1'-. 80 ohms only.WIRE-WOUND POTS. 3 WATT. Pre-

T.V. Type, All v.- IS 28 Ohnu to SO K., 3- ea.on K..4-. (fail.on 5(1 K. to 2 io.. 3/-.I

WIRE-WOUND 4 WATT. Pots. 2]in. Spindle.Values. I"" ohms to 50 K., 5'6 : 100 K., 6'6.CONDENSERS. New sleek. .001 mfd. 7 ItV.T.i'.c.. 5,6. Ditto, 20 UV., 8 .'6

; 100 pf. to 500 pf.

Micas. Od. ; TubuBtr SOO v. .ii"l io .01 mid.. 9d. :

,0.7, . 1 , 1/- : .25, 1/6'; ,5/880 v., 1/9 ; . ! '380 v., 9d. ;

. 1/600 v., 13; .1 mfd. 2,000 volt.-. 4,-.

CERAMIC CONDS., 500 v., .:! pf. to .01 r !!,lOd.

SILVER MICA CONDENSERS. 10%, 5 pf. to 500pf., 1/-; OHO pf. to 3,1 .'.. 1.3. DITTO I'

,

1.3 pf. lo .700 pf., 1/9: .717 of. lo 5.000 pf., 2.-.

1 F. TRANSFORMERS 7,6 r

4m Ke's Sing :; xtin dtb.By Pye Radio. Data nheet supplied.

NEW ELECTROLYTICS. FAMOUS MAKESTUBULAR TUBULAR

1/SSO v.

•2/450 v.

4/480 v.

g/450 v.

8/500 v.

16/480 v,

16/500 v,

:i2/4;j()v.

BO/25 v.

50 50

2/- 100,25 v. 2/-

2/3 8 ! 8/800 v. 4/62/- IO + 1'i/./OO v.

2,3 6/-

2,9 CAN TYPES36 Clips 3d.4 16/400 v. 3/05/6 32/350 v.

1/8 64/330 v.

1/9 ,.700/12 V.

tl 8i18/450

CAN TYPES8 ! 16/900 v.

16 : 16/600 v.

23| 20/450 V.

32+33/880 v.

ISO v.

BO ! 50/8M v.

64 ! 120.27.7 v.

loo ; -2011,27.7 r.

12.61,000 1-1,000/0 v.

6

5/6

4/6

6/67/-

76

Base Type .112, M/.liKI v., 3/- ; Id 1"o v., 4 '-.

SENTERCEL RECTIFIERS. E.H.T. TYPE FLY-BACK VOLTAGES. K.I/25 2 kV.. 5/- ; K3/40 3.2kV., 7/- : K8/48. :t.fi kV.. 7/8 ; K-1/10 I kY.. 8/- :

K3/100 S kV.. H4/8 MAINS TYPE. CONTACTCOOLED 27ov. 50 in A.. 8 6, 83 mA., 9,6.

COILS Wearitc, "P" type, 3/- each. Osmer Midget"ii," ti-pe adj. dust, core, 4/- each. All ranges.TELETRON, h. b Med. T.R.F.. with reaction, 3'6.

FERRITE ROD AERIALS. M.W.. 8/9 : M. ft I... 12,6.

T.R.F. COILS A/TIP. 7/- pair. H.F. CHOKES. 2 6.

ALUMINIUM CHASSIS. IS s.w.g. iiu.li ill,-,|.

With 4 <i.!es, riveted oorners and lattice livingholes, 21 in. sides, 7 x 4in., 4'6

; 8 x Bin., 5/9 :

11 x 7in., 6/8 ; 13 x 'Jin.. 8/6 ; 14s 1 tin., 10 6 ;

13 x 14iu.. 12/6 ; 13 x 10 x :iin., 16/6.

FULL WAVE BRIDGE SELENIUM RECTIFIERS.2, 6 or 12 v. I! amp.. 8/9 : 2a.. 11'3

: 4 a., 17/6.CHARGER TRANSFORMERS. Tapped input BOOj210 v. for charging at 2, « or 12 v., 11 amp., 13 6 :

4 amp., 21/-.

VALVE MANUALS I, II & DX 5 - each.TOGGLE SWITCHES. BJP. 2/-. I). P. 3 '6. U.P.D.T. 4'-

ACID HYDROMETER. New I'.x Cut. Unbreak-able. Packed in metal ease 7 x llin., di.u. 4/6.

WAVECHANGE SWITCHES.5 p. 4-way 2 wafer, long spindle 6/8

2 p. 2-way, 3 p. 2-way. short spindle 2/6

2 p. 8-way. 4 p. 2-way, 4 p. 3-way, long spindle 3 6

3 p. 4-way, 1 p. 12-way. long spindle II BVALVEHOLDERS. Pax. Int. Oot.. 4d. EF50. EA50,6d. B12A, CRT, 1/3. Ens. and Amer. 4, 5, 6, 7, and

pin, 1/-. MOULDED Mazda and Int. Oct. 6d.

B7G. B8A. B8G. B9A, 91., B7G with can, 1/6.

VCR97. 2/6. B9A with can 2/6. CERAMIC. EF.50,

B7G, B9A, Int. Oct. 1-, B7G with can 1/9.

BLACK CRACKLE PAINT, air dryin;. 3,- lin.

We have no connection w:th any other firm. Pleasa address all Mail Orders correctly as below.

RADIO COMPONENT SPECIALISTS JS.BPBSSL11?-,

WEST CROYDONDAY—(Wed. 1 p.m.) 10 page list 3d.

Tel. THO 1 655, Buses 133, or 63 pass door. 48-hojr postal Sarvice. P. & P. I/-, £2 orders post free. {Export Extro.) C.O.D. Service 1/6.


A NEW (fyrfd) TRIUMPH IN SOUND REALISM

If low CostMODEL G.A.4 HIGH FIDELITY AMPLIFIER4 watt 4 valve circuit wich a frequency response of 40-1 5,000 c.p.s.Neat Control Panel, size 6in. x 4in., on fly leads for individualmounting (main chassis, I4in. x 4in. x 5Jin.). Input-telector switchmatching to Radio, L.P. and 78 r.p.m. records. Separate Bass andTreble Controls giving wide range of cut and lift. Volume Control.Rotatable Mains Transformer for hum cancellation.

Price £9.9.0

Pickup

Motor

H.4 RADIOGRAMCHASSIS AM/FM

7 valve 4 wave band superhet

with F.M. (VHF). Magic Eye

tuning indicator. High sensi-

tivity. Bell-clear quality. Dial

size I I Jin. x 5;in, Sockets to

connect Speaker (3 and IS ohm),

i

Aerial, Earth, F.M. Dipole and provide power for Gram.

from mains.

Price £24 . 6 . 6 inc. tax.

fiers and Tape Recorders. 75radiation. Highly sensitivereproduction.

All these Chassis use the latest B.V.A. glass miniature valves. For use on 200/250 volt A.C. Mains.H.4T (AM/FM) Tuner Self-powered for Radio or Amplifier.' Pries £20.17.0 inc. tax.

We supply and fit our pre-amplifier to Collaro Tape Transcriptors.

Direct from Manufacturer to all other Enthusiasts.

THE DULCI COMPANY LTD., 97-99 Villiers Road, London N.W.2.

F.M. (VHF)TUNEROutstanding design andperformance. Self-poweredto work direct into yourAmplifier or Radio. Magi:Eye tuning indicator. 3-

stage I.F. amplifier. Presetoutput level. Panel sizelOUn. x 5jin. (cut out9[in. x 5in.). Switching in-

corporated for connectionto Pickup sockets. Ampli-

ohin Aerial input. Negligibleand designed for top quality

Price £17 . 10 . 3

inc. tax.

WRITE FOR DETAILSTO REF. P.W.

WILlesden 6678

TRANSISTOR PUSH-FUL1. AIDIOAMPLIFIER

(100 Milliwatts Oulpul)Build this Push-Pull Amp-lifier which is ideal forCrystal or Magnetic Pick-up Amplification. BabyAlarm, Microphone Ampli-fier, etc. Powered by G-voliDry Battery lasting formonths.< umplctc Kii of Parts in-cluding 4 Translators andall Components with Cir-cuit (less speakcr).£4.10.0

TRANSISTOR SQUAREWAVE GENERATOR

Ideal for sisnal tracing.Complete Kit with 2Transistors and Com-ponents and Cireu it . 25/-.

TRANSISTOR SIGNALTRACK

R

Complete Kit with 2Transistors, Componentsand 'Phones with Circuit.

42/6.

CATHODE RAY Tl BF.SVCR138A £1.15.0.VI-R139A. 2!in. £1.15.0VCH97. Guaranteed fullT.V. picture (carr. 2'-)

£2.0.0.VCR517C. Guaranteed fullT.V. picture. £1.15.0.

MU-METAL SCREENSfor VCR97 or 517. 10'-.

6in. ENI.ARCER forVCR97 or 517. r.r. l.ii.

17/6.

TRANSISTORSII:.VCTION TYPE (Red-Spoil (IW.P.l

OFFERED AT LESS THAN HALF-PRICE,

Designed for A.F. application up to BOO EC'S and are suitable foruse in amplifiers, signal Tracers, Local Station Receivers,Radio Control, Oscillators, Transistor Voltmeters, BabvAlarms. Microphone Pre-Ampliners, etc.

10/-(Tested and complete with Data it Circuital

N.B. These Transistors may be used in place of Milliard (IC'TIor similar Transistor*.

|R.F. TRANSISTORS (ItLUE SPOTj J..6 Mo/s 15- eat-h.j

I

PRESELECTED TRANSISTOR-SIN •

Pt'SH-PCLL PORTABLE SLPERHF.TJust switch to your favourite Station. No tuning, no aerial orearth, pre-select 3 stations. Complete with all components and

Jsix Transistors. 7x4 Elliptical speaker. Teletron Superhet.

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February,. 1957 PRACTICAL WIRELESS 837

EQUALISING CIRCUIT:USEFUL DESIGN DATA FOR THE A.F. ENTHUSIAST

(Continued from page 748, January issue)

By Hugh Guy

Bass Cut

VERY simple form of bass cut circuit is oflcn

used in amplifiers whose function it is to repro-

duce only speech frequencies. The cut is

introduced to reduce the effects of mains hum and is

effected in the normal R.C. coupling by using a low

value of condenser.

Such a condenser, of course, has a high reactance

at low frequencies and a large proportion of any

low-frequency signal passing through the coupling

is dropped across the condenser leaving compara-

tively little across the associated grid leak for subse-

quent amplification.

The response of this form of coupling is exactly the

reverse of that of Fig. 2b which can, therefore, be used

as a design chart for this type of coupling, reading

-I" dbs " for — " dbs '* on the vertical scale.

A rather novel circuit for bass boosting has been

developed around the cathode follower and is an

adaptation of a circuit widely used in television

techniques for the high frequency compensation of

video amplifiers. It relies for its operation on the

effect of only partially decoupling the cathode

resistor in an amplifying stage.

It was mentioned earlier that the gain of a pentode

is GmRL. Strictly this is only true if there is no

cathode resistor in circuit ; should there be such a

resistor, R, then even if it is decoupled by a condenser

Ck, the gain now becomes

G = r HHr \< where Zk is the parallel impedance1 |

Gk.Zk

of Ck and R, and is.

/, .„,-,.„

and Gk is the mutual conductance or slope of the

valve at the cathode. It

is not often realised that

the cathode slope is

greater than that of the

anode and in the case of

the 277, Gk is 1.25 xGmover a wide range ofanode voltage.

Returning to the ques-

tion of pentode gain,

however, it is apparent

from the formula abovethat, due to the decrease

of Zk with increasing

frequency, the gain will

increase as the frequency

rises.

To dispel any qualmsthe reader may have over

his existing circuitry it

should be mentioned that

when a normal amplify-

ing stage is built using a

cathode resistor for bias

purposes, as a rule the

value of bypass condenser Fig. 5A.

used is sufficiently large

300 v-f-

to reduce the value of Zk to a negligibly small value.

Hence it is quite legitimate, under such conditions,

to assume that the gain is constant at all useful fre-

quencies, and is GmRL.If the cathode impedance Zk at low frequencies is

denoted byfZk', and that at high frequencies by Zk",

then the ratio of the gains at high and low frequencies

will be given by A, and

Practical bass cut

circuit.

A = 1 -\ Gk. Zk'

where Zk' =

and Zk" -vr

Gk. Zk"R

-i-(w'CR)-

R

-rr, i.e. at low frequencies

(to" CR) 2

This value A, then, is the •"lift" that the circuit

will give. As it stands, however, the formula is rather

unwieldy and to eliminate the square root signs wemay make one or two simplifications which do not

detract from the accuracy of the result to any extent.

If we always make o'CR - 3, then Zk' is approxi-

mately R/3. Also if wc call the ratio of the highest

to"

frequency to the lowest frequency n, then n = — , and

Zk" is approximately R/3n. A little trouble on the

part of the reader will enable him easily to deduce

these simplifications if he so desires.

Armed with easier symbols we can now return to

the formula for A.

1 - Gk.R/3 / 3 -f-Gk.R\.n.

.

ThusA=TTGk^./3n Un - Gk.R^

We will invariably know the amount of lift, A,

we require, and also the ratio of the upper and lower

frequencies, n, in which we intend to accomplish

this lift. Having selected a valve we will know the

value of Gk. The only unknown now is R, the value

of the cathode resistor. Changing the above formula

around gives us this valve as

R =c'kU a)

—

5rO KX> 2iX) SiX)

A' /

4

5

? 'r /

/

Sri

Frequency —»-

Fig. SB.—Response of bass cut circuit.


From this formula, therefore, we can determinethe value of the cathode resistor. To obtain thevalue of the condenser, we revert to the earlier assump-tion where we made w'CR 3. Knowing that to' is

2rr times the lower frequency, and the value of R,

we can obtain the value ofC which is C -;^-77K

This method gives us the components we requireto produce a given lift in a given range of frequencies.

Just to show how the method works out in practice,let us consider a simple example, and examine theresponse actually obtained from such a circuit whenit is built, to see how design and practice compare.

J

\

t<o IU

%

/( >f) ?(X) .« o / » £ IOrU K - /•5 At

Frequency—».

Fig. 6(a).— Tape playback characteristic

Practical ExampleImagine we are trying to improve the high frequency

response of a tape recorder.

We require a lift of 7 over the frequency range1.5 kc/s. to 15 kc/s. to offset the characteristic tapeplayback droop illustrated in Fig. 6a. Hence n in theformula is 10. In practice the amount of droop variesconsiderably from one machine to another dependingon several factors ; amongst these are the appliedrecording equalisation, the type of head in use, andthe coercivtty of the tape being used.

Normally the amount of lift would be expressed in

decibels in common with normal A.F. practice anda lift, or voltage gain ratio of 7 corresponds to a lift

ofl6.9dbs.

It remains now to choose a valve for the stage in

question. Considering the Z77 again, valve datainforms us that a Gk or cathode mutual conductanceof 5 mA/v can be realised when the valve drawsapproximately 3.5mA anode current. We can nowproceed to determine the value of R. and substitutingin the appropriate formula gives R as :

The value of C is next solved from co'CR s=3

where c» 2.7 1,500. Thus C 0.025// 1".

To obtain the necessary bias for the valve necessi-tates returning the grid to a positive potential, a

few volts negative with respect to the cathode voltageand the final circuit for the stage appears as shown InI "\>a. 5a. The plotted response of this circuit, givenin Fig. 5b, shows the accuracy of the design method.

where the lift over the specilied range is seen to be7.36 or 17.34 dbs.

Tape Recorder Equalisation

The general playback response of a tape recordedfollows the curve of Fig. 6a, and it is seen to consistof a steady rise at the rate of 6 dbs per octave fromthe low frequency end to a maximum at about1.5 kc/s. This frequency, or crossover as it is some-times called, varies from one type of amplifier toanother, of course, but after the crossover, thefrequency fall off tends to be rather curved, andtherefore perfect equalisation is extremely difliculr.

unless feedback techniques are used.The bass response can be equalised by the type of

circuit outlined earlier, but the treble attenuationthis circuit produces will extend beyond the cross-over frequency. It is, therefore, necessary to devisea circuit which is dormant up to the crossoverfrequency, but then produces the equalising curvedresponse, at the same time nullifying the effect ofthe continued treble cut introduced by the bassresponse circuit.

Such a circuit exists in the form shown in Fig 6b.It consists of the customary C and R shunting theanode load of the valve. In series with this arrange-ment, however, is a parallel tuned circuit, CTand LT,which is designed to resonate at approximated6 kc/s.

At low frequencies, when the bass correctingnetwork is effective, the impedance of the high-frequency network is negligible and hence the gainincreases steadily at 6 dbs per octavo, as desired.After the crossover frequency, however, the reactanceof the condenser C is very low, and the impedance

fig. 6(b).—Tape playback equaliser.

of the parallel tuned circuit increases to a maximumat 6 kc/s. and hence the gain increases also, followinuthe characteristic of the impedance variation withfrequency. The shape of the characteristic can becontrolled within limits by adjusting the variabledamping resistor across the tuned circuit.

Similarly, the 3 db point and hence the positionof the bass correction can be shifted by variation ofthe resistance in this network.


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840 PRACTICAL WIRELES: February, 1957

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February," 1'957 PRACTICAL WIRELESS 84]

A Transformer for a Single-valve

Output StageUSING AN OLD COMPONENT AND SIMPLE FORMUL/E TO OBTAIN THE

DESIRED PERFORMANCE By N. P. Fish

THERE is a widespread idea that satisfying repro-

duction in the home cannot be obtainedwithout a 10-watt amplifier employing a push-

pull output stage. An actual listening comparisonbetween such equipment and a conventional " domes-tic " receiver with single pentode output valve

usually argues convincingly in favour of the larger

output. Yet, of an available 10 watts, how many are

called for in the course of ordinary domestic listening?

A simple output meter in the speech coil circuit of the

loudspeaker will cause eyebrows to be raised !

The writer has recently constructed a three-watt

amplifier to a published design and has paid special

attention to the problem of feeding a good, clean

3 watts, at all required frequencies, from the

output valve anode to the speech coil of the speaker.

With this achieved and with a good, wide range,

adequately baffled loudspeaker, then the gulf between

the 3-watt output and the much more ambitious

(and expensive !)" hi-fi " equipment narrows so

much that at times it cannot be detected.

The object of this article is to take the reader

through the various steps which lead to the successful

construction of that vital component, the outputtransformer. The transformer described is for use

in an EL84 output stage ; other values, of anodecurrent and load impedance would, of course, be

used in the calculations as valve and circuit conditions

dictate.

First let us see where an inadequately designed

transformer fails when used with a single-valve

output stage. Fig. 1 is a graph showing how magneticflux in the core of the transformer increases as current

in the primary winding increases. Suppose this wind-ing to consist of 1,000 turns ; then 25 mA (.025 A).:

1,000 gives 25 ampere-turns to magnetise the core,

and the graph shows that the core will be magnetised

to the point p on the curve where the flux, read on the

vertical scale, is 22,500 lines. Increasing current fromto 25 mA increases flux proportionately— the

graph is a straight line over this part. But whereasincreasing current from '10 to 25 mA increases flux

from 9,000 to 22,500 lines, i.e., by 13,500 lines, afurther equal increase to 40 mA only increases flux

by 7,500 lines. This is because at the point p the core

is about to saturate and become increasingly less

responsive to changes in magnetising ampere-turns.

Now suppose this primary winding to be con-nected in the anode circuit of an output valve whosesteady anode current is 25 mA. The core will be held

steadily magnetised to the point p. Then let an alter-

nating current with a peak value of 15 mA be super-

imposed on the 25 mA D.C. anode current. Thevalve's anode current will now be rising to 40 mAand falling to 15 mA during each cycle. This is

shown on the graph by the wave-form plotted belowthe horizontal scale. To the right is plotted a wave-form showing how the flux in the core varies in

response to the changing anode current. This wave-form can equally well represent voltages across bothprimary and secondary of the transformer, since

voltage is proportional to flux. Obviously, here wehave a very distorted picture of the original current

wave-form, and at the loudspeaker the transformer's

inability to deal with large current and voltage

swings will manifest itself by lack of bass, wherevoltage and current swings are greatest. The damagehas been done by allowing the core to saturate

;

this is largely as a result of the D.C. anode current

pushing the working point p too far up the curve. In

passing it may be noted that this problem of coresaturation does not arise with a push-pull outputstage as the ampere-turns due to the anode currents

of the two valves cancel each other out. Which is

why some push-pull amplifiers are belter than they

otherwise might be ! And having seen one importantreason why some single-valve output stages are worsethan they might be, the gulf begins to narrow.

First Steps

From the spares-box or among the unused ex-

government gear choose an old transformer or chokewith a suitable core. It should be appreciably larger

than the conventional " loudspeaker transformer."

but not quite of mains transformer size. The centre

limb might conveniently have a cross-sectional area of

§ sq. in. There must be sufficient window space for

the windings. Fig. 2 shows the core selected by the

30,000 -

I sspoo-

£ sopoo -

15000 -

.o IOPOO-

-o SPOO-

PO ', 30 4P 50 60 70Ampere- turns '.due to current in

' primary winding

Fig. 1.

—

Graph showingmagnetic flux and cur-

rent variations.


writer, that of an ex-government, 5 henry 200 mAchoke. Remember that more iron in the core meansproportionately fewer turns on the windings. Stripthe core down, taking particular care of the frame andclamping bolts. Discard the old windings and giveit a clean up generally. Pickling in strong caustic-

soda solution will remove old varnish from frame andbolts. Remove obvious rust from the core lamina-tions, but do not scrape them to expose bright metal.At this stage it would be as well to repeat the funda-mental transformer equation to which frequentrecourse will have to be made.

4^44'/' ft

i"oo,6oo,oooE =R.M.S. volts across winding.= Maximum number of lines of magnetic fluxreached in each half cycle,

f frequency in cycles per second.t number of turns on winding.This equation will be rearranged from time to

time.

Fig. 2.—Detailof the core.

Magnetic Measurements on Core

It would be merely groping in the dark to proceed

further without reliable knowledge of the magnetic

behaviour of the selected core. This will be obtained

by actual measurement and the following apparatus

will be necessary : an A.C. ammeter, say 0-3 amp. ;

an A.C. voltmeter. 0-12 volt ; a transformer, prefer-

ably tapped, giving about 15 volts 2 amp., and a

variable resistance about 5/2 and capable of carrying

3 amp. The transformer may present a little difficulty;

a rece ver mains transformer with valve and rectifier

heater windings connected in series would provide

rather over 12 volts and tappings as well. Theresistance can be improvised by making crocodile

clip connection to a length of fire-element or even

galvanised wire. The resourceful reader will have nodifficulty in arranging gear to give him the necessary

readings. One point is important : a separate

ammeter is essential : it is useless to expect a single

multi-range instrument to serve by disconnecting

it as an ammeter when current has been adjusted andthen taking the voltage reading.

Make a rough cardboard former to fit the centre

limb of the core and on it wind 100 turns of about

20 s.w.g. wire. This is a search coil which will provide

a known number of ampere-turns to magnetise the

core. It can be wound quite roughly. Carefully

reassemble core with the search coil in place. Butt

joints between the stampings should be carefully

tapped close and the whole core firmly bolted in its

frame. Connect it up on the test bench as shown inFig. 3. The object now is to take a series of readingseach giving current through the winding and thevoltage set up across the winding. The IR dropin the search coil will be negligible so the voltmeterreading may be taken wholly as volts induced in it

by the changing flux. It is ampere-turns that matterrather than the R.M.S. amps, indicated by theammeter. This point is mentioned as the reader mayfind it expedient to tap his search coil at, say, 50turns, and change his tapping as the readings proceed.Start with a small current and increase for eachreading until further ampere-turns produce little

increase in voltage. Tabulate the readings as shownin Fig. 4 which gives the figures obtained by thewriter with his core. These figures will be used in thefew simple calculations which follow, "so that inworking out his design from his own results thereader will have no difficulty in substituting his ownfigures.

Plot the CurveThe next step is to construct a graph from the

figures given in the table. Do this to a convenientlyarge scale so that there will be no difficulty in

taking readings from it. The horizontal scale is

marked off in ampere-turns R.M.S. and thevertical scale in voltsR.M.S. Make fine neatcrosses at the pointswhere the ampere-turnsline and the voltage line

intersect for eachreading. Then draw afine, evenly curving line

through the crosses. Donot worry if some ofthe crosses lie a little

above or below thecurve, which should follow an even coursethrough the mean positions of the crosses. Suchcrosses as lie off this curve merely indicate slighterrors of manipulation or reading. This, then, is themagnetisation curve of the chosen core. Fig. 5 showsthe magnetisation curve of the writer's core, plottedfrom the data tabulated in Fig. 4. A further, andextremely useful, vertical scale can now be addedto the graph. This will show the value of <X> for anypoint on the curve, and therefore for any numberof ampere-turns. Rearrange the transformer

IOO turn coil

3.

—

The set-tip for measuringmagnetising current.

equation thus :—100,000,000

4.44 f t

For E put in the highest voltage reading given

by the table (Fig. 4), for f the mains frequency (50),

and for t the number of search coil turns in use whenthe reading was taken. In the present case this gives :

r 9.8 < 10,000,000 IAnnn ,.

4.44 x 50 x 100Draw a vertical line to the left of the voltage scale

on the graph : carry across to this a line from the

point on the voltage scale corresponding to thevoltage used in the above flux calculation ; markthis point on the flux scale with the value given b\

the calculation. The vertical distance between this

and the horizontal line of the graph must now bedivided evenly, say in five thousands, to give a scale

from to the calculated flux value. Dividing up this

(Continued on page 845)


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scale should be quite simple and extreme accuracy

is not called for. The completed graph is shownin Fig. 5 and it now presents the " vital statistics

"

of the core in a readily accessible manner.

Valve Requirements

Consider an EL84 valve delivering 3 watts into a5,000 ohm load. The equation for power in acircuit is :

—

ca (W power in watts.

W _ orEK

WR where E volts R. M.S.R resistance in ohms

putting in values E" 3 >: 5,000and E \/ 15,000 -123 volts.

So that at 3 watts output there will be at the

anode of the EL84 an alternating voltage of 123

volts R.M.S. superimposed on the 300 volt H.T.supply. This A.C. voltage must, of course, appearacross the primary of the output transformer at the

lowest frequency which is to be reproduced. Forconvenience, and a small margin of safety, call it

125 volts.

Having seen what the valve will demand of the

transformer primary, turn to Ihc graph again to rind

out how these demands can be met. With no signal

the steady anode current of the valve must magnetise

the core to a point at the middle of the straight part

of its magnetisation curve. The reader must fix this

point for himself on his own graph. In Fig. 5,

it is marked at p where the flux is 17,000 lines, andthe voltage it sets up across a 100 turn coil is 3.6 volts.

This, of course, at a frequency of 50 cycles. Thesefigures will be used again, and should be noted. Whenthe valve is handling a signal, flux will rise and fall

above and below this Working point value of 17,000

lines by an amount which must be the of the

transformer equation.

Looking at the graph, it will be seen that flux

cannot be allowed to rise above 32,000 lines, for fear

of going "round the bend." For the transformer

calculation <T> may, therefore, be taken as 32,000 -r

17,000 15,000 lines. The reader will obtain his ownfigure from his graph, the pattern being clear. Suffi-

cient data have now been accumulated to enable the

transformer equation to be used to find the numberof turns required by the output transformer primary.

E - 125 volts, ffi 1 5,000 lines, f^ lowest frequency

to be reproduced say 40 cycles.

Rearrange the equation thus :

—

E 100,000.000

4.44 f

125-100,000,000 ._._,put ,n values t —^^ 4Q

^4,700 turns.

Now these turns on the transformer primary will

be carrying the valve anode current. Take this as 40mA (.04 A). Multiplying amps, by turns gives

.04 > 4,700- 1 88 ampere-turns. The graph shows that

these ampere-turns would magnetise the core well

t

beyond the chosen working point. This would bedisastrous and will be corrected by introducing an air-

gap into the magnetic circuit of the core. But this

adjustment will be left until final assembly of the

transformer.

The secondary winding must now be considered.

The number of turns on this depends on the impedanceof trie speaker to be used. This impedance appears

at the transformer primary winding multiplied by the

square of the transformer turns ratio. The ratio ofprimary to secondary turns on the transformer will,

therefore, have to be the square root of the numberby which the speaker iropedance has to be multiplied

to make it equal to the load impedance required bythe valve. The formula is :

/f: i r pri/sec ratio.

r= »/ -- where { Rl valve load impedance.' Rs speaker impedance.

It is convenient to be able to match either a 15i2

speaker or a 3.75-'-* speaker to the valve, so alternative

impedance outputs are desirable from the trans-

former secondary. For a 15-'i output the turns ratio

must be :

V5-™10

15

turns ratio must be r

1 and for a 3.75 Q output the

./5.000

V 3.7536 : 1

.

Dividing these ratios into the primary turns gives

for 15'^,4

'

7™ 257 turns and for 3.75-V,4"^° 114

turns. A 257 turn secondary will, therefore, be used,

lapped at 114 turns to provide a 3.75<-> output.

Construction

It is not proposed to describe the winding of the

transformer in detail. Every serious reader wi|,l by

now have had some experience of coil winding of this

kind and will have evolved his own techniques. Thewriter made up a bobbin with paxolin cheeks andpartition pieces to provide three equal winding spaces.

A cement made by dissolving Perspex in chloroform is

a very useful adhesive. Cheeks and partilion pieces

must be adequately supported during winding or they

will be pushed out of place. Choice of wire gauge

is dictated by the window area of the core stampings.

Wire tables and simple arithmetic soon settle this

issue. It is essential to keep the D.C. resistance of

primary and secondary as low as possible If, for

instance, the resistance of the primary is allowed to

be as high as 1,000-^, then at 40 mA the valve anodewill be robbed of 40 volts H.T., and its output

considerably lowered.

In addition, power which should be fed to the

speaker is dissipated in the primary winding. Asecondary winding which is supplying 3 walls to a

3J2 speaker is generating 3 volts to drive 1 amp.through the speaker winding and through itself. If

Search Coilturns . ... 100 100 100 100 100 ! 100 100 100 100 100 100 100 100 100 100 100

Volts R.M.S. .8 1.6 2.4 3.15 3.9 4.85 5.6 6.4!7.0 7.6 81 85

;

9.0 9.3 l>.5 9-8

Amps. R.M.S. .2 .4 .6 1 -8 10 1.2 1.4 1.6 1.8 20 2.2 2.4,

2.6 2.8 30 3.4

Ampcre-lurns 20 40 60 80 100 120 140 160 180 200 220 240 260 ,280 : 300 340

Fin. 4.

—

How the readings are tabulated.


the resistance of the secondary winding is allowed to

be as high as V.2, current is halved and power loss

becomes considerable because of the doubled im-pedance. Things may not be quite as bad as this,

but use wire gauges to fill all available winding space.

The writer used 36 s.w.g. enamelled for his primary,which was wound in two sections with the secondarybetween them. This is desirable in every case to

obtain maximum coupling between the windings.

The first 1 14 turns of the secondary (3.75-C^) werewound with 22 s.w.g. enamelled and the remainingsecondary turns with 24 s.w.g. With the \5Q windingcurrent is less, there is more voltage to play with, andthe effect of winding resistance not quite so serious.

IOO 150 200 250 300 ISO

Ampere—turns (ffMS)

Fig. 5.

—

The magnetisation curve of the chosen core.

Assembly and Gap Adjustment

Assemble the core around the bobbin with all the

. U " stampings facing in one direction and all the

"T" stampings in the other. The core is shownassembled in this way in Fig. 2. Where the two stacks

of stampings meet, at a and b, insert small pieces ofsome hard, incompressible insulating material, eachabout .01 in. thick. Thin paxolin will do. The writer

used mica ; this is convenient because its thickness

can easily be built up or reduced. Tap the stampingsgently together, compressing the mica in the gaps.

Boll up securely in the frames and connect up to the

measuring equipment on the test bench. This timethe 3.75-'*? secondary winding will be used to provide

the known number of ampere-turns which will be

exactly equal to those set up by the primary when it

is carrying the valve anode current. These will be.04 amp, (for EL84) by number of primary turns. Inthe present case this is .04x4,700=188 as notedpreviously. Now comes a snag, but not an insur-

mountable one. The curve on the graph indicates themaximum flux value reached during each half cycleof alternating current, because voltage is proportionalto maximum value or flux. But the ampere-turns.scale is based on the R.M.S. value of the current

which is only .7 of the maximum value reached bythe current in any half cycle. This means that at thepoint corresponding to 70 ampere-turns on the scale

the flux value shown by the curve is that which is set

up at the instant the current is peaking up to 100

ampere-turns. Now, a steady D.C. maintainsa steady "peak" value all the time. Therefore, toreach the same point on the curve, using A.C., aswould be reached by 188 ampere-turns D.C, it will

be necessary to multiply the 188 by .7 and thenadjust the search coil current to provide the reducednumber of indicated ampere-turns. 188 :

.7= 132ampere-turns to be provided by the 1 14 turn coil.

Dividing ampere-turns by turns to find the amps.132

required gives - = 1.16 amps., to which reading the

ammeter must be kept while adjusting the core gap.It was noted previously that with flux at 17,000 lines,

the chosen working point, the voltage set up acrossthe 100- turn search coil was 3.6 volts. Across the 1 14

turns the same flux will set up a proportionately higher1 14

voltage: 3.6 — =4.1 volts. The stage is now setI UU

for the final adjustment of the core gap. This is doneby adjusting the thickness of the mica spacing pieces

until with 1.16 amps through the 3.75/.? winding avoltage of 4.1 volts is obtained across the winding,and this with the stampings tapped as close as the

spacers will permit them and with the core firmly

bolted up. Switch off for each adjustment of the

spacers and readjust current for every reading.

Your Own DataWhen the correct readings have been obtained, check

over the frame bolts and test again. In describing the

adjustment of the core, flux, voltage, current andampere-turns figures have been used which relate,

of course, to the writer's transformer. All essential

substitutions will become obvious to the reader as hetakes his own readings and records his own data.

PRACTICAL TELEVISION JAN. ISSUENOW ON SALE PRICE 1/3d.

The current issue of our companion paperPRACTICAL TELEVISION which is now onsale contains a very interesting article on the

A.T-V. Empires. Several well-known EmpireTheatres or Music Halls have been taken overhy the I.T.A., and our contributor has visited

them, both in London and Manchester, and the

article contains interesting details of them,together with illustrations of various aspects ofthe set-up.

For the practical man there is an article onSlot Aerials, both indoor and outdoor. Thearticle covers both the Band I and the Band IIIarrangements. On the subject of aerials there is

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various parts of different commercial television

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faults.

The Servicing article this month covers the

Bush TVl and TV2, whilst the Beginner's Guideto Television deals further with colour tubesand the problems of Bands, Wavelengths andFrequencies.

Your Problems Solved, Underneath the Dipole,Correspondence and Telenews, together withData Sheet No. 2 on the G.E.C. BT3251 andBT9343 completes this issue.

February, 195/ PRACTICAL WIRELESS 847

MAXI-Q

POWER REQUIRED: HtrS.6-3V.T-5A:

F.M TUNER

THE GUARANTEED COMPONENTS DES-CRIBED BELOW HAVE BEEN ACCLAIMED BYTHOUSANDS AS THE FINEST OBTAINABLE.Full construct ional details, point-to-point wiring diagram andalignment instructions for building the complete F.M. TUNER.Also full details lor modifying existing tuners to a pre-set version

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F.M. SCALE. A bronze finished scale with yellow markings (0-20

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RDT. 1/10.7 Mc.'s. A transformer for use in ratio discriminator

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GENERAL CATALOGUE covering technical information on lull

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STOP PRESS :

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PRACTICAL, UP -TO- THE - MINUTEI.C.S. training . . .

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Complete the coupon below and post it to us today

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Write to : Dept. I70F, I.C.S., 71 Kingsway, W.C.2.

INTERNATIONAL CORRESPONDENCE |

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When buik this famous JasonF.M. Tuner provides goodsensitivity with freedom

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• JASON "ARGONAUT" A.M.-F.M. KITSFor building as a tuning unit or complete self-poweredreceiver. Book by Data Publications, 2 - (1/3 post free).

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Best Buy at Britain'srWO-WAI MORSE TRAINING SETS. W.T Mk. 3. Consist.- oftwovau >rs (Apia's) (one with pitch controlj.for one ortwo operators. Has provision for creating •' Atmospherics."in polished oak :ase 12iin. x lOIn. x 8in;, wt., .10 .lbs. Complete withvalves, leads, 2 keys, v-wa.v tonninfii board, circuitandinstrui !

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CHARLES BRITAIN (RADIO) LTD.II, Upper Saint Martin's Lane, London, W.C.2.

TEMple Bar 0545

Shop hours 9-6 p.m. (9-1 p.m. Thursday). Open All Day Saturday.


Alternative Mains-bridgeEnergising Circuits

MODIFICATIONS TO THE NOVEL C/R BRIDGE By F. W. Austin

CERTAIN readers have found difficulty in obtain-

ing a suitable mains transformer for use with

the Novel CjR Bridge, described in the January,

1955, issue of this journal. There may also be others

who are interested and would like to know or alter-

native arrangements for energising the bridge.

The principal difficulty appears to be the additional

50 volts/50 mA. winding which is commonly used on

mains-energised bridges in general. This difficulty

AC Mains -=-

fig. 1.

—

Direct substitution (separate transformer).

was foreseen at the time of constructing the original

model and different methods were tried out with

varying success, but it must be appreciated by all

readers that a mains-driven bridge could hardly be

presented at the outset in any other than approved

and conventional style.

The problem has now been thoroughly explored

and certain recommendations can be made.

Direct Substitution

The simplest and most satisfactory course is to

employ a separate transformer with mains input,

supplying the 50 volts/50 mA. from the secondary

winding as shown in Fig. 1.

Voltage " Step-up " Method

If we cannot obtain the separate transformer as

above, we must discover how such a voltage can be

obtained by other means. If the 6.3 volts winding of

our mains transformer can be " stepped-up " wehave a most excellent alternative.

Transformers " In Reverse "

This will entail the use of a transformer in reverse

(in other words, making use of a low-impedance

secondary winding as a " primary '* input source,

whilst using the original primary as a " secondarv

for energising the bridge). 'In making our choice for

this purpose there is a certain latitude permissible,

but an L.S. Output Transformer and a Television

Frame Output Transformer, have both been found

entirely suitable.

" Tapping " the Tnput

Fig. 2 shows the most convenient and practical

means of employing this method with such trans-

formers. The resistor marked simply " R *'in the

circuit can be a 20 ohms variable component as

usually employed for volume control purposes on

low-impedance extension speakers. This resistor is

adjusted until a voltage of between 30 and 35 volts

A.C. is obtained across the 2 K ratio arms.

If the constructor wishes to try this arrangement

out before incorporation in the bridge, great care must

he taken to ensure that the output from the trans-

former has 3,000 ohms load shunted across it before

taking any measurements. Unloaded transformers

employed in this manner are capable of delivering

quite a nasty shock unless one is fully prepared. The

shunt loads the transformer and limits the output to

reasonable proportions.

When the correct voltage has been secured, the

resistor " R " may be replaced by a fixed component

equal to the value of " R " remaining in circuit. It

may even be dispensed with entirely if the voltage

output stipulated is not exceeded. One Frame Output

Transformer tried by the author needed no limiler

for the input and delivered approximately 26 volts

across the ratio arms. This was found quite adequate

for operating the bridge on all ranges.

"^- To Rectifier

8oo

200 Volts

P. M.S.

impedanceO

Transformer(see text) /KC11 J Watt

(—WJVWVWWoog Patio

^ armsOO

n6'3 Volts

I Amp.

Fig. 2.—Alternative arrangement using tir-" formers" in reverse " (see text).


Infra-red-Its Problems andPossibilities

"

THE FOLLOWING IS AN EXTRACT FROM THE SYNOPSIS OF A LECTUREGIVEN TO THE RADAR ASSOCIATION ON NOVEMBER 14lh. 1956

THERE is a well-known saying which goes "I

shall not believe it until 1 see it with my owneyes." The eye is, of course, a very well

designed receiver of electro-magnetic radiationworking on a narrow band of wavelengths around]/2,000th of a millimetre, i.e., 0.5 microns (1 micron is

one-millionth of a metre). It sees each particularwavelength as a colour : for example, at 0.4 microns it

sees violet and at 0.75 microns it sees red. Beyond0.75 microns, where the eye ceases to respond, and upto 1,000 microns lies the infra-red. The regionimmediately beyond 1,000 microns, or 1 millimetre,is the radar spectrum well known to the RadarAssociation, and although the first wavelength to beused for equipment works on 8 millimetres (highresolution airfield radars) this is only becausetechniques are as yet insufficiently developed onwavelengths below 8 millimetres.

The main advantage of short radar wavelength is

that it gives high resolution with a small aerial size.

The resolution of a radar act is proportional to D/Awhere D is the diameter of the scanner and 7. thewavelength. Thus on X band (wavelength 3 cm.)a radar with a 1ft. diameter scanner can separateout two aircraft at 5 miles range if they are 1 mileapart. On a wavelength of 8 millimetres it coulddistinguish between them if they were j mile apart.In the infra-red on a wavelength of 1/500 millimetre(2 microns) an infra-red receiver even with a 3in.diameter scanner could resolve the separate engines ona single aircraft at a range of 5 miles.

Transmission

All warm bodies transmit infra-red radiation, theamount and wavelength depending on the temperatureof the body and on its surface. The amount trans-mitted depends on the fourth power of the tempera-ture, i.e., PAT3 . Thus a body at 1,000°K PK C-J-273), say, a jet engine, transmits more than 250 timesas much power as a kettle (if boiling water with atemperature of 373 K. In addition, the band ofwavelengths transmitted is also a function of thetemperature, the wavelength ;. max. on whichmaximum power is transmitted being given by thesimple formula

3,000/. max. microns.

Thus we see that for the following bodies the /.

max. is as follows

Temperature

6,000

1.000

Radiating Body

Sun

Jet aircraft engine

Piston-engined air- 750crafl

Kettle with boiling 373water

Human body ... ?00

/. max. mmicrons

0.5 (visible light)

3.0

4.0

8.0

J 0.0

Thus, theoretically, we have only to make areceiver to work on the various wavelengths and wecan detect the body concerned— the hotter the bodythe easier the problem is because the more power it

transmits.

Reception

Broad-band receivers.which receive all infra-redwavelengths equa11y

J

"WelE'f)ave been known for manvyears. These are the thermal detectors known asradiation thermo-couples and bolometers. They relyfor their action on the warming-up effect of theincoming radiation and in general they are toosluggish in their response-lime to detect rapidlvmoving objects, although they are still widely usedlor laboratory measurements.The modern infra-red detector is one based on a

German war-time development—photo-conductivitym the infra-red. In this type of detector a semi-conductor is used- the same class of material as isused in transistors. A semi-conductor, as its nameimplies, is a material that lies between a conductorand an insulator as far as its electrical properties go.In a photo-conductor infra-red detector the semi-conductor is in Ihe form of a thin layer between theelectrodes, across which a potential is supplied. Theresistance of the layer is usually fairly high (in excessof 1,000.000 ohms) and when infra-red radiation is

allowed to fall on it the resistance drops, and this is inturn indicated by a fall in the applied potential. Thistype ot detector does not require that the temperatureof the layer shall change—the effect is caused by theabsorption of radiation in the layer. Thus each unit ofinfra-red radiation absorbed releases an electron inthe layer which would not normally have been free,and these freed electrons flow across the layer and addto the steady leak current caused by the appliedvoltage. The effect causes measurable changes involtage for \ev\ small amounts of infra-red radiation,and, what is very important, the change takes place ina few micro-seconds. Thus even the Fairey Delta IIwill only have gone about 2in. in the time that" it

takes a photo-conductor to respond !

Selective Devices

These photo-conductor detectors only work overcertain wavelengths ranges, i.e., they are selective,and the particular semi-conductor material must bechosen to suit the required wavelength. The mostcommon materials for the layers are lead sulphidewhich responds to about 3 microns, lead telluridewhich responds to 4.5 microns, lead selinide to 6microns, indium antimonide to 7 microns, andgermanium which responds out to very long wave-lengths -possibly 100 microns. All these materialsmust be specially treated to give them infra-redsensitivity, and all of them with the exception of leadsulphide and possibly lead selinide need to be kept

'

cool. i.e.. refrigerated, lo make them sensitive.


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News from the TradeNEW PLESSEY TURRET TERMINALANEW tvpe of rolled turret terminal, which

combines similar efficiency with lower cost when

compared with conventional types made from solid

materials, is now being manufactured by the Plessey

Company. Limited.

The design of this new terminal represents a con-

siderable advance on previous types as a series of

serrations has been added to the underside of the

flange, thus preventing the terminal from rotating

when overheated or when knocked.

Designed to meet the requirements of the Joint

Services Radio Component Specification, these

Plessey turret lugs are made from brass to B.S.267

and are silver plated.

A view of the

new Plessey

Turret Terminal

Terminals of this type are particularly useful in

that they can be applied to tag-boards and terminal

strips made to manufacturer's individual requirements.

They are available in two sizes as follows :

X.T.I with a base diameter of 0.078in., for use where

maximum wire size for centre hole is no greater than

0.028in. diameter (22 s.w.g.).

X.T.2 with a base diameter of 0.100m., .for use

where maximum wire size for centre hole is no greater

than 0.048m. diameter (18 s.w.g.).- Plessey Co., Ltd.,

11 ford, Essex.

SIEMENS-EDISWAN TRANSISTORS

THE Siemens-Hdiswan Organisation now manufac-

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transistors, covering uses for low frequency amplifiers,

intermediate frequency amplifiers, radio receivers and

recording/reproducing equipment.

Other types of transistors are being actively de-

veloped bvSiemcns-Ediswan Laboratories. Literature

is available from the Edison Swan Electric Co., 155,

Charing Cross Road, London, VV.C.2.

E.M.T. HAND STROBOSCOPEANEW Hand Stroboscope (Type 5) is the latest

addition to the range of EMI Stroboscopes

which includes the well-known high power while light

type 3 and the general purpose Type 4.

The Type 5 is a hand-hold instrument built on

simple and robust lines and designed primarily for use

in small workshops, factories and garages for the obser-

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scale covers a range of 300 to 6,000 r.p.m., and oper-

ation is from A.C. mains of 220-240 volts, 50 cycles.

The price of the Type 5 Stroboscope is £18 18s. 0d..

and it is now available for early delivery.—EMIElectronics Ltd., Hayes, Middlesex, England.

CHANGE OF ADDRESS•DUNBAKEN ELECTRICAL PRODUCTS have^ recently removed their head office, sales and

service departments and account offices into a new

building at 45, Oxford Road, Manchester, I.

A USEFUL HANDBOOK"ELECTROTHERMAL ENGINEERING have*-* recently published the second edition of their

well-known valve retainer and valve data handbook.

This book has been brought right up to date and

considerably enlarged to include the majority of

CV valves and their commercial equivalents with the

appropriate data on retainers and top-cap connectors.

Copies are available from the publishers. Electro-

thermal Engineering Limited, 270, Neville Road,

London, E.7.

NEW MULLARD VALVE FOR U.H.F. MOBILERADIO

THE V.H.F. band now in use for mobile radio was

allocated for Band 111 television some time ago.

Eventually, therefore, it will be cleared of mobile

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The QQV02-6 is a miniature double tetrode power

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tapped heater can be operated from either a 12.6

volt, 0.4 amp. or a 6.3 volt, 0.8 amp. supply. Ahigh value of mutual conductance (7 mA/'V per section)

has been obtained by incorporating the latest type

of control grid, by means of which very fine grid

wires are positioned very close to the cathode. The

grid-anode capacitances are internally neutralised,

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As a power amplifier at 490 Mc/s, the QQV02-6delivers 3.5 w. to the aerial under typical circuit

conditions when operated at maximum ratings with

anode and screen modulation. The drive power

needed is 1.4 w., and this can readily be obtained

from another QQV02-6 operating as a frequency

tripler from about 163 Mc/s. The H.T. voltage

needed is 180 volts. No special cooling arrange-

ments are necessary.— Mullard Ltd., Century House,

Shaftesbury Avenue, W.C.2.


Programirtiiiler

NONE ol the plays in the R. C. SherriJl" Festivalequalled "Journey's End'' in those qualitiesol heart and mind that go to the making of

the realty -great" play. But they make goodentertainment. Each asks us to ponder over somesocial problem or other. In "The Telescope," forexample, we are confronted wjlh the family life andbackground of children in the East End of London.One boy in particular, with a very bad record, comesunder the aegis of the new vicar, a young manwhose forebears he considers were largely responsiblefor the slum conditions he finds in his new parish.Promising to do " all he can " for the lad the boylies to him over the loss of a telescope from a localshop. The police come. A false statement from thevicar will save him untold hardship as well as hisplace in the merchant navy. But the untruth is notlorihcoming, and we are left with the voungdelinquent cursing the vicar in no measured "terms.I y pica I Sherrill".

The piece was well acted by, among others.Sebastian Shaw as the vicar and Bunny May. Theybrought conviction to the characters.

" Math ray Beacon" was a strong and originalpiece of play writing, by Giles Cooper, about anunusual army detachment. It had an awful lot of"shuns" in it. and various other commands.Maurice Penham was excellent as the ranker type ofofficer. Lieut. Gann, who gives all these orders.Shaw's " You Never Can Tell " rippled along with

inconsequential gaiety (he wouldn't mind my sayingthat as he only ranked it as a box -office pot boilerhimself). Rowena Cooper as Dolly, Robert Benin I

as Valentine " the five-shilling dentist," Allan Geayesas Cramplon the landlord, Eric Anderson asMcComas the lawyer, all shone in the good cast.

Flotsam's new role of presager of items in verseand with tinkling accompaniment won't be every-body's cup of tea. Perhaps it is a slight infiltrationfrom across the ocean ; 1 wouldn't know. Or maybeit has its own personal significance : again i am inthe dark. One can only hope that, like fine days insummer, it will be used sparingly.

Music" Music to Remember " is a pleasant series of

concerts given by the various regional and provincialorchestras on Mondays between seven and eight onthe Home service. Each item is prefaced with speciallyunsophisticated remarks by various well-knownmusical broadcasters and commentators. Theprogrammes are, almost without exception, blamelessand unexceptionable, consisting, as they do, of themost popular numbers from the most popularrepertoires. Large audiences—they are held in public-

applaud them to the echo.The title of the series gives rise to speculation as

to what apparently should be remembered and, bytheir planned omjssion, those works which pre-sumably arc best forgotten. Needless to say, wide

Our Critic, Maurice

Reeve, Reviews Some

Recent Programmes

differences of view would be revealed on this if areferendum were taken, especially concerning thosecompositions we have not yet heard. Many of thesewould receive votes for inclusion. But, rather likeCaesar's Wife, or The Golden Treasury, there areother times and other programmes over which thefeathers of criticism can be let Ply, Sufficient is it thatthese particular ones possess considerable entertain-ment value to those large numbers who like a nicedollop of jam on an already well sweetened pudding.And who can blame them '.'

ShamAdmirers of Shaw's " St. Joan " must have turned

with avidity to a Frenchman's 'treatment of the SameSubject Anouilh's " The Lark " was given twice onthe " third." Whilst I preferred Shaw's greaterpassion and lorthrightness the Frenchman's clarityand cold logic were fascinating. Of one scene therecannot, surely, be two opinions. Of Joan's renuncia-tion o\' her confession. Shaw has built up one of thegreat climaxes of all stage drama. Anouilh's inter-pretation contains nothing that is dramaticallycomparable.The piece was beautifully given and produced.

Monica Grey played Joan. It was greatly praised bythe critic.-, when produced in London last year.

HancockThe episode of " Hancock's Half Hour " T recently

listened to concerned his making a statue a laHenry Moore. To obtain material For it he demolishedWaterloo Bridge, Nelson's Column and various otherpublic monuments. Imaginary news bulletins werebroadcast giving day-to-day progress reports onthe destructive work. Tt was all mildly amusing.Someone 1 was listening with told me it was not oneof the best. 1 hope she was right.

Coates

The gulls continue to mew, the waves to break onthe rocks and Eric Coates's music to beguile usregularly every Monday at 1.10. as Roy Plumleyinsinuatingly invites us to join some well-knownperson on his "desert island." accompanied by theeight records and unlimited supply of needles.Knowing both what a " desert " and an " island " are, 1have always been at a loss to get at the geographicaldefinition of a " desert Island," rny gazetteer beingunhelpful. The signature tune of this series clearlyconnects it, as 1 say, \ytfh waves, birds and surf. Butwhy? It might, surely, just as likely be an oasis inthe Sahara.


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CALIBRATED POTENTIOMETERSFOR RC BRIDGES. A few WirewoundPots complete with hand calibrated scalesuitable for workshop RC Bridge, 10 6 withcircuit.

.WO VALVE TESTER. Holler panel type,used, in good condition, £9.15.0 post paid.AVO SIGNAL GENERATOR. Used,good condition, 194G model. £7.10.0 postpaid. Another with mains transformerfault. £6.5.0 post paid.

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RECEPTION SETS TYPE H.109. K.v-Army 8 valve superhet receivers employing5 ARP12-S (VP23) ana 3 AR8's (HL23DD).Fitted with miniature speaker and vibratorpower pack for operation from 6v. accumu-lator. Frequency range 1.8 to 8.f> Mete (35to 187 metres.', front panel is fitted with allcontrols including UI'CW. switch and 2jacks for alternative headphone reception.Size approx. 13 x 12 x llin. In good condi-tion, supplied with circuit diagram andaerial tested. PRICE ONLY 85- or lessvalves PRICE ONLY 45 -. Carriage 8/8.

AMERICAS I.I'.I'. I NITS. Containswealth of useful components includingrelays, 10 valves <6-iSH7's. 2-7198'.-,, 3-686*3)and a rotary converter rated at 480v. D.C.output for 18v. D.C. input. One end ofconverter is fitted as a Blower Motor whichoperates from either6v. or 12V. accumulator.The other end is fitted with a gear box.easily removed if desired, and the twodriving shafts which protrude rotate atapprox. 4 and 18 r.p.m. for 12v. input andhalf this for (iv. input. In good condition.price only 30'-. carriageLOREKZE HIGH FREQUENCY SPEAK-ERS, Specially designed to reproducethose higher frequencies in the soundspectrum from 1.8 to 20 Kcs. Connectedacross your existing speaker is

to bring reproduction to life and lor it toacquire a soarkle and realism previouslyunobtainable. Essential for the highquality reproduction or modern L.p. re-cordings, P.M. and T.V. transmission;.Can be used with any standard speaker andloaded up to 25 watts. Size approx. 261.din. x 2?in. deep. Supplied with full conneilion details or send S.A.E. for

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The Editor does not necessarily agree with opinions expressed by his correspondents

Amateur Licence

C1R,—I note from recent correspondence in " Opento Discussion " that S.W. listeners continue to

press for the issue of novice licences, seizing every

opportunity to reopen the campaign.

Having read " Thermion's " article several times [

still cannot reconcile the need Tor a national amateurs'

association with the needfor a novice licence. To •-—.-. ...,.,...«—.—................................._....-.....—........ crystal

(c) Tn U.S.A. there are several grades of licences.

Surely if that principle was adopted in this country a

great many problems would be solved ? The various

licence grades could be allocated roughly as follows :

(I) Novice : The applicant must complete question

paper sent to him under the invigilation of someoneelse who then has to sign the answer paper to say

that the applicant did not cheat.

Allowed only to use

controlled trans-

start with, the article deals

specifically with those in-

terested only in reception,

which implies those whodo not wish to graduate to

a transmitting licence ; whythen the red herring in the

shape of the novice licence?

Discounting the manyingenious excuses put for-

ward to support the case for novice licences, it is

patently obvious that the root of the matter is the

apathetic approach by a minority of listeners to the

technical and Morse examinations.

If, as one correspondent suggests, the G.P.O.

requirements are a deterrent to the listener, this surely

is a matter for the listener's conscience, and not a

reason for circumventing them.

Those whose ultimate goal is a transmitting licence

should, by virtue of their interest and determination,

accept the examinations as a necessary and justifiable

test of their competency to operate transmitting

equipment in order to fulfil the conditions of the

licence.

Whilst we are always pleased to assist readers with •

their technical difficulties, we regret thai we are unable '

to supply diagrams or provide instructions for mollifying \

commercial or surplus equipment. We cannot supply •

alternative details for receivers described in these pages. •

WE CANNOT UNDERTAKE TO ANSWER QUERIESfOVER THE TELEPHONE. If a postal reply is required\

a stamped and addressed envelope must be enclosed with jthe coupon from page iii of cover. i

mitters.

Allowed to operate onrestricted frequencies.

Allowed to use certain

types of emission only.

Allowed to operate withrestricted power.And a licensed amateur

must examine the station

before it goes on the air

and then every month afterwards, signing the log

book at each visit.

(2) Phone : For the operator who intends to workphone only :

Must have radio amateurs' examination.

Morse test not necessary.

(3) General : For the phone and C.W. operator as

the present-day licence with both Morse test and radio

amateurs" examination necessary.

I shall await with interest any correspondence con-

cerning the above.— F. B. Biakf. (G6786) (Beacons-

field, Bucks).

The demands for novice licences are in reality gTR,--I was indeed interested in the letter in

individual admissions of the lack of ability and deter- *\ above heading, in your .December _issue.

under the

mination to tackle these examinations and should be

dismissed as such.

There is only one way to make the grade in this life,

that is to work for it, and it is to be hoped that the

present widespread doctrine of " something for

nothing "is not allowed to spread to amateur radio.

—L. O. Richardson (Kent).

SIR,—With respect to the letters of H. F. Barker and

L. G. Hutton : (a) Of what use is the G.P.O.

Morse test for an operator who intends to use phone

only ? Admittedly it is necessary for the code operator

in order that he does not spoil other people's Q.S.O.s.

But no amount of experience with the key will makea phone operator operate any better.

(b) Originally one used to obtain a transmitting

licence by filling in a question paper sent to you by the

G.P.O. Surely this principle could be used for a" novice " licence ? This would give the " ham to be

"

some practical experience so that he could then take

his R.A.E. and his Morse test and become an operator

with the authority of the ham today.

In the late "thirties I dabbled (as a schoolboy) in

S.W. listening on a very meagre pocket, and am under

the impression that there were two different licences

for transmitting—full power and " artificial aerial."'

1 am now a married man with my own family andfind it impossible to purchase the necessary equipment

to break into the licensing operators' field, as the re-

quirements needed are indeed expensive and wouldhave to be purchased outright, whereas a " novice

licensee '-' or '* half-power type " could learn the use

of his smaller equipment and slowly build up his

apparatus as well as his knowledge until he could

join the " full powered brigade." Is not this one of

the biggest stumbling blocks 2

This class would be of immense value to the Services

in the case of another national emergency, requiring

minimum training, possibly limited to the apparatus

in use.

May I suggest representations be made to the

P.M.G. on these lines? 1 would leave the initial

vetting to a P.O. official rather than a licensed

operator, mainly on the ground that " official vetting"

858 PRACTICAL WIRELESS

would avoid trouble with ihui bodv of persons in thefuture.

Analysing it down 1 would say ; (a) Limited power•for transmitting (say 100 mile radius), (b) Crystal-controlled equipment vetted beforehand by P.O.official who could call and inspect for a small chargeand possibly give advice on operation, (c) Knowledgeof Morse code, say 5/6 w.p.m. (which is most essentialto start in the field), (d) Small annual fee.

I would be prepared to put my name to suchrepresentation.—D. A. Gkiiihh (Wisbech).

Battery-operated Tape Recorder

C1R,— 1 have received since publication of the article" Battery Operated Tape Recorder " many

enquiries regarding technical aspects of the instru-ment. 1 have, therefore, picked out those querieswhich occur many times and enumerate them andtheir answers below.

(1) What is the valve line-up?Three ARP12s and one ATP4.(2) Can the instrument be converted to operate

from the mains ?

For this one would require a conversion unitsupplying 90 volts H.T. and 3 volts L.T. from 250volt A.C. supply. Such a device could easily be con-structed. However, a far superior plan would be toredesign the amplifier using mains valves.

(3) Would it be in order to use an electric gramo-phone motor to drive a capstan ?This would indeed be possible. The only reason

why a clockwork motor was referred to was to makethe instrument independent of the mains. Capstandrive is, of course, superior to direct drive, in that thetape speed is constant.

(4) How are recordings erased ?

Fig. 8 in the article shows erasing. The tape is madeto run past a smooth permanent magnet. This, ineffect, saturates the tape with magnetism, therebydestroying the recording.

(5) Is there any danger of the biasing magneterasing the recordings as they are made ?No, providing the magnet is placed as shown in

Fig. 7. Simply, the tape must pass the magnet beforethe recording head.—B. JL. Wilkinson (Exeter).

A Transistor Hint

QIR,—Ts it generally known that with a minutevoltage at one side of a germanium diode and

1.6 volts from a grid bias battery at the other anastonishing degree of amplification can be realised ?The circuit to achieve this result is simplicity itself,but I will not bore readers with the details as this fieldis already well mapped.Actually 1 discovered this phenomenon quite by

accident when carrying out some experiments oninductance.—Robert D. McCXwm (Beasley).

Radio Society Correspondents WantedC JR.—The radio society of which 1 am a member^ would be very interested to hear from other

February, 1957

school societies. If any other schools are interestedwe will gladly take up correspondence with them.We should be grateful for the help of hams andamateurs with spare radio parts because the increasedprice range for radio parts is making it increasinglydifficult to run a radio society efficiently.—C. .(. Lawson (Bootham School. York).

A Reader's Views

§1R,—-As a reader of Practical Wireless sinceround about 1948 might 1 give mv views?

First of all about these nice bright covers : theymay look attractive on the bookshop counter, butwhen 1 buy a different radio magazine at odd timesit is because the front cover has a list of articlesone of which 1 wanted to read. A list just likePractical Wireless used to print.

Having got past the cover next comes "Open toDiscussion." It is nice to read the other chaps' views.stu.fi put together and results. So whv not an extrapage ?

After this 1 read Mr. Camm's " Comments of theMonth."Then *' Servicing Radio Receivers," always hoping

it will be one I own. Although it works it would stillbe of interest to see the circuit.

For F.M. 1 use the Denco unit and a Williamsonamplifier. Would an expert like to say the point ofde-emphasis in the F.M. unit only to do the oppositeon the pre-amp. As is well known, loud speakerresponse is not so good at the top end. As cuttingtop cuts some noise, why not at the last stage ?Taking the other end of tone control, how nice

some of the old pre-war sets sound as far as bassresponse goes, even although you might have only a6in. speaker. I think this is because the boost isjust low enough to miss speech and catch music,whereas on these push-pull amplifiers any boosting ofbass is at so low a frequency it can only be heardonce in a while.

The aerial for F.M. that I use is supported by oldbean sticks and string over the front room. Areflector is used, a former dinghy aerial. Althoughshop type aerials have been tried, one up a 25ft.pole, this ugly mess still gives most signal. On theEM80 it is just enough to send the bright light towhere the glass curves.

Speakers used—one 12in. Goodman's and anelectrostatic tweeter. I think the cross-over frequencyof the latter is too high (2,000 c.p.s.) for it to do muchgood, or maybe the output is just not up to movingcoil standards.

One tip before I close. With push-on spring-loaded knobs 1 find a little solder on the spindlemakes the loose ones fit much better than trying towedge them with matchsticks, etc. The solder beingsoft is easy to file to shape.—G. Arihlkim(Croydon).

WIRELESS COILS, CHOKES AND TRANSFORMERS8th Edition. Price 6/-, by post 6/9.

&&££%£^J^^^B^^. a S.^.&1 S^!?aI^iuietwUa¥e/or Publication in "Practical Wireless." Such articles should be

gff§S!<Sf jg&tiama&E&mXSSg^Ji^J',"'" K£&?fSE2S8 '" ""7/(;S'P of irireless apparatus and to our efforts to keep our mdmtn touchitSfitWtetatert *S2sJZ£&rL°,!Zh"<",

!

,

va7,a1

l« ihat OBWroiSi Sserttei tn our columns is not the mbfect of letters potentmSt aele'°V™ntS-

copyright, in all druwings, photographs ami articles published in •Practical Wireless " U soecificaUu resumed ihmmhnvi ii.a „„.«*-i„„

9B8&%£&Si ®8SKS ttr!"™ productions or UnitationsZf aft'of SJ^SSSUSTSS^SflSSSS^ »,

February; 1957 PRACTICAL WIRELESS 859

^ RADIO ft TELEVISION

iINTERFERENCE

by B. L. Morley. S/- Postage 4d.

TRANSISTOR CIRCUIT HAND-BOOK. By L. E. Garner, Jr. 40/-.

Postage I/-.

IMPROVE YOUR RECEPTION.m By J.

Cura and L. Stanley. 5/-.

Postage 4d.

k TRANSISTOR TECHNIQUES. AGernsback Library publication No. 61.

k 12/-. Postage 6d.

I TV CONVERSION FOR I.T.A. By

% C. E. Lotcho Price. 25/-. Postage 9d.

^MAINTAINING HI-FI EQUIP-MENT. By ]. Marshall. 23/-.

Postage I/-.., ,

RADIO VALVE DATA. Compiled

by "Wireless World." 4/6. Postage

te 6d.r RADIO DESIGNER'S HAND-BOOK. By F. Langford-Smith. 42/-.

Postage I/-.

The MODEM BOOK CO.k BRITAIN'S LARGEST STOCKISTST of British and American Technical Books

19-23, PRAED ST., LONDON, W.2

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AMUR KAN MADE B7(i VALVIC PINSTRAIGHTENER. Bench Type 2 6. post1'- This little gadget will save you pounds.

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MIXED RADIO PANELS. Full of resist-

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PARTS REMOVED FROM MAYT.l It. UNITS. Micrometer Drive, com-plete, 2 6. post, i '-, Bandies, 9d„ post 6d

Coil Formers fPot). 6<l.. post " J

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NORMAN H. FIELD ElectronicsDept. PH., 68, Hurst St., Birmingham, 5. Birmingham's Largest Constructors' Store

Switch and

WHY WASTE TIMEGive that set its best chance

FIT QUALITY COMPONENTSCatalogue I/.

Parts for the following : Manual

Osram "912 " Plus Amplifier ... 4/-

Mullard 10-watt Amplifier ... 3/6

The Coventry2-watc Amplifier ... 1

4-watt Amplifier ... ? 1/-

6-watt Quality Ampliner )

The Coventry A.M. Tuner Unit 1/-

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Complete Component Price lists will be

supplied with each Manual

COVENTRY RADIOEST. 1925

IC9, DUNSTABLE ROAD,LUTON,BEDS.

Phone : Luton 2677

W. B. SUPPLIES96, OLDHAM STREET, MANCHESTER, 4

TERMS.- Cash with order. Orders under207- add !'d., over 20.'- add 1 M postage.

^•1-Finger Pianists^.

Build your own electronic keyboard

and play everything ! Send lor free

leaflet. Guitar, cello, flute and trumpet

are all easy. Wri te now. .

.

C & S, 10 Duke St., Darlington,

Co. Durham

SPECIAL OFFER. Collaro RC54 Auto-change Units. :3-speed, packed in raaKer'ssealed cartons, guaranteed perfect. Ourprice 7 ens. plus 5,'- carriage.

Malnsbridee Condensers.—4 mid. M0 v.

and mfd. 350 v.. 2- : .1 mfd. 4.000 v., 3 -;

Can Cond. : 8 mfd. 500 v.. 13.

II.F. Chokes on 8ln. former, ideal Crystalset coil. 1/-,

Microomp Meters. Double movement. 10,-.

Mixed Resistors. 3 doz.. 5'-: Condensers3 doz., 51; Our selection. 5K wire woundpots, pre-set, 1/-.

Headphones suitable for Tape Recorders.10-.

Morse Keys, Air Ministry. 2 6.

Amplifiers for Record Changers, one valveplus rectifier. 50,'-.

T.V. Aerial Rook on how to make aerialsfor Bands 1 and 1U. 29 post paid.

Coaxial Gable U.T.V.) 22ft. length. 3 3.

Radio Aerials, insulated. 50ft.. 19 ; 100ft..

3;-;Speaker Fret, expanded metal (gold).

12in. x 12in.. 4 6 ; 12in. x 18in.. 6 9 ; NeonScrewdrivers. 110 v. to 380 v.. 3 11.

CoabUatlOO Bon Spanners, interchange-able. 2. 3. 4. 5, 6 B.A., 3/11. Variable Con-densers, air spaced, 40 pP., 1,'-

; 75 pF., 2- ;

115 pF.. 2,6 ; 75 pF Twin. 3 6.

rilain.nl Trass. 230 volt. 6.3 volt 2 amp.,6'6 ; C.R.T. Isolation Trans, with 25",',

boost, 2 volt input or 6.3 volt input. 10 -each.

Crossover Vtais for BBC & I.T.V.. 7 6.

Portable Amplifiers complete with Crystal

mike on Moor stand and cabinet speaker all

enclosed in speaker case. Ideal for clubs,

etc. 18 ens.

860 PRACTICAL WIRELESS CLASSIFIED ADVERTISEMENTS February, 1957

RECEIVERS & COMPONENTSELECTROLYTICS, capacity, voltage.size, type of mounting, prici postpnid. "1.000

! 1.000. 6v, 1x3, clip.3'3; 1,000 \- 2.000. 6v, 1 x 3, 3:9;100. 12v, | x lij. tag. 1/9; 500. 12?,i X lj, W/E. 2/-; 2,000. 12v, U x 2.

WE, 3/6; J.0, 25V, J- x 1}. WE. 1 3;25, 25v. fc X 1J. W/E. 1/3; 50. 25v.I x 13. W/E. 1/9; 100. 2Sv. g x ljW E. 2/ -J 1.000, 25v. 1 x 3. clip. 4/-;3.000, 25t lji x 4*, 5/6; 5,000. 25v.1? x 44, -clip, 6/6; 500. 50v, 1x3,clip, 2/9; 200. 250v, II x 3, clip. 3.6;5 150v. ii x 11. WE, 1 3: 8. 150v.•. x If tag. 1/3; 40 H- 40, 1 s 2.

clip, 2/9; 200. 250v, 1* x 3. cliu. 3'6;103, 275,350V. lj x 3. clip. 3 .-:'

: ii

16. 275v. 1 x 2, clip, 3'-; 32 ' 32-'- 8. lij x 2, Clip. 4/3; 16 | B

I4.

275v, 2 x 4-i, clip. S'6; 60 4- 250. 275360v. l:i x 41. clip. 6:3; 32 (2

8. 350/42Sv. 1.3 x 3. clip. 5.-; 16I

16, 350V. 1 x 2. Clip. 3/6; 32 (- 32,350V. 11 x 2. clip. 4,-; 2, 350V. I X2. tag, 1/-; 103. 350,425V, 1, g :;.

clip. 4/-; 50 i- 50. 350.425V. 1. X 3,clip, 4/6; 100 ' 200. 3S0Y, 11 x 4.'..

clip, 76; 8. 450v. 1 x 2. cliu. 1.9;20 10, 450v, 1 x 3. clip. 4,-; H -

8, 500v. 1] x 2, clip. 4/-; all allcans, some with sleeves, all voltages,wkg.. surge where marked, new stockguaranteed. Television Chassis, cad-mium plated steel, size 13 It 13 :<

2iin., complete with 13 v.ilv.

(9-B9A Pax.. 1-B9A Ccr.. 2-B7G Cer.,1-Int. Oct. Amph.i. 2D various tagstrips, cut away for metal ree.. HfieI rails., etc., 9/11 each, posl paid;front and rear tube mounts to fit

above chassis, 3/- pair, posl pasP.M. focus Magnets. wide angletetrode tube, fully adjustable 9.'ii,post paid, Scanning Coils, wideangle, with mounting lugs, 19/6, postpaid. Vi-sion l.P.s (2nd. 3rd andwin. (tea, 34 me b, slug tuned, size13 '16 x 13.16 x 2'.iu. can Sel oJ

3, 5/6, post paid. T.V. Rectifiers.H.W.. 250v. 250mA. 2.;in. fins S hilong. 12.6, post paid. 100s; WWPots. 3w. lin. spindle. 26. 8 ml.600'750v, Purer Conds., 4 x 2in. x U.6/6. RADIO CLEARANCE LIMITED,27. Tottenham Court Ro'id. London.W.l. (Telephone: Museum 9188.

loudspeakers repaired promptlyMODEL LOUDSPEAKER SERVICE,Bulliugdon Rd.. Oxford.

PANL, the air-drying black crack 1'

paint. 3'6 per 1 '8th pi. can, Q, A.MILLER. 8. Kenton Pafk Ores ,

Ken I on, Middx.

TAN IN 24 HOURS. SupertonicSunray Lamps, ultra-violet iuir i-redcombined: automatic exposure; con-trolled emission; all mains: Hate i

£7..10/-, our price 80'-. S.A.K.brochure. Dept. 14. SCIENTIFICPRODUCTS. Cievclevs. Lanes,

THE HIWAYMAN. A new superPortable Radio for the home con-structor: all-dry 4-valve superhetwith Ferrite rod aerial, easy wiringdiagrams and instructions. 1,6 (post3d.). RADIO EXPERIMENTALPRODUCTS LTD.. 33. Much ParkSt., Coventry.

HATES I 5/6 per Mile or partthereof, average Bve words m lino.minimum 2 lines. Itox No. 1- extra.Advertisements most lie prepaid andaddressed to AdvertisementMaiu^cr, •• Praelieni Wireless,"Toner House. Southampton ,st..

Strand, London, W.C.2-

SITUATIONS VACANT

RADIO TELEVISION. Servicecapable man required:

ability to drive an advantage;wage; halt-day Saturday. ApplySTAFF manager. DamagesHo! born.

OSMOit would like you to have FreePractical Wiring Diagrams of thelatest published circuits with fulllists of components required. Send7«d. (stamps) to OSMOR RADIOPRODUCTS LTD., 4 IB, Brifiinnn Rd.,Sth. Croydon. (Croydon 5148.J !Seiadvert.. Cover Iv.J

R1155, as new: P.P.,- O.P.St,optional; P.W.. Sept. 49-August 56.less one: P.T., full set, less No. 1.

Offers. Write : 4, Central Drive.Roys; on, Barnsley. Yorks.

MAKING YOUR OWN? Telescopes,Bnlargers, Projectors, or. in fact,anything using lenses. Then gel ottrbooklets " How to use Ex-Gov.Lenses & Prisms."' price 26 e a.

Comprehensive lists of optical, radioand scientific equipment free forS.fl.e, H. w. ENGLISH. RavleighRd.. Sutton, Brentwood. Essex.

TELEVISION. -9in. Models. £7,10 -;

12m. Models. £15; nil makes: work-ing: carriage paid, tomlins. 127.Brock'.ej- Rise. Forest Hill. S.E.23.

SEVERAL EARLY MODELS Gin I'ele-vision, complete and mostly working.£5 5. - each; carriage paid. TOMLINS,127. Brockley Rise. Forest Hill.S.E.:t. (FOR 5497.1

GUARANTEED TELEVISION, 12in,Models, first-class picture, 5-channel.£2.j each; carriage paid. THEGRAMOPHONE SHOP. 19-21. Brock-,ev Rise, Forest Hill. S.E.23.

TELEVISION. 12:n. Televisions.£13 10 - each: curr. paid. TOMI INS.127. Brockley Rise. Forest Hill,

S.E.23. (FOR 5497..

OSMOR NEWS. E.M. Switch-tunedCoilpack. Circuits and full informa-tion available shortly on request.OSMOR RADIO PRODUCTS LTD..418. Brighton Road. S. Croydon.

SERVICE MANUALS SHEETS. TelRadio for hire, sale and wanted.S.A.E. enquiries. VV. J. GILBERT(P.W.i, 24. Frithville Gardens.London. W.12.

SKILLED RADIO MECHANICS ANDSERVICEMEN. -A large organisationhas vacancies for men who are pre-parer! to travel and work anywhefein the world. Periods abroad, (i CO24 mouths. Salary £75 per month,plus all found. Candidates must besingle, medically fit and have a goodknowledge of radio theory and prac-tice. Initial engagements one Uthree years with excellent opportuni-ties for men with ability and righttemperament to obtain permanenciesWrite Box PW.998. c o, 191, GreshamHouse, E.C.2.

VALVES

WANTED, Valves EY51. ECL30.KT61. 6U4GT. PL81. 35Z4. etcprompt cash. WM. CARVIS LTD.,103. North Street, Leeds. 7.

ALL TYPES of Valves required forcash. State quantity and condition.RADIO FACILITIES "LTD.. 38, Cha!cot Road, N.W.I. I PRXmrose 909'J. i

EDUCATIONAL

FREE ! Brochure giving details o!

Home Study Training in Radio.Television. and all branches ofElectronics. Courses for the HobbyEnthusiast, or for those aiming atthe A.M.Brit.I.R.E,. City and Guilds.R.T.E.B.. and other Professionalexaminations, Train with the collegeoperated by Britain's largest Elec-tronics organisation. Moderate fees.Write to E.M.I, INSTITUTES. Dept.PW28. London, W.4.

ALL TYPES oi' new radio valveswanted, small or large quantities;cash payments. R. h. s. ltd. iW),155. Swan Arcade, Bradford, 1.

LEARN IT as you do it—we providepractical equipment combined withinstruction in Radio, TelevisionElectricity, Mechanics. Chemistry,PhotograDhy, etc. Write for full

details to E.M.I. INSTITUTES. Depl.PW47. London. W.4.

MIDDLESBROUGH. Largest slocks onN.-East coast. Radio. TV components.FM Kits.' Gram. Cabinets. TapeDecks. Leak Ampliliers, valves, etc.Callers only. PALMERS, 106. New-port Road. (Phone: 3096.1

AMERICAN RADIO Plans and De-vices Now available. Hundreds olnew and startling devices you canmake. Only designs of this typeavailabli in UK. Receivers, walkie-talkies, amplifiers, recorders, magiceye alarms, etc.. etc. Full lists, data,illustrations. Free for stamp. Sendto-day.—A-P.S. t.PW.i, Scdgeford,Kind's Lynn.

WIRELESS. See the world as .

Radio Officer in the Merchant Navy;! short training period: lowI scholarships, etc., available. Board-' ing and Dav students. Stamp for' prospectus. ' WIRELESS COLI EGE,Colwyu Bay.

MERCHANT NAVY Wireless School,Oversells House'. Brooks' Bar. M er 16.

A.M.I.Meoh.E., A.M.Brit.I.R.E., Ciivand Guilds, etc.. on " no pass—nofee " terms: over 95"^ successes. Fordel ails of exams, and courses in allbranches of engineering, building,etc.. write for 144-pa.fe handbook,free. B.I.E.T. iDept. 242BL 29Wright's Lane, London. w.K.

AMERICAN MAGAZINES. Yearssubscription " Audio " 35 -, " HighFidelity" 50,'-. Spec, copies 4,- &£/ei. Cat. free. WILLEN LTD. (Dept.40 >. 9, Drapers Gdns., London, E.C.2.

WIRELESS. -Day and V:instruction lor P.M.G. Certificate olProficiency and Amateur WirelessLicence, Morse instruction only i:

required, also postal courses. ApplyBST.. LTD.. 17H. Cltipham Rd^,London, s.w,!,'.

February, 1957 PRACTICAL WIRELESS CLASSIFIED ADVERTISEMENTS 861

T/V and RADIO. A.M. Brit.I.R.E..

City and Guilds. R.T.E B. Cert., etc..

on " no pass—no fee " terms. OverMrA successes. Details of exams.and home training courses in all

Ranches of radio and T/V: writelor 144-page handbook free. B.I.E.T.

(Drpl. '242GI, 29. Wright's Lane,London, W.8.

INCORPORATED Practical RadioEngineers home study courses of

Radio and TV Engineering arenised by the trade as outstandingand authoritative. Moderate fees to

a limited number oT students only.

Syllabus of Instructional Text, is free."The Practical Radio Engineer"journal. sample copy 2/-. 6.000Alignment Peaks for Superhets. 5/9.

Membership and Entry Conditionsbooklet. T-. All post free from thesecretary. I.P.R.E.. 20, FairfieldRoad. London, N.8.

CITY AND GUILDS lElcctrical, etc.)

on " no pass—no Tee " terms. Over95' ; successes. For full details of

modem courses in all branches (.1

Electrical Technology send for our144-pasc handbook free and postfree. B.I.E.T. iDcpt. 242A). 29.

Wright's Lane. London. W.8.

VALVES-GuoranfeedDAF91 6.6EA50 2.'-

F.BCXS 7 6ECC33 86EP36 5'6

6-

VU1UW770554IS5IU53DS4D16A8(iAKIiISA MB

EV.Vi

EF50EF91EL32PCC84

11.'- 6AQ5PY81 10- BAU6TT11 4'-|6B8VRG5A 3 6 1 1>BEI>

VR66 3/6 * 6BH6VT20 3/6 6BS7Postage 6tl. extr

"Jason." F.M.£6.17.6

JBW0 6 66C5 6,-

6CH6 7.'-

6F12 7.'-

6J5 6-6K7G 4 66K7M 6 -

6SA7 8 -

,_ 6SG7M 7 67 - 6SN7GT76 867 '6 6U5 7,'6

6- (iU5<L'X)71- 767 6 6U7 6/67 6 6V6 7.'-

a. (Also all comInner Kit,

., plus 2.6 post.

6X46X57117

8D28D39D29DK 5-

12BAG 7.612BE6 7 612BH7 7'612J7 8612K7 8.'-

15U2 5-50C5 8 650L6 86ponants)complete,

TELEKIT SUPPLY104. HiRh Streeti Heckenham, Kent

Phone : BEC 3720.

THE ROYAL NEW ZEALAND

AIR FORCEhas vacancies for

BRITISH EX-SERVICEMEN

in the following trades :

RADIO MECHANICS

RADAR MECHANICSCommencing pay between £10.16.2 per weekand £17.1.3 per week according to previous

experience. Ages between 21 and 40. married

or single. This is an opportunity to stai I a

new life in New Zealand with excellent

Conditions of .service; [and free ;

Limited vacancies also exist in other trade

groups. Write for full information to :

—

THE ROYALNEW ZEALAND AIR FORCEHEADQUARTERS (Depi. P.W.)

ADELPHI BUILDINGJOHN ADAM ST., LONDON

W.C.2.

NEW BOOKSUnions Kail in ami T.V. Diary 1957. price

4,3. postage 4d.

Improve your T.V. Reception, by JohnCura. 5.'-, postage 4d.

Radio Valve Data, by Wtreless World (NewEdition). 4.6. postage lid.

.

Transistor Tecttniflues' (GernStoacK Li-

brary). 12'-, postage 9d.World Radio Ilandhook 1957. by LundJohansen. 12 6. postage 1 -.

The Home Electrician, by F. J. Camm.12,6, postage 9d.

Suppressing Kudin and T.V. Inter-ference, by Morley. 5 '-. postage 4d.

Beginner's Guide to Radio, by !'. J.

Camm, 76. postage 6d.

Loudspeakers, by Brlggs, 7 6. postage 6a.

UNIVERSAL BOOK CO.12, Little Newport Street, London, W.C.2

i adjoining Lisle Strer-l)

Morse Code operating . . .

. . . as a PROFESSION45 years of leaching Morse (ode is proof<if the efficiency »r Che Candler system.

Send 2ul. stoma tor /'aimwnt I'ttmx and Full

Detail* of ail Courses.

CANDLER SYSTEM CO. Dent. 5I.O

581), Abingdon Road, London, W.8.

Candler Stistem <"o.. Denver, Colorado. U.S.A.

VACANCIESFOR SKILLED CRAFTSMEN

IN GOVERNMENT SERVICE

AT CHELTENHAMExperienced in one or more of thelollowing :

—

1. Maintenance of radio communi-cation receivers.

2. Sub-assembly lay-out. wiring andtesting of radio type chassis.

3. Cabling, wiring and adjustmentof telephone type equipment.

4. Fault, finding in. and maintenanceof, electronic apparatus.

5. Maintenance of Teleprinters orCypher Machines and associatedtelegraph equipment.

BASK' PAY : £8 lis. -Id., plus up to£2 10s. merit pay, assessed at Interviewand based on ability and experience.Opportunities for permanent and pen-

sionable posts.Five-day week, good working condi-

tions, single accommodation available,

Apply to : Personnel Officer

G.C.H.Q. (FOREIGN OFFICE)

53, Clarence Street, Cheltenham.

GALPIN'SElectrical Stores

Send for Free List (or Small PowerTransformers, Electric Light and Slot

Meters, Volt. Amp and Milliamp-

meters, etc., Transformers made to

order'

•Radio Bargains for Visitors.

OPEN ALL DAY SATURDAY.

408 HIGH ST. LEWISHAM

OSCILLOSCOPE(MINIATURE TYPE)

Supplied in kit fofor workshop

Complete with i

instructional nogiving details of ap-plications to radiowork. Can be operatedfrom power supply of

AC domestic radio re.

equipmene or from power unitsupplied as an extra.

Price £10 &«£«**»)(Power unit, if required, £3 extra)

Order now or send stamp for further details to:

E.M.I. INSTITUTES,Dept. 32, LONDON, W.4

(Associated with "His Master's Voice", etc.)

VALVESNew Tested and GuaranteedIBS 7 6 8BR7 8 6 BCH35 9'-|EL84 1076IBS ", 6 6BWK 7 6 BCH42 jRY5111/61T4 7/6 6.TSG 5 6 10 - BZffl 8-3S4 7 6 12AT7 9,-ECLoO K':

;1V4 7 6 12AU7 9- 10 6 UBC415Z4G 8.6 807 6'9:EF39 5 6 10-GAL5 e.'B'STKl 86 EF-U 10 - UCH-1210 -6AMH 7 6KflC!l H 6 EF81 9 6 UK'll 10-6ATR 8'-'EBF80 EF92 4 9UI.U 10-6BE(i 7 '61 10-ET.41 10-UYH 8 -

MATCHED PATHS. ELM, 23 -: 6V6G and

GT. 17/-: 6BW6. 18/-: KT33C, 1.9/6; 1)07,

14.6 per pair.VOI.IML CONTROLS, small, loner spd..

L;'S, 3- ; B.P.. 4- ; D.P.. 4 6. All valuer.I'APLR IU.OCKS, 4 mid.. 1,000 v. wk«.. 3 3.

1*. & P. (id.

R. J. COOPER (G8BX)32. SOUTH KM), <ROVIM>\. SI It HI.V

Croydon 9186

ASTRAL RADIO PRODUCTS'HOME RAOIO." :)2 page lUnstratedbooklet. Simple wiring Instructions for

Crystal Set, 1. 2. 8 Valvers. SI: post 3a.

THI' COILS. Specified lor 'Bedside PUHD-luilKin 4.' All Dry 3 Band. 3." ' Puxli-iiiiiiou 4." etc., 6/6 p:.. post 6cL Push-button Unit with modification data I

-.

DUAL WAVE IIF Coil. Specified for• Summer All Dry Portable,' ' Modern 1Valvar,' "Modern 2 Valvar, "7 <; BatteryMiniature,' etc., 4 3. post 3d.iKT's Miniature. 1' xli"x2}"ln cans. Extrahigh ' Q.' Special oirer. 86 pr., post Gel.

K COILS. ' AC. B'pass :i.' 3 3 each, post Gd.

FitAM P. AKKIA LS. M.W.. 5 -. post 4d.n. r. < iiOKi: (Osmor Q.c.i). 6 9. post 4d-.

Crystal set Coils, f.. & M.W., 26. post 3d,

82, Centurion Road, Brighton

A.NNAKIXS WINTER BARGAINSBalanced Armature phone inset. 30 ohms.New. Boxed. 210. Unit with toggle switch,a Ol 24 v. wedge lamps. New, Boxed. 1.6.

Morse keys, well made, 3 3. Thermal DelayRelays, 6V. New, Boxed. 2 10.Unit with.5 ampThermo couple 2in. meter. New, Boxed. 7.6.Mains Transl". 200-240 v. in 111) v. 30 mA. out.,

5 9. Mains Transf. 100-240 v. in. mo v. 250mAout., 12.6. All above Carriage Free. Main landculv. Money Back Guarantee. Free Lists.

25, ASIII'11,1.1) PLACE, OTI.KV.VOKKS.

LONDON, S.E. 13 (

IS/CAP. BRIDGE *bChecks all types of resistors and

condensers

Easy to Build Up Easy to Use

READY CALIBRATED[Stomp for details of this and other kits.

1

1 RApiO MAIL, 6 Ralaigh St., Nottingham

PkACTICAL wireless February, 1957

kn asaartiueni nf 60 pwtstors, no two dHkp. itS

; |i and - «»1 hi ; rnadi hj . u<-

I— i ui n i"

• eei in -. S i u iiIlib

HIGH WATTAGE OFFER ol S, 6 in I 16 rati

n I'torgjHncludii _ k li a n Ire- ro md. 20 fax fi-

''PEStBRAID" GREEN 1mm. SLEEVING.(2 shade*) i.i. r

I!3M jtlo., 9.6. i"FLEXIBLE SPINDLE COUPLERS.- -lin., 6(1. b. li.

MIDGET WAXED TUBTCA'RS (450 v.), "1. ,01

.3.6 d<*.

NEW SURPLUS MICAS. -WinG, I

Oiu ili -. each mit* tor S 8 U* DflI

NEW SURPLUS 500K POTENTIOMETERS. 1 3 :

1 5 8.

VALUE FOR MONEY STOCK LINES500 v. MIDGET WIRE-ENDED CERAMICS. I

i. .«.-i prlnus oil ili'' market for cwreni•..

i',•• i". U . 22, a?. 38, '.'. 17.

W ... 100, 150, •••.!'«>, 9T0, 330, HOO, 470, I.I ,

i.-'iic, -'.Him. y.i'i.iii i.i., sa. 7'« doz. s.ooo, iv.nodl4>.10fl. 9.8,<1"/.

RELIABLE SURPLUS VALVES. 12H«, 1-.Yrill.2'3: Kl'W:'.. I.i ::;.-i '>;.;; 6 nil... 20::i..i. :-. . HJ7, W<:, T\ ; 4 9 • •.,'7141. 6 9

LATEST " GEN " BOOKSPRACTICAL TRANSISTORS & TRANSISTORCIRCUITS. I'.ni I these nev ..n-uil- ;•

a ' own I n iwk iransLuirs. 3 8. Pout 3<J

TRANSISTORS & CRYSTAL DIODES,klmpie, but thorough Thenrj .-,- ebenit*. 5'-.

HOME-MADE AERIALS FOR TV AND F.M. 10IC-lgu* Hinj u.lunlih: iImi... 2 8. Poei Sd.

PRACTICAL F.M. I'.M. Cull ' h lol

>«« tor '.--..- i-i in, ti.. ii. 5 -. fust lii

RADIO CONTROL OF MODELS. \ mil • r- ,1-n-inhi

I h. ti.,.-ii,.,'i ii-, I bj ui Mem \ bjI

-. .

M.A. 5-, [. .-I 1,1

-iai> i in; ii i.i. i '. v l; < . US l.i-j- 84,

Pico - ii:-- ,. ... pat* ;ion urder> wulit t2.

REED & FORD 273-

?0S%$^REET -

THE LAST WORD IN

HI-FI AMPLIFIERSThe world renowned LEAK TL'IO

AMPLIFIER jives tD the music lover a

quality of reproduction unsurpassed by anyother equipment at any price. Leaflet onrequest. Leak TL/10 Amplifier, £17/17 -.

Leak Point One Pre-amplifier, £10/10-.COLLARO TAPE TRANSCRIPTOR.

High Fidelity at low cost, 3 speeds, 3,'. 1 :,

:md I5in.persec. Twiri^rack operation, £20.

THE NEW LIAS MONARCH 4-SPEEDAUTOCHANGER.vVitli High Fidelity crystal pick-up with dual

sapphire styli. £9/15 -.

We also stock Whiteley Electrical speaki

and cabinets, Bernards & Price publications.

tools for the radio engineer, and a widerange of valves, condensers, resistors,

potentiometers, etc. Send a 6d. stamp for

our new season's list. It will contain item;of interest to you.

RADIO HAM SHACK LTD.

155, Swan Arcade, Bradford, I

VALVE SUPPLYGLAZEBURY NR. MANCHESTERVALVES GUARANTEED

6SNT 7-J12AU7 7'6 ECUin B'6|5Z4 7/6BACi 5.6 12AX7 7.

,

6,EF'fifl 8'6'UUi 4'->!.' 9-KFiu 6-IM.:;: 9,'6|6GS 6'6HI ; 6/6 KF50 3/61'VHl 8 6 .">/:.

'. 8'-

fiC-1 6/6IBYM 6-KY7j! 8 6 ti.l'i 6 68F33 p/-lKT33C 8/6 35Z4 6 6.B1J HO

-

PUCASK ADIJ 6<J. POSTAGR

HI-FI EQUIPMENTWe can supply anyCabinet to yourown specification.

Bureau"

£16.16.0: ulw walnut bureau cabinet

reneered with the Quest selectedWalnut and beautlfullj polished In amedium shade. Designed to accommo-date any type of Automatic RecordChanger, Tape Dee)?, Amplifier, chassis,etc., ami DO t j£6 BTl

'

'.

•1

.

i; also supply and Qt this or ancabinet 'viih the latest Hi Pi amplifierstuners, tran.sciipi.ion units, recordchangers, speakers, etc,

led cata-o Hneit autoflmnoei - speakers,

on easy n.r. terms.

LEWIS RADIO COMPANY120 (PW3) Green Lanes Palmers GreenLondon N13 Tel .- BOWes Park 1155/6

DISCOUNT ON PR,CES ,

"Th» 2 Han"book

JiT9,

Cons*«ctor »

*H.P.<;> lyn°rnta''"S

" «h»a Tu.iinrJ'r-''-:.fr, »- '»•;»,-

."'^iuoii "' **Hcatorror

I ,..:;;. r^,.Am^ifi,,.s. ,'..,,:.;

*?«-^K»u'lVl-s'-i'K',1

n'

,lt-

•

ponal details ,oonsfa-u

*< OH. PAfl.- „ ,,

"own dctuiVlm k'.""•i"'

f-'>uff,^«;» i>K:H.deCsil ,

: • H,^:;-//:"-^v ! 'i,:iv,,„ u,

'.ii'-(1pri

,.(

. I !v.--| .'- , "".-.ely aiUS-

to?5?S?ILS «« BU,l". MarkhousD Hi Lm i- i

8, a

ENSON'SETTERARCSA INS

BELAYS: Hiei i« II-; 950*26(1 ,

- "ii 61 II, 80 : il.l-.o. i;i.

-' break, 18. Potfintioraetcrs : I

rai g • B00Q iaL. 18 : \\ 'woolBOOB i" 100k, 2/8, I'nlnsnlated WwoniKl,'"'•if !•• 30k. 18. RESISTORS: Hi-stab,or Vitrmms roamellnl, 1- pach, raamCERAMICONS. S'73fl k., 2.0 .'•.«, 6.S, 10. I'J,

l.i. -JV. :::;. :!••. iv. r-. innt,;<.. 6d. each,

THROAT MICS., in-» . 2 8. MIC. TRANS..mail, a-, boxes, «itb i« tnggii witches,7/6. BATTERIES, nev B0. IS, 3, I

' l«, (i -:

•U t. heavy duty . 2 6. ROD AERIALS, H i.icvi

.

new, 10 6. PIN STRAIQHTENERS. B7«, 2'8.

BC684A. (Bt'KSM), n>« oomlltion, wiih 10«il \ lnii'i.i !„45- Crail .- --. keys.10 8: small S/0. COMMAND RXS. i.r.-::.i,

in,.. Brand new, with t'alves. 66/- ; BC454.:;.ii n.r-.. 45- i|i.-i :: -i. Condensers, nr,-iiinilli.-il.

i a iin : ,-. 13, ';, oi f-.. l:!pin., J '6 • bntterflj 28 pfn., 1 8. SPEAKERS.in-., am., i,

i mad wr.-y metal am 27 6 (p.ri,

RXS. 112 114 (TB10fl71 with H/EF91•J. i:i.'.'l. ,i uang tnner, new, 37 6, l.

-76. (Circuit !-> MOTORS: SYNCH. S30-T.

• I i.i. in. final, new, 22,6 : Synch,100 v. :i,nnn r.p.ffl,, IOTA, 10-. SUPPRES-SORS, nnli i interference, ex-JL1C, 6/8 (post 2,-).

BRAND NEW R.F. 26. 27 6 (posUlge 2/fl)

RF'-M. KPj-i. 10 6. DYNAMOTORS [pnsl :: -..

1.9 v. I.. 9..I. v. 68 mA.,and 6.3 I.15A., 10 6.EDDYSTONE. 19 >. to I!'" v. 7 1 ri.A., cased,15.-. II r. tu ::'«i v. 200 m.\.. <-;i=ed, 16'-i.i.itrr. S'BJ. CLOCKWORK I 'gn lai ' on . 2impulses pel >.,•.. 8.'6. I.-..A. type, -null. 98.METAL RECTIFIERS: nnn v. :;.i ,,iA.. 6-.600 v. 500 niA., 10/6. 1,0011 . . 30 a \.. ," 8.

WAFER SWITCHES. I pole II was 2 Bank,3 6 :

-I I' :: W I P2 W, I P 6 W 5 B, 2 8. IFAMPLIFIER 178. L3.0 mo «. »hli ml van, 15 6(postage 2,'fl). CHOKES, L.P. 10H, 120 m

A

Screened, 7'6. 511, 200 m.v, 5 6. HEAD-PHONES, r„ l;. Kupwughtweighi HS308,17/6.

Bnqulries B.A.K, please : Terms:

(' « u. Postage extra. InnCaJlen and poll : W. A. BENSON 'PW>, 136.Rdthbone Road, Liverpool, 15. •/./

fialthrt : SUPEBADIO iW'ohapel) LTD..llff.r.Whiieohapel, Liverpool, 2. Jf(ir 1130.

u PERMATIP "

AND

" PERMABIT "

INSTRUMENTSFOR

GREATERSOLDERING

EFFICIENCY

The soldering bit which maintainsits face indefinitely without atten-tion. 25 models available for mainsor low voltage supply. Bit sizes 3/32to 3/8 inch. Full details in bookletS.P.I0 from sole manufacturers :

—

LIGHT SOLDERINGDEVELOPMENTS LTD.,106, GEORGE STREET, CROYDON,

SURREY. Tel. CROydoa 8589.

F M and H l-F I ComponentsDENCO F.M."" TUNER circuits Is. id.RADIO CONST'TR. F.M. „ Is. 0d-KULLARD AMPLIFIERS „ 3s. jid.

G.G.C. 912 PLUS AMPLIFIER „ <s. Orf.

G.E.C. F.M. PLUS TUNER „ 2s. 6d.Separate price lists available on request (o

J. T. FILMER M^^v. EKSETrfTTE '

Tel Box/eyheat/t 726/.


PULLINSERIES IOO

TEST METERAC/OC io.ooo.rvv

21 RANGESICOuA to IOOOV

FOLLY GUARANTEED

SEjNT POST FREE FOR ". 10.0 ANDNINE FURTHER MONTHLY PAYMENTS

eiP 11.4.6. CASH PRICE S12.7.6.

FRITH RADIOCRAIT LTD69-71 CHURCH GATE LEICESTERft IS HIGH ST NEWPORT PACNEU. Bucks

GRAM-PAK AMPLIFIERSComplete £3.19.6 . & p.

2/6

This midget 4-watt amplifier tits neatlviniu iinv record player leaving ample, roomtot speaker, 7" >: 2!" x II". Suitable withanj speaker and all modern crystal ;)-speed

BlGk-UpS. For 200-250 v. A.C. Perfect, dis-

tortionless, ouality guaranteed.ACCESSORIES :

bsr crystal turnover P.U.. £1.14.6.

r :; -i" elliptical speakers. 19s. 6d.

BSR 3-speed player unit with aboveP.U., £4.12.6d.

The complete outfit ready for

your cabinet, £9.10.0 post free.

>'d. .'lamp jar details of tins and Other models.

ELECTRO-ACOUSTIC LABS.TAIN : ROSS-SHIRE : SCOTLAND

HAP EQUIPMENTNoted for over 18 years for . . .

S.W. Receivers "fid Kits of Quality.

Improved desftrns with Denoo coils :

Oni-Valve Kit. Model "*X" Price, 25;-Tw*> „ ,, ., "K" .. '50*-

All kits complete with all components,accessories, and hill Instrucitofis.Before ordering call and inspect ademonstration receiver, or sendstamped, addressed envelope tordescriptive • atsioguC.

"H.A.C." SHORT-WAVE PRODUCTSlUept. Till, 11. oi.i Bond Street,

London, W.l.

PORTABLE

TEST

PANELfor workshop orlaboratory use Rang£S (AC & DC)T w o s e p a r a t e - 30 mAme°teV^

8on«

Cfor - '°v, - 25v

voltage and he . 500vother for currentmeasurement. |0- 10,000 ohmsSupplied in wood- < pi" cl"« fen cas; with metal ilze e a * - S **from and with test light and portableprods.

Price £6.10.0 Mid. post/pkg.)

Order new from:—E.M.I. Institutes, Dept T.P.32, London,W.4

(RADIO) LIMITED

3-34 lisle street. london.w.c.2telephone: gerrard 8204/9155

AMERICAN GEARED MOTORSBrand new 24 v. D.C. motors withbuilt in precision gear box with twinshaft outputs, 20 r.p.m. and 6 r.p.m.

Size 7in. x I J in. Shaft dia. 3/l6in.Will also operate on 12 v. giving

reduced outputs. Only 29/6 each.

CRYSTAL MICROPHONE INSERTSExtra sensitive, 4/6 each.MORSE BUZZERS. Brand new, 3 v.,

2/6 each.

DEAF AID EARPIECES. Brand new,30 ohm., 3/6. Deaf aid valve, CK.505, new,2/6. I meg. pots w/switch, I/-. Midgetswitch, I pole 3-way, I/-. Midget outputtransformers, 2/6 each.ROTARY CONVERTORS. Inpu: 24 v.

D.C. Output 230 v. A.C. 50 cycles, 100

watts, new, 92/6 each.

MODULATOR TYPE 67Bargain instrument containing a com-plete A.C. mains power pack, 230v. -input. Output 350 v. 120 mA.,and 6.3 v. 5 amps. Choke and con-denser smoolhed. uses 5Z4 rectifier.

Many other useful components, in-

cluding II valves, 5 SP6I, I VRII6.2 EB34, and 3 EA50. Brand n-w, 49/6each.

MODEL MAKERS MOTORS. P.M.type reversible. Operates from 6-24 v.

D.C. Size 2in. x I .< in . with i in. spindle.

Brand new, 8/6 each.

AR.88 WAVECHANGE SWITCHES.Brand new and boxed, 17/6 each.

YAXLEY METER SWITCHES. I pole,

12-way, 8 banks, 7/6 each.

SOUND POWERED EARPIECES. Idea

for intercommunication, no batteries

required, new, 3/6 each.

AMERICAN ROTARYGENERATORS

Input 12 v. D.C. Output 250 v. D.C.80 mA. Brand new. 22/6 each. Ditto"

6 v. Input, 22/6 each.

COPPER AERIAL WIRE. 300ft. reel, 3/6.

CHARGING TRANSFORMERS. Input200*250 v. Output 9 or 15 v. I amp., 9/9 ;

3.5, 9 or 17 v. 2 amp., 14/3 ; 3.5, 9 or 17

v., 4 amp., 16/6.

METAL RECTIFIERS. Full wave andbridged. 12 v. I amp., 6/3 ; 12 v. 2 amp.,

9/3 ; 12 v. 4 amp.. 13,9.

SLIDER RHEOSTATS. 14 ohm 4 amp..

7/6 ; I ohm 12 amp., 6/6.

GRAM MOTORS. Garrard 200/250

v. A.C. gram motors complete withturntable. Speed adjustable by gover-nor 0-45 r.p.m. Only 22/6 each.

HEADPHONE ADAPTORS. High to

low impedance matching, 1/3.

POWER UNIT 285. Input 230 v. A.C.Output 2.000 v. 5 mA., 350 v. 200 mA.,6.3 v. .7 amps. Fully smoothed, ideal for

'scope, etc., 59/6 each.

FIELD TELEPHONES. Type DonMk. 5. Buzzer calling. Ideal for inier-

house or office communication. Sup-plied complete with two 1.5 v. cells

ready to operate. Only 39/6 each.

Hours of Business : 9 a.m.—6 p.m.,

Thursday, I p.m. Open all day Saturday.

Please' print name and address clearly andinclude postage or carriage on all items.

Broadcast in Your Own HomeThe Now HighlySensitive Mleio-plionv incorpora tinga specially woundtransformer de-signed to match anyRadio or Radiogram,mains or battery.Hours of amusementat a party, good funfor all the family.Suitable for baby-

alarms and manyother purposes. Not

a toy but a guaranteed working Instru-ment. Full instructions enclosed.

Made to sell at 21/-. -f K I TOSTOL'll PRICB ***l FREE.Trade supplied

E. GLAPSHAW369, Alexandra Rd„ Miisw.ll Hill,

London, N.10.

BROOKS (RADIO)4 CHARLES STREET, MORECAMBE,

LANC8.

New - VALVES - Guaranteed1A71C5.Illf,

1N5IR51S51T43843V45U45Y35Z4fiAL56A M6OATHliBAfi

BBSSPC

ll;-i«K7•Mi i.Kii

9;6 HOT6SN7fiVfi

8X46X57B77C57C67S77Y412K7

5/6I35Z4 8:68:6: 80 8,-

9,'-'EABCB010-

EAF4210-EBC41

106BBFIIH 10 -

FOOiii 11

8.68.6

86 12K88-I12U786 2r,Z4

8'6l35L6

8/6

ECCB2 11 -IFY81ECC83 ] 1 - PYM2

8,:!BCH*211r-ff.K'UBll -

,. EF8B 1.0-

; ; BF88 11 6« I BL41 10 66'6iEM34 10 6S'6 iBYSl 126

EZ4B B/fl

tam 8'6PCC84

11:6PCF82 12/-PL01 11/6PI .82 9:6PL83 12/-PVW.I 9/6

10/-91-

l'YrEI 11/6UBC41 9/6ECH4211/-UF41 10 6DL4i 10,6UY41 8,6VU:» 8 /6

t and packing 6d. per valve extra

*•>•> !•:<

I uh'lhs %HAND ABUILT aRADIO AUNITS A

THE«>FIDELIAA

...Fidelia W MAJOR 10..• AMIFM models give reception of*AV.H.F. high quality transmissionsA

plus norma i wavebands. Maior .VAMIPM 12 valves, £44. De l.uxeVAAM'FM 11 valves. £33/12/-. P.M.AJ Toner, £14/3 -. Data sheets free. J** Electro Aeouitic Developments, 2,*»*

AAmborst Road, Telacombe Cliffs, Sussex.

A

..^aaaaaaaaaaaaa:.:.

SPARKS' DATA SHEETSConstructional plans of Guaranteed and

Tested Radio Designs

THE "SEAFARER"A New Low-consumption batteiy-operated2-Valver with unique features.

SKEWHAT MOM i:hsUNLIMITED THKILIA" ! A IVILKIXT

O.N 80-160 M. AMATE I It HA MI'S.Al.ltONAi: IK A I. HAM IS.

THK KIl.tTKAMI.KH HANDSll IP- I M-SIIOH K I It AMM .

MEDIUM- A I.OMi-H.WIXPlus Simplteily el Operation and Cow . ac-tion and Lew Upkeep Costs,full-size Data Sim • t Witt generous Instruc-tions and Com p. Lists. g>. Chassis and all

Components In Stock.

L. ORMOND SPARKSValley Road, Corfe Castle, Dorset

864_ PRACTICAL WIRELESS February, 1957

YOU CAN BUILD A QUALITYTAPE RECORDER

with

" ASPDEN"Tape Deck and Amplifier Kits

TAPE DECKS, 2 speed, twin (rack, easy to assemble kits.fully complete wi'.h finest motor and Ferroxcube heads.

Model 521 lor Sin. spools, kit, £7 10-Model 721 for 7in. spools, kit, £8 10,-

Either model assembled and tested, 27/6 extra.

AMPLIFIER kit. 2] watt, record replay with two recordingpositions, neon indicator, etc.. £518-. Power pack kit forabove. £2 18 6 (both without valves). Carr. and packing extra.

THIS TAPE DECK AND AMPLIFIER IS BEING USEDIN THE ANTARCTIC BY A MEMBER OF THE

EXPEDITION.From I he Equator to the Pole they are giving good service.

sir. .v.. ni Twickenham, write.'. :

"• The whole assembly has a smooth sweet run, which is

worthy of the most expensive deck. May I congratulate youon the line value your deck oilers."

Sc/ul ii Stamp for full particulars In :—10, Market St., Wesham,

KIRKHAM, LANCS.W. S. ASPDEN

ELECTRONICSTrain to meet the need for pioneers in this

expanding field.

Every day the demand for the expert in electronics grows.Radio, television, radar and the whole field of industrial

automation are rapidly expanding, and the trainedspecialist assures for himself a well-paid career in this

quickly developing profession. Here is your opportunityto enter For

I -year course

Full-time day course in the Principles and Practice ofRadio and Television. Mainly designed for the trainingof Radio and Television Servicing Engineers. Nextcourse, commencing May 22nd, is already fully booked.Enrolments for following course, commencingSeptember 1 Ith, novy being accepted.

The E.M.I. College of ElectronicsDept. 32, 10, Pembridge Square, London, W.2.

Telephone : BAYswater 5131/2

The College associated with a world-wide electronics industry,

including "His Master's Voice," Marconiphone, Columbia, etc.

*ft*M^

JUNIOR

UNIVERSAL

METER

Model 120AA small 2l-range instrument ideal for the enthusi-astic amateur. Sensitivity is 1,000 o.p.v. A.C.and D.C. Accuracy: 2",, D.C. ; 3% A.C.

RANGESVolts D.C. : o-. 25-10-50-250-500-1,000-2,500.Volts A.C. : 0-10-50-250-500-1,000-2,500.Milliamps D.C. : 0-1-10-50-500-5,000.Resistance : 0-2,000 ohms, 0-200,000 ohms.Can be extended to 20 megohms. Automatic-overload protection fitted to meter movement.

PRICE £9.15.0. PROMPT DELIVERYCREDIT TERMS : Nine monthly paymentsof £1.4.4.

TAYLOR ELECTRICAL INSTRUMENTSLTD.

Montrose Avenue, Slough, Bucks.Telephone : Slough 21 381. Cables: Taylins, Slough

SPECIAL OFFERof this famous chassis

hi im.oym: 8 valveRADIOGRAM CHASSIS R. G. I

I

TWO YEARS'GUARANTEE

YOURSfor the first of 9 equalmonthly payments of

only

5F4NO

I NTERESTCHARGES

Carriage & Packing 7/6.

22 gns.

A fine chassis for the connoisseur wantingonly the best at a price within his means.Undistorted push-pull output giving K

watts of qualify reproduction—andusing negative feedback. Separate bassand treble controls.

E. & G. MAIL ORDER SUPPLY CO.The Radio Centre

33 Tottenham Court Road, London, W.I.T-'

: MUSeum 6667

February, 1957 PRACTICAL WIRELESS

r

Practical Wireless

BLUEPRINT SERVICEPRACTICAL WIRELESS

No. ofBlueprint

CRYSTAL SETS2/- each

193? Crystal Receiver ... PW71*The Junior*'' Crystal

Set PW94*

2 6 eachDual - Wave " Crystal

Diode'" PW95*

STRAIGHT SETSBattery Operated

One-valve : 2;'6 eachThe "' Pyramid " One-

valver CHF Pen)The Modern One-

valver

1"wo-valve : 2.6 eachIhc Signet Two CD &LI I

3, 6 eachModern Two-valvcr ftwohand receiver)

Three-valve: 2, 6 each$ummit Three (HI Pen,

I) Pen)

The " Rapide " Straighl

3 (D. 2 LF (RC &Trans))

F. J. Camm's " Sprite"

Three (HF, Pen, D,Tet)

? 6 each

The All-dry ThreeFour-valve : 2 6 each

Fury lour Super CSG,SG, D.Pen)

Mains Operated

Two-valve : 2,6 each

Selectors A.C. Radio-gram Two fD. Pow I . .

.

Three-valve : 4, - each

A.C. Band- Pass 3

Four-valve : 26 eachA.C. Fury Four CSG, SG,D.Pen)

A.C. Hall-Mark (HF. Pen. D, Push Pull) ...

PW93*

PW96*

PW76*

PNV9S 11

PW37*

PWK2*

PW87*

PW97*

I'W'-K

PWI9*

PW99*

PW20*

PW45*

SUPERHETSBattery Sets : 2 6 eachI . J. Camm's 2-valve

Superhet .... ... PW52*

Mains Operated : 4'- each" Coronet " A.C.4 ... PWTOO*AC/DC " Coronet "

I our PW 101*

No. ojBlueprint

SHORT-WAVE SETSBatten Operated

One-valve : 2 6 eachSimple S.W. One-valver PW8S*Two-valve : 2 6 eachMidget Short-wave Two

CD. Pen) PW38A*Three-valve : 2,6 eachExperimenter's Short-wave Three CSG, D,Pow) P/W30A*

The Prelect 3 CD, 2 LF(RC and Trans)) ... PW63*

The Band-spread S.W.Three CHF, Pen. D,(Pen). Pen) PW68*

PORTABLES2 -

The " Mini-Four " All-

drj (4-valve superhet) *

MISCELLANEOUS2 6 eachS.W. Con verier-Ada pier

Cl valve) PW48A*I he P.W. '-speed Auto-gram C2 sheets). H,-*

I he P.W. MonophonicElectronic Organ (2 sheets), 8/-

TELEMSIONHie " Argus *'

(6in. C.R. tube), 3 '-*

The " Super-Visor " C3 sheets), X -*

The " Siriiplex"

... 3 6*

The P.T. Band III Converter I 6*

All the following blueprints, as well astin PRACTICAL WIRELESS numbersbelow 94 are pre-war Unions. :. r.; ;.

circulation for those umuteunto utilise old components which theymuii have in liwir spares box. flumajority of tlie components lor thesereceivers ore no longei ttoeked byretailers.

AMATEUR WIRELESS ANDWIRELESS MAGAZINE

STRAIGHT SETSBattery Operated

One-valve : 2 6

B.B.C. Special Onc-• valver AW387*

Mains Operated

Twb-valve : 2 6 eachConsoclectric Two CD,

Pen). AC AW403

SPECIAL NOTET-1IKSI.1

size.

ilupprlnts iv.r drawn 'uil

The issues ontainin*desorfptlons ol I hi a< Bet - are now outi>i print, but an osterisls denotesthat constructional details are avail-

able, tree with the blueprint.The Index lit: cede 1 1 r

Bluepi Int Number indli fttt 1

1

ical in which the description appears.Thus P.W. refers to PRACTICALWIRELESS. A.W. to AmMeutW.M. to

Send tprBferably) a postal order to

coyer the cost of the Blueprint(stamps over lid. unacceptable) to

PRACTICAL WIRELESS. BlueprintDept., Georcre Newnea, Ltd;, TowciHouse. Southampton Street. Strand.W.C.2.

fio oj

Bhtffpriitt

SHORT-WAVE SETS

Battery Operated

Out -valve : 2 6 each

S.W. Orte-yalvcr for

American

Two-valve : 2 6 each

Ultra-short Battery Two(St.. del Pen) ...

Four-valve : 3/6 each

A.w . Short Wave World?beater CI 1 1 Pen, I). KC.Trans)

Standard Four-valve*Short-waver CSG, D,II. P)

Mains Operated

Four-valye : 3 6

Standard Four-valve A.C.Short-waver (SG, l>.

RC, Trans) ...

\w4:->-

VVM4021

AW436*

WM3S3*

WM39T*

MISCELLANEOUSEnthusiast's Power Am-

plifier (10 Wans, (3/6) W\l 187

Listener's 5-waJti \.C.

Amplifier (3/6) ... WM 192'

l»e Luxe Co/icerl

Llectrogra/iC2'6)

\.c.

WM403*

(|ii:ii v («ii'o\This coupon is available until Feb. 6tl.

1957 and must accompany a!l Queries.

sent In accord with the notice on

our " Open to Discussion " [age

PRACTICAL WIRELESS, Feb. 1957.

____ I

I

PublisandGOKone year

PRACTICAL WIRELESS February, 1957

d. in sun

OSMOR

Simple press home fixing S -

ips lor circuits, wiring diagrams, coil-pack leaflets, componenc lists, chassis drawings, ter

and switch tuned frequency controlled FM Tuner, price lists.

P.W.7 418 Brighton Road, South Croydon,Surrey. Telephone Croydon 51.48/9.RADIO PRODUCTS. LTD.

30h

JP'JCJFCOALL-IN-ONERADIOMETER

* Circuit Test

* L.T. & H.T. Tests

* mA Test

* Valve Test

lie PtFCO All-m-Onc RADIOMETER for the

practical testing of al I types of radio and electrical

apparatus. You can carry out continuity andresistance tests, cheek HIT.. L.T., and G.B.voltages, also Household Appliances, Cai

Lighting Systems. Bell Circuits, etc- M'ay.bc

used on AX', or D.C. mains. ^L y

32,6Obtainable from your lota) dealer.

Write lor informative folder io :— complete

PIFCO LTD..WATL1NG ST., MANCHESTER 4

and 36-i7, UPPER THAMES ST., LONDON. E.C.4

CONSTRUCTORS build these at

DOWN-TO-EARTH PI

PERSONAL

PORTABLERADIOThis little set was designed to give you

a real persona! portable radio that you

can enjoy anywhere without disturbing

others. Use it on camping trips, in bed.

in your office, or just anywhere.

Send 2,'- for layout. V/irins diagram and

Components Price Hit.

lv SHORT-WAVE* Covers 10-100 metres

* World-wide reception

ic Low drain valve.

* Picture diagram and instruction

for beginrfers.

* Assembling time I. hr.

Thi< I valve S.W, receiver can be built from our list of componentsfor Mi'- "icluding valva.and I coil covering 20-40 metres. Provision

is msle -jcrease to 2 or 3 valves if required. All componentcan be purchased separately and are colour-coded so that r S«

beginnri can build this sec quite easily.

Post and Packing : Under 10/- add 9d. ; under 40'- add 1/6 ;

over POST FRE€.

Send 21- for specification, wiring diagram, layeut and price list to .'—

R.C.S. PRODUCTS (RADIO) LTDOLIVER ROAD, LONDON. E. 17 - Mail order only.

.

practical wireless 1957 february - the-eye.eu archive... · tv•valves•radio 6j5 6.17 6vfi 6k7...

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