Dc`v,!$.r.1(770slt77,7717;%,

,trcri.N1 and Amateur ireless, Febik,sry 22nd, 1936.

I

" GEORGEN EWNESAd/kat/at

Vol. 7, No. 179.reinuary 22nd, 19de.

vrah

issimaraomesate~tutaa04.011~1ftrioaaweare,atiialeistaitonatowliessifteargoozainvems0

THE HOME . MECHANIC. ENCYCLOPAEDIABy F. J. CAMM (Editor of " Practical Mechanics" etc.)

With627 From alf booksellers or 4/- post tree from-

Illustrations GEORGE NEWNES, LIMITED, 8-11, SOUTHAMPTON STREET, STRAND, LONDON, W.C.2.

41111111101 111.11/11~110111/10%1110.1114

-OnlyAn up-to-date and comprehensive guide to the Mechanical, Scientific and Technical Interests of the day-with expert articles onAircraft, Television, Models, Astronomy, Electricity, Photography, Chemistry, Woodwork, .Motor Cars, Wireless, Home Cinema, etc., etc. 3/6

2( net

A VT.

PRACIICAL AND AMATEUR WIRELESS

Illustration shows model 368. Models 363 and 369A are generally similar.

COSSORTHIS Cossor Receiver isavailable in three splendid

Models. All incorporate thelatest "Super-Ferrodyne" de-velopments. Their selectivityis exceptionally good. Due tothe Cossor H.F. Pentodes inH.F. stage and Detector stares,a high degree of distortionlessamplification is assured. Allmodels are fitted with full-sized

RADIOMoving Coil Loud Speakerscarefully matched to give aquality of reproduction whichis really magnificent-rich, clearand true-to-life. Other CossorReceivers are illustrated anddescribed in our catalogue -send coupon to -day.

To A. C. COSSOR LTD., Melody Dept., Highbury Grove, London, N3.Please send me, free of charge, a copy of your latest catalogue in fullcolour giving details of Cossor Receivers and Radiograms.

Name.-.Address

8.29 PRAC. .41

'6+

February 22nd, 1936

ThreeSplendid Models

Battery Model 363With Variable -mu H.F. Pentode, 11.F.Pentode Detector, Economy PentodeOutput. Super -selective iron -cored coils.Proision for Pick-up and ExtensionSpeaker. 8" MovirgCoil Speaker. Price £6.15s.

(without batteries)H.P. Terms : 13 - deposit and11 monthly payments of 13;-.

A.C. Model 368With Variable -mu H.F. Pentode, ELF.Pentode Detector, Triode Power output.Heavy duty Rectifier. Super -selectiveiron -cored coils. 8" energised MovingCoil Speaker. Provision for pick-up andextension speaker. For A. C. Mains200/250 volts adjust-able 4o/loo cycles.VaVSa

Price -

H.P. Terms : 14 6 deposit and12 monthly payments of 14 6.

D.C./A.C. Model 369AUniversal type. Variable-rnu H.F. Pen-tode, H.F. Pentode Detector, Super-power output, indirectly heated Rectifier.Super -selective iron -cored coils. 8'energised Moving Coil Speaker. ForD.C. zoo,25o volts (adjustable) andA.C. zcoizso volts(ad-justable) 50. -Ion cycles. X8.8s.

Price -H.P. Terms: 14,15 deposit and12 monthly payments of 5416.

Prices do not apply in I.F.S.

February 22nd, 1936 PRACTICAL AND AMATEUR WIRELESS 721

F. J. CAMM'S MONITOR TOP OF ITS CLASS!

Technical Staff:W. J. Delaney, H. J. Barton Chapple, Wh.Sch.,

B.Se., A.M.I.E.E., Frank Preston.

VOL. VII. No. 179. Februari 22nd, 1936,

ROUND the WORLD of WIRELESSRadio for the London Fire Brigade

EXPERIMENTS are being carried- outin radio transmission from cars

equipped with apparatus to permit com-munication with headquarters when thebrigades are dealing with fires. Thiswould supplement the telephone -systemnow existing between H.Q. and the variousstations.Improved Reception of U.S.A.

Broadcasts

THErecently resumed series of B.B.C.

broadcasts featuring Five Hours Beekfrom the U.S.A. have demonstrated theprogress made in the reception of trans-atlantic transmissions during the past fewmonths. At the B.B.C. Tatsfield stationthree separate receivers coupled to threedifferent aerials arc used to pick up thebroadcast, and by this means much fadinghas been eliminated.

Round -the -World Radio

PREPARATIONSare being completed

by the B.B.C. for a special celebrationof Empire Day in May. Not only shall webe taken round the Empire, but may begiven as an " extra " a relay of a broadcastfrom the new Radio Jerusalem station.

Proposed Move of Radio -Paris

WITHthe inclusion in the French State

Network of the new P.T.T. high -power Paris station; the Authorities areseriously thinking of transferring thetransmitter of Radio -Paris to a site incentral France and thus Provide a long -waverelay for the whole country.

Radio Television and Publicity Pro-grammes

IN view of the cost of the new televisionservice in France, a suggestion has been

made to the Ministry of Posts and Tele-graphs to defray a portion of the expensesby organising sponsored televised pro-grammes, at least- during the months inwhich experimental tests are to be made.Offers from publicity firms have alreadybeen made, by which the Government canbe guaranteed a fixed monthly revenue ofhalf a million francs !

Interesting StatisticsA CCORDING to figures published in thePl. United States of America, it iscomputed that : at present there are

56,221,784 radio receiving sets in theworld. Of these North America alone owns25,632,881, with Europe a close secondpossessing 22,897,981. Asia is representedby 2,553,396, of which Japan's share is2,190,040. South America, notwithstand-ing its great number of stations, can onlyshow 1,088,374, and Africa is last on thelist with 209,201.

Proposed Television Transmissionsin Sweden

FOLLQWING the example of Germany,England, and France, Sweden is

shortly to have its first television service.

ON OTHER PAGES

A Useful Valve -VoltmeterSimple Wireless ArithmeticFor The Experimeter .. .

0 Practical Television ..On Your WavelengthThe Monitor-Second Stage .

Modern Coil Connections .. .

Beginners Supplement0 Short -Wave Section ..

Readers' LettersImpressions on the WaxClub Notes

/ Queries and Enquiries

1

Fage723725727730731 I

735737738 0

741 0

744745747749

The Svenska Radioaktiebolaget has erectedtwo transmitters at StockholM and willshortly carry out tests.

The Salzburg Music FestivalTHIS annual festival will take place in

the period July 25th -August " 31st,and as in previous years the most importantconcerts and operatic performances Will bebroadcast through most European andAmerican transmitters. Four of the lead-ing conductors have already been engagedfor the Festival ; they are Toscanini,.Weingartner, Bruno Walter and Monteux.

Another Station for Paris.RADIO MIDI (Beziers), is to close donW

shortly and the plant transferred tothe French capital. It has been acquired

by a Paris daily, Paris Soir, which is thethird newspaper to own a private broad-casting station. The Radio Midi tram-mitter will be re -erected at illicit-Mahnaison. Whether it will be allowed towork on its wavelength of 209.9 metres(1,429 kc/s) is a moot point, as the channelis very close to that used by the EiffelTower, considering the respective sitesof the stations. The power employed is300 watts.

Radio Telegrams to YachtsON 163.3 metres, the channel used by

coast stations for calling ships, theG.P.O. transmits telegrams in telephonyat specified times, for the benefit of yachtowners whilst cruising. The service iscarried out by all post office coast stations-With the exception of those at Rugby andPortishead.

Nearly 7?,- Million British ListenersITH a total population in Great

Britain and Northern Ireland ofroughly forty-six million inhabitants, theBritish Isles can boast of nearly millionlicensed listeners. Taking an average offour persons to each receiver, we canassume that thirty million people hear theB.B.C. programmes daily.

At the Bottom of the BandFREQUENTLY below the Bournemouth

and Plymouth channel (203.5 metres),broadcasts may be occasionally picked outof the welter of small Belgian and Spanishstations working on wavelengths between201 and 203 metres. Of these the Belgianare the most frequently heard, and fromtheir calls may be identified as RadioWallonie (Binche) on 201.8 metres,Chtitelineau-Charleroi, Radio Anvers(Antwerp) on 201.1 metres, which havedifferent time schedules.

Viennese NightsWITH the New Year, the Austrian

stations have extended their dailytransmission until midnight, and offer,from roughly G.M.T. 22.25, dance musicrelayed from the most popular hotels,restaurants, and palais de dance in thecapital. In addition, on certain nights avisit is made to some of the resorts of thePrater, the " Earl's Court " of Vienna:

722 PRACTICAL AND AMATEUR WIRELESS February 22nd, 1936

ROUND the WOFestival Choral Society's Concert

THE Birmingham Festival ChoralSociety is one of the oldest musical

societies in Birmingham, having beenfounded ninety-one years ago, and it hasnearly 200 active members. For its annualconcert this year, to be broadcast onFebruary 20th from the Midland Regional,

L of WI............/..11400.4NNION 14111114

INTERESTING and TOPICAL

aen.....141M141IN.1=404M.....1111.....Fami.e.....1p.

give a programme in the evening ofFebruary 27th. This combination has hadcontracts for resident seasons at Chel-tenham and Malvern. It was begun by

PARAGRAPHS

THE NEW COSSOR ALL -MAINS SET.

Eddie Hapgood, the well-known back of the Arsenal football team, and Internationalcaptain, tunes in on his new Cossor receiver. This is an all -mains model (367) and

is priced at 9i guineas.

the City of Birmingham Orchestra hasbeen engaged, and the work to be given isDvorak's cantata " The Spectre's Bride."Harold Gray is the conductor. The soloistsare May Blyth (soprano), Parry Jones(tenor), and Watcyn Watcyns (bass)

" Blackbirds " in CarlisleTHOSE two popular coloured comedians,

Battie and Porter, who scored -such ahit in " Blackbirds," head the varietybill at Her Majesty's Theatre, Carlisle, onFebruary 26, when an excerpt from theshow will be broadcast to Northernlisteners.

" I Remember "IN the series of personal recollections

from Wales and the South West, thefifth talk will be given by E. J. Plaisted inthe Western Regional programme onFebruary 22nd. Mr. Plaisted has foughttwo Parliamentary Elections : the Isle ofThanet in 1929, and Salisbury in theGeneral Election last November. He workedin the coal -mines for twenty-five yearsand has been unemployed for five years.Mr. Plaisted possesses a voice with unusualvibrations, and it -was always a source ofamusement to his parents in his childhoodwhen the sound of his voice caused objectsto vibrate in sympathy. In his own words :" When I came near the bath in my homemy voice invariably made the bath giveforth a terrific rumble."Dance Music

BILLY GAMMON and his Star Players,a recent addition to broadcasting

dance bands in the Midland region, will

Billy Gammon and Ken Lancey. Threeof the members-Ken Lancey, Al Brownand Jim Donnelly-also form a vocaltrio.

Debate on Land SettlementTHII;question whether land settlement

offers an effective alternative to massunemployment has been brought intoprominence by the talks given by S. LBensusan after a rural survey of theMidland counties. Under the chairmanshipof Lord Phillimore; this question is to bediscussed at the microphone in the Midlandregional programme on February 21st. Mr.Bensusan leads off for, the affirmative, andis seconded by Robert Aldington, J.P.,who farms in the Vale of Evesham, and hascontested the Evesham Division in theLabour interest. For the negative, thefirst speaker is ._a well-known authority onagricultural economics, C. S. Orwin,,Director of the Research Institute of OxfordUniversity, author of a number of books,and a former President of the AgriculturalSection of the British Association. Hisseconder, F. S. Milligan, comes from theNorth. He has had experience of urbanunemployed at a social service centre onMerseyside.

Rugby Town BandTHIS popular band, which was founded

sixty years ago, will give a programmeof marches and overtures ; William Comptonwill conduct. One of the oldest Midlandbroadcasters, Charles Dean, of Birmingham,is to sing a group of baritone solos. Justbefore the band concert, which Will be given

IJLLSS (Contd.)on February 28th, one of the popularoriginal entertainments by Ronald Gourley,who is a Warwickshire man, will be broad-cast.

Cinema Organ RecitalTHIS relay of a cinema organ, which is

to be broadcast on February- 24th,is a new feature in Midland programmes.The Forum Theatre, Coventry, was openedabout sixteen months ago, and Lew Harris,then at the Commodore, Soutbsea, wasappointed organist. Mr. Harris, who isto give this recital, studied under ReginaldFoort at Bournemouth. In childhood hewas keenly interested in music, but onleaving school he qualified as a marineengineer and draughtsman, and it was not -until he was twenty-two that he became aprofessional musician as pianist -leader ofthe resident dance orchestra at the EmpressRooms, Portsmouth. In the days of theBritish Broadcasting Company, he broad-cast two pianoforte recitals from theBOUrnemouth station.

Music -hail MemoriesMIRIAM FERRIS, the popular music -

hall artist who has been well knownin radio for many years, will, on February22nd, produce the second of her amusingprogrammes called " Music -hall Memories."The idea of these programmes is based onMiriam's unique connection with Savoy Hilland early radio. They entail considerableresearch work. This versatile artist firsthas to find out what Savoy Hill music -hallstars will be available on a certain dateand then to discover what material theyused in those far-off days. After arrangingher programme4-with frequent disappoint-ments owing to cancellations-she, eventu-ally, writes up her commere material andpresents it to the Variety Director at St.'George's Hall. As a rule the whole pro-gramme is perfectly balanced and a gem ofproduction, for Miriam Ferris knows hermusic -hall from " gods " to stage door,'She will have the assistance of Alma Vane,now so well known for her " All GirlsTogether " parties, Tommy Handley, Jean'Allistone, Foster Richardson, John Rorke,'and Florence Oldham.

OWE IRS!PROBLEM No. 179.

Jackson built a 465 kc/s superhet, but wasdisappointed to find that the selectivity wasnot as good as he had expected. What stepsshould he take to improve the selectivityThree hooks will be awarded for the firstthree correct solutions opened. Address yourletters to the Editor, PRACTICAL AND APLATEURWIRELESS, Geo. Newnes, Ltd., 8-11, South-ampton Street, Strand, London, W.C.2.Envelopes must be marked Problem No. 179in the bottom left-hand corner, and must beposted to reach this office not, later than the firstpost Monday, February 24th, 1936.

a'.....

Solution to Problem No. 178.The whistle which troubled Jones was due to the

fact that the internal wiring of the L.F. transformerwas reversed. Reversal- of the external leads to theG. and G.B. terminals of this component shouldprovide a remedy.

The following three readers successfully solvedProblem No. 177, and books are accordingly beingforwarded to them : William Eastham, 172, Welling-ton Rd., Eccles, Manchester ; G. Wooldridge, TheLimes, South Rd., Stourbridge. Wores : J. A. Milton,45, Tyzack Rd., Sheffield 8.

February 22nd, 193"6PRACTICAL AND AMATEUR WIRELESS

723

Fig. I.-The com-plete instrumentbeing placed in theneat carrying case.

ANY constructorspurchase a simpletype of voltmeter

in order to make varioustest readings of bat-teries under- workingconditions and also in orderto ascertain whether or not -the valves in a receiver arereceiving the correct workingpotentials. But a voltmeter,or a measurer of voltages,can be made to perform avery much greater servicethan this, provided thatit is designed in a certain manner. In acheap meter, the visible indication of thevoltage applied across the ends is carriedout by the movement of a piece of ironsuspended in a magnetic field, and, owingto the fact that the resistance of a meter of

this type is very low, -a high current is

passed and thus in many circuits and tests afalse reading is obtained.

A better class of instrument employs amooing coil connected to the pointer, andthis particular type of instrument is woundto a very high resistance and thus operateswith a very small current. Consequently,it has a much greater field of utility and canbe used under more general conditions.There are, however, certain conditionsunder which even an instrument of this

/2 000 C24,44C:AMMAM4

hvpur

000c2imis

An EfficientValve - VoltmeterAn Easy -to -build Portable Type of Meter which has

Many Useful Applications to the Keen Experimenter

nature is of littleuse, and then it isessential to call toaid the valve volt-meter, in whichthemeasurement ofvoltage is carriedout by applying itto the grid circuitof a valve andmeasuring thechange in anodecurrent.

How it OperatesFor the benefit of

those -to whom thistype of instrumentis not familiar, itmay be brieflystated that a valvegives a certainemission o currentwhen the filament,grid, and anodevoltages are adjus-ted to definite

values. Any change in any one of thesevoltages will result in a change in thecurrent flowing in the anode circuit, and it

is found that by maintaining the filament

and anode -voltages constant and changing

the applied grid voltage, it is possible, by a

simple law, to ascertain the degree of change

in such voltage simply by the change in

the anode current.The usual difficulty with such an instru-

ment is to maintain a constant setting of

the anode current with a deterioratingH.T. or L.T. supply, and this is one of thedefects which has been overcome in theinstrument now being described. This has

been developed in the Graham FarishLaboratories and, in view of the novelty of

the complete arrangement, we thought that

/1)0/N7...114// Tell

Were,e Z/6 -NTFig. 2.-Theoretical circuit of the valve voltmeter.

o /a:74

z --

o L. z-7

readers would be interested in the design,andaccordingly we havemade arrangementsto publish the full wiring diagram andconstructional details.

A Portable InstrumentFrom the photographic illustrations it

will be seen that a neat carrying case is

provided, and this may be obtained, with

the necessary internal supporting structure,direct from Messrs. Graham Farish. The

valve which is employed is of the screen -

grid type, and it has been found that this(Continued overleap

/0,000 0A61,15'"oar WETER.4m,oAvAir...574//7-c/i

LT 0

`4. 0 1. I /0, 0007.

cwArs

MLL/444"-AIETER

-4.11kIllii

/ 20

.04AL ZiaHr. 0

SGVAL

G.

YE

aAl,roe

e 0AICO. AF F

S6

HI 8,4 r TER V

Fig. 3.-Wiring diagram showing all theconnections.

724PRACTICAL AND AMATEUR WIRELESS

February 22nd, 1936

.40.4.0/./VGFig. 4.-This sketch shows the front of the instrument and the connectionsto the input and loading terminals:

may be employed with a varying screenvoltage to compensate for the falling H.T.supply, as well as to set the meter to zerofor use when taking measurements. Novalve -holder is specified for this valve, andit is simply held on the bottom of thecabinet by means of a strip of brass or othermetal bent across the ceramic base of thevalve and screwed direct to the woodencabinet base. The leads from the valve aresoldered direct to the valve legs and theterminal cap, and to simplify constructionthese connections should be made beforethe valve is placed in position.The small L.T. battery is held in positionon the upper shelf, whilst the H.T. batterymust be retained by means of a clip con-

structed from a stripof brass or aluminium.This may be madeup to any individualidea, provided thatit holds the batteryfirmly in place,_ and,as this will not need

renewing very often,there is no necessityto introduce,any formof quick release.

The Dial LightIn order to facili-tate easy reading, the

original model is pro-vided with a smallbulb enclosed in ametal screen arrangedat such an angle thatthe light is thrownon to the face of themeter. This light isoperated from theL.T. battery and, inview of the verysmall capacity of thisbattery, it is essentialthat the additionalload imposed by the

lamp shall be extreme-ly low. A special bulbmust, therefore, beemployed, and on no

LIST OF PARTS FOR USEFULVALVE -VOLTMETEROne " Laurence " cabinet (Graham Farish).One SWG2 short-wave valve (Graham Farish')One 10,000-ohm combined potentiometerand 3 -point switch

(Dubilier).One milliammeter type M.C.1 (Bulgin).One terminal mount " Pop " with twoterminals (Graham Farish).One Formo clip mount (Formo).Two 2-mfd. foxedcondensers (Graham Farish).One 10,000 -ohm Ohmite resistance andholder (Graham Fetish).One low-consumption dial light (GrahamFarish).One 2 -volt dry cell, type Gel-Cel PRP3(Made).One H.T. battery,

Type X.325 (Exide).Wire, strip, brass, screws, etc.

account should a pocket lamp bulb beused for the purpose.Using the Voltmeter

The meter may be employed formeasuring the output voltages of amplify-ing stages, pick-up characteristics, valvecharacteristics, and numerous other pur-poses where it is essentialthat the additionalload of the measuring instrument must beextremely small. The source to be measuredis joined to the two clips, and the readingobtained on the meter is used as the basisfor computing the voltage applied acrossthe clips. In the instrument as describedthe maximum reading is 2 volts, and it is,therefore, necessary to ascertain roughlythe magnitude of the applied voltage inorder that suitable adjustments may bemade to accommodateany voltage which isin excess of that shown by the meter. Forthis purpose, the anode circuit is brokenand two terminals

are provided on the frontof the instrument.Normally, for the lowranges these terminals will be kept bridgedby means of a piece of wire, and in theoriginal model this is mounted on a smallstrip of paxolin provided 'with two lugs, sothat it may easily be slipped into theterminals and held' in position. Resistancesmay be similarly mounted for inclusion inthis part of the circuit in order, to modifythe range, and a number may be madeup on small strips and kept handy, witha suitable indication on the paxolin stripto indicate the difference in' the meterreading. A calibration chart would be veryuseful with this instrument in order toavoid working out each range, and thesemay be included in the form of a smallbooklet kept with the instrument.

To Track That Fault-to learn hOva wireless receiver works, obtain'

EVERYMAN'SWIRELESS BOOKby F. J. Carom, 5/-, or 5/6 by post fromGeorge Newnes, Ltd., 8-11, Southamp-ton Street, Strand, London, W.C.2." Tale Twisting "

Wr EST COUNTRY folk who had suchVV extraordinary experiences to telllisteners in theprogramme called " TaleTwisting " on January 29th last will come'again to the microphone on February 26th,to tell of the adventures they have had inthe interval. Honest John Plym is flyingback from the Pacific so as to be in timeto spin his latest yarn, and perhaps theitem of greatest West Country interestwill be the story of King Arthur and whathe did with the Round Table. " TaleTwisting " will be repeated on February27th in the Regional

programme.Theatre Variety

A'RELAY of a variety bill on February26th from Aston Hippodrome willbe preceded by reminiscences of the historyof this theatre, which has been a home ofvariety since 1908. The Aston Hippodromeis under the same ownership as the CoventryHippodrome, and Charles Shadwell, who,conducts the orchestra at the latter theatrefor broadcasting, is also in charge of themusic at the Aston theatre. The residentconductor is Ernest Moss. The theatrehas recently been renovated so as to provideup-to-date amenities, but without sacri-ficing the intimateatmosphere of the oldmusic -hall. In the variety bill to be broad-cast, Henschel Henlere is the chief turn.

0.4.1.U11M.t-O!U_p4111..0

PROGRAMME NOTES/610.0.041101.141111.11111.0.1M1.0.041.11041.110.111.111.14111-100.:" The Dreaming Man "THIS is the title of a play, by LeonardCrabtree, which will be broadcastfrom the Regional on March 5th, and fromthe National on March 6th. The spiritof the, play is very similar to the nowfamous radio comedy " Matinee." In thiscase, a rather Wellsian

character, the sametype of man as the hero of " The PurplePileus," rather disgruntled with his lifeboth domestically and otherwise, ex-periences in, an intermittent dream onessummer afternoon a more complete wishfulfilment of -worldly silecess than most ofus are able to conjure up in similar dreams.The audience goes with him in the impossibleand entertaining situations which hisdreaming mind conjures up, as he leaps towealth and power without having to under-go any of the intermediate processes whichare unavoidable in the world of real fact.The producer, Lance Sieveking, is going totreat the play in somewhat the same manneras he treated his radio version of " Emil andthe Detectives," where the, nightmare inthe train attracted so much attention amonglisteners. The fact -that the hero is dreamingwill be conveyed in a most convincing,manner.

" Nets in the Sea "THE second talk in the series called" Netsin the Sea," under the general editor-ship of Lieutenant W. B. Luard,will be givenon February 28th in the Western Regionalprogramme. This series of talks deals withWest Country fishing. In Cornwall thereare about two thousand 'men employed invarious forms of fishing, of which the pil-chard drift fisheries, the herring fishery,long -lining, and shell fishing (crab, lobster,and crayfish) -are undoubtedly among thebest known.

Police MusiciansTHIRTY-FOUR Yorkshire policestables, constitutingthe Military Landof the City of Sheffield Pollee, will broad-cast from the Leeds studios on February25th. The, band was originally formed as abrass band it passed out of existenceduring the War, and in 1926 was 'reorganisedas a military

combination. In 1933 MajorF. S. James, the Chief Constable; securedthe appointment of E. W.' Hesse, of -theSeaforth Highlanders, as bandmaster. Sincethen the band has progresSed and now ranksas one of the country's leading militarybands. Sir Henry Coward, Sheffield's" Grand Old Man " of music, bars alwaystaken a keen interest in the band, 'and hason several occasions acted as its " guestconductor.

February 22nd, 1936 PRACTICAL AND AMATEUR WIRELESS 725

Simple ® ArithmeticIt is Not Necessary to be a Mathematician to Make the Few Simple Calculations = Entailed by Wireless Con;

structional Work, and This Article Deals With the Most Important of the CalculOons Involved. By FRANK PRESTON

THERE are many constructors whodo not enjoy their hobby to thefull because they will not take the

small amount of trouble necessary toenable them to make the few simple calcula-tions required to determine, say, thecorrect value for a decoupling or biasresistance, the wavelength range which canbe covered *hen using a certain coil andvariable condenser, or the sizes of resist-ances required to form a fixed potentio-meter. It is often thought that thearithmetic involved is of a difficult nature,or that the equations are for mathematiciansonly, whereas the calculations are often agood deal simpler than those required todraw up a cricket analysis or in workingout the sums that are regularly done atschool by boys of twelve ; the only realdifference is that a little knowledge ofwireless practice is required in additionto that of arithmetic.

/0,000sz

/0,000 .52

boo y

2q 0001Z

Fig. 1.- A simple circuit which shows the re-lationship between current, voltage and resistance.

Ohm's LawOf all the calculations that must be

made time after time that in connectionwith resistance values is the commonest,as well as being the easiest. All calcula-tions involving resistance, current andvoltage, are based on Ohm's Law, whichstates that the current flowing in a circuitis always equal to the voltage causing theflow divided by the resistance which tendsto oppose it. Thus, if a voltage of 100were applied to the simple circuit shownin Fig. 1, the current passing through itwould be 100 divided by 20,000, which is1/200 of an amp. It is generally moreconvenient to work in terms of milliamps,which are one -thousandths of an amp., sothat the figure becomes 5 m.A. The simplecircuit shown is typical of all valve anodecircuits, and the fixed resistance might bea coupling resistance or it might representthe resistance of a transformer or othercomponent.

The formula for Ohm's Law which wehave just used is written, in mathematical

terms, thus : I = -, where I is the currentR

in amps., B is the voltage, and. R is theresistance in ohms. This simple and usefulformula can be re -written in at least twoother ways in order to, make it moreconvenient when the voltage or resistanceis required, the other two factors being

known. For example, we could write :E

R =-, or E =I x R.I

Bias Resistance ValueLet us see how it works out when we

want to find the value of the bias resistanceshown in Fig. 2. In this case it is knownthat the current passed by the resistance(the anode current of the valve) is 10 m.A.,and that the required voltage drop across -

the resistance-the bias voltage-is 20.The required resistance is obviously foundby dividing 20 by 10 and multiplying by1,000 (to change the milliamps into amps.),and the answer is 2,000 ohms.

A SPECIAL ARTICLE

I FOR THE BEGINNER.

FACTS AND FIGURES

SIMPLIFIED.

Now suppose that in the circuit shown inFig. 1, we know that 5 rnilliamps is re-quired to flow through the valve and thatthe resistance of the valve is, say, 5,000ohms, while the anode resistance has a

a value of 10,000 ohms ; we want to know'-' the voltage necessary to ensure the correct

current. All that we need to do is tomultiply the current in amps. by theresistance in ohms, and we get 5/1,000 x15,000, which is 75 volts.

Once we have seen these applications ofOhm's Law it is not difficult to apply it toall resistance, voltage and current calcula-tions, when two of the values are knownand the third is required.Resistance -Wattage Rating

There is another application of Ohm'sLaw which must be used when it is requiredto find the correct wattage rating for aresistance. Power, in watts, is actuallythe product of the voltage and the current,in amps., but we often know the currentpassing and the resistance value of, say,a coupling resistance, without knowing the

Fig. 3.-In order to determine the wattagerating of an anode resistance, it is necessaryto know its resistance rating, and the curren

passing through it.

exact voltage dropped across the resist-ance. But it is not difficult to see fromthe above equations that wattage can bedetermined from the formula : W=I2R.In words, this formula reads : the wattageis equal to the current in, amps. multipliedby itself and by the resistance in ohms.Thus, in Fig. 3 we have a resistance valueof 25,000 ohms and a current of 10 m.A.,

/0m A

B/A5.RE5/5TANCE

EFig. 2.-The method of determining the correctvalue of a bias resistance can be understood by

reference to this circuit.or 1/100 amp. We see, therefore, that thepower in watts which is dissipated (or

25,000lost) is 1/100 X 1/100 X 25,000, or

10,000which is obviously 2.5 watts. Havingmade this calculation we know that theresistance used in this circuit must be ratedat not less than 2.5 watts, and we shouldgenerally use a 3 -watt component to providea sufficient factor of safety ; a resistance oflower wattage rating would be liable toburn out in use, duo to the resistance beingoverloaded.

It might not be clear to some readershow the expression PR was found from theoriginal Ohm's Law equations to be the sameas ER-voltage multiplied by resistance-or, in other words, how P was found tobe the same as the voltage drop. But we

(Continued overleaf)

20 V

HT#

HT-

Fig. 4.-Several interesting points arise whencalculating the values of resistances required

for a fixed screening.grid potentiometer.

726 PRACTICAL AND AMATEUR WIRELESS February 22nd, 1936SIMPLE WIRELESS ARITHMETIC

(Continued from previous page)

saw that the voltage drop (E) is equal to Imultiplied by R, and if also we multiplythis by I we get the expression PR.

Finding the Wavelength Range-Now let us turn to another simple piece

of arithmetic which is not difficult to follow.Suppose it is required to find the highestwavelength that can be reached when acoil of 2,200 microhenries (a typical long -

wave toil) is used in parallel with a .0005-mfd. _tuning condenser. The wavelengthis found by using the equation : wavelength

1,8841/L x C where L is the inductanceof the coil in microhenries, and C is thecapacity of the condenser in microfarads,the wavelength being in metres. We havefirst of all to multiply together the induct-ance and capacity, and then to find thesquare root of the result, and finally tomultiply this by 1,884. Taking the firststep we get 2,200 x .0005, or

2,200 x 510,000

which works out to 22/20 ; when this ismultiplied by 1,884 we get as the result2,082.4, this being the wavelength inmetres.

If the required wavelength and. coilinductance were known, the correct capacitycould be found by reversing the calculation,and in the same manner the correct induct.ance could be determined from a knowledgeof the wavelength and capacity. Thesecalculations are slightly more involved,however, and since it is rarely necessaryto use them, we will not consider themfurther.

Screening -grid PotentiometersIn the opening paragraph mention was

made of finding the values of resistancerequired in forming a fixed potentiometer,

and this is a problem which often crops upin connection with an S.G. valve of whichthe screening grid is supplied from a poten-tiometer as shown in Fig. 4. If thescreening grid did not pass any current,the two resistances would have valuesproportional to the maximum supply vol-tage and the voltage required. In otherwords, if the H.T. supply delivered a voltageof 200 and 80 volts was required for thescreening grid, the upper resistance, markedR.1, could have a value of 60,000 ohmsand the lower one, marked R.2, a value of40,000 ohms. Alternatively, values of30,000 and 20,000 ohms could be used. Itwill be seen from this that the first step isto decide upon the approximate totalresistance ; with a mains set a maximumvalue of 50,000 ohms is generally suitable,and with a battery set, 100,000 ohms canbe used successfully.

In the above_ assumption of no currentwe simply made the lower resistance ofsuch a value -that its proportion to thetotal was the same as the proportionbetween the required voltage and the totalH.T. voltage -2 to 5, but let us see whatwould happen if the screening grid passed1 m/A. The voltage drop occasioned bythe upper resistance would be 1/1,000multiplied by, say, 30,000, or 30, andthus, the voltage actually applied to thescreening grid would be 80 less 30, or only50 volts. Consequently, either the resistancemarked R.1 must be reduced in value, orthat marked R.2 must be increased. Thisapparent peculiarity is due to the factthat the cathode screening -grid circuit is inparallel with the lower resistance, thusreducing its effective value. It is possibleto evolve an equation from which theexact values of resistance could be deter-mined, but it is generally better -for thenon -mathematical constructor to use trial -and -error calculations, and working onthe lines indicated above, until suitablevalues are found.

Series and Parallel ResistancesIn dealing with resistance calculations -

above we did not consider the effect ofconnecting resistances in series and inparallel. If resistances are placed in seriesthe,effective value is, as might be supposed,equal to the sum of the resistances. Thus,if resistances of 500, 1,000, and 20,000ohms were joined in series, the total valuewould be 21,500 ohms. When they arejoined in parallel the result is entirelydifferent, and the effective resistance ofthe combination is, mathematically speak-ing, equal to the reciprocal of the sum ofthe reciprocals. This expression is simpli-fied if written :

Total R = 1

1/R1 + 1/R2 - 1/R3etc. This means that if the three resis-tances mentioned above were connectedin parallel the effective value could befound by adding together : 1/500, 1/1,000,and 1/20,000, which equals 61/20,000, andreversing this to 20,000/61, which givesthe result as approximately 330 ohms.It will be noticed that this is less thinthe value of the smallest resistance.

Condensers in Series and ParallelWhen two or more condensers are used

together the effective capacity is foundby reversing the methods described inrespect of resistances. Thus, when con-densers are joined in parallel, the totalcapacity is equal to the sum of the capaci-ties of the individual components. Whencondensers are in series the resultingcapacity is equal to the reciprocal of thesum of the reciprocals. If, for example, a.0005-mfd. condenser is connected in series,with one of .0003-mfd., the resultantcapacity is 1

1/.0005 + 1/.0003.0015which is

1/858

or which.001is .0002-mfd. approximately.

Popular Radio TurnsDGAR WALLACE'S " On the Spot,"

" Mrs. Buggins Sees Stars," and the" Air -do -Wells" were the three most popu-lar radio turns of the week, ending December14th according Co the results of the secondof the competitions organised by the RadioCo-operative Advertising Committee.

A play has again come out on top ; inthe first competition Clemente Dane's " ABill of Divorcement " received by far themost votes. Radio comedians, who in thefirst week were accused of being dull andout of date, have made a triumphantcome -back. More than 25 per cent. of theentrants favoured Variety performances, andspecially commended the comedians.

Old-fashioned dance music was preferredto jazz ; Geraldo's orchestra in " DancingThrough " and Hamer's in " Old TimeDance Tunes " had three times as manyvotes as Ambrose, Henry Hall, and JackPayne. This apathy for -modern dancemusic may be due to the fact that thebest time for broadcasters was clearlyestablished as between 8 p.m. and 9 p.m.,when all the five most popular turns wereon the air. Light classical music was muchappreciated, particularly that in " The Tableunder the Tree."

Lord Snowden's account of Keir Hardiewas the most popular talk. Otherwisethere was little enthusiasm for talks or thenews, though a number of women chose theannouncement of the safety of the threegirl hikers as the happiest turn. Severallisteners regarded broadcast services asthe most important item of the week.

I HERE and THERE1111.14110(....=1.1.m...1400...1.01.. ......H.li

B.B.C. Symphony Orchestra toVisit Leicester

THE B.B.C. Symphony Orchestra, underthe direction of Adrian Boult, will

appear twice in the provinces in the springbefore starting on its Continental tour toParis, Zurich, Vienna, and Budapest.

Its first visit will be to Leicester onMarch 11th, when Dr. Boult will conductan attractive programme. Opening withWeber's Overture to " Euryanthe," a pieceof romantic music that time has not robbedof its freshness and appeal, the orchestrawill then play Beethoven's Sixth Sym-phony (the Pastoral "), which will be themain item in the programme. In thesecond part, modern music will be repre-sented by four numbers from GustavHoist's The Planets," and Ravers" Pavane " and " Bolero," all of whichworks will afford the full B.B.C. SymphonyOrchestra every opportunity to exhibit itsfine qualities. The four Planets chosen areMars, Mercury, Saturn, and Jupiter, repre-senting the contrasting moods of ferocity,sprightliness, serenity, and joviality. Mid-

land music -loverswill welcome espec-ially this opportunityof admiring onceagain the B.B.C.Symphony Orches-tra's rendering of" Bolero," which isbeing played on thisoccasion in responseto a general demand.This brilliant orches-tral" tour de force"brings a well-chosenprogramme to a fit-ting close.

Here is Stanelli,ofHorn-chestra fame, listening to

his Cossor radiogram.

February 22nd, 1936 PRACTICAL AND AMATEUR WIRELESS 727

rEzit 8VAICE4

ctirtire,6 '''

00 ato,1 9

V -w

HE previous article in this seriesdealt with the theoretical considera-tions and constructional work neces-

sary in the manufacture of a simple type ofvalve -voltmeter, and it is now proposed toshow the method by which this instrumentmay be calibrated, and a scale produced toenable voltages of any frequency to beread on the 0-1 milliammeter incorporatedin the multi -range meter.

It will be observed that we have provideda space on the front panel of the instrumentor a calibration scale to be gummed on,

H. F

aid mosT'® 01

rnfd.

Fig. 1.-Method of measuring the voltagedeveloped across a tuned circuit.

and also, than a circular white paper scaleis to be gummed to the panel under theknob of the 1-megohm multiplier poten-tiometer. Alternatively, if the surface ofthe panel is matt -finished aluminium, it isquite possible to omit these paper scalesand draw the calibration points on themetal itself in Indian ink, afterwardscovering the markings with a coat ofcolourless cellulose lacquer.

Before wp commence calibration it willbe neeessary,,to procure a 6 -volt accumu-lator, and a 250 -ohm variable potentiometer.If it is inconvenient to get a 6 -volt accu-mulator, four large -capacity- dry cellsmay be used to supply the calibration

-FOR THE

EXPERIMENTERSERVICING SETS FOR PROFIT

7-A Method of Calibration, and Some of the Uses of the Valve -Voltmeter

Described Last Week are Dealt With in this Seventh Article of tho Series

voltage, as their voltage will remainreasonably constant with a current drainof 24 milliamperes, over the short periodwhich we shall use to make measurements.The accumulator or dry cella, and the250 -ohm potentiometer, should be con-nected up as shown in Fig. 3, but theactual connection to one terminal of thevoltage supply should only be made whencalibration is in progress in order to limitthe current drain imposed and maintainthe voltage as stable as possible.

Connections and AdjustmentsNow connect the H.T., L.T., and G.B.

batteries to the valve -voltmeter, makingsure that the switch is " off " before doingso, and connect the milliamp. terminalsof the universal meter to the " meter "

terminals of the valve -volt -

PET.

VALVE -0 VOLTMETER,

P

meter. The positive terminalof the universal meter shouldbe connected to the " meter "terminal of the valve -volt-meter which is connected in-ternally to the H.T. positiveplug, and the switch shouldbe set at 1 m.A. The multi-plier potentiometer is thenrotated in a fully anti-clockwise direction, i.e., toratio 1, and the 20,000 -ohmvariable anode resistancemounted on the base -boardset until the whole of theresistance clement is incircuit. Now switch on thevalve -voltmeter, and it willbe noticed that the pointer ofthe universal meter gives alittle " kick" and then returnsto a very low reading on the

VALVE

VOLTMETER

6v /ACCUMULATOR

G

INPUT OFV/VOLTMETER

Fig. 3.-Theoretical circuit of the calibrationapparatus.

scale. It might he thought that the 25 -ohmzero -adjusting potentiometer on the frontpanel should now be set so that zem wasactually indicated on the milliammeter, butthis is not the case, owing to difficulty inascertaining the exact setting at whichthe milliammeter reads zero. A much moresatisfactory method, and the one adoptedin this case, is to adjust the 25 -ohm poten-tiometer until the pointer of the milli -ammeter reads .02 mill lamp., or, in thecase of the Ferranti instrument used bythe writer, to the first small division on thescale. This point will now become thezero point for the voltage scale of thevalve -voltmeter, and the meter shouldalways be checked before making measure-ments to ensure that, under the foregoingconditions, a true zero is indicated.

The valve -voltmeter should now beswitched off, the multi -range meter dis-connected, and its 10 -volt D.C. range

(Continued over:eon

L. --Adjusting the zero reading.

MULTI -RANGE

METER

728 PRACTICAL AND AMATEUR WIRELESS

FOR THE EXPERIMENTER(Continued from previous page)

connected across the leads from our-calibrating voltage supply marked : G andB, and the 260 -ohm potentiometer varieduntil exactly 5 volts (or half -scale deflection)is registered. Then re -connect the universalmeter to the " meter " terminals of thevalve -voltmeter and the calibration leadsG and E to their appropriate input ter.initials as shown in Fig. 2. Switch, on thevalve -voltmeter.- and it will be found thatthe pointer of the universal meter willnow give a reading somewhat higher thanthe zero reading which We previously se-lected. By rotating the 20,000 -ohm resist-ance On the baseboard until the universalMeter reads exactly 1 milliamp., the scalewill bc set to read 5 voltS between .02 milli -amps. and 1 anilliamp. It may be .advisable:now to disconnect the calibration voltageby removing one of - the leads from theaccumulator, or dry batteries, and to notethat the pointer. of the milliammeter fallsimmediately to our previously selected zeroposition. If it: does not do so, a alightreadjustment of the zero -adjusting poten-tiometer will be necessary. The internal20,000 -ohm resistance will not need re-setting unless the characteristics of the

F. TRANSFORMER

2 ND

DETECTOR

Fig. 4.-The meter is connected to the points XX,across the secondary of the I.F. transformer

nearest the second detector.

P2 valve change considerably, and with thelimited periods of use which we are likelyto give the instrument, the life of the valveshould, be almost indefinite. It has alsobeen found that the replacement of thevalve has very little effect on the calibrationof the instrument, provided the instrumentis reset for, zero and _maximum readingswhenever- it is necessary to make thisreplacement.Checking the Deflections

All that remains now is to make a noteof the deflections given by the milliammeterfor various voltages between 0 and 5 voltsapplied to the input terminals, and toobtain these teadings the required voltageis selected by adjustment of the 250 -ohmpotentiometer with the 10 -volt range of theuniversal meter connected across leads Gand E and then noting the deflection givenby the milliammeter when this voltageis applied to the valve -voltmeter. Somereaders may care to plot a graph of thesereadings, and so be able to measure inter-mediate values directly, but I have foundthat the valve -voltmeter calibration isnearly linear, and a chart prepared in thename way as the capacity chart describedand illustrated in Part 4 of this series isquite suitable.

Having prepared the graph or chart itonly remains to calibrate the multiplierpotentiometer. This is quite a simple matter,and should present no difficulty. Firstapply 5 volts to the input terminals of thevalve -voltmeter so that a full-scale deflec-tion is given by the milliammeter, thenrotate the multiplier knob in a clockwisedirection until the milliammeter indicates2.5 volts in accordance with our'calibrationchart. Mark the position of the multiplierpointer and call it X2, then if the pointer isleft in this position all the readings obtainedon the valve -voltmeter will be multipliedby two, and we have extended our range to

.-10 volts maximum. Again rotate the multi-plier knob until 0.83 volts is indicated andmark this point X6. This extends thejuvilemtlpeosnoem.1)..94moo.-oonwoastkoems421

FOR THE NEW READER.

Previous articles in this serieshave -dealt with a D.C. Multi -Range Meter; Adapting it for

I reading A.G. Voltages; and theI Construction of a Simple Valve-_

voltmeter.L.0..110.114112,004:111.1..00.04004MI.=.141111041.<1.0111114141114).

I

I

I

I

range to 30 volts maximum, and all readingsobtained with the multiplier knob in thiposition must be multiplied by six. Finally,carefully rotate the multiplier until 0.5volts are indicated, and mark this point X10.We shall now have extended the scale to50 volts maximum, and all readings mustbe multiplied by ten.

Usinag, the Valve -voltmeterThe calibration is now complete, and we

can start to make use of the valve -volt-meter. It will not be out of place here todescribe a few of the more obvious of itsuses, although later articles in this serieswill describe it in use in conjunction withother apparatus. It will find its majorapplication in the measurement of voltagesin circuits where the current flowing istoo small to actuate any other type of volt-meter ; for instance, it will measure thevoltage developed by a steady signalacross the load resistance of a diode detector-a very useful guide to A.V.C. efficiency.Also it will measure accurately the voltagedeveloped by a signal of any frequency

MARVELSof

MODERNSCIENCE

By F. J. CammAll about television, helicopters,streamlining, harnessing theinvisible ray, etc., etc., with thelatest pictures of all the newestand most thrilling inventions.

From all Booksellers

Only 3'6 netGEORGE NEWNES, LIMITED

---__-------:% A 4 :

February 22nd, 1936

across the secondary circuit of an outputtransformer.

To measure the radio -frequency voltagesacross tuned circuits it will be necessaryto prevent the H.T. voltages from reachingthe grid of the- P2 valve, and mica con-densers of .01 mfd. capacity should alwaysbe, connected in series with the- input ter-minals before making measurements inany circuit where D.C. currents are alsoflowing. When measuring A.C. voltagesexisting across, say, the anode resistanceof an L.F. amplifier, the capacity of thecondensers should be increased to as largea value as possible, though care shouldbe taken to see that the insulation of thecondensers chosen is high. Fig. 1 willshow the connections to the valve -volt-meter when measuring the H.F. voltagedeveloped across a tuned circuit, in thiscase the tuned -grid coil of an H.F. amplifier,and it will be noticed that the Gr"terminal is connected to the high potentialend of circuit and the " E " terminal toearth. This procedure should always befollowed wherever, possible because it isadvisable to keep the metal case of thevalve -voltmeter at earth potential toeliminate stray pick-up effects. The valve -

voltmeter connected as shown in Fig. 1

ANODE FEED'

RESISTANCE

LARGE CAPACITY FIXg...%CONDENSER

Fig. 5. ---Measuring the A.C. volts developedacross an anode feed resistance.

will actually measure the H.F. voltagepresented to the grid of. the detector valveif the set is tuned to a powerful local station,and by experimenting with the voltagesapplied to the H.F. valve and, incidentally,by making any modifications to the aerialcoupling coils, etc., it is possible to - seethe result Of such expkiments as a gain orloss in voltage. - The I.E. and- frequency -changer circuit of a superheterodyne couldalso be experimented with using the meterconnected across the secondary of theI.F. transformer nearest to the second'detector (Fig. 4), and, if the magnificationis not too great, -it is possible to measurethe amplification of a valve, and itscoupling components, by first adjusting'the voltage across its grid circuit by anH.F. volume control to 0.5 volts, thentransferring the valve -voltmeter to thecoil in the anode circuit of the same valveand again measuring the voltage. If thereading given is, say, 45 volts, then thestage gain is 4.57 or 90.

Many other -uses will no doubt be apparentto the experimenter, but a fuller descriptionof the uses of the instrument will be givenwhen we have constructed an L.F. andH.F. oscillator to provide the energy,required to mare our measurements. TheL.F. oscillator will be the subject of thenext article.

PRACTICAL AND AMATEUR WIRELESS 729February 22nd, l936

3 2Would members of the public takipg ad-

vantage of our FREE TECHNICALADVICE SERVICE please bear in mindthat we are able to make a much moreaccurate diagnosis of their troubles if acircuit diagram, no matter how rough, issent with the enquiry.

THE 362 RADIO VALVE CO. LTD.STONEHAM WORKS, E.5.

CG>sotd 6607.

The Story of a Gracious King

" THE LIFE OFKING GEORGE VCommemorating a Great and Glorious Reign

Profusely illustrated in

Gravure including HistoricFuneral Photographs 6D

On Sale

at all Newsagents andBookstalls

Pu5lis.',-oi by George N,wnes, Ltd., 8-1I, Sonthantpton Street, Strand, W.C.2.6111111M234,

es

METAL

USEhouse

RECTIFIERSAND "INSURE" YOUR POWER SUPPLYNo fragile filaments to

burn or wear out. Noth-ing to break. No replace-

ments. Constant output.

You can rely on Westing -99 l house Metal Rectifiers

' The All Metal TI -ay, 5936 "contains full details of, and rail"circuits for use with, these MUMreliable rectifiers. A 3d.stamp to Dept. P.R.A. Willbring you a copy.Westinghouse Brake & orm

Signal Co., Ltd.,82; York Road, King's Cross, /1111

London, PIA.

TWO COMPLETE WORKSon Practical Electrical Engineering !

Here are two practical works for everyone engaged orinterested in the electrical industry. Each is entirelycomprehensive, written by experts famous in their re-spective spheres, and fully illustrated by drawings, photo-graphs, tables and diagrams-post coupon now for freedescriptive leaflets.

THE ELECTRICAL EDUCATOREdited by Sir Ambrose Fleming, M.A., D.Sc., F.R.S. Complete in 3 handsomelybound volumes containing over I.,000 text illustrations and over roo plates and foldedinsets. Contributions by eminent authorities are included, amongst whom may be men-tioned Sir W. Bragg, Sir R. Hadfield, and R. Farraday Proctor. The work deals completelywith the application of electricity to all fields of industry and special sections deal with theproblems of wireless engineers. As textbook or reference work it is absolutely indispensable.

ELECTRICAL WIRING & CONTRACTINGEdited by H. Marryat, M.I.E.E., M.LMech.E The theory and practice of electricalwiring and contracting is here completely treated in 7 convenient pocket -sized volumes.Experts in every branch place their specialized knowledge at your disposal, the resultingwork being not only practical but eminently authoritative. This is recognized as thestandard work for this field-one which offers complete instruction in the simplest andclearest manner imaginable.

THE NEW ERA PUBLISHING CO., LTD.12-14; NEWTON ST., HOLBORN, LONDON, V/ C.2

Post the Coupon TO-DAY--

a

tl

I .A NV. .

MMMMM EIM1916.111111011=1Oliaatittillr

To: THE NEW ERAPUBLISHING Co., Ltd.,12-14, Newton Street,Holborn, London, W.C.2

Please send In? ty return, freeand postpaid, your descriptiveleaflets on

THE ELECTRICALEDUCATOR,

andELECTRICAL WIRINGAND CONTRACTING

Whilst this request is free ofall obligation, please send meat the saint time full particularsof how I may secure theseworks on out-of-incom2 terms.

Strike out the book not required.

Name

P.diirczs

.a-

730 PRACTICAL TELEVISION

THE TWO TELEVISION STANDARDS-IBy " CRITIC '!

THE publication of the TelevisionCommittee's report dealing withthe chosen site for the first high-

definition television station in London,namely, the Alexandra Palace, together withthe information that the two companieswho are to supply the transmitting equip-ment (that is Baird Television, Ltd., andMarconi-E.M.I Television, Ltd.) are towork on quite different standards, hasprovoked considerable discussion. Thishas centred very primarily round the wholequestion of these two different standards.

2 ------

ment value of television, it is a commonpractice (although in my opinion a wrongcomparison) to compare the results withmodern talking films. In any cinema thedetail which is observed on the screendepends very primarily upon the pictureillumination provided by the arc lampand optical system, the photographic grainof the film itself and, lastly, upon themechanical precision with which the record-ing and reproducing processes work. TheSociety of Motion Picture Engineers pub-lished in March, 1934, the standard of

34 ----567

ti

8 IIMININD

9

Two Scanning SchemesIn the case of the former the system

adopted is a picture definition of 240 linesscanned in sequence at 25 picture traversalsper second and 25 complete frames persecond. With the latter, however, it isproposed to use as a standard 405 -linedefinition, 25 pictures per second interlacedto give 50 frames per second each of2024 lines. It is further stated that theCommittee have satisfied themselves thattelevision sets can be constructed capableof receiving both sets of transmissions(they will be radiated alternately) withoutunduly complicated or expensive adjust-ment. The tenders submitted by thecompanies have been accepted, and eachfirm has furnished the technical informationregarding the characteristics of the tele-vision signals radiated, so as to facilitatethe design of receiving equipment capableof picking up these signals.

At first sight these rather bald factsappear quite satisfactory, but actuallythey have been instrumental in promotingmany discussions, primarily in connectionwith the reason for interlacing " and howsuch scanning operates, and also whetherthe higher line standard is a reasonableproposition at the moment.

The object of the scanning process is- to dissect the scene or, object to be televised

into a series of lines sufficiently great innumber that quite small detail will berecognisable in the received picture, assum-ing perfection in the scanners, amplifiers,radio transmitter, radio receivers, and finalpicture reproducers. Any form of ampli-tude, or phase distortion in a Single linkof this chain of events will naturally marthe picture, but this is a factor which lendsitself to remedy, once the technique whichis involved is mastered.

Cinema ComparisonIn assessing the pictorial or entertain

Fig. 1.-A nine line scangreatly exaggerated, showinghow an orthodox sequential

scan is built up.

performance laid down by the ProjectionPractice Committee in the following terms :" If the ,projector is in first-class conditionand the intermittent movement and picturegate are properly adjusted, the picturejump should 'not exceed one-third of oneper cent, of the picture height."

This standard can be interpreted literallyin one or two ways. First of all, if the pro-

jector is in first-class condition, then work-ing to the standard limits, an otherwiseperfect picture is blurred to the extent ofone-third of one, per cent. or, in otherwords, any object which is so small thatit occupies only one three hundredth ofthe total picture height is blurred intonon -recognition. This precision is reallyan extremely good one, for taking, say, ascreen loft. high the non -recognisable

6Fig. 3.-The second or inter-mediate section of an inter- 7calated scan, where, on thecompletion of the final line a.,trace, both time bases trip 0

together.

9

February 22nd, 1936

object only represents three -fifths of aninch. Furthermore, when seated in acinema the audience is occupied in dis-cerning (and no doubt enjoying) thecentral figure or figures, together with theaction portrayed and the story beingunfolded, and has little thought for suchminute details as have been quoted.

Conversion to TelevisionThe human element must, and will, play

an important part in assessing the valueof a television picture in terms of linedefinition, so if we convert the cinemastandard to one of television, the limitis a loss of detail identity to the extentof one-third of one per cent., that is asingle scanning line in a complete pictureof 300 -line definition (this being the re-ciprocal of one-third of one per cent.).When the Television Committee producedits report, their recommended minimumstandard was given as 240 lines, which isonly 20 per cent. below the cinema limitjust explained.

Communication ChannelQuite apart from this, however, there is

the all-important point of whether thewavelength which is to be used for theradiation of the television signals, that is6.6 metres, is capable of accommodatinga line definition standard which is in excessof 240 lines. While it is impossible to arriveat a hard and fast form of calculationto obtain the frequency spread involvedin a complete television signal, it is asimple matter to see how the limitingfactors impose conditions which must notbe exceeded if satisfactory results are toaccrue.

Considering for a moment a picture builtup of alternate pure white and blackstrips, the scanning spot or exploringaperture will just fail to reproduce theeffect or become blind in the televisionsense when the spot size is equal to thewidth of two strips (one black and onewhite). The actual response will be the

Fig. 2.-Showing how thefirst section of an intercal-ated scan is built up in asimilar manner to the ortho.dox, or sequential, system.

average of these two extremes and a greycolour will be seen. When this conditionoccurs, it can be said that the extremefrequency limit has been reached. Taking asan example, therefore, a picture repetitionfrequency of 25 per second, picture ratioof four horizontal to three vertical and2401ine horizontal dissection, the limitingfrequency becomes 240 x (240 x 4/s) x 25which equals 1,920,000 or 1.92 megacycles.

5

Febroaty 22 d 1936 PRACTICAL AND AMATEUR WIRELESS 731

n tiourWavelengA Danger Signal

'EE that music from one of the popularFrench stations is being heard by the

anialmen in boxes on the Great WesternBail way between Paddington and HighWycombe-and this in spite of the factthat there are no receivers in the signalboxes. The trouble is said by experts to bedue to leakage from rediffusion wiresattached to telephone poles near Wembley.It seems rather hard on the railway officialsthat even when at work they are unable toescape from the " plugging " of somebody'ssoap or some other item which is beingmentioned in the English programmes fromthis particular station. Imagine the plightof a signalman, anxiously awaiting an " allclear " signal, but who receives instead aninjunction from the announcer tq takeGreen Pills, or who is confronted by the" strains " of a crooner. It must be enoughto make him set all the signals at dangeror t o send the Cheltenham Flyer to Margate !

Assistance from a Club

AT the acoustics were so bad thata certain church in the Midlands

a was found that only the front fewest,: were within range of the pulpit,

nit t he padre, being one of the moderneisithead ministers, decided that a goodeubliisaddreas equipment would provee xi tamely valuable. Ho also conceived the

fitting a standard receiver in thet hat on occasions when there was

no sav its in the church he could pick upsalayei I aav ices and similar items andbrosdaat t hem in the church. To obtainthe ni"ney to purchase the necessaryupland I is he hit on the original idea (?)01 balding a bazaar.

The mothers met, and over the parochialsup of i it they decided that it would be an" ungodly act to place such a moderninvent Sin ire the precincts of the church"and refused to help with the bazaar.Luckily there was a broad-minded reader ofPRACTICAL AND AMATECTR WIRELESS ill the

A crooner in the signal box.

ict and he came to the aid of thecadre by collecting discarded apparatus

the local club members, and a reallyexcellent piece of apparatus is now installed.

" Calling All Cars "I WAS trying out a new short -waver the1 other night and whilst on the lowerranges I picked up a transmission fromPolice Headquarters in an American city,giving directions to a patrol car regardinga certain suspicious car in a shoppngcentre. It was most thrilling, but I failed

By Jhermion

to hear the scream of the syren or themagic words of the movies " Calling allcars."Quoth a Reader

MY remarks sometimes seem to upsetsome people, although others must

take my writings to bed with them. Hereis a short and to -the -point epistle from Mr.A. Jones, of Leicester : " I read yourremarks about not being able to tell thedifference between a highbrow violinist anda street musician, and I think you have avery poor taste for music. You owe asincere apology to the street musician.P.S.-But I agree with you about crooners."But what about this from Mr. G. Gay, ofHereford. He says : " I was pained toread your remarks on violinists in thecurrent issue (sorry to have caused you anypain), but I know you are-from yourremarks-extremely unmusical and thusunfortunate. (Am I unmusical ?) I havestudied the violin and have played firstviolin in the best amateur orchestras inLondon and Leeds, and also in dancecombinations, and I can assure you thatthe difference between street musicians anda £1,000 concert violinist is very real. Doyou' know that it takes ten years or moreof hard work-eight hours a day-to playthe simplest of things really well ? (Yes,I do, and so do 'many poor folk who lice inflats. There should be a law against it !)Street violinists would not be on the streetif they were any good (I seem to have heardof such misfortune). I have heard all theleading violinists and many street ' mu-sicians,' but my only reactions to the latterare ones which make me think of rat poison.Well, this is only a small part of what Ifeel when I ihear and read remarks suchas yours, and I think you ought to give usnews of the B.B.C., etc.-talk of somethingyou understand." The italics are mine !And that's that.

The Foundations of Musicother clay a radio critic tabulated

the " for and against " letters whichhe has received. I was not surprised to seethat there was an unanimous vote againstcrooners and the Foundations of Music(why do the B.B.C. continue to lay thesevery heavy foundations ? They must bethe most unpopular' feature of all thebroadcast programmes. Although I didsee a letter in a book the other day praisingthem-from Sacheverell Sitwell); but I wassurprised to see a heavy vote against HenryHall, mentioning particularly the Glee Clubwith its " churchy atmosphere."

Those Junk PartsMEMBERS of the Technical Staff are

constantly telling me of those readerswho write to ask for a wiring plan suitablefor .using a number of components whichthey bought cheaply at a junk shop.Sometimes the letters are accompanied byrather crude sketches of the coils and

similar components, but otherwise there isnothing to guide those genii whose work itis to design some of those excellent receiversthat are products of the PRACTICAL ANDAMATEUR WIRELESS laboratories, Theyhave therefore asked me to refer to thismatter in these notes, in the hope that theymay reach the eyes of a large number of" junk -shop " merchants. The fact of thematter is that second-hand and discardedcomponents are rarely of any real practicalvalue to anyone except those who arecapable of designing a complete set ; tothe inexperienced constructor they are oftenworse than useless, sinca they may resultin damaged valves and other good com-ponents due to incorrect use.

I should, of course, point out that theFree Advice Service offered so willinglyby this journal does not apply to theprovision of complete wiring diagrams ordesigns for receivers. Such a servicecould not operate satisfactorily, becausedesigns must be thoroughly tested beforethey are offered to the public, and it isobvious that the hard-working TechnicalStaff could not possibly make up, test,modify, and re -design those hundreds ofsets a day for which readers ask ! Itmight be asked why the policy of thisjournal is to refrain from giving wiringplans for untried receivers. The reasonis that every PRACTICAL AND. AMATEURWIRELESS receiver is covered by a veryvaluable guarantee, and the Editor hasrightly considered it most undesirable topass on to any reader details of an instru-ment which has not been fully tested andwhich cannot be guaranteed to functionin a perfectly satisfactory manner, withoutthe need for further experiment by theconstructor. Therefore, dear readers, donot be annoyed it in reply to your query,you receive a letter politely informing youthat the Technical Staff cannot undertaketo supply wiring diagrams and lists ofcomponents for a seven -valve all -wavesuperhet, to be built from parts taken froman old set, or a three -valve mains receiver

A gift from the local rad'o fans.

with A.V.C. constructed from a collect'onof components bought for five shillingsin Farringdon Market.

Believe me, it does pay-and pay well-to buy new and guaranteed componentsin the first place, if only because these canbe used over and over again with fullassurance that they will not let you down,

My Quality SetANUMBER of readers have written

for details of my quality receiverwhich I mentioned in these notes recently.

(Continued overleaf)

0 0

00

0 0

0. .0

. 0 0

0 0

0. .

0. 0

0. .

0. 0

0 0

0 0

00

0 0

0. 0

0 0

.0 .0

0 0

0 0

0 0

0 0

0 0

0 0

O. 0

-0

0 0

0 0

.0 0

0 .0

0 0

0 4

0 0

0 0

0 0

- 4.

0 0

0

[Pra

ctic

alw

aditu

ttrW

irel

ess

SER

VIC

E D

AT

A S

HE

ET

N?

18

;5

1.01

0.00

0.M

...1.

1.1=

0011

0.0.

111,

41.M

.17.

11M

1.0.

M15

.041

11.1

11.0

0=0=

10.1

101.

0=0.

11.M

.0.0

1110

.411

1111

.041

M41

0100

411.

1.1

FUL

L-S

IZE

BL

UE

PRIN

TS

OF

AL

L "

PR

AC

TIC

AL

IA

ND

AM

AT

EU

R W

IRE

LE

SS"

RE

CE

IVE

RS

AR

E

1.11

4 I.

P,04

.111

1.{)

.111

.11.

1.01

1100

1.04

1111

1.10

1M/t

IMW

I /4

101

10=

41.0

1S4

AV

AIL

AB

LE

.SE

E P

AG

E 7

48.

Top

of

Cha

ssis

Vie

w

App

roxi

mat

e V

olta

ge R

eadi

ngs

Vol

tmet

er-t

o E

+ to

1=

120

volts

.

-1-

to 2

=60

vol

ts.

± to

3=

115

volts

.

+ to

4=

120

volts

.

FOR

TH

EM

ON

ITO

R T

HR

EE

Und

ersi

de o

f C

hass

is

App

roxi

mat

e C

urre

nt R

eadi

ngs

Mill

iam

met

er c

onne

cted

at x

1=1h

m.A

.x2

=-1

1 m

.A.

X 3

=7

m.A

.

App

roki

mat

e R

esis

tanc

e R

eadi

ngs

Coi

lO

hmm

eter

con

nect

ed a

cros

s w

hite

lead

s an

d sc

reen

ing

can

=17

ohm

s.

Ohm

met

er c

onne

cted

acr

oss

whi

te le

ads

and

yello

w le

ad=

3 oh

ms.

Ohm

met

er c

onne

cted

acr

oss

blac

k le

ad a

nd s

cree

ning

can

=16

ohm

s.O

hmm

eter

con

nect

edac

ross

blac

kle

ad a

nd b

lue

lead

=-1

- oh

m.

Ohm

met

er c

onne

cted

acr

oss

brow

n le

ad a

nd s

cree

ning

can

=1.

1 oh

ms.

L.F

. Tra

nsfo

rmer

Ohm

met

er c

onne

cted

acr

oss

G a

nd G

B=

2,25

0 oh

ms.

J1!)

Con

. and

E=

750

ohm

s.

0 .0

0 0-

0 0

0 0

O.

O 0

February 22nd, 1936 ,PRACTICAL AND_ AMATEUR WIRELESS

EASY TO BUILD-

VonitorTHE SECOND STAGE

By F. J. CAMM-AND GUARANTEED !

This week we describe how to Modify the Novel Monitor Receiver in order to Proceed a Stage Farther in

the Development of this Interesting Educational System of Construction, and Notes are given concerning theFuture Developments

THOSE readers who have built the Monitor willundoubtedly have found that they now possessa really efficient little three -valve receiver which,

under average conditions, will give 'all that is desiredin the way of broadcast reception. Obviously, in sucha simple form it cannot be expected to provide stationseparation of the order of 9 kc/s, nor can it be expectedto deliver sufficient volume to fill a. small hall. Forgeneral use, in the average home, however, it will in itspresent condition fulfil the role ofthe domestic receiver.The idea underlying the design of this receiver, as waspointed out in our issue dated February 8th last, was totake a small more -or -less standard arrangement, whichwould be capable of development by easy stages, untila really powerful modern superhet would be obtained,and the various stages would provide really soundideas concerning the function of the circuit andcomponents. Thus, we may at this point considerthe next step in the conversion of the Monitor, and asmay be seen from the illustrations accompanying thisarticle, there are still only three valves in use, but thedesign of the tuning circuits and the general arrange-ment of the chassis has now been improved, and ahigher standard of performancewill be obtained.

The CircuitThe fundamental circuit is still

unaltered, and the combinationof screen -grid, detector; andpentode stages re-mains. It will beseen, however, thatthe grid, circuit of thedetector stage is nowprovided with a com-plete tuning circuitconsisting of a coilarid condenser,' andthis addition will pro-vide greater select-ivity. The incorpor-ation of any tuned circuitin a receiver may be ,

likened to the use of a graduated \sieve, and it permits only a certainband of frequencies to pass-thenarrowness of the band beingdependent upon the design of thecoil and the arrangement of theremainder of the circuit.

In addition to this increased selectivity, however,there will be a slight increase in volume in view of thefact that the toil which is employed is wound in theform of a high -frequency transformer, and the secondarywinding (which is joined in the grid circuit of thedetector valve) is larger than the primary winding(which is included in the anode circuit of the H. F. valve),and thus there will be .;,a step up in the voltage which istransferred from primary to secondary. It will thus beseen that -the modifications now introduced will result inthe acquisition of a more powerful receiver without anyincrease in running costs, and to enable full advantage tobe taken of the improvementi in tuning a control hasalso been included, so that the benefits of volumecontrol may be obtained and the local station thus keptwithin the limits set by the output valve to avoiddistortion due to overloading.

The New ComponentsBefore purchasing the extra components which are

The second stage in the developmentof the Monitor Receiver.

736 PRACTICAL AND AMATEUR WIRELESS February 22nd, 1936required for the modifications it is necessary first toconsider to what stage you ultimately wish to take thereceiver. In its final stage it will incorporate the superhetprinciple, but it is, as has been pointed out in the intro-ductory articles, possible to leave the receiver at anystage and it will be complete in that form. Themodifications which are introduced this week will demandthat a -new chassis is obtained, in addition to an extracoil and a further tuning condenser. The coil shouldbe ordered complete with a specialchassis which is designed to accom-modate three of these coils. Therewill thus still be room for a further coilat a later date, and this may take theform of a similar coil or a specialoscillator circuit coil. If you do notintend to carry the design any fartherafter this week you will need only atwo -gang condenser, but if you desireto proceed farther, you should obtain athree -gang model to avoid the scrappingof any part at some future date. Thepresent single condenser which is inuse should be placed on one side forthe. time being, but it will, togetherwith the two -point on -off switch, whichis also dispensed with for the timebeing, be required later on.

In making your choice of circuit youwill be guided in your selection of thecorrect type of three-gang condenser.If you wish to proceed to the superhetreceiver, you should obtain a three -gangsuperhet condenser having a specially -shaped oscillator tracking section,designed for use on an intermediatefrequency of 465 kc/s, and this sectionshould be at the rear of the condenser-that is, farthest from the operating spindle. If, however,you do not wish to make a superhet but would desire toincorporate a band-pass tuning circuit, the three-gangcondenser must be of the " straight " type. As men-tioned previously, however, if you are content to retainthe receiver in the form described this week, only a two-gang model will be needed. A volume control must alsobe obtained, and this will be mounted on a bracketin place of one of the switches now used, and the three-point switch is now employed for switching on and offthe battery circuits in order to break the G.B. circuit andavoid waste through the volume control potentiometer.Constructional Work

The modifications now incorporated will necessitate

THEORETICA

the use of a new chassis and this will have to be drilledin accordance with the Wiring Diagram which will begiven next week.

In spite of the increase in selectivity which has 'towbeen obtained, it must not be assumed that 'finality hasbeen reached. In very congested areas it may be foundthat a number of distant stations are lost on wavelengthsclose to the local high-powered stations, but this diffi-culty will be overcome quite definitely in the final stages

L CIRCUIT OF THE MONITOR -2nd STAGE

of the receiver. For instance, in the next stage to whichthe receiver is to be taken a further tuned circuit willbe added to introduce band-pass tuning, and, as mostamateurs are now aware, this will provide adequateselectivity for practically every case, although it doesnot surpass that obtained in the superhet arrange-ment.

No Further Chassis-

It may also be mentioned at this point that no furthermodification to the chassis will be required, as all futurecircuit alterations may be carried out with the receiverin its present arrangement. The final arrangementof the controls will form a symmetrical layout, using thebrackets already employed.

LIST OF COMPONENTSOne coil (B.T.S.).One .0005-mfd. Compax condenser (Polar).One airplane drive (LB.).One .00015 mid. differential reaction condenser (Polar).Four fixed condensers :.5 mfd., .1 mfd., .002 mfd., .0003 mfd.(T.M.C.).Two fixed resistances : 40,000 ohms, 1 megohm (Dubilier),One H.F. choke, type HF9 (Bulgin).One Senator L.F. transformer (Bulgin).One three-point.switch, S36 (Bulgin).One two -point switch, S22 (Bulgin).Three socket strips : A/E, L/S, 13/11 (Belling -Lee).

ADDITIONAL COMPONENTS REQUIREDOne Monitor coil, with special 3 -coil chassis (B.T.S.).One two -gang .0005 mfd. condenser (Polar), orOne three -gang .0005 mfd. condenser (Polar), orOne three -gang superhet 465 kc/s condenser (Polar). (See Text.)One .0001 mfd. fixed condenser (T.M.C.).

Three valve -holders : two 4 -pin, one 5 -pin (Clix).Four component brackets (Peto-Seott).Six plugs : H.T.-, H.T.1, H.T.2, G.B.±, G.B.---1,(Belling -Lee).Two spades : L.T.+, L.T.- (Belling -Lee).One metallised chassis, 8in. by 6in, by 2iin. (Peta-Seott).Three valves : 210VPT, 210Det., 2201IPT (Cossor).120 -volt H.T. battery.9 -volt G.B. battery.2 -volt accumulator (Exide).One " Pix " Indoor Aerial.Speaker, Stentorian, model 36/S (W.B.)

FOR THE MONITOR 3 -2nd STAGEOne .5 megohm 1 watt resistance (Dubilier).One H.F. choke, type H.F,9 (Bulgin).One 50,000 ohm volume control (Polar).One metallised chassis, 12in. by 10in. with 3in. runners Teo -Scott).

PRACTICAL AND AMATEUR WIRELESS 737February 22nd, 1936

Modern CoilConnections -4An Article dealing with Short-wave Units, Permeability Tuners,and General Mechanical Constructions such as Coil Mountings,Incorporated Switchgear, and Screening Cans. By G. V. COLLE

OWING to the fact that most tuningcoils- for home construction pur-

_ poses are fitted with terminals,which in turn must be screened, the screen-ing cans have to be removable, in order toallow the terminals to be accessible. Apresent tendency is to dispense with'terminals, and to provide bottom solderinglugs such as on set -makers' coils.

Stripped UnitsWhere the home constructor can make

neat soldered joints these stripped 'unitsoffer definite advantages, in that they areless costly, are slightly more compact (thediameter of the screening can may be re-duced without a noticeable loss, of

- efficiency), and -possess lower dielectricand capacity losses due to the smalleramount of insulating material and metalused in their construction.

A number of firms supplying strippedtypes of coils arrange them, where required,on switch chassis, thus obviating onesource of difficulty to constructors possessingonly limited kits of tools. It will be per-ceived that the alternative use of a_ emirateswitch allows more ambitious constructorsto arrange the control knobs- in a sym-metrical manner, assuming such is nototherwise possible.

Switch niechanism, which forms anintegral part of a coil kit, is often sand-wiched between the coils and the receiverchassis. In the event of a high resistancecontact developing due' to oxidisation ordirt at the contact points it is obvious thecomplete coil assembly must be removed,

somewhat laborious proceeding. Easyinspection and accessibility of vulnerableradio components is an essential in theinterests of service work on a modern com-mercial receiver, and hence constructorsare enjoined, where possible, to follow asimilar method of assembly, even if thisnecessitates a larger degree of initial labourin fitting a separate switch.

These remarks apply, of course, par-ticularly to the stripped tuning units,because the majority of coil assembliesfor constructors still embrace their ownswitch mechanisms; and cannot be obtainedin the form indicated. There are alreadyindications that component manufacturersare to list an increasing number of stripped -type coils without switches which will beequally suitable for home construction,and small set -makers' purposes (the massproduction companies usually make theirown coils).

Screening CansMetal screening cans average about

three dozen in sizes and in gauge fromabout 18 to 24 s.w.g. The most popularfixing method is to attach two eye -screwsby rivets to opposite sides of the can, andpars the screwed portions through corre-sponding holes in the metal chassis, thelatter acting as the base of the can and

thereby completely enclosingthe coil unit. The coil itselfis attached to the chassisby a single screw engagingwith a screwed flat brassstrip which rests in twoslats made near the bottomof the coil former.

Another scheme whereby both can andcoil are mounted simultaneously is to pro-vide a cupped metal base and indent around recess in it, as well as one in thetop of the can, so that the projecting metalfits into the inside spaces at the ends of thecoil former. With this latter method thecan and base are permanently lockedtogether to prevent the coil becoming loose.The coil ends are joined to tags projectingthrough holes in the cupped base or flexleads are fixed prior to canning."

Swiich ConstructionReverting to the question of switching,

there seems a definite trend towards theuse of the flat disc type, a number of makesof which have recently appeared in theradio market. The contacts are attachedto each disc in circular formation, andedgewise to each other, resulting in acompact and low capacity construction.Numbers of these switch units are con-trolled by a single knob, each switch beingmounted immediately facing (and usuallybelow) the coil it is intended to wave -change. Apart from the low capacityconstruction, it is obvious that, by isolatingeach group -of contacts, stray H.F. couplingscan be reduced to a mininum, particularlyas simple vertical screens can be intro-

- duced between successive switch units torender the effect absolute.

Commercial set -makers naturally employa multitude of different switch constructionsfor use in H.F. circuits, but it seems that

In this tuner the variable condenser has beeneliminated and tuning is carried out by thevariation in inductance caused by the iron core.

This is the Varley permeability tuner.

A B.T.S. intermediate frequency tuningunit in which the condensers and coil former

are mounted on a ceramic base.

with the introduction of all -wave sets theswitch specifications will become morestringent., and eventually lead to the adop.Lion of a type substantially as described.

Short-wave CoilsShort-wave coils must be mounted as

close as possible to their respective switchesin order to avoid undesirable capacity,effects, and thereby restricted wave=range coverage. Also, owing to the highradio frequencies covered, the H.F. coilfields spread to a far greater extent than onbroadcast frequencies. Close screeningby the aid of round or square metal canscannot therefore be tolerated.

The difficulty is overcome by employing'very small short-wave coils and metalscreening compartments rather than in-dividual canisters. Ceramic coil formerssuch as Frequentite " are extensivelyused, but ribbed ebonite and moulded low -loss material are equally in evidence.

Most of the all -wave sets introduced atthe last Radiolyinpia were arranged toinclude only one signal circuit, and anoscillator section for short-wave operation.Owing to the latter circuit " taking charge "of tuning, the aerial section being com-paratively flat, close matching of the twocoils in their respective spheres was notessential.

In the more ambitious 1936 receivers,attempts will ho made to eliminate the

image " response of each star ii ,n at thealternative dial position by providing twoor more signal coil circuits in addition to theoscillator. Hence the time is not far distantwhen short-wave coils will be made inmatdeed sets, representing a new standardof precision in receiver mass production.

Permeability Tuning -

The new system of permeability tuning,as introduced to readers of this journal inthe June 24th, 1933, issue, has not yet found aplace for itself in commercial receiver design,despite the lapse of two and a half years.

Among the various patents grantedon permeability tuners those ofPolydoroff, Varley, and S. G. Brownare outstanding by reason ofcommercialisation. Those firms

controlling the patents in question havealready evolved practical tuners, whichhave in turn been incorporated in a fewspecialised 'published receiver designs.

The present high cost of permeabilitytuning units has somewhat restricted theirpopularity, apart from the quest kin ofrendering gang condensers redundant, It

(Continued on pax. 739)

738 PRACTICAL AND AMATEUR WIRELESS February 22nd, 1936r.....-.111.141114100411.10414111104.111411.MINI.i11411.11.10.011..0.10.110041,01.!!l141141011.111M114O4 NUM 11.1111.11.1111,11M04OHAININ PIIIMPOI/M1110.411110,4 1.11M.il).114.0.M.Elwl )410.1.10. POW!

I using the correct number of turns in theprimary nntuned winding. It is advisable

I .f.-,<:.47to short circuit a section of this winding I...

by means of a switch if best results are(0,_ to be obtained.

FROM STUDIOSTUDIO To LISTENER -5The High -frequency Amplifier of the Receiver is Briefly Described this Week

By IDRIS EVANS

LAST week it was explained that theripples produced by the trans-mitter strike the receiving aerial,

and if this is tuned to the same wave-length as the transmitter a current willflow in the aerial circuit of the receiver,

I Unless the transmitter is very near to thereceiver, however, these currents are very

I weak, and therefore in most cases it isa found necessary to amplify them before

passing them on to the detector, or, toI be more correct, the de -modulator. There

are many receivers in use which do nothave a high -frequency amplifier, the aerialbeing connected to the detector stage.

j This form of connection is only recom-mended when the receiver is in close

j proximity to the transmitter, however, asapart from the fact that many of thedistant stations are missed, the qualityof reproduction suffers unless a reasonablystrong signal is applied to the detecfor ;this is especially true of the modern type

j of diode detector.

I SelectivityI The term selectivity is well known toa most readers as that applied to the

ability of a receiver to separate stations.Generally speaking, the selectivity of areceiver can be improved by adding atuned H.F. amplifying stage ; that is, bymaking the signal picked up by the aerialpass through more than one tuned circuitbefore feeding it to the detector. It willtherefore be realised that the use of ahigh -frequency stage serves the doublepurpose of amplifying the weak aerialcurrents and providing an improveddegree of selectivity.

i The H.F. StageThe H.F. amplifying stage consists of

a variable tuning condenser connected! across a fixed tuning coil joined to an

amplifying valve, this in turn beingcoupled through another tuned condenserand coil combination to the detectorvalve. The effective size (capacity) of

j the condenser is varied by rotating the! tuning control, and an easy method of

tuning the receiver to the same wave -j length as the desired incoming signal is! thereby provided. It is pointed out at

this juncture, however, that tuning canalso be effected by varying the effectivesize of the coil (inductance); keeping the

I size of the condenser fixed. This wasactually done in the earlier type of receiver

j and is done at present in what are knownas " permeability tuners."

Aerial CouplingThere are two main methods of coupling

a the aerial -earth system to the first tunedI circuit of the H.F. amplifying valve;j these are shown in Figs. 1 and 2. Fig. 2

indicates the tap method, in which the! aerial lead is directly connected to one

of the turns of the coil forming the firsttuned circuit. This method is verysatisfactory provided that the aerial

Fig. l.-Showing aerial transformer coupling.

lead is tapped to a suitable point on thecoil. In the older type of coil it wascustomary to provide one tap near thelower end of the medium -wave winding ;this gave satisfactory results on themedium -wave band, but provided verybroad tuning on long waves. If the tapmethod of connection is adopted, achange -over switch 'should be fitted asshown, so that the best tapping point onboth long- and medium -wave windings isutilised.

-Fig. 1 indicates the transformermethod of coupling. In this case the 0aerial lead is notdirectly c o n -nected to the firsttuned coil, trans-ference being ob-tained by passingthe aerial currentthrough an un-tuned windingplaced near thetuned winding.With this methodof connectiongreat care musthe taken to pro-vide the correctdegree of coup-ling between thetwo windings,this being doneby placing themthe correct dis-tance apart and

In some receivers it will be 'noticedthat the first valve is preceded by twotuned circuits-that is, two tuning con- Idensers working in conjunction with twocoils. The extra tuned circuit is em-ployed to improve selectivity, for as Ipreviously mentioned selectivity 'isgoverned to a great extent by tbe number

'

of tuned circuits used. These two circuits Iare coupled together by means of a small" -coupling coil or a small condenser, andthe co'.ubination is known as a band-passcoupler. The term band-pass is appliedto this form of coupler because a definiteband of frequencies can be passed, thewidth of the band (or in other words the jspread of the received signal) being !governed by the size of the coupling Ielement (coil or condenser) between the jtwo tuned circuits constituting the corn--plete coupler.

.H.F. Valves

Until about eight years ago the ordinarytriode type of valve was used as an H.F. Iamplifier, and unless great precautionswere taken in the design of the completestage, instability was experienced and the Iactual amplification obtained was very jlow. In many of the old types of receiver !employing this type of H.F. valve, the,only advantage obtained from the use of jan H.F. stage was that of improved !selectivity.

The advent of the screen -grid valveconsiderably improved matters, as with jthis type of valve a high degree of amplifi-cation can be obtained before instabilityoccurs. The modern H.F. pentode is a jfurther improvement on the screen -grid Itype of H.F. amplifier, and by using theformer in conjunction with suitablecomponents a remarkable degree of high -frequency amplification is obtainable.To obtain the full benefit of this type of jamplifying valve, however, it is necessaryto screen the components, especially the jcoils preceding the valve from those !*following it ; inadequate screening results Iin instability.

To

Zi/v/NsCONDE/Y.57ER

4/41/ECh'ACIGEJnrrcN

.44-,4,erN

Conzmws-4",eFig. 2.-Tap method of aerial coupling.

eI

February 22nd, 1936 PRACTICAL 'AND. AMATEUR WIRELESS 739

MODERN COIL CONNECTIONS(Continued from page 737)

is a matter of considerable interest to setconstructors to learn the reasons for theevolution of this class of tuner. The merefact that tuning by means of moving ironcores in and out of H.F. coils is a logicalstep from fixed iron -cored coils is nojustification or incentive in itself forscrapping existing apparatus.Advantages Offered

Permeability tuning must, therefore, offeradvantages which normal tuning schemesdo not possess. A dual -range coil of fixedinductance values, when timed by a stan-dard variable condenser, usually 'exhibitsa variable response over each waveband.On the medium waveband, for instance, thesensitivity or amplification is highest at thebottom end of the range, decreasing as thewavelength is increased. With regard toselectivity, this takes the opposite course,being low at the low -dial settings andincreasing with wavelength.

An examination of the dynamic resistancecurve of a typical tuning coilshows that thisfalls with increasing wavelength. On theother hand, the H.F. equivalent seriesresistance, which iepresents selectivity,decreases with increase of wavelength.When it is considered an increase in dy-namic resistance represents higher amplifi-cation and a decrease in H.F. resistancehigher selectivity, it will be seen the twofactors are diametrically opposed.

The provision of a constant Lill ratiorepresents the ideal condition of operation,as its -attainment would lead to sensiblyconstant sensitivity and selectivity. Theo-retically, by dispensing with the normaltuning condensers and linking up the move-ment of the tuning dial with that of themovable cores, the desired effect is achieved.Variation in wavelength is accomplished bygradual change of coil inductance, the ironcores merely increasing or decreasing thelines of force in the H.F. field surroundingthe coils. Constancy of H.F. resistance andhence selectivity may be judged in thefollowing manner. From the minimumwavelength, with the cores removed, to thepoint of maximum wavelength, with thecores fully inserted, the inductance increasesin value from 3.5 to five times. Commencingat the lowest tuning point; each coil withoutits core will possess a certain H.F. resistance,depending on its physical construction andlosses due to surrounding materials.

When the cores are moved say, halfway,in, the coils will increase in inductance,which in itself is sufficient to increase theirH.F. resistance. At the same time theincrease in wavelength tends to counteractthese H.F. losses for the reasons previouslygiven, the net result being a fairly constantH.F. resistance value z throughout -thetuning range.Amplification Factor

With regard to the dynamic impedanceor amplification factor, this is maintainedat a constant level by'the action of the coilin increasing its inductance and the corre-sponding lower losses of the powder -ironcore with decrease of frequency (that is,increase in wavelength).

To be strictly accurate, a theoreticallyperfect permeability -tuned coil assumesthat circuit and associated valve losses willbe constant at all receiving frequencies.The fact remains, however, that some ofthese losses vary with frequency, par-ticularly when stray capacitative eouplin.gsproduce slight regenerative effects betweenH.F. stages. Furthermore, there arecertain technical grounds for stating thatpermeability tuning does not lend itselfto band-pass couplings.

POTTEVERYTHIN

ETO-SC RADIO -CAStiC.O.D, or EASY TERM

IMMEDIATE Of all makes of Speakers, Eliminators, Kits, Pick -Ups, Testing Meters, Receivers, far

CASH, C.0.0., or H.P. PILOT AUTHOR KITS are only obtainable direct from

DELIVERY Peto-Scott. We 'can supply any Kit featured in this journal during the past 3 years.

B.T.S. INTERNATIONALSNORT WAVE 2 KITWITH

ASSEMBLYIN S T ITC-TIONS &FULL SIZEBLUEPRINT

different 2 -valve short-waver-the number of stations obtainableon this remarkable set willamare you !

KIT "A" Z2:12:6,Cash or 0.0.D. Carriage Paid.

Or 51- down and 11 mon,;Itly pay-ments ofi

Cent ainsevery partfor build-ing, in -eluding 2coils, 13-52 metres,

sembl tugand operating instructions and full size blueprint, less valves.

Set of 2 HIVAC valves, 9/3 extra.This remarkable two-valver has a range never before accreditedto this number of valves, and will bring you programmes fromall over -the world.

Send coupon below with 3d. in stamps for the B.T.S. " SHORT-WAVE CONSTRUCTOR" Magazine, Which fully describesthe above and TWO other amazing short -wavers.

LISSEISI Sigrapes.W.3FREE BLUEPRINT WITH EVERY KIT

A new easy -to -build Band Spread tliningS.W. Receiver. Range 13 to 55 metres. Com-plete Kit of components, including ready. -drilledchassis and condenser plate, 3 valVes and full in-structions. Cash or C.O.D. Carriage Paid, 53/9/6.Balance in 11 monthly payments of 6/6.

RECEIVE AMERICA DIRECT. ,

The, femme B.T.S. SHORTWAVE ADAPTOR on EASYTERMS. Simply plugs intoyour present battery or A.C.Mains .set. The only adaptor atthe price, incorporating 100-1ratio aerial tuning and slow-motion reaction fur use either

as Plug-in or Superhet ShortWave Adaptor. Walnut finishedCabinet illustrated.

READYWith. 2 Phig-ill ASSEMBLEDcoils, 13-26 and

B24 -5,5m2 metres.Mils. 46' 5 2 /6

96 and 90-190 !lash or metres, 4/6 each

and 11monthlypay-

mentsof 51-.

NEWPICK-UPCosy cord.

MODEL 276. Entirely new, SENDand designed to give highfidelity reproduction withlarge distortionless output.Incorporates special methodof Motionless armature sus-

pension. Attractive Mottled bakelite finish. ONLYComplete with volume control, screened

leads and combined pick-up arm rest and needle cups. ppiCASH OR C.O.D. CARRIAGE PAID, 1

or 5/- deposit and balance in 5 monthly payments of 51-.amount, A.0.6 Induction ELECTRIC MOTOR. Com-1 plete with 121n. turntable, Unit Plate and fullyautomatic Switch. For A.C. mains only. Cash or P.O.D. z/bCarriage Paid, 22/2/6.Balance In 11 monthly payments of 41, downetARRARD No. 30 Double Spring MOTOR. Coin

pletewith 12in. Plush -covered Turntable, Brake, Speed In- ,,,dieator, Patent Mrmding Crank. Will play 2 sides of a 121n. .15

record at one wind. Cash or C.O.D. Carriage Paid, 21/510.Balance in 10 monthly payments of 2/6. down

MODEL A.0.12 (illustrated). A.C.200/250 volts, 50/100 cycles. 120volts at 12 m.a. 4 tappings. CashOr C.O.D. Carr. Paid, 30/-, or 216 downand 10 monthly payments of 8/,MODEL A.C.25. 3 M.T. tappings25 m.a. at 150-v. A.C..;200/250-v.50/100 cycles. Westinghouse rectifier.Cash or C.O.D. FROM

Carriage 254 52/9/6, or 0/- down -and 10monthly payments of 5/...MODEL M.A. 10/30. With 0 -amp. TrickleCharger- for 2-v. Aocumulators. Far. A.C.200/250-v. 00/100 cycles. Westinghouse rectifier.4 tappings. Output 30 ma. at 1.50-v. Cash orC.O.D. Carriage Paid, 22/19/6, or 51- down -

and 11 monthly payments of 5/6.MODEL D.C.25. 3 H.T. tappings. Output 25m.a. at 150-v. For D.C. mains. Cash or C.O.D.Carriage. Paid. 51/7/6, or 2/6 down and 11 monthly payments of 2/6.

uiL'OT. AUTHOR KITSMONITOR 3KIT ulkly CASH or C.O.D. £2: 5 :0

Carriage Paid.Author's Kit of First Specified parts, YOURS FORincluding Ready Drilled Metaplex Chassis,

Balance in 6 monthly payments of 7/-. 716less Valves, Cabinet and Speaker.

ADDITIONAL COMPONENTS 0as specified in this issue:

1 Peto-Seott Ready -Drilled Metaplex Chassis 10' it 10-1 Polar Midget 2 -gang Condenser (Straight TYPOOR 1 Polar Midget 3 -gang Condenser,(Straight or Sups: bet

TYPOB.T.S. Monitor 3 Anode Coil as specified ..B.T.S. Switch Chassis, type AL as specified ..T.M.C. '0001 mid. Tubular Condenser ..Dnbilier .1 meg. Resistance ..BuIgin H.F.9 Choke 'Polar 50.000 ohms Potentiometer ...

C.O.D. PARCEL

d.

3 911 0

160

6 60

1 03 6

0

Comprising.B.T.S.Dfonitor3A Coil ,410Polar CASH ORCompax Condenser. 5.1.B. Airplane drive. C.O.D.

Peto-Scott Ready Drilled 31 etaplex 1816Chassis, 4 Component Brackets, all neces- CARRIAGEary connecting wire, wood screws and flex. PAID.

PREFECTSWAVE

KIT u A !, CASH or C.O.D.. £2:15:0. Carnage Paid.

Author's Kit of First Specified parts, YOURS FORincluding Ready -drilled Metaplex 716Chasms, less Valves, Cabinet,Speakerand Headphones.

Balance in 7 monthly payments of 7/9.

C.O.D. PARCELComprising B.T.S. 6 -pin Short -Wave CASE ORCoiltand Base. J.B.16 muff. Bandspread c.0).condenser, 40 B.T.S: Short -Wave valve -holders. 0 Wearite Short -Wave B.F. 22/6Choke. Pete -Scott Ready -drilled Meta-plex Chassis. 3 component brackets, CARRIAGEand all necessary connecting- wire; wood PAID,screws and ilex.

£4 SUPERHETBATTERY VERSION

KIT "A" CASH OR C.O.D. A4/4/0CARRIAGE PAIDAuthor's Kit of first specified components only:Or 7/6 down and 11 monthlyy-payments of 719 .

A.C. MAINS VERSION

KIT SEAR CASH OR C,0.1).CARRIAGE PAID £10/216

Author's Kit of first specified parts.- Or 17/6 down and II monthly payments of 18/6.

va,-scorc 1936 UP-TO-DATESENSITIVE S.G. 3 KIT02 -gang Air Dielectric Tuning

Condenser.°Automatic Grid Bias.4WD. Vision Slow-motion

Tuning.*Detector, S.G., Pentode

Valves.Modern Air -spaced Coils.KIT "A" 35/ -Cash or C.O.D. Carr. Paid,or 216 down and 9 month -17 Payments of 4/-.

Coupon Brings Full Details and Free Blueprint

POST THIS COUPON NOWPET0-SCOTT CO., LTD.. 77 Pr.W. 15, City Road, London,

E.C.1 Tel. : Clerkenwell 9406/7.

Please send me CASH/0.0,9i11.r

NAME

ADDRESSPr. W. 15

I am also interested inPlease send me full details without obligation.

740 PRACTICAL AND AMAtELIR. WIRELESS, February 22nd, 1936R '?OWE 4E-A t.tls., _1..,( P,c,._..._

'k :or..sAlrealte ,, r- ...4.0146:4111121111:211WVIN.. 0 GAMPINIAIIIII

MIITIMFAIRTALSN.

ireuurigim rutmi.\, imam A': 4 /BW 'A

all_111MAIL ; ., tlifliA -bigl&lik.^..zlittr.' IX lti; 5liAlg' IFIVINFai,

.._ ."`IIIMIIIIFINA. .. ....

;STUDY AT HOME IN YOUR SPARE TIME;

SIGNS of the TIMESThe Budget has restored

POLICE OPPORTUNITIES.The Air Force is to be increased.

AVIATION MUST DEVELOP,

Pay Cuts haVe been restored.

'CIVIL SERVICESuitable to both sexes. Ages 15 to 21.

G.P.O. ENG. DEPT.CUSTOMS AND -EXCISE. INSPECTOR OF TAXES. Ete,fEO EXPERIENCE REQUIRED. OPEN EXAMS.

.'. MATRICULATIONThere arc many ways of commencing a career, but Marlow;nation is the jumping-off board for all the beat ones.

We prepare candidates for all

INSTITUTE EXAMS.Technical, AcCountancy, Secretarial, Insurance, etc.

ENGINEERS ANDDRAUGHTSMENAll Branches-Employers. arc advertising , for them. -

TELEPHONY, RADIO and MOTOR ENGINEERINGare expanding rapidly. There are lots of vacancies.

Our postal courses will make you eligible. Advice on allcareers free.

.-

Also ask for our New Book (Free of charge)

THE HUMAN MACHINESecrets of Success

,

YOU CAN HAVE. A COLLEGE _TRAININGIN ALMOST ANY CAREER FOR A FEW*A.--

SHILLINGS MONTHLYAcountanoy Exams. MatriculationAdvertising and Sales Metallurgy,,,Management " Mining, all subject!A.M.I. Fire E. Exam. Mining, ElectricalApplied Mechanics EngineeringArmy Certificates Motor EngineeringAuctioneers and,pstate Motor Trade_-Agents - - -- . Municipal & CountyAviation Engineering EngineersBanking , Naval Architecture"Boilers , Pattern MakingBook-keeping, Accountancy Police, Special Course

and Modern Business Preceptors, College of' Methods Pumps and Pumping

B.Sc. (Eng.) MachineryElle. (Estate Management) Radio Service EngineeringBuilding, Architecture and Radio Communication

Clerk of Works Road Making andCambridge Senior -School Maintenance

Certificate SalesmanshipCivil Engineering SanitationCivil Service Secretarial Exams.All Commercial Subjects Ship -buildingCommercial Art Shorthand (Pitman's)Concrete and Structural Structural Engineering

SurveyingDraughtsmanship, all branches Teachers of HandicraftsEngineering, all branches, Telephony and Telegraphy, subjects . and examinations Transport Inst. Exams,

General Education Weights & MeasuresG.P.O. Eng. Dept. Inspector =Heating & Ventilating WeldingIndustrial Chemistry Wireless TelegralallYInsurance and TelephonyMathematics Works Managers

If you do not see your own, requirementsabooe,write to us on any subject.-,

IZAI

4, --Ad, k ....

.rZ.......:j. ,t....,,,,,,, .... AM*

Dept. 104. THE BENNETT COLLEGE, SHEFFIELD.

The New Twin -SpeakerMcMichael Radiogram

Mrecently released their new radio-gramcMICHAEL

RADIO, LTD., have

(Model 365), which isdesigned to provide critical listeners withan instrument of unquestioned quality andreliability, with every worth -while refine-ment of 1936 technique.

Externally, the design of the new modelfollows the style initiated in the firm'shighly popular 15 -guinea twin -speakersuperhet (Model 135). The inlaid walnutcabinet is bow -fronted in shape, supportedon gracefully curved .egs and although ofvery generous dimensions, has none of theexcessive solidity frequently encountered.Thus, whilst not ultra -modern, it isthoroughly in harmony with the surround-ings of the home in which it will be placed.Particular care has been taken over theconstruction and detail finish of the cabinet,and it IS interesting to note thatits genuine piano -finish is ob-tained by an entirely new processcombining the' virtues of bothcellulose and french polish, onwhich an ordinary wax -polishcan be used by the housewife;this process, used by pianomanufacturers, is here employedfor the first time in this countryfor a radio cabinet.

15411.,e CircuitThe circuit is a five -valve

eight -stage band-pass A.C.superhet fitted with full A.V.C.,and the constant -gain couplingsystem giving uniform perform-ance over both wave -bands.Multiple valves are employedin conjunction with seven tunedcircuits, and an elaborate maim --static filter which gives excep-tionally quiet operation; whileover 4 watts undistorted outputis supplied to the extra largetwin -stereophonic speakers. Thesuccessful McMichael Giant Dialis, of course, a prominentfeature, this time ten inches indiameter, is fitted with colour -

changing illumination for thetwo wavebands, the motor turn-table on the opposite side ofthe cabinet being recessed inharmony with the dial. Thehigh quality turntable and pick-up are provided with a separatesystem of overhead floodlighting-a most useful innovation-while thevolume control, operating on both radioand gramophone, is tone-compeniated toa new degree -of efficiency.

Model 365 possesses exceptional tone,high range and selectivity, extreme sim-plicity of operation, and a new low-levelof background noise; while its cabinet workis above reproach.Specification

Circuit.-Five-valve (including rectifier)eight -stage superselective band-pass A.C.superhet employing seven tuned circuits,full A.V.C., mains static suppression andmultiple valves. The valve sequence com-prises a triode -pentode frequency -changer,an H.F. pentode for I.F. amplification,followed by a distortionless double -diode

triode for A.V.C. second detection, andfirst stage of L.F. amplification; theoutput is a high -power pentode, while thelast valve is a heavy duty ET. rectifier.

Constant -gain Couplings.-The band-passinput circuits are specially arranged toprovide substantially level gain from topto bottom of the scale, and operate in con-junction with an efficient image -suppressiondevice.

Controls.-Four only-tuning, wave -change -gram., voltime and tone-neatlydisposed round the tuning dial. -Thetuning dial is 10in. in diameter, with twoconcentric scales, calibrated in both stationnames and wavelengths ; the medium -wave scale alone is 22in. in circumference;and all names are three times larger thanusual ; red and green illumination for thedifferent wavebands simplifies tuning still

This illustration of the new McMichael twin -speaker radiogram shows the fine lines of the

cabinet work, and the giant dial.

further, and greatly improves appearance.Twin stereophonic moving -coil speakers.-

Reproduction from' the two carefullybalanced energised speakers-an extralarge unit for middle and low frequencies,and a second unit for treble-is remarkably

-fine and very uniformly distributed.Undistorted output.-Over 4 watts, much

above average and enough for a small hallthis is a great aid in the rendering of heaVypassages and gramophone records.

Volume Control.-Very efficiently-tone-comPensated to preserve a constant musicalbalance at all volumes ; the tone control isof the wide7range type with even gradation.

Gramophone Equipmert,=.1;ligh7qualitypick-up and electric motor.

Price. -28 guineas.

February 22nd, 1936 PRACTICAL AND AMATEUR WIRELESS 7 4 I

\I\ I 1111Iiii/ III/// / 00 0

MN AY listeners have probably found,when using a short-wave receiverfor the first time, that much

difficulty is occasioned by what are loosely_termed " hand capacNy " effects, butiwhich should more correctly be describedas " body capacity " effects. Owing to thevery high frequencies which are dealt with

lin a short-wave receiver it is usually foundthat the H.F. currents are not stopped orblocked so easily as they are in a broadcast

'receiver, and it is to this that the troublesmay be traced. For the benefit of newreaders or those to whom the above state-

1

ment may be rather obscure it may be.stated quite briefly that the frequency ofthe normal broadcasting stations rangesdownward from about 1,500 kilocycles,whilst the short waves will vary in fre-

. quency from 6,000 kilocycles upwards1(50 metres and below), and thus there isa much greater risk of leakage as distinct

r from actual stoppage.We Will assume, for the purpose of this

article, that the short -waver consists ofa straight receiver, as the superhet typeof apparatus requires different treatment,

i due to the change in frequency LI-t which takes place. The

1-5.

H Ty-

HT- HT-LT- G T-

'Fig. 2.-The output circuit of an S.W. set and the

input circuit of an L.F. amplifier.

receiver may or may not employ' an H.F. stage, but it may be ignoredfor the purposes of this article, as theH.F. currents must be passed alongto the detector stage in order to providean audio signal for subsequent amplification,and it is usual to provide adequate insula-tion on this side of the circuit to ensurethat the maximum transfer of thesecurrents takes place 'without loss.

The Detector AnodeThus, we arrive at the point where a

large H.F. supply is fed to the grid of thedetector stage, and we must assume thatthe tuning circuit is so arranged that thereis no loss and complete rectification takesplace. At the anode circuit there will thusbe present a rectified signal oscillation,

SHORTWAVEECTION

THE S. -W. OUTPUT CIRCUITIn Some Respects the,Output Arrangements of the Short-wave Receiver Differ from NormalBroadcast Apparatus, and Some Interesting Points are Here Discussed. By W. j. DELANEY

in which will he found a fairly large per-centage of H.F., and in the interests ofgood theory this must be stopped at thispoint, or, if you prefer it, diverted directto earth. What happens if this is notdone ? Firstly, the presence of BY.

Fig. 1.-An output scheme which will be foundvery valuable for headphone work.

Fig. 5.-The correct method of wiring the detectoranode circuit to ensure correct H.F. by-passing.

currents in the L.F. circuits will lead toall sorts of instability and distortion;although the latter is generally unim-portant in a normal short-wave receiver,It will, however, become of greater im-portance when television transmissions areconsidered. .Jumping from the detectorstage to the output stage, let us assumethat the H.F. currents have leaked rightthrough the set and are to be found atthe output valve anode circuit. Whatdifference will this make to the operationof the receiver ? Any experimenter who

HT#

Fig. 3.-Hota to couple the circuitsshown in Fig. 2.

has used n pair of headphones with a short-wave set may have noticed that sometimeswhen wearing the 'phones it is impossibleto hear stations which are heard on thespeaker when this is in circuit:, or, alter.natively, that it is absolutely impossibleto obtain any signals whilst, the headphonesare being worn. In mostl noes this +illbe due to the H.P. currents at this isiint,and it will be found (hat there is a form offeed -back from the output to the detectorstage, due to the capacity effects of thebody to earth, and very little transfer ofsignal takes place through- the L.F. circuit.

H.F. FiltersAs an experiment the listener can in.

corporate high degrees of insulation to thedetector stage (using old Walla dishes, etc.,to avoid capacity losses to earth) and thenconnect a roil in series with the 'phonesand couple this to the detector tunedcircuit. It will, in almost every case, hefound possible to obtain strong oscillationby this method, providing proof of thepresence of the H.P. currents. Accuratetuning with headphones under such cow.ditione is impossible. Assuming the useof a good short-wave choke in the anodecircuit of the detector stage, a by-passcondenser to earth should be adequate tostop the passage of these currents, butwhere maximum results are required thefollowing precautions will be found desir-

Fig. 4.-An ohernotiue method ol carotin/ then

circuits shown in Fig. 2.

able and may be arranged on a veryinexpensive basis. Firstly, in the detesteranode circuit, the usual H.F. choke shouldbe sectional wound on the highest insula-tion material which can be found,1111,1shouldbe joined direct to the anode terminal(Fig. 5). If you cannot afford to buy oneof the modern H.F. chokes wound on isceramic base, wind your own on a glasstube, using a dab of Chat tertan's Compoundto retain the ends, and splitting the windingup into a number of small sections. Thechoke should be as compact as it is possibleto make it without introducing too large aself -capacity. This is where the commercialcomponent will genre, On account of thefact that a spvcial wayewound arrange-

(ContipossEJ on milt 74j)

at-

742 PRACTICAL AND AMATEUR WIRELESS February 22nd, 1936

Let "Ls Send Yon

Tills 40 -Page

Booklet-Free

E t.7C:i...A.

It gives full information regarding variousI.C.S. Courses of Instruction in Radio work.

The Radio industry is progressing withAmazing rapidity. Only by knowing thoroughly;the basic principles can pace be kept with it.II.C.S, Instruction includes American broad-casting as well as British wireless practice. Itis a modern education, covering every depart-ment of the industry.

OUR COURSESIncluded in the T.C.S. range are Courses

dealing with the Installing of radio sets and,'in particular, with their Servicing, which to -day'intimately concerns every wireless dealer andhis employees. The Equipment Course givessound instruction in radio principles andpractice.

There is also a Course for the WirelessAalesinan. This, in addition to inculcating thelilt of salesmanship, provides that knowledge[Which enables the salesman to hold his ownwith the most technical of his customers.

Then there are the Preparatory Courses forthe City and Guilds ttnd I.W.T. Exams.

We will be pleased to send you details andfree advice on any or all of these subjects.ijust fill in, and post the coupon, or write inany other way.

moo mp. m m am. mi =i 4ms imp

International Correspondence Schools, Ltd.,Dept. 94, International Buildings,

Kingeway, London, W.C.2.

Without cost, or obligation, please send me your" Radio " booklet of information about the CoursesI have markedCOMPLETE RADIO

1:1 RADIO SERVICING12( RADIO EQUIPMENTa RADIO SERVICING AND SALESMANSHIPEt WIRELESS ENGINEERINGEl EXAMINATION (st..e.:e wk1kh)

0-0 100 - - ''1V4Mi - . - .-. . - ..... /Lie . -

Address .....

B.T.S. Ultra- and Short-wave Components

Some Details of a Most Interesting Range of Components Designed to Fill a SpecificNeed of the Short-wave Listener

IN our various articles on short-wavereception we have dealt with thesubject of losses which aro often in-

curred owing to the use of apparatus whichis not designed for the purpose. Thedistinction between the design of apparatusused on the short- and ultra -short wave-lengths is almost as great as the differencesbetween standard broadcast apparatus andnormal short-wave components, and inthe illustration below may be seen some ofthe specially -designed ultra -short-waveitems selected from the B.T.S. range. Asmay be seen in this illustration, no eboniteor other rubber -base material is employedfor insulation purposes, and to make per-fectly certain. of the highest efficiency fromthe point of view of insulation a new ceramicmaterial is employed and this is known inthese components as " Megacite." Thishas a high -power factor and extremely lowlosses and may be used right down to2 or 3 metres without any difficulty inmany parts of the circuit,

which the primary winding is wound. This,also, is provided with an adjustable controlon the top so that the degree of couplingbetween primary and secondary may beadjusted to provide the necessary band -

width determined by the apparatus inwhich the unit is employed. Thus, forsound reception it may be loosened toprevent interference between adjacentsignals, whilst for vision reception it maybe set to provide a wide response curveand so avoid side -band losses. The designof the coils is such that a band -width of2.5 megacycles (2,500 kilocycles) may beobtained. The price of this particularcomponent is 9s. 6d.

Condenser AdjustmentsThe variable condenser seen in the back-

ground is also fitted with silver-platedvanes and the Megacite end -plates, but themost interesting feature in this componentis the large adjustable metal bush which isfitted to the centre spindle, and which may

An interesting group of short-wave components in which every precaution has been taken to avoidlosses. These B.T.S, components are characterised by silver-plated metal parts and ceramic material

for insulation purposes.

H.F. ResistanceIn addition to this use of Megacite, the

makers of these components have alsocarefully studied the question of high -

frequency resistance in those componentswhere H.F. currents may be found, and asa result we find that all metallic surfacesof this nature are silver-plated, and thisextends not only to inductances and othercoil windings, but also to the plates of thesmall condensers, the valve sockets- andterminals. It may thus be taken forgranted that all of this apparatus will befound highly satisfactory in the construc-tion of short- and ultra -short-wave receiversor transmitters.

Amongst the items shown in the illustra-tion may be seen a special I.F. unit and thisis to be seen in the centre of the group. Apiece of the Megacite material carries twospecial low -loss air -dielectric trimming con-densers which are provided with slottedheads on the upper surface of the Megacite,and adjustment may be made by means ofa Screwdriver -shaped piece of wood. Thesecondary winding of the I.F. transformeris carried on a tubular former of Megacite,and inside this is a smaller former upon

be seen close to the left-hand plate in theillustration. This adjusts the tension on thespindle and thus makes it a simple matter toprovide just that degree of friction whichwill enable the condenser to be operatedthrough any type of drive but will stillpermit of perfect contact being made, andcomplete elimination of noises whilst therotor is moving. The extended spindle willenable any number of these condensers tobe ganged together, and there will be nolikelihood:of the weight of the moving vanescausing the setting to vary, due to vibration.The price of this condenser is 7s. 6d.

Other ItemsAmongst the remaining items are the

tuning coil and oscillator coil, a trimmingcondenser and padding condenser, an H.F.choke and two valve -holders. The trimmingand padding condensers will be foundextremely useful for other purposes, al-though they are intended primarily for usein a superhet circuit. These two con-densers may be obtained with practicallyany capacity, the trimming condenser upto 40 mfds. and the padding condenser upto .0002 mfds.

February 22nd, 1986 . PRACTICAL AND AMATEUR WIRELESS

SHORT-WAVE SECTION(Continued from page 741)

meat may be incorporated. The by-pass,condenser should -also be joined to the

I" anode terminal, and the other side of thiscondenser should be joined to cathode orto the negative filament leg of the valve -holder.

As a further part of the filter, a secondcondenser should be joined from the otherside of the choke direct to the nearest-earthed point in the receiver, and both ofthese by-pass condensers should be of themica -dielectric type, as it has been foundon experiment that a number of peculiartuning effects have been traced to 4H etthe tubular type of condenser. Los

DET 4.e POWER

,1 Fig. 6.-A simple method of testing the efficiencyof the H.F. arrangements.

Isolating the 'PhonesTheoretically, no H.F. currents should

now be experienced in the L.F. circuits,but as a further precaution it is worth, whileto provide a good choke on each side ofthe 'phone or loud -speaker terminals, againarranging for good components, and thistime taking into account the anode currentwhich may be passing. As the valve willbe of the power type there will be probablya fairly heavy current- flowing, and thusthe component does not come within thesame category as the detector choke. Toconstruct your own is not so difficult here,and 100 turns of 24 D.C.C. on a lin. ebonite,paxolin, or glass former will be found quitesuitable. The first choke should again bejoined direct to the anode terminal on thevalve -holder, whilst the second choke shouldbe joined direct to the positive loud -speakeror 'phone terminal (Fig. 1). A fixedcondenser should be joined between anodeand earth, and again mica should beemployed for the dielectric, whilst thecapacity may be found to be critical, andthus some experiment should be carriedout with a view to finding the most suitablevalue for the valves and circuit in use.

Using Two SetsSome readers have built a simple short-

wave set and wish to increase the strengthof signals by adding the L.F. stages ofanother broadcast receiver. They haveasked whether it is possible to use thepick-up terminals on the standard set forthe purpose. In Fig. 2 the output circuitof the average short-wave set is shown bythe side of the pick-up circuit generallyemployed, from which it will be seen thatif the L.S. and pick-up terminals aredirectly connected, the H.T. will be appliedto the grid of the L.F. valve, or, if theterminals are reversed, the H.T. supplywill be short-circuited. The two pieces ofapparatus may, however, be coupled in avery simple manner, either by an L.F.transformer or by a resistance -capacitycoupling unit as shown in Figs. 3 and 4. Thetransformer should be of low ratio to avoidoverloading the first valve in the amplifyingchain, whilst if an R.C. unit is made upthe resistance in the anode circuit willhave to be of low value to avoid a seriousreduction in the H.T. applied to thevalve.

c.c.495$

-As

743

ey say in Atichterrnuchty

'BETTER BUY CAPSTAN.

theyre blended better-they're Wills's

CAPSTAN CIGARETTESPLAIN OR CORK TIPPED

10 for 6d,20 for 11v2d.

744 PRACTICAL AND AMATEUR WIRELESS February 22nd, 1936

LETTERS FROM READERSThe Editor does notnecessarily agree - withopinions expressed by his

correspondents.

Our Simple Short -waverSIR, -I recently constructed the simpleL., short-wave receiver, particulars ofwhich were published in the issue ofSeptember 14th, 1935, and below is ashort log of some of the stations I havereceived :-

W8XK, W2XE, 2R0, WIAXL, EAQ,CTIAA, HBL, W2AXF, PRFS,LKJ1.

To this circuit I have added anothervalve, and it is now possible to obtainquite a strong signal. Instead of the fixedcondenser in series with the tuning con-denser, I use a pre-set condenser. -D. LEVEY(Leek, Staffs).

A Good Log on 40 MetresSIR; Having noticed from time to time

various reports in your paper withregard to Amateur " S.W." Transmission,etc., I thought the following might be ofinterest. The receiver in use is a simple2 -valve (o -v-1) with very short aerial andearth.

Heard on 40 metres on January 4thto 6th were the following : W3QE, W2ISZ,W8OZU, W1QG, WIRY, W1IIE, W1H00,W211TO, W8NPR, W1JNL, W3DAJ,W8FSM, W3EOG, W5CGQ, W9DMF,W2CP, W3AUF, W2BVS, W3CDG,WIDEK, W3EPR, W8AUP, WSFIP,WlIEO, W8LED, W1BBS, W80QF,W3BUY, W2I0P, W2NTR, W2ABX,W1FH, W3DFX, W1HYV, W9TBW,W3CG G.

It should be Mentioned, of course, thatthe above ' were " all C.W." I have alsonoticed recently in your columns requestsfrom readers for articles dealing withamateur transmission.

I bog to agree on this matter. Simpleand easily understood articles on thisphase of radio would, I am sure, be verywelcome to a considerable number of yourreaders.

Thanking you for a very fine weekly,of which I have been a regular reader since1924.-S. GEOFFREY WOOD (Rotherham).

Club Membership WantedCIR,-I have tried for some time -to find

a wireless club in this vicinity, butwithout success. If there is such a clubin this district I shall be glad if the secretarywill get in touch with me at the addressgiven below. -J. R. WATSON (158, RunleyRoad, Luton, Beds.).

Jamming on the 40 -metre BandSIR, -Re the letter from A. E. Millinchip

(Hartlebury) on the subject of " 40 -metre Jamming," may I respectfullysuggest that if the above -mentioned gentle-man considers 40 metres too crowded, whynot do the most obvious thing -use the160-, 80-, 20-, 10-, or 5 -metre bands. Whyuse 40 metres ?

In all sincerity I think it is quite possibleto carry out a 100 per cent. QSO on 40metres if good operating is employed. Ifone takes a percentage of stations workingon the 40 -metre band on Sunday mornings,I am convinced that the 10 -watt amateurswill be found to be about 70-80 per cent.of the total. I am sure there arc com-

All letters must be accom-panied by the name andaddress of the sender (notnecessarily for publica-

tion).

who use the 40 -metre band for work onSunday mornings.

In conclusion, may I add that patienceis a virtue, and good operating an absolutenecessity. To grouse is the most obviousway out ; why not try to do something ?-H. J. CHATER, G2LU (Coventry).

An Unusual Circuit

SIR, Your readers may be interested toknow of the unusual circuit I use.

The set is a 11F.D.I.F. mains receiver,which I use for local station quality recep-

H.T

TO REACT/ON

SMh

-01/IFD

'000/MFO 70 L.P.

-

combinedcombined diode and power -griddetector.

tion with a diode detector. When foreignstations are required, however, a turn -ofthe switch, indicated in the accompanyingdiagram, changes over 'to power -griddetection with reaction, giving increasedsensitivity. -J. L. SaAw.

The 40 -metre BandSIR, -It would seem that your corre-

spondent " A, E." has been mis-informed in regard to several mattersaffecting the amateur transmitter and thefacilities which he may enjoy. In thefirst place, I must point out that there aresix bands from which he may choose andnot the 40 -metre band, as he appears tothink. Some of these, offer ample accom-modation but are -comparatively neglected.Secondly, whilst it is generally admittedthat most transmitters are members ofR.S.G.B., which is the only organisationwhich looks -after their interests,, never-theless there is no sort of compulsion

. whereby non-members are penalised." A.E." stands exactly the same chance ofobtaining his transmitting licence, whetherhe is a member of R.S.G.B. or not.

While not wishing to take up yourspace unnecessarily, I do, however, thinkthat one or two observations on ;the stateof affairs on 40 metres might not be outof place from an old timer.

- The reasons for the congestion can beroughly summarised as under :-

1. Stations using unnecessarily highpower to effect local contacts which wouldbe much more -reliable on one of the otherbands. The 100 -watt phone station on aSunday morning working over twentymiles is a pest.

2. The reluctance . to use the portion ofparatively few QRO telephony trawmiitters the band between 7,200 and 7,288 kc/s

A circuit for a

owing to its not being in harmonic relation-ship with the 14 mc. (20 -metre) band. Acrystal between these limits will, therefore,not " double " into the other band.

3. The general disinclination to workduring the week and boldly tackle theproblem of interference to broadcastlisteners when this occurs.

4. The over -modulated, unstabilised, andbad quality " telephony " emanating frommany foreign stations, particularly inFrance.

5. Many of the transmissions now takingplace on open aerials are unnecessary, andcould be quite as easily and efficientlyconducted with an artificial aerial.

6. The general lack of interest in the160 -metre and 10 -metre bands, plus thetendency of certain stations to use theirappaiatus for conducting a species of familyparty on the air, instead of getting downto the serious experimental work for whichtheir licences were granted.

I agree there is something wrong, butlike poverty, war, disease, and thehundred -and -one other problems of life,the remedy is in the hands of the victims,waiting to be applied.-AnTnun, 0. MILNE,G2MI (Maidstone).

(This correspondence is now closed. -ED.).

A S.W. Log from Chingfordregularly read with great

interest the logs of other readers,I have never yet seen one from this district,so I append a short log of stations I haverecently received. On 40 metres andupwards, W3AL, W8XK, W3XL, W2XE,W9XF, WEN, VE9BJ, YVQ, YV6RV,HJ4ABE, HJ3ABI, HjlABB, HCRLRW72, EA8AB. The amateurs are toonumerous to mention, and on Sundaymornings on 40 metres it is simply thesurvival of the fittest. My receiver is asimple - 3 -valuer, using 6 -pin heine,inadecoils, and all components came out of thejunk box. I should like to see a biggershort-wave section in your excellentpaper. -F. ANDREWS (Chingford).

CUT THIS OUT EACH WEEK.

-THAT when a tone filter is included in acircuit to compensate for very selective tuners,a switch should be included to eliminate thedevice for gramophone record reproduction.-THAT where -bare copper wires are em-ployed for short-wave tuners on the ultra -shortwavelengths, cleanliness must be observed toavoid H.F. losses.-THAT for the above reason certain cam-mercial coils are now wound with silver-platedwire to avoid corrosion.-THAT where a spark -gap is provided on theaerial lead, some form of protection frommoisture should be fitted.-THAT if the above precaution is not takennoises and loss of signal strength may beobtained due to leakage across the gap.-THAT where incurable H.F. instability isexperienced the H.F. valve may be suspectedof oscillation.-THAT to test for the above fault a milliam-meter should be included in the anode circuitand the grid terminal earthed. The meterreading will be increased when this is done ifthe valve is oscillating.

The Editor will be pleased to consider articles of apractical nature suitable for publication in PRACTICAL.AND ADIATEUR WIRELESS. Such articles should bewritten on one side of the paper only, and should containthe name and address of the sender. Whilst the Editordoes not hold himself responsible for manuscripts, ereryeffort will be made to return them -if a. stamped andaddressed envelope is enclosed. All, correspondenceintended for the Editor should be addressed: The Editor,PRACTICAL AND AMATEUR WIRELESS. Geo. Newnes,Ltd., 8-11, ,Southampton Street, St-mnd, W.C.2.

Owing to the rapid progress in the design of wirelessapparatus and to our effortsto keep our readers ill touchwith the latest developments, we give no warranty thatapparatus described in our columns -is not the subjectof letters patent.

February 22nd, 1936 PRACTICAL AND AMATEUR WIRELESS 745

H.M.V. RecordsTHE series of short plays presented

in triple bill form and grouPed underthe title of " To -night .at 8.30 " is

having extraordinary success at thePhcenix Theatre, London. Gertrude Law-rence and Noel Coward have recordedscenes from three of the plays, " ShadowPlay," " Red Peppers " and " FamilyAlbum " on H.M. V. C2815-7. They werespecially rewritten by the author forgramophone recording. " Red Peppers "is, perhaps; the best of three unusualrecords.

From the FilmsNEWCOMER to the film world is

Lily Pons, the operatic soprano,and she has recorded two of the

songs from her new film, " I Dream TooMuch;" on H.M.V. DA1456.

Frances Day's record of " Me and MyDog," from her film 'Public NuisanceNo. 1 " on H.M.V. BD323, is sung in herown inimitable style, and mention mustalso be made of Robert Ashley, the youngbaritone, who is yet another B.B.C. dis-covery. His numbers, " Thanks a Million"and " Moon for Sale," on H.M.V. BD315are from the film, " Thanks a Million."

King George's Last Message to .HisPeople

IN the past, the real personalities of ourSovereign Ruler have been known tofew. With this generation it is different.

King George will always be with us. Hissimplicity and kindliness,- his devotion toduty and his steadfast faith in his peopleare there for all to hear in a record of hislast Christmas .Day Message.' The number -of the record is H.M.V. BCS2811 and theProfits made by " His Master's Voice "from its sale are being given to charitiesnominated by the late King.

" Dance of the Hours ".

A RECORDING that should make itsappeal is the " Dance of the Hoursfrom Ponchielli's " La Giaconda."

This is one of the best-known pieces ofoperatic ballet music and is- played .by theBoston Orchestra (composed of selectedplayers from the Boston. Symphony Or-chestra) on 02812.

Gigli the famous tenor has recorded" Plaisir cl'a,mour," coupled with themournful " Elegie " by Massenet, onH.M.V. DB2530, and Miliza Korjus, the

Swedish Nightingale," sings two Italiansongs, " Funiculi, Funicula " and "LaDanza " by Rossini- on H.M.V. 02813.

Dancing TimeJACK HYLTON'S ORCHESTRA is

well to the fore with "She shall haveMusic" and" Do the Runaround" on

H.M.V. BD5017, also "My First Thrill"and -" May all Your Troubles be LittleOnes" onH.M.V. BD5018, all of which are;-rom their new film "She shallb.a,ve Music."

Noel Coward's latest tunes " You werethere" and " Family Album " waltz fromhis new show "Tonight at 8.30" are played

by the Phoenix Theatre Orchestra onH.M. V. BD5019. The first of these hasa vocal refrain sung by Sam I3rowne.Decca

HANDEL'S" Samson Overture " ap-

t pears in this month's list playedby the Queen's Hall Orchestra,

conducted by Sir Henry J. Wood, onDecca K812. I think you will like this.

A record which has no scholarly preten-sion is Mozart's " Serenata Notturno " onDecca K810-11. It is extremely wellplayed by the Boyd Neel String Orchestra.

ColumbiaTHREE new records in this month's list

form an important addition to theColumbia folk dance repertoire.

" The Long Eight," " Pipers Fancy," " TheFirst of April," " The Dressed Ship,"" Welsh Reel" and " Wyth " are thetunes which are played in correct 'dancetempo. The numbers of the records aroColumbia DB1621-3.

" Music when Soft Voices Die," " Love'sPhilosophy," "I Dare Not Ask a Kiss" and"The Jealous Lover," are the titles which'belong to a little group of Roger Quiltersongs that Columbia have just issued.They are settings by Quilter (who himselfaccompanies on the piano), of poems writtenby Shelley, Herrick, and the Earl ofRochester, and their interpreter is Mark'Raphael, the singer. The number of thisrecord, which will appeal to many, isColumbia DB1602.

Ho

136WHITELEYSole Agents

ears ?0°V

Believe it or not, there are in use this -minuteliterally hundreds of old moving -iron horn typespeakers, Their owners like the -purity of tone '(lack of bass).. The absurdly narrow frequencyrange, appalling resonances, and violent " colonra-tion " are not consciously noticed; and until thoselisteners hear a good modern speaker for a fewminutes they will never realise the true reason fortheir lack of interest in the broadcast programmes.

This is an extreme instance of the commonphenomenon known as ." aural tolerance." Youare not proof against it. Nobody is. You mayeven now be satisfied with radio reproduction farinferior to that which your set could give with aW.B. 1936 Stentorian, simply because your ear hasbecome accustomed to the present imperfections.

Make this test. Ask yourself "Am I delightedwith my set's reproduction ? " " Do I get vividlife -like entertainment from my radio, as distinctfrom merely treating it a8 a pleasant ' backgroundaccompaniment' to other activities ?

If you cannot honestly answer " yes," go straightto- your radio dealer and ask to heat a W.B. 1936Stentorian loudspeaker. Afterwards, in the in-tervals between listening to the vivid presentationof broadcast items which it brings you, you can

reflect on " aural tolerance "-andthe pleasure of which it has cheatedyou for so long.

1936 STENTORIAN CHASSISMODELS.

Senior 421-.. 326kiziyor .. 23/6

- 17/684/ -Midget

Stentorian Duplex ..Type EM/W 70/ -

CABINET MODELS.36S JuSeni or? V63A.

36B (Ba36Jng)

STENTORIANELECTRICAL RADIO CO. LTD. (Technical Dept.), MANSFIELD, NOTTS.

in LF.S., Kelly & Shiel, Ltd., 47, Fleet Street, Dublin.

746 PRACTICAL AND AMATEUR WIRELESS February 22nd, 1936

COMPONENTS TESTED IN OUR NEW LABORATORYBulgin Community Aerial CouplerfiN the past the experimenter has foundI it often necessary to arrange for separateaerials in order that the standard familyreceiver could be used in one room whilsthe experimented in another with a differentreceiver. It is difficult to arrange forseparate aerials to prevent interaction, andalso to avoid making the house look like asmall transmitting station, and thus thenew aerial coupler introduced by Messrs.Bulgin will be found especially welcomein such

.instances.. In many modern

..........\)- 1., G

A diagrammatic view of the new Bulginmulti -set aerial coupler.

homes it is now the custom to provide aseparate receiver in tip kitchen, with alarger receiver in the drawing -room, forinstance, and perhaps an experimental orshort-wave receiver in another room, andthis new coupler will enable all these setsto be operated from one aerial withoutinterference. As may be seen from theillustration, the device consists of anebonite base and screening can, inside whichis an inductive unit with separate capacitors.Separate tapping points are provided andfive terminals are fitted. A shielded lead-in is taken from the aerial to terminal No. 1,and from the remaining terminals screenedleads are taken to the aerial terminals onthe additional receivers, with an earth leadto the fourth terminal to complete thecircuit. If the receivers are placed neareach other and the length of the additionalaerial lead is less than twelve feet, thescreening may not be found necessary.The coupler is effective over a wavebandfrom 20 to 2,000 metres, and the -price is 5s.Screened cable for use with the couplermay be obtained for 6d. per coil, or 2s. 3d.for fifteen feet.

Cosmocord Pick-up

THE recently -introduced 5s. pick-upwhich was reviewed in our issue dated

December 28th last, has been tested witha number of amplifiers and records andfound to give every satisfaction. The armclamp which is provided enables it to bemounted on practically every type ofstandard acoustic gramophone arm, andno difficulties will be experienced fromrattle or looseness at this point. The lengthof lead provided may be twisted round thearm or passed through a hole in the motorboard for connection to the amplifier orreceiver, and it was not found necessaryin the majority of cases to screen this lead.With one or two receivers, however, it wasfound desirable to pass the lead through alength of metal braiding and to tie this tothe carrier arm, afterwards earthing themetal parts. With the majority of simplebroadcast receivers this will not be neces-sary unless the lead from the pick-up tothe receiver is of undue length. The weightof the pick-up is not sufficient to cause anyundue wear and it was found, in fact, thatit was lighter than certain acoustic instru-ments. The actual weight is slightly over4 ozs., but this may, of course, be reduced,if desired, by fitting a counterweight onthe rear of the carrier arm. The responsecurve is, to all intents and purposes, straightwhen used with a good amplifier, and it isnot essential to fit any form of tone com-pensator. The slight rise in the character-istic at the lower end of the scale compen-sates for the reduced recording strength ofthe lower frequencies, and thus produces awell-balanced bass response, whilst a dropwhich is not sharply accentuated at theupper- end of the scale helps to reduce tosome extent the surface noise or needlescratch. The volume produced by this neatlittle component is sufficient to enable it tobe satisfactorily employed with a two -valvebattery amplifier.

Two New Mullard ValvesTHE introduction of two new valves by

the Mullard Wireless Service Co., Ltd.,is a further contribution to the developmentof battery -operated receivers. TheP.M.22D, listed at 13s. 6d., is a high -sensitivity output pentode, and has beendesigned to take the fullestconsumption of anode cur-rent (the rated figure is lessthan half that of Class " B "or Q.P.P. valves).

The operating data, etc.,is given below :-

Operating DataFilament voltage

2.0 voltsFilament current

0.3 amp.Max. anode voltage

150 voltsMax. aux. grid voltage

150 voltsBase Connections

Standard B.V.A. 5 -pinbase.

The second valve whichwill be released with theP.M.22A is a battery double -

diode which will be known as the 2.D.2.The price of this new valve is 5s. 6d.

The most interesting feature of the2.D.2 is its indirectly -heated cathode whichpermits the application of delayed automaticvolume control, a refinement unobtainablewith the directly -heated type of batteryvalve in which diodes are embodied.

It was designed essentially for qualityreceivers and will be largely employed in

those sets usingthe P.M.22D intowhich it can bedirectly fed with -

o u t an inter-mediate stage.

Like the outputpentode, the 2.D.2i s exceptionallyeconomical, i t sfilament con-sumption being nomore then 0.09amp. The valveis fitted with thestandard B.V.A.5 -pin base.

Both theP.M.22D and the2.D.2 will begenerally releasedin a few weeks.

Ediswan PowerValveANEW power

output valvehas just been re-leased by theEdiswan Com-pany, and isshown o n th eleft. It isknown as theE.S.100 and, asmay be seen, is

of the high -voltage type designed for usein public address amplifiers or in high -quality home receivers in which the advan-tage of a very large output is to be takeninto account when receiving high qualitysignals at moderate volume. The questionof handling peak voltages has, of course,often been mentioned in these pages, andmany listeners prefer to employ a very largepower stage, although it is only operatedat low volume. In this way one may relyall the time upon obtaining the utmostperfection in response, irrespective of thecharaoter of the received signal. Thespecial 4 -pin base is fitted, and it is recom-mended that the valve be employed in a

(Continued on opposite page)

A new power output valveproduced by the Ediswan

Company.

This illustrationshows the neat appearance of the

new Ave, oscillator.

February 22nd, 1936 PRACTICAL AND AMATEUR WIRELESS747

FACTS AND FIGURES(Continued from opposite page)

vertical position, although if certain pre-cautions are taken it may be used when

v mounted horizontally. The valve becomesvery hot whilst working, and thus ampleventilation is required. The main char-acteristics are as follows :-

Filament volts .. . . 6Filament current . . 3 ampsMaximum anode voltage 1,000 voltsImpedance . . . . 1,750 ohmsAmplification factor . . 5Maximum dissipation . . 100 wattsOptimum load, approx. 7,000 ohmsA.C. power output; -ap-

prox. . . 30 wattsList Price, £10 10s.

Characteristie curves and full operatingdetails can be obtained from the RadioDivision, The Edison Swan Electric Co.,Ltd., 155, Charing Cross Road, London,W.C.2.

Avo OscillatorTHE illustration on page 746 shows the

oscillator which: has been producedby the Automatic Coil Winder Company,and which was reviewed in our issue datedJanuary 25th last. This particular instru-ment is now being tested in our laboratoriesand is being found very satisfactory inevery way. It is -very neat and compact,the actual dimensions being only bin: by4in. by 3in. The price is £5 10s. completewith shielded lead, valve, and self-containedH.T. and L.T. batteries.

RADIO CLUBSAND SOCIETIES

Club Reports should not exceed ,200 words in lengthand should be received First Post each. Mondaymorning for publication in the folldwing week's issue.

'THE RADIO, PHYSICAL AND TELEVISION SOCIETYE32133ERS of this society from all parts of London

ILL had the pleasure of hearing a lecture entitled" Advances in Receiver Technique," given by Messrs.L. A. Moron, B.Sc., A.C.G.I., and S. E. Marshall,M.E.N.G., at a meeting held on Friday, January 24th.

Mr. Marshall, in introducing the lecturer, indicatedsome of the problems encountered by the designersof modern receivers, and Mr. Moron outlined the waysin which these problems are being tackled. He -dealtluckily with the superhet circuit And its pitfalLs. -" Thechief fault of this circuit," he said, " is image inter-ference, which takes the form of whistles. Theremedy,"he explained, " is pre -detector selectivity." Theadvent of ganged condensers enabled many tunedcircuits to be used together, and the screen -grid valvesolved other problems.

A.V,C. was dealt with fully' and lucidly, while pro-blems, such as noise suppression, valve noises, and in-terference, were explained. Full particulars of thesociety may be obtained from the Hon. See., M. E.Arnold, 12, Nassau Road, Barnes, S.W.13:

THE SURREY RADIO CONTACT CLUB

THESurrey Radio Contact Club, which was- formed

last autumn, has met with a ready responsefrom enthusiastic amateurs.

Formed as it was with the definite object of bringingtogether those transmitters and listeners who sofrequently spoke and listened- to each other " onthe air " but rarely met in person, it was thought thatit would attract but few members. However, itspolicy of having -no " figureheads," having a com-mittee composed of three active transmitters andtwo " A.A. ' men, and of providing a programmekeeping the members in touch with the latest technicaladvances seems to be popular with- a large number ofamateurs.

Recent lecturers have been Mr. H. L. O'Heffermin,G5BY, a well-known transmitter, and also a memberof the club, who gave a talk on "Five -Metre Trans-mitters and Receivers." On December 10th Mr.P. G. A. H. Voigt, well-known P.A. and microphone

technician, visited the club, and at the last meeting -on January 14th, so that the members should havethe latest information possible, Mr. Edwards, of the362 Valve Co., lectured on the new R.F. pentoderecently introduced by his company.

Apart from these regular meetings, visits have beenmade to the Physical Society's Exhibition on January8th, and to the Ongar Radio Station on January 12th,and arrangements are being made for visits to theWestern Electric Co.'s theatre and to the Dellis HillResearch Station of the G.P.O. A suitable locationfor a club transmitter is being sought, and if possible aclub entry will take part in the A.R.R.L. D.X. Testnext March.

Visitors to the club are cordially welcomed, andshould communicate with the Secretary, Mr. E. C.Taylor, of No. 35, Grant Road, Addiscombe.

A CLUB FOR WYTHALL !IT is proposed to starta Radio Society in the Holly-

wood and Wythall District, nr. Birmingham,and interested readers in this district are invitedto write to I. Qulton (2AGV), " Jesmond-Dene,"Shawhurst Lane, Hollywood, Nr. Birmingham.

THE CROYDON RADIO SOCIETY.

MEMBERShad been waiting for just such an

opportunity as happened at a recent meetingin St. Peter's Hall, South Croydon. It was a Questionnight, and it was soon apparent that many teasingtopics had been saved for the occasion. For instance,Mr. J. T. Haynes, a new member, discussed twoaerials which did not "play the game." In otherwords, they disobeyed all the rules. The- first onebegan all wrong by fixing itself to a water pipe at -thetop of the house ; then it travelled downstairs to theset in the dining -room. Earthing of the receiver waseffected normally to a water pipe in the cellar, so thataerial and earth were attached to the same system.Mr. Haynes insisted that the aerial must be earthed asdescribed to get the best results. The second aerialalso contravened the tradition of the old school.Its lead-in shocked members by trailing along a walland ending at its pole with no insulator. Even so itgave better results than another aerial on the samepole properly insulated. Mr. Chubb then described hiscircuit, and how it was affected by substituting awire -wound resistance for a choke. Mr. P. G. A. H.Voigt's loud -speaker demonstration, postponed fromJanuary 21st, took place on Tuesday, February 18th,and many PRACTICAL AND AMATEUR WIRELESS readerswere able to attend the meeting-Hon. Pub. Sec.,E. L. Cumbers, Maycourt, Campden Road, S. Croydon.

OUR FREE CATALOGUE SERVICECOSSOR RADIOA VERY attractive book-( -I let has just _beenissued by A. C. Cossor,Ltd., which gives full de-tails of their very compre-hensive range of wirelessreceivers. There is a setfor every purpose andevery pocket. For example, there are the super-feirodyne models for battery or mains operation ;battery And A.C. mains superhets ; and a fine rangeof radiograms. The receivers range in price from £515s.to £14 14s., and the radiograms from £16 16s. to 55guineas. There are sixteen pages of information,together with full colour illustrations, printed on artpaper, and a complete specification of each model isgiven. A postcard addressed to A. C. Coseor, Ltd.,Publicity Dept., B29, Highbury Grove, London, N.5,will bring you a copy of this booklet, post free.

MARCONI VALVES AND RECEIVERSconiphone Company have recently Issued

catalogues, one dealing entirely with thevalves bearing the Marconi trade mark,escribing the various types of Marconi-rs. The valve catalogue gives, in,omplete guide to each valve, with allabulated, a comparative table of Mar-

aud various technical details, suchconnections, various A.V.C. circuits

To save readers trouble, we undertake to send oncata/ogues of any of our advertisers. Merely state, ona postcard, the names of the firms from whom. yourequire catalogues, and address it to " Catalogue,"PRACTICAL AND AMATEUR WhitELESS, Geo. Newnes,Ltd., 8-11, Southampton St., Strand, London, W.0.2.Where advertisers make a charge, or require postage,this should be enclosed with applications for catalogues.No other correspondence whatsoever should be enclosed.

push-pull arrangements,and so on. The receivercatalogue is fully illus-trated and describes all thepresent types of receivers,which range from a£7 12s. 6d:battery receiverto a fifty -two -guinea -nine -

valve automatic radio-gram. The list also includes details of cabinet loud-speakers and the new Marconiphone gramophonepick-up. The lists may be obtained free from RadioHouse, Tottenham Court Road, London, W.1., ordirect from this office.

FULL 0' POWER BATTERIES,ULL particulars of the complete range of these

batteries suitable for battery set users are givenin a compact little booklet (No. 667), issued by SiemensElectric Lamps and Supplies, Ltd., 38 and 39, UpperThames Street, London, E.C.4. In the single capacitytype there are two series, the " Cadet," which issuitable for modest sets requiring from 6 to 7 milliamps.of H.T. current, and the Standard," designed for themore ambitious receiver taking up to 10 milliamps.Where space and weight are of little importance,there is the power and triple capacity series, whichis recommended for a discharge rate of 10 to 20milliamps. There is also the super radio batteryintended for use where a discharge rate of from 15 to30 milliamps is required.

ELECTRADIXYour voice amplified from yourradio set to loudspeaker.

5/ -.BUTTON MICRO,PHONES for all purposes. -Usually sold at 3/6.Our price has alwaysbeen 1/- Wo have 77e

supplied thousands.N.W. No. 11 TABLE MIKE.This is a splendid Microphone forspeech and music. The bakelitecase, containing a- 21n. mike andtransformer, is on a brehzepedestal, detachable for sling.Switch and plug fitted. Unrivalled

for quality and price, 15/, Other types: Lesdix No.10B Pedestal, 10in. high, 12/6; Lesdix Superior No.12B13 Ring, 14in, Pedestal, 16/6. Hand Mikes in 2in.case, No. 11, at 516; Superior- type No. 11A, 7:6.Eilsel public address and band Mike (Reiss principle),55]-. Ask for Illustrated MikeList of 25 models. Our famousPARTS for making your own mike.Carbon Granules in glass capsuleGrade 1, 8d.; No. 2. 1/-; No. 3,fine, 1/6; No. 4, extra fine, 2-/-;Black Blocks, 44.; Diaphragms,6d.; Button in Wu. hard woodcase, with 2in. mica, diaph. 2/6;Ditto, mounted on pedestal, '3 /6.AMPLIFIERS. We can supply-from stock 3, 6, or 10 watt mainsor Battery Amplifiers in portableor chassis form at- .lowest prices.Special A.C. or D.C. Public Addressor Dance Band Portable with mikeand speaker.HOME RECORDING IS THELATEST HOBBY. Home record-ing on your Gramo. can be done by

N.W. No. 11.anyone with a gramophone. Complete sets, with acces-sories, in carton. De Luxe, 21/-; No. 2 Mivoire, 12/6;Junior, 7/6. For Electric Recording Electric MotorTurntables, 25/-. Tracker Record A: Carriers No. _2C.M. Screw -thread Traverse, 7/6; Type F, CentralSpiral Drive, 4/6. Recording, Pick-ups: Tyne K..1216;

Jewel cutter, mounted. diamond,7/6. DYNAMOS. CHARG-ING OR- LIGHTING. 240watt Enclosed Dynamo, 12.'20v.12 amps... Ball Bearings. YeePulley, Type C.SWITCHBOARD (Marinetype),:with Ammeter. nia ximuniand minimum AutoCut -mit

- main Switch and Fees, FieldRegulator, etc., 50/-.

DOUBLE CURRENT GENERATORS, B.C., 600volts, 100 ma., and 6 volts 3 amps., 40/,CRYSTAL SETS are still popular for perfect, quiet.personal reception.. All -Wave Permanent DetectorSet, 5/6.HEADPHONES tor' short-wave work, 2,000 cr4,000 ohms, 4/6. - -

Send for New Illus. Bargain List " N," Free.ELECTRADIX RADIOS.

218, UPPER THAMES ST., LONDON, E.C.4.tommoammomanan'Phone: Central 4611'

Everything Radio supplied on the lowest terms, Sendlist of requirements for quotation by return. Prompt 4delivery.Cash and C.O.D. Orders Despatched try Refuse of Po.: 4

W.B. -STENTORIAN36.8

Cash Price £2 f 2 0. 42/6 with order and 11monthly payments et 4 - 4

36.3Cash Price £1 2 6.or 2/6 with order ..:

11 monthly paym,of 3 /ROLA L.S. U.,it; 4supplied on similar 4

terms.

VALVES (every type supplied)6 S.G., Det. and Power, any make. Cash r!r £1.5.0, or 5/- with order and 5 monthly paynw: e

of 4/6. ALL CARRIAGE PAID 4

NATIONATHORN nEstd. 1925 TH.E- L 1977

RADIO SUPPLYCOMPANT-i..

II,OAT LANE-NOEttE STREETLONDON,E.C.2

BRITISH SHORT WAVE LEAGUEa British organisation catering exclusively for the Short. Wavelistener through. the medium of its own publication, the

"BRITISH S W L REVIEW"a bookleffull of interesting data for the D.Xer,on Broadcasting, Amateur and commercial stations, tem.of station addresses, signals and slogans, new Qs1.,.,collect them, Postal indentification Service, SWL, ,

correspondence exchange Bureau, etc., etc.BUY YOUR COPY NOW and JOIN the B.S.W.L. l.9^o 6D.or old. by Post from the publishers

SHORT WAVE LEAGUE - - Ridgewel. Esser.

PATENTS AND TRADEMARKS.yons PATENT AGENCY, LTD. (Director: D. T.

King. Regd. Patent Agent G.B.,and Canada). Advice, Handbook and Consultations free.50 years' refs. -146a, Queen Victoria Street, E.0.4.

'Phone : City 6161.

\ 748 PRACTICAL AND AMATEUR Wilt:EliS February 22nd, 1936

Practical and Amateur WirelessBLUEPRINT SERVICE

PRACTICAL WIRELESS.STRAIGHT SETS. Battery Operated

One -Valve : Blueprints, is. each.Date of Issue. No. of

Blueprint.All -Wave Unipen (pentode) . 14.10.33 PW31ATwo -Valve : Blueprints, is. each.Four -range Super Mag. Two (D,

Pen) .. 11.8.34 PW36DThree -valve : Blueprints, is. each.Selectone Battery Three (D, 2 LF

(trans.)) .. PW10Alpha Q.P.P. Three (D,Q.P.P.).. 25.3- .33 PW14Ferrocart Q.P.P. Hi-Mag Three(SG, D, Q.P.P.).. . .. 25.3.33 PW15Sixty -Shilling Three (D, 2 LF(RC. & trans.)) .. 2.12.33 P1V34ALeader Three (SG, D, Pow.) .. PW35Summit Three (HF Pen, D, Pen) 18.8.34 PW37All -Pentode Three (HF Pen, D(pen), Pen) .. 22.0.34 PW30Hall -Mark Three (k, D, Pow.) PW41Hall -Mark Cadet (D, LF, Pen(R.C.)) 23.3.35 PW48F. J. Camm's Silver Souvenir (HFPen, D (pen), Pen) (All -waveThree) .. 13.4.35 PW49Genet Midget (D, 2 LF (trans)) .. June '35 PM1Cameo Midget Three (D, 2 LF(trans)) 8.6.35 PW511936 Sonotone Three -Four (HFPen, HF Pen, Westector,Pen) .. .. 17.8,35

Battery All -wave Three (l, 2 LF(ILC.)) 31.8.35

The Monitor 8.2.36Four -valve Blueprints, is. each.Fury Four (2 SG, D, Pen) .. -Beta-UnNersal Four (SG, D, LF,Cl. B).. 15.4.33Nucleon Class B Four (SG, D

(SG), LF, Cl. B) .. 6.1.34Fury Four Super (SG, SG, *D, Pen)Battery -Hall -Mark 4 (HF Pen, D,

Push Pull) . 2.2.35F. J. Camm's Superformer (SG,

SG, D, Pen) .. 12.10.33Mains Operated

Two -valve : Blueprints, is. each.A.C. Twin (D (pen), Pen).. .. 22.4.33A.CAD.C. Two ($G, Power).. 7,10.33Selection A.C. Radiogram Two

(D, Pow.) 20.4.33Three -valve ; Blueprints, ls. each.Double -Diode -Triode Three (HF

Pen, D.D.T., Pen) .. 10.6.33D.C. Ace (SG, D, Pen) .. 15.7.33A.C. Three (SG, D, Pen) .. 16.9.33A.C. Leader (HF Pen, D, Power) 7.4.34D.C. Premier (HF Pen, D, Pen) 31.3.34Ubique (HF Pen, D (Pen), Pen). .28.7.34Armada Mains Three (HF Pen, D,

Pen) .. _ .. 18.8.34F. I, Camm's A.C. All -Wave Silver

Souvenir Three (HF Pen, D,Pen) . - .. 11.5.35Allwave " A.C. Three (D, 2LF(R0)) .. 17.8.35

A.C. 1936 Sonotone (HF Pen, HFPen, Westector, Pen) .. .. 31.8.35

Four -valve : Blueprints, is. each.A.C. Fury Four (SG, SG, D, Pen) 25.2.33A.C. Fury Four Super (SG, SG, D,

Pen) ..A.C. Hall -Mark (HF Pen, D, Push-

Pull) .. . .'Universal Hall -Mark Pen, D,

9.2.35

PW53

PW55P1V61

PW11

PW17

PW34BPW34C

PW46

PW57

PW18PW31

PW19

P723PW25PW29

PW35CPW35BPW36A

PW38

PW50

PW54

PW56

PW20

PW34D

PW45

PW47SUPERHETS.

Battery Sets: Blueprints, is. each.£5 Superhet (Three valve) . - PW40F. J. Canom's 2 -valve superhet

(two valve) .. .. 13.7.35 PW52F. J. Camm's £4 Superhet 4 .. 16.11.35 PW5E3Mains Sets : Blueprints, 1s. each.A.C. £5 Superhet (three. valve) .. PW43D.C. £5 Superhet (three valve) .. 1.12.34 PW42Universal- £5 Superhet (three

valve) .. .. 15.12.34 PW44F. S. Camm's A.C. £4 Superhet 4 7.12.35 PW59F. J. Camm's Universal £4 Super -

het 4 .. 11.1.30 PW60SHORT-WAVE SETS.

Two -valve : Blueprints, is. each.Midget Short-wave Two (D, Pen) 15.9.31 PW38AThree -valve : Blueprints, is. each.Experimenter's Short-wave Three

(SG, D, Power) .. 23.9.33 PW30APORTABLES.

Three -valve : Blueprints, Is. each.Atom Lightweight Portable (SG,

D, Pen) 2,6.34 PW36Four -valve : Blueprints, is. each.Featherweight Portable Four (SG,

D, LF, Cl. B) PW12

MISCELLANEOUS.S.W. Converter -Adapter (1 valve) 23.2.35 PW48A

AMATEUR WIRELESS AND WIRELESS MAGAZINECRYSTAL SETS.

Blueprints, 6d. each.Four -station Crystal Set . 1934 Crystal Set ..150 -mile. Crystal Set .. -

STRAIGHT SETS. Battery Operated.One -valve : Blueprints, is. each.B.B.C. Special One-valverTwenty -station Loud -speaker

One-valver (Class B)

AW427AW444AW450

AW387

AW449

Two -valve : Blueprints, 1s..each.Melody Ranger Two (D, Trans) - AW388Full -volume Two (SG, Det, Pen) ,-- AW392Iron -core Two (D, Trans) - AW395Iron -core Two (D, Q.P.P.) _ 12.8.33 A'W396B.B.C. National Two with Lucerne

Coil (D, Trans) . , - AW377ABig -power Melody Two withLucerne Coil (SG, Trans) . - AW338ALucerne Minor (D, Pen) .. - AW426

Three -valve : Blueprints, Is. each.P.T.P. Three (Pentode -Triode -Pentode .. _ _ _ jure '30 w31389Class -B Three (D, Trans, Class B) 22.4.33 AW886New Britain's Favourite Three

(D, Trans, Class B) .. .. 15.7.33 AW394Home-Bulit Coil Three (SG, D,

Trans) .. .. .. .. 14.10.33 AW404Fan and Family Three (D, Trans,Class B) .. .. .. - 25.11.33. AW410£5 5s. S.G.3 (SG, 11, Trans) _ 2.12.33 AW4/21934 Ether Searcher: BaseboardModel (SG, D, Pen) . .. 20.1.34 AW4171934 Ether Searcher : *ChassisModel (SG, D, Pen) .. .. - AW419Lucerne Ranger (SG, D, Trans) .. - AW422

Cossor Melody Maker with LucerneCoils

'. .. - AW423

P.W.H. Mascot with Lucerne Coils(D, RC, Trans) .. .. . W. - A337AMuliard Master Three with.Lucerne Coils . _ .. - AW424£5 5s. Three : De *Luxe Version(SG, D, Trans) .. . , . 19.5.31 AW435

Lucerne Straight Three (D, RC,Trans) .. _ - .. - AW437

All Britain Three (IF Pen, III, Pen) - AW448" Wirgless League" Three (HFPen, D. Pen) .. .. .. 3.1.34 AW451

Transportable Three (SG, D, Pen) - WM271£6 6s. Radiogram (D, RC, Trans) Apr. '33 WM318Simple tune Three (SG, D, Pen) .. June, '33 WM327C.B. Three (D, LF, Class B) .. . - WM333Economy -pentode Three (SG, D,

Pen) .. .. .. .. Oct. '33 WM337" W.M." 1934 Standard Three(SG, D, Pen) _ _ _ - WM351£3 3s. Three (SG, D, Trans) .. Mar. '34 W31354Iron -core Band-pass Three (SG, D,QP21) - .. .. .. June '34 WM3621935 £6 6s. Battery Three (SG, D,Pen) .. - .. .. - WM371Graduating to a Low -frequencyStage (D, 2LF) .. .. .. - WM378

Four -valve : Blueprints, is. 6d. each.65/- Four (SG, D, RC, Trans) . - AW370" A.W." Ideal four (2SG, D, Pen) 16.9.33 AW4022 H.F. Four (280, D, Pen) .. AW421Crusaders' A.V.C. 4 (2HF, D,

QP21) .. 18.8.34 AW445(Pentode and Class'B Outputs forabove: blueprints 6d. each) 25.8.34 AW445AQuadradyne SG, D, Pen) .. - W31273Calibrator (SO, D, RC, Trans) .. - WM300Table Quad (SG, D, RC, Trans). - W31303Calibrator de Luxe (SG, D, Rd,Trans) .. . W3.1316Self-contained Four (SG,Class -B) Aug. '33 W711331Lucerne Straight Four (SG, D, LF,Trans) . - WM350£5 5s. Battery Four (ID', D,2LF) .. Feb. '35 W31381The H.K. Four Mar. '35 WM384

Five -valve : Blueprints, is. 6d. each.Super -quality Five (2HF, D, RC,

Trans) .. . May '33New Class -B Five. (2SG, D, LF,

Class B) Nov. '33Class -B Quadradyne (2SG, D, LF,

Class B) . Dee. '331935 Super Five (Battery* Super-

het) .. . -

W3/320

W31340

WM344

WM379

These blueprints are full size. Copies of appro.priate issues containing descriptions of these setscan in most cases be obtained as follows:-" Practical Wireless "at 4d., " Amateur Wireless "at 4d., " Practical Mechanics " at Nd., and" Wireless Magazine" at 113, postpaid. Indexletters " P.W.' refer to " Practical Wireless " sets,P.M." to " Practical Mechanics "sets, " A.W."refer to " Amateur Wirelers " sets, and "W.M."to " Wireless Magazine " sets. Send (preferably)a postal order (stamps over sixpence unacceptable)to " Practical and Amateur Wireless " BlueprintDept., Geo. Newnes, Ltd., 8-11, SouthamptonStreet, Strand, W.C.2.

Mains Operated.Two -valve : Blueprints, is. each.Consolectrie Two (D, Pen) A.C..

.. 23.9.33 AW403Economy A.C. Two (D, Trans)A.C. - WM28tiThree -valve : Blueprints, is. each.

Home -lover's New All -electricThree (SG, D, Trans) A.C. - AW383S.G. Three (SG, D, Pen) A.C. .. 3.6.33 AW390A.C. Triodyne (SG, D, Pen) A.C. 19.8.33 AW399Pentaquester (HF, Pen, D,Pen) A.C. _ 23.6.34 AW439D.C. Calibrator (So, D, Push-pullPen). D.C. July'33 W51328Simplicity A.C. Radiogram (SG,D, Pen) A.C. Oct. '33 WM338Six -guinea A.C./D.C. Three (HF,Pen, D, Trans) A.C./D.C.

W.11304Mantovani A.C. Three (H.F, Pen,D, Pen) A.C. Nov.:34 .n1374

Four -valve : Blueprints, is. 6d. each.A.C./D.C. Straight A.V.C.4 (2HF, D, Pen) A.C./D.C... .. 8.9.34 AW446A.C. Quadradyne (2 SG, D, Trans)

. . . - WM279All Metal Four (2 SG, D, Pen) .. July '33 WM329" W.M." A.C./D.C. Super Four Feb. '35 WM382Harris Jubilee Radiogram .. May '35 WM386

SUPERHETS.Battery Sets. Blueprints, ls. 6d. each." W.M." Stenode - WM373Modern Super Senior .. - WM375Mains Sets . Blueprints, is. 6d. each.1934 A.C. Century Super A.C. .. 10.3.34Seventy-seven Super A.C. - -` W.M." D.C. Super D.C. ..May '33Merrymaker Super A.C. . Dec. '33Heptode Super Three, A.C. .. May '34" W.M." Radiogram Super A.C..." W.31." Stenode, A.C. .. Sep. '341935 A.C. Stenode.. Apt. '35

PORTABLES.Four -valve : Blueprints, 1s. 6d. each.Midget Class -B Portable (SG, D,

L.F, Class B) . . 20.5.33 AW389Holiday Portable (SG, ID, LI',Class B) . _ 1.7.33 AW393Family Portable (HF, *D, RC,Trans) . . 22.0.34 AW417Town and COuntry Four (SG, D, "RC, Trans) .. WM282Two H.F. Portable (2 k,QP21) - . . . June '34 W31363Tyers Portable (SG, D, 2*Trans) Aug. '34 WM367

SHORT-WAVERS-Battery Operated.One -valve : Blueprints, is. each.S.W. One -valve converter (price Gd.) - AW320S.W. One -valve for America .. - AW429Roma Short -waver - A11-452Two -valve : Blueprints, is. each.Home-made Coil TWO (D, Pen) 14.7.84 AW440Three -valve: Blueprints, is. each.World -ranger Short-wave 3 (D,RC, Trans) .. - AW355Experimenter's 5 -metre *Set (5,

Trans, Super-regen) 30.6.34 AW438Experimenter's Short -waver Jun.19, '35 AW463Short-wave Adapter .. Dec. 1, '34 AW456Superhet, Converter .. Dec.1, '34 AW457The Carrier Short -waver .. July '35 WM390Four -valve : Blueprints, is. 6d. each.A.W. Short-wave World Beater

(HF Pen, D, RC, Trans) - - 2.6.34 A.W436Empire Short -waver (SG, D, RC,Trans) .. - 1E1,1313Standard Four -valve Short-waver Mar. '35 WM383

AW425WM305W111321WM345WM359WM306W.111.370WM385

Mains Operated.Two -valve : Slueprints, 1s, each.Two -valve -Mains Short-waver (D,

Pen) A.C. . AW453" W.M." Band -spread Short-waver(D. Pen) A.C./D.C. .. ...Attg '34 W31368" W.M." Long -wave Converter .. W31380Three -valve : Blueprints, is. each.Emigrator (SG, D, Pen), A.C. -Four -valve : Blueprints, Is. 6d. each.Gold Coaster (SG, D, RC, Trans)

MISCELLANEOUS.Enthusiasts Power Amplifier (1/G) JNewstyle Short-wave Adaptor (1/-) JTrickle Charger .. Ja)

is illustrationearance of the

scillator.