three valve receivers

No. ro4

THREE VALvE

RECEIVERSComprehensioe instructions for

building 5 three oaloe sels

AN RF GRAM PLAYER

A BATTERY.OPEMTED RECEIVER

A PUSH.PULL RECEIVER

A SUPERHEI'ERODYNE RECEIVER,

AN ALL-WAVE RECEIVER

*

B E R N A R D S R A ' D I O M A N U A L S. . ; _ t

THREE VALVER E C E I V E R S

Comprehensive Instructions

For Building 5 Three V ilve^Sels

L O N D O NBE,RNARDS (Publishers) LTD.

BERNARDS RADIO MANUALS i',Io. 104

General Editor: W. J. MAY

F irst Published 1952Reprintetl 1953

" 1954

" 1955" 1956

,, 195?,, 19b8

,, 1960.. 1961

,, 196s

Printed by V. Cooper & Partners Ltd. Fl i tcrof t Street , W'C'2 ' , - for

b" i r " rar ipurt l isher i ) l . td. . The Grampians, western Gate ' London' W'6

Ir

C O N T E N T S

I An RF Gram Player ..

2 A Battery-operated Receiver.

1 A Push-pull Receiver ..

4 A SuperheterodYne Receiver.

5 An All-wave Receiver.

Page5

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THREE VALVE RECETVERS

AN RF GRAM PLAYER

Gramophonc record enthusiasts will find this three valve unit interestingfor several reasons. Firstly, the normal record player has either to bebuilt into the existing radio equipment or else situated close by it. Thisis not always convenient and often looks unsightly; further the playermayhaveto be specially set up for operating, and dismantled and packedaway at the end of the session. This unit requires no direct connectionwith the radio receiver; it may be placed conveniently at the side ofan armchair by the fue, from where it will operate a re@iver situatedin any part of the room. It does not matter whether the main receiverhas pick-up terminals or sockets provided, since the recordings arepicked up by the receiver in the same way as a normal broadcast pro-gramme. A glance at the circuit drawn in Fig. I will show how theunit functions. Vl is simply a pre-amplifier for the miniature pick-upand is necessary on account of the very small output provided by suchpick-ups. V2, which is a pentagrid or heptode, combines the functionsof modulator and oscillator. The frequency of this R.F. signal is governedby Ll-2 and the output is fed via C8-9 to the radiator or aerial. Fromthe foregoing it will be seen that the unit is in reality a miniature lowpower transmitter. No transmitting licence is required because of itsexceptionally low power, in fact its radiation properties can be calculatedin feet. The aerial will consist of a few feet of flex, which may be laidunder the rug or carpet. Its precise length will depend on the physicaldistance between receiver and player and must be determined byexperiment.

Returning to the circuit, V3 is a conventional rectifier used in a half-wave circuit, no chokes being used in the smoothing circuit since, withthe small current drain resistance capacity, smoothing is both practicaland adequate.

The unit is designed for AC operation; but, in order to reduce costas far as is compatible with high performance, AC/DC technique hasbeen adopted for the power supply. This means that one side of themains will be connected to chassis and gram. motor. To avoid thepossibility of a shock the neon Nl is incorporated, and an earth con-nection is essential for it to function. An earth connection may be takenfrom the third pin of the mains plug. If the mains socket is not of thethree-pin type an alternative earth must be provided, though all mainssockets should be of the three-pin pattern, otherwise no metallic appliancecan be connected with safety. When connected and switched on it willbe found that with the mains connected one way round the neon willglow, whereas with the connections reversed the bulb will remain dead.It is this latter condition which is correct; no attempt should be madeto use the player with the neon glowing, since this indicates the chassisis live.

Any form of construction can be used, but it is suggested that thelayout shown in Fig. 2 will be found convenient and satisfactory.

On completion the ',rriring should be thorougJrly checked. the valves

THREE VALVE RECEIVERS

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plugged in and the unit srvitched on. For preliminary tests the aeriaroutput of the player shourd be connected oi placed "iosr to the aeriarsocket of the receiver prolrer. After both thi player and the receiverhave warmed up, the receiver should be tuned to a quiet part of thebroadcast band between 500 and 600 metres. with the gain of ihe receiverturned well up the oscillator trimmer cil on the playerihould be adjusteduntil the carrier is heard in the receiver's loud

-speaker. This cariier is

easily identified since all mush and background noise *ill disappear irrthc receiver duc to the AVC action, in the same way as when a lozalstation is tuned in rvhile no actual music or speech is bcing transmitted.9.n* u suitable setting has been found Cl I may be sealed with wax.The volume control vRr should be used in conjlnction with the mail.rreceiver volume control so that a satisfactory icrcl rvithout distortionmay be obtained.

.To cater for the less experienced constructor a practical point-to_pointwiring diagram is provided (Fig. 3).

THRIJE VALVE RECEIVERS '9

COMPONENTS LIST FIG. I

Cl 25 n.rfd l2v. ElectrolyticC24 0.1 mfd oaperC3 0'05 mfu papera5 47 pfd micaC6-7 16 mfd 350v. ElectrolyticC8 10 pfd micaC9 2000 pfd micaC10-13 0.01 nrfd paperCll 450 pfd padderC12 200 pfd micaR l I M OR2 3 .9 KOR3 100 KoR 4 1 . 5 K OR5 l0 KOR6 5.6 KOR7 10 KA 3 watt

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470 Kr)150 O 2 watt0'5 MO potentiometerPick-up transformerFilament transformer

Pri.200-220-240Sec. 6.3v. 3 amp

P.O.l WeariteD.P.D.T. toggle switchI n t e r n a t i o n a l v a l v e

holders6J5GT Brimar6A8-GT B;:imar6X5-GT BlimarDecca high fidelity pick-

up or sinri larNeon lamp G.E.C. Type

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A BATTERY OPERATED RECEIVERFor listeners situated some distance from a B.B.C. transmitter who

for various reasons are compelled to use a battery-operated receiver,the design shown in Fig. 4 is particularly suitable. The circuit is perfectlystraightfbrward and is representative of a type of circuit popular as farback as 1929 when everyone was building kit sets designed by the technicalstaffs of the leading valve manufacturers. From this it should not bethought that the circuit is in any way out of date; on the contrary,variations of this design are found in every current T.R.F. design.Standard valves with two-volt filaments have been retained because,as extensive correspondence shows, many amateur constructors havesuch valves by them and naturally wish to use them when possible.They may stil.l be purchased, as they are freely available. The circuitconsists of a tuned RF stage coupled to a leaky-grid detector. Thisform of detection is more sensitive than the plate or anode-bend detectorand, since regeneration is used, a diode or infinite impedance detector isimpracticable. Transformer coupling is used to couple the detector tothe output pentode because the stage gein is much higher than thatobtainable with R.C. coupling. The audio transformer is parallel-fedfrom the detector and since no DC flows through the primary windingone of the midget mu-metal core components can be used if desired.To avoid the use of a separate grid bias battery the necessary grid voltagefor Vl and V3 is provided automatically by the resistor network R6-7.

Variable selectivity is effected by Cl in the aerial circuit. In use itwill be found that rhe higher the capacity the louder the signals; at thesame time the llining tvill tend to be flat and the more powerful trans-missions may overlap. Should this occur the setting of Cl should bereduced when, though the volume level may drop a little, the tuningwill be noticeably sharper. Usually any drop in volume can be com-pensated by advancing the regeneration control C7. It is suggested thatconstruction should be carried out on a foil-covered baseboard with awooden panel. Suitable sizes are l}'t x 9" for the baseboard and 10" x 6',for the oanel.

After construction the only adjustment necessary is that of the trimmersacross C2, C8. A signal, preferably weak, is tuned in towards the highlrequency end on the tuning condenser-that is with the vanes almostdisengaged. While such a signal is being received adjust C3, C9 fornaximunr strength, slowly rocking the main tuning condenser over thesignal at the same time. Once this simple operation has been carriedout no further adjustment is required.

Figs. 4 and 5 show both theoretical and practical wiring diagrams forthe recelver,


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COMPONENTS LIST FIG. 4

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C1-7 300 pfiJ solid dielectricvar iab ie

c2-8 2 x 500 pfd gang con-dc nser

47 KO180 cl420 clvP2B IPM2HL I MullardPM22A )B7 valve-holderB5 valve-holder84 valve-holderDPST toggle switchHF chokeLoudspeaker with trirns-

f o r m e r P r i . l o a d20,000 c)

PA2 WearitePHF2 Weariic

C3-9 50 p-li trimmenC4 500 pfd micaC5-6 0.1 mfd paperClO 100 pfd micaCll-12 300 pfd micaCl3 0.25 mfd paperCl4 0.005 mfd paperCl5 25 mfd l2v. ElectrolyticR I I M OR2 82 KOR 3 I K OR4 2 .2 MA

R5R6R7VIv2v3IIIs lRFCt

Ll-2L34

A PUSH-PULL RECEIVER

The receiver shown in Figs. 6 and 7 is not intended for long_rangereceptiorr, but rather for local station listening and gramophone-recoicreproduction. Pcrhaps the most unusual aspeit of this pariicular dcsignis that while only three valves are employed, the design provides firpush-pull output and the output stage is capable of deliviring over eightwir,tts of audio for a very modest input. This is accomplishid by uslngdouble triode valves throughout. one harf of vl is used as a lealy griidetector while the other harf is working as a conventionar cliss Aamplifier. V2 is another doubre triode but with somewhat differentcharacteristics to those of vl. This valve has its two sections strappedin parallel and is used as a driver for v3. The driver stage is transformer-coupled to V3 and when thia component is purchased ii should be madeclear that it is required to match a parallel-connected 6N7 to a 6N7Class-B amplificr. Every care must be taken to ensure that an outputtransfornrer of the corrcct ratio is chosen, otherwise severe distortionand numerous otirer troubres are likely to arise. The required pri*uivimpedance is 80000 anode-to-anode; the ratio will, of iourr.,'A.p.nion the speech coil impedance. Should there be any doubt on tili;;;in;the speaker manufacturer should be consulted. Thi ratio is given by G./.;^^formula R :V $ where R is the ratio and S the speech coil impedance.A popular speech coil impedance is l5o and for such a coil the requiredratio is 23 : I since ̂ : ,/19 : \/-533: 23 approx. Construction ofthe receiver is sinrplr ' : end the'wir inc can be fol loweO lrom frf ; Z. t_l

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and L2 ars wound on a ;" dia. x 2" forrner, Ll consists of 120 turnsof 36 swg enantclled., tapp.:d at 75 turns from the start. The start of thewinding is tl-re grid en,l rrrd the finish the earrh end. L2 is wound overthe earth end of Ll rnaintaining the same winding direct ion 40 turns ofsimilar wire are nccessary. Tlte two windings may be separated by alayer of insulat ion tape. The start of L2 is taken to C3/RFC and thecnd to Vl anodc. Fig. 6 aiso shows detai ls of the coi l construction. Oncompletion, should the regcneration control C3 prove inoperative, itis likely that the connections to L2 have beconre reversed. This will,ofcourse, provide degeneration rvhich for this application is undesirable.Changing over the connections to L2 provides the remedy.


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l1 t ic0 01 rn f d 1000v . paper0'5 NtO potentionreter2.2 N4!t100 Kf)47 KO82 r(()22 KO3 . 3 K O

l K O9 KQ 15 wattDRM3 BrimarSee Text15 henries 120 rnfDPST toggle swi(SPDT toggle switc'rH.F. chokeSee TextPush-pull output trans-

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A SUPERHETERODYNE RECEIVERThe receiver shown in Fig. E is a sr-rperheterodyne and differs from all

the other receivers in thls book. Such receivers are necessarily morecomplex than TRF or st fa ight designs: but the extra pat icnce involved intheir construct ion is rvel l uorth r , ,h i le. The standard of select iv i ty andsensitivity cannot be approached by a straight receiver using a similarnumber of stages. Much has been written about the improved quality ofthe straight receivcr over the superhcterodyne, but with station separationf ixed at 9 kc 's on the nrediunr uu' , ,e bani l . nei ther the argument nor theinrproved qual i t l ' cxrsts

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THREE VALVE RECETVERS I7

Quite a number ofconstructors feel a trifle apprehensive about tacklingsuperheterodyne construction because of alignment problems and becausEthey do not understand the way in which the system operates.

It is not possible to examine the working of thi superheterodynecompletely in a manual of this description; but it will be sufficient ifthe c-onstructor grasps the main essentials. Referring to the circuit,Fig. 8, the signal is tuned by C5 and appears in the normal ,ray on giof vl and is amplified. contained in the same valve is an RF oicillatorformed by L3-4 and tuned by C7. This oscillator provides a similarsignal to the broadcast station but at a different wave length and is mixedelectronically with the incoming signal in vt. The result of this mixineprocess is that at the output of Vl the signal is present not only at itioriginal frequency, but also at the sum of the signil plus that of the localoscillator and at the difference between that of the local oscillator andthe signal' For practical purposes it is this latter combination that is ofinterest. Now the condenser C5 which tunes the signal is ganged to thelocal oscillator tuning condenser c7 so that as oni is variedso is theother, and the difference in frequency between the two remains constant.The difference between the two in this case is 465 kc's.. From this it will be seen that, no matter what the frequency of the

incoming signal, the local oscillator will mix another signal i65 kc'saway with it, and the signal will always appear at the output of Vl at465 kc's. This difference between the two frequencies mixed in Vl iscalled the intermediate or IF frequency, and thi transformers Tl andT2 are designed to work at that frequency. y2 is the I.F. valve: it is anormal RF amplifier working, due to Tl and T2 at the IF frequency of46-5 kc's. The amplified IF signal is rectified by the diode section of V2.After rectification the signal is passed to v3 and amplified in the normalway. It has probably been noticed that there are two diodes in V2. Oneis used for detection, as explained; the other rectifies the IF carrier anduses the resultant voltage to bias vl and v2 to compensate for fluctuatingsignal strength. This application is termed A.V.C. or automatic volumecontrol. The receiver is designed for AC/DC operation. constructionis-simple. No particular tuning dial is specified since there are a numberof excellent dials on the market. A nebn safety circuit has been incor-porated comprising Nl.Rl6 (its action is fully explained on page 5).On completion the receiver should be switched on and allowed io *arn.,up for five minutes, having made sure that the correct mains voltagetapping is being used. A weak signal should now be tuned in at theh.igh frequency end of the dial (between 200 and 250 metres). The signalshould be identified and by adjustment of Cg the pointer of the tuiingdial should be brought into line with this station position on the dial.Now adjust C6 for maximum volume. Following this, tune to the B.B.C.Third Programme at the low frequency end ofthe dial, or some otherknown.station, and adjust the position of the dial poinier by means ofthe padder C9. It will now be necessary to return to the original settingand repeat the whole process several times. when this has been comoletedtune. in any weak signal and peak ail the IF transformer trimmeis formaximum output. No further adjustment should be necessary.


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match speech coil to3000 O load

Neon lamp anrl holderG.E.C. Type ii

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iiz'_ii' )0.01 mfd paperC3-4-13-21 0.1 mfd paperC5-7 2 x 500 pfd gangC6-8 47 pfd trimmerC9 470 pfd padderClO 47 pfd micaCll 220 pfd micaCl4-15-16 100 pfd micaCl8 25 mfd 25v. Electro-

lyticCl9-20 32 mfd 350v. Electro-

lyt icRl 220 KOR2 2't KAR3 18 KOR4 220 0R5 22 KAR6-10 47 KOR7-8 I MoR9 330 f)Rll 0.5 MO potentiometerR l2 56 KO

AN ALL-WAVE RECEIVER

Short-wave enthusiasts will find the circuit of Fig. l0 particularlyinteresting. As every short-wave listener knows, the success o1 a receivercovering the short-wave bands depends to a large extent on the smoothworking of the regeneration. If this is erratic or .. ploppy', the receivercannot be operated at maximum sensitivity and many stations will bequite inaudible. With this particular receiver a separate valve (V3) isused for regeneration working quite independently of the signal detector(Vl) and this refinement, coupled with the use of high efficiency all_glassvalves, provides a combination of outstanding merit. The receiver coversfrom 400 kc's to 10 Mc's and is designed for AC operation, but foreconomy AC/DC technique is used. The valve heaters are suppliedfrom a filament transformer (T2) and rectification of the HT supply iseffected by a selenium rectifier which avoids costly valve replacements.A suggested laycut is shown in Fig. ll, which, together with Figs. l0and 12, will enable the receiver to be constructed without difficultv. Theonly point requiring detailed explanaticn is the construction of thl c<ril".

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which are also shown in Fig. I l. It will be se€n that Ll is wound by itsellon one former andL2-34 are wound separately on another, One of thocoils, L5, is not suitable for home consrruction because of its highinductance, and a wave-wound HF choke, wound in sections, shouldbe used. These chokes are available from any good component supplyhouse. The inductance is not critical and it may have any value betweco2'5 and 6O millihenries.

Enamel wire was used for the coils on the original, but there is noreason why silk, rayon or any other available covered wire should not bcused. It should be remembered that wires other than enamelled aremore costly and require more winding space, thus necessitating a longetcoil former. When wiring up the coils in the receiver, note that theearth return ends of L2-34 are taken to a common earth point.

The neon tube Nl is a safety device used to avoid the possibility ofshock and is fully explained on page 5.

COMPONENTS

Cl 100 pfd variableC2-3 2 x 350 pfd gangU-9 100 pfd micaC5 20 pfd mica or ceramicC6-12 300 pfd micaC7 500O pfd micaC8 0.25 mfd paperC l 0 . l l 8 + 8 m f d 3 5 O v .

ElectrolyticCl3 0'5 mfd paperCl4 25 rnfd 25v. Elcctro-

lyticIj0'01 mfd paper

16 + 16 mfd Electro-lyt ic

l M ( )4't KO470 KO2.2 MO150 c)22KO0.25 MO potentiometerEF4O Mullard

LIST FIG. IO

V2 Elzll Mullard, Nl50Marconi

V3 6C4 Brimar, L77Osram

15-20 henries 60 mAOutput transformer.

Ratio to matchspeech coil to 6000 O

Filament transformerPri. 0-2N-220-240Sec. 6'3v. 2 amp

See Text2'5 mH RF chokeAll-wave RF choke5-way single pole

rotary wafer switchDPDT toggle switchSB3 BrimarB7G valve-holder with

screenB8A valve-holdersNeon lamp G.E.C

Type G

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BERNARDS RADIO BOOKSNo.56. Radio Aerial Hilalbook57. Ultra-Shortwave Hmdbook58. Radio lfinb Matrusl64. $;d bq"ip-""t Mr"""i :::68. Frequency Modulation Receivers' Manual ...73. Radio Test Equipment Manual83. Radio Inslroments and their Co$truction

if; 3fl"''i',,*'f":ti$#''"... :::100. A Comprehensive Radio Yalve Guide, Book 1103. "Raitiofolder" A, The Master Cotou Code Gder tor ti"aio iiia t.i.104. Three Valyo Receiyeg ...107. Four ValYe Circdts108. FiY€ ValYe Circuits121. A Comprehensive Radio Yalye Guide, Book 2123. "Radiofolder" F. The Begimex' Push-Pcll Amplifi€r ...126. Boys'Book of Crystal Sets and Simple Circuib ..,129. Universal Gmm Motor Speed Indicator134. F.M. Tuner Constructiotr135. All Dry Battery Portable Consimction13E. IIow to Make F.M. and T.V. Aerials, Emrls 1, 2 and 3141. Radio Servicing for AmatetrB143. A Comprehensive Radio Yalvo Guide, Book 3I45. Handbook of AM/FM Circuits and Components146. High Fidelity Louilspeaker Enclosurcs147. Praciical Tape Recording Ilandbook148. Practical Transisior Receivels, Book I149. Practical Stereo Handbook150. Practical Radio Inside Out151. Trilsistor Superhet Receivers ...155, Portable Transistor Radio and Rndiogram ..,156. Transistor Circuits Manual, No. I ...157. A Comprehensive Radio Yalve Guide, Book 4l5E. Radio, Television, Industrial Tubes, Semiconductor ed Dioate

_ -E_quivalents Ilardbook (208 pags)159. Realistic lligh Fidetity ...160. Coil l)esign and Constructim MilEal161. Radio, Television and Electronis Data Manusl ...162. High Fidelity Stereo Gramophone163. Transistor Circuits Milual, No. 2164. High Fidelity Tape Recorder for the llome Constnctor165. Hartley on Hi-Fi, Book I, Radio Tucrs ...166. Public Address Systems167. Transistor Circuits Man[al, No. 3168. Transistor Circuits Milual, No. 4169. Hi-Fi Transistor F.M. Tuner for the Homc Constructor170. Iransistor Circuits for Radio Controlleil Modets ...171. Super Sensitive TEnsistorised Pocket Sct Construction ...172. International Radio Stations List173. Practical Transistor Andio Amplifierc...174. Transistor Subminiature Receivers llandbook175. Tnnsistorised Test Equipmena and Seryicing Ma![al176. Transistor Audio Amplifers Manual ...177. Modern Transistor Circuits fdr Beginnen ...I78. Comp_rehensive Radio Yalve Gtide, Book 5179. Transistor Circuits Manoal No. 5lEo. British Semiconductor Survey .,.16l. 22 Tesied Circuits Using Mim Atloy Transiston ...lE2. "At A Glance" Radio Valve & T.V. Tqbe Eqoivslentr...183. How to Receive Foreign T.Y. Progwmcf on' your Teleyision Sct [y

- simple ModificatioroResistor Colour Code Disc CalculatorEngineers' Refereoce TablesInternatioual Radio Tube Encyclopaedia-3rd Editiotr

Prie2162/62/62/62/62/62/6U-r/6<t-t/62br l62/6s/-r/62/6r l -2/62162163/6

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216216

2/62/62/63/67163/6a

3/6s/-3/66/-7/66/-

rs/-sl-3/6

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three valve receivers

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