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Jun - American Radio History

1. lt E v ut A 3 SUPPORT PLATES 2 OFf CONTROLS ing these CUTAWAY VIEW OF CHASSIS UNDERSIDE SHOWING REAR TUBE SVBPORT FIXING the long rod moving in and out With two 4 BA nuts and bolts join the shorter crank Parts Mentioned in Text 2 to the arm on the focus magnet and tbe long Chassis bushes mechanical parts and 8 ot rod These are not bolted tightly sufficient Wide Angle Deflection Coils Denco Clacton ET 5 34 ra de te beng ane for thon to act as Ltd 2a amp 58 g pivots Also for smooth noiseless action cut Fous AA 7 x K i z gnet Duomag Focaliser and 5 s A a iwo small pieces of rubber or PVC sleeving speaker type 5 45 Elac Electro Acoustic 2 z hd B S to ae es ste ea the bolts A locking Industries Ltd z r 2 B nut is added to both bolts F 33 S Two 4BA bolts or 1 8 Whitworth 24 17 Escutcheon Prepared Perspex and z3 long and one 1 long with nine nuts are Cabinets Lasky s Radio 2 required for fixing the speaker The sketch To be continued 2 z y TERA a ee 5 D i n DON T MISS THIS HANDBOOK cass INDISPENSABLE TO ETN ER THE AMATEUR tor orenaTon s HA TRANSMITTER neasi AND LISTENER CHASSIS BOLTS Details of structure assembly It contains all those details of informa tion which the transmitter and SWL i constantly require 5 Right up to the minute Amateur Band Prefix lists both alphab
2. CONDENSERS The abbreviated ranges of two popular types given here pre Side he of A i the wide variety of T C C Condensers available Magnaview Hi K PEARL CERAMICS m te i Gees Dalen od Tele King Viewmaster No A C Length Dia 250 3 5 5 SPG 250 mm mm SPG I A i 250 to zo SPG 250 7 7 SPG l 250 mm mm SPG PRERE E TUBES MASKS t4 in rectangula CR t b E ri DARK SCREEN FIL I7in rectangular CR el ed a AE New aspect ratio TERS LATEST tsi d i 23 12 8 e TINT in round metal cone ion trap tube 2 410 Yin Sorbo 5 Carriage and insurance extra i Wks Dimensions 10in Double D Metal Capacity Voltage Type I2gin x l4 in For 16 ALLEN WIDE ANGLE COMPONENTS 7 6 pF ff No and 7in cr tubes Line and frame scan coils T IZin 15 D C A C Length Dia 19 6 Ilin x 138i For Width coil Type Piney dels Gee eT ae I2in Flat Face 15 mem PTET n an in cr ine linearity coil Type GLI6 lin Rect 21 f 250 1 mm SE mm yeu HENN tubes 5 11 Focus coil Type FC302 a T ls a l in Double E 31 6 os ne mi IC SIS INV PERSPEX Lite output and EHT transformer I I7in Rect 27 6 ees mm ser ai 134 x JO x 4 l kV Typa L308 gt tg o H l in Soiled 7 6 Simm 4 5 mm 3CTH 315 W Neutral shade slightly frame output transformer Type FO305
3. HT GRID BIAS HTH GRID BIAS FIG 2 a SERIES TRANSFORMER COUPLING o PARALLEL REISS As a rule filaments and heaters as they are called in valves with a cathode fall into a definite number of voltage ratings Battery yalves that is those without a cathode are normally 1 4 and 2V AC mains types 4 and 6 3 and AC DC types sometimes known as universal types are in many voltages from 12 to 117 Obviously with a mains type there is no battery problem and economy of supplies is not so important so that valves provide higher gain and power output than can usually be obtained in the battery range WWW americanradiohistorv com convert it into power which brings us to points ii and Gii Normally one valve cannot produce suf ficient gain to make such small signals com fortably audible in a room through a loud speaker Therefore the output of one valve has to be fed into other valves until sufficient gain has been achieved There are a number of ways of coupling one yalve to another Two of the more commonly used systems of coupling between valves are shown in Figs 2 and 3 Fig 2 shows trans former coupling This is very simple and 538 RADIO CONSTRUCTOR FIG 3 RC COUPLING THE VALUE OF THE COUPLING CONDENSER MUST BE HIGH ENOUGH TO FASS THE LOWER FREQUENCIES ie NOT LESS THAN OOF REISS economical but if high quality i e if the reproduction of a v
4. Reg Design No 860302 British U S and Foreign Patents Designed for wireless assembly and Maintenance Supplied for all volt ranges fram 6 7v to 230 250v 3 16 Dia Bir Standard Model 25 6 Sole Maaufacturers ADCOLA PRODUCTS LTD Sales Office end Works Cranmer Court Clapham High St London Swa4 MAC 4272 G4G2 s BARGAINS Pye plugs and sockets 8 doz prs Double circ jack plugs and sockets 2 6 pr 24 doz prs 25 pfd air spaced ceramic trimmers 7 6 doz OImfd mica condensers 500v 4 6 doz 807 EF50 ceramic vihidrs I each 10 doz 4 bank wafer switches each bank 2p 4w Total 8p 4w 4 6 each 45 doz 6SH7 metal valves slightly soiled ex equipment all guaranteed 4 for 9 6 27 6 doz 954 955 956 5 6C4 6AG5 6J7G 9002 6 VSEIGA 6U5G 6 6 6J7M IT4 155 IRS 8 6 IZAU7 12AX7 I2AT7 3V4 9 616 6V6G 6SL7GT 5Z4M 5Z4G MUL2 14 9 6 6Q7G 6F7 6A05 10 6 Ali goods by return of post Please add post packing J T ANGLIN 160 CLEETHORPE ROAD GRIMSBY LINCS Telephone 56315 R F P COMPLETE f WITH HIGH GAIN 2 BATTERY DUAL RANGE AND COIL WITH 2 MAINS REACTION CIRCUITS PRICE 4j POST 3d Trade Supplied Radio Experimental Products Ltd 33 MUCH PARK STREET COVENTRY WWwWw americanradiohistorv com RADIO CONSTRUCTOR 549 Small Advertisements Reader s small advertisements will be accepted at 2d per word minimum charge 2 Trade advertise m
5. 1 6 0005 mid 12 5Kyv EO CALL WE TEACH YOU Basic Electronic Circuits 75 mfd I2 yw I ot mfd 7 Ky I5f Amplifiers Oscillators Power Units etc ALL BRAND NEW AND GUARANTEED NOT EX GOYT pot mfd 8 Ne ribs NONE TO BEAT Complete Radio Receiver Testing amp Servicing i All other types Paper Tubular Waxed etc in stock Hae case single bolt LASKY S POST IMMEDIATELY FOR FREE DETAL JTO E M INSTITUTES Dept 178 X Grove Park Rd Chiswick London W 4 INSTITUTES EM e ltt a hal id OT ae Assscaedwitr O MV MAIL ORDER amp DESPATCH DEPARTMENTS 485 487 Harrow Road Paddington London W 10 1 i Terms Pro Forma Cash with Order or C O D on post items only Postage and packing on orders value l I j extra Address medemens oD es Se te ARGONIPHONE 5 2 extra 10 3 6 extra Over 10 carriage free All goods fully insured in transit i COLUMBIA amp His Master s Voice A I C i n a EA Www americanradio historv com LASKY S RADIO croncrentonsde ws Opposite Paddington Hospital Telephones CUNningham 1979 and 7214 Hours Mon to Sat 9 30 a m to 6 p m Thurs half day p m 370 HARROW RD All Departments 6 amp VALVE Y H F SUPERHET RECEIVER CHASSIS Six channel switching tuning 30 5 to 40mc s Receives TY Fire Taxis many British and Continental ama teurs atc Components include 30 ceramic trimmers 30 small condensers 30 r
6. 10 5 db be several times the impedance of the head at the highest recorded frequency The bias should be about 50 kc s and of sinusoidal waveform with a rejector circuit to isolate it from the audio output The correct bias level for good response will be found by experiment On playback the frequency response of the head and any head matching transformer should be flat with the possible HOLE N BOTTOM COVER OPENED OUT TO e DIAM OUTER MU METAL 5 SHIELD SPACED FROM aa 4 moz f FIXING BOLT F1G 4 5 MODIFICATION TO HEAD TO PREVENT SHORTED TURN EFFECT A REMOVE OUTER NUT B BOTTOM PLATE g INNER NUT A D OPEN HOLE IN BOTTOM PLATE TO DIA E REPLACE BOTTOM PLATE BUT DO NOT USE INNER NUT O MOUNT HEAD ON INSULATED BLOCK AS SHOWN TO PREVENT BONDING TO BOLT RGIS exception of a shunt resistor and condenser to giye cut off beyond 9 kc s The pre amplifier and network may also be used with a high fidelity pick up for gramo phone reproduction if the pick up output is less than 0 3 volt Bass and treble boost controls can be adjusted as required Any treble cut required for scratch filter etc should be in the form of resistor and capacity shunt directly in parallel with the pick up and should therefore be mounted on the player unit There is a slight drop in valve gain indep endent of the network at 50 cycles of about 3 0 db due to the value of the screen decoupling condenser If it is desired to r
7. RADIO CONSTRUCTOR that should be in y adjustments or i e a Eny receive It location Edited by inley S these J yy a hac and have no hes itation in recomi ng am t all televisic icemen ar iret uctors 68 pages Purchase from www A PDF com to remove the watermark A PDF Merger DEMO Data Publications Pub Londen W9 Printed by A v ITHUSIAST RADIO CONSTRUCTOR Sound Reproduction by G A Briggs 3rd edn I7s 6d Postage d Amplifier Circuits by N H Crow hurst 2s 6d Postage 2d Radio Engineers Servicing Manual THE MODERN BOOK CO TV Fault Finding compiled by The Radio Constructor 5s 0d Postage 4d The Radio Amateur Operator s Handbook compiled by the Staff of The Radio Amateur 2s 6d Postage 2d inexpensive Television for the Home edited by E Molloy 42s Qd Post age Is Od Personal Receivers by E N Bradley 3s 6d Postage 2d Constructor 2s d Postage 2d Television Receiver Practice by R Holland 5s Od Postage 3d The Amateur s Guide to Yalve Radio Interference Suppression by Selection by Mullard Is d Post G L Stephens 10s 6d Postage 4d age 2d Television Engineers Servicing Radio Valve Data compiled by Manual edited by E Molloy 42s Od Wireless World 3s 6d Postage 3d Postage ts Od The Radio Am
8. 2 6 RECEIVERS PRE SELECTORS AND CONVERTERS DATA PUBLICATIONS 57 Maida Vale London Telephone CUN 6518 similar valyeholder and designed to allow easy fitting in place of existing larger holders of obsolete types These are also reasonably priced at 3s 6d per dozen The firm also supplies valves components and sundry other items and readers interested are invited to send a 24d stamp for their lists Clydesdale Supply Co Ltd 2 Bridge Street Glasgow C 5 have sent us copies of the new List No 8D and Supplement These are charged at ls 6d which is refunded on the first purchase We cannot think of a more comprehensive list than this with its 260 pages which with the numerous iflustrations forms a mosi handy reference book apart altogether from HS primary purpose DATA BOOK No 7 WWww americanradiohistorv com Radio Control Equipment PART 4 By RAYMOND F STOCK Manual Unit A simpler but very effective device which also carries out the same function is the pulsing switch shown in Fig 18 which I recently developed for another purpose men tioned later A is an insulating arm conveniently cut from a thick perspex and it is mounted on the end of a short control shaft The latter complete with its bush can be taken from a discarded potentiometer Pivoted on a 6 BA bolt at the end of the arm is a small swinging link B which is nor mally kept at 90 to the arm by the light spri
9. 2 Bank 2P1IW 4P5W 6P3W BP4W 7 6 each All above are NEW and have 2 Spindles METAL RECTIFIERS RMI 5 3 RM2 6 3 RM3 7 RM4 21 K3 45 8 2 K3 50 8 8 K3 100 14 8 Westinghouse 36EHTI00 29 4 14A86 20 4 14D36 11 WX6 3 9 WX6 3 9 RADIO SERVICING COMPANY PE RADIO VALVE TECHNIQUE RSGB 3 9 RECEIVERS RSGB TELEVISION INTERFERENCE RSGB SIMPLE TRANSMITTING EQUIP MENT RSGB ef RSGB Catt Book 3 WorLD RaDio VALVE HAND BOOK O Johansen 11 9 NSTRUCTOR RELY ON US COILS COILS Wrearite P Coils eee Osmor Midget iron AJl types in stock in Seems Ce ERN ap i A duding AF I RFL SSNS oni Sere ells tee Price ye Se ee each eallet on re i t quest Coilpacks Type H O 52 LM 43 4 MTS 54 2 TRF 43 4 ali including Tax TRIMMERS All new Postage Stamp Ceramic 4 70pf 8d 40 O0pf 10d 20 150pf I 100 550pf 1 3 LINECORD 3 way 3a at 60 ohms per foot d ft 2a at 100 ohms per foot 8d ft MAXIMITE AC DC SUPERMIDGET SUPERHET Full Plans T c c CONDENSERS Midget Picopack imfd 350v Zmid 150v 1lOmfd 25v 20mid Fv each 2 6 Yisconol High Voltage 001 6ky 6 00I 2kv 10 OOF Sky 1O Ol kv 10 7kv 20 Micadiscs 500pf 1 6 Type 543 l 500v 1 3 750v 1 6 ENGRAVED KNOBS 1 WALNUT or VORY Yolume Focus Contrast Brilliance Brightness On Off Record Play To
10. 8D2 3 DI 2 6 SP6l 3 6 6B8 7 9D2 3j E148 3i e VRII6 3 6 6C5g j OF 7 6 EASO3 for 5 VU39A 10 6 j 6CD6 11 6 I2AT7 10 6 EBS 9 6 VUIII 3 6 6CH6 9j 128 Sim ECC32 0 6 VUI20A 3 6 6F6 B 6 12 5 S EF36 j VUI33 3 6 G 7 6 I2K7 12 6 EF39 6 6 U2I 6 6 6H6 3 6 I2SA7 8j All the above Yalves Tested Boxed and Guaranteed Free replacement if faulty LARGE STOCKS of NEW and EX GOY T COMPONENTS The shop with the helping hand for Hams NORMAN H FIELD 68 Hurst St Birmingham 5 Telephone MIDland 3619 RADIO CONSTRUCTOR 351 i Small Advertisements continued from page 549 FOR SALE Radio enthusiast disposing of complete Gear including Text and Servicing Manuals Rack and Bench combined Instruments for servicing in fact all one would expect to find No reasonable offer refused Box No C122 FOR SALE Ideal for sports or show ground Amplifying Unit Type II Ex WD 200 250 volt mike and gram input 60 watt 4 KT66 output with Parmeko horn speaker 21 Elliott 3 Burne Street London N W 1 FOR SALE VCR97 EHT Transformer new 30 par PT15 s new 5 each carriage extra Farrar Charlestown Ackworth Pontefract Yorks FOR SALE Ever Ready All Dry Portable good condition offers to Box No C118 FOR SALE Projection TV 25 kV EHT Unit complete 7 10s Od MW6 2 CRT 6 10s 0d GEC 6505A Mazda CRM924 CRT s 8 10s Od Garrard RC70B 8 All new unused guaranteed F Miller 7 Mon
11. S Reynolds in your April issue For the benefit of readers who may not have noticed I should like to point out that at 1000 volts the resistor network passes 100 2A and according to Ohms Law passes I mA at 10 000 volts An ex Govt 100 pA FSD meter that I bought quite cheaply passes 100 pA on all ranges but allows me to load most circuits especially TY EHT without detrimental effects However the basic circuit if used in con junction with the circuit by Mr T Hatton in the October 1950 Radio Constructor which had a sensitivity of 100 000 ohms per volt should prove a prize winner P WILKENS Southend on Sea Essex Can Anyone Help Dear Sir Would you please be so kind as to insert the following letter in your mag under the Can Anyone Help column J am desirous of building a really good class scope and wonder if any RC readers have any circuit of tried and proven jobs using current range of valves say EF80 ECC80 ECL80 0 1A type to have response to 3 Mc s switched attenuator X and Y shifts cathode follower input timebase up to 250 ke s and VCR138 or 139A I would greatly appreciate full details of any circuits or ideas of any readers on this subject L A BROWN 33 Barnoldby Road Wal tham Lincs Dear Sir Can anyone assist me to identify three metal rectifiers purchased with a quantity of other ex Govt surplus components Each was 3 in length have 2
12. fall out of synchronism or the local oscillator in a superhet to become detuned Another and perhaps more troublesome result of over heating is that it may well have an adverse effect upon the life of certain components Capacitors and metal rectifiers are particularly affected in this way Some idea of the importance of providing adequate ventilation is gained when it is realised that almost all the power which is drawn by a receiver is dissipated as heat within the cabinet Steps must be taken to get this heat away from the power consuming components before it has a chance to reach other parts of the receiver This is achieved by removing the warm air from around the chassis and replacing it by cooler air from outside the cabinet It is well known that warm air rises so provision must be made for a free passage for the air both above and below a heat generating component It is quite often difficult to obtain this space above a component particularly if the receiver is of the semi pertabie type and under such conditions it is necessary to mount the hot parts at the rear of the chassis Having done this a heat screen is erected between them and the remainder of the receiver to channel the rising air out of holes in the back panel of the cabinet This is not in itself sufficient and holes must be drilled in the chassis to allow cold air to take the place of that which rises Reference to Fig 1 will indicate the general layout of thi
13. go to the expense of installing full wave rectification as is usual Theoretically and probably practically full wave rectification would be an improve ment and this is a point to bear in mind when building this receiver One point in favour of the metal rectifier is that it is cheap It is also cool and requires no heater supply Conclusion No definite layout is shown as constructors will doubtless have varying ideas regarding this The original was built on a metal chassis l2in x 8in X 2in fitted with a black crackle finished louvred lid 7in in height both of ex WD origin No internal speaker is fitted and the underneath of the chassis is left open In case of breakdown or alteration all that is necessary is to turn the receiver upside down and the majority of the components are accessible immediately o The four controls tuning wave change tone volume on joff are arranged along the front panei in that order from right to left 316 RADIO CONSTRUCTOR Vee gt ae a T RCI93 BASS LIFT FOUR CIRCUIT _DIAGRA RADIO CONSTRUCTOR i 517 COMPONENTS LIST Resistors R1 250 k R2 R7 R17 10 kQ R3 150 02 R4 RIG R12 50 kQ R5 500 kQ R6 Ri 100 kQ R8 Ri4 000 2 R9 1 MQ R13 20 kQ i R15 1 MQ Pot and switch R16 490 2 RIS 50 KQ Pot Condensers Cl C2 CIO 0 01 4 F 350V ES 500pF ganged with trimmers C4 C8 Ctl C14 0 1uF 450V as 100pF trimmer C6 luF CINCY 100pF
14. methods unlimited advice Details 3 6 Carter A M LE T 101A High Street Harlesden N W 10 RADIO AMATEUR May Issue Praciical Frequency Modulation Petrol Generator A C Supplies for Field Day Grounded Grid RF Amplifiers Buffers and Doublers Bias Supply for the 807 Crystal Grinding Broadcast Bands Reyiew Amateur Bands Commentary On the Higher Frequencies Round the Shacks G8UA Club News efc etc 532 RADIO CONSTRUCTOR Ex Services Electronic Equipment CLYDESDA EF Bargains in Ex Service Radio and Electronic Valv Equipment RECEIVER UNIT TYPE 25 Ref LOP tl part of the TREI96 equipment Frequency range 4 3 6 7 Mc s es 2 VR53 EF39 2 VR56 EF36 YR55 EBC33 VRS7 EK32 2 IFT 460 Kejs plus various microdensers mic and output transformers pots condensers resistors etc plug cohnections brought co 10 pin Jones type chassis Circuits are provided in the unic which is totally enclosed in case Stinx dinx 4in Would make the basis of an All Wave Receiver required cuning pack and power supply ASK FOR Ne ASK FOR No MA Out 3A POST B H299 39 6 PAID Conversion Data R Con Reprinc 1 6 FOR INEXPENSIVE TELEVISION R3i70A RECEIVER UNIT CARRIAGE PAID 4 12 6 B H492 For P T Beginner s Receiver INS TRANSFORMER 200 250 v A C Input put 350 0 350 v 150 m 6 3 v 444A EN ae RT MH22 Choke WBIO4 15 6 Components pric
15. the brilliance must first be reduced of course The spot is then moved from side to side using one shift control only and observing the spot shape as this is done The experiment is then repeated this time moving the spot up and down In all probability it will be found that movement in one direction will have little or no effect on spot shape Movement in the other direction however is likely to cause the spot to change from an ellipse with its major axis say vertical through an inter mediate circular shape to an ellipse with its major axis horizontal Fig 1 illustrates this This is because altering the potential of one plate alone changes the mean potential of the pair The fairly obvious remedy and the one which is given in the text books is to fit a second potentiometer to control the potential of the second plate of the pair which exhibits the effect This enables the spot to be moved about the screen by adjusting the sliders in opposite directions and thus maintaining the mean potential and the spot shape constant It may be necessary to do this for both pairs of plates Figs 2 and 3 show the normal circuit arrangement and the modification respectively This method is capable of good results but there are drawbacks Ht might seem that the procedure would be to adjust the spot position to give a central picture and then with a stationery de focused spot as before to adjust the shape Unfortunately when the spot is
16. triode on the B9A base for these two valves All the circuitry following V3 is the variable slope steep cut off filter and if it is desired to RADIO CONSTRUCTOR 531 run nn UM omit this the output may be taken from capac itor C38 The switch S3 provides various frequencies of cut off and a straight through position where the stage functions as a negative feedback amplifier B the feedback factor being given ave R21 xRa R22 R23 R2i1 Ra R2ixRa R29 4 R30 R32 R22 R23 R Ra where Ra is the AC anode impedance of V2 Assuming Ra to be 60kQ this expression becomes 60x 100 22 100 500 160 60x100 637 5 100 100 500 100 500 Tep 13373 by The gain is therefore 1__ 1337 5 B 637 5 2 1 6 4 db The resistor R33 is the slope control and its variation affects the feedback factor and thus the gain Jt may be seen by a similar calculation to that already performed that the gain when R33 is shorted will be 1137 5_ _ Thus TT z 1 8 5 db the maximum change in gain is 1 4 db and as 3 db is a just perceptible change 1 4 db will be unnoticed The capacitors C25 C37 with resistors R29 R30 R31 form the frequency sensitive parallel T network while C19 C20 C21 provide the required capacitance to cause a suitable phase shift around the feedback loop C15 C18 provide in conjunction with R22 high frequency loss to counteract the rise in response of the unbalanced parallel T before resonance R28 is includ
17. 17in diagonal grey glass face A feature of this new tube is the incorporation of a new form of electron gun which is designed to give uniform focus over the whole screen In this new gun assembly the functions of electron acceleration and prt focusing which have hitherto been combined by the first anode have been separated by the inclusion of an additional electrode The first anode in the MW43 64 acts as an accelerator having a potential of 200 to 410 volts with respect to the cathode The second anode exerts a pre focusing action on the electron beam thus influencing the spot size and uniformity of focus When the potential on this anode is zero or negative with respect to the cathode the spor siz at the centre of the screen and the width of the unfocused beam are such that optimum uniformity of focus is obtained over the whole picture area Further technical details of the MW43 64 can be obtained on application to the Technical Service Depart ment Mullard Ltd bets Get Starled a a 2 Quart from a Pint Pot By A BLACKBURN Don t let that title lead you astray I am not suggesting you are getting something for nothing when you use an amplifier But that you are getting more from the litile that you already have Such a prospect is always attractive particu larly if the process of multiplication is a simple one And in this article I intend to show you just how easily it can be done Amplification often requires
18. 514 n wr S RADIO CONTROL Eie aes ji by ata F Stock AR THE UNIVERSAL LARGE SCREEN AC DC Tersvisos described by AUDIO PRE AMPLIFIERS PART 3 by D Nappin 530 A SMPLE AC DC AMPLIFIER by gues S engal Assoc Brit Ie RE M 1 P R E 3534 Let s GET STARTED O Bier FROM A Pir Por by ne teh ae a USG Query CORNER A RADIO CONSTRUCTOR SERVICE FOR READERS BP ta neg RADIO COMPONENTS EXHIBITION 1953 Visited by L A Chinnery G3LIZ 542 From Our MAILBAG 5 Some UseruL Hints by J S K W le RADIO MISCELLANY by Centre Tap a Pe 522 A S Torrance A M I P R E A M T S 6 524 ASTIGMATISM IN ELECTROSTATIC CATHODE RAY TUBES a c R Doi 528 R o a o T53 A Zi i 544 NOTICES THE CONTENTS of this magazine are strictly copyright and may not be reproduced without obtaining prior permission from the Editor Opinions expressed by contributors are not necessarily those of the Editor or proprietors THE EDITOR invites original contributions on con struction of radio subjects All material used will be paid for Articles should be typewritten and photo graphs should be clear and sharp Diagrams need not be large or perfectly drawn as our draughtsmen will redraw in most cases but relevant information should be included All Mss must be accompanied by a stamped addressed envelope for reply or return Each item must bear the sender s name and address TRADE NEWS Manufacturers pu
19. LTD VICTORIA WORKS ASHTEAD SURREY ASHTEAD 3401 np il SS WWww americantadiohistorv com 500 RADIO CONSTRUCTOR Your set deserves a Mullard LONG LIFE TV TUBE If you are building a television receiver leave nothing to chance choose a Mullard Tube Mullard Television Tubes owe their high reputation for performance relia bility and LONG LIFE to the unrivalled facilities for research possessed by Mullard to the com plete control of manufacture from the production of raw mate rials to the completed product and in particular to the ion trap which safeguards the screen from damage by heavy at negative ions produced in the Tarimas region of the cathode 2 MULLARD LTD CENTURY HOUSE SHAFTESBURY AVENUE LONDON ph Sere The Vol 6 No 10 Annual Subscription 18 Radio Canet wenn June 1953 Editoral and Advertising Offices 57 Maida Vale Paddington Telephone CUNingham 6518 London W9 Edited by C W C OVERLAND G2ATV totototo toe CONTENTS SROROROHOR OHA CHAS SUGGESTED Circuits AN ACCURATE NULL INDICATOR by G A French 502 In Your Worksop by J R D 504 VALVES AND THEIR POWER SUPPLIES PART 7 by F L Bayliss A M LE T 506 MAGNETIC RECORDING EQUALISATION WITH SOME AMPLIFIER MODIFICATIONS by L F Sinfield A M LE R E S51 Book REVIEW Bass LirT Four For AC MAINS N aN E T AE E TRADE Review
20. PLATE GLASS I5in Actual size I8 in x I94in x gin 7 11 _t2in Actual size 3in x FO in x in 4 9in Actual size 9in x Bin tin 3 ALL THE NEW W B COMPONENTS NOW IN STOCK ELECTROLYTIC CONDENSERS 11 19s d with slight screen blemishes 12 19s d absolutely perfect Carriage amp insurance 15 per cube extra LEARN THE PRACTICAL WAY A specially prepared set of radio parts from which 8 mfd 450 v w 2 3 124 12 mfd 350 v w 3 6 we teach you in your own home the working of amp mfd 509 v w 2 l ziii 16416 mfd 500 v w 4 6 T C C VISCONOL WE HAYE fundamental electronic circuits and bring you easily 16 mid 350 v w 2 6 16432 mfd 450 v w S IL ee beeen THE GOODS to the point when you can construct and service a 16 mfd 500 v w 3 6 324100 mfd 450 v w 7 6 CATHODRAY z radio set Whether you are a student for an examina zmia poo AE up a 60 100mfd 350 v w 9 6 im ae e ar e tion starting a new hobby intent upon a career in A TSA BIAS Ol med 15 Kye Tole WRITE industry or running your own business this Course 250 mid 350 v w 4 11 25 mfd 25uw 6 O01 mfd 25 Kv 18 PHONE is intended for YO and may be yours at a 8 8mfd 450 v w 4 6 50 mfd I2vw i6 0005 mfd 25 Kv 18 d very moderate cost Available on Easy Terms 8416 mid 500 v w 2 4 11 50 mfd 50 v w
21. Sets worth 50 or less and for Sets valued at more than 50 the cost is in proportion Cover b i and i costs only 2 6d a year if taken with Cover a or 5j if taken alone Why net BE PRUDENT AND INSURE your installation it is well worth while AT THE VERY LOW COST INVOLVED If you will complete and return this form to the Corporation s Office at the above address a proposal will be submitted for completion NAME Block Letters If Lady state Mrs or Miss ADDRESS Block Letters J8 RADIO CONSTRUCTOR 497 Did you build your own T V receiver If so and you have a 9 or 12 set and now want to convert to big screen viewing how better than by using an ENGLISH ELECTRIC 16 Toor Metal C R tube To help you carry out the work our leaflet EV103A gives you the complete line and frame scanning information necessary together with a suggested list of required components And why a Toor because it offers you brilliance long life high safety factor ease of handling and withal it is British made It is the tube specified by the design ers of the Tele King and Magnaview circuits and Viewmaster conversion circuit Brilliant black and white picture focussing over entire screen area with excellent contrast range high optical quality glass face plate wide angle scanning 70 fitted ton trap overall length 17 ik diameter 16 ENGLISH ELECTRIC BRITISH MADE
22. The receiver should be so set up that the point of balance is indicated by a fall in audio frequency and not by a rise Sufficient input to the receiver will in most cases be obtained by positioning its aerial Jead close to the oscillator Teil me how long have you been suf Jering from reversed line scan Www americanradiohistorv com In which J R D discusses Problems and Points of Interest connected with the Workshop side of our Hobby based on Letters from Readers and his own experience It is interesting to note how popular in the United States are commercially made cathode ray tube rejuvenators for television receivers These rejuvenators are used with cathode ray tubes whose emission has fallen with age and it is claimed that they bring a large number of these tubes back to their original emission and brightness They func tion by applying a greater heater voltage to the tube than is supplied by the set in which it is fitted and for which the tube was designed Not quite so popular apparently are reacti vators These are intended also to bring low emission tubes back to normal and function on the flashing principle which was applied to battery valves many years ago A reactivator subjects the tube heater to some thing like a 50 per cent overload for a minute or two this being reduced to a slight overload which is held for a longer period Reactivation does not seem t
23. are permissible C3 should have a DC working voltage of at least 750 An EAT Circuit If the constructor has a transformer rated at 500 0 500 volts he has no HT problem except to drop this voltage to a value suitable for the sound and vision receivers If he were content with a fairly low EHT voltage 1 500 volts his EHT too could be obtained in a manner similar to Fig 19 previously discussed The connections for such an EHT arrange ment are shown in Fig 20 MR1 and MR2 may each be rated at 600 volts The capacitors C4 Cs and Ce should be rated at 1kV DC working voltage at least 1 5kV if possible With this arrangement the cathode ray tube anodes and deflector plates are connected to the HT line via their control resistors and potentiometers whilst the tube grid and i i 1 RCI9I Www americanradiohistorv com CHASSIS LINE RADIO CONSTRUCTOR HEATER FIG 2 TRANSFORMER AN ARRANGEMENT FOR POSITIVE EHT ONJOFF ON OFF Ac MAINS 507 Magnetic Recording Equalisation with some amplifier modifications By L F SINFIELD 4 M 1 2 R E One of the chief difficulties in magnetic recording is to obtain correct frequency com pensation in the amplifier Jf a recording is made on good grade tape such as Scotch Boy tape at 74 second with a head sap of between 0 5 and 0 75 thou then if the recording ts made at constant current the playback amplifier w
24. factors which need careful attention in order to produce maximum gain with required bandwidth The attainment of satisfactory noise level and the calculation of nee factor is of particular interest where the design o fringe area receivers is concerned 3 xposition such as this where one specialized of dean technique prevails it is inevitable that the mathematics of the subject should be given some prominence The author has kept the matematics ae simple as possible in the main body of the Sook an gives the derivations of many of the formulae in the e ndices t E bandwidth with two terminal and four terminal networks ccupy only a few pages but tiac applications in multi stage amplifiers employing staggere tuning and the response curves obtainable are given fuller treatment Distortion in double and vestigial sideband systems is discussed in another chapter The effects and the use of feedback in I F amplifiers is given over to a large part of the book It is enlightening to read that the chassis can become a wave guide for feedback energy and that E remedy is to be found in e of a long narrow chassis i neh iekea considerations of circuit design have not been forgotten a chapter on this aspect deals wiin some typical examples of sensitivity gain selection o valves staggered tuning and distortion r i There is no doubt that this reasonably priced boo can be of considerable value to the design engineer
25. grid bias battery is called the grid leak It would be as weil to say a word or two here about grid bias We will not go too deeply into the reasons for grid bias at the moment but that does not mean that it is not important The recommended grid bias value for every valve can be obtained from the valve table referred to last month If during your experiments you should find that the recommended bias doss not appear to give good results wrong bias can usually be detected by severe distortion in the amplifier then simply change the bias until the results improve So much for grid bias for the moment We will assume in our specimen amplifier shown in Fig 4 that the input terminals aa are to be connected to a gramophone pick up giving one volt maximum output and that one watt is to be delivered to the loudspeaker The voltage from the pick up is applied to the triode V grid through a volume control R This component merely taps off some of the voltage in order that the required RADIO CONSTRUCTOR 539 VOLTAGE AMPLIFYING TRODDE FILAMENT BATTERY 2V GRID BIAS BATTERY OV TAPPED EVERY 1 VOLTS OMAT switch T 1 1 FIG 4 A SIMPLE GRAMOPHONE AMPLIFIER RCI9O volume level may be obtained The output voltage from V1 is applied to the pentode V2 through a typical resistance capacity coupling network V1 amplifies the voltage of the signal V2 converts this vol
26. in other fields Painting printing and filmcraft readily spring to mind The disadvantage of additive systems for photo graphic and TV purposes is that it entails the use of filters The high absorption of light in the colour filters reduces the recorded image to a dimness that demands an extremely high order of sensitivity or an intense subject lighting or more usually a combination of both The subtractive system widely used in cinematography produces colour by sub tracting from white which is a combination of ail colours A limited colour system can be obtained by employing only two colours red and blue green In fact a two colour system was actually used in a pre War Baird demon stration which employed a twin cathode ray Be RADIO CONSTRUCTOR 523 a a R tube projecting two beams on the same fluorescent screen The superpositioning gave a fairly wide and reasonably accurate colour range The RCA system has been developed on similar lines Three separate images after sotting out from the signal are superimposed on the same screen Such a system although it means complication in the CRT is theore tically practical and development will lead to its simplification It would however make all our present equipment obsolete Not only are three separate beams each from their own gun required inside the tube but a great many circuits in the receiver will have co be in triplicate No won
27. or 3V4 ac 32 6 Sec SET OF BATTERY VALVES 2 volt MAZDA TYPES TP25 HL23 DD VP23 PEN25 or QP25 at 27 6 Set COMPLETE SET OF 10 SPECIFIED VALVES FOR PRACTICAL TELEVISION PERSONAL REC 5 6AM6 2 6AKS l EA50 l 636 l 6J4 and 3BPI C R Tube in case at 5 32 6 Sec LT RECT S v amp G E C ah oa ae a 4 l2v 2 amp Westinghouse th sha wee 12 6 I2v 4 amp 5 7 0 aye T 17 6 I2v 8 amp ST Co ens a 32 6 S T C RECT S E H T K3 25 650v I mja E T A Ta As 4 7 K3 40 1000v I mia ea ca a 6 K3 100 8 500v m s af Ae n 14 8 K3 200 10 500v 1 mja i Ji 26 H T RECT S S T C 150v 120 mja iia ka a 4 6 C 250v 250 mfa nA BE 18 G E C m a Meter Rect E 3 a we UE 6 RECEIVER RI355 As specified for Inexpensive Television Complete with 8 valves VR65 and each SU4G VUI20 YR92 Only 55 carriage 7 6 Brand new in original case RF24 25 RF25 25 RF26 59 6 RF27 59 6 CATHODE RAY TUBES C97 Guaranteed full picture 40 carriage 5 VCRSI7 Guaranteed full picture 40 carriage S 3BP1 Suitable for scopes 25 carriege 3 Mu Metal Screens 12 6 6 Enlargers 18 6 PYE 45 Mis STRIP Special purchase of M O S Type 3583 Units Size 15 x8 x2 Complere with 45 mc s Pye Strip 12 valves 10 EF50 EB34 and EASQ volume controls and hosts of Resistors and Condensers Sound and vision can be incorporated on this chassis with minimum space New go
28. position gives a level response with a gain of where B the B feedback ratio is R9 As R9 is 22kQ R8 R9 and R8 220kQ this gives a gain of 11 or 21 db The capacitor C5 introduces extra degenera tion at high frequencies to cater for the top boost in Decca discs If desired this feature may be deleted from the pre amplifier and incorporated in a plug in equalizer In this stage good HT decoupling is essential and at least 16 uF was found necessary despite the power supply having a two stage filter with 32 uF smoothing capacitors A To allow for larger inputs from radio feeder units etc a third position was provided on switch 5 allowing VI to be cut out and feeding the input directly to the volume control R10 V2 is a normal voltage amplifier providing sufficient gain to counteract the loss in the tone control network It will be noted that double decoupling is provided in the anode circuit this being to provide reasonable attenuation of hum without the use of electrolytic capacitors Immediately consequent upon this follows the previously described frequency compensa tion circuit feeding directly into V3 to avoid modification of its characteristics by shunting of the output The valve V2 is preferably an EF37A or similar type but due to the higher signal level it is possible to use an EF36 or The same comments apply to V3 which is again a simple voltage amplifier although it may be possible to employ a 12AX7 a double
29. shortly is a Simple Communications Receiver circuit Further announcements will be made shortly concerning equip ment for the F V home constructor including wide band pre amplifiers etc at prices which will be right for your pocket Get your name and address on the ars Pra by sending your S A E to J H G Box o 5 AMATEUR STATION RECORD CARDS 6x4 best quality card for recording that QSO and full details of the contact An invaluable aid to quick reference of stations worked etc 3 per 100 from Data Publications 57 Maida Vale London W 9 GLOBE KING Resd Miniature Single Valve Receiver gets real Dx Amateur Radio enthusiasts should send for free copy of interesting literature and catalogue enclose stamp for postage Write to makers Johnsons Radio 46 Frair Street Wor cester BOOKBINDING Volumes of Radio Constructor and Radio Amateur fully bound imitation leather gold lettering 7s 6u post free Prices for other publications on me ta Jerome Alcock CHEADLE Stoke on Trent JOIN THE ISWL Free services to members including QSL Bureau Translation Technical and Identification depts Dx certificates contests and activities for the SWL Monthly magazine MONITOR duplicated containing articles of general interest to the SWL and League member 10 6 per annum post free ISWL HQ 86 Barrenger Road London N 10 BLUEPRINTS High Gain 10 Metre Converter with a de luxe circuit comprising EF91 RF sta
30. the electrodes from the influence of the demagnetising field Readers who wish to try demagnetising valves may proceed by using a speaker energising coil of almost any resist ance above 2000 connected across the mains A 1 diameter coil should serve to demagnetise miniature valves and those of the EF36 EF37 class however for such valves as the SP61 and EF50 a 14 diameter coil will prove necessary Nore A misprint occurred in Part 1 of this series in section 3 Non Linearity Distortion para 3 where the ratio of intermodulation to harmonic distortion was given as 2 This should of course have been 2 4 2 Fig 6 and Component Values are given on i next page References 1 Roddam T intermodulation Distortion Wireless World April 1950 2 Cocking W T Diode Detector Distortion Wireless World May 1951 G Williamson D T N High Quality Ampli fier Wireless World October 1949 4 Correspondence Wireless Worid Decem ber 1949 5 Olson H F Elements of Accoustical Engineering pages 481 2 6 West R L and Kelly S Pickup Input Circuits Wireless World November 1950 7 Williamson D T N High Quality Ampli fier Modifications Wireless World May 1952 RADIO CONSTRUCTOR 533 eee COMPONENT LIST om RADIO CONSTRUCTOR a INPUT CIRCUITS HIGH IMPEDANCE PICK UP CRYSTAL OR MOVING IRON 5 Resistors Cl 50 uF 12V Electrotytic 2 5 R
31. to choose to day and what alternatives are open to us Firstly we can supersede it completely while we temporarily carry on the present system side by side with a modernised system until the existing sets wear out This sounds very nice but it s wasteful nationally and we still shan t know if the new system is going AHS AHA STEREOSCOPIC AND COLOUR TY amp NI A GADGET NL WE SCOT WC HR ET CH TC eS J a time in America and a number of receivers sold but it had to be discontinued by govern ment intervention on the grounds that it would upset the Defence Programme Pye Radio EMI the Marconi Co and the BBC are al carrying out experiments along these lines and although satisfactory colour demonstrations have been given just what sort of results could be achieved on ordinary domestic receivers in the home is rather problematical Those of us who are still beset with nightmares of our disc scanning days will fnd some difficulty to work up much enthusiasm for mechancial colour discs Nor does anyone dare to commit themselves on the question of cosis not only the cost to the viewer but also at the transmitting end We still need three times the bandwidth and a move to the HF means lessened ranges and more relay stations RCA are making strenuous efforts to develop an improved all electronic system and those of us who think mechanical colour discs too high a price even for reasonably accurate colour watch with e
32. use every means of furthering understanding The special con tribution broadcasters and telecascers can make is by sending through the air over all frontiers news and pictures of what their peoples are doing and thinking and of how their work and their life fic into the story of man s struggle to master his environment and himself WORLD RADIO HANDBO OK brings together all rhe information needed by broadcasters and radio listeners desirous of following programmes in any other country We find it indispensable ourselves and cordially commend it to others Peter Aylen Director United Nations Radio Division VALVES BY RETURN OZ4 6 6 635 6 6 12SC7 6 EFSO 5 6 JA5gt 7 6 656 10 12567 Sim EF54 5 ILDS 6 6 6 7 9j 2SH7 S EPS 10 6 ILNS 6 6 6K6 7 6 125 j EL32 7 6 IRS 8 6 6 K7gt 6 6 1 2SK7 8 EL35 154 8 6 6K7g 6 6 125Q7 9 6 EL 9I 8 6 155 8 6 6KBm 10 6 12Y4 7 6 HL2 3 6 1T4 8 6 6K8g 10 6 15D2 4j KT24 5 1625 4 6 6L6 g 0 6 35L 10 KTH 9 6 2C26 S 6Q7 10 6 39 44 5 KT63 8 6 2034 4 6 6SA7 9 6 SGl gc I0 KT66 10 6 2Y3g 3 6 6SH7 j 75 12 6 KTZ41 7 6 3D6 2 3 6SL7_ E6 76 7 6 KTW6i 7 6 384 8 6 6SN7 10 6 77 7 6 N78 10 6 4Dl 3 6807 7 6 2158G 5 P l 3j SR4g 12 6 6557 7 6 846Z4 7 6 PEN46 8 5U4g 9j 6V g 9j 807 12 6 PEN220A 5 SY3 O 6XSge 7 6 956 3 6 QP2I 7 6 5Z4 t0 7C7 7 6 1626 4j RK34 3 6 6AB7 6 6 7D8 gj 1632 7 6 SI3Q 5j 6AC7 10 7Q7 7 6 AQIS S SP4l 3 6B7 9j
33. well as making the best use of whatever illumination happens to be available The price of the frame ends is 2s 6d per pair and panels of any required length can be supplied at is 9d for six inches plus 3d for each additional inch The address of the manufacturers will be found under the review of a selection of other items from their extensive range of laboratory and workshop metal ware A Simple AC DC Amplifier By JAMES S KENDALL ASSOC BRIT LR E M I P R E There are on the market today some valves of very low heater consumption only 100 mA in fact Three typical examples the UBC41 UL41 and UY4 are used in this circuit The base used is the B8A which is of the eight pin pin type the valves being of the all glass type alleviate the troubles due to the loosening of the valve base owing to the heat from the valve itself The writer has had experience of quite an amount of this trouble with octal based valves especially in some of the conti nental types where the base is very shallow The circuit is quite conventional except for the bass lift circuit It is well known that in recordings the level of the bass has to be cut so that the needle does not have to be moved excessively for the reproduction of the low notes The anode load of the UBC41 is divided into two portions separated by a smail condenser joined to chassis This has the effect of reducing the gain at the higher fre quencies and increasing it at the low
34. 2 resistors 7 con densers three 4 way sockets the whole mounted on a chassis x6 x3 deep complete with cover open at one end to take glass screen 17 6 Post 2 6 Mine Detectors Consisting of 2v amplifier complete with valves satchel search coils headphones etc Ideal for locating metals hidden treasure ete 45 Carriage fe Controllers Electric No Contains 5 push buttons 5 indicator lamp holders I telephone key switch in small box 54 x2 x4 with 12 way Jones plug at rear 6 6 Post 1 6 Receivers 1125 Complete with 2 valves 10 6 Postage 2 6 Potentiometers Wire wound 300 ohm 2 10K 2 6 Post 6d Fuse Boxes 4 way Bakelite 20a Takes glass fuses 2 6 8 way 3 6 Post 9d Large Condensers Oil filled 10 watt 3000 ohms 2 Post 6d Telescopic Aerials 4 section 3ft long dia 2 aerials contained in 3 foot canister 9 Pest 2 6 Slow Motion Dials 67 200 1 ratio scaled 0 100 ref JOA I5319 4 6 Post 1 3 Large mew fist No 10 now available Price 6d inland J6 overseas Air Mail A T SALLIS 93 North Road Brighton Sussex Telephone BRIGHTON 25806 ROTARY CONVERTERS 12V BC to 200V DC 50 MA l 100 24V DC to 230V AC ISOVA 6 00 S A E FOR MODEL RAILWAYS EQUIPMENT PRE WAR VALVES TRANSFORMERS Lawrence Frankel MAIL ORDER 134 Cranley Gardens London N 10 Telaphene TUDor L404 ADCOLA Regd Trade Mark SOLDERING INSTRUMENTS
35. 5 is the diode load C8 is the coupling condenser and R9 serves as grid leak The grid is fed from the junction of R6 and R7 Output from the anode of V2 is fed via C11 to the volume control potentiometer R15 and thence to the grid of V3 which is another RF pentode This vaive acts well as an LF amplifier when connected as shown Coupling to the output valve is by means of a para fed LF transformer with a ratio of 1 4 This was used in place of RC coupling so that the negative feedback circuit C17 R17 R18 could be used to cancel out distortion WWww americanradiohistorv com wich may be as much as 10 in the output valve The introduction of feedback causes a decrease in gain as may be expected but this has been taken care of in the earlier stages Operation of the potentiometer R18 varies the amount of feedback and with the values specified gives a wide range of tone control With feedback at a minimum speech is crisp and clear As the control is rotated bass becomes more and more evident The writer uses a 10 inch speaker mounted on a sheet of asbestos 3 7 6in x 2ft Repro duction is good and in the order of 5 6 watts Bass is plentiful Lower Supply In the original receiver a selenium metal rectifier is used in conjunction with a half wave mains transformer This transformer is of ex Govt origin and has a secondary of 300V at 100mA plus a 6 3V winding Mains hum is not noticeable and so it was decided not to
36. 8 fins are grey in colour and bear the following in scriptions Positive End Red Negative End Black 280 LU or CO 422B VIA B 280 LU 422 R or B V1A B 280 LU 422 R or A B or P VIC D I should be grateful if someone can advise me if possible the input and output voltages of these rectifiers as I have no meters to hand STANLEY W J GREEN 6 Elmwood Avenue Baldock Herts i Some Useful Hints gt By J S K Precautions on Renewing the Output Valve Often after the radio set has been running for a number of years a fault develops in the rectifier valve and it will not pass the required current The H T voltage falls so that the electrolytics do not get their full voltage and tend to De Form and renewing with a new valve can cause the components to rupture as the voltage applied is higher than the con densers are used to Re forming is essential and can be done quite simply by slowly raising the voltage across the condenser with current from a separate power pack The condenser should be disconnected whilst re forming The voltage to which the condenser is raised should not exceed its rated maximum Changing an indirectly heated rectifier valve for a directly heated one Often the constructor or repair man sees that two rectifiers have the same current and voltage carrying capacity and thinks that they can be interchanged For instance a GZ32 used in a T V receiver would appear t
37. C12 25u F 12V C13 164F 450V C15 32u F 500V C16 50uF 12V Cl7 0 0024 F C18 8u E 500V C19 C20 0 1u F 2000V Mains transformer 300V 100mA 6 3V 1 5A Or see text Selenium metal rectifier 250V 100mA Chassis I 2in x 8in x 2in LF Choke 20H 100mA LF Intervalve transformer 1 4 Premier Radio or similar Aerial and RF coils long and medium wave Premier Radio 2 pole 2 way Yaxley type switch High Frequency Choke Tapped output transformer Four IO valve holders e Fuse 2 5V bulb Valves V1 V3 6SH7 v2 EBC33 V4 EL32 Trade Review We have received from Kendall and Mousley 99 Dudley Port Tipton Staffs samples of their products for review One of these a pair of meter stands was at once snaffled by Centre Tap and is described by him in Radio Miscellany in this issue The other items submitted consisted of a cabinet front panel chassis and a pair of handles These were stoutly constructed and nicely finished in black crinkle The prices charged are reasonable for example a cabinet 104 x 12 x 104 deep with light alloy panel costs 2Is A chassis to suit measuring 10 square by 24 deep is available at IOs 6d Ttems are obtainable in other colours than black Brown blue and green can be supplied at 10 extra Another useful item and one which we nave not seen elsewhere are metal plates punched to take an international octal or Now available
38. LONG LIFE METAL C R TUBE If you have any difficuity in obtaining supplies write to WWWw americanradiohistorv com The ENGLISH ELECTRIC Co Ltd Television Department Queens House Kingsway London W C 2 498 RADIO CONSTRUCTOR WIDE ANGLE TV Allen Denco Colvern Dubilier Elac McMurdo Morgan STE TCE TELEKING VIEWMASTER CONVERSION and MAGNA VIEW Radio Constructor also TUBES VALVES amp CABINETS etc Price Lists on receipt of SAE H L SMITH amp CO LTD 287 9 Edgware Road London W2 Telephone Paddington 5894 Hours 9 till 6 Thursday I o clock Nr Edgware Road Stations Metropolitan amp Bakerloo For SUCCESSFUL wide angle scanning ALLEN DEFLECTOR COILS 70 Scan with minimum deflection defocusing High efficiency castellated FERROXCUBE core Suits any wide angle C R T up to 27 double d Scan LARGE SCREEN TELEVISION Can only be achieved by using high efficiency components throughout ALLEN can supply the complete range For prices and details of For circuit diagram of the full range of ALLEN fine and Time Base send 9d and stamped compenents Write to addressed envelope to ALLEN COMPONENTS LIMITED Crown Works 97 Lower Richmond Rd Richmond Surrey Telephone Prospect 9013 ARTHURS HAVE IT LONDON S OLDEST RADIO DEALERS LARGE VALVE STOCKS AVOMETERS IN STOCK Avo Test Meters and Signal Generators and Taylor Meters Leak Point Gne Amplifie
39. NORMAN CASTLE a pines cess ll 7 Bass Lift Four For AC Mains By A CARPENTER The receiver to be described was built originally as a simple 3 valve arrangement using an RF stage diode detector and LF amplifier feeding into an output pentode This proved fairly satisfactory but the out put was not quite sufficient and as the author likes plenty of bass experiments to obtain it still further decreased the output as is usually the case After various changes the following circuit was evolved Cirenit As will be seen from Fig 1 four valves are used V1 is a high gain RF pentode supplying a good signal to the detector and fed via a small trimming condenser C5 to the second tuned circuit This method provides a certain amount of variable selectivity and when the best position is found should require no further adjustment Demodulation is obtained at the diode of V2 which is a duo diode triode The second diode normally used for AVC purposes is not used and can be connected to cathode The triode portion of V2 is usually used purely as an LF amplifier but in this circuit it is arranged principally as a bass amplifier The resistors R6 R7 and the condenser C10 cause the valve to discriminate in favour of the lower frequencies and afford a considerable degree of bass lift This is not achieved without a severe loss in gain and the output from V2 is therefore only small HF is filtered out by R4 and C9 R
40. R POSTAGE TRANSFORMER for use on trains models etc giving outputs of 3 v a 4 v 5 Ya 6 B v 9 va 0 v 12 v E5 va 18 va 20 v 24 v 30 v at 2 amps from normal mains input ONLY 17 6 postage TRANSFORMERS Ex W D and Admiralty built to more than 50 per cent safety factor with normal A C Mains Primaries All Brand New and Unused 300 v 0 30 v 200 ma 5 v 3 4 6 3 v 5 an C T 20 v 750 ma 70 v t00 ma Weight 12 Ib ONLY 42 6 postage etc 2 6 330 v 0 330 v 100 ma 4 v 3 a Weight 7 Ib ONLY 22 6 postage 1 6 L T 5 v 0 5 v 5a 5 v 0 5 v a 5 v 0 5 v 5a By using combina tion of windings will give various voltages at high current Weight II Ib ONLY 35 postage ece 2 6 L T 6 3 v 7 7 a 4 2 2 5 a 4 a ONLY 19 6 postage 1 6 EHT 1 400 v 2 ma 520 v 10 ma 300 v 10 ma 2v 1 5 a ONLY 21 postage 1 6 j Cash with order please and print name and address clearly Amounts given for carriage refer to inland only U E I CORPORATION The Radio Corner 138 Gray s Inn Rd LONDON WCI Open until p m Saturdays We are 2 mins from High Holborn Chancery Lane Stn and 5 mins by bus from King s Cross Small Advertisements FOR SALE Eddystone S640 choice of two mint condition matching speakers two German receivers and spares model 18 receiver Offers buyer collects Fawkes St Chloe Green Amberley Stroud Glos RADIO CONTROL that model Circuits
41. TRUCTOR 535 RCI63 Theoretical circuit of AC DC Amplifier 625 Line Transmissions The Television Society to Start Experimental Service Speaking at the Television Society s Annual Dinner m April 13th Sir Robert Renwick President of the bce said thar they would shortly be building an tpccmmenzal 625 line transmitter in order to provide a evic to both amateurs and the radio industry and thus kip the export market _ tn wes reslised that receivers intended for the con Enem ssee ord of 625 lines could be more conveniently bemoessered and rested on a radio signal under working Dotas esc with the approval of the radio industry bee Socetr bes cndertaken to operate a suitable trans pe _ Dscessoes are shortly taking place between the bocey 2d SRE M A on a suitable site and design the eget S Robe s54 1 want to make it clear that this is experimental propect undertaken for the advancement E iie eoe subject to Post Office approval 22 xE Set sid piares for experimental purposes Se 28 cake atvice from the B B C and the industry Dl bore thet the export trade will benefit accordingly The erm g s at the Dinner was Mr David ames MP Assitiant Positmaster General WWww americanradiohistorv com An Improved 17 inch Rectangular Television Tube Mullard Ltd have recently made an addition to their range of Long life Television Picture Tubes it is the MW43 64 an all glass rectangular tube with a
42. Wafers 2P Aw 3d ea 2 6 doz 005 1 000 volt Tubluar Condensers d 5 and 25 350 volt d ea 4 doz 240 0005 5w Carbon d ea 4 doz 0803 T C C Mica Condensers d each 77 NEWINGTON BUTTS ELEPHANT AND CASTLE LONDON SEII RODNEY 2180 IKOPATENTS LTD 1 Managing Director E G O ANDERSON Consultants RADIO TELEVISION ELECTRONICS 17 CRISP ROAD RIVERSIDE 2678 w6 WORLD RADIO HANDBOOK Seventh Edicion 1953 Price 8 6d New Edition just published Revised and enlarged contains all information covering the world s broadcasting stations Compiled from authoritative data WORLD i RADIO HANDBOOK is an invaluable Who s Who and a ready made log book for ali in any way interested in Broadcast station listening on a world scale The detail given is designed to facititate easy identificacion of Broadcast stations covering announce ment procedure interval signals wavelength person nel and station addresses and concaining information about Television stations from all over the world WORLD RADIO HANDBOOK is recom mended by such authorities as the United Nations Organisation International Radio Union and che United Nations Educational Scientific and Cultural i Organisation 1 iin the new edition che Uniced Nations publish the folowing message about WORLP RADIO HAND To build a lasting peace it is essential to
43. acy since the ability of the ear to differentiate between audio fre quencies even when they closely approach each other is greater than its ability to judge volume levels To use the indicator described here it is essential that the bridge to which the indicator is connected is operated from AC instead of DC The choice of AC has no effect on the AF tone heard by the operator and its fre quency may lie anywhere between say 10 Mc s and 25 cjs A simple resistive bridge is shown in the diagram but this is merely for purposes of illustration and may of course be replaced by any other type of bridge Operation The operation of the circuit is quite simple A varying amount of AC from the bridge is fed to the CR circuit C1 R1 The values of these components are such that the rectified negative voltage relative to cathode appear ing at the grid of V1 very nearly equals the peak voltage of the AC output from the bridge The grid voltage of V1 varies therefore according to the AC obtained from the bridge When this AC is at a minimum corresponding to the point of balance the negative grid voltage of V1 is at a minimum also its anode current being consequently at a maximum The result of this is that the voltage dropped across R2 is at a maximum also V2 is an RF oscillator which receives its anode voltage via R2 When the bridge is balanced the action of V1 causes this anode voltage to be at a minimum Owing to th
44. ager eyes Www americanradiohistorv com to prove the ultimate one Secondly we can have a patchwork arrange ment whereby we attempt to make existing receivers adaptable by minor modification or additional stages to gain partial improve ments Unfortunately the BBC seem to be moving along these lines This sort of com promise has little to recommend it and there is always a danger that we shall land ourselves in such a tangle of makeshifts that further progress becomes impossible without at some remote date having to make a completely fresh start Timidness on the part of the BBC may be storing up a much bigger hardship for viewers in future years The third possibility is wired TV In any case VHF gives only a local range Wired circuits could give nation wide coverage with alternative programmes The question of bandwidth no longer has to be solved It would however be an enormous undertaking and might take years to get into operation even if there are no unexpected snags By Continued on page 533 The UNIVERSAL Large Screen AC DC Televisor Part I Described by A Torrance A M LP R E A M T S By kind permission of IKOPATENTS LTD A recent survey of the electricity supplies in this country has surprisingly revealed that many people are still tied down to the limita tions imposed by DC direct current mains It was therefore decided to present a design encompassing both AC and DC mains and wh
45. ar Sir Referring to the diagram on p 338 of the March issue there is an error The positive lead of the 4 5V battery should go to the positive test lead and NOT to the common switch arm If this is left as per the diagram there is no indication when in the Ohms position FRANCIS A GRANT G3FTV Wakefield Yorks Picture Tube Defects Dear Sir Reference Gordon J King s article on p 349 of the March issue When discussing heater cathode S C on a cathode modulated tube he quite rightly points out that a mains isolating transformer cannot be used to supply the heater The objections mentioned are truly applicable to the normal type of heater transformer There is however a special transformer available for this particular application at a reasonable price The capacitive and leakage inductance losses are extremely low and very little loss of definition is noticed The sec _ ondary has tappings for 6 3 4 and 2V heaters plus a 3V tapping for low emission 2V tubes I am bringing this to your notice as I feel jt may enable some constructors to avoid the rather tedious and possibly more expensive _ method of using two valves as shown in the article The manufacturers of this particular trans former are Norman Rose Ltd Hampstead Road London N W 1 A WARD Hayes Middlesex Www americanradiohigtorv com Yalve Multi Meter Dear Sir It was with great interest I read the article by Mr J
46. ard use of a selector is given in Fig 21 which shows the circuit of a nine step selector wired to give four port four starboard and one amid ships position Each of the selector contacts is wired to its own brush and these nine brushes bear upon the surface of an insulating disc driven at slow speed by a permanent magnet motor Mounted on the disc are two copper segments with a small gap between them and they are RADIO CONSTRUCTOR 521 polarized positive and negative by pigtail con nections to a battery Since the motor is connected between the battery centre tap and the selector common it is supplied with power via one of the brushes the one selected and either of the two segments whichever one the brush happens to be resting upon will decide the polarity of the voltage applied to the motor and thus determine its direction of rotation This direction is such that the insulating space between the copper segments always moves towards the supplying brush In effect then the gap between the segments homes on the selected brush and the unit forms a simple follow up device sensitive to nine different positions c22 radio connection strip bent into an are Flexible insulated pigtails carry power to the two moving segments The final power take off to the steering gear can be by a push pull rod pinned to the end of the operating lever shown which moves with the disc The lever on the rudder shaft can be the sa
47. areful marking by the makers will avoid any possible confusion between the two and in addition an explanation of their working will be given as the description proceeds RADIO CONSTRUCTOR 325 FOCUS MAGNET FOCUS CONTROL illustration of complete assembly annotated to indicate sections See also diagrams on page 521 A simple yet effective method of keeping the tube screen dustproof has been evolved and this together with a perspex protection guard is permanently attached to the structure shown in the photograph Order of Assembling Chassis and Parts First study the photograph and sketches To avoid any confusion which may have resulted from an overdrawn set of sketches the valve holes and component drilling have been omitted The chassis A is the fundamental item and all other parts are attached with BA nuts and bolts The use of shakeproof washers is recommended Item B is bolted to the front of A This is further strengthened by the two angle brackets WWww americanradiohistorv com at the sides which also provide eventual fixture to the base of the cabinet Next attach and assemble parts G To the insides of these stick with Bostik or other suitable adhesive four pieces of felting 1 thick Carpet felt cut into strips is very suitable Bolt into position the rear tube support C and underneath the section E with at the same time the two small angle brackets Seen at the rear sides these als
48. ateur s Handbook by The Use of af Transformers by the A R R L 1953 30s Od Post N H Crowhurst 3s 6d Postage 2d age ls Od We have the finest selection of British and American Radio Books in the Country Complete fist on application 19 23 PRAED STREET Dept RC LONDON W2 PADdington 4185 SCOTTISH INSURANCE 62 63 CHEAPSIDE CORPORATION LTD NZ3 LONDON E C 2 i TELEVISION SETS AND SHORT WAVE TRANSMITTERS Television Sets and Short Wave Transmitters Receivers are expensive to acquire and you no doubt highly prize your installation Apart from the value of your Set you might be held respon sible should injury be caused by a fault in the Set or injury or damage by your Aerial collapsing A Scottish special policy for Television Sets and Short Wave Transmitters Receivers provides the following cover a Loss or dafnage to installation including in the case of Television Sets the Cathode Ray Tube by Fire Explosion Lightning Theft or Accidental External Means at any private dwelling house b i Legal Liability for bodily injury to Third Parties or damage to their property arising out of the breakage or collapse of the Aerial Fittings or Mast or through any defect in the Set Indemnity 10 000 any one accident ii Damage to your property or that of your landlord arising out of the breakage or collapse of the Aerial Fittings or Mast but not exceeding 500 The cost of Cover a is 5 a year for
49. bed in a previous issue May 1952 As the input circuit is of high impedance it will be seen that hum may be very easily intro duced electrostatically from either heater leads or mains leads Jt is therefore advisable in construction to screen the grid lead and to keep the heater leads close to the chassis It may be found necessary to employ a centre tapped resistor across the heater line with the tap connected to a point on a potential divider across the HT line and earth of equal potential to the input valve cathode The writer however has achieved a suitable low hum level with one side of the heater supply earthed The valve employed has a considerable effect upon the hum and random noise level and may if badly chosen introduce microphony and acoustic feedback from the speaker Thus it is seen that the valve must have a rigid electrode structure to avoid microphonic vibration and be suitably designed to reduce shot and partition noise The heater is best of balanced helical construction to reduce the hum field The Mullard EF37A has a suitable structure for this job and is also available in the miniature range on the B8A base as the EF40 A similar valve is the Brimar 8D5 or 6BR7 on the noval base The first stage employs a modified form of Williamson s single valve pre amplifier in which negative feedback is applied from anode to grid via a potential divider composed of either R7 C5 and R9 or R8 and R9 The latter
50. blishers eic are invited to submit samples or information of new products for review in this section ALL CORRESPONDENCE should be addressed to Radia Constructor 57 Maida Yale Paddington Londen W 9 Telephone CUN 6518 A Companion Journal to THE RADIO AMATEUR WWW americanradiohistorv com N a ata Sugges ed Circuits for the A oo A p09 2 k we Exp rimenter The circuits presented in this series haye been designed by amp A FRENCH specially for the enthusiast who needs only a circuit and the essential relevant data No 30 An Accurate Null Indicator The accurate presentation of null indications as obtained from bridges and similar measuring devices can sometimes be a little difficult to achieve When a high degree of accuracy is required it is usual to employ a meter or a cathode ray indicator Magic Eye to indicate the point of balance Very often however an aural method is employed in which case the point of balance is given by an AF tone at minimum volume level This month s circuit illustrates a simple device which is capable of giving a very accurate presentation of balance The indica tion is still of an aural nature but the point of balance is not shown by changes in volume level Instead it is shown by variations of frequency of an AF tone the null point corresponding to maximum frequency change It is this point which gives the indicator its high degree of accur
51. ct from the mains by half wave rectification and I found that American metal valves used to cope quite well with the resultant 200 volts or so which appeared between heater and cathode The rectifier used was a 6J5 with grid and anode strapped It says a lot for the manu facturer that it never broke down An even more spectacular circuit for which I was not responsible gave half wave rectifica tion at 300 volts with no limiting resistor The builder had fitted a 200 mA fuse in the HT circuit but the ripple current used to burn it out now and again The heater of the recti fier was at chassis potential In this case a metal 6L7 was used It seems incredible that valves can be so exectably tr ated and still continue to work These two circuits incidentally are very definitely not recommended for present day use WWwWw americanradiohistorvy com Tag Board Leakage recently had the task of servicing a receiver which had an HT leak This leak showed a steady resistance of approximately 500 ohms between the HT positive line and chassis and was a little difficult to discover I eventually ran it down to a tag board which had a hidden leak on the underside of the paxolin between an HT positive tag and a chassis mounting rivet Leaks on the surface of an insulator of this type are common enough although it is rare for them to have a constant value of resistance They are usually caused oxiginally b
52. cuit will be incor porated We should like to make it clear at this stage that this is an assembly design for which all items will be available from com mercial sources i All the mechanical structure is being supplied by Denco Clacton Ltd and may be obtained through your usual supplier Valve holes etc will be ready drilled A device enabling external focus control unusual with permanent magnet type focusing has been incorporated into the design This has been done to obviate the necessity to delve into the back of the set and particularly to avoid any contact by the unwary with pos sibly live parts in a set operating under AC DC conditions when a focusing adjustment is required The Elac Duomag Focaliser to be used is undoubtedly the most advanced type of PM focus unit and an explanation of its functioning will be given later The cabinet which will be available from Lasky s Radio is also unusual and worthy of special comment Basically a table model the manufacturer will construct a lower section exactly conforming to the upper part in design and style It is hoped in the near future to produce a first class radio gram unit for inclusion into the lower cabinet thus creating stage by stage the complete home entertainment which the reader may build in instalments To return to construction Voltage selection will be achieved by resistors one for the heaters and the other for HF These resistors are tapped C
53. der designers have given much thought to pro viding a means of producing colour with minor modifications and additions to our existing receivers Mechanisation The most direct way of adding colour to our existing system is mechanical Again of course we are dependent on the mixing or subtraction of primary colours Columbia developed a system using a revolving filter disc in front of the camera A similar disc has to be rotated in synchronisation in front of the CRT of the receiver It was used for LL AE Centre Tap Oa about Unfortunately the development of colour TV in Great Britain at least is not solely based on the near perfection of any system It depends on the provision of programmes No programmes no receivers No receivers no programmes Thus we find ourselves in a vicious circle but having completed that circle we ourselves have gone round in another We get back where we came in sponsored TV This might yet prove our ray of hope If sponsored FV doesn t develop colour it may very well help by relieving the BBC of some of its programme commitments so that they can Open up new fields in experimental colour transmissions Alternatives Colour and stereoscopic TV must come and we all want to see Great Britain in the van guard With the present set up we are ham strung to our 405 line 50 traversal interlaced f p s system which we started in 1936 Would we decide on it again if we were free
54. e fact that a simple oscillator such as the tuned grid circuit of V2 varies in frequency when its anode voltage varies it follows that the frequency of V2 will vary as the bridge is balanced maximum variation occurring at the point of balance The oscillations gener ated by V2 are picked up on any receiver fitted with a BFO whereupon the change in oscillator frequency is converted to a change of AF tone Practical Details _ The circuit shown here should offer little trouble in practice The valves used may be of the 6J5 class and if desired can be combined in a single double triode V2 should be capable of oscillating comfortably over the fairly wide range of anode voltages passed to it The choke in the anode circuit of Y2 should be an RF or an AF component according to the frequency of the AC used by the bridge If the frequency of this AC is very low C2 may have 2 value of l uF For higher frequencies 0 1 pF should be sufficient The value of R2 will need to be determined ne ss RADIO CONSTRUCTOR 503 BRIDGE OUTPUT HT IQ0 200V AN ACCURATE NULL INDICATOR experimentally It should be sufficiently high to cause a relatively large variation of oscillator frequency without dropping the anode voltage of Y2 to too low a value at the point of balance a yale of 5 to 50 kQ will probably be needed The oscillator should work between 10 and 20 Me s the actual frequency being unim portant
55. e list free on request NEW LIST No 8D gives details and illustrations of ex service and other items Price 1 6 Credited on first 10 purchase Order direct from Telephone SOUTH 2706 9 CLYDESDALE ir 2 BRIDGE STREET GLASGOW C 5 Branches in Scotland England and North Ireland We are sorry that we cannot repeat our December publicity offer buc as we are continually being asked for the L M S 2 coil pack together with the specially matched pair of F transformers we are now offering a parcel comprising these items The price is surprisingly low at 2 7 6 post paid L S 2 Miniature Coil Pack 38 6 Post amp Pkg 1 6 3 wave band High quaiity outscanding performance Only 5 wires to solder one nut to tighten Miniature 465Kc I F Transformers I2 Post amp Pkg 1J Specially matched to LM S 2 Coil unit Supplied Separately or in bargain parcel 5 Loud Speakers brand new nearly all sold last few 11 6 post paid DEAL COMPONENT Co 105 Evering Road N16 Small Advertisements Continued from page 551 Announcement New Service for the Amateur and Experimenter A stamped addressed envelope will bring you details of the new series of blue prints of aerial tested circuits from single valve to six and seven valve superhets In the near future kits of parts will be offered both for the home constructor and the Amateur Transmitter and Receiver Coming off the drawing board
56. ed a Toast to the Guests An organised patty of important buyers from the U S A attended establishing a precedent in Transatlantic radio marketing Yt is also to be noted that the Federation plan to hold a similar exhibition later in the year the venue being Stockholm Your contributor was invited and attempted to view through the eyes of the Radio Amateur and Home Constructor The first call was at Stand No 105 where a display of the AVO range of products was to be seen Their Electronic Multimeter a most comprehensive instrument was first to catch the eye The name of Belling and Lee is not at all unknown in amateur radio circles and this company were showing their popular products These included plugs and sockets aerial and other insulators mains and ignition suppressors and valveholders etc Also featured was a thermal delay switch for TV receiver use Making investigations on behalf of the TV enthusiast we visited the Aerialite stand where a novel colour photographed display analysed TV receiving locations and recom mended suitable aerial systems Vision aerials L Af CHINNER S G3NZ gt i _ rane of a variety of types were on show including the Aerfringe a multi element outdoor system for the fringe viewer Still with TV in mind a visit was paid to the Mullard stand where an interesting exhibit was their long life Rectangular picture tube By virtue of a development in electron gun design
57. ed to provide a grid return for V4 a further EF36 via R32 R30 and R34 Further Notes It has already been mentioned that good smoothing is essential hence the power pack should be designed to provide 250 volts or thereabouts with an extremely low hum level The writer has achieved good results using what is in effect two power packs in series employing separate smoothing The pre amplifier and radio feeder are fed by one power pack while both in series supply the main amplifier for which a higher hum level is tolerable For the benefit of those who have laid in stocks of 6SH7 s it may be stated that this valve is quite suitable for V1 provided normal precautions to avoid hum are taken It was found essential to well clean the vaive base and socket with some form of cleaning fluid to remove flux residues and dirt as leakage otherwise occurred from heater to grid WWww americanradiohistorv com Methylated spirits or lighter fuel may prove useful although carbon tetrachloride should be better The writer successfully employed a mixture of trichlorethylene and ethyl acetate for this purpose A ceramic socket improves matters as dirt is more easily detectable and removable from a glazed surface Some authorities claim that hum may be reduced by demagnetising the valve The writer has not noted any appreciable difference in hum level by demagnetising a 65H7 how ever the metal envelope of this valve probably screens
58. educe this drop then this condenser should be increased to 0 25uF or 0 5uF j Modification to Magnetic Recorder in Sept Oct and Dec 1952 issues The recorder previously described can be improved by incorporation of this network in place of the original bridged T After experimenting with the Qualtape head certain improvements have been found possibie In its normal condition the fixing bolt shorts together the centres of the head cover plates Therefore a continuous shorted turn is formed by the case and the fixing bolt around each pole piece By insulating the bolt from the lower cover plate the shorted tum is eHminaied and the inductance impedance and output are increased and damping con siderably reduced Fig 4 gives full details of the alteration In view of the increased impedance the load resistance on the secondary of the input transformer should be increased to about 500k Another alteration is in the deck layout One of the guides is removed and the erase magnet mounted on a swinging arm RADIO CONSTRUCTOR 513 FIGURES FOR COMPENSATION NETWORK OF MAGNETIC RECORDER AMPLIFIER These are actual figures taken with calibrated attenuat i 3 or and oscilloscope The bass bo is actually greater than the calculated value as the shunting on the 6J7 ae load is na at low frequencies on playback so giving greater stage gain The figures also allow for valve and stray capacities normally encountered if bu
59. el and signal to noise ratio would not be so good The usual type of simple compensation filter consists of a bridged T network as in Fig 1 and such an arrangement was used in the magnetic recorder described in the Sept Oct and Dec 1952 issues The condenser C2 is shorted out on record giving top boost only When C2 is in circuit on play both bass and treble boost results While such a circuit can give correct bass compensation the rate of rise at treble fre quencies is not sharp enough to give perfect correction at the top end It is important that negligible boost occurs in the region of 1500 2000 cycles relative to other frequencies either on record or play A method employed by some commercial recorders is to use an inductance tuned to about 7 ke s This method has many dis advantages however a expense b it is prone to hum pick up by magnetic induction c the circuit rings on transients and the response to square wave testing is in general undesirable unless some form of artificial hangover is required to compensate defects elsewhere in the system tt a a raai RADIO CONSTRUCTOR 511 c3 200 250 V RCI95 VOLUME i IMO SWITCH CLOSED ON RECORD F1G 2 PRE AMPLIFIER AND COMPENSATION NETWORK After extensive tests with an oscillator and oscilloscope on a large variety of networks the circuit of Fig 2 has been found to be most satisfac
60. ents will be accepted at 6d per word minimum charge 6 If a Box number is required an additional charge of 1 will be made Terms Cash with order All copy must be in hand by the 12th of the month for insertion in the following month s issue WANTED to buy or Ioan Service Manual for Invicta T 103 TY Box No C119 WANTED Yolumes one two and three of Radio Con structor s complete with indexes Good price paid Yates Linwood Lodge Knowle Birmingham WANTED Metal case for CR100 front panel immaterial A Thornton 110 Waterford Road Ipswich Suffolk WANTED 12 static CRT type VCRI3I NC20 or VCRSIIA Must be OK Price etc to Hill 1 Hardwen Avenue Lea Preston Lancs WANTED Information on Ex Gov Receiver Identi fication Unit RDF No I ZC13312 Henshaw 23 Culver Road St Albans Herts WANTED Service sheet for Romac TV 189 G Caunt Fl Crescent Green Kendal Westmoreland WANTED Two stage Preselector built in Power Pack 20 to 80 metres T Smith 42 Wormholt Road London W 12 WHAT OFFERS Globe King kit new Xmas Jenner 53 Clifford Road Hounslow Middx WANTED HRO dial and Meter Your price for oew or perfect condition Haworth 15 Regent Street Haslingden Lancs FOR SALE H M V Television Model 1804 10 inch tube going what offers Killick 194 Lyham Road London S W 2 FOR SALE Peto Scou Trophy 8 Communication Receiver 5 bands 520 ke to 43 mcs complete with ke
61. er The actual value of the condenser will depend to a large extent on the listener There is no reason why several different values could not be joined to a wafer switch and so provide a selection The writer however has found that one of 0 005 F is about right it has an impedance of some 50 000 ohms at 700 cycles and only some 5 000 at 7 000 cycles The higher the value of the condenser the lower will be the value of the frequency that is lifted The coupling to the following valve the ULAI1 is by means of a 0 01 pF condenser into a 1 MO resistor These values of condenser and resistor do not appreciably affect the lower end of the audio range but help to reduce the chance of motor boating in the amplifier The condenser chosen for the bias of the UBC41 was one of those very small ones made by T C C whereas that for the output valve was amp normal sized 50 uF 50 volt job as it has to carry 4 much higher amount of AC The smoothing used was very efficient two 32uF condensers of the hole and nut type made by Hunts were used in conjunction with a 10 Hy choke of 50 mA carrying cap acity As the condensers were so large a surge limiting resistance of 150 ohms is joined between the cathode of the rectifying valve and the reservoir condenser If this resistor is omitted it is highly probable that the rectifier valve will be severely damaged in a very short time The writer has had experience on more than one occasion of t
62. er transitron timebase circuit Usually only the anodes of four paraphase valves need to be supplied at 500 volts and the current is well under 20 mA By taking 250 volts from the cathode of the full wave rectifying valve via C3 Fig 19 to the junction of the metal rectifier MR1 and MR2 the ripple voltage across MR2 is again rectified by MR1 and the full mains voltage 250V appears across each rectifier giving double the voltage between the final HT point and chassis The value of Cs is chosen to pass a current not exceeding the rating of MR2 The rating of MRI and MR2 should be adequate to cover the external circuit current 20 mA Selenium rectifiers rated at 250V 30 mA are quite inexpensive and are suitable To find the value of Cs MR2 may be assumed to have negligible DC resistance and therefore the voltage across Cs to be the full 250V The reactance of C5 is 106 2rfC where f mains frequency and C uF As by Ohm s Law this reactance also equals E we may say that I 106 250 x 1 000 2riC 30 i where 250 the supply voltage across Cs and 30 the current to be passed by C5 to the rectifier rating 106x30 Therefore CuF mix 20x i000 038 uF In practice MR2 will bave resistance although its value compared to the reactance of Cs at 50 c s 8 3330 will be small As the current through MR2 is not steady DC the value of Cs may be much greater than the calculated one and in practice 0 5 pF or 1 0 F
63. ery wide range of fre quencies is required then the transformer has serious Hmitations Quite satisfactory results can be achieved however if the transformer is a well designed product If it has a step up ratio from primary to secondary some voltage gain is obtained in the transformer itself For example if it had one volt in its primary and a step up ratio of 5 1 then there would be 5V developed across the secondary Although the subject of the design of audio transformers is a very deep one which I do not here propose to go into here is a word of guidance Generally the better the trans former the larger it is Recently it is true new techniques in this direction have resulted in the manufacture of very fine transformers of light weight and of reasonable size but these are expensive in comparison with the older types which can be found in any friendly enthusiast s junk box Another widely used coupling method is the resistance capacity system shown in Fig 3 You will see that the valve has a resistance in its anode and as in the simple amplifier described last month the output voltage is developed across it The output voltage at the anode is transferred to the grid of the next valve by a condenser This condenser also serves to prevent the HT voltage in the anode of the first valve from reaching the grid of the second There is a point here which I know many people find confusing I did myself The signal volta
64. esistances 4 to watt six valve holders cans and covers All complete for 7 6 Also offered complete with valves at 17 6 Drawings available and modification for conversion to mains operation RADIO GRAM CHASSIS AND CORONATION FREE GIFT Choice of chassis six wave Export Model at 15 5 0 or three wave Home Market Model at 10 17 6 carr 4 6 Both types have five valves gram pick up sockets flywheel tuning negative feed back and measure 14 x77x8 Free gift of 8 P M speaker and or special REDUCTION to 12 6 of a 10 P M speaker ACCUMULATORS 2Y I4a H 19 x1 x 6 4 6 Post Ij MAINS TRANSFORMERS Brand new by famous maker Frimary tapped 9 205 225 245 300 volts at 200m a Secondary 5v at 2A and v ac 7A Tested BARGAIN PRICE 2 6 Post 1 9 O P TRANSFORMERS Store soiled unused Match all normal O P valves to 2 5 ohms speech coil To clear ac 1 9 Post 9d CONDENSERS Store soiled unused Tested two gang 0O05mfd tuning condensers offered at 2 9 Post 6d Sate offer of 3 for 7 Stamp for complete catalogue C W O or C O D DUKE amp CO 621 ROMFORD ROAD LONDON EI2 Money back guarantee GRA 6677 RADIO CONSTRUCTOR indicator Unit SLC No 5 Suitable for conver sien into oscilloscope using a 139A or a 3BPL Tube Unit consists of 3 valves two VR65 s and VR66 condensers 24 mfd 500v working tube holder and base 4 potentiometers group boards containing 2
65. etically and by country Zone Boundaries Cail Areas Mileage Tables OSL Bureaux Q and 74 Codes WWV Skeds and much other information as well as a selection of maps of DX areas SPEAKER SUPPORT STRIP FELT PACKING FRONT VIEW PLAN OF CHASSIS ASSEMBLY Price 2 6 postage 2d DATA PUBLICATIONS 57 MAIDA VALE LONDON W WWww americanradiohistorv com Astigmatism in Electrostatic Cathode Ray Tubes By C R DRAYTON Many amateur television experimenters have managed to get really well defined pic tures from their war surplus six inch cathode ray tube receivers Many too thust have reached the point where it seems impossible to improve no matter what is done in the way of band width adjustment video valve comp ensationetc When this stage is reached it would seem to indicate that maybe the tube itself is the limiting factor Et is well known of course that these small tubes possess character istics not ideally suited to television In this connection the writer has found it profit able to devote some attention to spot size and shape So far as size is concerned the best procedure seems to be to use as high an EHT voltage as possible Quite often however there remains the defect which has been termed astigmatism Astigmatism is usually apparent when focusing It may be possible to detect two distinct positions of the normal focus control which give relative sharpness At one point the scan
66. f their full introduction There is however one outstanding develop ment which may have an important bearing on the proof of their practicability I refer of course to sponsored TV The Assistant Postmaster General recently revealed that 46 enquiries for sponsored TV licences had been received There were also 26 enquiries about buying time in the sponsored pro grammes The possibility of alternative TV programmes being available before the end of next year will for many make cheerful reading Unfortunately the more alternative programmes we have the narrower the chances of getting colour or stereoscopic transmissions become All present systems require three times the bandwidth of monochrome TY and the only way of squeezing them all in ts to move them to still higher frequencies Apart from disturbing the present allocations in the VHF spectrum the further HF we go the more restricted becomes the range of each transmitter Competition Nevertheless it is becoming increasingly important for these problems to be seriously tackled We must regain our diminishing lead in technical developments A couple of years ago we and America had a very long lead over the rest of the world But TV has expanded rapidly since then According to Unesco 55 countries are now engaging in some form of regular TV activity Japan Cuba and most of Jatin America are all well in the running Even the small republic of Dominica has had regular tran
67. fectrofor driving a gear train of 1000 1 ratio On4 5 V applied to the motor the current consumption light was 0 254 A load of 1 6 was then applied to the output lever which had an effective radius of 1 7 and the current rose to 0 35A the lever taking 4 seconds to move through 60 A force of 1 6 is of course far more than is needed to shift the rudder of a model boat and in this case was designed io operate the steering gear of an armoured car model total weight 83 5 2 Selector systems similar to the one described can be designed with any number of positions the limiting factor being the time delay that can be accepted for operation through a complete sequence Any selector shouid be capable of interpreting at least 10 pulses per second in model work it is advisable to check the positive operating speed when the batteries have fallen to their accepted miminum voltage To be continued TV and its alleged rival the third dimensional film have been much in the news of late and this added to my recent comments on colour and stereoscopic TY seems to have provoked a number of letters from readers So much so that I feel I am left with no other alternative than to treat these as the topics for the month As so few details of the colour and stereoscopic processes have been made public it is only possible to consider them in a general sort of way and we are still very much at the guessing stage about the probable date o
68. ge ECC91 double triode mixer and oscillator EF92 IF amplifier with stabilised voltage supply via a 7475 ls 8d ost free with full instructions A S W P 57 Maida ale London W 9 REPRINT Converting the TRiI196 Receiver Full details on converting this unit which may be purchased quite cheaply into a very sensitive all wave receiver d post free A S W P 57 Maida Vale London W 9 Miller s PANL the air drying black crackle enamel From dealers 3s 6d jar or direct 4s 6d including postage 8 Kenton Park Crescent Kenton Middx OSMOR for efficient coils coilpacks etc Send Sd stamp for FREE circuits and lists Dept RCC Osmor Radio Products Ltd Borough Hill Croydon Surrey Tel Croydon 5148 9 VALVES VALVES VALVES i2AT7 12AX7 12AU7 636 9 EF91 EC91 6X4 7 6 6AL5 6 6 EF92 6C4 EACS1 6 Skillman 74 Franchise Street Weymouth INSTRUMENTS RECTIFIERS t MA 6 230 AC to DC F W Rectifiers 300 MA 1 0 0 3A 9 0 0 5A 12 0 0 many others S A E LAWRENCE 134 Cranley Gardens N 10 RADIO CO YOU CAN Midget LF Transform ers Type 800 21 per pair Standard Type 500 501 465Kc s 20 pair HIGH IMPEDANCE HEADPHONES New Ex Government Price 12 6 per pair SCOTCHBOY TA 200ft Reels 35 Spare Reels 4 3 The WAVECHANGE SWITCHES Midget rectangular Type 2P2W 2 6 2P3W 2 6 Midget Circular Type IPI2YV 2P6W 3P4W 4P3W each 3 6 Standard Yaxley Type
69. ge developed across the anode resistance is actually developed at the anode with respect to the HT end of the resistor Now in our circuit we have caused this voltage to be developed between the grid of the next valve and earth the latter via the grid bias battery the resistance of which is negligible To explain this it must be appreciated that there are virtually two currents flowing in the anode load resistor one is direct current flowing from the battery through the valve and the other is the variation in this current caused by the action of the valve In other words there is a direct current and an alter nating current Now the HT battery is connected from the upper end of the anode load resistor to earth However the variation in current i e signal current in the anode circuit develops only a tiny voltage across the HT battery due to the battery s internal resistance a voltage which can be ignored in comparison to the signal voltage developed across the load resistor We may say then that the upper end of this load resistor as far as the AC is concerned is in series with a very small resistance the internal resistance of the battery and is connected to earth In actual fact the signal voltage is developed between the anode and earth because as we have seen above earth and HT are connected together from the AC point of view Final Comments The resistance connected from the grid of the second valve to the
70. he valve pinch in the older types of valves being blown out through the envelope with serious results to the valve The chassis used for the construction was one of the type 10 made by Kendall and Mousley of Tipton Staffs The fact that the amplifier is of the AC DC type makes it unsuitable for use in a metal case and if a wooden one is used plenty of air space must be given The mains dropper used is in the form of a 40W 250 Volt lamp This gives the correct amount of voltage drop when used on the 230 volt mains The use of an electric light bulb for a dropper is by no means new it has the effect of reducing the surge through the valves as it warms up very quickly As the valves warm up and increase in resis tance the current is reduced and the resistance of the lamp drops so that any small voltage Shema dons of the mains are compensated or The components required are One Each UBC41 UL41 and UY41 Three B8A holders One 0 25 M volume control W S One 50 k Tone control One 2 2 KQ resistor One 1 MQ resistor One 300 ohm resistor One 30 kQ resistor One 150 kQ resistor One 150 chm resistor Two 32 uF 350 Volt or higher condensers One suitable smoothing choke One suitable output transformer One 8 pF 6 volt condenser One 50 uF 50 volt condenser Two 0 01 uF 350 volt condenser One 0 005 uF 350 volt condenser One Lamp holder One 250 volt 40 Watt Bulb One suitable chassis RADIO CONS
71. i 500 kQ2 4W HS C2 16 uF 350 V Elect S R2 4 7kQ 3W HS C3 0 25 uF 250V Paper THET R3 220 kQ 4W HS C4 0 1 uF 500V Paper a sa We R4 47k0Q 5W Composition C5 100 pF Silver Mica 10 mi a R5 470kQ 4W HS C6 25 uF 25V Elect o j R 68k23W HS C7 0 5 uF 350V Paper 5 o C R7 220kQiW HS Cs 0 5 nF 350V Paper 5 Tg R8 220k Ww HS C9 0 1 gF 500V Paper x ROATA R9 22kQiWHS CiO 0 005 uF 500V Paper S 3 RIO 250 kQO Logarithmic CII 0 05 uF 500V Paper Erd RIL 3 3 kO W Compo Cl2 100 pF Silver Mica o RI2 47 kQ W Compo CI3 1000 pF Silver Mica rar R13 22 k amp W Compo Cl4 25 wF 25V Elect ie Rl4 22 kO 4W Compo C15 100 pF Silver Mica 5 gt i RI5 100 kQ 4W Compo C16 200 pF Silver Mica 5 aii 2 R16 250 K9 Logarithmic C17 300 pF Silver Mica 5 D RIF 10 kQ 4W Compo C18 500 pF Silver Mica 5 R18 100 kQ Linear CI9 50 pF Silver Mica 5 3 R19 10kQ 4W Compo C20 100 pF Silver Mica 5 R20 1kQ24W Compo C21 250 pF Silver Mica 5 R21 100 kQO W Compo C22 25 F 25V Elect R22 100 kQ iW Compo C23 0 5 uF 350V Paper R23 470 kQ 4W Compo C24 0 5 uF 350V Paper a R24 3 3 kQ W Compo C25 0 1 uF 500V Paper amp R25 00 k2 W Compo C25 Sopa 4 R26 22 k2 W Compo C27 100pF aa x R27 22 kQ W Compo C28 150pF 38 gt R28 1 MQ iW Compo C29 200 pF ey 2 R29 i100 kQ EW 1 C30 200 pF Silver Mica w R30 100 kQ or Cal E 12 ES R31 50k2 matched C32 JOOpF or aa R32 470 kQ 1W Compo C330 O75 pF Matched 3 R33 1 MQ Logarithmic C34 150 pF Capac
72. ications R T E B and other professional examinations Train with the College operated by Britain s largest Electronic organisation Moderate fees Write to E M 1 INSTITUTES Postal Division Dept RC28 43_Grove Park Road London W 4 Associated with H M Y METALWORK All types cabinets chassis racks etc to your own specification Philpott s Metalworks Lid Dept R C Chapman Street Loughborough KENDALL AND MOUSLEY Manufacturers of Laboratory Equipment chassis and instrument cases also suppliers of B V A valves Radio and T V com ponents 99 Dudley Port Tipton Staffs WWww americanradiohistorv com TRANSFORMERS Manufactured to our specification and fully guaranteed Normal Primaries 425 v 0 425v 200 m a 6 3 v 62 6 3 v 6 an D Y 3a 02 463 v 3 a ONLY 72 6 425 v 0 425 v 200 ma 6 3 v 4 a 6 3 Y 4 a 5 v 3 a ONLY 50 350 v 0 350 v 160 ma 3 v 6a 6 3 v 3 a2 5v 3a ONLY 42 6 250 v 0 250 v 100 ma 6 3 v 6 a 5 v 3 a ONLY 32 6 The above are fully shrouded upright mounting Universal Mount ing 350 v 0 350 v 80 ma 0 4 6 3 v 4 a 0 4 5 v 2a ONLY 18 6 Top shrouded drop through 260 v 0 260 v 70 ma 6 3 v 32 5 v 2a ONLY 16 6 The following are upright mounting EHT for VC97 Tube 2 500 v Bima 2 0 2 v l l a 2 v 0 2 v 0 2 v 2a ONLY 37 6 EHT 5 500 v 5ma 2 v ba 2v a ONLY 72 8 EHT 7 000 v 5 ma n 4 v a ONLY 82 6 PLEASE ADD 1 6 PER TRANSFORME
73. ich also covered all voltages from 200 to 50 Fortunately valves and equipment are available for this design which is based on series heater chain technique and is approved by Mullard Ltd Such a design also of course means that the intending constructor must bear in mind at all times the dangers attendant upon the chassis being at mains potential This need for caution is particularly important whenever operating tests are carried out during the building period when the chassis is not protected by the cabinet and a careless moment may have serious results We do not intend to be macabre but you will not be allowed to forget this highly important aspect of AC DC technique for we shall make constant reference to it The system also has its advantages and the compact and remarkably lightweight design possible with this method is readily appreciated from the illustrations which will be appearing A good idea may be obtained from the accompanying view of the chassis structure which when properly installed in a cabinet wil be perfectly safe for all members of the family to handle On the structure shown will be the complete receiver CRT speaker sound and vision strip timebases and all the requirements to suit electrically the various Mains supplies wherever it may appear All five transmitting channels will be covered by a modern superhet design and of particular interest to fringe area dwellers a highly efficient sync cir
74. ill require approx 18 20 db boost at 100 cycles no boost around 2 kc s and approx 15 18 db boost at about 8 ke s To obtain maximum signal to noise ratio it is obvious that the maximum recording level should be used but the peaks should not extend into the saturation point of the tape This is almost unavoidable however in general practical applications but the number of such peaks can be kept down by good recording technique and the best use of microphones and the best recording level can soon be determined with experience The fall off in bass reproduction at a rate of 6 db per octave is a basic characteristic of A ELG BRIDGED T NETWORK SWITCH CLOSED ON RECORD RCS magnetic reproduction of a constant amplitude recording cimilarly the bass fall off in disc recording Consequently it is not advisable to emphasize the bass frequencies during recording as the tape would easily saturate If the microphone response lacks bass how ever enough compensation can be added to correct it The drop at the high frequency end is due to the transfer characteristic between head and tape and includes iron losses and gap effect losses These are common both in recording and reproduction so that an equal amount of top boost may be applied in each of these positions Jf in fact all th boost were applied only on playback the recording signal level at these frequencies would be correspond ingly down relative to tape noise lev
75. ilt to the instructions which were given 190 ROL Oe 6OpF 657 RC 98 Alternative values are given for C0 01uF and C2 0 00SuF i y ative va 0 005uF is sh ait position and no pass boost occurs on this position ae gye for _ireble response is given for a trimmer set to a fixed 60 pF capacity If the recorder circui trimmer is set to zero the treble response of the network will 5 i ee re ETEA A ill of course be flat with no treble C 0 01 uF SS kL is a oS A ee ee ee a Frequen y i 100 c s 200 c s 509 c s 1000 c s 2 ke s 4 ke s 8 ke s Record C Out 0 0 0 E 4 5 lee Play C 1n ree Pag sa igi e 3 0 63 Total Sei 53 SS E C 0 005F he Frequency 100c s 200 c s 500 cis 1000s 2ks Ake 8ER Reord COu 0 0 o 0 1 8 ne a Play C In 19 7 Ca ee i a eee Total 179 952 ol oe Dime sa Fe Use 0 01uF for 74 ins sec normal heads medium coercivity tape Use 0 005 for 15 ins sec normal heads medium coercivity tape These figures do not include other slight compensations incorporated in the amplifier Www americanradiohistorv com a 514 BOLT SWINGING PLATE PRING WASHER ORIGINAL GUIDE REMOVED RS SE MAGNET ROU 7 TRAILING 5 EDGE Zo FROM 7 ERASE POSITION FIG 5 ERASE MODIFICATION TO_REDUC THREADING amp TO STABILIZE TAPE_FLATNESS RCI97 There arefseveral reasons for this a Les
76. ined with a triode Usually one can say that the higher the mutual conductance the higher will be the ampli fication or gain as it is often called of the valve The fifth electrode of the pentode valve is the suppressor grid between the screen and the anode which serves to overcome certain CATHODE EIG 0 TETRODE OR SCREEN GRID VALVE b PENTODE VALVE HEATER c MAINS TYPE TRIODE disadvantages present in an ordinary tetrode There is 2 type of tetrode available nowadays from which such disadvantages are removed by using plates mounted in the electron stream between the screen and anode to form the electron stream into a beam Because of this characteristic these plates are called beam forming plates and this type of valve is called a beam tetrode All the valves so far described have only been suitable for use with DC filament supplies If AC were used to heat the filament the AC signal would cause the electron stream to vary and would therefore produce a small alter gt RADIO CONSTRUCTOR 537 ee eee T zA nating current in the anode circuit In a practical design ths would be evident as an objectionable hum If for example we were to use the mains via a transformer to heat the filament a 50 c s hum would be superimposed upon the signal You could of course overcome this by changing the AC voltage to DC by the use of a rectifier but this would be expensive and clums
77. ired to an electrically driven follow up device and re presents a definite rudder position Initially Fig 21 9 Way selector in simple steering unit pawl which works on a ratchet wheel Very often a detent is provided against the wheel to prevent reverse rotation as shown in the drawing Each time the magnet is energised on receipt of a signal the pawl rides over a tooth of the wheel when the signal terminates the armature returns by spring tension and carries the wheel round one tooth A wiper arm or arms is mounted on the shaft of the wheel and rotates over a ring or rings of contacts thus switching various circuits Obviously the limitations of this device are decided by the number of wiper arms and the number of positions and an enormous number of combinations are available In most cases the constructor will arrange these to his own requirements but some illustrations of the commoner circuits in which selectors are used will be given this may seem no advantage over the escape ment but there are two important differences the follow up mechanism need not operate until the selector finally homes on a selected position thus avoiding moving the rudder through unwanted positions Secondly the selector can work at very high speeds so that a larger number of steps can be used in the sequence providing finer control without slowing down the response An example of this straightforw
78. itors C35 200 pF zia Where no voltage rating or tolerance is given C36 300 pF 7 amp these may be taken as 250V and 20 respect C37 400 pF eg K ively C38 0 1 uF 500V Paper a RADIO MISCELLANY ae continued from page 523 workshop control console transmitting table a or laboratory use way of an afterthought we might also add there could be no more pirates Only this week somebody was quoting their number with a siring of five noughts on the end Judged on present form unless the unexpec ted happens as it so often does it looks as if aiternative two will be the next step and my guess is that sponsored TV may prove a two fold blessing Gadget of the Month From a number of specimens received for review from Messrs Kendall and Mousley of Tipton Staffs a pair of meter stand ends took my eye While their first appeal was largely prompted by novelty I certainly cannot remember anything like them having previously been popularly marketed their usefulness makes them worthy of recommendation for Wwww americanradiohistorv com They consist of a Hght but rigid frame neatly finished in crinkle enamel upon which panels of various lengths can be fitted Thus a single meter such as an S meter or a whole row of instruments can be mounted at an angle of 45 degrees from bench or table level This is an ideal angle for observing meter readings or other visual indicators whether one is standing up or Sitting as
79. l 1 0 lin Soiled with fitted Simm 4 5 mm 3CTH 315 W parked 5 11 Fer pees ELAC P M FOCUS MAGNETE aan a fmm 6 mm 3CTH 422 Ww THE TELE KING For l4in and l6in Tetrode tubes 4 212 6 p THE VIEW MASTER Guaranteed noc less than stated values at 25 C Large screen celevision For 4in and I7in Triode tubes 217 6 J Television for tha home constructor at f its finest 32 page book let and 8 fullsize wiring diagrams PRICE 7 6 Post Free State station required IS INCH CATHODE RAY TUBE for home construction Superher 5 channel 32 page booklec and full size wiring diz grams PRICE 6 POST FREE i THE TELEGRAPH CONDENSER Co Ltd Radio Division North Acton London W3 Tel Acorn 006 B J ic RA INSTITUTES THE MAGNAVIEW Large screen television Construction booklet PRICE d POST FREE SPECIAL CORONATION C R Meee eae an TUBE OFFER MASKS No Cream rubber Lasest Brand new and unused 12 inch ion crap aspect ratio Overal dimensions U7ins VERSION Write for hode Ey canes Banot Mantlacture wide 3ins high Price 17 6 Postage Details er 6 3 volt heater 7 9 Ky E H T 35mm Zieta An R R neck Biack and white picture No 2 Plastic incorporating gold finish tube escutcheon and dark screen filter Latest aspect ratio Overall dimensions Sin wide I2in high Price 21 Post age 2 extra 4 ARMOUR
80. lloscope given last month C22 is given in the Component List as 0 1 uF but appears on the diagram as 0 05 This component is not critical and either value will be quite satis factory Two resistors in the tube network bear the number R 40 The lower one going to the focus pot should be 300 KQ whilst that going to H T positive is 50 KQ There should also be two 2 MO resistors in series across the shift pots the centre tap going to chassis The CRT used in the original design is a VCR 138 RADIO CONSTRUCTOR 545 WIDE ANGLE TELEVISION COMPONENTS FOR MAGNAVIEW ENGLISH ELECTRIC AND BRIMAR CIRCUITS HAVE NOW BEEN CHOSEN EXCLUSIVELY FOR THE NEW AC DC TELEVISION RECEIVER DESCRIBED IN THIS ISSUE SOUND amp VISION COILS amp CORRECTOR CHOKES fm roage wo CH 1 CH 2 CH 3 2 6 ea L 5 with condenser 3 9 ea Pip Sa ee 4 6 ea L 7 with condenser 3 6 ea ETAB te 2 9 ea I2A B with conden L 3 4 6 and 8 2 6 ea et ge SO a T Sorea SCANNING COMPONENTS Deflection Coil Assembly Focus Coil WAJFCA 1 31 TWA DCA I i amp 3j Width Control WA WC 1 7 6 Line Linearity Control WYAJLC I 7 6 Line Output Trans Frame Output Trans WAJFMA I 21 WAJLOT 1 w Rj Frame Blocking Osc WA FBT I 16 Smoothing Choke WAJSC I 19 Drilled Chassis complete wich all Brackets will be available soon er ee ee SS a SS ee Obtainable from ali repu
81. me length as the operating lever so that the two move in step and in this case one obtains full control from port 20 to starboard 20 in 5 steps Any small commercial motor will do for a power unit a number of inexpensive permanent magnet motors being available As an index of performance the following notes may be of interest An electrically driven actuator was recently Fig 22 9 Position follow up mechanism Fig 22 is a drawing f an easily made unit on these lines The small motor is coupled by a short length of spring to a reduction gear train which is most compacily made from two worm and wheel stages as shown but if these are not available the gear train from a small clock will do very well often the motor can be coupled to the seconds hand shaft which projects beyond the frame sufficiently to take a soldered coupling and the final drive can be mounted on the hour shaft thus giving a reduction ratio of 3600 1 The resi of the mechanism is cut away The contact disc shown is a circle of paxolin bolted to a brass hub contact segments are cut with scissors from hard brass or copper foil having mounting lugs turned over through corresponding slots in the paxolin Copper foil brushes are arranged firmly to bear on the disc at 5 intervals their fixed ends being supported by a perspex arc alternatively they can be soldered to the tags of a suitable WWW americanradiohistorv com made up using an E
82. ndition Modification data supplied Price 5 carriage paid INDICATOR UNIT TYPE 182A This unit contains VCRSI7 Cathode Ray 6 Tube complete with Mu mecal screen 3 EF50 4 SP6l and SU4G valves 9 wire wound volume controls and quantity of Resistors and Condensers Suitable either for basis of Television full picture guaran teed or Oscilloscope Offered BRAND NEW less relay in original packing case at 79 6 Plus 7 6 carriage YCRSITC BLUE AND WHITE 6 in TUBE This Tube replaces the VCR97 and VCRSI7 without alteration and gives a full Blue and Whice picture BRAND NEW in original crates 45 plus 5 carriage WEYMOUTH 3 WAVE BAND COIL PACKS Short Med and Long with Gram Switch Brand New Miniature type complete with circuic 19 6 P P 1 6 Absolute bargain SEND 3d FOR 28 PAGE CATALOGUE 550 RADIO CONSTRUCTOR FRED S Radio Cabin Olympic Coil Packs 3 Wave Band 24 6 AC DC Amplifiers Be eae 3 15 0 AC TRF Midget Sets rae 6 100 Tyana Soldering Irons oie on a 16 9 Sleeving 12yds oe ae oy 219 4000 w w Pots Ta fe 2 6 gt VR54 oes win ot Ss 2 6 6K 7K 10K 30K w w 2 Low Res ae 1 6 50 pF and 20 pF Ceramic Trimmers nae tjn 3P 3w WCS dc oh tfc cue 2 3 Indoor T Aerial oh ae nee 7 6 10 Amp Mains Filters een eae an 10 4P 2w WCS e een ri R 2 6 8 way Jones Plugs I 6 Pin d 3 Link Aerial Insulators fee aes d 1 14 Plastic Tube I yard Yaxley
83. ne Bass Treble Wavechange Tuning Radio Gram Brill OnOff S M L Gram All 1 6 each Dept K 444 WANDSWORTH ROAD LONDON MACaulay4155 Swe BOOKS WorLo Rapio O Johansen HANDBOOK How To LISTEN TO THE Worcip O Johansen INEXPENSIVE TELEVISION ASWP tds 2 5 TY Fault FINDING aswP etd i a 5 Above prices inclusive of postage ete DATA PUBLICATIONS Lyon Court 7 Maida Vale London W9 WWW americanradiohistorv com Telephone CUN 6518
84. ned whilst on the other hand no one is surprised when the tube becomes un rejuvenated all over again within a month Before concluding on this subject I should like to point out as my own opinion the fact that some of the spectacular successes claimed to have been given by these rejuvenators might perhaps need to be taken with a pinch of sait Low mains voltages and inefficient mains transformers are not unknown even in the States It might happen in one or two cases that a cathode ray tube has been working for a long time at a heater voltage say 10 per cent lower than that it was designed for Increasing that voltage by 25 per cent or even increasing it just to the correct value would be almost certain to result in higher emission for quite an appreciable length of time Cheap Rectifiers I was very interested in R W Hill s article in the December issue in which he described how he managed to use a surplus double triode as a full wave rectifier by strapping together the anodes and grids of each section It also brought back war time memories to me and doubtless to other readers of some of the haywire power supply circuits we used during this period when rectifiers and transformers could not be obtained I remember building one receiver a four plus one with 6V6 output in which a single home made 6 3 volt transformer supplied afl the heaters including that of the rectifier HT was obtained dire
85. ng C soldered between the link and an 8 BA screw in the arm A al 6 1 Pam crs Fig 18 Manual pulsing unit scale in inches In the sequence diagram A S and P represent Amidships Starboard and Port RADIO CONSTRUCTOR Fig 19 Manual pulsing unit complete on perspex base As the arm is rofated through its three positions the link tends to move through an arc of a circle but it carries a small peg at the end which interferes with the two guides D and E These cause it always to move under them when travelling away from the centre but trap it above them when travelling inwards The peg therefore follows a kind of figure eight path as the arm 4 is rocked from side to side i Several contact strips F are soldered to pillars screwed into the insulating baseboard and as the peg moves through its path it brushes against these strips and in so doing keys the transmitter The keying leads are taken one to all the contact pillars and one via a copper pigtail to the end of the spring C Jf the movement of the peg is studied against the small sequence diagram printed along side it will be seen that the correct number of pulses are sent to step the escapement round correctly In making this device the peg at the end of link B should be allowed to pass weli clear of the ends of guides P and E or there may be a tendency for the peg to return along the incorrect path The position of the peg at the end
86. ning lines will be sharp and horizontal picture detail somewhat lacking The second point will give improved horizontal definition the vertical elements of the picture will be sharp but the scanning lines will have disappeared or nearly so The effect is easily explained Each pair of deflector plates acts as a focusing electrode but being split into two parts can only be effective as such on one axis Thus if the mean potential of a pair of plates is varied the spot will be compressed or elongated in one direction only That focus does not vary to any extent when the tube is being scanned is due to the fact that with a push pull timebase the mean potential of the plates does not change It does not necessarily follow that a little astigmatism is a bad thing A spot which is slightly elongated in the vertical direction _ may give a solid and sharp picture The effect is similar to that obtained by spot wobbling or spot squashing and merely serves to fill in the spaces between the lines On a six inch tube the spaces between the lines are very narrow and little vertical spot elongation is tolerable as the lines will soon merge and vertical detail will be lost Before attempting any correction it is as well to determine the degree of the defect and whether or not both pairs of plates are involved This is easily done if the timebase is discon nected and the stationary spot de focused to about 3 16 diameter
87. o are used for cabinet fixing Note that the rear holes are used in the bent up parts of the chassis D may now be loosely fixed in position with four 6 BA screws but these should not be tightened up until the deflection coils are purchased It will be seen that provision has 4 526 been made for rotating the coils for straighten ing the picture and for a vertical movement for centralising the coils into line with the focus magnet The focus unit fixed with four 13 2 BA bolts may be attached to C and the external focusing device placed into position The small supporting bracket is fixed as shown and the two chassis bushes inserted front and rear Thread through from the rear the long angle section of 4 rod Two half links are threaded on the rod between supporting brackets the purpose of these being to prevent RADIO CONSTRUCTOR and final assembly will explain this The holes provided are accurately disposed to fit the Elac 5 speaker type 5 45 Eight 4 BA bolts nuts and washers are necessary for part C It is not expected that anyone will encounter any difficulty at this stage of the assembly The one thing that we can think of is the possibility that the longer 4 BA screws or bolts may not be easily secured In such a case it is quite permissible to use the nearest equivalent 1 8 in either Whitworth or BSF threads there should be no trouble in obtain RADIO CONSTRUCTOR n TY 5
88. o be able to be replaced with a 5U4G as they have the same voltage and current carrying capacity The snag comes with the warming up times with the 5U4G it is only a matter of seconds whereas with the GZ32 it is longer than the rest of the valves In the first case the voltage fed into the set is 1 4 times the R M S whereas in the second it may only be a few volts over the R M S This can cause the electrolytics to rupture and cases have been met where they have exploded Conversely a directly heated valve can be replaced with an indirectly heated one without fear of trouble Increasing the size of the Reservoir Condenser With the modern trend to use larger and larger condensers it is very tempting to cut down on the size of the choke and increase the capacity of the condensers This can cause _ trouble as the reservoir condenser is charged by a series of short pulses rectified by the valve if these are of too heavy a current the valve can be ruined quite quickly If the maker s data sheets for the rectifier valves are consulted it will be found that a table of surge limiting resistors to be placed in series with the valve are given These should be used In the case of A C receivers it is good enough just to bring up the primary resistance to the required value but in A C D C receivers the full value must be used VERSATILE OSCILLOSCOPE ERRATA There were one or two errors in the circuit diagrams of the osci
89. o offer as many cures to worn tubes as does rejuvenation Rejevenators Rejuvenators function by permanently in creasing the heater voltage to the tube this being achieved usually by connecting a simple step up auto transformer between the heater voltage supplied by the receiver and the heater pins of the tube The voltage increase given by the auto transformer is around 25 per cent Some rejuvenators use transformers with iso lated primaries and secondaries this being done mainly to obviate cathode heater shorts which may occur at the increased temperature One rejuvenator uses a transformer with a mains voltage primary The heater voltage originally applied to the tube then heats a resistance element fitted to a bi metal strip On switching on the receiver the original heater voltage causes this strip to bend thereby switching in the primary of the rejuvenator transformer This type of rejuvenator is especially useful for receivers with AC DC power circuits Owing to the fact that the low voltage trans formers used in nearly all rejuvenators may be made very small indeed these components can be more or less hung in the wiring or built into plug adaptor housings All rejuvenators appear to have an adaptor plug and socket joined together by a short flexible harness and are installed by simply unplugging the tube socket and fitting the adaptor socket in its place The original set socket is then fitted to the rej
90. od shown in Fig 4 is particularly applicable if control of spot shape is required on one pair of plates only This is to retain the single potentiometer control of shift and to supply the final anode of the tube also from a separate potentiometer Valves and their Power Supplies Part 7 Bye E Bayliss AMLE T Voltage Doubling Circuits This short series of articles is not meant to be a treatise so much as a handy and possibly useful guide to the radio constructor in his dealings with power supplies It cannot there fore even pretend to cover the subject fully but even as such it cannot be conducted without a mention of television and voltage doubling practice The two voltage doubling and television are not mentioned together because they have always been associated thus Voltage doubling existed long before television even left the dreams of its pioneers only latterly has the matriage occurred and a highly convenient wedlock it has been and is In fact it is pretty safe to say that nowhere except in television will the constructor have to use a doubler circuit Our first circuit however is not concerned with doubling a high voltage in order to get an even higher one It may be of close interest to the constructor of a VCR97 tube televisor though He perhaps taking his HT voltage from a 250V transformer for vision and sound receivers is left stranded for the 400 to 500V necessary to operate a Mill
91. orm is sinusoidal for similar input if input level to the 6J7 is kept below 0 3 volts However the output of microphones or tape heads is well within this limit If a condenser of 0 00025uF is fitted in parallel with the 100kQ in the network then the treble boost can be limited to 9 kejs Beyond this frequency the effective shunt on the anode load reduces the output This condenser also improves the phase shift of the network but gives a slight amount of treble boost at minimum position of treble control 3 db at 10 kc s this amount is negligible however when compared with tape losses Its fitting is optional The compensation given by this pre amplifier and network almost perfectly com pensates for tape losses in a good system The amplifier following should be flat pre ferably with negative feedback The output resistor for constant current recording should 312 RADIO CONSTRUCTOR Fig 3 Relative gain of pre amplifier and network Maximum treble and maximum bass Frequency Record Playback Overall Minimum bass and db db db minimum ireble db 50 c s 3 0 423 75 20 75 3 0 100 c s 1 25 20 75 19 5 1 25 200 c s 0 17 5 17 5 0 b 500 c s 0 11 0 11 0 0 I ke s 0 4 75 4 4 75 0 2 kc s 1 0 0 10 4 kejs 5 3 58 4111 0 6 ke s 7 5 8 6 16 1 0 8 ke s 8 7 10 0 18 7 0 10 kels 93 10 5 19 8 0 Valve gain at 1500 c s a 3 35 db i Network loss at 1500 c s 24 5 db Overall gain at 1500 c s
92. ously there are two positions of the core which give the same resonant frequency one is as the core is entering the winding and the other when it is leaving it on the opposite side Now between these two positions the circuit may peak somewhere near the required frequency but it may not actually be on tune If this is occurring in the sound channel under discussion it will in all probability result in a response curve which has two resonant peaks though not necessarily of the same magnitude If this is in fact found to be so the turns on the coil in question must be adjusted or conversely if the coil has a shunt capacitor it may be more convenient to change this for one having a slightly different capacitance If a coi is tuning up correctly the resonant peak will be reached before the centre of the core has reached he centre of the coil Radio Component Exhibition 1953 Visited by A private Exhibition organised by the Radio and Electronic Manufacturers Federation was viewed by a specially invited audience on April 14th to 16th inclusive The Exhibition was officially opened at 11 am Tuesday April 14th by Sic Robert Renwick Bart President of the Radio and Electronic Manu facturer s Federation from the gallery of the Great Hall Grosvenor House Park Lane London W 1 Later at 1 p m Sir Robert presided at a private opening luncheon attended by the Minister of Supply Mr Duncan Sandys M P who propos
93. problem of ventilation occurs in television receivers due to the necessity of screening the components of the line timebase Such screening is necessary to prevent radia tion affecting adjacent broadcast sets and indeed it may wel cause trouble in the televisor itself by direct pickup in the vision channel t is normal to enclose the line output trans former and the three or four valves which make up the timebase in the screening can with the result that a considerable amount of heat can be generated Ventilation is most easily arranged by cutting some large holes in the top of the screen with a chassis cutter and a series of smaller holes about in diameter around the sides of the screen near the chassis Another series of holes are cut around the valveholders and provision made to provide a passage of air to the underside of the chassis as already discussed Enough has been said to indicate the general line of approach to the problem of providing adequate ventilation and the fact that it is a problem which is worthy of serious considera tion cannot be too highly stressed Vision on Sound I have just completed my first television receiver and have been successful in eliminating most of the more common fau ts but one stymied me The sound quality is poor and seems to be affected by the vision signal Sometimes the sound is accompanied by a harsh buzzing sound A Welsh Tewkesbury This trouble appears to be due
94. r good condition 10 carriage paid Box No C121 FOR SALE Eddystone 640 with speaker and Meter excellent condition 18 25 watt Transmitter with Xtals ideal for beginner Clapp VFO power packs offers delivered London area Watton 20 Edencourt Road Streatham London W 16 FOR SALE Master Oscillator Unit No 1 VFO 2 range 2 to 4 and 4 to 9 mes arranged Crystal control complete with power supply 230 volts AC New 10 WwW Makin Sevenoaks London Road Davenham Cheshire FOR SALE 155A with power pack top band and 6SG7 RF 5 or offers Hartog Elm Cottage Debden Green Loughton Essex FOR SALE Few valves BSA base cheap SAE Type aumbers Box No C123 FOR SALE Practical Radio and Television Caxton 3 Vols Cost 93 accept 50 or near offer Box No C120 continued on page 551 HENRY S 5 HARROW ROAD LONDON W2 Open Mon to Sat 9 5 30 Thurs p m Telephone PAD 9008 9 and 9401 SPECIAL VALYE OFFER Pen EFSO Brand New Ex Units 55 sec SET OF 5 MAINS VALVES 6K8CT 6K7GT 6Q7G 5Z4 6V6G or KT l at 42 6 Set SET 5 AC DC VALVES 6K8GT 6K7G 6Q7G 25A6G I5Z6G at 42 6 Sec SET 5 AC DC VALVES 6A7G 6D6 6C6 43 25Z5 ac 42 6 Set SET 5 AC DC VALVES 2K8GT I2K7GT 2Q7GT ISZ4GT 35L6GT or SOLEGT at 42 6 Set SET 5 AC DC VALVES I2SA7GT I2SK7GT 28O7GT or I2SR7GT 35Z4GT 35L6GT or SOL6GT ac 42 6 Set SET OF 4 BATTERY MINIATURE 1 4v VALVES IRS 155 1T4 154 or 354
95. returned to its normal brilliance and re focused the good work will probably i continued on page 505 RADIO CONSTRUCTOR 529 CHANGE OF SPOT SHAPE DUE TO SHIFT TO FINAL ANODE FIG 2 SHOWING USUAL ARRANGEMENT OF POSITIVE END OF EHT NETWORK WWww americanradiohistorv com FIG z ap 4 xx a ae TO FINAL ANODE SHOWING FIRST MCDIFICATION OF POSTTIVE END OF EHT NETWORK EHT 4 4 TO FINAL ANODE FIG 4 SHOWING SECOND MODIFICATION OF POSITIVE _ END OF EHT NETWORK Reise Audio Pre Amplifiers By D NAPPIN PART 3 Design of a Pre amplifier The requirements for a pre amplifier have already been stated however certain other problems present themselves As the pre amplifier is necessarily a high gain unit steps must be taken to reduce hum and other extraneous noises such as Johnson noise Such noise is introduced mainly at the grid of the first stage as the amplification at subsequent points in the circuit is not sufficient to cause any appreciable contribution to the over all noise by extraneous signals introduced at these points To reduce noise in the input resistor it must be of the high stability cracked carbon type as the composition type often possess a very high noise level due to the semi conducting properties of carbon This resistor is Rf in the circuit diagram Fig 6 which represents a pre ampiifier suitable for use with the quality amplifier descri
96. rs and Tuning Units Chapman Tuning Units Crystal and Moving Coil Mics Decca Replacement Heads and Pickups Goodman s Axiom 150 Speakers Partridge Output Transformers for William son Amplifier Alil Components for the Radio Constructor s 16 Televisor Weare amp Wright Tape Deck 35 LATEST VALVE MANUALS Mullard Osram amp Brimar No 4 5j each Mazda 2j each Postage 6d extra TELEVISION SETS WIRE AND TAPE RECORDERS ALWAYS IN STOCK Goods offered subject to price alterations and being unsold Est Arthurs lt first PROP ARTHUR GRAY LTD OUR ONLY ADDRESS Gray House 150 52 Charing Cross Road London W C 2 TEMple Ber 583314 ond 4765 WRITE FOR LISTS TELEVISION CABINETS All Sizes up to t6 Tube Specially Designed for Radio Con structor Set and Illustrated on the September Front Cover Price 1 8 z 0 Carriage 1 SEND FOR ILLUSTRATED LEAFLET H ASHDOWN 98 HERTFORD ROAD TOT 2621 EDMONTON N ange RADIO CONSTRUCTOR 499 Recognised as the Most Reliable Valveholders The Best Valveholders on the Market specially chosen for the Magna View Home Constructor s Television Set Gece TYPES BIA o International Octal BM7 U and XM7 U BM9 U XM9 Uand BM9 UB B8 U and X8 4 U Wholesale Enquiries CYRIL FRENCH LTD HIGH STREET HAMPTON WICK MIDDLESEX KINGSTON 2240 Manufacturers Enquiries THE McMURDO INSTRUMENT COQ
97. s arrangement In a standard receiver the greatest amount of heat is generated by power and rectifier valves and large voltage dropping resistors Com ponents such as these should be given the form of ventilation outlined above To gain the free flow of air past a valve it is convenient to drill a series of small holes around its holder A particular Jayout may result in a hot valve being located near a frequency deter mining component which must be kept cool When this happens a series of holes should be drilled around the valveholder as already RADIO CONSTRUCTOR described and a metal funnel made up to enclose the valve The heat within the funnel will cause a steady current of air to flow up through the holes round the holder past the valve and out of the top An arrangement such as this not only prevents the heat reaching other components but it also assists in cooling the vaive Under chassis ventilation is important this is particularly so where air is drawn from below the deck to ventilate components which are located on top of it In general a space should be left between the chassis and the bottom of the cabinet or conversely the bottom of the cabinet should contain ventilating holes or slots and should be raised off the table An alternative system is to drill holes in the sides of the chassis However regardless of the layout employed the aim must be to obtain a free path of air past all hot components A particular
98. s of its travel is of course determined by the travel permitted to lever A The guides are made up from scraps of 18 swg brass sheet bent to shape and sufficient ly accurate dimensions may be taken from the scale in Fig 18 The sketch Fig 19 shows a view of the completed parts When either of these two pulsing units are used a simple press button should be included in the control box wired in parallel with the wir amet oan aera t pulsing contacts This is useful for getting the mechanism in the model into phase and enables the operator to correct any error which may creep in when under way A means of sending signals by hand should always be available as the chance of a spurious or undetected impulse is always present and once the system gets out of phase it can be most confusing Selector Mechanisms A more complex and therefore generally more flexible way of using a sequence system is by utilising a circuit selector Fig 20 Selector operating mechanism r 520 RADIO CONSTR CTOR mn i a Most readers will know how these com ponents work but Fig 20 is a guide to the construction of a typical unit A is the electromagnet which in radio control work is energised from the receiver relay contacts B is its armature and C is a In one scheme the selector can be regarded as the equivalent of an escapement with a set sequence of positions provided by the various steps Each step can then be w
99. s threading is involved b As threading is similar on both rece ord and play the frictional losses and load are equal and so ensure correct speed c The greater wrap around the pillar adjacent to the head eliminates tape tilt which was found to occur when feed spool braking was light enough to eliminate capstan loading The arrangement is shown in Fig 5 The magnet will produce least background noise if the trailing edge is spaced about 1 16th inch away from the tape by tilting the magnet The leading edge has been rounded and polished to prevent it scraping the coating off the tape A further modification incorporated was to increase the series constant current resistor in the amplifier from 500 to 1009 due again to increased head impedance The bias isolation choke can be made to give better rejection by tuning it and making it into a proper tuned rejector circuit A value of about 0 02uF should be satisfactory for the tuning condenser 7 Book Review TELEVISION RECEIVER DESIGN 1F STAGES A G W Uitiens 172 pages 114 illustrations Price 215 Distributed in England by Cleaver Hume Press Ltd 42a South Audley Street London W 1 ilips Technical Library has this taiest addition on SLA as a companion volume to those already established as standard references on radio theory Dealing entirely with the I F stages in television receive design this present book adequately covers al k e
100. smissions for aver eight months Admittedly we have supplied much of the transmitting equipment but the sales of our receivers has not been in proportion With the entry of Japan into the receiver market at cheaper prices the need for retaining our technical superiority becomes paramount The same too applies to a lesser degree to Germany Before we can sell colour or stereoscopic FV to the rest of the world we must provide a system which necessitates only a cheaply produced reliable receiver and a daily service to prove its practicability Just how important the 3 D aspect will become is a matter of speculation Colour seems to be not only the more important but also the more logical step To meet a few requests and for the sake of beginners a brief review of the colour systems is included in augmentation of my comments of a couple of months ago Two of them are based on the fact that by adding together in suitable proportions red green and blue light any desired colour can be produced This may be achieved in two ways Firstly by projecting them simultaneously and secondly by scanning them consecutively Just as it is impossible for the eye to detect a single scan repetition at a high rate presents an apparent single complete colour picture to the human eye The principle of adding two or more colours to produce another generally referred to as the additive system has already been widely used
101. table stockists or in case of difficulty direct from Works For complete details of these and other products send 9d for General Catalogue DENCO CLACTON LTD 357 9 OLD ROAD CLACTON ON SEA Coronation QSL s Why not send a distinctive QSL this year N AS A VALUABLE BOOK which details the wide range of Engineering and Commercial courses of modern training offerad by E M 1 Institutes the only Postal College which Is part of g world wide Industrial Organisation Courses include training for City and Gullds Grouped Certificates in Telecommunications AMBrit LA Examination Radio Amateur s Licence Radite amp Television Servicing Certificates RE JA Generat Radio and Television a Courses Badar Sound Recording etc HOME Aiso Courses in all other rann EXPERIMENTAL eu KITS NOW Engineering AVAILABLE E M I OST NOW Please send without obligation the Instit ut 85 i FREE book E M Institutes associated with 1 Depe 179k 43 Grove Park Road MARCONIPHONE Chiswick London W 4 COLUMBIA iamen H M V exe Add Special designs to celebrate Coronation Year available from G6MN who has supplied special QSL s for discrimin ating users all over the world Attractive Coronation 1953 designs now available from G6MN Castlemount Worksop Notts WWww americanradiohistorv com See the Coronation on Large Screen TV 546 RADIO CONSTRUCTOR
102. tage into power This is necessary because the loudspeaker cone has to vibrate and move about small quantities of air which strike the ear drums in the form of sound Movement of this air requires power It will be seen from the diagram that in the anode circuit of V2 there is a transformer the secondary of which is connected to the loudspeaker This transformer has a large step down ratio from primary to secondary and is called the output transformer The same remarks concemming good quality performance apply to output transformers as to coupling transformers But whereas an output transformer must be used a coupling transformer can be replaced by R C resistance capacity coupling So it would be to your advantage to see that your output transformer is of the best quality available There is only one ratio for any set of circumstances that can be used for an output transformer because it is used to correctly match the valve into WWW americanradiohistorv com the loudspeaker Incorrect matching results in distortion and loss of power The ratio is determined from the following expression RL N vV Rs where N is the ratio RE is the recommended load for the valve which can be obtained from the manufacturer s data and Rs is the speech coil impedance of the loudspeaker Speech coil impedances are normally about 3 ohms for small speakers and 15 ohms for larger sizes Unfortunately space does not permit me to give a design me
103. tem Road New Malden Surrey FOR SALE R1155 brand new no DF 5 valves only 7 Vickers Madryn Bearsted Near Maidstone Kent COMMUNICATION EQUIPMENT for sale EF54 Preselector 4 switched bands 32 mcs to 1 6 mes continuous coverage black crackle case louvred to match 640 Receiver calibrated Eddystone full vision dial slow motion drive Controls On Off RF Gain Aerial Rx change over Wave change switch pilot light Power taken from Rx 4 Box No C124 TRADE FREE CATALOGUE now available Viewmaster Tape Gram etc at lowest prices Swift Radio 21 Hibbert Road Harrow Middlesex OAK TYPE SWITCH SERVICE Multi Way Switches made to specification approx cost 2 6 Clicker Plate 2 per wafer Components new Vol OnjOr Switches m m Long Spindle 3 Controls 100k 250k 500k 1 Ceramic Trimmers 5 80pf 5d High Stability Resistors 2 9d SM Condensers 6d cach Flex iid yard 3 W B Coil Pack with circuit 19 Box No C117 LP R E PUBLICATIONS 5 500 Alignment Peaks for sitperhets 5 9 Sample copy The Practical Radio Engineer 2 Membership examination particulars 1 Syllabus of TV and radio courses free and post free Secretary I P R E 20 Fairfield Road London N 8 FREE Brochure giving details of Home Study Train ing in Radio Television and atl branches of Eelectron ics Courses for the Hobby Enthusiast or for those aiming at the A M Brit LR E City and Guilds Felecommun
104. the makers claim uniform focus over the whole screen area On the Taylor Electrical Industries stand the instruments for television servicing were worthy of mention including as they did the Television Wobbulator 260A and the Pattern Generator 240A Audio enthusiasts will be pleased to note that Messrs Birmingham Sound Reproducers Ltd showed their new Monarch auto changer Features include three speeds and crystal tumover pickup On the tape recording side of the audio world Visitors were advised at the Truvox stand of that company s Tape Deck Mk III and other audio gear including special speakers etc Salford Electrical Instruments Ltd were exhibiting the quartz crystals for which they are well known together with equipment for crystal calibration and measurement of activity Erie Resistor Co Ltd showed the first printed circuitry that your contributor has seen in the flesh so to speak and included their high voltage ceramicons and small size type 7AD resistors The well known trans formers of Ferranti and Partridge were to be seen on their respective stands and the pro ducts of Messrs Rola Celestion Ltd were displayed to good advantage Other famous names represented at the Exhibition were Multicore Telegraph Condenser Co Ltd NSF Ltd Oak switches potentiometers etc and Hunts Capacitors a RADIO CONSTRUCTOR 543 Mailbag General Purpose Test Meter De
105. the use of two more complex types of valve in addition to the triode we discussed last month but once you have seen how the simple types of valve work it is easier to understand the tetrode and pentode with which we are going to deal as they really have the same basic construction as the triode with extra electrodes incorporated in them SUPPRESSOR GRID SCREEN GRID b RCI More Electrodes _ The tetrode valve shown in Fig la has in addition to the filament anode and control grid of the triode valve a fourth electrode placed between the anode and control grid This is the screen grid which by shielding the control grid from the anode reduces the capacity between them making the valve more stable for some types of amplification However as we are only concerned in this article with simple amplificatidn more advanced systems will be dealt with at a later stage I do not want to confuse readers now with half explained complexities REEN GRID Although popular for many years the tetrode valve has been largely superseded for amplification of very high frequencies by the pentode valve see Fig 1b The screen in both types has a positive potential upon it and therefore increases the current from the filament to the anode We will not worry a great deal at this stage about the special characteristics of these valves suffice it to say that the mutual conductance is higher than that which can be obta
106. thod for driving a loud speaker with one watt from a crystal pick up but in a later article I shail be showing the steps involved in practical design Here we have dealt with the whys and where fores of simple amplification There is of course more to this technique then we have mentioned here but these basic facts will apply to more complicated systems Once these have been understood the greater part of the groundwork in this particular aspect of radio will have been done A Radio Constructor service for Readers Receiver Ventilation A significant proportion of the enquiries which this Department receives are either directly about problems regarding ventilation or they are about faults which have occurred due to inadequate ventilation This subject is a most important one and it ts surprising how frequently it is entirely overlooked by constructors who make an otherwise perfect job of a radio or television receiver The effects of overheating in equipment are often most annoying and can also be expensive The most obvious effects are caused by a change in value of components these fre quently manifest themselves as a change in TOP OF CABINET SLOTS CUT IN BACK OF HEAT CABINET SCREEN KOLES CUT ROUND VALVE HOLDER HOLES CUT K BOTTOM CF CABINET RC185 Fig 1 Method of obtaining uninter rupted flow of air around a hot component Query Corne frequency probably allowing a timebase to
107. to a part of the vision signal reaching the sound channel The sound section of the set should be sharply tuned with a bandwidth which is probably in the region of 100 kc s The full curve of Fig 2 indicates a typical sound and vision response for a lower sideband television WWW americanradiohistorv com 541 l SOUND CARRIER VISION CARRIER RCIB6 Fig 2 Response curve of a lower side band television receiver showing how the sound response may overlap the vision pass band receiver It will be seen that the sound sen sitivity is such that no significant part of the vision response curve falls within the sound pass band Now should the sound channel be mistuned or should it be correctly tuned but have too wide a pass band the two curves may overlap as shown by the dotted line of the figure Under this condition a component of the vision signal will be accepted by the sound channel and may in conjunction with the sound signal cause severe overloading of one of the valves in the sound RF circuits The cure is obviously a matter of checking the tuning and selectivity of the sound channel and making good any deficiency in these directions Whilst on the subject of tuning TV coils it is worth while pointing out how a false res onant point is sometimes mistaken for the correct tuning position Most TV coils are tuned by means of adjustable cores which pass down through the centre of the winding Obvi
108. tory The bass boost action is similar to that of the bridged T of Fig 1 The treble boost however now consists of a two stage high pass fiter C1 R1 C2 R2 The bridging condenser C3 corrects a small chip in the curve caused by phase shift R2 is made a variable to have some form of boost control This is effective on both record and playback to allow for acoustic and other conditions The 1 Meg bass boost control is only effective on playback and this combination will be found to be most adaptable in practice The actual bass boost is rather more than the calculated network boost as there is a reduction in shunting of the anode load at low frequencies so giving greater stage gain in the valve Figures of gain etc at maximum boost are given at Fig 3 These were taken with about a foot of screened lead to the 1 Megh output load next stage grid resistor to simulate actual installation conditions This 1 Meg grid resistor should be in fact a 1 Meg volume control to the second stage The second stage should also be a pentode WWww americanradiohistorv com in order to reduce input capacity caused by Miller effect which would attenuate high frequencies especially at midway settings of the volume control The overall gain of the pre amplifier and network at 1500 cycles the point of maximum network attenuation is 10 5 db valve gain being 35 db and network loss 24 5 db The output wavef
109. uvenator adaptor plug In one or two instances however the rejuvenator transformer is mounted in a case which has to be screwed to the set chassis or cabinet Many American technical radio magazines nowadays carry rejuvenator advertisements and it is possible to obtain a very good idea of their respective physical sizes and trends in circuit development by studying these advertise ments The retail prices lie between three and ten dollars Rejuvenators seem to be becoming fairly standard servicing practice in the United States so far as one can judge from isolated articles on this subject Whether the same will occur in Great Britain is difficult to decide So far as the home constructor is concerned of course rejuvenator transformers would be very easy to make or adapt One point not stressed in the American literature or advertise ments however is that whilst a rejuvenator may bring a new lease of life to a Jow emission tube it may also ruin it Nevertheless if a tube is in such a bad state that if would be thrown away in any case the use of a rejuven ator transformer might not be disadvantageous mmen m e a E d y tn nten me RADIO CONSTRUCTOR 505 Another point which is also not stressed is the question of how long a tube stays rejuven ated at its new heater voltages This is under standable of course because such a period of time can hardly be predicted Apparently increased lives of a year have been obtai
110. y However we can easily get over this problem by causing the filament to heat a small tube placed around it This tube called the cathode is coated with a material which gives off electrons very easily when heated We now have a valve in which the filament emits no electrons at all this duty being transferred entirely to the cathode A cathode may be incorporated in any valve whether it be diode triode tetrode or pentode or even more complex types And in genera whenever a cathode is fitted it is called a mains yalve Coupling The primary points we have to consider in the design of a simple amplifier are as follows i what it is we want to amplify ii the overall gain iii the power output gt The first of these is obviously of considerable importance to us In this article we shall confine our attentions to the amplification of signals in the audio range that is to say those frequencies which you can hear Suppose for instance we wished to amplify signals from a microphone a gramophone pick up or the tiny audio signals present in the detector stage of a radio receiver where these fre quencies cover a range of approximately 30 to 15 000 cycles per second For the purpose of our elementary design we will consider the gramophone pick up The voltage produced by a crystal pick up is about one volt at the very most The problem with which we are faced is to amplify this signal and finally v
111. y a spark which breaks down the material on the surface of the insulator and so causes a fine carbon track This assists further sparks until a definite leak or short is established The fault is usually prevalent if the equipment has been kept for a long time in a steamy or humid atmosphere which had allowed condensation on to the surface of the insulator An easy way of discovering such a leak consists of connecting an ohmmeter between the two associated lines such as HT positive and chassis in the case just mentioned and lightly pressing suspected tag boards and similar components one by one As the uawanted carbon track makes contact to the circuit via solder tags or chassis mounting nuts riveted to it this pressure causes it to be momentarily connected and discovered where upon the ohmmeter needle flickers or shows a new reading The same sort of fault occasionally occurs in valve holders and switch wafers In switch wafers it can sometimes be particularly difficult to find since the leakage may occur in the small rotating disc in the centre of the wafer ASTIGMATISM IN ELECTROSTATIC CATHODE RAY TUBES Continued from page 528 have been undone and the spot will be e liptical once more The only method would appear to be to carry out the adjustments on a picture or test card This can be a little tricky It is not too easy to adjust two potentiometers at once and observe the effect accurately A rather simpler meth

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