An Ultra- Modern 9 -Tube Superheterodyne

How to Build An Ultra- Modern 9 -Tube Superheterodyne

Reactivating Oxide -Filament Tubes -A Modern Reflex Radio Set Tuning Meters -A Portable S. - W. Test Lab. -Tube Adapters SPE E D SPEED SPEED

EFFICIENCY! Ever the Goal of the Progressive Manufacturer EFFICIENCY!! Ever the Need of the Service Man

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SPE E D Gives this and more....With Radio's Premier Tube Developments

TRIPLE -TWIN TELEVISION t. FOTO- LECTRIC TUBES

Write for latest free bulletins -Turn to Page 256A for our Card -Keep up with progress by contact with D

CABLE RADIO TUBE CORP. 230-240 NO. NI NTH ST. BROOKLYN, N.Y. i A ii; c NIV:RSL-5'S

WIN FAM [and [OkT11 N E

Don't spendRADIQ/ your life slaving away in some dull, hopeless job! Don't be satisfied to work for a mere $20 or $30 a week. Let me show you how to make money in Radio -the fastest -growing, biggest field on earth? JOBS LEADING TO SALARIES OF $50 A WEEK AND UP! Jobs as Designer, Inspector and Tester -as Radio Salesman and in Service and Installation Work -as operator or Manager of a Broadcasting Station - as Wireless Operator on a Ship or Airplane, as a Talking Picture or Sound Ex- pert - HUNDREDS of OPPORTUNITIES for fascinating, well-paid Jobs! 10 Weeks of Shop Training At Coyne in Chicago You are given a thorough train- you -right here in the Coyne Shops man. Here is a great new field of Radio -the actual practice and experience that has just started to grow ! Prepare ing in Radio at Coyne -in 10 you'll need. NOW for these marvelous opportunities! Learn Radio Sound Work at Coyne, short, pleasant weeks by on actual Talking Picture and Sound actual work on real Radio, Tele- TELEVISION Reproduction equipment. vision and Sound equipment. Is Now Here! Coyne is 32 Years Old We don't waste time on useless You get Free Employment Help as theory. We give you the prac- And TELEVISION is already here! Soon long as you live. And if you need part - there'll be a demand for THOUSANDS of time work while at school to help pay ex- tical training you will need. TELEVISION EXPERTS! The man who penses we'll gladly do all we can to get it learns Television NOW can have a real for you if you will tell us your problems. Coyne Is All Practical Work at Coyne future in this great new field. Get in on 32 years old! Coyne training is tested -proven be- the ground -floor of this amazing new Ra- yond all doubt. You can find out everything ABSO- You are not trained by book study LUTELY FREE. JUST MAIL COUPON FOT'. dio development! Learn Television at MY BIC FREE BOOK. telling all about Jobs- at Coyne. We train you on a great COYNE on the very latest, newest salaries- opportunities. !flail the coupon - NOW! outlay of Radio, Television and Television equipment. I= MI IMM Sound equipment -on scores of rH . C LEWIS President modern Radio Receivers, huge Broadcast- Talking Pictures Radio Division, Coyne Electrical School ing equipment, the very latest Television 500 S. Paulina St., Dept. 72-811 Chicago, III. apparatus, Talking Picture and Sound Re- A Great Field production equipment, Code Practice Talking Pictures and Public Address Dear Mr. Lewis: - equipment, etc. You don't need advanced Systems offer thousands of golden Send me your Big Free Radio Book and education or previous experience. We give opportunities to the Trained Radio all details of your Special Offer.

H. C. Lewis, Pres. Radio Division Founded 1899 Name Coyne Electrical School Address 500 S. Paulina Street Dept. 72-8H Chicago, Illinois 1 City State RADIO -CRAFT for OCTOBER, 1932 173 (dio. FOR THE aft\ SERVICE MAN DEALER RADIOTRICIAN

HUGO GERNSBACK, Editor -in -Chief

LOUIS MARTIN R. D. WASHBURNE Associate Editor Technical Editor

CONTENTS OF THE IN OUR NEXT FEW ISSUES: OCTOBER, 1932, ISSU E ACOUSTIC FEEDBACK. In this article the author dis- VOLUME IV Number 4 cusses the factors involved in obtaining howl -free, high - gain microphone amplifier operation. EDITORIAL: Radio in Europe Hugo Gernsback 201 ONE -TUBE REFLEX LOUDSPEAKER SET. High -gain potentialities existent in the new tube types become NEW DEVELOPMENTS IN RADIO: dynamic in a novel receiver design that bids fair to Describing the Latest Tubes Louis Martin 204 attract widespread attention. The New "K" Tube C. Bradner Brown 206 A Portable Phono -Radio Receiver- Recorder Dr. F. Noack 207 CHURCH SOUND INSTALLATIONS. Technicians today The Latest Radio Equipment 208 must be prepared to successfully handle a sound instal - A Modern "3- Tube" Reflex Receiver. H. G. Cisin 212 lation in any one of the 200,000 churches in the U.S. The problems in this profitable field are discussed. SERVICE MEN'S DEPARTMENT: Operation and Service of Automatic Volume Control Systems W. S. Williams 211 THE SPECIALTY TESTER. Service Men long have Constructing Adapters for Test Equipment wanted this instrument, which solves the problem, "What F. L. Sprayberry 216 was the resistance of that burned -out resistor ? "; also, How to Rewire the Hi -Q 29 for the New Tubes it will indicate capacity values from 250 mmf. to 14 mf. Hubert Lee Frazier 218 Profits Via the Service Lab. M. C. Mancill 219 How to Reactivate Oxide- Coated Filaments Raymond Shaw 220 RADIO -CRAFT is published monthly, on the fifth of the month preceding The Service Man's Forum 222 that of date: its subscription price is $2.50 per year. (In Canada and foreign countries, $3.00 a year to cover additional postage.) Entered at Short -Cuts in Radio Service _ 223 the post office at Mt. Morris, Ill., as second -class matter under the act of Operating Notes Bertram M. Freed 224 March 3. 1879. Trademark and copyright by permission of Gernsback Publications, Inc., 98 Park Place. N. Y. C. RADIO SERVICE DATA SHEETS: Text and illustrations of this magazine are copyright and must not be No. 75: Galvin Motorola Model 61 Automotive Re- reproduced without permission of the copyright owners. We are also ceiver, (with type 85 duodiode- triode tube) 226 agents for WONDER STORIES and WONDER STORIES QUARTERLY. Sub- scription to these magazines may be taken in combination with RADIO - No. 76: Wells- Gardner Series 062 Automotive CRAFT at reduced Club rates. Write for information. Superheterodyne 227 Copyright 1932. GERNSBACK PUBLICATIONS. INC. TECHNICAL RADIO TOPICS: Building and Operating an Ultra -Modern Super Clifford E. Denton 202 H. GERNSBACK. President J. M. HERZBERG. Vice- President A Lapel Microphone (Part II) Dr. Irving Saxl 210 S. GERNSBACK, Treasurer I. S. MANHEIMER. Secretary Some Interesting Loudspeaker Facts Eli M. Lurie 213 Published by TECHNI-CRAFT PUBLISHING The Why and Wherefore of Tuning Meters CORPORA- L. van der Mel 214 TION. Publication office: 404 No. Wesley Ave., Mount Building Your Own A.F. Choke Coils Morris, Illinois. Editorial and Advertising Office: 96-98 C. H. W. Nason 215 Park Place, New York City. Chicago Advertising Office: RADIO -CRAFT Kinks 228 737 North Michigan Avenue, Chicago, Ill. Western Adver- tising office: 220 No. Catalina St., Los Angeles, Calif. The Radio Craftsman's Page 229 L. F. McClure, Chicago Advertising Representative. Loyd A Portable Short -Wave Laboratory H. Harrison 230 B. Chappell, Western Advertising Representative. RADIO -CRAFT's Information Bureau 232 Servicing New Receivers Floyd Fausett 233 London Agent: Hachette & Cie.. 3 La Belle Sauvage. Ludgate Hill, E.C. 4 Quasi -Optical Home Experiments John B. Brennan 234 Paris Agent: Hachette & Cie.. Australian Agent: McGill's Agency Over -the -Counter Suggestions Jack Grand 256A 111 Rue Reaumur 179 Elizabeth St., Melbourne An Easily Built 0 -800 V. Peak Voltmeter for Rectifier Work J. S. Williams 256B OBITUARY: R. A. Fessenden 207 BOOK REVIEW: N.R.I. Practical Laboratory Training Course 247

194

toACTUALo ' ' GUARANTEED a cu-o-zC- 'o

Features of the Scott Allwave Deluxe

15 -550 Meters Includes major European, Asiatic, Aus- traban, African, South American and Domestic voice stations. Single Dial Tunes both R. F. and Oscillator circuits in perfect alignment automatically from 15 to 550 meters -without '!'here is no question -no doubt -no gamble in possible an absolute guarantee of actual world- trimmers. the purchase of a Scott Allwave Deluxe. No wide reception. Only the Scott Allwave Deluxe No Plug In Coils mere hope, to be followed by bitter disappoint- has a sensitivity of 4.1000ths microvolt per The Coils are not tapped. Entirely new ment. You KNOW - before you spend your meter at 1400 K. C.! That's one reason. system -actually MORE efficient than money for a Scott Allwave Deluxe-exactly second is that the Scott Allwave Deluxe is the plug in coils. what you are going to get in performance. ONLY receiver having such a low natural You KNOW you will hear England, France, noise level that the 4- 1000ths microvolt per New Class A Germany, Spain, Australia, South America and meter sensitivity can be used to yield loud, clear Linear Amplifier many more of the 300 intensely interesting for- reception over distances up to 10,000 miles! Gives perfectly uniform response to eign stations regularly received by owners of all frequencies from 30 to 8000 cycles know these Send for PROOF! at low as well as at high volume. Scott Allwave Deluxe receivers. You things, before you buy because this receiver is A great independent laboratory has charted Twin Speakers positively guaranteed to give you astud world- the sensitivity, selectivity and tone of the Scott Give actual reproduction to the per- wide reception ... every day ... regardless of Allwave Deluxe. These charts PROVE, beyond fect, linear output of the amplifier. which state you live in! any question of doubt that the Scott Allwave Deluxe will POSITIVELY give you the foreign Non Oscillating Why This Amazing Guarantee reception you want ... the 90 channel broad- 100 per cent shielding enables use of Is Possible cast selectivity you want, and the tone you maximum sensitivity without annoyance of oscillation. It might seem strange that no one else can offer want. Send today for this convincing PROOF the purchaser such absolute certainty of satis- ... then, you will understand fully why the faction on the subject of foreign reception. Yet Scott Allwave Deluxe is the only receiver that it is not strange when all the facts are under- CAN be sold with a definite, unconditional stood, because... only the Scott Allwave Deluxe guarantee of actual, world wide reception. Clip has the electrical characteristics that make the coupon. Mail it at once. THE E. H. SCOTT RADIO LABORATORIES, INC. SCOTT 4450 Ravenswood Avenue Dept.RCIO Chicago, Illinois 1, l-1. SCOTT RADIO LABORATORIES, INC. A L L W AV E 4450 Ravenswood Ave., Dept. RC10 Chicago, Ill. Send me fully detailed technical description of the new Scott Allwave Deluxe.

DE LUXE NAME /5-550 frstete,z, STREET ¡ TOWN STATE 1 RADIO--CRAFT for OCTOBER, 1932 195

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I WILLTRAINYOU AT NOME

Many Make $50 to $I00 a Week in Radio-- the Field With aFuture \lv bunk, "Rich Rewards in Radio,- gives you full information un the opportunities in Radio and explains how I can train you quickly to become a Radio Expert through I :roa (casting Stations employ trained men con- my practical Home Study training. It is free. Clip and mail the coupon NOW. Radio's tinually for jobs paying up $5,000 a year. to amazing growth has made hundreds of fine jobs which pay $50, $60, $75, and $100 a week. Many of these jobs may quickly lead to salaries as high as $125, $150, and $200 a week. Radio -the Field With a Future Ever so often a new business is started in this country. You have seen how the men and young men who got into the automobile, motion picture, and other industries when they were started had the first chalice at the big jobs -the $5,000, $10,000, and $15,000 a year jobs. Radio offers the same chance that made men rich in those businesses. It has already macle many men independent and will make many more wealthy in the future. You will be kicking yourself if you pass up this once -in -a- lifetime opportunity for financial independence. Many Radio Experts Make $50 to $100 a Week In the short space of a few years 300.000 Radio jobs have been created, and thousands more will be made by its future development. Men with the right training -the kind of training I will give you in the N.R.I. Course -have stepped into Radio at 2 and 3 times 'olice Departments are finding Radio a great their former salaries. Experienced service men as well as beginners aid in their work. Many good jobs have been praise N.R.I. training made in this new field. for what it has done for them. Many Make SS, $10, $15 a Week Extra In Spare Time Almost At Once My Course is tvorld- iauwus as the one "that pays fur itself.- The day you enroll I send you material. which you should master quickly, for doing 28 Radio jobs common in most every neighborhood. Throughout your Course I will show you how to do other repair and service jobs on the side for extra money. I will not only show you how to do the jobs but how to get them. I'll give you the plans and ideas that have made $200 to $1,000 a year for N.R.I. men in their spare time. G. W. Page, 110 Raleigh Apts., Nashville, Tenn., writes : "I made $935 in my spare time while taking your Course." My book, "Rich Rewards in Radio," gives many letters from students who earned four, five, and six times their tuition fees before they graduated. Spare time set servicing pays many N.11.1 men $200 to $1,000 a year. Full time men make as much as $65, $75, $100 a week. Get Ready Now for Jobs Like These Broadcasting stations use engineers, operators, station managers and pay up to $5,000 a year. Radio manufacturers employ testers, inspectors, foremen, engineers, service men, buyers, and managers for jobs paying up to $6,000 a year. Radio dealers and jobbers (there are over 35,000) employ service men, salesmen, buyers, managers and pay up to $100 a week. Talking pictures pay as much as $75 to $200 a week to men with Radio training. There are hundreds of opportunities for you to have a spare time or full time Radio business of your own -to be your own boss. I'll show you how to start your own business with practically no capital -how to do it on money made in spare time while learning. My book tells you of other opportunities. Be sure to get it at once. Just clip and mail the coupe,Il.

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S400.00 S800.00 Chief Talking Movies -an invention made possible Each In by Radio -employs many well trained radio Spare Engineer men for jobs paying $75 to $200 a week. Month Time 0 Station WOS

'1 spent fifteen years as trateling "Money rould not pay for what I '1 hate a nice position and and a good salary as Chief En- salesman nd a : making good getting got mull of your course. I did not gineer of Radio Station Noll. Ile- money but could sees tide opportuni- any t know a single thing about Itadlo hive emeriaa Itadlo, s laq a year. is t me I hurrly Il.iou.un It ties In Itadlo. Itellese sin a berme I enrolled. but 1 faune made $2.4011.00 y ear. Before entering not surly. for I lime made moro (Welk, lay cork a more or lei:, t800 In fir' spare time although a drudgery` It is tt now a pleasure. money than ever before. I hate my mock keeps me auay front home All of this Is the result of the made more than $100 each month N. R.I. training and study. Your from 0:00 A.M. to 7:00 P.51. eau by far and It really teas your course that roe is the simplest. clear- Every word I ever read about your est I hale yet seen. Tau got me mite Io that. I can't say Pm brought wy first import pndtion.- mow I have found true. " -Milton lit Twit for N.11.1.--j. G. Pahl stead, n. If. Lance. 're evision -the coming field of many great Radio Station WOS. opportunities-is covered by my course. Bathe Sta. EYA. San rtatui +ru, cal. I. Lrlby. Jr.. Topton. Pennsylvania. Jefferson City. IMLuourl.

198 RADIO-CRAFT f o r OCTOBER. 1 9 3 2 TO BE A RADIO EXPERT C, Act Now - - - Mail Coupon Below for Free Book of Facts and Proof You Can Learn at Home in Your Spare Time to be a Radio Expert Hold your job. There is no need for you to leave home. I will train you quickly and inexpensively during your spare time. You don't have to be a high school or college graduate. My Course is written in a clear, interesting style that most anyone can grasp. I give you practical experience under my 50 -50 method of training -one -half from lesson books and one -half from practical experiments with equipment given without extra charge. This unique and unequalled method has been called one of the greatest developments in correspondence Radio training. N.R.I. pioneered Special FREE and developed it. It makes learning at home easy, fascinating, practical. Offer

Act now and receive in addition to Learn the Secrets of Short Wave, my big free brook "Rich Rewards in Radio," this Service Manual on Television, Talking Pictures, O. C., A. C.. and Battery Operated sets. Only my students could have Set Servicing, Broadcasting this book in the past. Now readers more training than you need to get a job -I'll give you of this magazine will receive it free. I'll give you Overcoming hum. noises of all kinds, your choice, and not charge you extra either, of my Advanced Courses fading signals, broad tuning. howls on these subjects -(1) Television, (2) Set Servicing and Merchandising, and oscillations, poor distance recep- (3) Sound Pictures and Public Address Systems, (4) Broadcasting, tion, distorted or muffled signals, Advanced poor Audio and Radio Frequency am- Commercial and Ship Radio Stations, (5) Aircraft Radio. plification and other vital service in- specialized training like this gives you a decided advantage. formation is container) in it. Get a free co by mailing the coupon be- Your Money Back if You are Not Satisfied low. ACTAn NOW, I will give you an agreement in writing, legal and binding upon this Institute, to refund every penny of your money upon completing my Course if you are not satisfied with my Lessons and Instruction Service. The resources of the National Radio Institute, Pioneer and World's SPECIAL Radio Equipment Largest Home -Study Radio School stands behind this agreement. for Broad Practical Experience Find Out What Radio Offers, Get My Book Given Without Extra Charge

)Iv r,nu.t I. not all theory. l'll One copy of my valuable ha -page book, "Rich Rewards in Radio,.. i. you .hale hoo- to use n special /ladle free to any resident of the C. S. and Canada over 15 years old. It has equipment for undoeth,g experiment, of men and young men on the road to better jobs and a and building eirruils wild, illustrate started hundreds kunmrtant nrlmIplea 11,011.ed in mull well bright future. It has shown hundreds of men who were in blind alley nown sets s ne.t General better paying work. It tells gimme, Phi ben, it l' A.. Virtu. jobs, how to get into easier, more fascinating, .Majestic. and other:. VCm work n you where the good Radio jobs are, what they pay, how you can quickly w It It your urn harms ,any of tLr thing, v r read In our Clemson book,. Coupon will bring you a -.o and easily fit yourself to be a Radio Expert. The TL i' iC wet hod of training make- copy free. Send it at once. Your request does not obligate you in learning at home easy. any way. ACT NOW. i nl a resting. f a .einat ing. I n t ensely J. E. SMITH, President I-r tl:tl. Dept. 2KX, National Radio Institute Washington, D. C. Clip and mail NOWfor FORMER PAY FREE INFORMATION Experienced Radio Man J. E. SMiTH, President Praises National Radio Institute, Dept. 2KX N. R. I. Washington, D. C. Course Dear mfr. Smith: I want to take advantage of your

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RADIO -CRAFT for OCTOBER, 1932 197 96 PAGES OF NEW DATA HAVE BEEN ADDED TO THE OFFICIAL REFRIGERATION

SERVICE MANUAL *, f_. To bring this useful service manual right up -to -date, Mr. L. K. Wright, the Editor of the OFFICIAL REFRIGERATION SERVICE MANUAL, has added a wealth of entirely new material on electric refrigerators. This new section, which totals 96 pages, has contained therein dozens of new models of recent manufacture which have been placed on the market during the past few months and in addition, information regarding improvements on older models. As usual every refrigerator has been accurately described from the viewpoint of servicing- diagrams to illustrate the essential parts, and simplified so that repairs can easily be made. NO EXTRA COST FOR THIS MATERIAL The addition of these new pages will lint increase the cost of the hook to those who order their copy now. With the inclusion of more pages, the OFFICIAL REFRIGERATION SERVICE MANUAL will have over 1,200 diagrams and over 450 pages. Its flexible, loose - leaf hinder accommodates the extra pages very easily. When the material has been placed in the manual, you will have a complete 1931 -1932 OFFICIAL REFRIGERATION SERVICE MANUAL. Radio Service Men -Turn Idle Hours Into Profit by Servicing Electric Refrigerators with the aid of this New and Complete Service Manual. THE idea of electricians, radii, service men and Irther mechanically inclined men, servicing refrigeration units is self -evident and the thought has occurred to perhaps untold thousands ever since electric refrigeration started. Yet nothing was done, because the average man knows little or nothing about refrigeration. Compared with servicing a radio set or wiring a home for electricity, the servicing of a refrigerator is absurdly simple, NOW once you get the hang of it. The OFFICIAL. REFRIGERATION SERVICE frigerators than radios. Why not increase OVER 1,200 DIAGRAMS MANUAL has been edited by L. K. Wright, your earnings with a full or spare time who is an expert and a leading refrigeration business by servicing refrigerators. 450 Pages authority. He is a member of the American Here are some of the important chapters: Society of Mechanical Engineers, American introduction to the Refrigeration Servicing Society of Refrigeration Engineers. The Business Flexible Looseleaf Binder History of Refrigeration National Association of Practical Engineers, Fundamentals of Refrigeration etc. Description of All Known Types of Refrigera- Complete Service Data In this Refrigeration Manual every page tion. Service Tools and Shop Equipment is profusely illustrated; every refrigerator Motors part is carefully explained; diagrams are Trouble Shooting furnished of every known machine; special Unit I'arts, Valves and Automatic Equipment care is given to the servicing end. The tools Makes and Specifications of Units ì Manufacturers of Cabinets needed are illustrated and explained ; there Refrigerants and Automatic Equipment are trouble shooting charts, and other ser- and Many other Important Chapters. r- vice data. Several thousands of copies of the OFFICIAI. Remember there is big money in the re- REFRIGERATION SERVICE MANUAL. have been frigeration servicing business. There are sold; and there still remains the greatest thousands of firms selling refrigerators opportunity for thousands more to learn how every day and they need to he cared for to make more money in a short time through OFFICIAL often. Eventually there will be more re- openings in this new field. REFRIGERATION SERVICE MANUAL THE FIRST COMPLETE r GERNSBACK PUBLICATIONS. Inc. RC-10-32 96 -98 Park Place. New York. N. Y. REFRIGERATION I mel000 herewith remittance for $ia0 wk. stamp.+ or Money Order e eeeptedl for ,Ph , o in Fiendnd t . ptutnne Prepaid. nn SERVICE MANUAL of the OFFICIAL REFRIGERATION SKit- V II 'E )l.1 NI -A L. together with the extra 98 pages of new material at no extra Cost. EVER PUBLISHED Name Clip and Mail Coupon Address TODAY! Oily Stat'

198 RADIO-CRAFT for OCTOBER, 1 9 3 2 litet' Completely IL-WAVE Assembled with Large V1ll tlt11 1'1 `' DUAL 1933 FEATUItE, AKERS HAT a radio! One complete 16- tube chassis with one dual -ratite dial -new Super- Hetero- dyne circuit with a range of 15 to 550 meters STAT -OMIT Tuning Silencer . . . . New Class "B" Push -Push Power Amplifier Color -Lite Tuning . . . Full band automatic Volume

Control . Duplex Duo - Diode Detection . . . . Dual - Ratio Single Dial . . . No Trimmers, No Plug-in Coils, No Tuning meter or Neon light required . Fractional Micro- volt Sensitivity . . . . Dual Powered (2 separate power Transformers) . Absolute Tone Fi- delity . 18 Tuned Circuits . New Mercury Rectifier . Full- Floating Variable Con- . 30 denser Low Operating Cost . and many other sensational new features. The new Midwest 16 -tube set actually DAVIFS uses less current than previous sets of 8 and 10 tubes, A bigger, better, more powerful. more selective, finer toned radio than you've ever seen before FREE offered at an amazingly low price direct from the big TRIAL Midwest factory. Mail the coupon or send name and address on a postal for all the facts. Remember! Every \ I i,1 west set is backed Deal Direct Factory! by a positive guarantee of With SAVE satisfaction or your money Don't be satisfied with less than a :Midwest lb-tube A. C. hack. 30 DAYS FREE radio. A receiver covering only the regular broadcast TRIAL in your own home waves is only half a set. Improvements in short -wave i-P TO makes you the sole judge. programs have made ordinary broadcast sets obsolete. Midwest, now in its twelfth The Midwest gives you regular, foreign, police and ama- successful year, offers big- teur broadcasts in one single dial set. No converter or mor ger, better, more powerful, Complete Line any extra units required. e_11 more sensitive radios at low- of New Consoles Remember, you buy DIRECT FROM THE MAKERS. er prices than ever before. Tho big new M idwest The coupon or a catalog shows gorgeous No middlemen's profits to pay. You get an absolute guar- postal une of art bile consoles antee of satisfaction or money back. You try any Midwest TERMS brings you big new catalog In the new six -leg designs. 1I all the run..t. 30 DAYS before you decide to keep it. Then, if you visll. as low as and complete infor- Get the frg -. now. all you pay in mation. \ fail It Learn bmc t ,u I.an s can small monthly amounts that you'll scarcely '500 DOWN 30'.4 to 50';1 on a blg pow- a NOW! refit r:dil., I, ordo, ing miss. Mail coupon for full details or write us postal. tire, from Oa fa, o,n. Read These Letters From Midwest Owners BATTERY lust two of the thousands of letters praising \Iidwest Radios Gets France. Spain. Italy. Japan W8XK- W3XAL-WIXAZ -W2XAF SS RADIOS "Have rere i cerI foreign short -wave I ant ter' noon satisfied in eseo AGtio st atlons suri. as IVA. Franey GAM. way with my M ldeest radio. 1 heard uStiR U sing the New Madrid. Spain; 12 ItO, Rome. Italy: Sydney. Sunday l.nn t. \I. al.., v:5-11'N and but not least, Tokyo. t\'TXR; w'3X,L; WIXAZ-; W2XAF; Gory AIR (-E1.L last JIAA, Raaio Japan. I really think tire Midwest in the evening. On the regular band wae`' ep\\s .et Is a miracle." have some 55 stations so far. d BATTERY tot Two ssssss .on al valuer . S A. F. GRIIH.1 {Y. Aug. ltalbi. 1427 Myra Ave., SOSa -,Ia. l'I:i. 1.,.: . \ngele t'.ilif. OFte, wmper.hrt for standard. wty reception d 9aubs 1 peuµ \ a1. n ca óoAaSV ALL.WAVE. bah using the Investigate ! Mail Coupon NOW! td newt CELL A" G`°` battery - a the .Iidwest catalog Learnt r tarty aboutb .f 1 eat J. 12 and e b \1.1.- dun AIR r needs charging nesa\13y\lbttitOT sets, Leant about ourur se low factory ,,Ares, easy % factory s. Coupon 5 µ.ta\tóne[- and sail

...... MIDWEST RADIO CORP. p, ,aw,n...... State ,...... DEPT. III (Est. 1920) CINCINNATI, OHIO s RADIO -CRAFT for OCTOBER, 1932 199 1 RI4 Tune the NEWway ârWorld-Wide Reception zui h the LINCOLN DE-LUXE-SW 33 SILENT TUNING» The weakest carrier wave is registered on the signal indicator and can be tuned with precision and perfect silence without disturbing atmospheric noises. SIGNAL INDICATOR A meter directly above the dial indicates, not only the weakest signal, but allows the operator to tune into a signal perfectly. Guess work is entirely eliminated. Comparative signal strength is indicated. UNDISTORTED HIGH AMPLI FI CATI ON Three stages of push pull with new system of twin -grid detection allows tremendous undistorted amplification of the high gain I. F. amplifier. The handling power of this system seems to be unlimited and tremendous volume on weak signals can be had if desired. THE NEW DEVELOPMENTS have made the new DeLuxe SW -33 just about as ideal a receiver as one could hope to own. The use of five variable mu tubes controlled by the AUTOMATIC VOLUME new twin grid second detector and followed by two transformer coupled push pull stages has opened the gates to new ideas of enjoyable distant CONTROL reception. The There are two paramount advantages in good signal indicator locates carrier waves which are difficult to hear; many times is is automatic volume level. First, in tuning from the carrier not being used or modulated as the case in weak to strong signals; and secondly, in holding transatlantic phone. The signal indicator registers these silent carriers and enables you to be accurately tuned, ready for the voice to be heard. a steady volume level on fading stations which is so common in short wave reception. The WHEN THIS CARRIER IS TUNED, ATMOSPHERIC NOISES effect of this new Lincoln feature is so efficient that a near -by stroke of lightning registers ARE REDUCED TO A MINIMUM, AUTOMATICALLY. only a muffled sound in the speaker; it has the Distant stations can be tuned silently, and volume then same effect on all sharp electrical interference. brought up to desired strength (volume control does not affect sensitivity). Perfect volume level on short wave stations is another great asset in the new Lincoln. If you have ever tuned in a foreign short wave station, or even many of our short wave stations in the U.S.A., you NEW FIDELITY will appreciate the great value of uniform volume level. Twin -grid detection preceded by push pull in- The performance of Lincoln equipment has been known the world put I. F. transformers and followed by two over for years. Its use by Polar Expeditions, broadcasting stations, both stages of transformer coupled push pull stages, domestic and abroad, U. S. Naval Station operators, and hundreds of super produces an undistorted register of a wide band critical DX fans, has proved Lincoln's exceptional merit. of frequencies, giving a perfectly balanced out- Complete equipment consists of chassis, power equipment, auditorium put with realism hard to associate with radio. type speaker and complete set of laboratory tested tubes. Chassis is finished in highly polished nickel over copper and presents a handsome All of the new reactions in the SW -33 model appearance. Precision laboratory construction is employed throughout, are what we all have wanted for years,-they and every receiver is tested on distance before shipment. are here for you today -thanks to Lincoln's Write for description of new developments and new sales plan which foresight in radio possibilities. overcome the present defects in the present custom built radio merchandising.

LINCOLN RADIO CORPORATION Dept. RC -10, 329 S. Wood St., Chicago, Ill. Please send information on A.C. D.C. receivers. LINCOLN Name Address

Defuxe Receivers City _ _ State Print name and address plainly

200 R A D I O - C R A F T f o r OCTOBER, 1 9 3 2 àdio raft Fon THE SERVICE MAN DEALER RADIOTRICIAN "Takes the Resistance Out of Radio"

4, 1932. Editorial Offices: 96 -98 Park Place, New York. N. Y. HUGO GERNSBACK, Editor Vol. IV, No. October, RADIO IN EUROPE An Editorial by HUGO GERNSBACK would make listening FORthe purpose of making an intensive study of radio higher sensitivity would bring in and television conditions as they now prevail in the quite impossible. I listened to a few six and eight tube foremost European countries, i recently visited Ger- superheterodynes in some radio laboratories, and it was many, France, England and Belgium. absolutely impossible to keep the set on for more than a Every facility was placed at my disposition, and in the few minutes as the din and racket was so nerve racking course of my travels I visited every important radio and that it became positively hopeless to listen to it. television laboratory on the continent. I also had numerous Indeed, as a general thing I found that Europeans who occasions to personally operate a number of radio receivers had been in the United States and who had owned or used in all the countries visited. radio sets here, do not own radios in Europe now. The In my opinion, the present radio conditions abroad may explanation usually was that after being accustomed to be best summed up in a single word -"Deplorable." The American radio reception, they found themselves unable general quality of the European programs is, as a rule, to listen to European programs with their eternal talks, mediocre. There are good features, and in some cases their accompanying noises, and preferred to be without excellent one to' be sure, but they are few and far between. radios rather than listen to the assorted din. What music there is, as a rule, is good, but European broad- I have never been a friend of our American radio prac- casts suffer from entirely too many talks. Surprising as tice whereby programs are sponsored by advertisers, and it may seem, there is no such thing as a continuous pro- where advertising blurbs clutter the air all too frequently. gram from early morning (5.45 A.M.) until after mid- Of course, in Europe there is little advertising on the air; night (1 A.M.) -even by large stations -such as American practically all broadcasting stations being owned by the listeners are accustomed to. Even the big stations go oft various governments. However, after listening night after the air for hours at a time. There is also not the snap night, for three weeks, to the European radio pande- and go to the average European stations that we are accus- monium, I am certain that American radio listeners, if tomed to in America. They take things easy, and a few they had been treated to a like experience, would forget minutes wait-anywhere from 3 to 10 minutes -between their present antagonistic attitude toward our radio pro- programs means nothing to the European broadcaster. grams and come to the conclusion -as I have -that after all But when it comes to radio reception in Europe, the con - is said and done, American radio, today, is so far above ditions-to the American-are not only deplorable but cha- that of Europe, that a comparison becomes silly. otic. It is practically impossible to listen to a radio pro- As I have mentioned before, the average European radio gram in the large cities, such as in Berlin, Paris, or London. set is composed of three tubes. In fully 80 percent of the The amount of man -made interference is simply terrific, sets, regeneration by the tickler method is still being used. and at prggent no steps seem to have been taken to remedy This means that the sets produce the same sort of howls this sad NItuation. Time and again I have tried to listen and cat music that we had to contend with up to about to programs in these various cities, but found it absolutely 1928. Of course, since that time, we have not had sets impossible to do so, particularly at night; but even in the that whistle and howl, but in Europe, such sets are still daytime, listening often became impossible. In the country the usual thing. The condition is aggravated also by the districts, conditions are somewhat better so far as man- fact that all European sets must tune up to the higher made static is concerned, but all to no avail, because of wavelengths of over 2,000 meters, as some of the best sta- the present European radio chaos. tions are broadcasting on these frequencies. This makes elaborate switching arrangements necessary, which switches In the United States we have the Federal Radio Com- have not been worked out very happily in Europe so far. mission, which polices the various wavelengths so efficiently Speaking broadly, it may be said that a great majority that broadcasters must remain on their allotted frequency. of the sets are of the regenerative and tuned radio -frequency In Europe, there is no central authority to enforce this type. Only very recently have superheterodynes been in- prime radio rule, that is, that radio stations must stay on troduced, but so far, only a very small percentage of the their assigned wavelength. Berne (Switzerland) is sup- receivers sold are what might be termed modern sets, such posed to regulate the stations, but in practice, broadcasters as we know in the United States. do much as they please. As to the general appearance of the sets, they are of the The result is that there is a terrific amount of interfer- 1928 vintage, according to American standards, and they are ence between the stations where wavelengths overlap. This practically all of the table -model type. While it is possible naturally gives rise to heterodyne whistles, and only rarely that someone is building consoles in Europe -I saw hun- is a program free from such annoyances. Of course, we dreds of sets and operated dozens of them -I never glimpsed have heterodyne whistles on some of our stations in the at a single console during my whole stay in Europe. All the United States, too, but generally these stations are in what sets I saw, with but one exception, had separate loud- is termed the "graveyard" wavelength, below 250 meters. speakers, such as were in vogue in the United States in In Europe, there are heterodyne whistles on the best fre- 1926 -28. In Europe, the radio set is still just a radio set, quencies. and it is seldom that you can select a wavelength and no one seems to know what radio furniture is, such as that is free from this annoyance. This, of course, accounts we know the term here. for the fact that the average receiver in Europe consists Summing up, it may be said that radio in Europe today of but three tubes. When you talk to Europeans of an is just about five years behind us, and it has been so ever eight, ten or twelve tube receiver, they cannot conceive of since it started abroad. It is also quite likely to remain such a thing. Indeed, if you had such a receiver in Europe so, due to present economic conditions, and the slower it would be useless. The amount of interference that the adaptability of Europeans to new Ideas.

201 55 '80 . T. BUILDING V6 } V 7 17 v9 P. AND OPERATING vai,-- 58 I.FL3 1 VS

I.F.T. 2 ?, AN ULTRA- MODERN SUPER.

By CLIFFORD E. DENTON

101 AL DISTANCE VOLUME TONE choke arrangement, The new Duplex -Diode Triode is used as SWITCH CONTROL CONTROL maximum output is the second detector. (See description of from Sept. Fig. A secured the R.F. this tube in the issue of RAUIo- CIIAI-T. Front view of the completed receiver. The designations refer to the stage, VI, over prac- -Editor.) This tube, the 55, is fed from schematic circuit below. tically the entire the I.F. secondary, and has both plates broadcast band. connected together in a half-wave connec- WHILE there are many good re- Oscillator tracking is accomplished by tion; a center tapped I.F. transformer ceivers available today, at the means of a series of padding condensers, must be used for full -wave detection, and suggestion of RADIO-CRAFT, the C3A and C4 in the diagram. However, since such transformers are not as yet author constructed a 9 -tube re- best results will not be secured unless available, the half -wave connection of this ceiver of the superheterodyne type, util- care has been taken in the construction tube was used. This is also desirable izing all the new tubes that would be of the coils. since a greater voltage is available for practically beneficial; a band -pass an- An interesting feature of this receiver A.V.C. action, also secured from this same tenna system, to provide sufficient selec- is the fact that the oscillator is coupled tube. Hence, titis tube is a combination tivity for those located in metropolitan to the first detector both conductively and diode detector, A.V.C. tube, and since it areas; automatic volume control; and a inductively; conductively by means of the is equipped with an additional grid and diode detector. The sensitivity of this common resistor In the cathode leads of plate, it also acts as an audio amplifier. receiver is in the neighborhood of 1 micro- the oscillator and first -detector; and in- An especially interesting feature is the volt-per -meter, which should more than ductively through the physical location of fact that the diode portion of the tube is satisfy the most ardent DX fan, and at the two sets of windings, that is, the os- resistance -coupled into the triode portion, the same time enable distant stations to cillator and first- detector secondaries. and the latter transformer -coupled into be received with ease. Both of these coils are wound on the same the push -pull output stage. If the instructions given in this article tube and separated by about '/, inch. A tone control, consisting of C20 and are followed, then the entire set may be Extremely high gain is obtained in the R13 is shunted across the secondary of built for about twenty dollars, assuming I.F. stages by virtue of the fact that both the push -pull transformer to facilitate the nothing in the "junk box" but a few tools. the primary and secondary of each I.F. accentuation of the lower register, if so transformer is The Circuit tuned; and since there are desired. three such transformers, there are six The Automatic Volume Control A study of the circuit diagram of Fig. 1 tuned circuits in the I.F. stages alone. reveals that a total of 9 tubes are used, In view of the fact that the receiver is Automatic volume control is obtained including the rectifier. Starting at the equipped with A.V.C., the sensitivity of in a novel manner. Tube V6, the Duplex - antenna, a band -pass tuning unit feeds the various tuned stages varies with sig- Diode Triode, supplies the voltage. Note the signal into the receiver proper. The nal strength. This is so in the first R.F. that the cathodes of both the first R.F. output of the first R.F. tube is loaded by and first I.F. stages; the second I.F. stage and first I.F. tubes return, through grid a choke, L4, which resonates at a fre- is not in the A.V.C. connection and con- bias resistors R2 and R8, directly to the quency just below the broadcast band. sequently works at high sensitivity at all cathode of V6. Therefore, the bias voltage Coupling to the first detector, or modu- times. A local -distance switch is used, in appearing across R11 supplies the triode lator tube, is made via a small, mica series with a resistor, R14, to decrease the portion of V6. The voltage across R10 fixed condenser, C24. With this resonant- gain of the second I.F. stage. supplies the potential for the tubes oper-

Fig. 3. Complete schematic circuit of the receiver. Note the use of the new 55 in the second -detector circuit.

202 RADIO-CRAFT f o r OCTOBER, 1 9 3 2 -CRAFT always attempts to bring before its readers RADIO VOL .^. TUNING TONe the latest devices and the latest application of these devices. CONT. DIAL CONTROL To accomplish this we have prevailed upon Mr. Denton to construct the receiver described here. This receiver uses, as may be seen, type 58 tubes in the R.F. and I.F. stages; the new type 55 Duplex -Diode Triode as combination second detector, first A.F., and A.V.C. tube; and two pentodes in a push -pull connection. A single evening's test convinced us of the tremendous sensitivity and selectivity of the set. Between the hours of 9 and 10 P.M., over 50 stations were logged, and without any interference of any sort. Local stations were tuned out in a half a degree on the dial, and a distant station tuned in on the next channel!

We believe that this is the most up -to -date receiver ever described that may be constructed at home. ating under the influence of A.V.C. Man- Lions are given in ual control of volume is obtained by vary- Fig. 4, but must be ing the arm of the potentiometer R10. changed if material The time of delay of the A.V.C. action other than that speci- Fig. B receiver. The simplicity is evident. is about .1-second, the exact amount de- fied is used. A cad- Under -chassis view of the pending upon the accuracy of the time - mium- plated chassis delay circuit composed of R7 and C23. may be purchased fully drilled and folded 53/4 Additional isolation in the form of R3 in accordance with the above specifica- (ANT) IIST. Na.)AD.SC and C26 decouples the first R.F. stage tions. Made of steel and with welded -t-.. from the remainder of the set. joints, it presents an attractive appear- NI Ne II SOS WA ance. SEG J Coil Data Mount the sockets, band -pass coil, elec- 1 details of the coils trolytic condensers, four -gang tuning con- II Full constructional L are given in Fig. 2. Note that the antenna denser, and the power transformer on top 1-1 1. ff I--W - t 4" %Y'b Til i5f 3/3i -A- 3Sz/. coil in Fig. 2A is wound in honeycomb of the chassis as shown in the photographs BAND PASS COIL of and is in Figs. A and B. Place all tube shield - fashion at one end the tubing 4' osc bases on respective sockets, and held in place by means of collodion and their moetECTOa OSCILATOR COIL GRID COIL GAIO COIL ow small pieces of adhesive tape. The three after this is done, mount the intermediate - coils on this form are all wound in the frequency transformers. Be sure that the -I I.F.T. -grid run------..1 T -- BOT '1 same direction. third has its control lead MY.30E i -B- -_ o30l DIA. The first -detector and oscillator coils ning down through the chassis to the -I 1 -_ -1 __B are wound on a second form as shown in plates of the 55 tube. All other material i -1 - S- iL,. esce: e Fig. 2B, a half -inch separating the two is mounted under the chassis. The fixed 3 161 ire 16 G 1 COIL NAS 3/!2' TAP AT coils. Care must be taken to place the condensers and the resistors are sup- 3$ 4o,á TURN plate winding of the oscillator on that ported solely by their leads; the two 1. I Si DETECTOR AND OSCILLATOR COIL. mf. -pull end of the grid coil nearest the end of bypass condensers and the push Fig. 2 the tubing, as shown. The list of parts transformer are bolted down. Constructional details of the R.F. coils. The at the end of this article gives the name band -pass unit is shown at A, and the detector - on page 237) of the manufacturer of the coils, in the (Continued oscillator unit at B. event the constructor desires to purchase them. SPEAKER Ih Winding data for the I.F. transformers PLUG bi are given in Fig. 3. Each of the windings (both primary and secondary) consist of 3- 800 turns of No. 36 D.S.C. wire on a wooden -half diameter. core one inch in -2'/4- Further spacing details may be secured from Fig. 3. Construction J} The set Is simple to construct although there are nine tubes employed; simply use mounting I7 mr care in and soldering all for electrical connections. specifica- -LEFT Chassis SIDE-

LIS-._..,,3 ' >_.,.,4.--1 I_ 32 16 I 32 p-. 1 Irrt y. z -- :'\'\ ._ 5 I I TOP- T- T OA. -re OIA 34 DIA. _BEND EDGES DOWN - - } ON ALL DOTTED 1 ALL HOLES ARE 11"-ig LINES, UNLESS 1 WM' . -F _L OTHERWISE NOTE SPECIFIED / -WONT SIOÉ'AND'Leer SIDE TO BE ASSEMBLED TO FOLDED BASE AND 7/2- SOLDERED. ( TACK OR i 3/4 IS' SPOT WELD PRE- FERABLE) - MATERIAL 3/64' THICK SHEET STEEL Fa.3 Fig. 4 Winding ht llIs of the I.F. transformers. Complete chassis layout. The location of the parts is Indicated by their respective cut -outs.

RADIO-CRAFT for OCTOBER, 1 9 3 2 203 DESCRIBING t THE LATEST TUBES

A new universal automotive output tube and a special combination amplifier and power rectifier complete this month's description of the latest tubes used in radio work.

By LOUIS MARTIN

IIIS month The three -fold application of the 89, limited and this results in limited power there are two shown in Fig. A, to audio power -amplifier output. Theoretically, the maximum plate tubes that we circuits is made possible by different con- circuit efficiency for class A operation is will describe. nections of the three grids incorporated 50 percent, assuming a sine wave input The first of these in the tube's structure. Thus, one ar- signal. The actual plate circuit efficien- is of the automo- rangement of grid electrodes provides a cies, however, are of the order of 20 per- Fig. A tive type; the sec- triode for class A service with a low am- cent for triodes and 40 percent for pen- ond, a special tube incorporating a power plification factor, a low plate resistance, todes. rectifier and radio amplifier in a single and a high mutual conductance; while an- envelope. The latter tube, while it is not other provides a triode with an amplifica- Characteristics of the 89 commercially available at titis time, indi- tion factor so high that negative grid bias cates quite clearly what the trend is. is not required for its operation as a class Figure 1 shows a family of plate B amplifier. A pair of 89's so connected voltage- plate- current curves of this tube The 89 in a class B output stage is capable of sup- when operated as a triode, that is, when The 89 is a triple -grid power amplifier plying a large amount of power with rela- the suppressor and screen -grids are con- tube of the heater -cathode type recom- tively low plate voltage and with unusual nected directly to the plate. The applied mended especially for use in automobile overall economy of power consumption. A signal is then fed between the control receivers or for other types of mobile third arrangement of the grids makes pos- grid and the cathode in the conventional service. The triple -grid construction of sible the use of the 89 as a class A power manner. In Fig. 2 is shown class A oper- this tube, with external connections for output pentode capable of giving large ation when this tube is used as a pentode, each grid, makes possible its application power output with relatively small signal that is, with the suppressor or third grid as (1) a class A power -amplifier triode, voltage input. connected directly to the cathode and the (2) a class A poweroutput pentode, and In class A service, the grid of the tube screen -grid to some positive voltage higher (3) a class B power output triode. is maintained negative with respect to than the cathode. the cathode by an amount such that some In class B service, the tube is operated e0 plate current flows at all times, and such so Ef 6.3 VOLTS D.0 that the plate current is practically 70 ib that the grid takes no appreciable current zero with no grid excitation. When a sig- P C60 during the most positive swing of the signal of sufficient magnitude is applied to N i- nal voltage. These operating conditions the grid, there will be no plate current 6 5D t rl, S .I...B are obtained when the normal bias with - flow over a substantial part of the nega- F ..A 1s .M out signal gives sufficient operating plate tive half -cycle. In other words, plate cur- . LOAD ...... O ... current to permit the application of a flows 130 EJRESISTANCE rV'.=rliir. , rent only during the least negative . 6.. 20 ONMS FLIP2L t..-/PA.I.g 30- peak signal equal to twice the bias value excursions of the signal voltage. A con- . ref .I.f.5.iaì". Wi.. -35 4 without reducing the plate current below siderable amount of second and even 10 ...um.t:lwL/%5m.:'..ç PSIEß.CWL%Éiri/díl....trmo..lc -r,... a certain predetermined minimum value higher order harmonic distortion is thus o under the load conditions employed, or 20 40 60 80 100 120 140 160 I80 200 220 240 introduced into the power output of a PLATE VOLTS (Eb without swinging the grid positive. Thus, single tube. However, with two tubes in Fig. 1 the value of grid signal voltage which can a balanced push -pull circuit, the even har- Plate -voltage- plate- current curves of the 89. t e applied to any given type of tube is monics are eliminated from the power

eo .. 466 VOLT60C á 10 GRID VOLTS -IT a cDNTROL GR,O ILO VOLTS Eu re SEEN VOLTS Ec2.163 Ec +25 _i**.... fe 60 4 ...eli.. * 50 ....Ì... .. + î ..PA...... _ " Ve lO..CEM.. ° 40 GA...mw"-A/... ú .%1.... .M.... Li 30 .r,I..i....t..__ï...... vic:.....UTIMI C1+10 rr.m...... _--- ./ . . g 20 ai.eiGeiáiii .. ...:.G.ïI.\..lil,.. -20 MES +IS.\i2.....-ii E.... á 10 co ! + .15 C.gA\rCiGG...4ti.. f2! 6aR 012g4a==gP;44254@3711 v QZI.-t® ú 0 c 0 20 40 60 80 100 120 140 160 160 200 220 240 PLATE VOLTAGE

Fig. 2 Fig. 3 Fig. 5 Curves Illustrating pentode, class A operation. Cu f the 89 as a class B amplifier. Socket connections of the new 89.

204 RADIO -CRAFT for OCTOBER, 1932 t . output. In such a circuit, therefore, two current characteristics are also shown. tubes may be employed as class B ampli- Class B connection may be secured by fiers to supply virtually undistorted out- connecting the suppressor grid directly put. to the plate and the screen directly to the In class B service it is possible to drive control grid. The input signal is then ap- the grids of the two amplifier tubes posi- plied in a conventional manner as in all Uve to a certain amount and still obtain triode tubes. An inspection of the curve reasonably undistorted output, provided will show that high grid -current flows that sufficient input power is available to when the plate voltage is low. supply the grid current required by the Figure 4 is an interesting set of curves positive grids. This power is conveniently inasmuch as they indicate how the power supplied by a class A power amplifier output and plate current varies when two feeding the grids of the output tubes type 89 tubes are connected for class B through a push -pull transformer having operation, which in turn are driven by a proper characteristics. Usually this trans- single 89 in a class A connection. At A, former has a step -down ratio. the transformer ratio between the class By designing class B amplifier tubes A driver and class B stage is 2.4; the out- with a sufficiently high mu- factor, it is put load impedance from plate to plate possible to operate them with zero grid being 9,400 ohms. In B of the figure, the bias, and so dispense with biasing resist- input transformer ratio is 3.7 and the out- ors whose effect would be to produce con- put impedance from plate to plate is 13,600 of will be seen that in the first Fig. 6 siderable loss in sensitivity because ohms. It External view of the amplifier -rectifier. degenerative effects. Since provision for instance, the total harmonic distortion is grid bias is unnecessary with such tubes, about 8 percent and at B, the harmonic the entire voltage of the rectifier is avail- distortion is about 5 percent for maximum able for plate supply. signal input. Distinguishing features of this class of The base of the 89 is of the small 6 -pin service are that very high output of good type as shown in Fig. 5. Its pins fit the quality may be obtained with fairly small standard six -contact socket which may tubes operating at relatively low plate be installed to operate the tube either in voltage; and that unusual overall econ- a vertical or in a horizontal position. For omy of power consumption is possible be- horizontal operation, the socket should be cause the plate current is very low when positioned with one filament pin opening no signal is applied to the grid. To give vertically above the other. these advantages, the class B amplifier The D.C. resistance in the grid circuit circuit requires the use of two tubes in of the 89 operating as a class A amplifier a balanced output stage preceded by a (either with triode or pentode connec- driver stage capable of supplying con- tion) should not exceed 1.0 megohm if siderable undistorted power and the use self -bias is used. Without self -bias, the of a power supply capable of maintaining resistance should not exceed 0.5 megohm. good voltage regulation regardless of the The use of resistances higher than these variation of average plate current with may cause the tube to lose bias due to signal intensity. It should be noted that the grid current with the resillt that the the distortion present in the high power plate current will rise to a value suffi- output of class B amplifiers is usually ciently high to damage the tube. negligible, but is always somewhat higher The direct -current requirements of class for the ordinary range of signals than B circuits are subject to fluctuation un- that obtained with class A amplifiers em- der operating conditions. The power sup- ploying much larger tubes capable of ply, therefore, should have as good regu- operating at the same maximum power lation as possible to maintain proper op- output. erating voltages regardless of the current Figure 3 shows a family of plate - drain. For this purpose, a high voltage voltage- plate -current curves of the tube "B" battery or a suitably designed "B" when operated as a class B amplifier. In eliminator may be employed. If the lat- the same curve, in dotted lines, the grid- ter is used, a rectifier tube of the mer - Fig. 7 (Continued on page 235) Details of the internal construction of the tube. i n 11 11 20 19 r -2l

Ie 12 lz ilI/ 1 RI TE `--9 16-.-iiiiiii OA HAIM.. C -A- ar:JJMìNUJ MF 23v t10 20 19 Fig. 8, above. á2 a u Details of the grid support and plates. ,21 21, 0 'o 60 pr a 0: 4i e1 Fig. 9, right. la 2; á 1 o° Schematic circuit showing how the tubes may 12 il 1 Iz 17--I /1/ 1//111 oë 1 1 1 0 2 4 10 12 14 be used in a power rectifier circuit. With the 4 6 1 0 1 2 4 6 , 6 6¿ proper connection of the grids, which are self 9 16+iiiiil CANER SY,NALVO T5 (AMS) 00.1VEa SIGNAL VOLTS(RMS) biasing, the tube may be connected to a source -B- of A.C. and operated directly without separate Fig. 4 rectifier tube. Variation of power output and plate current.

RADIO -CRAFT for OCTOBER, 1932 206 THE NEW "K" TUBE

, The efficient use of relays demands a vacuum -tube that has been designed specifically for such purposes. The author describes

such a tube in the article below.

By C. BRADNER BROWN

in the flow IIE new "K" tube was developed is very low which will result s. Fig. A --r in response to the need for a of large plate currents. It is necessary to The "K" tube, designed vacuum tube which would have use a filament which will withstand the especially for relay work. more favorable characteristics for bombardment of the positive ions which relay operation. The author having done are necessarily released to be attracted to considerable experimenting with photo- the filament. The coiled tungsten fila- 26 ======aa1= 122 VOLTS cell amplifier and associated relay equipment used in the type "K" tube is admir- 24 ment has come to the conclusion that ably suited for this duty as it is very 22 the present high- vacuum tubes are not rugged and not affected noticeably by the 20 Il0 105 VOLTS eminently suitable for relay operation. positive ions. le II The main reason for this is found in the If the grid is made sufficiently negative, 16 III0 85 VOLTS I of be CC 14 IIIIa inherent action a high- vacuum tube. the plate current will reduced to zero ct II 12 Ifili When is by uiiuo the grid voltage changed, the as all electrons emitted the filament IO I 62 VOLTS plate current is changed, the amount de- will be returned to the filament by the W F 8 IIIII pending on the change in grid voltage. negative grid. The tube will be inactive a 6 IIIIIII II 40 VOLTS II I1' This change in plate current, however, in this condition, but current will begin D 4 I II I ICf NOTE. II follows a smooth curve and therefore a to flow again as soon as the grid voltage 2 I II I1 ALL PLATE I VOLTS READ point will be found which the relay is reduced to the cut -off point. When II at I I IIA o II I BEFORE II is pulled in with not quite enough force the current starts to flow, the tube will E3 -0-6I -6 IONIZATION -20 -26.21.2220.18-16.14.2I 4-2-0 GRID VOLTAGE to operate the armature. This point is ionize and its resistance reduce to almost called the "threshold" of operation and zero. Once started however, the grid i; Fig. 1 when held at this current, the relay will powerless to stop the flow of current as A family of grid -voltage- plate -current curves. chatter, resulting in the burning or pit- the electrons arc being released by the 30 ting of the contacts. Even when oper- gas itself and not by the filament. The 28 ated at the point of grid voltage cut -off, ionization can only be stopped by reduc- 26 uni this condition will be found unless a coning the plate voltage to a value sufficient 24 siderable grid shift is used to operate the to stop ionization. If IONIZATION alternating or pul- 22 S ARTS HERE' tube. sating voltage is used on the plate, this 2 20 YI The thyratron tube offers a much better condition is fulfilled at every cycle or a 18 characteristic for relay operation as the alternation. The output of a full -wave u 16 action of the grid is to turn the plate rectifier particularly adapts itself to the 14 current on -more in the manner of a operation of the type "K" tube and was 12 IO snap switch. The type "K" tube is an used in the experimental relay hookups á 8 adaptation of the thyratron tube using which were set up to test the operation 6 neon gas instead of the customary mer- of the tube. 4 cury vapor. The conducting gas is the The remarkable characteristics of the 2 secret of its peculiar characteristics which type "K" tube are shown in the form of 0 will be discussed later. It was con- a family of plate -voltage -plate- current O 20 40 60 80 IOO 120 140 160 PLATE VOLTAGE structed using the elements of the old curves in Fig. 1. The sharp cut -off actio -i type CG1162, because this tube has a when the tube is operated with a negative Fig. 2 circular construction using a cylindrical grid bias is extremely valuable when Ionization starts with a plate voltage of 120. the plate which considerably simplifies the operation of a relay is to be considered. calculation of electrostatic field strengths The corners are naturally rounded off and surface densities. The operation of slightly when used with rectified A.C., the gas filled three -element tube is as but this action is not noticeable in actual follows: tests. It can be seen that a sudden in- The electrons emitted from the filament crease of plate current from zero to some are accelerated toward the plate by the positive value takes place when the nega- positive plate voltage. These electrons tive grid bias is reduced past a certain collide with molecules of neon, knocking critical point. It is this "breakover" ac- loose electrons from the outer rings of tion which prevents the chattering of the atomic structure. These released elec- relay contacts and allows the use of much trons are also attracted to the plate and, more insensitive equipment than normally in turn, break up other molecules of the is the case. Fig. 2 shows the ionization gas increasing the electron flow until the characteristics in the form of a plate - gas is thoroughly ionized. When it is in voltage- plate- current curve for zero grid Fig. 3 this condition, there are plenty of free bias. The current increase to above 200 Schematic circuit showing the use of the "K" tube. electrons in the tube, and the resistance (Continued on page 245)

206 RADIO -CRAFT for OCTOBER, 1932 ABLE The idea outlined in this descrip-

tion of a novel German develop- óO-RADIO ment, introduced at Leipzig Spring ER-RECORDER Fair, may be applied in many ways. P By DR. F. NOACK*

instance of bringing "the mountain o erman Radio Expo- graph is designed to operate at 110, 127 this w to Mohammed," the only requisite is a by the German or 220 volts, A.C.) nown 110 -volt line. veral sets for the By means of a switching system it is power acture of phonograph possible to arrange the circuit for a num- one exception, these ber of services, to wit: (1) Disc record- 2 designed that only an amateur ing of radio programs; (2) disc repro- disc re- .dro enthusiast could manipulate them - duction of radio programs; (3) since they consisted mainly of the com- cording of impromptu programs; (4) disc ponents requisite to making such records, reproduction of impromptu programs; and were not designed for convenient (5) radio program reproduction. operation by the layman. In this particular machine the cutting This exception was the equipment in- needle may be steel, diamond or sapphire. troduced under the name Schacktograph; The magnetic reproducer may be conveni- it is illustrated in Fig. A in finished form ently disconnected from the circuit, and and is the instrument shown at the suc- the output run into a dynamic reproducer, ceeding Leipzig Spring Fair. if desired; the field excitation current be- on the receiver. incorporates a radio ing supplied at terminals The Schacktograph The magnetic unit built into the chassis receiver chassis which includes a 3 -stage an is used not only to reproduce the radio A.F. amplifier capable of delivering but also of this programs picked up by the set, output of 2.5 watts; the output out- into a as a means of monitoring the audio section of the instrument feeds of the which also is part put of the A.F. amplifier portion magnetic reproducer or during the recording then, there is the turn- assembly, before of the assembly; of impromptu programs (such as singing its associated motor; finally, table and or talking by the operator or his friends, and a recording - there is a microphone etc.). reproducing head. (To meet the demands ver- of German power systems the Schackto- A device of this nature achieves a satility combined with utility that cer- 'It,rlin C"rrcapwulent. tainly places it in a class by itself. In Fig. A. The Shacktograph receiver-recorder.

R. A. FESSENDEN DIES

In the passing of Professor Reginald Aubrey Fessenden, who died July 22 at Hamilton. Bermuda, at the age of 65 years, the technical world mourns the loss of one of its most colorful pioneers. Although of Colonial American ancestry -the family came to Cambridge, Mass., in 1628 -Professor Fessenden was born in Milton, Province of Quebec, Canada. His experimental work with radio dates from the early '90s. when he first investigated "Hertzian waves" and at that time held, against the opinion of other investigators, that these radiations, in their method of propagation, bore a direct relationship to light: and that they traveled as "continuous waves" and not as a "whiplash" action. He accomplished the radio transmission of speech by a commutator method in 1900. at Cobbs Point, Md.; in 1903 the distance had been increased to 25 miles through the use of the continuous arc. He instituted radio broadcast programs from Brant Rock, Mass., in 1906; a high- frequency alternator of his design made this practicable. Professor Fessenden's inventions include the loop antenna, silicon iron for transformers. high frequency alternator. the heterodyne principle, automatic relay radio, induction telephony by means of a copper diaphragm and exciting coil, Empire cloth. submarine telephone, echo -type depth finder, iceberg and submarine locators, the tracer bullet, ultra -audio sound signalling, and three hundred others. In the magazine series. "Men Who Made Radio, " appeared a short biography and cover illustration. in colors, of Professor Fessenden. A man of strong will, he fought to maintain his convictions and often against almost overwhelming odds. He created a furore in the commercial world when, in 1925, he propounded the following oft- quoted Law of Invention: "No organization engaged in any specific field of work ever invents any important development in that field, or adopts any important development in that field until forced to do so by outside competition." A man of high ethics. Professor Fessenden contributed greatly to placing modern invention on a plane by itself as a field worthy of the best efforts of an individual; in this connection he is quoted as follows: "Invention is an art; just as much so as painting, or doing fine machine work." In Memorium, we again, humbly, quote Professor Fessenden: "We shall be remembered for a hundred things, our literature, our surgery, our medicine, our chemistry, our wars. But most of all we shall be remembered for our inventions."

RADIO- CRAFT, January 1930, page 309.

RADIO-CRAFT for OCTOBER, 1 9 3 2 207 THE LATEST RADIO EQUIPMENT

NEW NA -ALD SOCKETS RADIO CITY ADAPTERS OAK S.-W. SWITCH THREE sockets, all of the 6 -prong type NbEW \ tubes mean new adapters, if test OAK MANUFACTURING CO., b re now available for consumer use from equipment is to be kept up to date. fecting an all -wave switch tha the Alden Manufacturing Co. The type Shown below, at the extreme left, is an noiseless in operation, has solved the pr illustrated at the extreme left is for base- example of a 5 -hole to 5 -prong adapter lem of "switching noise" for short -way board mounting; that in the upper center suitable for use in tube testers, analyzers, receivers and converters. This new switch radio sets, in fact anywhere where tubes are used. Manufactured by the Radio City Products Co., they have been especially designed to accommodate the Service Man who must have the proper adapter at a low cost. They are made in all types and sizes for all the new tubes including the new 7 -prong tubes which will be announced shortly.

R.F. CHOKE FOR THE 82 THE recently announced 82, mercury - New Na -Ald sockets. vapor rectifier, functions because of the New Oak all -wave Switch. for subpanel mounting; and that at the ionization of the mercury in the tube. As extreme right has a special flange suitable the voltage applied to the tube Increases, at is said to have a lower contact resistance for subpanel mounting with two screws - the mercury starts to ionize, slowly than any other radio switch now available first and then more rapidly until the maxi- that shown in the center having but a -actually less than .001 -ohm. The contact mum current flows. This rapid increase single hole. They are known respectively is of the double surface- cutting type as in current generates high- frequency cur- as types 486, 426, and 436. may be seen by reference to the photo- rents which must be prevented from en- graph above, and is silver plated to tering the radio set if efficient operation LYNCH ANTENNA KIT minimize deterioration. Other important advantages are a well -defined stop action. of this magazine THE September issue Bakelite dielectric, and rust -proof cadmi- I on short -wave col- contained an article um- plated frame. lectors. This article stressed certain types of construction for the antenna in order to efficiently receive short waves. Another recommendation was the use of an an- NEW BEEDE METERS tenna coupler connected as shown in the THE Beetle Instrument Co. announces a article -Fig. 2 at C -and pictorially illus- new line of meters for the Service Man, trated below. Reduction of noise pickup one of which is illustrated below. They Left, adapter; center, R.F. hoke; right, 7 -prong is by transposing the lead - are low priced and some of the features accomplished socket, in by means of transposition blocks con- include a D'Arsonval moving coil move- structed as shown in the article and pic- is to be secured. Manufacturers of the 82 ment; large, laminated permanent mag- tured below. All of the above apparatus recommend a small R.F. choke to be in- nets; new method of gap spacing which are now available from the Lynch Manu- serted in series with the "B" minus lead minimizes the collection of dust; and facturing Co. between the power transformer and the sapphire bearings. They are made in vari- filter unit. Such a choke, manufactured ous sizes and sensitivities to accommo- by the Sun Radio Co., shown above at the date every purpose. center, is rated at 2 milli -henries and is capable of carying a current at 250 ma., the rated value of the 82 rectifier.

NEW 7 -PRONG SOCKET ALTIIOUCH the new 7 -prong tubes have not been announced at this writing, they are "just around the corner," but manufacturers have already produced the socket in anticipation of future business, as may be seen by reference to the photograph above (at the extreme right). The socket illustrated has many desirable features: the terminals are well spaced; riveted to a single piece of Bakelite, and a lasting, firm contact is insured by the fact that additional springs keep the contact surface tight against the tube pins Lynch antenna kit. at all times. New Beede meter.

208 RADIO-CRAFT f o r OCTOBER, 1 9 3 2 CROSLEY ROAMIO MAGNETIC SPEAKER VOLT -OHMMETER new and distinctive mechanical speakers seem to be com- THE Franklin Radio Corporation has MANYfeatures have been incorporated in MAGNETICing into their own again, to judge recently announced their new model 1 the new Crosley Roamio automobile re- from the number of receivers, especially Voltmeter- Ohmmeter. Mounted in a ceiver depicted below. This small receiver of the automotive type, that are making laminated bakelite panel, and housed in their appearance. As an aid toward port- ability, the new unique magnetic speaker, shown here, fills a long -felt want, for it is only 6/ inches in outside diameter and but 3 inches deep. An unusual type of rotary drive between the armature and the cone is employed, which places the resonant frequency of the driving mechanism outside of the audible range. The pole pieces are of laminated iron and the rotary drive shaft is insulated elec- trically and acoustically at both ends by

The Crosley Roamio.

is contained in a gray- silver metal case of a size small enough for easy installation either on the floor in front, between the driver and passenger; below the dash; in the rear, either fitted snugly against the driver's seat or between the passengers in front of the rear seat. A new type antenna, slung under the chassis of the car by two clamps, eliminates the removal of the upholstery in order to secure a satisfactory antenna. The tubes used are as follows: A '36 as a combination oscillator and detector; a '37 as A.V.C. and second -detector; a '39 as first I.F. amplifier; a '36 as second An volt -output meter. I.F. amplifier; a '37 as first A.F. amplifier; and a 41 output stage. a hardwood finished case, this instrument is designed for voltage ranges of 3, 30, A small magnetic speaker. and 600 volts, and ohmmeter ranges of SPUN" RESISTORS "OHM- rubber washers, to insure uniform repro- 0- 10,000 and 0- 100,000 ohms. When used OIII- SPUN," is the name given to a duction. as a voltmeter, the instrument has a manu- woven, new type resistor unit, speaker, a product of the Best sensitivity of 1,000 ohms per volt. is a This factured by the States Co. It light, Co., is specially desirable All necessary pin -jacks and push but- of wind- Manufacturing non -inductive resistor. Instead in portable receivers, or in any location tons are mounted on the front panel; a wire an Insulat- ing the resistance on where space is at a premium. 41;_ -volt battery for the ohmmeter is ing form, it is spun in a plane, as housed in the case itself. Of course, pro- shown below, so the current in adjacent vision is made for battery- voltage com- wires flows in opposite directions, thus A UNIQUE VOLUME CONTROL pensation. reducing the inductance to practically BECAUSE the ear is more sensitive at zero. the middle than at either end of the They are available in two types; the audio register, it is desirable to vary the type A for frame and the type B for flat - volume of a radio receiver in such a man- TWO -SPEED MOTOR surface mounting. They are 6- inches ner that the low and high notes are not f--HANGING from 3.3 -1/3 to 78 R.P.M. is square and available in sizes up to 1,000 distorted. This feature is accomplished accomplished by a single lever in this ohms, ?; ampere each, in the type A in the new device manufactured by the phonograph motor produced by the Gen- mounting. Allen -Bradley Co., shown below. eral Industries Co., Inc. They are made

A two-speed phonograph turntable.

in two types, the model D for 10- and 12 -inch records, and the model H for 16- inch records. All gears are enclosed and run in oil. Two additional features are the facts that (1) it will not overheat in closed cases and cabinets, and (2) absolute uni- formity of speed under severe variations of voltage fluctuations and record drag is The Ohm -Spun resistor. Here's a real volume control. maintained.

RADIO-CRAFT f o r OCTOBER, 1 9 3 2 209 A LAPEL MICROPHONE

In this the final of a series of articles concerning the Lapel Micro- phone, electrical characteristics and application are discussed, for the first time, by Dr. Saxl, authority on physics and radio.

PART II By DR. IRVING J. SAXL*

N our last article in RADIO-CRAFT we be matched to the impedances of the in- have seen how the new lapel micro- put transformer, as shown in Fig. 1, the phone makes possible free movement best performance taking place if the im- of the speaker before the audience; pedances at the output and input sides non -obvious pickup of his voice; and al- have approximately equal values. lows sound amplification to be thus intro- Another important item is the amount duced in places, and with individuals, of current sent through the microphone. where microphonic amplification would While it would seem probable, at first not be feasible heretofore. glance, that the amount of current would We have a tiny button, almost invisible, influence only the total quantity of elec- controlling the energy of many watts in tro- acoustical impulses transmitted loudspeakers all over an auditorium or through the microphone, it will be readily convention hall. How is the transforma- seen by reference to Figs. 2A and 2B that tion of the sound impulses into electrical not only quantitative but definite qualita- impulses from the lapel microphone tive changes of the transmitted sound take achieved? place, in accordance with the amount of We know already that the sound waves, current transmitted through the micro- Fig. A striking the membrane of the microphone, phone. x produce a variation in resistance of Figs. 2A e the and 2B show the frequency 24 this microphone because the carbon gran- response characteristics of this lapel mi- 22 ules filling the space between the carbon crophone taken both at a current of 10 button and the actual membrane is and 20 milliamperes passing through the 20 pressed more or less together. If a volt- microphone. It will be readily under- 18 Z o age is applied between membrane and stood that the total acoustical energy 16 F carbon button, the carbon granules will produced with 20 w W milliamperes is differ- I\4 be able to conduct more current than if ently distributed over the entire frequency I ` ° 1 \ 1Z Ó no pressure takes place. A sound wave range than it would be with 10 milliam- 1k W is nothing but a succession of variations peres. It is especially remarkable that I I° of the production the pressure falling upon the lapel of the highest frequencies, -UTION "\ BUTTON_ 6 N microphone. These variations, which are about 6,000 to 7,000 cycles, and the lowest IIIIIIIIIIIIII/ \! 4 almost proportionate to the sound energy frequencies, have increased several times I1.111/21.111.11.01J- produced, are converted through this mi- more than the maximum 2 energy output, rirld=1111.111 0 crophone as a variation of electrical which takes place at 3,000 cycles per sec- 8000 6000 2000 ipoo impulses. ond. This means, that by passing more FREQUENCY N HC. (Continued on page 238) Dependency of Sound From Microphone Fig. 3 Current /SINGLE MICROPHONE BOT TON TRANS, AFT1 OUT. / '29 - MF 45 MF TRANS While there is, at present, no receiver r ! '50'5 ti 41 I I í existing-the action of which is perfectly I linear to sound waves falling upon it- si it is possible by proper engineering to ' select its electro-acoustical I characteristics I l Io ol in such a way that a satisfactory sound Two OUTPUT reproduction is received. The first part BUTTON I[rL^! of this transformation from sound into electrical energy takes place in the microphone itself, and from here, naturally, 400 the first control of the sound is affected. OHMS ÓS Consider, for instance, the electrical resistance of the microphone. By choos- 4.sv. ing proper carbon grains it can be varied BGTT. from less than one hundred to several hundred ohms. This resistance 1Il1lr has to 5.000 ONM5 PT

Consulting Physicist. Fig. 1

210 RADIO -CRAFT for OCTOBER, 1932 DIODE AND 2 LET. -AMP. OPERATION AND SERVICE OF A.V.C. (A.F.) AUTOMATIC VOLUME

0.2-MES TO GRIDS OF . RC CONTROL SYSTEMS CONTROLLED TUBES MANUAL VOLUME CONTROL This is the final article dealing with the operation RESISTOR VALUES ARE APPROXIMATE AND vs RV WITN EACH MODEL RECEIVER. and service of automatic volume control systems. Fig. 5 Circuit showing the method of operating a diode detector and A.V.C. arrangement in one tube. By W. S. WILLIAMS

THE September issue of this magazine the amount of current that flows being as detector and volume control. A con- contained the first part of an article proportional to the impressed voltage. ventional three -element tube is usually dealing with the theory of operation Now, on the negative half of the cycle, used, one element being connected to the of A.V.C. systems. In this issue, the since the tube is already biased so that cathode, while the other, either the plate practical application of A.V.C. systems no current flows, an increase of negative or the grid, serves as the anode (plate) will be discussed. voltage cannot produce any change in of a simple rectifier. In some instances The hookup of a complete receiver us- plate current. This results in an inter- the plate and the grid are connected to- ing A.V.C. is shown in Fig. 4. This re- mittent flow of current, which in the case gether and used as one element. ceiver was built by the author and all of the power detector, produces a voltage Since the tube functions as a rectifier resistor and condenser data are given. In drop across the primary of the first audio there is no gain, in fact there is a dis- other types of receivers the bias voltage transformer. In the case of the A.V.C. tinct loss which requires some amplifica- and the plate resistor for the volume - tube, this current, flowing through the tion before it is applied to the output control tube will probably have to be plate resistor, produces a voltage drop. stage. In many instances, two or more changed, and the best means of arriving This voltage is added to the normal bias stages are used before the output stage. at the proper values is by trial. afforded by the cathode resistor and de- The advantages claimed for this system We have considered the necessary creases the sensitivity. Now, with the vol- are better fidelity, ability to handle a parts, the adjustment of the various op- ume- control tube operating under the same greater input, and the fact that the de- erating potentials and some of the conditions as a power detector, as soon tector also functions as a volume control. troubles encountered, but have said little as any signal is impressed on its grid This last sounds like doing the same about how the automatic volume control the sensitivity would be reduced and the work with fewer tubes, but this is offset worked. The A.V.C. tube operates under output would be very low. But as said by the A.F. amplification needed. As conditions similar to a power detector. before, it is biased to cut -off and a little for fidelity, it is doubtful whether a power That is, it is biased to cut -off, or until beyond, and current does not begin to flow detector introduces more distortion than no plate current flows. When a tube op- until the signal is strong enough to pro- the extra audio stages. Besides, when a erating under this condition has an alter- duce a satisfactory output. tone control is used, fidelity becomes al- nating voltage impressed upon its grid, Diode A.V.C. Systems most an unknown quantity. With refer- the bias is reduced by an amount equal The second type of A.V.C. to be consid- ence to its power handling ability, one to the applied voltage during the positive ered is the diode or two- element detector. cynical observer, after viewing a hookup half of the cycle, and plate current flows; In this system, a single tube serves both (Continued on page 239)

Fig. 4 The antenna and R.F. coil secondaries are wound with approximately 110 turns of No. 28 enameled wire; oscillator-grid coil, 85 turns of same size wire; tickler. 50 turns No. 32 enameled. All forms 11/4 ins. in diameter. The oscillator and grid coils are wound end to end (grids adjacent); the spacing between windings is áe in. The antenna coil and R.F. chokes consist of 400 turns of No. 38 wire, scramble wound on a bobbin "2 -in. in diameter. Tuning condensers, .00035 -mf. The I.F. transformers were made at home by winding chokes as described and shunting them with 75 mmf. tuning condensers; the primary and secondary are spaced about 1. inch. The fixed section of the oscillator trimmer condenser has a capacity of about .00065- mf.; the variable section, a capacity of 200 mmf.

RADIO -CRAFT for OCTOBER, 1932 211 A MODERN "3- TUBE" REFLEX RECEIVER

Here's a description of a "three- tube" receiver which revives the once much -used reflex system.

A very compact unit; it may be located in By H. G. CISIN, M.E. almost any convenient spot.

THE PZ pentode and other more recently announced tubes by small fixed condensers wherever necessary, thus assuring offer many fascinating possibilities to experimentally - smooth operation. inclined radio fans. These tubes may be used advanta- Volume is controlled by means of a 10,000 ohm "tapered" geously in T.R.F. circuits, superheterodynes and prac- potentiometer connected in the cathode circuit of the type 58 tically all other standard circuits. Realizing this, it was decided tube. A fixed series resistor 11, limits the minimum negative to try out some of the new tubes in the "reflex" circuit; several grid bias. different combinations were tried, with very excellent results. An Amperite is employed in series with the primary winding It seems as though the reflex circuit has been unjustly of the power transformer. This keeps operation normal regard- neglected by radio engineers. Five or six years ago, the writer less of line -voltage fluctuations and also serves as a protection had occasion to test a number of the reflex sets designed by to the tubes and other components of the receiver. David Grimes, and even at that time, remarkable results were obtained with the circuit. Taking advantage of the great ad- Constructional Data on the 3 -Tube Reflex vances and improvements in vacuum tubes, it is now possible Six drilled in sheet before the reflex, capable of outperforming a modern socket holes are the aluminum to design a three -tube for The hole four -tube T.R.F. receiver and superior to the old reflex sets latter is bent to the size specified the chassis. for the flush -mounted power is also cut time. having six and seven tubes. transformer at this After the is formed, the wafer sockets are mounted. In the reflex circuit described in this article, a PZ pentode chassis One of these, the speaker connection socket 26, is mounted on serves the dual functions of first R.F. and power A.F. amplifi- the rear chassis wall. cation; the first R.F. portion of the circuit being untuned. The power supply transformer, 31, is mounted next and then A tuned circuit is used to couple the two R.F. stages. A the dual variable condenser 7, 17 and the antenna binding post, variable -mu type of pentode, the 58, is used in the second stage. 1. No ground post is necessary, as no external ground is used. This is coupled by means of a tuned impedance to the detector. The trimmer condensers, 7A, and 17A, are fastened in the in- The is the secondary of a standard R.F. coil; the inductance sulated framework at the side of the dual variable condenser. is by the second .00035 -mf. section of the capacity furnished is next upside R.F. dual variable condenser. The chassis turned down and the choke 2, and the three electrolytic condensers 25, 25A and 29 are One of the new general -purpose, type 56 tubes is used as a fastened on the rear chassis wall. Fixed condensers 21 and detector. The A.F. output of the detector is reflexed (fed back) 16, R.F. choke 20 and the potentiometer- and -switch unit 12, 32 through the type PZ pentode, which is thus made to function mounted on chassis wall. The 6 doubly the first instance, as an R.F. tube, and, finally, as are the front R.F. coils and -in 15 are mounted on underside of the chassis; dual condenser the A.F. output tube. the 8, 9 is mounted on the side wall. Finally, the various fixed The 2,500 -ohm field coil of the dynamic reproducer serves as condensers, flexible resistors, etc. are fastened in position. These the filter choke; this inductance is bypassed by two 4 mf. elec- are soldered as close as possible to the part with which they trolytic condensers; the capacity specified is sufficient for re- function. ducing the hum to a negligible value. This reduces and simplifies the wiring. Having completed the assembly, the set is now ready for the The screen -grids, cathodes, etc., of all the tubes are bypassed wiring. A break is made in one of the leads from the primary of the power transformer 31, and the switch 32 and Amperite socket 33 are connected in series in this circuit. Diagonally opposite socket terminals are used for the Amperite, (viz: one small prong terminal and one filament prong terminal). The PZ tube uses a 5 -prong socket. The control -grid connection Is made at. the terminal separated from the other four. Of these other terminals, the two center ones are for filament connections. Looking at the underside of the socket, the plate terminal connection is at the left, while the screen -grid is at the right. Looking at the underside of the 6 -prong type 58 tube socket, Fig. 1 the two large terminals are for the filament leads. The next Schematic circuit of the receive . terminal to the right is for the cathode connection and to the Note that it is, in reality, a fou - right of this is the suppressor -grid terminal, which is connected tube set, although only three are back to the cathode externally: Le., used for reception; the fourth be- at the socket terminals. ing a rectifier. A 58, a PZ pentode, To the left of the filament terminals is the plate terminal and and a 27 are the tubes used in the the remaining terminal is for the screen -grid connection. The radio receiver proper; while a stand. control -grid connection is made at the cap of the tube. and '80 is used in the rectifier unit. Refer to the List of Parts for the The 56 -tube socket is connected the same way as a '27. The constants. (Continued on page 239)

212 RADIO -CRAFT for OCTOBER, 1932 MAGNETIC DYNAMIC 65.0Ó0 65 SOME INTERESTING 60.000 áa 60 .t[ÿi 55 55,000 ii p M Ela G1YE 45.00O ° lammmlam 44 45 40.000 mums era. 40 Z ri r 35 FACTS 30.000 WÓ MN mmi>i>m P/001 30 LOUDSPEAKER 25.000 Ft ,,-/ty 25 2Q000 {iE/LlMEMEli{iN 20 IOrRiBEMINitMEI 15 10.o0oit.I,A.lita..tata..tata.ta..fa15,0005 t0 5.000 Some preliminary loudspeaker data is given in this first of 90 í.Y...... mmmmm ° O ° O ° ° 28 88888 ó ó ó which will deal with the use of multiple ?4N Va n b r o a series of articles FREQUENCY speakers in radio sets. Fig. 4 Impedance variations of magnetic and dynamic speakers. By ELI M. LURIE

was engineered over thirty years ago. This resonant positions of one will not coin- sane principle is used in the Telauto- cide with those of the other. If each is graph writing machine, the device used allowed to vibrate separately, it is pos- in banking institutions, hotels etc. for sible to draw two resonant curves of the the reproducing of one's handwriting at situation as in Fig. 2. a remote location. One of the greatest handicaps in the Harmonics in Speakers BAFFLE design of a loudspeaker is inherent reso- the present time there is no In any electrical circuit where close nance. At circuits type of speaker that does not have some coupling between two separate exists, a resonant curve of the complete Fig. 5, left. A tuning fork baffle. resonance. By this is meant the ten- a This Fig. 6, right. Energy distribution from dency of the different parts of the speaker unit will have two distinct humps. dynamic speaker. combining to continue to vibrate after the signal has phenomenon is analogous to the gen- stopped. of both the reed and cone, which is MANY technical articles have been erally done by fastening the reed securely of ra- In the magnetic type of loudspeaker nut written on various types or vi- to the apex of the cone by means of a To read and the cone driven by a prime mover drawn diu loudspeakers. or steel rod and thread. The resonance curve avalanche of brating reed, usually a brass will be of a understand this A per- for this combination that of about 3/64 -inch in diameter. have information would require considerable polariz- composite vibrating system and will obviate such manent magnet is generally the the two effort and time. In order to mover or reed two humps similar to that of this article has been ing agent. Now the prime circuits. The a tiresome procedure, mechanical system that has a tightly coupled electrical Although it is by no means a is a tuned have not been shown; the ac- prepared. definite resonant point. This resonant harmonics on the subject, it does effect of these would be to superim- complete thesis point can be varied by damping or limit- tual the basic principles behind the pose little ripples on the main curve. contain ing the vibration of the reed, but if damp- modern loudspeaker. Some of the ma- Thus it can be readily understood why, while ing is used in order to either raise or terial has been compiled from notes, or below up to the present time, we have been un- been taken lower the resonant point above repro- most of the information has spectrum, there will able to obtain flawless and perfect journals dat- the audible- frequency would be unwise to directly from engineering be a considerable loss in duction. Perhaps it 1925. naturally reproduction is impos- ing as far back as intensity. say that perfect We generally associate the dynamic sible, but it is true that, until we learn with recent progress but Referring to the diaphragm or cone of how to entirely eliminate the natural ef- loudspeaker take though the speaker of today is really new, the speaker, resonance will usually fects of resonance, perfect reproduction the basic idea is not. As early as 1898 place at the fundamental frequency, and is very improbable. Efforts have been Sir Oliver Lodge, the renowned English will always be accompanied by a series made to design a speaker with a continu- et in regard scientist, was issued a patent on this of overtones which will vary ance of resonant positions, the ultimate identical thing. As a matter of fact, it to the fundamental; in other words, they idea being to approach the ideal by mak- was he who made the first permanent may be two, three, Live or six times the ing use of resonant points all over the magnet dynamic type of speaker. In frequency. In fact, there may not only complete spectrum. so that the aperio- any odd number Fig. 1 is shown a sketch of his idea. A be even harmonics, but dicity of the speaker will depend on the bar -magnet is used to supply a constant as 3.6 times the fundamental frequency. resonant points and not on the vibration field. The voice coil is suspended as This, naturally, aggravates the resonant that is normally associated with the cone shown and when a fluctuating current condition, and in a way is similar to the when in unresonant oscillation. The big passes through the coil it moves right and reed in that they are both tuned resonant problem with such a speaker is to cause left. Thus, a real dynamic speaker systems; the difference being that the the amplitude of vibration on the resonant positions to conform to the applied input in such a manner that a linear condition between input voltage and power output is the result. Otherwise, the amplitude of some of the resonant positions will be much greater than others, with the resulting non -linear response characteristic. The more resonant points that are used and the closer together these points FREQUENCY 5" DIA. are grouped, the closer the ideal condition will be approached, provided of course, 3 (Continued on page 241) Fig. 1 Fig. 2 Fig.

213 a RADIO-CRAFT f o r OCTOBER, 1 9 3 2 THE WHY AND WHEREFORE OF TUNING METERS

By L. VAN DER MEL

TUNING METER, as the name necessarily mean that no current is implies, is a device used to flowing through it -in fact, if the peak indicate when the radio re- value of the A.C. through a D.C. meter ceiver is tuned to the peak of is great enough, the meter may burn the signal (tuned exactly to reso- out while it is reading zero! nance). It is not necessary that the device itself be a voltmeter or a mil - Where to Use the Tuning Meter liammeter; all that is required is some If the above is true, where, then, form of Indication when the signal has may such a meter be connected in a been fully tuned in. Tuning meters radio set in order to indicate the sig- are used in sets where the selectivity nal strength? Suppose it is connected is high, and therefore some means is in the plate circuit of an amplifier as necessary to determine exactly when indicated in Fig. 2. If the amplifier is the carrier is tuned in, so good quality of the class A type, the plate current may be secured. (Especially useful Photograph of a commercial tuning meter. Note that the variations through the meter will infor short -wave work.) scale Is reversed from top to bottom. crease above and decrease below the In receivers of the superheterodyne value of current flowing when no sig- type, a hissing noise may be heard nal is received; furthermore, the when tuning between stations, which dis- POSITIVE amount of increase is equal to the amount appears when tuned to resonance because D. C. of decrease, and hence the signal varia- of the demodulation of the noise by the METER tions have no effect upon the normal read- stronger carrier. If, in such receivers, ing of the meter with no signal received. a tuning meter is employed to indicate NEGATIVE Obviously, the plate circuit of a class A exact resonance, clear reception is in- amplifier is no place for a tuning sured. In any event, they are used in meter. modern receivers, and a knowledge of If it cannot be placed in the usual am- where they may be used and "why" is plifier, let us see what happens in the essential for good servicing. detector circuit. If the value of resistor in 2 be so The D.C. Meter It Fig. increased the tube is now a detector (which is the same as Most people are familiar with the ac- connecting the meter in the detector cir- tion of the ordinary D.C. milliammeter B+ cuit), the amount of increase above nor- used so extensively in modern radio serv- AVERAGE PLATE mal current (the increase being due to ice work. It is commonly known that CURRENT WITH SIGNAL a signal) is greater than the decrease they will not read A.C. Why? Refer to below - NORMAL PLATE normal (due to the negative half the diagram of Fig. 1. Here is shown AI CURRENT NO SIGNAL cycles of the same signal). The plate A.C. D.C. meter. an voltage applied to a lab current now flowing through the meter, During the positive halves of the cycle, because of the signal, is shown in Fig. 3. the pointer of the meter tends, let us say, It is seen the plate reading GRID VOLTAGE that current to move up the scale to the right, and of the D.C. meter has increased by an during the negative half of the cycle it Fig. 1, above. A typical sine wave. amount A because of the signal. Thus tends to move off the scale to the left. Fig. 2, center. Where the tuning meter may we may conclude that a D.C. milliam- If the frequency of the voltage is very be placed. meter may be inserted in Fig. 3, below. Why the tuning meter reads. the plate cir- low, the pointer of the meter is able to cuit of the detector (power detector as- follow the variations of the impressed R.F.1 DET1 I. F.1 I. F. 2. sumed) and the meter may be called a voltage, although no steady reading can "Tuning Meter." be obtained. As the frequency of the Further, it should be pointed out that voltage is increased, the mechanical in- if the detector circuit In which the meter ertia of the pointer prevents its following is inserted is of the grid -leak and grid - the rapid variations in the applied voltage condenser type, the reading of the meter so that its reading (if it reads any value 1)»l=I)l will decrease with an increase in signal at all) is the average value of the im- strength which, of course, is contrary to pressed voltage or current through the the action of power detector. meter. In other words, any D.C. meter reads average values only. The Tuning Meter in A.V.C. Circuits The average value of the sine wave s;TUNING An examination of some of the more shown in Fig. 1 is obviously zero, and METER recent commercial receivers employing hence the meter reads zero. Even if the automatic volume control (A.V.C.) will frequency is so TO ,SCREEN COMMON TO A V.C. low that the pointer is NEATER VOLTAGE PLATE TUBE! indicate that the tuning meter, if any, able to follow the variations faithfully, RETURN is connected in the plate circuit of the the average reading of the meter is zero. BIAS RESISTOR-.. amplifier circuits, usually the I.F. ampli- This leads us to the conclusion that just fier Circuit showing how the tuning meter may be in superheterodynes -which at first because a D.C. meter reads zero does not used in a superheterodyne. (Continued on page 240)

214 RADIO -CRAFT for OCTOBER, 1932 BUILDING YOUR OWN B A. F. CHOKE COILS

800 -D- By C. H. W. NASON 500

500

200 FILTER chokes designed for a given magnetic material the relation of B to H loo in Fig. IA. If the current I0 is io 60 100 260 inductance require calculations far is as shown A.C. FLUX DENSITY- GAUSSES outside the abilities of the average through the winding is now decreased it path of the Fig. 1 amateur. Before discussing actual will not follow the original simplified design methods it might be curve but will take another course as well, however, to discuss briefly the fac- shown in Fig. 113. Thus for a given tors involved. Certain relations are in- value of H a twofold value of B corre- volved in the design of the magnetic cir- sponding to Q and to R in Fig. 1B are cuit which are briefly as follows: found. (This is clue to the residual mag- condition is Factor Equation Unit of Expression netism in the core and the II (the magnetic known as "hysteresis." Naturally, the force) 4 pi N I Gilberts per Cm. smaller this loop the better is the core 4, (the flux) u II A Maxwells material for magnetic purposes.) (the flux density) Gausses It +/A a fixed D.C. magnetizing force a is (the permeability) B /II Numeric value. If with minor In these equations: small A.C.voltage is superimposed,a 1 = the magnetic path in ems. hysteresis loop appears as is indicated in A = the cross section of the core in sq. ems. Fig. 1C. It is from the minor loop that we N = the number of turns. permeability of the core ma- I = the current in amperes. determine the pi = .1416 terial to alternating currents, and it is If we pass a gradually increasing cur- u:.,. that we employ in calculating the in- a (Continued on page 243) Fig. 2 rent through the winding surrounding

.050 190 I I I e0 BEST AIR GAP (TOTAL) 70 SQUARE CURVE SECTION Al .045 60 EI-il 50 a I 60 MA.- VpQ 40 80 MA .040 - 30 4 120 MA. - GP÷ "Q .035 20 I t / 100MA. OJ `OC/ % 2 100 MA 120MA. u 1,200 f MIIPI .030 10 A pJ N? 1000 &) P`/0 tt LL a ii.i!i y1- ._ 7 ///I N2 34 700 w N .025 6 -%//_ .rl`.`- MAE=80 MA. NO 5 -II _I/V GP N333 4 _,I 400 cwt 020 y\yP? -`60MA.- 3 300 Q. N? 32 r o Ae .015 2 / 200 z NB31 o r z .010 3 100 u rmilINMI N230 o Ó8 80 w .005 .07 V .06 N2 299 60 z .05 .000 .04 40 g~i No 28 rn 1,000 2,000 3000 4000 5,000 6,000 7,000 8,000 .03 30 TURNS óc V 27 .02 20

Fig. 3

For a given inductance and D.C. through the core, the number and size 10 wire may easily be determined by means of the chart above. For an .01 41)00 6,000 Z000 inductance of 20 henries, with 120 ma. through the core, 6,700 turns of 1000 2,000 3,000 5,000 8000 TURNS No. 35 wire should be used on the core indicated in Fig. 2.

RADIO -CRAFT for OCTOBER, 1932 215 SPADE TERMINALS U C O N S T R U C T I N G TWISTED PAIR

O O O ADAPTERS FOR O O By F. L. SPRAYBERRY* tJJl :ñ tr

11E average Radio Service Man new equipment. This is not strictly true. KELLOGG TUBE views with dismay the ever chang- Two courses are open to owners of old CAP 52° LEADS ing design of vacuum tubes. Each test equipment. This equipment may be season sees new types differing in rewired (old testers may easily be re- design from previous ones. For a long wired and brought up to date), or; the G P time the standard tube was of the three - owner of such equipment may use stand- O element type, the base of which used four ard adapters making it possible to test was O prongs. However, the public demand the new tube circuits. Rewiring is usu- for A.C. operation, and the four -prong ally more expensive and for that reason

P tubes available at that time were not many Service Men prefer to use adapters. suited for operation on raw A.C. -this The purpose of this article is to inform 141 was particularly true of detector stages. owners of old test equipment just bow Therefore, the five -prong tube emerged they may bring their equipment up to F-111 111'F+ and became a commercial product. At date by using adapters. We shall cover FIG 3 FIG.4 least one was used in every A.C. operated each well -known line in the following or- receiver. der: Jewell, Weston, Supreme, Hickok, The next major change in design was Dayrad and Readrite. Data is given as 48" LEAD the screen -grid tube. First there was the to the type of adapter required for each J four -prong '22 type which was to be op- of the most popular testers of these makes. 0* LEAD erated on batteries. It was not long As these adapters are commercially avail- G P until the companion tube for A.C. opera- able, they are best described by reference 0 0 tion was released; this was known as to their regular (Na -Ald) stock numbers. the '24. The next change in radical tube O design was the power pentode or '47. Adapters for Jewell Testers The present season sees a variety of No. 942, Fig. 1, is used with the 133 o new tubes announced, several of which and 133A testers. It permits testing from have a six -prong base. There will also a five -hole socket. It is to be attached be a tube having a seven -prong base. The to the regular test plug. next will be a No. 945J, Fig. 2, is used with models 11. F+ -? FIG.5 Radio testing equipment is, as a rule, 133, 133A and 137. The plate and grid designed to test the circuits of tubes in connections are crossed, the cathode be- use is ing open. - 48" LEAD general at the time that equipment The adapter is placed in a five 1eLEAD being manufactured. The manufacturers, hole socket and the test plug in the e LEAD of course, have no way of knowing the adapter. Refer to the instruction booklet types of will in fu- Ci G tubes that appear the for these testers for the further use of O ture. As a consequence of the continued this adapter. change No. 3, O in tube design over a period of 952J, Fig. may be. used with all several years, many fine pieces of radio Jewell models. It is a UX adapter having O test equipment have become obsolete, as a split -plate circuit with two 52 -in. ex- they will not test the more modern tube ternal leads for connecting a pair of head- circuits. phones or a milliammeter in series with Many Service Men think that it is neces- the plate circuit. sary to junk this equipment and purchase No. 949K, Fig. 4, is a UX adapter hay- b rv . c, ,,.,at: , t, : u,,, :a n:,,r tn.rt, t, w,,,hington, D. C. FIG. G 4 FT. LEAD SEPARABLE PHONE -TIP JUNCTION SEPARABLE PHONE-TIP JUNCTION -171 CI- r6' LEAD 54" LEAD LOCKING STUD G G G IN CENTER O o t OF ADAPTER O O ©P K H 0 o O H H H

G G

H FIG.7 FIG.9

215 RADIO -CRAFT for OCTOBER, 1932 CATHODE Twenty -nine out of one hundred eighteen adapters are CLIP described in this first of a series of practical articles. TEST EQUIPMENT

ing 8-in. leads from both filament ter- grid leads which are to be connected to S.P.D.T. TOGGLE SW. Kellogg the tip jacks provided on the Jewell 444. UP FOR DIODES DOWN minals. Used to test "overhead FOR TRIODE filament" type tubes. It is inserted in Also tests types 41, 42, PA and PZH tube the tube socket of the receiver. The fila- circuits as directed above. P to the No. 964DS, Fig. 10, changes a six-prong ment leads are then connected P r. 20.000, plug to a four -prong plug, used with the 12.000 overhead filament contacts of the receiver. OHMS OHMS May be used with Jewell Models 133, Jewell 660. May also be used with any H 133A, 198, 199, 408, 409, 444, 577, 578, tester having a basic six-prong plug. H H 579, 581 and 660. No. 965DS, Fig. 11, changes a six -prong No. 932, Fig. 5, is a twin-adapter for plug into a five -prong plug. Used with testing the circuits of types '22, '32 and the Jewell 660 May also be used with P K '34 tubes, using old -type 198, 199 and 581 any other tester having a six -prong plug. testers. One adapter is placed on the test No. 982, Fig. 12, is used with all tube HW H H plug and the other in the tube socket of testers having a 2.5 volt socket. This IfH the receiver. The control -grid circuit adapter is made for testing the type 82 FIG 24 FIG.25 FIG.26 is completed with the lead provided for and 83 rectifiers in tube testers only; do CONTROL- that purpose. not use with a set analyzer. It incorpor- GRID CLIP No. 992, Fig. 6, is a similar adapter ates a switch for changing from one plate to adapter No. 932 except that it is made to the other and includes the necessary Pl for types '24, '35, '36, '38, '39, '44 and '51 resistor. Use the type '45 socket in the P o 0 P2 G P2 tubes. It is to be used with old -type 198, tube checker for the 82 and the type socket for the 83. Used with mod- 199 and 581 testers. '71A O © 209, 210, 214, 534, 535, 536, 538, 540 O No. 974, Fig. 7, is for testing the cir- els F- F cuits of pentode tubes. This includes the and 597. H H types GA, LA, PZ, '33, 46 and '47. The No. 944JY, Fig. 13, permits the reading G P G P adapter is of the twin type; one -half goes of plate current for the 2nd plate of an ÌI ÌI on the test plug and the other in the tester '80 rectifier. May be used with the fol- ÌI ÌI socket. May be used with the models lowing Jewell testers: 198, 199, 209, 408, O © o o F+ F- F+ F- F4 198, 199, 408, 409, 577, 578 and 579. 409, 577, 578, 579 and 581. F- I' V No. 965 DW, Fig. 8, is used for circuit No. 965CG, Fig. 14, may be used with FIG.21 F IG.22 FIG. 23 tests on six -prong tubes such as the types Jewell Models 214, 533, 534, 535, 538, 540 57 and 58. It is a twin- adapter, one -half and 597 tube checkers to test the types LOCKING STUD on. 41, 42, PA and PZH tubes. The adapter IN CENTER OF of which is to be placed test plug and ADAPTER the other in the tester socket. May be is to be inserted in the '36 socket, or any used with models 198, 199, 408, 409, 477, five-hole socket wired for a filament po- 578 and 579. By breaking the suppressor - tential of 6.3 volts. grid lead this adapter may also be used No. 954 KPC, Fig. 15, is for testing the o to analyze the types 41, 42, PA and PZH GA, PZ, '33, 46 and '47 type tube in Jewell tube circuits; connect the short lead to 209 and 210 tube checkers. It is to be H H the control -grid stud on the analyzer plug inserted in a 2 or 2.5 volt (filament) four - control -grid pin - hole socket. G P and the long lead to the o No. 965KS, Fig. 16, is for testing the jack in the analyzer. III No. 965DSW, Fig. 9, is for testing the types 57 and 58 tubes in the following O 57 and 58 tubes. It is Jewell tube checkers: Models 209, 210, circuits of types F- III lF+ a twin- adapter having split suppressor- (Continued on page 245) FIG.19 FIG.20

CURRENT 5. P. DT. LOCKING TUD IN S.P.D.T - TOGGLE LIMITING CENTER OF CONTROL- SWITCH1 RESISTOR SWITCH GRID STUD G G3 62 P G G G G G G2 6 G2 o K o i " H® 4. 10.000 OHMS (EACH) o P K OHMS i G

H I H H F+ H UU UU H F. n FIG.10 FIG.13 FIG 14 FIG.15 FIG.16 FIG 17 F IG .18

RADIO -CRAFT for OCTOBER, 1932 217 AFTER CASE 15 VOLT IS REMOVED SECONDARY. (SAME THIS HOW TO II0 VOLT PRIMARY WINDING OFF)

POSITION OF INSULATION WINDINGS v'' PAPER ETC. BEFORE ( DO NOT CHANGE REMOVE) REWIRE THE HI -Q 29 /- 15 VOLT LEADS 110 VOLT LEADS

7AMP 2 AMP FOR THE WINDING NEW TUBES WINOING

INSULATION TAKE OFF PAPER CENTER -z TAP HERE By HUBERT LEE FINISHED FRAZIER TRANSFORMER L CORE 11 TURNS OF 9 TURNS OF N4 14 N4 14 ENAMELED ENAMELED WIRE WIRE

Fig. 3 mum; also, the sensitivity and tone of the post marked C on the filament wind- Constructional details of the new filament the receiver are greatly increased. transformer. Figure ing of the power pack to the bottom of 1 is a complete wiring diagram of the the "C" bias resistor, and connect the wire who owns one of the finished receiver and power supply, with that was taken from terminal P on the Hammarlund Roberts Hi -Q 29 re- all the parts marked for identification. tube socket to the post marked C on the ceivers is familiar Disconnect EVERTONE with their all the reproducer and power - filament winding of the power compact. around good performance. The R.F. supply unit from the receiver chassis and Now remove the wires from the posts coils are designed to be used with the remove both the power -supply unit and marked F on the power compact, and run high -gain type of radio tubes and the R.F. the set chassis from the cabinet. Remove new leads from these posts to the socket circuit is sufficiently filtered and shielded the tubes from the power supply unit and terminals marked F. The filament trans- to permit the use of the new type tubes the set chassis, and begin the rewiring former is now disconnected from the A.C. without adding any parts to it. of the latter unit first. line cord. This transformer is either re- The Hi -Q "Master A.C." model is de- wound according to instruction in Fig. signed to use the 15 -volt type of tube in Rewiring the Receiver 3, or is replaced with a new unit having all but the last A.F. stage. This tube is Remove the wires from the socket one 2.5 volt, 2 ampere winding, and one both difficult to obtain and expensive. terminals marked P, F and F, connecting 2.5 volt, 7 ampere winding. Mount the Now, by making the changes described the wires taken from terminals marked F new or rewound filament transformer on here, the operating cost and expense of to the terminals marked P and G of Fig. the power supply unit and continue with tube replacement are reduced to a mini- 2. Next, remove the wire that runs from the rewiring. Connect the wires taken from the posts TO 110 V. THORDAR5ON POWER f 2MF GO CYCLE A.0 2MF 4MF. 0.1-1 -1 MF I.MF COMPACT R -171 k. SERIES 400 ) on LINE SERIES 200 SERIES 200 SERIE 200 SERES tl marked F the power pack to the 2.5 C F -200 /I volt, 2 ampere winding on the filament --_....------7--- ACME) PAR VOLT transformer. Upon tracing these wires NOR DARSON FILTER FILAMENT CONDENSERS they should be found to connect to the SUPPLY TRANSFORMER fahnestock clips numbered 5 and 6. These ELECTRAD TRU VOLT are the filament supply leads for the last HI. ,5Vi2.5V . Witp 0.29 A.F. tube. Connect the two wires taken Q RESISTOR BANK from the filament secondary of the 15- WOOD volt transformer to the 2.5 volt, 7 ampere BASE BOARD t1d 13 "KB-K' winding of the new filament THICK /2 transformer; at BOTTOM from OF C the center -tap of this winding con- t © BIAS nect a wire to RESISTOR the bottom of the "C" bias Cmilmi. resistor. The center-tap of the 2.5 volt, '80 7 ampere winding connects No. 10. SOCKET to clip FANNESTOCK Reconnect the primary of the filament --Eb Ci7 Ckp ai Bi Fi ei IIi H Fi CLIPS 2 3 4 5 ti ti transformer and the A.C. line cord. 6 7 8 fo u 12 The power supply unit is now ready Fig. 2 for testing. Use a high- resistance type of Pictorial diagram of the revised HI -Q 29 receiver. A new filament transformer must be rewound as shown In Fig. 3. (Continued on page 235)

REPRODUCER AFT 1 AFT 2 AFC ,ISQO 24 19i 7 '27 <' 45

CII

CHASSIS

Fig. 1 Complete schematic circuit of the revised HI -Q 29. The old tubes have been replaced by the types '24 and '27.

218 RADIO -CRAFT for OCTOBER, 1932 pRqpÁFFRipipigÁáßÁIaRRRRRR1Fifäf7FRiAE9F9rlf1[!1 ®A®.: BAeQ,,ERraRfaRRRRRRRRRRRRAIIpRRRF1RRFIQ!`1ARp®p:lQ®aa ®[aARRRRRRRRRRRRRRRRRRRRíitORRRRRRRflálá7F9 BAAGRIDDRRRRRRRRRRRRRRRRAFIRRRRRRLIP',R6".1P5+RR7Ai,761aE1n®MPi!

PROFITS VIA THE SERVICE LAB. By M. C. MANCILL -O- used for checking bypass F. have found, after a thorough but was replaced with a Sylvania Vis equipment is test over a period six and Dieter. and filter condensers. 0 to 150V. one-half years, that a well- Panel No. 2 is a decibel meter which is Panel No. 6 contains an service department is used to test speech amplifiers and audio A.C. voltmeter and an 0 to 5 A. A.C. am- W equipped the to the radio sales department as systems in radio sets. meter. These are used for finding an asset of from a servicing stand- Panel No. 3 is a tube rejuvenator which power consumption or current drain well as profitable is point. These statements are based on was used in the early days for rejuvenat- the set under test. This combination our operations as the radio service de- ing thoriated- filament tubes; it is still also very handy for locating intermittent partment and RCA Victor sales division very useful, but to make it even more power pack trouble. Jewell ana- of a music house which has been estab- valuable, six UY sockets have been wired Panel No. 7 is a Standard lished for 27 years. in for preheating, in conjunction with a lyzing panel. This laboratory, illustrated above, was Weston 565 analyzer (which is kept in Panel No. 8 is a grid -dip instrument or built with the intention of expansion the laboratory). resonance indicator which Is used mostly short - as business increased and as improved Panel No. 4 is a Leeds and Northrup for locating variable condenser equipment was brought out. There are Wheatstone bridge which is used for circuits. ten (10) panels in use, most of them be- checking resistances and for making vari- Panel No. 9 contains an 0 to 10 V. and also a ing either 12 x 12 in. or 12 x 24 in. The ous other measurements. an 0 to 250 V. D.C. voltmeter; connections are shown below. The first Panel No. 5 is a neon glow tube with 3 -0-3 A. D.C. ammeter and an 0 to 100 tanel reading from left to right is blank; a self contained power supply delivering ma. D.C. milliammeter. To these meters 237) It was at one time a tube analyzer, about 10 ma. at about 450 volts D.C. This (Continued on page

0-100 N A "t Y h0-10 V. 3-0-3 V. LOF O- 250V,D C DC D. C. V// 1000 OHMS PER VOLT. D.0

YAXLEY MULTIPLU6 N* 660

I B- 1A+ I PANEL .11/ 16 *múmÑVs i r._._._._._._._._._. 00025YF `. 3" DIA .000075-M.F. WEB il iOKAK i O -f`ALV, i o NOICATOR I INCA. +' A B PANELN*5 PANEL N*9 S:: ELIMINATOR 25- é 1 If I B.I WEN o --, iT111 JACKI .0W5- 1 I B- M.F. FI L. BALLASTA Toor . I L._._._._....J I 2MF6i TUBE PANEL 6 ó25T Rim CH 3 -SIX 1 0-1SVpC. /SOCKETS) NATI LIMA OovAC wAn NEIER I o. j15V

I ® L. ¡AMMETER) .9! BALLAST". ^00YACI _.NEON GLOW -IA* 1 LAMP 0, JACK I I A:- II 0¡¡ L.-:_.-LO01LE1 . L.-._._. L._._._._._._. -._. L_._._.__._._._._._._._.J

RADIO -CRAFT for OCTOBER, 1932 219 HOW TO REACTIVATE OXIDE -COATED FILAMENTS By RAYMOND SHAW

Rejuvenated Tubes Stand Up The author has been regularly rejuvenating A.C. tubes for over a year at this writing, and most of the tubes so treated are in service to -day. A charge of twenty -five cents is made for each tube and a clean profit of many dollars has been made during 1931. This has resulted in convincing customers of his ability as a radiotrician and so has sent him many new customers. The time required to treat most tubes is from ten to thirty Fig. A seconds and the first figure is sufficient for most tubes; how- Front view, showing the location of the controls. ever, it takes longer when treating heater -type tubes. The author wrote to the manufacturer of one of the best known tubes asking if A.C. tubes could be renewed. They replied "that there was no known method of reactivating A.C. tubes as the oxide -coated filaments would not stand high- flashing voltages without burning out." The latter part of their statement is true, but as to the first part, the author had been successfully rejuvenating A.C. tubes for over six months at the date of their letter! The Theory of A.C. Rejuvenation The average vacuum tube has four important constants, elec- tronic emission, plate impedance, amplification factor (mu), and mutual conductance. All of these constants are governed by one major element -the condition of the filament. If the physical structure of the tube elements have not been altered and the filament is intact, but does not emit the necessary number of electrons, then the tube cannot correctly function and is generally spoken of as having come to the end of its life. Now if we could force the filament or cathode to emit the proper number of electrons, then its life would be renewed; this is exactly what we will do. Most Service Men are per - Fig. B fectly familiar with D.C. Rear view showing the location of the component parts. reactivating tubes wherein no plate or grid voltages are applied; but to reactivate A.C. tubes, high grid- and plate -voltages are necessary CAN hear some of you Service Men and normal filament saying that you have voltages are used on no some tubes while others require twice interest in rejuvenating tubes since their cost has dropped their normal filament voltage. to the present low level; also, In A.C. tubes, the abundance that you can make more money of electrons necessary for i selling new tubes -but: their operation is due to an oxide coating on the filament or cathode, depending upon the First, how many of you Service Men, on a hurry -up job, have type of found filament or heater used in the tube. When this oxide coating one or more weak tubes in a radio set and discovered is burned that your stock in away, sufficient electrons are not emitted for satis- that kind of a tube was low? Of course, this factory operation should never happen, but it does! and the tube is useless. Application of high How handy it would be to grid and plate voltages will be prepared to build up those weak overcome this condition in the tubes; majority cases by Second, how many of you have of reconditioning this oxide coating and so taken a job where the cus- renew the tube's life. tomer's finances are low (and many are during this depression) and the job must be done at the lowest possible figure at which Construction of the Rejuvenator you can make a profit or you don't get it? In an emergency, any high- voltage transformer (preferably Third, how many of you would like to cut down your tube one with a 700 -volt secondary) can be hooked -up. and the job replacement costs when reconditioning sets for resale? can be done without switches of any kind. But it will more Fourth, also, how many of you have an unsatisfied customer than repay the cost of parts and time to build a permanent whose ninety -day guarantee has expired? My answer is to hookup if carefully assembled and housed, either in a portable rejuvenate, if the tube is weak, and impress your customer form or in any small box for shop use as shown in Figs. A with the fact that you know a thing or two. and B. An R.C.A. model 16 cabinet will do very well, as an To my knowledge no article on the subject of A.C. rejuvena- A.C. oscillator may also be placed in it and operated from the tion has been in print and while it is known to a small number transformer used for the rejuvenator. of radiotricians, it has been jealously concealed from Service In the portable outfit shown, the laminations of a defective Men at large. R.C.A. model 60 power transformer was used. First heat the

220 RADIO -CRAFT for OCTOBER, 1932 While tube reactivation is not new, nevertheless if is 0 >O a very suc- generally conceded that the process is not CUT ON OOTTEO LINES cessful one with oxide -coated filament tubes. In this

interesting article, the author describes how to build 4 SENO `DRILL /16 DIA HOLE '10 and use a device that really works -the editors made Fig. 3 exhaustive tests -and its cost is about five dollars! Breaking apart the phone jack.

for (turned upside down) over a flame and voltage. This may sound very difficult but it really is not, cased transformer excessive voltages are used on two wooden strips in a pan covered with an old few tubes burn out except where place it only one to blame. But do not -CRAFT for April, 1931, page 492). Unease the and then the operator is the can. (See RADIO burn out the filaments of the first transformer and as soon as the remaining compound begins become discouraged if you few to congeal, remove it; now carefully remove the laminations. tubes. to loosen the tar Place them in gasoline and leave over night Table of Voltages to be Used clean with cloth. If the primary winding coating; then wipe The author has successfully treated the following tubes at is intact, save it. In any case, be sure to count the turns of so as to know the turns -per -volt the voltages as given: the 2.5- and 5 -volt windings Type of Voltage of Voltage flashed on required when rewinding. Tube Filament Grid and Plate voltage winding was burned out in my case, so it The high '12A 5 200 -400 with No. 28 enameled wire and tapped for 200, was rewound '71A 5 200 -400 volts. (See RADIO-CRAFT for Sept. 1931, page 166 325, and 750 '26 1.5 200-400 of Power Transformers. ") Then wind on the on the "Design '30, '31, '32 2.5 200-400 at 1.5, 2.5, 5, and 7.5 volts, as shown filament windings, tapping '45 2.5 400 circuit of Fig. 1. in the schematic '50 7.5 400 -600 Special Switches '27, '24, '35, '51; apply 5 V. approximately one minute and test While high grade push buttons were used in the portable before applying grid and plate voltages; then apply 200.400 outfit, the author prefers special constructed switches (SW 1 volts if necessary. and SW 2 of Fig. 1) as very rapid-acting switches are required. Some '80's will respond to the treatment; especially where A miniature D.P.D.T. knife switch was used because no D.P.S.T. one plate shows full emission and the other, low. switch was in the "junk box." Refer to Fig. 2. The cross -bar was removed. Two fiber rods 1/, x 11/_ inches were slotted and Color the Important Thing drilled for rivets made from No. 18 copper wire. These rods Set your apparatus up in a dark place, or at least shade the made excellent handles when attached to the switch blades; tube from strong light, for you must watch the color changes the miniature switch was then mounted on a piece of bakelite. brought about in the spaces inside the plate and surrounding A phone jack was torn down and two of the springs were cut the grid and filament. Most tubes show a blue -green color in to 1 -inch lengths, as shown in Fig. 3. the above mentioned space when the desired results are obtained. How to Apply High Voltages Better to test the tube frequently than to over -do the process. use the lowest possible voltage on grid and plate Those tubes that develop this blue -green color are the easiest In general, will will give results. The high voltage to the grid and plate treated. Some tubes will not develop this color but show that will show an O.K. must be flashed; never use voltages so high that the filament a bluish color not very pronounced and still turns white and emits a large number of sparks, because it test. Experience, only, will fix in your mind the colors required Do not flash high voltages long enough or so to develop full emission from the tube. will burn out. with rapidly as to turn the plate of the tube red. As a general rule, Heater -type tubes of the 2.5 volt group should be treated 1/., 3 then tested begin using flashing voltages of 11/2 times the tube's normal 5 volts on the filament from to minutes and plate voltage and, by steps, raise it to 2 or 21/, times normal (Continued on page 250)

NO CONNECTIONS MADE AT CAP OF (NOT BROUGHT SCREEN- GRID OUT TO TUBES PANEL)), RHONE OR JACKS HIGH VOLTAGES tl) ARE APPLIED TO (H) (M) SCREEN -GRID AND PLATE 1í00V 600V 400 V S-G)

Fig. 4 Fig. 1 Fig. 2 details of the knife switches. How the five -prong tubes are reactivated. Schematic circuit of the reactivator. Construction

RADIO -CRAFT for OCTOBER, 1932 221 THE SERVICE MAN'S FORUM Where His Findings May Benefit Other Radio Technicians

SERVICE MEN PREFER RADIO -CRAFT him to increase his income, it should be alive. Pulling out the first R.F. tube and realized there Editor, RADIO- CRAFT: that are thousands of ex- sticking the aerial into the plate recep- perimenters who have no commercial in- tacle of the socket produced music, thus I have just purchased my July issue of terest in radio and to whom the thrill of localizing the source of trouble. Finding RADIO -CRAFT and I want to say it's a watching experimental ideas put into it was a different thing. dandy. Just the information and data practice means more than the lure of gold. Everything checked O.K. down to the that most Service Men would like to have. A few general -interest articles, and miscel- volume control (which is a potentiometer I who am one buys his radio magazines laneous kinks serve to keep these folk across the input -and in these models ay, after a glance through to see "What it posted on "doings" of interest to them. with a serial number above 5050 the aerial has for the Service Man." Let's all shake hands, in RADIO- CRAFT, "for connects to the aerial). A few minutes The Editorial, more dope on ohmmeters, the good of the order. " -Editor.) thinking gave me my answer -the slider circuits, latest equipment, two new tubes, was not insulated from the shaft. The how to use a set analyzer, operating notes, shaft, in turn, made contact to the chassis the Service Man's Forum, a simple oscil- "RAH! RAH! CORRESPONDENCE through a small metal plate used to sup- lator, RADIO -CRAFT kinks, information SCHOOL!" port the unit. Therefore, the aerial was bureau and, especially, Mr. Silver's article completely grounded. I questioned the on audio systems -and, just what I have Editor, RADIO -CRAFT: owner as to other Service Men working been waiting for, a tube table. This is to bridge the space between us on it. Here is the rub: It would make me go plenty far out of and to pat Oscar Prescott, of Vinton, Iowa, The owner, fearing to trust his radio to the way to get the July issue if I didn't on the back. The sum total of my radio a correspondence school man in a village purchase it next door. knowledge was gained through a corre- of 1,200 people, had taken it to a high - I spread the good news around and also spondence course, augmented, of course, powered, well advertised service shop in have been asked, "Did you get the July by keeping up to date via the monthly is- Appleton, 21,000 population, 40 miles issue of RADIO -CRAFT ?" sue of RADIO- CRAFT. away. The owners of the shops are gradu- There are three magazines most Service A short time ago a Heritage radio set ates of Wisconsin U. They had replaced Men buy: RADIO -CRAr r, Radio News and (U. S. Radio & Television Corps.' old the original control with an Electrad unit, Radio Callbook. Whichever has the most model 80) was brought in to me to fix; but had overlooked that one point, and data or, we might say, dope for the Ser- the thing was deader than any door nail the set carne home worse than when it vice Man, is taken along to the shop. you ever saw, as far as reception was con- left. Evidently, they had not tested the I feel that the majority of Service Men cerned, although the speaker sounded set after making the repair. buy RADIO -CRAFT, if they One of several things I have not already a sub- THE Official Radio zine and is have done was to cut a scription. So I can in maintained see, Service Mens' Asso- solely for the interests mounting plate out of my light, that if you con- ciation, sponsored by of Service Alen. Mem- heavy fiber and, presto - tinue putting to press a RADIO - CRAFT, invites all bership cards are issued the job was done. magazine such as your Service Men who are not upon passing a written All this is no argument July issue you certainly members of the Organi- examination which is zation to write for an forwarded against the residence will have us all buying by mail. school, application blank. It is Write for yours today. but just the same. your magazine every you can get to know your month. the official service or- The O. R. S. M. A., 98 ganization of this maga- Official lapel button of Park Place, N. Y. radio from a correspond- Remember, radio is our the O. R. S. M. A. ence course if you really bread and butter and we study the material fur- are not interested in ex- nished s CALL YOUR NEIGHBORHOOD you. At least, you periments, etc. We want more issues just Ball learn fundamental principles and like your RADIO DOCTOR July number. WHEN YOU HAVE RADIO TNUVBLE after that, it is up to you. So, therefore, I write a this as matter of information ALL MAKES Or RADIOS REPAIRED. TESTED, INSTALLED AND I say, "Rah! Rah! Correspondence IMPROVED AERIALS to you and for my own lookout; also, I - ERECTED, TUBES TESTED, ETC. School!" L. W. NYGAARD, can safely say, the lookout of the majority Prompt, Reliable, Honest Service Box 36, of men who are in the service business. Gillett, Wis. Nothing is more disgusting than to pur- GILBERT W. CRAMER (And, we might add, three cheers for chase a radio magazine and find that MI KELLWOOD AVE., BELLWOOD PHONE BELLWOOD 4!57.1 "horse sense" -for who in this day and three -quarters of it are devoted to foolish age would expect to repair a radio set and experiments for some office man in his then turn it out of the shop without run- leisure hours. ning an operating test on it! Apparently, Well, I bet there are plenty of us that population hasnt a thing to do with rea- have your tube chart enclosed in cello- soning ability. However, the fact that the phane and hanging over the bench for receiver left the shop without being tested reference. may have been an accident. It so happens AL. MCNEILL, that the Service Men may have thought 2315 E. 75th St., that the set was tested when, in fact, it Chicago, Ill. was not. Accidents will happen, even in the (Thanks for the bouquet. Although we best of families, and no one can be blamed try to present to the Service Man new for making a mistake once in a while; and original material on every phase of Printed on opposite sides of yellow cardboard for the man who never makes a mistake this branch of radio which might enable measuring 31/4 x 51/2 inches. never does anything.- Edito))

222 RADIO-CRAFT f o r OCTOBER, 1 9 3 2 SHORT CUTS IN RADIO SERVICE

MAKING A BI -POLAR SWITCH $10 for Prize Service By G. A. Sherwood in Wrinkles IN Fig. 3 is illustrated the manner Fig. 1 writer made a successful bi- Shake well before testing. which the Previous experience has indicated that polar analyzer switch to meet an imme- many Service Men, during their daily work, excellent Wrinkles, diate need. have run across some very of Prize Award which would be of great interest to their A series -parallel switch; two pieces fellow Service Men. copper; a small piece of /inch bakelite; HOW OLD IS THAT TUBE? As an incentive toward obtaining informa- twenty, y_ -inch, 6 -32 flat -head brass RADIO -CRAFT will pay By Leon J. Fox tion of this type, screws; four, 3/8-in. flat -head brass screws; AT the present time there is no way to 810.00 to the Service Man submitting the complete the list of best all-around Radio Service Wrinkle each and two stop pins tell the age of vacuum tubes. When month. All checks are mailed upon publi- parts. Countersink the flat -head screws the Service Man replaces the tubes in a cation. 1 /32 -in. below the panel to prevent the receiver he wants to be sure that they The judges are the editors of RADIO - contact blades shorting two of the contact will perform a reasonable length of time CRAFT, and their decisions are final. No points. The switch made by the writer in order to satisfy the customer. While unused manuscripts can be returned. and illustrated in the figure had over -all there are old tubes in the set that test Follow these simple rules: Write, or pre- dimensions of 41/4 x 4'/ ins. O.K., the Service Man does not know how ferably type, on one side of the sheet, giving In many cases he a clear description of the best Radio Service long they will last. Wrinkle you know of. Simple sketches in COMPENSATING CAR -RADIO will have to replace free -hand are satisfactory, as long as they may get a recall and BATTERY DISCHARGE these tubes free of charge. explain the idea. You may send in as many as is eligible By L. Z. Tucker Upon turning the doubtful tube upside Wrinkles you please. Everyone for the prize except employees of RADIO - THE writer, specializing ill automotive down and tapping gently, it will be no- and their families. CRAFT radio service, has experienced difficulty ticed that there will collect a deposit coat- The contest closes the 15th of every month, in keeping car batteries correctly charged, ing from the filament. After a careful by which time all the Wrinkles must be to the fact that the cars often make examination of a number of tubes of received for the next month. due long runs, thus making it necessary to of this coating Send all contributions to the Editor, Ser- known age, the quantity the generator (normally adjusted will determine how long the tube has vice Wrinkles, c/o RADIO- CRAFT. 98 Park adjust Place. New York City. compensate for drain due to the radio been in operation. The heater -type tubes to set being operated on short runs) so as will show less coating. See Fig. 1. not to over -charge the battery. I have found that it is a good idea to To make generator adjustment easy show this defect in the old tube to the illustrated in Fig. 2; turn on the radio for the car operator, I now mount on the customer as a reason for replacement. set and fill the condenser with distilled cowl a 6 -ohm rheostat of heavy -duty type water until the hum stops. Then, add and run two wires to the generator, as to raise level CURING RECEIVER HUM enough water the solution shown in Fig. 4. This resistor is con- By Randolph Mufschelknaus in the condenser about t/z -in. or more. nected into the circuit by breaking the NO doubt many Service Men have found Seal the hole in the condenser top with field coil lead to the adjusting brush, sets using electrolytic condensers that wax and the set is ready for many more completing the circuit through the vari- will operate all right for half an hour or months of service. able resistor; then, advance the third, more, then develop an abnormal hum; Be careful not to touch the condenser adjusting brush on the charger to its and after trying everything the manufac- connections or the tenter container (if it full limit. After this, the rheostat will recommends hum, have is metal), while filling, or you may re- i turer to cure this afford a charging range of 2 to 20 am- a replaced the electrolytic condenser and rire shock. p .res. thus cured the trouble. 1n the event that a replacement unit CONTACT COUNTERSUNK CONNECTIONS is not available, the Service Man may be SEMI -GRCLE .a FLAT -HEAD TO CONDENSER MOUNT ,7 SCREWS interested in the simple procedure fol- `" lowed by the writer in eliminating this ;u(1ltYmeel,Pre' hum and giving the customer service un- ,X STOPS w til a new condenser of longer life can be i11.I connected into the set. Ir¡ GAS Drill a small hole in the top of the i VENT condenser (through the hard rubber), as ti.mse

SOLDER HOLE TO SINK DRILLED HERE '/32- BE BELOW

Fig. 3, above. switch for that analyzer or tube A home-made ELECTROLYTIC tester is described. CONDENSER

Fig. 4 Fig. 2, right. A very neat device for regulating the charging Filling the electrolytic condenser with water, rate of the car battery. similar to a storage battery. may reduce hum.

223 RADIO-CRAFT f o r OCTOBER, 1 9 3 2 THE ANALYSIS OF RADIO RECEIVER SYMPTOMS OPERATING NOTES

By BERTRAM M. FREED

THE servicing of radio receivers is In the first set where this condition was ordinary candle, rubbed into the cord will becoming more complex with each encountered, the tone control was thor- also help to eliminate this fault. succeeding day. Manufacturers are oughly checked. Each condenser was releasing new models so quickly that tested separately and each proved satis- Philco 90 the Service Man has all he can do to keep factory! A new tone control was then in- The Philco 90 receiver, in the pentode - abreast of the different tube designs, tube stalled and when this did not help, the output models (See the circuit pg. coupling devices, and automatic on 160 volume original unit was connected into another of the September, 1932, RAOIO- control Caer-r) has systems. Each problem has its chassis and it performed in correct man- furnished grounds for much own solution distress to and the only saving feature ner, creating a puzzle of "how come ?" many Service Men. The is the fact chief complaints that the same faults are found Upon a happy thought, the Philco '37 with this model include not only fading in each model, the latest model receivers tube (this receiver employs automobile - or intermittent reception, as previously providing as much food for thought as type, 6.3 -volt tubes, discounting the '80 described, their predecessors. but also noisy reception. Both rectifier ) in the first A.F. stage was re- of these effects are caused by the A.F. placed and the tone control worked Philco 91 splen- coupling condensers. didly. Despite the fact that the tube had This receiver utilizes three of these In a number of the new Philco 91 twin - been checked previously and found to be speaker bakelite encased units: one, coupling the receivers, the complaint of "no normal in all respects, it would not func- diode detector to the detector -amplifier control of tone" has been met. The same tion in this stage; in the oscillator stage, tube; the four second, coupling the plate of -point switch as used in previous it worked perfectly. To satisfy curiosity, the detector -amplifier tube Philco models to the grid of is employed here, as shown the tube in question was placed in a num- the first A.F. tube; and the last, coupling in Fig. 1. With the switch in the "bril- ber of receivers of the same model and liant" the grid of the pentode to the plate of the position, there are no condensers in the same result was obtained, "no control first A.F. tube. the plate circuit of the first audio ampli- of tone." All in all, six of these tubes Their value is given as .01 -mf., but .1 -mt. fier tube. As the switch is placed in the have been found. When this condition is tubular condensers next position, have been used for re- a condenser is added to the encountered, all that is necessary is to placement with much success when the circuit. The third and fourth positions switch the sockets of the oscillator and former were not hand, each add at the value not a condenser, so that in the "bass" first A.F. tube. being critical. In several cases, or "deep" position, however, there are three paral- After the Philco 91 has been in opera- where the .1 -mf. condensers were leled used, it condensers connected from the plate tion for a short time, the dial may be was found necessary to replace of this the first stage to chassis. However, in these found to slip. This receiver makes use A.F. grid -leak resistor and sometimes, the several receivers, as soon as the tone con- of a -cord dial whose tension, or slack, is pentode grid -leak resistor, with 100,000 - trol was switched from "brilliant" to the taken up by a coil spring. It is only ohm units to eliminate the tendency to next step, the tone became so muffled and necessary to move this spring up one or motor -boat. deep and the volume dropped so much that two steps in tile series of notches cut out In this same model, second it was the coupling impossible to understand any voice in the dial to remove any slipping condi- condenser has been found broadcast clearly. mainly re- tion. Rosin, or warm tallow from an sponsible for noisy reception, although, on

LI R.F.1 GANGED TUNING CONDENSERS DIODE DIT A. F.S 111 A AVC A F 1 ;11a AMI AI YE All PUSH PULL CI,' 44 LI C2 La IST1 1 O L 44 -37-S '17 '37 42'5 TWIN REPRODUCERS 0E11 12 v Tr.? & OSL.

PICKUP COIL IN 1.ME6.

10,000 OHMS OLUME gaol-CONTROL 200 l5ME1 OHMS TONE 2 A CONTROL .1S-MF / (001121, STOLE .OSMF .066 REPRODUCER; THIN MITER 100 .01 -MF CODE III, LIGHT MME 15,000 REPRODUCERS CHASSIS PILOT 116447 OHMS 1 r 260 KC,

CABLE FROM 5 YE LOW FROM SLDERMHII CWREEN trf FIELD COIL SLUE NITS R4 RS SLACK CABLE FROM SET YELLOW OILV WHITE PRIMARY FROM FIELD COIL OFF ON FIELD SWITCH COIL YELLOW FROM SECONDARY , FROM FIELD COIL i.` WHITE 110V. VOICE COIL OISMF A. C. RI 205 OHMS 1I, BREEN _6 RS 100 OHMS PRIMARYMARY .111-1.4F At 2700 OHMS WHIT, CODE RS SS OHM& FROM iMAROON FROM 1. 121 / WKE COIL RS 30S OHMS SECONDARY EMT VOICE COIL IMF PIA FRE OHMS At MAROON FROM BLACK SLACKS BLUE WHITt RIA 15000 OHMS VOICE SLACK FROM COIL WHILE r... /IA OS OHMS FIELD COIL ¡ MAROON FROM VOICE CO. HITt IRON VOICE COIL Ly R1A

Fig. 1 Schematic circuit of the Philco 91 receiver. The volume control has a value of 350,000 ohms; the tone control has one .05 -mf. and two .01 -mf. condensers; the field coils, a resistance of 3,200 ohms; and the filter choke, a value of 285 ohms.

224 RADIO-CRAFT f o r OCTOBER, 1 9 3 2 two occasions, the third was the offending be disassembled), and to melt out the by- full sensitivity but without any control member. This may be eliminated by ap- pass condenser. The transformer and of volume. The schematic showed the plying the soldering iron to the lug of shield are then re-assembled; a bypass function of the A.V.C. tube to be that of the condenser. Usually, it will be neces- condenser of sufficient voltage rating is varying the control -grid bias of the R.F., sary to replace the unit. Any method then connected externally across the cor- first detector and I.F. tubes. may be pursued in determining the noisy rect terminals. As a similar experience with a Radiola condenser, although the writer has found No doubt, it is much simpler to replace 67 (described in the July, 1932 issue of that removing each one, in turn, from the the I.F. transformer, but this is a some- RAmo-Ca-trr, page 33, where an inopera- circuit, and substituting a new condenser what expensive proposition if a genuine tive receiver would perform without the is the most certain and quickest pro- replacement is desired, although an or- A.V.C. '27 tube) inspired further tests, cedure. dinary high -gain I.F. transformer, peaked the control -grid circuit of the A.V.C. '24 at 175 kc. may be employed, together with was checked. Zenith 91, 92 an external bypass condenser. The wire connecting to the control -grid The next receiver to be considered is If the entire shield is carefully insu- of this tube runs through a hole in the the Zenith 91. 92 superheterodyne; in lated from the chassis and the trans- chassis and is soldered to a small ter- chasses below Nos. 373, 334 and 301, 394, former mounted on the chassis by means minal on a square, insulated strip directly respectively, we experienced no end of of insulated bushings or an insulated alongside the socket. A green wire, which trouble. The symptoms in this case, are: strap, this will disconnect the shorted should have been soldered to this lug (a) marked fading; (b) no dip- action on condenser from the chassis. The second- was moving freely about in the joint the tuning meter, and; (c) little or no re- ary return of the first I.F. transformer (Continued on page 251) sponse on the local side of the local -dis- does not connect to the shield can but tance switch. A glance at the schematic connects to the A.V.C. circuit externally; SEPARATE WINDING the trimmer condensers one or FOR PILOT LIGHTS ONLY detail. Fig. 2, will disclose two resistors, have side '51'S AND series each connected to the shield can and the Rl, R2, which are connected in .- - 275 N1 across the D.C. voltage output as bleeder other side connected to the plate and grid of the primary and secondary windings, resistors, the values being respectively, mismpwl. R1 2,800 ohms and 3,600 ohms. These carbon respectively. The grounded sides of each units, not capable of withstanding the condenser may be disconnected, and re- load placed upon them, are the source of connected to the "B +" side of the pri- R2 the entire complaint. mary and the grid return of the second- These resistors break clown under load ary, so that each trimmer is connected A.V C. and the electrical values vary, resulting across and tunes each respective coil in "24 in the above -mentioned complaint. The conventional manner as depicted in Fig. 3. :I 1NA111g11t71111 only remedy is replacement with resistors Servicing this model, recently, two in- :j whose 10 watts or more. The stances were encountered where no sig- rating is (-) defective units are easily located, as they nals could be obtained unless the A.V.C. CHASSIS type '24 tube was withdrawn. When Fig. 2 are the two largest resistors mounted upon this Schematic circuit of the Zenith 91, 92 receiver, the resistor strip. The other means of was done, the receiver performed with used it chasses Nos. 373, 334, and .301, 394. identification will be the discolored or burnt portions to be found on the resistors as well as a collection of dust under the OET 1 I. F. T.1 I. F. 1 I.F.T.2 DET. 2 units, such as is found under beds and '51 S1 '51 dressers in a bedroom, when the floors r have been neglected for a few days. (! ) 0 It must be mentioned that the last lot of 0 this model that was released incorporated T1 wire-wound resistors of sufficient carrying capacity in place of the troublesome car- V1 V2 bon units. T- ---c- _J J C1 C2 Majestic 61 -A- -c iñrir" 250 OHMS On service calls marked "Majestic 61," .01-M.F a common complaint is "no reception," or 1_ "dead." A check will often reveal no TO A.V.C. PLATE plate voltage on the I.F. tube or first - detector and very low plate voltage, if B C any, on the other tubes. DET.1 1.F.T.1 I.FT.2 DET. 2 The use of the ohmmeter will show an '51 '51 '51 almost full short-circuit between the I.F. plate or first-detector plate -as the case i may be-and chassis. Unsoldering wires will finally localize the trouble to the primary of either one of the two I.F. transformers. A low -range ohmmeter, V1 V2 capable of measuring the D.C. resistance -r of the I.F. primary, will show the "short" (C1 SHORTED) BREAK C2 to chassis to be at the "B-f-" end of the BREAK INSULATE CAN BREAK FROM CHASSIS (C2 SHORTED) primary. The circuit is Fig. 3. This short is caused by the breakdown of the bypass condenser connected from INSULATE CAN FROM the "B-f-" side of the primary to the shield CHASSIS .4M.F t2 OHMS _. C4 can of the transformer. The condenser C3r- .1-Mf j is sealed in pitch within the riveted shield can of the I.F. transformer, and before TO AV. G. PLATE CHASSIS/ the defective unit may be removed from the circuit, it will be necessary to drill Fig. 3 out the rivets (so that the shield can may The Majestic 61. A shorted I.F. transformer primary causes trouble here.

RADIO -CRAFT for OCTOBER, 1932 225 75 Radio Service Data Sheet

GALVIN MOTOROLA MODEL 61 AUTOMOTIVE RECEIVER

(Incorporating a type 85 duodiode- triode tube as a combination second -detector, automatic volume control and first A.F. amplifier.)

This automotive receiver incorporates the should consume not more than 2.25 A.; the Chrysler: Right side of ear under cowl; following tube combination: ' l'une CI, type voltage drop across the 5,000 -ohm load Pontiac: Left side of motor compartment '30 screen -grid as an 1110. amplifier ; V2, should be between 160 and 170 volts, pro- or right side of car under cowl; type '39 variable-mu It. F. pentode as a eom- vided the battery voltage is exactly 0.3. I)iSotn: Ditto; binatIon oscillator and first -detector; \::, The following precautions should be ob- Plymouth : Left motor con pa rtment or type ':16 screen -grid I.F. amplifier; V4. type served : 1ío not remove the receiver section right side of car, under cowl; 85 duodiode- triode as a combination serond- of the set from the power pack, with the Cadillac : Ditto ; detector, automatic volume control and A, I', set turned on : the BR tube, V6, should Lincoln: t'enter of motor compartment or amplifier ; Cú, type 41 high -mu special autonot be removed fr its socket unless the right side of car, under cowl ; motive pentode second A.F. set is turned off. Since the 'A" supply is Packard: Ditto; (Light Eight, left side Iligh voltages are obtained from the polarized, it is necessary to make certain of motor compartment.) ; storage battery of the car by means of that the red wire connects to the positive Oakland, \'R: Below cowl on right side or tr an interrupter system and step -up trans- terminal and the white wire to the nega- right side of car, under cowl; former, in the manner described in the tive terminal of the battery : do not operate Studebaker: Left motor compartment or Sept. 1932 issue of R.tnto- Ctt.tvr, pg. 152. the set with the ".L" leads reversed. other- right side of car, under cowl; 152. wise the Elkonode will be do magetI bey I Oldsmobile: Right motor compartment or Following are the values of the com- repair. For this reason, the polarity of right side of car, under cowl; ponents of this modern radio set : Con- the cur battery should be double -cheek[') by Auburn: Right motor compartment or right densers Cl, C2, C3, tuning condenser gang; means of a voltmeter before the set is put side of car, under cowl. C4. eft, coupling condensers; ('5, Cli, C7, into operation. (Reversed connection to the (The "bulkhead" is the partition in the 1.F. trimmers ; t'n' I'13, (17 (buffer). .95- "A" battery will he indicated by low "It" car which separates the motor compartment mf.; CIO, 0.5- in t 'I I (1.25 -mf. ; Cl2. :MO voltage, spasmodic operation of the Elkonode from the driver's compartment.)

mmf.; CH, .0112 -mf. ; C15, .01 -mf. ; CIO. I. and err° tic flashing of VII.) Car manufactures have furnished the mf.; C18, C19, 8 mf.; C20, C21, 0.1 -mf. An ideal place for the reproducer is face - following data regarding their provisions, Resistor RI, volume control potentio- out, with the reproducer flush with the in IÚ32 models, concerning automotive radio instrument board, but such it position is meter, 0.i -meg. ; R2, Ito, Ií7. RS, 0.1 -meg. ; antennas: because of space lend lt: ;, 75.(100 ohms ; 115, 5,0(10 ohms ; I16, undesirable the factor. Chrysler: Roof antenna with -in and Therefore. first is 500 oh nos ; I19, 0.2 -meg. ; RIO, 50.000 ohms the alternative to leave provisions for "B" battery box; 1111. 11.7 -meg. it at the same level but to move it back (lodge: Ditto: It is not recommended that any repairs to the bulk -head, for good operation, l teSoto : (Otto : be made to a defective Elkonode (interrup- If there is not room to [noun t the re- Plymouth : Ditto; ter.[ All such units should be returned producer In that position, n sec 1 method Itco: Equipped with roof antenna and to the factory (Galvin Mfg. Corp.. Chicago, is to face the reproducer toward the floor- lead -in Ill.) or to the manufacturers of the El- boards, with the front -edge of the repro- Itockne: Ditto; k le (see label on unit). ducer against the instrument board and Studebaker: Ditto; the side against the side of the car, a posi- Buick: Ali models, $6.00 additional for An open buffer condenser, C17, will he tion available in most caws. antenna installation: indicated by failure of rectifier tulle the It generally necessitates two holes bring Franklin: hoof antenna but no lead -in ; vo to slay ionized. A purple glow In the drilled t h roa gh the instrument board to Ford : Ditto; tube is an indication of correct operation hold the reproducer and an additional Cunningham: All models, additional charge of this type of rectifier; n shorted C17 con- bracket run from the adjacent side of the for antenna installation. denser will be indicated by spasmodic reproducer to the side of the ear. This Check the proposed antenna for ground operation of the Elkonode, as well as failure location is rather new to some by means of 0.200 V. meter, of 1,000 of C6 glow. installation a to As a general rule, when men, but Its acoustic properties are superior ohms -per -volt type, and a 200 V. battery. spasmodic operation of the Elkonode is because of the additional baffle effect which Even on damp days the leakage should not observed It is an indication that the El- results from the close proximity to the in- exceed 2 V. Lack of peak resonance on the konode Is not feeding into the correct load; strument boa rtl. antenna trimmer indicates n leaky antenna. it either is underloatled or overloaded; Following is a listing of the preferred or one having too groat capacity; in gen- two undesirable conditions. location for automotive radio receivers to eral, an antenna screen area of about 9 After the Elkonode has been removed, it be used in the 1931 car models specified: sq. ft. will be satisfactory, may be tested by applying O volts to the Ford, Model A : Motor compartment on The dynamic reproducer may be checked large terminals, with positive polarity to the left side; for a rubbing voice coil by applying 50 C., the brown wire; It is also necessary to Chevrolet: Motor compartment on the left 60 cycles, to the two outside or "B" term- connect a :.900 -ohm resistor across the red side or below the cowl on the right in- inals of the output transformer; instead of (or green) and black wires, together with side; (For 1932 model, remove carburetor a clear. steady hum, a rubbing noise will an 8 mf. electrolytic condenser and a volt- and air cleaner, temporarily.) ; be heard, if the voice coil is not floating meter. With this setup, the Elkonode Buick: Below the cowl on the right inside; entirely clear.

(GANGED TUNING CONDENSERS DUODIOMTRIODE PO W ER A P T ANT R.i.1 DF Tt Av(.tA.EI tiYNAMIC 4E14 01C. LS C4 LL1 WTOTRANSF. PENTODE 66 C° . '35 LET./ LET CIS (HI, 41 T^- e Q

R11 R6 AIO 'IETERRUUPOTÉ ) SPEAKER __ FIELD TYPE IR 6AMOUS CIt)Ifli CHA3313; rr R YP i CABLE DATTERE 1r00 VOLUME M3 CONTROL O 1 a CONTROL PLUG CARLE LET

CONTROL PANEL T

226 RADIO -CRAFT for OCTOBER, 1932 Radio Service Data Sheet 76

WELLS -GARDNER SERIES 062 AUTOMOTIVE SUPERHETERODYNE

(Incorporating types '36, '37, '38 and '39 tubes; also A.V.C.)

Numerous mail -order louses sponsor this unit are open so that readings are not made ing connections of the installation have chassis under their particular trade name; under load conditions. been completed -this is extietnely important. consequently, it is better remembered by '1'n read the voltages at the sockets the To adjust the antenna trimmer, tune in its OirenIt connections than by the name chassis box, in most cases. will have to a weak signal at the high frequency end of the chassis manufacturer. be removed from its mounting. In some of the dial with the manual volume control On one end of In the No. (N;: Series automotive receiver instances, the cables, which may be attached about three- quarters on, following electrical values are used: to the dash of at other points. will have the chassis box is a small metal plate. 11e- the plate. Resistor RI, o.5 -meg.; It2, 7,000 ohms; to be removed, The voltages can be read the two screws holding this sockets with a long plug or with a Directly under the hole In the chassis box I iEt. Itl3. 0.i -nug. ; Iti, 1312, at the 1t3, toot.: screw. (1.l -tort.: 116, It7. Rs. 2 mets.: ItO. 1,000 pair of lung. insulated test prods. is the antenna trimmer condenser ohms: 1110. 2n (rom ohms: It I I. 15,000 ohms; All tubes must be inserted and all units Adjust this up or down until maximum 111.1, 310 ohms; It16, 1,300 ohms. connected. A signal will effect the control output is obtained. voltages on \'I, \-3 and \:S. If signs is are Noise, in some instances. may be due to Condensers Cl, C2, C:t, equipped with reel.' veil, ground the antenna and remove weak pickup caused by a poor antenna. The trimmers, constitute the tuning gang : C4 \_4 to take the other readings. action of the automatic volume control, due b. the aseiIlator padding condenser; C:1, CO, 'l'he diode current establishes a drop to the law pickup, causes the set to operate C7. LF. trimmers; C8. .00O -tot.: CO. .02- across at resistor network: this potential nt maximum sensitivity. thereby increasing C10, Cl d, 4 C11, -mf.: ('12, ntL: ntf.: .(I(I is used as an additional bias potential on noisy reception. due both to external pickup ('IS, 05-ml.; C13, C13, C16, 0.1 -mf.; C17, Cl. Y:: and V5, giving A.V.C. action. and internal conditions. .001 -tit, The full control potential is applied to Noisy operation is also caused in some Operating potentials nee as follows: Fila- Cl, two- thirda to C:3, and one -third to V5. instances by lause parts 1n the car body ment potential, all tubes, 6 volts. Plate As the signal inurea ses In intensity, the or frame. 'fies,' lause parts rubbing to- potential, VI, \'3. 177 volts: \2. 17:: volts; applied control potential is Increased. thus gether affect the gr ling and cause V4. zero: V5, is volts: \'6. 150 volts. giving uniform output as set by the manual nuises, clue ta the rubbing of wiping action. Screen -grid potential, VI, C3, 80 volts; volume control. The manual volume con- Tightening up the (none anal body at all V2. 70 volts: C-{, zero: \5, 77 volts: \'6, trol varies the diode .\.l'. potential applied points and, in some cases, the use of copper 115 volts. Control -grid potential, \'I, C:3, to V5. Jumpers, will eliminate noise of this nature. volts: V2. 7 (depending upon dint set- Tile tone control is mounted on the dy- Loose limps or wiring are 11 ISO at COMn»it tings : V4. zero: CG, 6 volts; C6 15.5 namic reproducer, which deli l'es its field canuse of noisy operation. volts. flatte current. normal, \'I. \'3. :l.6 supply from the storage battery in the car. Compensate for the increased battery drain ma.: V2. 0.9 -ma. (depending upon dial Aerials are preferred In the following occasioned by the radin set, by Increasing setting): V4. zero; \5. 1.2 ma.: \'O, 10 order: hoof antenna: tape antenna uu roof the charging rate of the car generator. ma. All bias voltages must be read from (this is not very effective where a grounded After a week of car operation. check the cathode to ground. chicken -wire matait remains inside the roof) : condition of the battery and re- adjust the Do not check the "A" and "B" potentials plate antenna (strung underneath the run- changing rate accord) ugly. nt the multi-paint socket on the cable head, ning Is,ardl : under -en r n nt eta na to wire Two fuses are used on this receiver. The as the pilot light may be burned out when fastened from the right side of the rear 10 A. "A" fuse is located on the multi- the switch is turned off. I'l'tis is due to axle to the lowest point under the motor, point socket; the 1 /N -A. "I3" fuse, inside the high inductance of the speaker field, then back to the left rear axle, forming a the control unit. The pilot lamp is a which will Increase the voltage at the break V. At the vertex of the V is a spring standard 6 volt No, 40 nuit, of the circuit.) Also. when the cable head to take up the slack, The Iced -in is brought Poor operation may be due to moisture, and multi -point socket are taken off, the up f the vertex end.), from car -washings or storms, seeping Into connections between the chassis and power Do not turn the set on until all the wir- undesired places.

LF.T.2 DIODE DET 2 A.F.1 PENTODE A.F2 RF.1 L DET.l4o5C. IfT t CS ._j Itt'39 AND A.V.C. '39 C9 '3B '39 '36 f_

I o á I ó ó a $ C5

-IÌ C12

R2 Rs I CIO

R14 RS' CHASSIS Gus. 5HiELD

A' POWER ELIMINATOR I SWITCH I OR Y8 -AMP BATTER./ FUSE

=1II11 _J Ti e RI

FIELD COI MANUAL VOLUME CONTROL

RADIO -CRAFT for OCTOBER, 1932 227 RADIO -CRAFT KINKS Practical Hints From Experimenters' Private Laboratories

RAW Prize Award $5 for a Practical SIDE AND SELF -VULCANIZED RUBBER IN Radio Kink iW

RADIO WORK As an incentive toward obtaining radio TEST PRODS METALS PLIER HANDLES short -cuts, "Radio - SOLDER By G. L. Garvin hints and experimental Craft" will pay $5.00 for the best one sub- WEN IN Fig. 1 are illustrated several ways in mitted each month. Checks will be mailed which the experimenter may use self- upon publication of the article. LARGE NEEDLE - vulcanizing, tire- repair rubber in his radio The judges are the editors of "Radio 1 'Seer RAW Craft" and their decisions are final. No un- ^", EDGES SEAMS ON work. AFTER COVERING GROMMETS INSIDE used manuscripts are returned. A twenty -five cent can contains sufficient D- -E- -F- Follow these simple rules: Write, or about 84 sq. ins. of material to make preferably type, on one side of the sheet. Fig. 1 rubber. giving a clear description of the best radio Here's real efficient insulation. Out of this I am able to make rubber "kink" you know of. Simple sketches In "spaghetti." rubber grommets, test -prod free -hand are satisfactory, as long as they and pliers insulation, and insulating plates explain the idea. You can send in as many of any size. kinks as you wish. Everyone is eligible for Glue is not used -the secret lies in the prize except employees of "Radio - with Craft" and their families. tightly pinching the surfaces together This contest closes on the 15th of every pliers, then cutting along the seam with month, by which time all the Kinks must be scissors to make a neat -appearing job. received for the next month. This rubber juncture cannot be separated Send all contributions to Editor, Kinks -the rubber will tear elsewhere first. Department, c -o "Radio- Craft," 98 Park Place, New York City. REMOTE -RADIO OPERATION By W. B. Matthews N Fig. 2 are shown the circuits of a sys- For the connection between the two lo- tern which I have set up between my cations, I use a small cable, but on a long laboratory and my regular household set run it may be necessary to use a separate which is located in another part of the pair for the output of the set in order to building. The circuit was first designed prevent capacity feedback into the input in order that I might snake use of the pair. Also, it is necessary to keep the rather powerful A.F. amplifier with which capacity between the two sides of the out- the set is equipped without either moving put pair to as low a figure as possible to the set to the lab., or impairing its value prevent distortion. Fig. 2 for ordinary use. Now for a few notes about the appa- You can make extra money with this idea. By plugging the output of a short -wave ratus. All three of the relays must be microphone wound suit the voltage of the battery tuner, phonograph pickup, to REMOVE SUPPORTS AND INNER transformer, or any other A.F. source into supply. If they are properly designed ELEMENTS jack A, it may be fed into the detector or their current consumption can be kept SHIELD GROUNDED A.F. stage of the set. The jack contacts quite low. For the power- control relay, I THROUGH NON- MAGNETIC CORE, close the circuit from the battery, operat- rewound an old automobile generator re- -A- MAY BE con- GROUNDED ing the relay (Rel. 1) which opens the lay which I found had large enough DIRECTLY last R.F. secondary winding and applies tacts to carry the set load. These contacts S the input to the grid of the detector. In are connected directly across the regular this way, short -wave programs may be set switch. For Rel. 1 and Rel. 2 any picked up in the lab. and be heard from relays with suitable contact arrangements the regular set speaker. If a plug is in- will do. The contacts of Rel. 1, which CUT HERE v serted into jack B, the relay (Rel. 2) is are normally closed, are cut into the de- SHIELD NOTCHED output of the set tector control -grid circuit. Care must be TO ADMIT operated and the SOLDERING LUGS switched back to the lab. to a speaker taken to make sure that the input is cut ON EITHER connected to the plug in jack B. If the into the grounded end of the R.F. second- SIDE. plug is removed from jack A the armature ary circuit so that the receiver's tuned of relay (Rel. 1) falls back and the regu- circuits will not be thrown out of balance. Fig. 3 lar broadcast program may be heard from Slightly different arrangements may be Shielding R.F. coils -an Important thing. the speaker in the lab. The set can be necessary for different sets at this point, turned on or off by operating the switch or it may be wired so as to apply the in- SHIELDING FOR SMALL COILS S which controls the power- control relay. put to the first A.F. stage. In any case, By Wm. R. Thames The jacks and the control switch are it is connected the same as a phonograph THE writer has successfully used screen- mounted in a panel along with other jacks pickup would be. Any type jacks with an grids from old '22 and '32 tubes as and equipment located in the lab. The extra pair of contacts may be used as shield cans for small R.F. choke coils. relays (Rel. 1 and Rel. 2) are mounted shown in the diagram. Perhaps this idea will interest some of in a small box located immediately back Many interesting uses of this or similar the readers of RADIO -CRAFT. of the chassis in the radio cabinet, as is arrangements will suggest themselves to The details of this arrangement are il- the power control relay. the experimenter. lustrated in Fig. 3, at A and B.

228 RADIO -CRAFT for OCTOBER, 1932 THE RADIO CRAFTSMAN'S PAGE The Bulletin Board for Our Experimental Readers "THE RADIO 'TREASURE' FINDER" IMPORTANT NOTICE is, of course, a change in volume. but it is Editor. RADIO -CRAFT: very slight and the ear is not very sensi- In the interest of those readers who do not in the June issue of RADIO- CRAFT, on pg. tive to slight changes in volume.) The like to mutilate this magazine, we have 716, you give the construction details con- asked metal sheet could be detected at a distance our advertisers not to place coupons in their cerning a "treasure" finder. I had one of four feet from the receiver loop; a built just the way the article specified, advertisements. typewriter was detected at a distance of Instead of the usual you will using the parts that were supposed to be coupons, find six feet. a number used, but the resulting machine will only of convenient post cards inserted be- Some who have used similar apparatus tween the last page and the back cover of work a little bit. It seems to me it is state that it works better outdoors during that this magazine. too short -wave. In other words, it will rainy weather. The reason for this is not This new service will save you time work. work only when is on metal and definitely known. Perhaps the buried obit setting - need No to cut coupons, nor is it necessary to It had to be right on the metal. jects, having better electrical contact with setting hunt for and address envelopes. Moreover, What could be the matter with it? I moist earth, produce a greater effect. In the space for your name on a coupon is usually sure would like to get it working as I have one case that came to our notice a couple so small that the advertiser is often not able spent quite a lot of money on it. If there of swords were unearthed; they were to make out your writing and then you wonder is anything you can give me light on I about four feet below the surface. why you do not get the literature sent for. sure would appreciate it. One writer states that he could get a Then, last but not least-the postage for a R. L. RIDDLE, good balance of zero sound indoors, but postal card is only lc whereas a letter now The Kiva, could get no zero balance outdoors. Per- costs 3c. Imps body capacity and Santa Rosa. N. M. Read the advertisements and then to between his head turn the the earphones unbalanced (Below is the comment of the author, page containing the special postal cards. the apparatus De- when were Mr. Clyde J. Fitch. Note that a slight tach, fill out and mail the card of the adver- his feet in contact with the ground. Wearing change in the wiring is necessary to ob- tiser whose literature or offers you want to have rubbers should prevent tain satisfactory results from this practi- sent fo you. this if this Is the cause of the trouble. cal metal locator; this circuit modification Mail your card today) Show the advertisers Check all potentials with an accurate, is illustrated in these columns.-Technical that you appreciate their cooperation and high -resistance voltmeter. Make certain Editor.) thoughtfulness. that grid -leak resistors R1 in Fig. 1 and R in Fig. 4 have the correct values. Try several tubes in their respective positions; CONCERNING WHICH MR. FITCH this admonition holds true particularly for REPLIES to pass through the headset. Under this V1 in Fig. 1 -and to nearly the same de- Editor. IIADlo- (:RAFT: - condition the receiver would not work as gree, V3 in the same figure. Try revers- The treasure finder described in the well as it should. The corrected diagram ing the connections to the primary of the June 1932 issue of R.uno -CRAFT has published herewith must be followed in R.F. transformer, R.F.T., in Fig. 1. Test aroused so much interest that the editors building the instrument. all of the condensers for short -circuit; have literally been swamped with in- The apparatus as built by the writer also, if possible, check them for their quiries to answer -and these in a group - was tested by placing a piece of metal rated capacities -or, at least, for open - this means has been taken so that others, about one foot square near the receiver circuit. Note that unless resistor R in who may be interested, will not be con- loop, and while a perfect balance of zero Fig. 4 has the correct value it will not fronted with the same difficulties. sound could not be obtained by adjusting be possible to obtain a satisfactory audio It is unfortunate that almost all who the angle of the loops, the presence of the modulation note from the transmitter; in have built the apparatus are disappointed metal could be detected by means of a fact, it may not be possible to obtain any with the results (the letter of Mr. R. L. change in the quality of the sound. (There audible modulation of this section of the Riddle is a good example). In metal -locator. many instances we believe this CLYDE J. FITCII. is due to the fact that an error was made in reproducing the diagram of the receiver (Fig. 1 MORE TUBES? (!) on page 749) and therefore we Editor. RADIO-CRAFT: are publishing the corrected As one who has been inter- diagram. herewith. We were ested in radio for many years not aware of this error until (I was one of the subscribers quite recently and were at a to the splendid magazine "Ama- loss to know why so many teur Work" at the time it could not get the apparatus to passed and recall that your own work. "Modern Electrics" was sent to In the original diagram, the subscribers to the first -named plate supply for tubes V1 and publication by way of complet- V2 was taken from the plate ing the periods for which they terminal of V3, instead of the had paid their respective sub- plus "B" lead; this caused the scriptions to "Amateur Work"), plate current of all three tubes "Treasure" Finder circuit correction. (continued on page 238)

RADIO-CRAFT f o r OCTOBER, 1 9 3 2 229 A PORTABLE

n N!3 .á LABORATORY N! N74 ill c2 17 0 -9 +A-f! 2500. N! 5 CYCLES

+45 i. 19 re- N!6 standards can be tions down to 2,500 kc.; but the tube .ÿ! inexpensively, fused to oscillate above 5,000 kc. A final -A built r 20 value of 2 megohms was selected as giving N!7 ,+SOOY ruggedly, and quite by almost the best output for the different fre- + - r. 2. accurately N8 N0001 anyone. The ulti- quencies. N. The was encountered in SV,. 22 mate test of an in- same trouble N!9 .A.9- strument is not al- the selection of an R.F. choke. While a 15 V ,. 23 ways cost, but its choke may seem to be excellent at one N°I0 . AK1 practical workability. frequency, it may be very poor at an- 150V 24 The simplicity of a other because of either too large a dis- N'11 v - c circuit, the ease with tributed capacity or, if this is not an 750V N2S which it can he built objectionable feature, too litle inductance. N! I2 ,. -+22% a and used, the care It was necessary to make a choke having CONI .. N26r, lowest N13 with which it must high enough inductance at the be made are the fac- working frequency and negligible dis- tors that should be tributed capacity at the highest frequency. kept in mind when The final choke was a nine section layer - Fig. A wound affair having very low distributed Front view of the very versatile short -wave tester. building any piece of equipment. capacity and an inductance of 30 milli - Expensive henries. This is illustrated in Fig. 2A. For soma unaccountable reason, short -wave parts receivers do not seem to enjoy the same up-to- and "trick" circuits The "band spread" effect was accom- dato testing that is being given to broadcast can never equal good workmanship and plished by having a fixed 60 mmf. con- receivers. That this may be due, in part, to lack of efficient test equipment seems to be a proven design. The test laboratory to be denser, Cl, in parallel with the variable generally accepted fact. To overcome some of described in this issue was built to these 50 mmf. condenser C2. This arrangement the difficulties involved in testing short -wave apparatus, the author of this interesting article ideals. It will perform equally as well necessitates the use of more plug -in coils has designed and built the portable testing lab- for anyone, so long as care is taken in than are usually needed to cover the de- oratory described in this article. ad- This device consists of a vacuum -tube volt- construction and adherence to the values sired frequency band. However, the meter; a short -wave oscillator, which may be given. This unit, Figs. A and B, was vantage of this method of tuning fully made to include the broadcast band by the addition of the proper coils; an audio oscillator, built specifically for one of the smaller compensates for the labor involved in which may also modulate the R.F. oscillator if manufacturers by whom it has been used winding the coils. The economy of the so desired; continuity tester; capacity tester; more and may also be used for the measurement of both in the shop and in the field. circuit is shown by the fact that not Inductance. Aside from the above, the instru- than 2 ma. is drawn by the plate of the The Variable R.F. Oscillator ment may also be used for an ohmmeter; as an tube at any frequency. external voltmeter (either A.C. or D.C.) and Keeping in mind as a D.C. milliammeter. that the oscillator Modulation of the oscillator is accom- The entire unit may be built in a box 9% must be as simple and trouble proof as plished by x 10y x 3% inches. supplying a pulsating voltage possible, the features emphasized in the to the plate of the R.F. oscillator tube design were: Vl. The plate lead of the R.F. oscillator (1) One coil in the oscillator circuit. connects to a tap on the A.F. choke, A.F. OMEHOW, to a large number of This would automatically eliminate 1, in which is present the A.F. current people, the idea of anything con- bothersome feed -back arrangements and due to the A.F. oscillations generated by nected with the word "laboratory" simplify the wiring; the modulator tube V2. The oscillator immediately suggests expensive and (2) The circuit must be absolutely de- plate voltage is then modulated by the delicate apparatus which is far beyond pendable and must oscillate easily, since A.F. voltage drop across the portion "a" their financial and technical means. There the maximum available "B" supply is but of A.F-1, and hence the R-F. output is is no basis for this state of mind. Good 45 volts; modulated. (3) Since the oscillator is to be cali- The output of the oscillator is taken brated, the frequency should be spread through L1, C3 and R2 which form a A 1 %is' over CHOKE the entire dial, as the error in cali- "dummy" antenna. The output is coupled brating and reading is less. directly to the receiver under test. Values The circuit that was finally adopted is for Ll and L2 are given in Table I. *t6. riL a modification of the Colpitt circuit shown 50 TURNS: LAYER WOUND EACH SECTION in Fig. 1. The stability of this circuit The A.F. Oscillator A F. TRANSPORMER AS A.P. CHOKE depends upon both value of - F the the grid There is nothing difficult in the build- OOQJIOO TO 3Y3 TO R.F. CYgKE leak Rl, and more particularly on the ing of an oscillator to generate audio 014M 90000000 size SHUNT IP To MOOULATOR of the R.F. choke, R.F.C. It was frequencies. The requirements are an C9 --a. IMO found that with values of R1 varying A.F. transformer, a socket, a few con- from 5,000 to 100,000 ohms, the circuit densers, a grid leak, and an A.F. choke. "A. F. OUTPUT oscillated sharply, but only at certain The transformer Tl has a turns ratio points. Using a 10,000 -ohm leak, the os- of 3:1; the primary is connected to the Fig. 2 cillations At A, details of the choke; at B, method of centered about 4,000 kc.; a 100,- grid and filament of the tube. The sec- connecting Ti. 000 -ohm leak brought the circuit oscilla- ondary corresponds to the usual "tickler

230 RADIO-CRAFT f o r OCTOBER, 1 9 3 2 WP

C4 R2 -RI C3 s /+ ! r . R9N°1 ¡ N°150. e TI er A N'2 C, SHORT -WAVE N°160 , C9' . N.3 t ?" R .C. h . liC6 ¡¡,,,,.. . . R2 C-8 R2a ?, N°17Orw ; O F} lN4 4 ° i' By H. HARRISON 1 . ti N'S \ 's C2ì,/ N. N°19

N{20l. N!7 coil" which provides the feed back from ing the amplifier, that ' -,- - ot 19' the plate to the grid. The precaution is, so there is no here is to reverse the secondary leads if alternating signal, N2Ie_ the tube does not oscillate. adjust the plate -cur- R 23) The chosen frequencies of 400 and 2,500 rent reading (MA2) N°2290.. cycles are obtained by switching either to the smallest read- to a .02- or .005 -mf. condenser respectively, able value. This ad- by throwing SW1 to position 1 or 2. The justment is made by A.F. output may be secured separately by varying the potenti- connecting leads to the terminals marked ometer R3. Note the e MA .I "A.F. output." The common coupling plate- current reading CIO. °'\ choke A.F.1 may be the secondary of a and the grid -voltage reading on the meter standard input push -pull transformer, or '-'1111N°13 a 6:1 A.F. transformer with the primary (MAI) across the po- d tentiometer. N o w COPPER OXIDE and secondary windings connected in RECTIFIER series. The connection should then be start the amplifier so as shown in Fig. 2B. Switch SW2 con- that there is alter- Fig. B trols the A.F. into the R.F. oscillator. nating voltage across the output winding. TAJI! 1 R.9uae7 No. ef tuens !o. of tuen. Ir..10. Vaeuum Tube Voltmeter The plate current meter reading is m tc. of u of 1.2 D.S.C. changed. Keeping the signal voltage on, The vacuum -tube voltmeter used in the 1,600 2,660 50 IT 26 adjust the potentiometer until the origi- unit is simple to ( Aerate. The input ter- 2,640 3,260 20 13 29 nal plate current reading is obtained; minals must be through con- 3,260 4,160 20 26 connected a read the voltage. 10 tinuous-current-carrying circuit, which grid Subtract the original grid voltage reading from the 4,160 6,360 li s 26 may be either a resistor or coil in parallel new reading. Their difference is approxi- 6,330 4,440 32 9 24 with the input terminals. If there is no mately equal to the peak input voltage. 3,460 T,1w l3 26 such input circuit, the input terminals Divide this reading by 1.41 or multiply 1,130 6,200 s 24 should be connected to a resistor of 1. by .707 to obtain the R.M.S. (or effective) megohm. The plate milllammeter should 4,100 100000 10 22 value. During the test, SW3 must be 10,003 11.400 20 also be properly adjusted before applying closed. 32 the input voltage to be measured. To 11,300 32,1100 10 2G The desired range of voltage measure- make these measurements, it is necessary 12,00 32,450 20 ments may be obtained by selecting the to connect the terminals under test (as- 32,430 14,450 22 sume it to be from the output winding proper tap on switch SW4. Multipliers 302!, Coils w ta Mawr.", art newt& an r1Andat of of a transformer) to the input terminals R4, R5, R6, and R7 have values of 1,000, 1-1/5 Iamb. la Innunerl Ll ..6 12 o...F...s of the V. T. voltmeter. Without operat- (Continued on page 248) 1/3 N 1/4 Snob. See tab for further 4.t.si..

R.F. 05CILLATOR A.F MODULATOR VACUUM-TUBE VOLTMETER 459.2 CS TRANSFORMER 3'I r 59.16 .00OI-MF R-F.OUTPUT , C5 TI I 50 CIO - Ce .005 -MF, P .0001MF 30 R2 500MM5-. .1 -MF - Ll-- R4 C7 .02 -MF MA T_ 1 o 0-1 1.000 OHMS sH1Elo o R19 522 MEG III 2 RM.S 0.42 RS 13 OHMS C2 .00005-MF.- 5.000 0-1 04 -5HIEL0 INPUT lJ1 1 Q)-NNNV-- Cl .00006-MF _ V2 1 0 I r SW RE SHUNT C6 .002-MF 10.000 OHMS 0 -2 C4 .000I-MFr 55.1 CON- f SW 5/ MA TINUITY I OMW1M^ RI /r Ir Ry 20.000 OHMS 2 MEG R 20.0p00MS (R.F 20 llLNSISO CHOKE SW.2 41 OHMS 41 OHMS VI WE STON N9.26 Br'45V - 41 BI-POLAR SWITCH N9 25 Q N9.24 B_ { N9.23 R10 /TAPPED COIL C 22y2 V 50 5 "C-'22%2v 45 V. G SW.5 A+- 445V 5,7 a- NO 5 N9 6- I we tee 52.27 AFI / _ 1 5 V3 OHM SHUNT 4 I6 5217 R15 b 0-10 MA C9 I O-100 -O-1.MA RB 10,000 OHMS (050.) EXTERNAL I MA NS 190 +10Y. I .2-MF A F. OUTPUT r0 MS O.C. P14 R 13 12 I 0-10 R 9 100.000 OHMS ESTTERNAL R R 11 CUTESTRRENT R16 N9.20o +100V, 500.000 75.000 I MA 6500 1000 y/VOLTAGE OHMS OHMS OHMS OHMS L 6 510 500.000 OHMS oN2 4 NC +500V TEST N9 12 Ne 11 / 2IA I Nó 10 N9 9 No_.0, OHMS .A/ 1AÁ4 \1 33 44-...... 750V 1.50V 15 VV +p R 23 5V J COPPER-OXIDE 1.000,000 OHMS 459.22+1000 EXTERNAL A.C. VOLTAGE MEASUREMENTS 1 RECTIFIER N

Fig. 1

RADIO -CRAFT for OCTOBER, 1932 231 RADIO-CRAFT'S INFORMATION BUREAU SPECIAL NOTICE TO CORRESPONDENTS: Ask as many questions as you like, but please observe these rules:

Furnish sufficient information, and draw a careful diagram when and the appearance of its answer here. needed, to explain your meaning; use only one side of the paper. Replies, magazines, etc., cannot be sent C. 0. D. List each question. Inquiries can be answered by mail only when accompanied by 25 cents (stamps) for each separate question. Those questions which are found to represent the greatest general to avoist interest will be published here. to the extent that space permits. Other inquiries should be marked "For Publication," At least five weeks must elapse between the receipt of a question misunderstanding.

circuit arrange- RELAY should increase to about 3 ma. %shca the micro- mentors who may try out this SOUND -CONTROLLED phone is connected into circuit and actuated. ment. (17:1) Mr. II. Young. Allentown. l'a. Relay No. 1 Is adjusted to Chair at abnnt (Q. 1.1 Please print the schematic circuit nut.: No. 2. nt about 4 mat. The latter value of an amplifier system suitable for operating is obtained lay varying the Control -grid bias of "MOBILE P. A. SYSTEM" a rely- by whistling or hand ehggdng. the second tube until the plate current Is 2 !1701 Mr. IL flaira g, at the (:1.1.) By courtesy of Good News are re- nul.: then 4 ma. After adjustment IQ, 1,1 Io the Aligns! Issue of 1Ltuno- CRAFT li stiiUd values, reduce the plate address sys- produce in Fig. Q.17:: a schematic circuit of rst and then is described an interesting Public this nature. current to 1 mut. tem amplifier consisting of a type '24 tube of which will - The following parts were sass's-hied ln the An arrangement this nature. feeding n pair of 511's in push -Pull: a direct original layout: light an illuminated sign at is whistle, and put coupled circu it arrangement is 050 (1, clap banals. is a good money- One singl- button microphone; it out at the of Please furnish the following data regarding a of One mierophone battery (two large -size flash- maker as novelty attraction. components of this lunplilhr: hating power type of resistors used. and; light cells) : transformer: one One microphone transformer with a ratio of method of eenuerting More thou repro- 00 to 1. approx.: 7 -PRONG TUBE SOCKETS ducer into the circuit. (.1.1.1 'trie power used in this One A.F. transformer, ratio 4 to 1, approx. ; (1741 Mrs. L. G. Jensen, Weehawken. N. J. transformer powerful, high- lidelity public address system sockets 1 two type l'Y and one type construction Three 11). 1.1 Is latere an approved high- for 7- a nstl Iiier is rated at 200 watts: the design for hases and sockets designed each side One power transformer hosing a 000 colt s-oh-age sa'nndauy delivers 730 volts prong tubes: Note use of separate seconday. center- tapped. one 2.5 volt wind- 174 are Illustrated the of the center -tap. the IA.1.s In Pig. Q. of filaments ¡this Is ing and 3 volt winding; base and socket designs approved by the Radio windings for each the Two snap switches: 3lanufarturers Association. The original illus- necessary t obtain correct bias potentials). 'full' two 11.125- IIV'g. and the two O.1-meg. Two condensers. 2 mf.. 400 V.. D.C.: tration %tas made available by courtesy of une 1. watt ; the remaining One choke, 30 by.. 40 mn. rating; ilygrade Sylvania Corp. re-4sto1s rated nt One potentiometer, 111,000 ohms. 40 na. rating; resistor units are rated at 75 watts lin order under One potentiometer. 1.000 ohms, 40 nia. rating. to accu ras tely maintain correct values resistor, 3.000 ohms, 20 watt rating; load 1. One use One resistor. 4 watts. 1.on ohms: MODERNIZING THE FLEWELLING Additional reproducers will require the ,.f output transformers. One resistor, 4 watts. 1.000 ohms: SIMPLIFIED SUPER -REGENERATOR individual One 4 watts, 200 ohms: resistor, lie"Ihe, ouste. One resistor. renter- tapped. ::0 ohms; 117 "'u Mr. .tutee Smith. Phil 11-211 (li, 1.1 What would be the circuit arrange- Two Western Electric. Type holding re- I IIII lays, (G, E. Type CII- 2810- 1245A); ment for the old Flewelling "sintpliiied" super- H VGR A DE ver ns redesigned to use the SYLVANIA CF-2930-10S0- regenerative vomi One G. E. Master Relay, type newer types of tubes--for instance, the Srreon- MEDIUM C2 . grid? -{- 7-PIN Three Radiotrons (two type '27 : one type BASE 'R01. We have not had any Practical ex- .500 The relays are sin adjusted that a low in- perience with this interesting circuit modified of sound will cause one relay to net. in the manner suggested. However, we re- tensity is 1.377 iAA This in turn rouses a power switch to close. produce in Fig. Q.175 the schenust circuit proposed by 311-. Rivard Well. writing in is The second senslt t -e relay breaks the current 5l° 51° 5 PINS through the in terloeking power switch and recent issue of the radio Sert' of the New .125' opens the 110 V., A.C. circuit. York Nun. ±.003" O. DIA. A circuit tuner. L. is used. The Adjust the slider on the 10000 ohm resistor standard 1° until the drop aeross the 3 ono ohm resistor most important Portion Of the circuit is Ilu, is about 1::5 volts- then nd.l usa the slider of grid leak, the value of which must be vas i-d the 1.000 ohm potentiometer to obtain a bins until satisfactory operation is secured sri111 potential within 4.5 to 22 volts on the control - the particular tube used. Note that the !I"n- ion 2 PINS grid of the second -stage '27. Make provision ntt% fixed condenser mast be of mica- insnlat 156" current of either tube type, Colliding transformer 'r must have n 52° for rending the plate BOTTOM VIEW =.003" out very high- Impednn el. primary. Position 1 of O. DIA. during adjustments. With the mierophone OF BASE 26' 26 of the circuit. the plate current of the first Sw. is the usual connection; Position 2, super - '27 should be at t 5 ma.; the second then roga'nerat t ion. should read about 1. ma. 'l'he latter value \\'c will he interested to hear from experi- Fig. Q -174. An approved 7 -prong socket design. V

T1 '27 r2 '27

GROUND TO B 2G CASE, RELAY NS 1 IF METAL CASE Sw2 IS VSFD +IiIiIiuIsf 826 RELAY N4.2 -30DIaMS MICROPHONE HOLDING RELAY TO HEAD- PHONES 5w.1 OR TO LIGHT FIERR,L AMPLI- f MASTER y4- t t0 v, R-- 30 H. RELAY 45 TO MEG A C -^ 2V Á+ 135 V.' 60 CYCLES

Fig. Q -173. Schematic circuit of a power-control circuit ope atad by audio sounds. Fig. Q-175. Flewelling "super- regenerative."

232 RADIO -CRAFT for OCTOBER, 1932 IP

SERVICING NEW RECEIVERS By FLOYD FAUSETT IN order to increase his income, the active any one of five tube circuits for tube tests. In radioman must keep himself equipped to the Model Mi. the battery may be connected render better service to more customers. The into any one of the six grid and plate circuits. radioman who fully appreciates this funda- Although the Supreme Dl ode Is 70 and 00 mental factor of profitable radio servicing is oscillators were designed before superhetero- Let I.R.C. interested in testing equipment which will dyne radios became the rule rather than an assure less time-per-job for service which is exception, there has not been a single super- better than the service rendered by his com- heterodyne designed with an intermediate fre- petitors. quency which cannot be aceommoda ted by the Supply All Statistics recently compiled by It.tnto- Clt.trr original Supreme oscillators which ph creel indicate that only about term of the owners the harmonic principle of commercial oscilhiI of manufactured radio tube socket testers are tuning. your Resistor equipped with manufactured oscillators, and Since ninny radiomen already have hundred - it is probable that most of the oscillators in- of dollars invested in testing equipment. the cluded in this iKé do not provide the necessary are anxious to have such equipment recon- frequencies for all the newer superheterodyne structed to meet the testing requirements of Needs radios. It may, then, be conservatively con- the new 0 -pin and 7 -pin tubes and circuit s. cluded that not more than 9% of the owners Arrangements are being made for such remodel- Come to resistor headquarters no matter of radio analyzers are equipped for performing ing of older Supreme products. In addition. what your problem. Test for yourself the better service wIth less time-per-job. Those new ohmmeters. volt- ohmmmeters, resistance money- making devices the International of the 9% classification ought to complain less decade boxes, capacitor leakage testers, and Resistance Company provides for Service about cut -rate competition and let the public nicterless tubo checkers are being added to Men. know of their better facilities for rendering the Supreme line. It is believed that the better service. nleterless tube checker will nowt a long -flt METALLIZED Resistors for Replacement Many radiomen rightfully consider themselves need (Or It tube checker which can be epee :i niI as professional men, but professional pride or in coti,lntietinn with the meters of an) ethics should not prevent their resorting to nnnlyzrr, This meterless tube checker ..will other than very modest advertising. For in- Incorporate the cathode -heater leakage t-I uud stance. chiropractic doctors believe In advertis- the capacitor leakage test of the . %A.t -I Iinc- ing their training and clinical f;eilifies, and nometer, but will be available at a cost nee li why should "radio doctors" be less modest? is less than that o1 tube chokers of comparable there anything wrong with a radioman's adver- quality. WIRE WOUND RESISTORS FOR tising that his is the only Incal service estab- Resstance Measurements METER CONVERSION lishment equipped for meter adjustments of all The analyses of radio receiver'- by resistants ypes of superheterodyne radios when his cut- measurements is iI I. undoubtedly. he ret.n111- rate competitors are not so equipped? lutgltiel In futon, radin service manuals. and the Supreme prndaels are designed to utilize all of the advantages of those methods as well as affording the usual potential and current measurements during analyses. For service on radio recchrts on which resistance data is not published, a decade resistance box has been HANDY CERTIFIED KITS designed at a low- cost. This unit eau, by connected across an open resistor In a receiver and adjusted for correct potential and current values, when the adjustment of the decade box will indicate the prnper resistance vale, which should be permanently connected in place of the defective resistor. Terminals are provided for measuring the potential across The Supreme 56 Analyzer the decade resistors, so that flit- power re(1uiln- meats of a required resistor can be determined The newer types of radios with R.P. pen- as well as the °limit. value. This box covers todes. class A and class It a tnpl [lieu then. muting the entire range of resistance values found in circuits, etc., will introduce service complica- commercial radios. It is obvious that. with tions which make it necessary that radiomen the proper testing apparatus. resistance keep up with the rapid developments Of the analyses will greatly- simplify and expedite the new radio technique, and keep his equipment handling of radio service jobs. It is almost up -to -date- In adding to his equipment. he Kit No. 1 containing 20 1 -watt Metallized i'nits impossible for new radio developments to make Kit No. 2 containing ya 2-Walt :Metallized ]'nits must be interested in the equipment which is °hmnleters and decade boxes obsolete. Grid Ill:u Nit iuntal n tug Ill assorted Metallized designed with the least likelihood of obsoles- 111tca11V and wire wound units. ]Canty radiomen who do not have Meter Suppressor Kits 4. 6 cence. The ma n u faetu rers of equipment -fur and 8- cylinder ears. test g 1 testing units are interested in obtaining which are endeavoring to design apparatus all of the essential egnipmcnt in a single port- I R C Resistor Replacement Guide will not become obsolete in a short time. Most able unit, such as the AA.\ -I I)iagnnnlete with to limitations -a loose-leaf manual which gtres full redstor data of the obsolescence is due the its improvements for accommodating the new ghoul any popular res dee, stn order for 20 imposed by the switching arrangements em- 0 -pin and 7-pin tubes without adapters. All Metallized its or 1 It No. 1 or Nu. 2. brings yMl ployed. Furthermore. the moving of the Guide u FREE. Or It may be bought singly parts of flue testing functions required in practitnl fur $1. complicated switches constitute a possible mile servicing are incorporated in this unit. source Of trouble. Including n stabilized oscillator with 10Or; I R C Color Code Chart 'l'he Stgil-01110 Model 30 is an example Of an modulation for covering all intermediate and In R if :t colors -tells Instantly the resistance value analyzer which eliminates these disadvantages broadcast frequencies. The oscillator, analyzer. of ans. tesistur It M A color coded. FREE. by eliminating the use of rotary and push checker. tube and olunmeter functions of the button switches for connecting the meter to I dagnomefe are separated SO flint it is prac- I R C Meter Conversion Charta of the various circuits. Each range the meter. tically impossible to harm any of Its parts by They .dew hoir to build your t a test rq ulpo unl and each extended radio rircuit has its own inadvertent connect Ions. ut astonishingly small cost. Free for the asking. sot of insulated terminals. and any desired The nhmmter ranges extend to 7.00.0on connection can be conveniently made by means with Make Your Own Set Analyzer ohms a self -contained 4:7.-volt battery. Keep of the test lends provided with the analyzer. and higher ranges are available with external your equipment tip to date With the new tubes. .t i impleie in strtlow folder tot the Spra)- The cathode ei roe i t. the filament circuit. the power. The INagnorneter power unit supplies berry Set Anal'zer will be sent without cost. top cathode connection of the new a -pin Wun- a 1),('. potential of 27.0 volts for leakage tests. derlich Isbe or any other required circuit Feet free to write us at any tittle. Cot etc. Some users of the A. \.1 -I Itiagnnmeter list and have the new I R C sortite helps is . may he taken as the reference circuit for keep records of overall measurements made on voltage measurements. each serviced receiver at several tuning fre- INTERNATIONAL RESISTANCE CO. In the usual analyzer with its complicated quencies before and after adjustments. to tad PHILADELPHIA, switching nrrangemen ts, a two -way switch these records become valuable for making- PA. TORONTO, ONT. provides the possibility of only two reference comparisons between receivers. This procedure circuits: that Is, cathode and negative filament. also enables the radioman to determine the Heretofore. analyzers have provided means for percentage of improvement in sensitivity ad- connecting a self -contained 4.. -volt battery into justments In daytime and whether or not a the fat control grid and h21 the normal grid receiver has sufficient sensitivity for distant circuits for tulle testing. The latest 0 -pin and reception nt night. It is bellev ed that such 7 -pin tnhes have infrndured complications servicing practices with the hest of equipment and Precision Wire may Wound which require battery connections into will cnntinne to enable active radiomen to to t. money been use of better service rendered Chief I:u_iuee, Supreme Instruments Corp. e customers. RESISTOR S RADIO -CRAFT for OCTOBER, 1932 233 QUASI- OPTICAL HOME AUTO -DIAL RADIO EXPERIMENTS Quaty tone, selectivity, and power Write By JOHN B. BRENNAN, JR. Down behnv I hat cad of t inequency spec- Today trum where the short waves are to be found, Sensational there is a band of frequencies so short In wavelength that they are classed as either light or for heat waves and are more correctly termed quasi - AUTO optical frequencies. Information In consequence of the present popularity of experiments and investigations into the realm of television and the transmission of intelli- 011 RADIO gence over short distances by extremely short waves, much attention has been focused on the COMPLETE ; various and unexplored usages of special types This suppressor All. ar..l of radio apparatus and equipment such as photo- $17.85. Dealers aAm ed. Write tralar. electric cells, crater lamps, neon tubes, straight - 1 -14P MANUFACTURING CO., INC. 3958 Fond du Lac Ave.. Milwaukee, Wis. line frequency audio amplifiers, photo -voltaic and other forms of light -sensitive cells, para- bolic reflectors, sound- operated light modulators and the whole galaxy of new and unheard of equipment associated with this field of investigation. Mr. SElivI4'1; MAN To that dyed -in- the -wool and ever growing group of serious minded experimenters who are fast becoming sated with the rehash of present day offerings in the line of radio receiver designs. any new field of endeavor which shows promise of providing an outlet for their pent up energies is eagerly embraced. Thank You Our advertisement in It is with the idea in mind of providing - the swh an outlet through the agency of planned In roue experiments in the quasi- optical field that this department, from this issue of RADIO- September issue brought us hundreds of re- CRAFT on, is offered for your serious consideration. Each month, in this space, one simple ex- plies, and periment will be described and explained in NOW hundreds of copies detail, so that those of you who have the time. equipment and inclination may find out for yourselves the marvelous commercial possi- of "GOLD SEAL Radio Tube Sales bilities in the quasi -optical field. The experiments will use only apparatus which can be easily and economically constructed on the Plans for the Service Man" are on kitchen table. As an example of what may be expected the following tentative experiments, to be described completely in later issues of the way. Step to GOLD SEAL Radio this department are listed and partially described.

Tubes and Profits! CARDBOARD wiTH PHOTO VARIOUS SIZED VOLTAIC HOLES CELL The tubes you need -for receivers, transmitters, public address or television are FLASHLIGHT MILL SAIH METER made by GOLD SEAL. A simple experiment to demonstrate current variations with light intensity. GOLD SEAL Sales Engineers have devel- (L) Carious types of light -sensitive cells and how they work : a simple photoelectric cell and amplifier to demonstrate its ability to change light variations into variations of elec- oped a special "Selling Plan" for the trical current. (2.) A typical photo -electric cell amplifier Service Man. It's yours in return for and how to build it. Newly (R.) The uses of various kinds of lenses to Made concentrate, magnify or focus sources of light the coupon. on photoelectric cells, Fully Guaranteed (4.) Clow light may be bent through n quartz tube to actuate a photoelectric cell. Long, Useful Life (5.) Forms of light modulators: crater tubes, neon tubes, their uses. Licensed by RCA (G.) Mechanical light modulators. And so the list might go ou almost in- And Double Tested definitely. Slime.. it to say that the main pur- Mail Coupon TODAY! pose of this department will be to explain. describe and demonstrate only those experi- An Experienced Staff ments which the home experimenter can GOLD SEAL MFG. dupli- COMPANY cate at a minimum of expense and labor, to the Standard Specifications 5 Central Ave., East Newark, N. J. end that his store of knowledge and experience in Please send this particular field of radio may be en- me by return mail Speci- hanced. Best of Materials Used fications on GOLD SEAL Radio Tubes As an example of what can be done, and your "Sales the New and Modern Equipment Plan" for Service Men. following rather simple experiment is outlined. The parts required for it are: a flashlight. a photo -voltaic cell. a milliammeter (0 to 5 ma.) Name and some bits of connecting wire. 1 Connect the two terminals of the photo- Address voltaic cell to the two terminals of the milli - STEPS TO GOLD SEAL ammeter. as shown in the accompanying dia- City State_ gram. it is possible that even the daylight, depending upon the light conditions under RADIO TUBES J (Continued on pane 247)

234 RADIO -CRAFT for OCTOBER, 1932 MODERNIZING THE HI -Q 29 ((oafia ncd from page 2181 voltmeter with a scale deflection of at least C19: The New Way 50o volts. D.('.; connect the negative lead to One Parvolt 1 mf. series 200 filter condenser, clip No. 12 and the positive lead to clip No. C20; II. .\ type '80 tube is inserted in the tube One Durham metallized resistor 2 megohm, R4; To Analyze socket and the unit Is plugged into the A.C. One Yaxley 20 -ohm center tapped resistor, It7 ; line. The "no load" voltage reading should One Yaxley No. 012 cable connector and cable, be approximately 418 volts. Note: Do not leave the power supply unit turned on longer One R.N. Electrad Truvolt III -Q 29 type re- Modern Sets than necessary to make this test. sistor ; One Thordarson No. It -171 power compact, I "l'; List of Parts One Federated Purchaser filament trans- forms catalog No. 2010 'l' Five Ilnmmariund No. ML 17 .0008. -mf. Mid - F: line condensers. Cl, ('2. ('3, C4, C5; One Parvolt 4 mf. series 21)0 bypass condenser. Point-To-Point One No. III -Q 29 coil set, Ll, ('15: liammnrlund No. 422 jacks, L2. 1,3. L4. L5, LO: Two Yaxley insulated phone tip Three llammnrlund No. IIFC 85 radio tre- L.S. Resistance quency chokes. f.7. L8, L9; Two Eby engraved binding posts. ANT. GND; and No. !1uVW I socket. One Sangamo M0025 mf. fixed mica condenser, Two Benjamin VT.0: Nn base mounting type l'Y sockets, CO; Four -.\ld Y'rl \"l'2, \-T8. \'T4 ; One Sangamo .00025 -tuf fixed mica condenser, Capacity Tester One. 'l'ru -test 10.000 -o11m % watt resistor, C12: R3; One Yaxley wire -wound potentiometer 1,500 to 000.E -mf. 190.000 ohms. Ito: One C midget variable condenser, 500 -ohm flexible resistors. Rl. I.SL : Two Electrad One Screen -grid cap connector and wire: 112: unit containing Thordarson n -800 audio transformers, III -Q 29, master foundation Two type drilled and engraved panel three complete AFTI. AFT2 ; steel One Thordarson type 1.190 choke coil, AFC: aluminum shields. Drilled and formed 200 C4, chassis. Fa hnestork clips, Brackets. clips. Six Parvolt .5-nit series condensers. washers, and all necessary CS. CO. C10, C11: wire. screws, nuts, -7. hardware to ,onhp lote this receiver. Ode Parrott 2 mf, series 400 filter condenser, % C10; One steel shaft 22 inches long, inch in One Parrott 2 mf. series 200 filter condenser. diameter. C17: No. 1000 One Parvolt 4 mf. series 200 filter condenser, Indicates additional parts other than the C1R; regular kit of parts necessary to construct One Parrott 3. mf, bypass block, series 200, this receiver. NEW TUBES (Continued from pago 205) cury -vapor type is recommended because it has flea factor, 4.7; plate resistance, 3.000 ohms; a low and practically constant spa(1'tl1 rge- mutual conductance. I.570 nticromhos; undis- voltage drop within its operating limitations. torted power output. 3110 milliwatts, As a further means of abtaitting good regula- For class .\ pentode operation, the following tion. the filter chokes and transformer wind- ,haraclerist i.s ebtuin: Plate voltage, 1811; ings of the 'Il" eliminator sl Id have as low screen -grid voltage. 1811: control grid bins, -lö; resistance as possible. In the design of a plate current. 20 milliamperes; screen -grid mover supply for a class R amplifier, considera- current. milliamperes; power output, 1.5 tion should be given to the peak current de- watts; load resistance, 8,1100 ohms: amplifica- mand of the amplifier. tion factor. 1:15; Plate resistance. 52.5011 ohms; cundutthtihce, 1.835 mieromhos, As may be expected, the grid (No. 1 and mutual No. 21 of the 89 is operated sufficiently posi- Combination Amplifier and Power $ Net tive to cause grid current to flow in its input Rectifier 33 circuit. This feature imposes n further re- amplifier stage. The first advantage of the unique tube to quirement on the preceding be described is to provide an electron emitting It must supply not only the necessary Input device hawing an electron producing area and a Two cable plugs connect set voltage, but it must be capable of doing so of electron is plurality emitting cathodes adja- sockets through selector switch under conditions where appreciable power cent areal. S,.und, to provide a device It tube. to this taken by the grid of the class amplifier that can be used in radio circuits and in which to the precision volt- milliam- Since the power necessary to swing the grid the filament or heater current, as well as the positive is partially dependent on the plate source of pere- ohmmeter, -an exclusive e®- plate, can he taken direct from a load of the class It tube, and since the current. Third. and this is a rather Henry of transfer from the preceding alternating Readrite feature. Speeds up power unique advantage. to provide ah tube leaving on transformer design. stage is dependent the a multi -potential grid, that is, different parts tests without removing chassis. it is apparent tint the design of n class It of the same grid to have different potentials 11111110, power amplifier requires that more than with respect to the cathode. Fourth. to pro- Measures resistances up to ordinary attention he given to the effects pro - vide a self-biasing dneed by the component parts of the cireu it. grid. thr'ee megohms D.C. Volts The sketch of Fig. I; illustrates the external - These effects may be prod lived In the first-stage wires of unique Fig. is this rather tube. 7.\ up to 600 and milliamperes up amplifier by the design factors of the power- view of is output stage. For this reason. the design of a plan the Internal assembly; 7II an end view of the assembly shown in Fig. 7.\ : to 300. Also A.C. line volts a It audio amplifier with its driver stage class 7(' is a cross section view along the line 4 is for a class -4 somewhat more involved than of Fig. 711; Fig. 711 is a section showing the and capacity of dry and elec- .\ system. and must be checked for each change relative positions of the elements; 7l: is at in component trolytic condensers. the parts. cross section of Fig. 7D along the line 0 -0. The following ratings and characteristics 8.\ shows the insulating frame that supports obtain: Heater voltage, 0.3 volts: heater cur- the elements: Sit show's one Method of con- A fine instrument in leather- rent. .4- ampere; for class A triode operation, structing the elements. Two schematic cir- ette case. Complete with bat- plate voltage 1011; control -grid bias. -211 volts: cuits showing the application of this tube fire plate current. 17 ma.; load resistance for un- given in Pic. !1.\ and hilt, teries, test cords and full distorted power output, 7,000 ohms; amplifica- , r,,,,tinned on page 230) instructions. CORRECTION NOTICE Scud for Catalog Due to an error in printing, the cost of constructing The Radio -Craft READRITE METER WORKS Universal Analyzer was inadvertently printed as $28.00. A compre- Established 1904 hensive investigation by Radio -Craft indicates that the average price 17 College Ave. Bluffton, Ohio for which the parts may be secured is about $48.00.

RADIO -CRAFT for OCTOBER, 1932 235 Our FREE Tube Extended! NEW TUBES Offer (Continued front pape 235) So many of our customers have taken advantage of our

bonus that we decided to extend this offer . . . . In Fig. C a glass envelope is shown at 1. the upper end of which is provided with a Take advantage of our offer -25 UY -227 Tubes FREE with screw type of socket connection having terminals 2 and 3, which a 'ct to filament or every purchase of 100 assorted tubes. !cater leads 4 and a respectively. These leads servo' to support the elements of the tulle by (This offer is until October 7th) good being fastened to sleeves (i, the hatter forming Give to your customers the advantage of buying OM-quality licensed R.C.A. tubes at prices that are excep- an integral part of the insulating frame which tionally low. We cam' the longest variety of tidies in the world, many for special purposes, and every may he made of lava rock, porcelain or any tulle is replaceable within three months, providing the filament is not burnt out. \Ve either have the other suitable material. tube you require or we will make it for you. The horizontal positions of 7, Fig. SA, aro COMPLETE STOCK READY FOR IMMEDIATE SHIPMENT provided with slots 8 adapted to receive the Order from this page -Remit 20°r with order, balance C.O.U. all prices elements, of are )'.O. It. FACTORY. Newark. Shipment, go funrard express or parcel heater the ends which terminate post No order for less than 55.00 accepted. -OR- into leads 4 and 5. When an equipotential TYPE ANY QUANTITY cathode, 511,11 as ill the ' '24, etc., is UX- 201A- Amplifier r detector $0.30 UX226 -AC amplifier .30 desired, another element, 9, is provided. These ÚY227 -Ar amplifier or detector .30 Extra cathodes are in the form of plates as illustrated UX -171 -Same chararterisl des as 171A on tungsten filament. 14 amp .30 by 10 of Fig. 71t held into longitudinal slots UX171A -Power output amp. for AC or DC operation. 4 imp .30 Special UX -240 -Designed for Impedance and resistance coupling .40 11 as illustrated in Fig. SA. The Outside faces UX -120 -Power amp. used In last stage of audio freq. .40 of these plates are coated with an electron long .40 with UX -199 -Detector and amp. tube. prong. emitting substance. TYPE 0 U V199 -Standard base. has a 201A base. same characteristics as 199 .40 every Potassium UVI09 - characteristics as CX -199 .rely short prangs .40 Part 7 illustrated in Fig. 8.\ is provided Photo Cell. 4" UXI12A -Power amp. tube for low cur. consume.. 11 amp. .40 order for with 4 vertical rows of holes arranged to re- overalL $2.10 UX -112 -Power Amp. 'S amp. .40 UX- 200A- Detector tube omm led for weak signals .40 $5.00 ill NI. the Peat col grid. 'Pills grid may be in ÚY224 --AC screen grid s amplifier .40 the furor of a continuous wire arranged in UX -245 -Power amplifier .40 of tubes 110w- UX- 2018 -1/8 Amp. Amplifier and Detector .60 parallel positions close to the cathode. UY -246 -Power Amplifier .60 we will ever, where it is desired to place st negative UY -247 -Power pentode .60 potential on this grid, the may consist W DII -Detector Amp. .60 give grid WD -12 -Detector AMP. .60 of a number of thermo- couples each consisting UX -230 -Dry cell atop. and detector, 2 pelts .60 of two dissimilar wires as illustrated in Fig. UX -231 -Dry cell stage. 2 colts .60 snip. -last audio 7).'. UX -232 -Dry cell screen grid amp.. 2 volts .60 FREE UY233 -Parer Amplifier Pentode. 2 toll. .85 In this figure the positive and negative metals UX234 -Screen Grid Pentode R.F. Amplifier .85 2 UY -227 are shown connected alternately and indicated 11V235 -Super control screen grid ano. .60 as l' and N respectively. Thus, when cen- UY.236 -Screen Grid Radio Freq. Amp. .85 TUBES the UY -237 -Detector Amplifier .85 tral rote of jtuatues I points at which the dis- UY -238 -Power Amplifier Pentode .85 similar connect I. le in figure. becomes UY -239 -DC R.F. Pentode Autpiifer .85 For liars the ÚY551 -Variable Mu .60 multiples heated because of radiation by the heater tl, ÚY56 -A.F. and R.F. Amplifier and Oscillator .60 of the outer rows of junctures at C of Fig. 7C UY -57 -e prong Screen Grid It. F. Amplifier 51111 Detector...... 60 $5.00 TYPE V UY50 -6 prong Variable Mu ILF. Amplifier and Super Detector.. .60 proportionate will remain relatively cool thereby generating TleStisi endn Tube U X-210 -For power amplifier. high voltage 1.10 amounts a direct urrtnt in the grid. Bence, each U X-222 -Screen grid radio frequency atop. 1.10 grid wire will have a potential different from cathode. oter- UX250 -lower amp. used in but stage of audio freq. 1.10 of free 11 sis 2 "x6 ". liar last tube to prevent tubes In set from blessing out 1.10 its adjacent wire. $3.85 Special super- semlthe Audio Freq. 201.1 .60 tubes 'l'he plates illustrated in Fig. SH surround Special super -sensitive Radio Freq. 201A .60 will be Special 171 AC SI amp. extra coated filament -good for electric sets .60 the grid structure in the conventional manner. T -14 1201A High Mu) high emission .60 given. These plates are connected by straps 13 and Switch tube. 201A or 112 or 171 double life .60 rest against surface 14 of Fig. 8.1. Adapter tube 226, 227. 171A, to consert bat. sets to AI'. each .60 UY227A -AC amplifier or detector, saute as 227 Ibut quirk beaten .60 When the I 1111 is to he used in the circuit UY.224A-AC screen grid amplifier. same as 221 (but quick heater) .60 which is to rectify the . \.C. applied, more than RECTIFIER AND CHARGER BULBS two anodes are required as shown in the 125 Mil. rectifying tube (B. 11.1 (Raytheon Type) 1.25 6/10 snip. trickle charger bulb (Tunger Type) 2.00 schematic circuits of Fig, t). Likewise. when 2 atop. old and new type charger bulbs (lit 64.001 (Ungar Type) 2.00 more than one cathode is desired. the sections 5 and G amp. charger bulbs (list E8.1101 (TUnger Type) 3.75 may be insulateal fr another or sepa- 15 atop. charger bulbs (Tallier Type) 7.50 rate leads brought by UX -866 -Hot Cathode Meury Vapor Half-Wave Rectifier (Heavy 1)0(y ) 2.75 out each cathode. The UX -2801M-Hot Cathode Mercury Full -late Plat Bier same as UX588 1.25 advantages to be gained are quite obvious, First, TYPE R UX -281 M --flot Cathode Meu,' Vapor Half-\Vase Rectifier 1.90 this tub,. may be used in circuits requiring Caesium Photo UX -871 -Hot Cathode Mercury Vapor Iteeltfier 1.25 Cell, overall UX -280 -Full-Wave Reetlfier for High Emission .40 more than one grid, each grid having a dif- length 3-1/16". UX -281 -half- \Vase Rectifier 1.10 ferent potent hit with respect to the cathode $5.90. UX -282 -Full- Vase Mercury Vapor Rectifier 1.10 but all of then having a common input cir- PHOTO CELLS cuit. Second, this device may be used con- I'hotoelerlrle cell, "Potassium" Type 0 2.10 UX- I82- Sparton Type .... 85 in Photnelectrir cell. "Caesium" Type A. 41,4" merall length 7.90 U X. 183 - Sparton Type .... .85 nection with well -k nuwi type of battery coupled UY- 484- Rparton 'type ... .85 Photoelectric cell. "Caesium" Type R. 3 1 /16" overall length 5.90 .3.F. amplifiers in which UX- 585 -Spn,, Type .... 2.10 "C"' bias is required. TELEVISION TUBES UT-686-Sparton Type ... .85 With the device as abseriis'd here. It ran be Tenon Reflection Neon Television Tube, 1" Cathode Square Type C... 3.85 Erlingg Ty pc 1.50 U X40i- .... seen that an i t I VIni thermo- electric potential Teflon Nenn Television Tube. 114" Cathode Square Type V 3.85 UX403- Kellrgg 'ripe .... 2.00 Telion Neon Television tube, 1" Cathode Square Type X 2.10 Is derived for use in such circuits. Of special interest to us are the diagrams ARCO TUBE COMPANY, 40 Park Place, Newark, N. J. of I "lg. 9. A source of alternating voltage is npplled to the healer 9. as well as to the pr1- mary winding 10 of a transformer, the sec- Be sure to turn to page 256 of this issue and read about the new ondary 17, of which, has at center tap S. can fleeted to our lead 111, Of the L.C, terminals 1933 OFFICIAL RADIO SERVICE MANUAL which shall be 19 and 20. published shortly. Turn NOW to the announcement. The tube drawn in Fig. 9.\ has two anodes 12. connected in parallel as shown. which lead SERVICE into a series of condensers 21 and choke coils 22, before connecting to the points 19 and 20. MEN! IMPROVE YOUR BUSINESS It may be seen, therefore, that the two out- BY KEEPING YOUR NAME BEFORE Yt1Uft CUSTOMERS EVERY DAY side terminals of tie secondary 17 apply volt- FRONT ?lest people forget the day. the t, the dial number BACK age to the two inside plates, causing it pulsat- and hour of their favorite pmgr., .. end will appreciate ing L.C. to flow through the filter unit which Itadloudndcr Cards with spares to ire I such infonnat Ion. RADIOM5NOU5 They will be kept for the longest time in any home. Give in turn is applied to the two plates 12 which Nadlomhlder Cards with your ad printed of to your custom- function in the normal manner. Fig. 011 dis- ers or place a few in torn' home In your neighborhood closes the somewhat similar and they will constantly remind the people of you and full -wave rettitier thus think and talk about you. circuit with the exception that the terminal 20 There's No Better way To Make k derived from a tap between resistors People Think of You Every Day connected in series. 'rho anodes are rnu fleeted These r rds are superior to business cards and their far 10 A Intl gnifirant en .sidering the benefits you will derh e. the oat !side terminals of the secondary 17 Trial orders uvepted for as little as and the cathodes to parts 23. finders with ywr It would be extremely interesting to note the Ad of 5 Lines Printed for 25 application to which this tube will be put, for Each additional 100 Cards it will evidently bet a commercial product. 100 50e Postpaid It illustrates. SS stated previously, that the Card sire 3% x 5% inches. \d mare 1 it 3 inches. Printed nrari i rely on heavy Gulden Hod Rrinol Card. list Ink and trend in modern tube design has been toward handprint your copy and mail today with remittance to a minimum of tubes and an increase Insensi- ROTH PRESS, 825 Sutter Ave., Brooklyn, N. Y. tivity.

236 RADIO -CRAFT for OCTOBER, 1932 AN ULTRA -M ODERN SUPER. Your Career Today if'wllinucd Jr oil page 203) Start Wiring line it.B. choke, La I '!'his may be constructed In the world's fastest -growing industry - by winding 700 turns of No. 36 enameled The wiring should be done with a good Vou can, if you will, start your career today in wire on at wooden spool y -inch in diameter grade of push -back wIre and all connections the world's healthiest and fastest -growing industry and V2-inch long) ; carefully soldered. Wire the filament circuits The biggest and most talked of build- Une oscillator- detector tuning unit, -RADIO. of all tubes first, twisting these leads together. Atratest ing project in the world -RADIO CITY but an 5308, 1.:., LO, L7; -is '!'hen wire the plate -voltage supply, including type sign of the future this industry holds for Acratest transformers. as described, advance rectifier tube, electrolytic condensers, choke, Three I.I'. the man who gets started in it today, while the in- the I.F.T1, LF.T.2, I,F,T.; (consist- the socket used for connections to the speaker type 5358, dustry is After ing of cois 1.8, 1:1, Mu, 1,11, 1.12. I.l:ti ; field, and the voice -coil transformer. ohms, still young. this portion of the wiring is finished, complete Une .acratest 1: watt resistor, 20,000 The first plate and plate-return leads tu their re- Rl; Move is up all ohms, 112, spective socket and high -voltage supply term- Two .\ tratest .5 -watt resistors, 400 to you. inals. Rs; Read this Three .\crates( 5 -watt resistors, ,5- meguhm, The grid circuits are wired last : and be sure advertise- It7 ; that Nec connections of Ulis portion of the type 5860, it3, ment care- 6,000 -ohm 114; are na shown in the schematic circuit. Une Acra test .5 -watt resistor, fully and circuit 115; Any deviation tuait prevent the proper opera- Une .trratest .5-watt, 2,000-ohm resistor, then send flame . 25.01)11- olimts, Itli; tion of the automatic volume control tube. \era test 1.-watt resistor, in the at- Study this portion of the circuit carefully and um . \ era rsl . watt, 500 -ohne resistor. Ili: tached cou- 1 1110: follow the connections as shown. oie Frost .:i- upgolim vn11m11' control, pma. But do une .\crnt,st ..-, -watt. 750-011m resistor. 1111; it now. Speaker Selection One Arm i, -I -watt, .1 -meg. resistor, 1112; Get started. nue Frost uuguhm put.uti ter with switch As the speaker field is a portion of the filter The three volumes of !hi, l i L rn n- cover the entire circuit, it is important that the field have F\ \.2, Ill::: field of building, 01,1 iriuc and -trouble-shooting," 5 -watt resistor. 2011 ohms, 1114; the proper resistance. This circuit lues been One Aerates( on mudeni radio nel .cr.. '1'114' Library is up-to-the- 40,000 ohms, designed so that considerable variation in the One .\ern list .5 -watt resistor, minute in every respect anal is based ate the very latest of field is iiii'nìissable without 1115: developments in the design and manufacture of equip- resistance the ment. The rapidly -growing interest in short -wave and upsetting the balance of the rn rions voltages One Pu.wa led cadmium-plated chassis; mer, type 2527, television reception is thoroughly covered in a com- used throughout the set. Do not use a field our .\rrafcst power transfer plete sect inn which deals with the construction of will a resistance of less than 1.1)00 ohms or this typ,. A .ppu rat ua. mure than 2.5011 ninas. The plate volt nage on One Atratest filter choke, :0 by.. CII.i the plates of the 1.1'. tubes. with a speaker I ae rotary snap switch. 5\ \'.I ; type field -resist a net of 2.7u11 ohms, will be just One .\cria l est push -pull input transformer, ; Radio under 200 volts: speaker fields with lower 58:14, .\.F.'1.1 values of resistance will rase this voltage to One Aerates( tuning dial. type 4047; about 250 volts. If the D.C. resistance of the Four knobs for the controls: Construction speaker field is dropped below 1.11(111 ohms, the Five screen -grid clips: tiItering'nelion will he impaired and the applied Five Acru test tube shields, type 58; wafter sockets, four marked Library plate voltage will be too high. Five ('inch 6-prong INCLUDING The speaker must be provided with an output ":55" and one marked "55"; CONSTRUCTION 4 s. ekel marked °2611"; transformer to ma tri the two pentodes used IIne Cinch -prong waiter OF SHORT-WAVE AND in the output stage. Rn provision having Two Cinch 5 -prong wafer sockets marked "47.. TELEVISION RECEIVERS socket marked ller "; been made in the set for placing the output One Cinch :, -prong wafer By JAMES A. MOYER and must be mounted on the One Cinch 5-prong wafer socket, no marking; transformer, it rap, type speaker. une Alden -prong plug with short JOHN F. WOSTREL 5.q1Ú; Faculty. University Extension, Massachusetts Department Testing and Adjustments Five feet of lamp cord and plug; of Education One Irby antenna -ground strip, . \, U; After the set has !s'en completely wired and Three Volumes 1087 Pages, 6x9 Cour I'll type ass tubes; - checked. it is ready- for test. Fs,- an oscil- 605 Illustrations tune the intermediates to 175 k4'. 'l'wa. lilt type '17 tubes; lator and one VOLUME When has been done, the set can he con- Hit type 'sil rectifier; I: presents the fundamental principles of this radio so clearly and simply that anyone of tuned -in. One Calf type I toplex -I .ide Triode; average nected to an antenna, and stations training will be able to read, understand and apply One Elt type -. :0;; tube. Adjust the oscillator pudding rooden sers for them. It gives actual working drawings and lista of maxi muni sensitivity over the Iwoa tu ast band. materials for the coast nact iuu of many typical sets. Condenser (_'Si .\ Is used to trim the oscillator VOLUME II: fully discusses all of the elementary tuning at the high- frequency cud of the tuning A SERVICE LAB. principles of radio construction and repair. An explanation of Scale and C4 trims this circuit at the low - l ton, fun, I run, page 1Pa the necessary steps for "trouble- frequency end. Use the slotted plates of the shooting," repairing, servicing and constructing radio be and C" potentials sets successfully. practical data is also given condenser. Ca. for points may connected ".\ " "It" on oscillator tuning required to test Litt tery- operated receivers; antenna systenw, battery eliminators, loud speakers, between the high- and low- frequency settings charger., etc. This volume I he sattmections frond these but loci's are includes complete metro... compensated for by l'8.\ and ('4. The care I funs for the e0101 1111.t ion brought out to binding posts at the lower lelt- and operation of short-wave used in tuning the oscillator tuning condenser and television reeeisen. hauad roruer lit' t 11111114 : there is a lsu in. will rellert in the over -all sensitivity of the VOLUME III: covers the essential principles under- cnrpnrated a rotary switch for chocking the receiver. lying the operation of vacuum tubes in as non- voltages various terminals of the an When the set is properly adjusted, there plate al the technical manner as is consistent with accuracy. supply. 'Piece art' too switrh's : one is It discusses the construction, action, reactivation, should he no difficulty in picking up at least a 'l'.1'. O.'i'. for the filament and -II"; a : Lstiug and use of vacuum tubes; and an interesting 011 channel!: without any interference from snitch controls the "R" plus potential. section is devoted to remote control of industrial adjacent stations. l'.1)'l'. processes; and precision measurements. When the two sw'ilrhes are In the upward po- Parts List sition they control the current to panel Vu. S; EXAMINE these books for 10 days FREE This One Itadio Condenser Corp. four -gang tuning when they supply the necessary current to Library is not only a thorough home -sl nay course, but a handy of 60 54, C2, C3, Panel Ni,, 10. minis reference for the more units. with trimmers, type CI, experienced radio experimenter, repair man, Nu. 10 is an 11.1,. oscillator which and radin c".\ C5; l'ancl shop -owner. To these men, as well as to those who Two \l ieaunold cundtnsers. 750 nmtf.. type 6636, tunes from .(I to 1;11111 k4'. This panel is also desire to advance in the radio profession, this u,fcr C4.\. C13; used for the tansndsslon of phonograph rec- of a 10 days' Free Examination is made. ords picked up in other pau'ts of the building - IInc Mica mold variable condenser. 5 to 100 Simply clip, fill in, and mail this coupon nimf.. type 2I'83, C'4: This covers a general description of all the Six .tyro test variable condensers, .0002 -nit.. mounted panels. McGRAW -HILL type 5:.18 (these are part of the LF, trans- 'l'he isolable equlpmeul consists of n shielded formers), l'0. C7. C'8. C9. C10. ell ; oscillator; microphone speech nnuili tier used in F R E E EXAMINATION COUPON Six Aerafest tubular condensers, .1 -cot., C12, public address work: n standard Jewell useil- 3 RA BOOK 1'26; lator; a (Llt, output meter; two Weston 131 COMPANY, INC., C14, C16, C17, 330 Street. New York. One .\era test tubular electrolytic condenser, tube checker-analyzers. 'l'he 565's are used Gentlemen :-Send me the new 61510, 50 10 by the outside Service Alen. RADIO CONSTRUC- type volts. mt., C1S; TION LIBRARY, all charges prepaid. for 10 days' Two \Iicamold condensers, :11111 mmf.. C19. C28; The too heavy bare copper wires, running Free Examination. If satisfactory will send $1.50 One 311camold condenser. .006 -mL, C20; parallel underneath the panels. connect to an In 10 days, and $2.00 a month until $7.50 has been paid. If not unlit ed I will return Ibe set at your Two Acratest dry electrolytic condensers. type ltl'.\ antenna system on top of the roof. This oxeenut. 5308, 8 mt.. C'21. C22; arrangement enables a set to be connected at Nome One Acrafest bypass condenser, type 2837, 23- any position on the bench. mf., C23; The steel cabinets are used to house a com- Rome Address One \Iicamold condenser, 50 (mf., C24; plete stock of resistors and other aecessotles City and State Two I9eehtheim bypass condensers, type OF- for which we are jobbers. Position 100.- ('25. ('27: 'l'lo' publie nddress equipment which consists One :aeratest band -pass tuning unit, as de- of ten Raton dynamic units with output trans- Name of Company It17 -10 -%2 scribed. type 0654, It.F.T.1 (consisting of formers and trumpets is not shown in the pho- (WRITE PLAINLY AND FILL IN ALL LINES) L1, L2, and 1.3) ; tograph. 1

RADIO -CRAFT for OCTOBER, 1932 237 A LAPEL MICROPHONE (Continued front pape 210) or less current through the microphone, toc sound of the speaker's voice carried to the not only change the volume, but at the saune furthest corner. time flac pitch and quality of the sound im- Thus, simple as it seems is its final solu- pulses. This is important from the repro- tion, a vastly improved means has been given ducer's viewpoint. to the speaker for amplifying his voice and making Ills speech clear to every person in One Man Control the audience. As mend 'd In our first article, this lapel microphone can be operated independently from the maim controls by having is small con. 24 frol device in the pocket of the speaker. It is thus possible fur the speaker, from his own 22 location, to operate the output of the loud- 20 speakers without being compelled to remain le z near the amplifier unit. thus giving him o grislier freedom and making ti second man 16 s uuuecessil r3. 14 Considering the curves as shown In Figs. 2.t turd 211, be readily understood 12ó CLAROSTAT Replacement Volume Controls are it will that even if a resistor is itsed as a volume conical r "CustomMade" to exactly suit the receivers for 10 w which they are offered. Not a makeshift job nand a small variable resistor can be easily lot idea. placed 84 The resistance. taper shape and shaft are mad. in a box and carried in one of the according to the proper specifications. pockets n, not only can the volume be changed r1 There Is no delay in installing them. There ore voluntarily by the speaker, but in addition, no comebacks when you use CLAROSTAT product. 4 See the new CLAROSTAT CONTROL HAND- ne.auts are given to him to change the pitch BOOK AND CATALOG for 32 pages of dope for of his voice as may be necessary. 2 service men. Send for your FREE copy. in can nec't ion with the elect ro- acoustical 0 characteristics of this small microphone, it 10000 1.000 might be well mention to the fact that the f FREQUENCY IN KC. CLAROSTAT MFC.Co. quality of sound Is also Intl ueuced by the direc- tien ill which the current passes. It makes a 285-287 differeuee whether the current comes front the -B- N.6TH ST.BKLYN. NY. metal membrane to the carbon ;:rains or the 27 euutiary -the resin tam o .dia :teem with the di- 1111IIMM1111111111111111 26 tl..- - rection Ill witch iirrut tins 11111tril\hM111111111111 24 Taking Sound Curves 11111111111111M I 22 11 tn 111111111 111111IMI These cur yes 11:1, I' I leer made by exposing 20ó

the microphone t.. I h, sound of a loudspeaker I I111111111111M1 1111111eallIt 18W which was fed with the same amount of cur- 11111111111/ 1611 -LYNNoise rent at all frequencies. .t ft er the electrical Illl11llIN -Reducing Antenna Products impulses coming from the microphone are am- 11111111=1111111111== 14ó Solve the Interference Problem! plified by nn amplifier of practically linear L .,UY noise -free results on all weirs, lane P1111111111111 121.1.; ehararterlstics between 20 and 10.1100 eyries. 1111111111Y .rt alike. For the broadcast 11 stoner. the L4 -1 wave and television experimenter and the they are impressed upon n ureter. 11111 1111111/. 10Ñ "amateur." No serviceman sl Id be without These curves show clearly that the general these LYNCH Antenna Products which hale proved 11111iMI 1111111111\= e .heir ability. by test. to eliminate background transmitting microphone is less sensitive to racket. Ideal for suburbs as well as the most the general frequency range and almost ex- 11111111IIM 1111!! 6 ,. ingested city areas. Very shuttle to "hook -uii' clusively pitched to one single frequency which, 1111111111. any ref-riser. Better performance assured. 111111MII 4 in our case, is between 2.000 and :1,000 cycles. LYNCH Transposition Blocks 111111011=111111111M1111 2 Extremely durable. Made Id "l.ynrhIle". a new It nay be remarked that curve 1 of Fig. 3 material, recognized for Its great resistance and corresponds to a two- button microphone, while MIMI= 11111= 0 a natural freedom front electrical losses. 1.000 Handy Complete Kit of IO Blocks 52.50 curve 2 of the same figure is taken with only 0.000 LYNCH Cafe -Aerial Spreaders one button. .t II these curves have been actu- FREQUENCY IN KC. Great Pick -up qualities and freedom from direc- ally measured and are Independent of any that tional elm t. Also trade of 'Lynrhlle... Fig. 2 Handy Complete Kit of 10 S2.50 may have appeared in commercial publications. LYNCH "U. S. Navy Standard" Antenna Insulators Present electrical lots or leakage across the antenna insulators. Kit of 8 $3.00 The Amplifier LYNCH Commercial Antenna Insulators The polarized Patterned after the "U. S.' but for use where microphone has prongs so as PAGE the tensile strength of the "U. S, ' is not re- to make sure that the current flows through CRAFTSMAN'S quired. Kit of 8 $1.50 the microphone in the right direction. 'l'he (Continued front page 229) LYNCH "All -wave" Antenna Coupler Secures best passible results with tiny of then i.r- prongs are plugged in the control -box carried May I submit the following for your com- reducing antenna systems rernninended by x 51.50 in the pocket and connected from there to the ments ris well as for the thoughtful considera- SERVICENEN-40% from aims List Prices amplifier shown in Figs.4 and A. As may be Send order TODAY or write ¡or new, tion of tube manufacturers? seen, a concentrated illustrated and descriptive folder setup has made possible There are on the market today numerous re- the placement of the loudspeaker and the :di- ceiving be sure; filament and LYNCH MFG. CO.. Inc. 1775 -RC Byway.. N.Y.C. tubes, to the electric amplifying equipment In one easily heater voltages vary from 11/2 to 17i and in transportable carrying case. certain cases even more. In the earlier days The microphone part of the equipment is of "all electric" receivers a common (-Ouibiuu- attached at the upper left corner of the box. 11on of tubes In a set included a type '27 de- This equipment is small and has thus the tector, type '26 in the 11.F. and first .1.1'. advantage of easy transportability which stages, and sometimes two '26 tubes in push - means, for instance, that at an election talk. pull in the setmml .t.lv, stage ; f if indeed two the spin kir is able to have his public -address stages of transformer- coupled audio fregneney Radio Corporation's Exclusive system with hint, as if carrying at suit case. amplification did not round out the cumbfnat-

and operate I1 all by himself. Arriving at his Ilon : I : later on the '71 and '71A tubes cruse Replacement Parts pia CO of destina Dun tae simply pushes the plugs Into use in the output stage, Service Bureau In at the lúwer -right of the case and the To say, definitely. ris to I many sets there apparatus is ready for use, use '26 Complete stock for all models. Write work. are in today. that type tubes, is Figure 4 shows a wiring diagram of this beside the point : in any event there are thou- for free parts list. Service data amplifier. The rest ifiea tien of the current sands upon thousands of them. In addition available. takes place in two 'SI tubes. The input from there are thousands of engineers, experimenters, the microphone is first amplified by is screen- amateurs and Service Men who use tubes of United Radio Service Co. grid tube which is resistance coupled tu one the '26 type in some circuit or another. The -Warner Bros. Building Brunswick '45 tube. The latter Is coupled by is trans- burn feature, of course. has been the drawback 619 West 54th St. New York, N.Y. former to two power tubes of the 250 type tu the more universal use of this tube. Big discount to Dealers and Service Men which are wired in push-pull, the output of 11'ith rho advent. recently. of the types '56i which is fed over a transformer tu the loud- it lid indirect-beater tubes, which operate speaker in the case. with a s heater voltage of 21/2 mud with a cur- Instead of one loudspeaker being attached rent intensity of only one ampere, a forward sure read the announcement on Page Ile to to the carrying case, this amplifier can be un - stride has been made by our friends the tube 256 which tells about the 1933 Official Radio nected to a number of loudspeakers which can manufacturers. Service Manual. be distributed throughout the hall and the (Continued On pap0 245)

238 RADIO -CRAFT for OCTOBER, 1932 A. V. C. SYSTEMS (Continued front page 211) where a diode detector was followed by four ful the signal, the further to the right the WHAT YOU NEED stages of audio (including the output stage), needle will swing, anti vice versa. remi rked that if the efficiency were to be The meter may be placed in the common judged by the number of audio stages, It had cathode lend as shown. or it may he inserted to Is able to handle a high input. in the "It" common load of the plate supply. TO SUCCEED IN The manner of operation is simple. Refer- Another location Is In either the plate or ence to 11g. 3 will show that one side of the cathode lead of any one of the controlled tubes. tuned secondary coil is connected t o the anode While there is no objection to the use of a the other side Is connected to the cathode moving coil Instrument, one of the inexpensive through two resistors, the sane side of the repulsion type instruments Is usually used. coil is also bypassed to the cathode which is When a meter of this type Is used in the grounded to the chassis. Since the tube func- cathode circuit, It will he necessary to reduce tions as a rectifier, current can flow in only the resistance in the cathode circuit, by an RADIO one direction, from the anode to the cathode. amount equal to the resistance of the meter, The unrectified halt of the wave is bypassed to prevent the minimum bins from being in- through the small condenser Cl. just mentioned. creased to more than the rated 3 volts due to The rectified half of the wave (lows through the extra resistance of the instrument. The the two resistors developing a potential across meter shown in Fig. 4 requires 15 ma. for n them, which varies with the strength of the full -scale deflection: if it is desired to he used signal. One of these resistors (Re t is by- with only one tube, tt meter that will show a passed with a fairly large condenser (C2) and full -scale deflection with a current of about 5 Its voltage does not vary w nth the signal modu- ma. should be USIA. lation. This voltage is used to control the bias Thin shun Id offer an opportunity for the on the radio -frequency tubes. The other re- alert Service Man to pick up quite n few sistor (Itll has only n small condenser across ti,.1141 S. There are thousands of receivers in use it (Cl t serving as a radio -frequency bypass, t has t employ automatic- volume -control systems and the voltage across it varies with the nuadu- without a tuning meter. Most of the owners lation and is fed to the audio stage. 'l'he re- of these seta will be glad to have their sets sistor It2 serves to block radio- frequency cur- modernized by the addition of this device. rents and keep them out of the audio-frequency Alignment Procedure end Of the channel. Alignment procedure on receivers using .'u, V. The in the grid circuit of the potentiometer C. has puzzled n great many Service Men. serves dual purpose of a grid A.F. tube the Obviously, an output meter cannot la used, be- Courtrai/ of the National Broadcasting Company leak and a volume -level control. So far now, cause if at powerful signal is applied. the A. a constant signal level we have shown that keeps at same level regardless of said about how V. t'. it the RADIO is a highly specialized business. As was maintained but have little ordinary adjustment of the trimmers. It is great this level was: usually. It is equal to it is becoming more exacting possible to align a receiver by car, using a it develops the maximum power that the output stage can signal too weak to operate the a u toast is vulture in its demands. But radio is the modern handle. Since is very seldom that such high it control, but this method is notoriously inaccur- volume is required, some means of reducing it field of opportunity for those who keep ate. If the receiver is equipped with a tuning must be employed. To achieve this end. one meter simply adjust for nun ximum swing of the step with its progress and pioneer in its of the familiar types of A.F. volume control needle. If a tuning meter is not used, it will opportunities! systems are used. This applies any desired the stage, be necessary to insert a milliammeter in portion of the total output to the output of one of the controlled tubes is for trained men set level. It is plate circuit There a great need and when it in fur any desired adjust compensators until it shows for all stations. The only excep- aid the in the radio industry. There is no place maintained minimutn current. In some cases it will be being those too weak to produce the tions found that one of the trimmers does not affect for untrained men. Experience must be normal output when a state of maximum sensi- t when control tube exists. lie mete'. This occurs the accompanied by technical knowledge. tivity coupled to the plate of the last It. F. tube, Another type of volume -level control is shown is and the condenser that does not n Rost the A pioneer in home study, the Interna- Fig, 4, which consists of a variable resistor in tuning meter tunes the input to the detector. across secondary of the input transformer. tional Correspondence Schools have kept the It will be necessary to use an output meter pace with the times and offer courses pre- The Tuning Meter to accurately adjust this one, or it may be adjusted by ear ; In most cases this is sufficiently pared by authorities, which give practical The tuning meter shown in Fig. 4 is merely accurate. instruction in fundamentals and latest de- a mil lin mmeter mount .41 upside down. It is It is hoped that this article will clear up mounted in this manner so that as resonance some of the mystery that shrouds the viol, velopments alike. The courses were pre- la approached and the bias applied to the con- subject of nutomnt is volume cuntruth utniI that pared and are constantly revised by the some readers of this article will fi 'i trolled tubes begins to Increase. with a conse- of the Who's Who of quent reduction of plate current, the needle like tackling the job of building an automatic Radio! Thus, reauntinre is volume control into their next receiver. will swing to the right. Composed of 24 basic divisions, the Cont. indicated by the point of maximum deflection. If any points lune not been made sufficiently it also gives some Indication of the strength dear I will try to answer any letter in which plete Radio Course is designed to give of the signal being received, for the more power- it stamped, self- addressed envelope is enclosed. thorough instruction in the whole field of radio. The I. C. S. Radio Servicing Course was prepared specially for men who wish i RECEIVER A MODERN REFLEX to become service experts. Study of it mq rvl fron page 212) makes possible leadership over competi- other Two uni -mf. tpp,. 1430 Aerovox Mien Con- grid terminal is the one isol,,t..l from tie tion. The I. C. S. Radio Operating Course f four. Looking at the socket from the underside drnwrs. 3. 22 and working clockwise from the grid terminal. I Inv .\trnr.ix Mica Condenser, .00013-111 f., type is vital to mastery of operating and the other terminals are cathode, filament, file- 1431), Is transmitting. ment. and plate. respectively. une Aert, vox Metal Case Resistor, .1 -m f., type After the wiring is completed and checked, 260. 10; We will he pleased to send you details One Metal Case Resistors. .1- the only adjustments necessary are at the trim- Aerovox Duplex of any or all of these subjects. Just mark mer condensers, 7A and 17A. nit. each section, type 260 -21, 14, 9; 'l'he Thre Tube Reflex Is amply selective. lins One Aerovox Metal Case Resistor. .3 -mf.. type and mail the coupon -the information will enormous volume and has remarkably tine tone 260, 21; be forwarded without delay. Why not do it quality. It should be used with a high quai- One Aerovox Dry Electrolytic Condenser, 10 today-now! ity dynamic speaker to realize its maximum ni f. type E30 -10 with mounting ring, 211; pussl611fties. Two Aerovox Ilry Electrolytic Condensers, 4 ntf.. type -4 with mounting rings. 23, 23.'i : 'l'op and bottom layout views may be secured l.. INTERNATIONAL CdRRESPONDENCE SCHOOLS merely for the mailing costs---3 cents. Two Find -all it. F. Coils, 6, 15; Two 'rimiest R. P. Chokes, S milli henries, type Box 6676, Scranton, Pa. List of Parts 2111oio0, 2, 20; Without costar obligation please tell nie all One Cardwell I1u:t1 Variable Condenser, .00035- One Trutest Power Supply Transformer, 1)e- the NEW RADIO COURSE Inf. each section. type 217 -1'. 7, 17; Luxe Model, type 2C- 1512. 31; One Ei,s'ttad 'Papered Potentiometer, type RI- Throe 'Protest 4 -prong wafer -type sockets. 2s. Name 4m 240-P, l'_' with switch. 33; 26; Street Address Two Electra,' flexible I: rid Resistors, 200 Two' Trutest 5 -prong wafer -type sockets, 4. ulnas. 3. 11 : 23; City Stare One Electra(' 1500-ohm Flexible Resistor, type One Trutest 6 -prong wafer -type socket 10; If vo reside in Canada, send this catpun to the In. 2r, I-ou0. 30: (Co/00ted on page 2301 ternati.nad Correspondence Schools Canadian, f.a1., 1f,nv,a1. (.,nudes

RADIO -CRAFT for OCTOBER, 1932 239 TUNING METERS "The

;dance sums to contradict the statement made Television preciously. If it is recalled that the fundamental func- Experimenters' tion of any A.V.C. system is to increase the New Edition Containing 100 Pages sensitivity of the amplifier for weak signals and decrease it for strong signals, the reason Magazine" for the connection becomes apparent. (See A -C RADIO! the article on -1.V.C. in this Issue.) To decrease the sensitivity of an amplifier, either We're glad to send a set to your one of two methods are employed: (1) increase NOW 25c A COPY home to examine and use as FLEXIBLE the control -grid bins when variable-mu tubes your own for 10 days show MAROON -to are used, and (21 lower screen you that here Is the most up-to- 8 VOLUMES the -grill po- date and complete work on Elec- 4300 pages, 3200 tential if non- varlable-mu tubes are used. tricity ever illustrations, deluxe published. Written gold stamped binding. Either melhtad of control reduces the plate by CIROCKER of Columbia D. Index in each book. current tlowvi ug in the amplifier stages con- -311LLIEAN of Calif. "Tech." general Index In Vol. nected in the A.V.C. circuit as the applied sig- -HARRISON of General Elec- 8. (*insert everY sub- tric and 26 other nosed Elec- ject in Elertrlcltr- nal incre ases. 'i'his decrease in plate current- trical Engineers. Starts off with Light. Power. Trans- reduces the reading of the D.C. meter which ÉLEYIS1pì Generators, elementary Electricity In simple. mission. is connected in the plate circuit of those tubes non-technical language for the Motors, Sei trhbaads, R News beginner Radio, Telephone. und furthermore. the greater the signal strength and includes every Wiring. Engineering branch for use of House ltail- the more the A.V.C. action reduces the plate experte on the jii,. current and the less the meter reads. This explains why the tuning meter reads full settle Complete Electrical Reading Course with 00 signal and reads less as the signal Increases. Electricity. the biggest industry in the world, continues III grow the host rapidly. And it offers better jobs, Regardless of the system used, let us suppose bigger salaries) and a brighter future than any other for the instant that we are turning the dial lieht. Every dollar, every hour invested in Elec- learning of a radio tricity will come back to you a thousand -fold. Learn in set equipped with no tuning noter. spare time vsi th these books at As we mounted' 'the extremity of the side band one -fifth the od of trade of a carrier. very little action results, but as courses. Online t for LOOK IT UP! organized soon Timonuds of the ;0 study. quiz -quest tons and a as we reeeh'e an appreciable signal Wile sets are used as REF- Year's free c nsulting member- signal voltage necessary for action varies with ERENCE books by ship in the v American Terhni- different reneiversi the current through men employed In ra1 so,i ety included without the lctrical, building extra east. if joss mall coupon tuning meter decreases and therefore the me- construction und al- iLolle hate], ter reads less. When we reach the peak of the lied lines. The JIFFY sigoal, the meter INDEX puts the AMERICAN TECHNICAL rends u very low Value which answers to 220.000 SOCIETY increases 0:4 we pass exact resonance. The at Dept. E -626 , lori lions right lowest rending of the ni.'t PI' Drexel Ave. 8. 58th St., Chicago represents the best your finger tips. setting of the dial far that particular station. If the meter Is connected In the plate cir- 0010101 cuit q.w.. WV* :.wrr 00..0.4 nn,..r, e,o.,o of the detector, the best position of the s,r..aa Is AppIM' ARdad Wed tuning dial indicated by the greatest reading GREATEST MAGAZINE Wieed' tgpMO. rtpltl. Arpla( Asdad btmipll EltcbkAl p tzd/ Retinae E,- of the tuning meter as explained above. IN TELEVISION lets rett DOM Bed* . .. y ,a W *LS 10 w Various Forms of Tuning Meters T MELT developments In radio's latest wonder. It a ti i , i... ! vns....,. Teles!slot, are published in every Issue of ** It is not necessary ` raÉ % to have a milli:unmetet' TELEVISION NEWS -Mr. Hugo Gernsback'.s lat- ..= .r. r..... ,v., --,....19 n.n. connected in the plate circuit in order to have est magazine. Rapid ash ancement In this art í a toning meter. 'l''e 'l'une -.\ -Lite described today is becoming a repetititn of the radio cycle of years ago. Daily bnredrasts are be- in the November, 1931 issue of (his magazine coming more numerous and experimenters aro AMERICAN TECHNICAL SOCIETY is an example of a so-called visual tuning me- following In quirk order In building television Dept. Drexel Ave. & 58th St.. Chicago ter. This particular device consists of a glass sets for experimental purposes. Foresight of its Please send for IO lays' free trial 8- volume set of Electrical deselepment ran be seen by ' the of Dube pioneers Engineering lust off the press, subject to return if I wish filled with neon gas and two electrodes. radio-they are equipping themselves now with to. (I pay the few cents express charges on receipt of It is connected in the same manner as a milli- tetes!shin experience. books, you pay express If returned.) If t deride to keep The ankles published in 'TELEVISION NEWS 10 days then 8:1.00 a ammeter would be connected. As signal them, I will pay $2.00 after trial, the are of primary importenee to experimenters- month until $31.89, special advertising price, Is paid, I arreases, t gas ionizes, but in this device Year's Consulting they are simple In construction, understandable after which books become my property. t of gird replete with Membership to be Included free. the Iirigh the ionized loyer s'a lies. This diagrams, photographs and device is used in sotte tommemial receivers Illustrations. Name and limy also be .secured separately. Articles in the Address Interesting Current Issue The Tuning Meter as a Trouble Indicator Television In Europe. Employed by Sight and Sound Broadcasting on One \W'aselensth. .\side from the obv' s advantages of the Vlsin- Telephony In France. Employer's Address tuning melee as an indienting device, it may Automatic Synchronization. be used, Tole, !sing the English Derby. with a little thought. no n 11',0lble A Two Way Cathode Ray Tube, indicator. If the A.V.C. II be of a receiver Controlling light oath Metal Films, You Can Become a Fast, Capable be 'vows-ed. the reading of the meter will not Tells !slim by the line Control Method. Ices sew of High Frequency Rereiser change as the SI reugl h of the applied signal Design. at Home .4 Simple Mirror Drum Scanner, RADIO OPERATOR changes, Thus the rending of the meter is A Highly Arcurate lens Scanner. an indication of the condition of the A.Y.C. Pointers on lens Dir )Design. A Neat Hanse Slade Teievisar. "Passed notateur exam - circuit. An Amateur Televiolon Tranaultter. CANDLER with 3rd lesson. " -E. -\ poor tube in the .\.V.C, be M1111er, Toledo, Ills. circuit my determined by Scientific Method "Studied 11 hours. can tuning -in stations of varying a w. ti. m. -E. J. intensity and noting the ehanze in volume. If In less than the usual time a ri., Chicago. there Is at SPECIAL you can get amazing results. raclent different, in the volume of Thousands of last Radio operai n taught by two loud stations, then the .\.\".I', tube is not CANDLER. FREE advice if yo 're "stuck." fuuI ion in g. I l owe ver. the method outlined AN questions answered personal Y. No obli- OFFER gation. If you are now a Radio operator ask above is far more efficient. If, upon test. the about ADVANCED COURSE fo SPEED and A.V.C. tube is found to be in good condition, COUPON Copying Behind, and "MILL" Course. FREE but the BOOK will save you time and money. Tune tuning meter does not function prop- in on Candler Short Wave Slat an erly. In all probability the resistors in the CANDLER SYSTEM CO., Dept. 47 A.V.C. circuit are defective and should he TELEVISION NEWS RC -10.32 6343 So. Kedrle Ave. Chicago, I II. tested. 100 Park Place, New York, N. Y. Ranges of Tuning Meters E i As per your Special Offer, I enclose here - World's Only Code Specialist ,,ids $1.25 ICanada and foreign $1.501 fer whis l, Although tuning meters are simply milliam- liter my subscription to TELEVISION NEWS meters b'r One )'ear. You will also send me FREE the used In a particular manner, neverthe- last TheRADOEEK CO two issues. 1 understand that the regular less meters are made especially for this purpose ,ate for such a subscription is $2.00. eREE/ 110 Canal Station usually having an inverted scale as shown in I 1 ]tall me satoldo copy of TELEVISION the photograph. When used in plate cir- NEWS fur which I enclose 15c (U. S. Stamps the wr coin accepted). Chicago, III. cuit of n power detector, the range of the me- Our new 1932 Radio Service- ter used should the about 5 nin, If the pointer Name man's Wholesale Price Guide swings off scale, then n shunt is necessary. be sent you upon 5 idress will to llowever, with n 5 mn. scale no using letter- shunts will request. Write, your be head or business card. Send for it today. usually required. State Won/blued on gage 250)

240 RADIO -CRAFT for OCTOBER, 1932 INTERESTING LOUDSPEAKER FACTS c'ontinucd from pato 21a4 that the amplitude of each resonant position matches the cone. This size cone is well able Service Men is proportional or equal to the necessary and to handle up to about 12 decibels with good required values. response. For greater power levels the cone should Im increased in size to about 22 inches. Case Design In the dynamic type loudspeaker it is not necessary to use such a large cone to get good TAKE NOTICE Much progress has been made in the design response the chief reason Is of low -frequency and of aperiodic cones from which the majority that the action of this type of speaker is dif- resonant positions have been eliminated. This ferent than that of the magnetic. In Ile mag- J. R. Williams, E.E.,° originator Jost - is the opposite extreme from that men netic the teed supplies the toot ire power to the and designer of such service instru- ti 'd; for in this case, all possible things crone, whereas in the dyna lute the rune Is pushed are ments as the Supreme Diagnometer, that might possibly cause resonant positions such a manner as to actually pump air. This was in Confidence English Reading Tube etu'efully eliminated. .\ fete year's ago it feature in itself would not he especially ad- quite common to hear a distinct and annoying vantageous were not for the greater ampb- Tester, etc., etc., is preparing com- loud- if it paper rattle in the majority of cone tude through which the dynamic speaker moves plete and minute details on the con- speakers. Analysis showed that the seam in in comparison to that of the magnetic. The was struction and use of all types of the cone where the cone was glued together direction of movement of the powerizer in Valeta why this mostly new one of the most important reasons type of speaker is also different. The reel to service equipment - tattle was prevalent. Therefore an expensive the mngiietie speaker actuates the cone with inventions. Nothing left out. Meas- process was developed that pressed the entire Fig. 3. In the This a flexing or sweeping movement, urement drawings and d e t a i l e d c ohs out of a siitgl piece of ma terlal. dynamic speaker, the voice coil is in a constant caused construction. Immediately eliminated the resonance magnetic field and the varal t sun in flux caused speakers by the setup and almost all cones in by the signal in the voice coil produces motor Within the next few months there today are made in this manner. action in accordance with Lenz's Law. The will be such releases as Condenser It was also found that the kind of material voice coil, is either sucked into the on therefore, Leakage Tester, English used In the cone itself had a direct bearing field or repelled outwards. 'i'hus the cone Itself Dielectric used the number of resonant positions. Metals follows the pulsations of the voice Boil and the Reading Tube Tester, "Resonator," a responded better as dia phra guts almost always emanating sound is produced through n piston- new method for peaking and align- on the highs than on the lows and therefore like action. The amplitude is so great its to amount ing, etc. resulted in a "tiny" response. AIsii the produce a much larger anoint of displaced air of resonance was high so that Ills is undoubted- than that which would he obtained with the You get this for $2.00 a year. not used ly the reason why metal cones are wine size come in the magnetic type of loud- Many months of research and de- today. It was found that a comparatively dead speaker. sign behind each release and you substance was the best thing if It could be lu conjunction with this more efficient are made into a substance hard enough to use. The method of radiation, the normal and usual will save over $2.00 on each and research departments of various organizations impedance of the voice coil is such as to place every construction. set to work, and now one of the best cones Is the speaker in the low impedance category. bag will receive detailed construc- that made from ordinary burlap material. This means that it is possible to connect the You cone It was also found that corrugating the volee coil directly to a transmission line and tion data on complete large Central had a direct effect on the response character- transmit the necessary energy to the speaker Service Station Test Boards. In fact, istic obtainable, and although this Is still a over this line without a worry about crosstalk you will receive one release after question of dispute, it is generally agreed that if more than one or two linos are used in the corrugation does materially aid the tone qual- same cable or run in the same conduit and another in such complete and concise ity, hut the main questions are, where. how operated at similar volume levels. detail you will be equipped with all much, and what shape? Even the wire used The principal reason why the dynamic necessary knowledge and drawings to on the voice coil of the dynamic speaker af- speaker has become so universally prominent and finest of all radio fects the response characteristic. The wire and well liked, is undoubtedly due to the low build the latest used in this coil is usually wound on the coil variation in impedance with frequency varia- test equipment. form and is of copper. Recently, experiments tion. This would sound as unconnected as the a have been made in which the wire is aluminum street All of this for $2.00 year. well -known chicken walking across the of and is molded directly on the form. It has because it wanted to get on the other side, yet You will know the problems boon fo I that a light metal is good but in- both reasons are quite correct and exact. each device. Nothing to guess about. creases the hissing type of background noises. The impedance of the usual magnetic speaker The first release of an English Read- The aluminum just mentioned has been used at 1,11(10 cycles is roughly about 7,500 ohms ing Tube Tester with all latest tubes quite successfully. (Fig. 4). The impedance of this same speaker The size of the cone used on any type of at 0000 cycles may be as high. if not higher. is ready for distribution. Way ahead speaker is of major importance. If we sot than 47.00(1 ohms! Can you imagine design- of anything. Next comes a real con- of a speaker into vibration the reed magnetic ing a matihing transformer or similar device tinuity tester and condenser leakage without any cote or load connected to it, then In exactly that will also vary its impedance guess work as information it most certainly would be badly imde'lon del. the same manner as the speaker? In order to tester. No Due to the small amplitude through which the produce linear response the matching trans- is complete. reed motes there would be practically no air former would have to do just that. displaced and no sound of any cumsequence (In the other hand the dynamic speaker has II would be hearth If a c were applied only a very IOW impedance variation over the Send your $2.00 now to to the reed, it would still be uuderloadcd and frequency spectrum. At 1,0(10 cycles its im- there would be no low frequencies. .ts the size polnnce is about 14 ohms (Fig. 41, while at J. R. WILLIAMS AND SONS, of the cone is Increased, the air displaced will 0.1111(1 cycles the impedance rises to approxi- also increase and with it the low frequencies. mately 40 ohms -this is certainly different from 519 Palm Street Now. if an extremely large cone were used that of the magnetic speaker. It is fairly then because the fundamental frequency of the easy to design at matching transformer that Little Rock Arkansas cone is lowered with the increase in the size of will operate within these limits. Of course the cone, and also because of the inherent in- there is the matter of the irun in the speaker too much energy will `Chief Engineer, Apparatus Design Company. ertia of the cone itself, being at little different than that of the trans- be extended in the lower frequencies with the former, but in the dynamic type of speaker result that the higher frequencies will be over- the transformer will only mismatch within n shadowed. few ohms of the actual true value while in What, then, must we do to obtain a balanced the magnetic speaker the transformer may response? The answer is that we must match mismatch by several thousand ohms on the the acoustic impedance of the cone to that of high- frequency end. Due to the iron influenc- the reed. This is done in most cases by tho ing the inductance of the speaker windings cone Is used law of trial and error. A large and also 1114. inductance of the transformers in conjunction with a long reed. A series of and thereby. in turn, affecting the impedanco. reed is J v .t NI PERITE response tests are made and then the it is sell that a perfect match is made shortened. More tests are made with different improves radio; pro- between the magnetic speaker output matching tects parts. A mone- nctker for the haw of and error combinations until trial t rauisfornler and the speaker into which it is Service Men. Send $1.40 to Dept. has definitely proved to the individual conduct- working. 'l'hus this is one gn:n handicap that RC -10 for dealers' sample and ing the test just which combination gives the is not present with the dya :unil' speaker. .cales brlps. best response. Ilistpcnrizairserstisn The amount of energy to he radiated also The Use of Baffles n61 e.OSawAV. tow rate lins a direct bearing on the size of the cone. If we have a condition where only n small room Let us assume that all the necessary re- is to be supplied. then a cone of about 14 to 18 quirements have been complied with and now inches in diameter will supply a pleasing and are desire to Install our equipment in various Self-Adjusting natural sound provided, of course, that the locations. The first thing to consider is the LTAGE CONTROL motor unit is well designed and the reed fact that our low -frequency response will de-

RADIO-CRAFT f o r OCTOBER, 1 9 3 2 241 pond directly on the size of the baffle that must be used in conjunction with our loudspeakers. The New POWERIZER Perhaps one wonders just why a baffle is so igood name necessary in order to obtain good low -frequency MICROMIKE response. Baffling is by no means a new idea, for for Public Address Systems as early as 1808, Lord Rayleigh, one of the most proficient of the old masters, showed, A -ALO and Home Recording by The MICROMIKE is a very sensi- in an extremely interesting experiment, tat radio ' tise, precision -built microphone, small preventing the air on one side of a tuning in sire and weight - easily circulating with that of the other and quickly fastened to the fork from clothing. This MIKE when side, the Intensity of the sound from the tun- Send stamps for charts showing attached. permits tom - ing fork could be tremendously increased. Con- f plete freedom of litote- adapters to use with different makes ment and expression. sider Fig. 5 .1s the tuning fork moves Simply attached by a towards "B, " the pressure of the air In this of testing equipment for testing all thin. flexible. 13 too' will be increased. .1t the same time - twisted cord which i- direction the new tubes, including 55-85-57-58 s "A" will be decreased due to run to connector. the pressure at 82- G- 2- 41.421Wunderlich and the new small "Mlkout rol" I of the fork in the connected between the the displacement tuning amplifier and the direction of 'B." Thus there will he created seven prong tubes. MICRO311KE - It can aaaa.a6 a difference of pressure between ".1" and "B-' be hidden in the pocket 104 . ' of higher pressure will move and controlled by hand. and the air the The 311CRO31IKE is quirk - to that of the lower, or the silr at 'B" will ALDEN MFG. COMPANY Iy adopted by educators, l ub- ".1." Now this movement of air Ile speakers and entertainers. move to BROCKTON Dept. R. MASS. It is not a toy microphone. Front View from ".1" to "It" is spoken of as the "Lateral but is extremely practical. It Motion of the Air." has a stretched alloy dlaphra gut, and Is gold-plated- finished In opal silver. Constructed to meet rigid tests. Lord Rayleigh found that by placing a piece Furnished with fastening clip. P+nubined with the of ca r(lboa Ili in such is position so as to pre- DRUM DIAL CABLES -a "Powerizer," the MICROMIKE makes an ideal portable sound outfit. vent the lateral motion of the air, the 42 strand genuine phosphor bronze PORTABLE PUBLIC ADDRESS SYSTEM from the tuning fork writs Brea tly increased. with Portable Powerizer PT-32, umoidete with 311rrumIke Lord Rayleigh, however, was not alone in his SPECIAL LOW PRICE Mikontrol and all tubes $96.00 most of Mleromike, $12.50 Mikontrol $3.50 experiments for, as n matter of fact. We stock at all times or will make MICROMIKE and 511KUNTROL sent prepaid to ally Part his work was based on the results of the ex- for you ANY DRUM DIAL CABLE of U.S.A. upon reel ill of trie, l'OM.:ItUAI:It Portable of the late Professor Stokes. To Address Syst ern sill tined anywhere in this annum' upon periments FOR 8 CENTS EACH receipt of $10,00 deposit, balance C.O.U. Guaranteed for indicate the importance of the elimination of 90 days. the lateral motion, Professor Stokes estimated DRUM DIAL CABLE WIRE Send for our bulletins covering portable and permanent that in connection with middle "C" of the Twisted 11/, cents per foot public address and central radio systems. out- piano. It world be possible to increase the Braided 1 cent per foot RADIO RECEPTOR CO., Inc. put -1(1,111)11 times by the complete elimination Send for samples and 106 Seventh Ave. New York, N. Y. of the lateral motion of the air, thereby causing the air in front of the unaided string to catalog sheets travel in a thin strip. PEERLESS RADIO PARTS CO. The above however dares not explain why it Amateur and is necessary to have a baffle for gaud low fre- Box 264 gncncy response. However, it Is the preven- Wilkes Barre Pennsylvania FREE Servicemen's tion of the lateral motion of the air that brings in those deep lows that are so hard Wholesale Guide to obtain. Hot off the press! Chock full of everything for Referring to Fig, G in which is shown the of the latest curves of various frequencies. the Radio Serviceman, Ama- radiation the S. GERNSBACK'S teur, Experimenter. Detailed viz; high. medium and low. It will be noticed illustrations; vital and ins t- that the very high frequencies are projected ing facts. Valuable tips that mean money in the form of a beam while, as the frequency RADIO in your pocket. Is decreased, the angle of cad ht lion bee, lows Astonishing Lon, Wholesale Prices larger until the very low frequencies the Hundreds of "Hot Shot" bargains at deep at ENCYCLOPEDIA waves literally. "creep a eon ud the a Now cut prices that challenge all America. What the WRITE TODAY -A free copy of this the erne is similar to the tuning fork shown New Second Edition Radio record smashing book is ready for you. Write in l'ig, :, in that it vibrates between two Encyclopedia Gives You for it today! points. If a signal of any frequency is gen- It gives you an explanation of every word BURS MIN-APPLEBEECOMPANY erated by the 1-1,11i', it will mdse first in is used In radio. I I," l'e direction towards The Itressll at "It- 2,201 RADIO DEFINITIONS will be increased while that at "A" will be 1,253 TECHNICAL decreased. Sound travels at 1,10u feet per ILLUSTRATIONS second. The wn ve genera tad by the movement 34 TABLES AND CHARTS towards "It" will therefore travel at 1,1011 24 PAGES OF APPENDIX feet per secohd in either n beam, is short angle Red Morocco- Keratol Flexible Binding or else will move around the face of the cone Printed on strong ledger paper, Loose-Leaf depending on whether the frequency- is high, Arrangement ri,91131110EAfdib:4:31111a>

242 RADIO-CRAFT for OCTOBER, 1 932 A. F. CHOKE DESIGN (Confin Jroot page 21J Order a set of the NEW ductance of a transformer or choke. The factor in time neighborhood of 30 henries for all u,.P. is defined as being equal to pit /,111 or normal values of D.C. flux and which will at CENTRALAB the increment in 11 divided by the corresponding the same time lend itself to an economical increment in II for a given .a,t', flux. It may be design in so far as DA'. resistance is concerned Motor Radio Suppressors readily seen that the value for u,.,.. is something may be achieved around the EI -11 lamination quite different from the arithmetical value for u of the Lamination Stamping Company (located Today! obtained from the original It /II curve. This at Brackenridge, l'a.) value is not really a constant as it varies over The dimensions of this core are as shown in a range of A.C. flux densities. The relation Fig. 2. 'rile characteristics of a core having to the A.C. flux is shown in Fig. 11) for a square cross- section are as follows: two values of D.C. magnetizing force. These Window aura. values are for a particular core material and Volume. 4.03 cu, in.: are consequently not for design purposes. ('ore weigh. 1.1 :1 lbs. : With u,., determined for a given D.C. flux Area. 4.94 sq. cm. or .7116-sq. in.: density the inductance of the winding may Length of path. 15.61 cm. or 6.13 in. the equation. Winding data from the charts is based on be calculated from of size 4 pi A N2 the use of enamel wire the indicated and with glassine paper between layers- The L- ends of windings should be straightened 10 x 1 with pieces of fiber and the core itself should It will be noted in Fig, 11) that the value Ito protected with several layers of brown increases slightly for the higher values paper. of A.C. flux density but the increase has the In forming the windings a piece of wood effect of slightly adding to the inductance of should be cut to slightly less than the core in its wrapped with one layer of for the NEW Centralab Suppressors are actually the winding and is therefore beneficial dimensions and 50x. to 5O0ci more efficient in reducing spark effect except where sharply tuned circuits an' string. After winding. this string may be noise than the average suppressor. out coil removed fr the involved. pulled and the The generous 1 ' ," of resistance material is baked If an air -gap be provided in magnetic core wool form. The values for the air -gap given at a temperature of 2700 degrees with its cerami: the D.C. flux den sit p Will fall off but an in- in the chart refer to the total gap and in the jacket; both together forming solid granite -like crease in the A.('. permeability will obtain. case of EI laminations the gap at the center unit. Simplicity itself! this very simplicity makes possible an un- There Is an optimum satin,. for this relation and in each leg should Ire just half the en l ue And of the Any machinist will lend usually LOW price. Order a set today . one which depends upon the characteristics the rend from chart, for each spark plug plus one for the distributor. particular iron chosen for the core material. you a micrometer to assist in building up That is to say : for some length of air -gap,- wafers of paper or of fiber to insert in the for some substitution of a material having unit legs. The holes provided in the core offer permeability for n portion of the magnetic ready means far mounting and for clamping path the A.C. permeability will be at a maxi- in position by means of iron or brass straps Retail Price Your Price mum. Not only this. but the D.C. flux density in methods which will readily suggest them- Set of 5 for may be varied over a wide range with but selves to the experimenter. 4 cylinder car $2.00$1.10 net of wind- in charts may slight effect upon the inductance the Variations from the data the Set of 7 for ing. be achieved by varying the "stack" of the 6 cylinder car.__ 2.75 1.50 net In most A.F. transformers a certain per- laminations. l'or double the stack (2 x .C75- of -gap is necessary (although It is in.1 the inductance will be doubled for a given Set of 9 for centage air 8 cylinder car.... 3.50 1.90 net provided In the case of the highest quality current density and number of turns: while transformers only). The air -gap may be dis- the resistance of the windings will be increased) pensed with only when the D.C. flux density by hot one -third. For one -half the stack speci- is at zero through time use of parallel feed fied. the inductance will he halved; and the systems. In push -pull transformers the D.C. resistance will be reduced by about 16 percent. components are assumed to cancel but there type We may thus achieve with this single RADIO LABORATORIES are high values of A.C. in the core and a of lamination any value of inductance up to CENTRAL certain amount of D.C. is always present due 60 liv with I/,('.: or up to over 200 henries to tube irregularities so that an air -gap is where no D.C. is employed. The core material 930 E. Keefe Ave. Milwaukee, Wis. still essential to an economical design. employed In calculating the charts was Alle- In order to offer a series of chokes for the gheny Super Dynamo I ; rade Steel Sheets and average experimenter to construct with a full the calculations are based on the assumption knowledge of characteristics that will the that 1 volt of A.I'. is superimposed on the obtain it is first necessary that a particular D.C.: for high A.C. flux densities a slightly lamination be chosen rr)ricl, will be area liable higher inductance will prevail. to him. A core form which will offer a range : \s an example. let us suppose. that we desire a choke having an lnductnnee of 20 henries at a current of 720 ma. on the core specified. moo ANYONE PAW H O PROVES THAT THIS IS Tracing through from the 20 henry line at the not the actual photo of myself left edge of the curve we find that this cuts showing my superb physique the 120 na. line at 6.700 turns. We find from You cannot posslbiq and how the Ross System has wire Increased me own height to the wire size- resistance curve. that the IDlu tobe without this fi ft. 3 3 -4 Inches. Hundreds of No. 35 size for this number turns is enamel: valuable book It is not of Testimonials. Clients un and the resistance of the choke will be lust to 45 years old gain from I to First In (307 that another CAUfo6 -11 if indeed 8 inches in a few weekst Furst To -day 1.100 ohms. Ender these conditions the second -gap is al .045 -in. LIAR ARIE ENCYCLOPEDIAofThe RADIO INDUSTRY No Aaslianees -Nn Drugs -No Dieting. ROSS chart shows that the air t SYSTEM NEVER FAILS. Fee Ten Dollars Cool. This means that .0225-in. of insulating material WHOLESALE PRICES plate. (convincing Test bonny and Pan !rulers 6 will be required in each leg of the choke core. cent st amp. ".allow time for return mails srn.n the Atlantic." G. MALCOLM ROSS, Height Speelallst, Now. an efficient choke should not have a All that is New in Radio is Listed (P. 0. Box IS). Scarborough, England. resistance so high as this unless designed for in this 100 -Page Money -Saving n specific purpose -for instance, let us sup- Autocrat Auto Radio $17.45 pose that it receiver employing as 2,500-alms 1932 FALL EDITION CATALOG 6 TUBE Complete less dy-namie field in its filter system most he WE ARE HEADQUARTERS FOR 175 to 550 Meters "B" Batteries with external speaker desire But Plus Tax used an and we illutai- to repine° the original speaker field with a Public Address Ampli- Complete accessories include mounting brackets, choke. In this case we would work backrrgndx nated dial. Lek raviteh, rems( e control, dymmnie streaker. fiers and Installations n RCA (Ll sr. t Tubes. spark stioniessors, and antenna. from the specifications that our choke must Everything except "It" Batteries. small and compact 5 " have n 2.500 -ohnt resistance On the basis of You Pay ONE PROFIT! Purchase Direct unties. No x Crere " x si.4 ". Distance range 100 to Iona economy. From the Manufacturer! Our Amazing Low rats log available. Send 52.00 deposit. Balance C.O.D. let us see what we can do with our Quotations Will Astound You! AUTOCRAT RADIO CO., Dept. R.C. choke design in order to reduce the resistance. It will par you to trade exclusively with 3855 N. Hamilton Ave. Chicago. 111. As we noted before. increasing the height the house of "Coast-to- Coast" . write for of the core stack by 100q ineren ses the in- your copy of our /ere catalog today! ductance of any form of winding by a like SERVICEMEN -DEALERS degree, On the basis of a square stark we ;OA T1/ `Q 5T Write for our Catalogue start with an inductance of 10 henries at 1 20 í1a)010 '. n1 Complete Stock of NEW ma. This calls for 5.000 turns of No. ::3 wire. `4 oxroaca zap# Radio Replacement Parts a total resistance of 450 ohms. Increasing the Hard to Get Parts-We have them. Send us stack by 100% likewise increased the resistance your repair work for estimate. by one -third. Our total resistance is therefore Grant Radio Laboratories 600 ohms. Reference to the second chart indi- 6521 -C South Ilalsted St., Chicago, Ill. cates a total air -gap of .035 in. or .0175 -in. 123R West 1711St, NewYorkN.Y. i i in each leg.

RADIO -CRAFT for OCTOBER, 1932 243 SEND NO MONEY-- Clip and mail to us the coupon below. We will send you either one or both books through the Express Company for your inspection. You have the privilege of keeping or returning them. If iliiii want to hare a complete set of all Radio Diagrams. both manuals should be in your file. Both volumes of the OFFICIAL RADIO SERVICE MANUAL will give you the most complete set of circuit diagrams ever published for the Radio In- dustry. Every Radio Service Man and Dealer should have them available for immediate use in his business. Professional set -builders and amateurs will find them instructive and helpful.

Briefly outlined below are the "high spots" Get Supplements FREE with the that are to be found in the 1931 Manual - the first complete radio service manual NEW 1932 MANUAL ever to be published. Over twenty-seven There is so much new material in this Manual, that thousand copies of this edition were sold a Service Man or deader would be Inst without it when called to service a set. Information about new model. to members of the radio industry. This which have been on the market only a few weeks are assures you of its importance to those en- contained in this book. The 1932 Manual makes tho gaged in radio and how valuable it is to service kit complete. then[. The 1932 Manual contains a Full Radin Service (;uid and a Complete I)irectory of all 1931 -1932 Ratti, Diagrams. also models of older design. Everyone is Partial Contents the Radio business should have a copy. Send for your. Edition today: Iblurnr 1, 1Y31 Wiring diagrams of radio sets manufactured since 1927, and many earlier ones of Partial Contents of Volume II which there is any record elsewhere. .\ step -by -step analysis in servicing a receiver which 650 pages of radio -servicing material. embodies in its design every pastille combination of modern radio practice; it is fully illustrated cmd thor- Complete course of instruction for Radio tghly explained. It is the greatest contribution to Service Men, dealers, manufacturers, job- the radio service field. bers, set builders and amateurs. ('hart showing the operation of all types of vacuum tubes, whether new. old or obsolete. An exclusive resu ni, (Here are but a few of the subjects covered of the uses of the Pentode and \'ariable3Iu Tubes in the special course of instruction). and their characteristics. Complete discussion of the superheterodyne 19 32 and its Amplifiers Power- Supply Systems inherent peculiarities. Also a special chapter on tools Official Antennae Radio Phonograph used on superheterodyne circuits. Schematic diagrams re and circuits complete with color codings. Radio Ser Automotive Radio Equipment Condensers Resistors Important chapters on commercial aircraft radio equip. , Manual meat; new data on commercial short -wave receivers Detectors Short-Wave Sets and converters. tse« coed,. . Eliminators Speakers Servicing and installation of public address systems Meters Tubes and talking machine equipment. Rs3'o Rc"' 9)1.1932 Standardized color -copings for resistors. Guid Operation Rule Servoce $4.50 of old and new testing equipment; tube Fug Complete with Supplements sodtmeters, output meters. oscillators and aligning tools. .\ full section on Midget radios -their design. circuits, 650 PAGES and types. !low to service them most economically. Hundreds of schematic diagrams of older radio receiv- (Complete with Supplements) ers which have never been published. Edition I :lank pages for recording notes, diagrams and sketches; 1932 1,500 these pages are transferable to any part of the hook. Volume fir Over Diagrates, Charts and Illustrations Coupon page for free questions and answers. $5.00 Complete with Supplements CLIP COUPON AND MAIL TODAY! Flexible, OVER 1,000 PAGES Looseleaf (Including Supplements) GERNSBACK PUBLICATIONS. toe. Ile-11) 96 -98 Park Place. New York. N. Y. Binder, Over 2,000 Diagrams, Charts Ple:ne send næ for FREE I1,11eei imp the hicks I have checked and Illustrations below. I understand I t examine them carefully, and should I decide to keep them. l' will ) pay the full cost. Ictus the few cents for 9 x 12 inches. carrying charges. This offer Is gait ont, In the F.S.A. Flexible, Looseleaf Binder, [ ] Volume I. 1931 Manual, with supplement, $1.50. 9 x 12 inches. [ 1 Volume II. 1932 Manual, with Supplements to ho walled Free every 60 days, $5.00

1 BOTH BOOKS FOR 99.00.

Name NOT ONE OF THE DIAGRAMS PUBLISHED IN VOLUME Address NUMBER I OF THE OFFICIAL RADIO SERVICE MANUAL city state IS REPEATED IN VOLUME NUMBER II.

244 RADIO -CRAFT for OCTOBER, 1932 ADAPTERS FOR TEST EQUIPMENT (f'outinu.r1 fr row ,,t!, 217; types 533, 534, 535, 536, 538, 540 and 597. No. 9ois-.1'13, Fig. 25. will also test the 214, it Is The adapter is to be inserted in a 2.5 volt 41, 42. l'A and 17.11 tubes. llowever. necessary to use the socket of the tester ordi- five -hole socket. '37 tube, or any No. 95511 -2, Fig. 17, is for testing the Ma- narily used for testing the type ,.....,.. ._.,_. ..,.a r:_.t -si td,os In the tollowinr live -hole socket wired for 6.:3 volts. for the checkers: Models 21)9, 210, 214, 533, 5:14, No 1115.55, Fig. 26. is used testing tube 85 "duplex -diode triode" tubes. Place in a Line 535 5:31;, 5:38. 5411, 597 and 1;75. 55 and Get Into the types '36, n 27 socket to test the 55 nnll and In it '37 to Where There's No. 975, l'ig. 18, is for testing with following YOURS tubes in the 209 and 210 Jewell test , the S5. May be used the Action '38 and '39 210, 214. 53: ;, - extra \indris 201). without tube checker's. Jewell Analyzers: 535, 5:36. 5:38, 540, 597 and 675, to check the Every Day -And a Pay. cost. 19, Is an output meter No. 9491'T, Fig. 55 tube. day Each Week - You This excel- 5110 adapter for use in connect itou with Jewell Fig- is for testing the Be the Boss! Also used with the 444 No. 9SS(,G il., 27, lent set ana- and : R:3 ...moors. live -prong \Vunderlich "A" tube In the type and and 4,151 set analyzers. May be used with all Idebt nmv while hundreds are lyzer '27 socket of testers. looklpi for work where there isn't trouble shoot- No. 954ÚS, Fig. 20. changes over a four -prong Jewell instrument models described In connee- any, the radio sort re field can

men. With the proper included plug to at five -prong plug. Used with Jewell tth,n with the No. 9135 -55 adapter. use trained er basic live - (raining and the necessary equip- 444 or any set analyzer having a No. 9651:11. Fi_. 25. is used for testing the ment you ran enter this field and with our prong plug using the Na -Aid latch -lock feature. types 29 and lilt Into,. When testing the 29, . Make a r confortable lining. We of include uah cur this course the Kel- a volt t lilntwnu I sneket; when testing No. 944FFL, Fig 21. is for testing use ..5 .set t anal,zer e and se trouble training. socket. \hey modern logg "overhead heater.' type tubes in the Jewell the 69. use a e,.:: Noll, live -prong shooter w any extra charge. Jewell Models: 210, This Piece of egpthnnent has 1 yet analyzer rump rising models 1115, 199, 408, be used with the following help After _ _ 5:;5, 54o. 597 and 675. proved to he a valuable to our members. 409, 444. 577 575. 581 and 660. 211 :14 5tí6, a brief period of training, you em take the set analyz r for the first No. 944131Uí,: Fig. 29. is used to test the out on service cals and really compete with o d No. 954KG1.. Fig. 22, is testing show NIII1 Inne u, vire rooms for radio adapter type BR tube which is made for use i inners." We section of a Triple-Twin tube. This Raytheon Install auto sets - -build and insta I slmrt -wave recentr. It is to be played of 'ma y is to be placed in a four -hole socket of the tube in auto "li" eliminators. -analyze and repair all Unes radio sets-and 295. and the in type 'S0 sneket of tube checkers. In- her profitable jobs ran be you s. tester: the '45 socket for the the Teaching you this interesting work Is our business and 211:;. May be used with cluded in the adapter is a current- limiting re- we have provided purse', es with every facility to help '71.1 socket for the possess 533 , 534, 5:15, of correct size. \InV be used with Jewell you analyzer models 209. 210. 214, sistor the ide.,Ire to make relreal progress n 31 udels 209. 210, 214. 533, 534, ntelligenceuianti 53tí, ,:38, 540, 5!17 and (175. instruments: )our men merits, ,vet still be interr,ted. second section 535, 5:16, 538, 540, 597. and 675. No. 9:54ú13, Fig. 23. tests the on ACT NOW -MAIL COUPON tube. May be used in all his pea ttitally completes the data of the triple -twin of Service Men Start this ery minute! Send for full details of our listed for the No. 9541í(3L: adapters suited to the needs how you the analyzer models also- it con- plan anti operating directions are the same as' for the who own Jewell test instruments; now h Inerouion quickly. put sit toff w'rite adapter. eludes the first part of our article on Adapters. aye:a Send No, 954úßI, will be pleased. indeed, to hear r -I No. 1144 l'IA'It, Fig. 24. Is for testing the type The author This adapter incor- front radio men who may wish In question any RADIO TRAINING ASSN. of AMERICA 866 tube in tube checkers. or Dept. RCA -10, 4513 Ravenswood Ave.. Chieaga, Ill. limit the plate carrent to of the statements that have been made. porates a resistor to additional in- Gentlemen: Send me details of your Enrollment meters. May be used with who would like to obtain any information on how to leant to nmko real prevent damage to design or use of these Plan and models 209, 210, 214, 5:33, 5:14, 535, 538, 540, formation regarding the money in radio quick. 597 and 675. Insert in 2.5 volt socket. very useful units. Name THE CRAFTSMAN'S PAGE Address (Continued front page 23S) t'ity State very knows of n number of instances volt supply circuit and which operated The writer long time. wherein the one -ampere detector tubes have satisfactorily for a substituted for Ile older types designed t', M. 1)t :l..txO. been Lilleld It, Neb. A New 13'4 ampere drain : furthermore, in for the proposal of Blr, Delano will nearly every- instance where such procedure has I. \11 hough the at chord in the hearts of many. been followed ln the case of an old receiving strike responsive been possible to substitute a second we question whether mathematical computation set It has of supplying Identifica- SHALLCROSS tube of the new type in place of one of the old could stand the strain first A.F. tube), and tion figlrresI Multi -Range type '26 tubes (usually the opinions-and Combination operate the beating feature of same from the At any rate. \Ir. Delano has supply winding of the detector tube that, certainly, Is worth writing home about. filament let us putt un A.C. without causing perceptible excess heating in Rince the ire has Isvn broken. (Adopters do the trick: or record the following suggestions: .\ line of di- the transformer. to be known as the "portable and the sockets may 1>e changed, where necessary.) reet-tenter tubes facts as a basis series," It should include tubes of screen -grid. With the above mentioned but with an for further consideration of the subject I sub- pentode and general- poreuse type, D.C. USIA for the Western mit that it would Its a profitable venture fer the envelope no larger than is to offer, at an early date, a tube Electric type N (No. 215-AI or "peanut" tuhe. Meter tube interests of ones little linger; their of the '27 type. designed to operate f the which is the size for filament is rated at 0.25 -amp. and 1.1 volts- - q;f, volt winding of transformers intended iug Type supply. and with a drain of not the proposed series should more nearly approxi- No. 610 type '26 tube series (00 ma, :nid Shalleruss Re- to exceed the one -ampere demand of the present mate tour present "2 -volt" on 2 volts), or perhaps be designed for 1.1 volt-- sistor Kit and tubes. and also it screen -grid tube operating du the Reston the same current drain. supply lut n current consumption of only or less. Mindel 301 As it of i n furnmt ion the writer had. ma.. i v e rsul i. matter et experimenters, en- I'n at one time, some tubes of the heater type What say- nia nu fa urers, Meter. >.t_ Service Men Editor.) which were designed for operation on as t gineers and I- This THE "K" TUBE (Continued from polte 206) Combination Meter measures when Ionization took place. and amperes Is available for operation. If more milliamperes the for this reason a limiting resistor must he is necessary, It is obtainable by increasing 4 D.C. Voltage Ranges destruction of the plate voltage. It is necessary to shunt the 4 A.C. Voltage Ranges used to prevent the self capacity tube. relay with about one microform' of 4 D.C. Current Ranges 'flue for the operation of a relay in order to operate on the pulsating current. .3 Resistance Ranges connections 3 Impedance Ranges in a photoelectric cell circuit are shown ht Operation was secured on light inputs to of the type a Fig. 3 using a single stage set -up t Ito photoelectric cell of much lower intensities Including Capacity, Inductance and Nigh "K" tube. .\ limiting resistor of :3.200 ohms than with any previous amplifier tried. In Resistance Range. 50,000 - was used In the plate circuit while a fart. the single stage here proved to be the Send 6e in stamps for Bulletin 152-P vvhiclt and a 15,000 -ohm potentiometer were USIA to equal of the two stage direct -coupled amplifier contains a diagram of this circuit and in- obtain bias for the grid. The potentiometer described in the October, 19:11 Issue of Rama format hat on its construction. was used to set the operating bias. The grid (1t.tFT. The action was very positive. the relay leak to be used depends entirely on the photo- closing with a snap. electric cell used, although, as in all gas con- ll'tless N could be obtained In hilt [`MY f appear to be Absolutely no chatter tent tubes, one to two megohms ELECTRICAL SPECIALTIESao the maximum practical values. The relay used any ease, even at the threshold of relay ,00 need not be sensitive, as from 20 to :10 millt- operation. ShiV a ie,gqe a.nu

RADIO -CRAFT for OCTOBER, 1932 245 di0'Caft lot\ EWBOOKS in the \.

Presented on these two pages are the new knowledge; you will find them a real help books of the RADIO-CRAFT LIBRARY - in your work and they will contribute to the most complete and authentic set of your money earning capacity. Read these volumes treating individually, important books during your spare time at home. divisions of radio. Each book has been de- The authors of these books are well - signed to give radio men the opportunity known to everybody. Each one is an expert to specialize in one or more of the popular radio man; an authority on the subject - branches of the industry. The material each is thoroughly familiar with the field contained in these books will increase your which he represents,

Book No. I Book No. 4 Book Ne. 7 RADIO SET ANALYZERS MODERN RADIO HOOK -UPS RADIO KINKS AND WRINKLES And How To Them Use The Best Radio Circuits For Service Men and Experimenters With Full Instructions and Desertptions A Complete Compendium of the Most Im- A Complete Compendium on the Latest of Set Analyzers, Tube Checkers. portant Experimental and Custom - Radie Short -Cuts and Money - Savers Oscillators. Etc. built Receivers By C. W. PALMER By L. VAN DER MEL By R. D. W ASH BU RN It often becomes n .sary for exited This book explains thoroughly the oper- It is fascinating lo the experimenter. menters and Sen ire d Men to call upon ation of set analyzers. tube checkers. or even to the uptn date Sert ice Man. their memory for nome shun rut or radio oscillators and other testing equipment. m take a commercial set and to ehange wrinkle that will solve a problem quickly. For ever' radio man this book Is ex- it Into one using a famous hroktgt that In business. ".short mean and Is ruts" time tremely helpful. it covers et er phase not found in any manufactured set. money saved. to Sen saluable short Many excellent have alti the ice Man of testing and gives you minuits never been "time saved" means money earned. cuts: completely Illustrated with photo- iced lard. but limited only tu None- This book Is a of set builders. Thousands of these popular compilation important graphs anti dl :tennis to fars lit ate the use t radio kinks and wrinkles of modern testers. vin uit. have been requested front time and discusses outline In time, and in tit's book we have only such Iteins as aro constantly used The following chapters briefly in- roda)'. the contents. INTRODUCTION ; THE AN- cluded over ISn circuits. which Inrinde the Here some ALYZER; Fundamentals. Switches. A.C. lalnus rtrid)ne, rash -Ito, A.1 . -D. C. aro of the more important and D.C. Voltmeters. Calibration and Set and others. chapters : Introduction; Seniring Short- Cut s; Testing F.qul Ife -ign; TROUBLE SHIIOTI NO WITH The tireuils cover the following : Broad - patent and Meters; TII E ANALYZER; Classlfieat ion of east Receivers, All -Wave Receivers, Short - Varmint Tubes and Circuits; Volume - Trouble. Analysis of Troubles. Uses of Wave Receivers, Converters and Adapters, murol Methods; Ainpliflers and Phono- Various Analyzers. l'are and Mainten- Television Receiven. Home Recording Ap- graph Reproducers; Power Supply Equip- ance; CONCLUSION. paratus. Automobile Receiven. Audio and ment: 1 'ells and Tuning Circuits; Short Power Amplifiers. Power Units and Mis- N'axes; Loud Speakers; Tools and Ac- cellaneous Equipment. cessories.

Book No. 2 Book No. 5 Book No. 8 MODERN VACUUM TUBES HOW TO BECOME A RADIO RADIO QUESTIONS AND ANSWERS SERVICE MAN And How They Work A Selection of the Most Important of 5.000 With Complete Technical Data on All How To Get Started and How To Make Questions Submitted by Radio Men During Standard and Many Special Tubes Money in Radio Servicing the Course of One Year By ROBERT HERTZBERG By LOUIS MARTIN By R. D. WASHBURNE MODERN Va CI'ryl 'rl'ItES describes The ambition of r n alp' men in radio Then have been whetted a wide variety the fundamental eleoiron theory. which is today is to become a first -grade Sers ire of questions which Irate cone into our Mas. is not as the basis of all s arum t tubc operation, It difficult as one might editorial offices during Use two years, believe. but past and goes progresslt'ely t (ront t he simplest il rtnnut be dente in a few and only those whose answers would pro- element tubes right up tu the latest client months. Following ver rare( u Ily the benefit of the majority of men engaged in pentodes and thyratrons. It is written attire Itr. dart lu, who has dealt with lmav the radio a been Incorporated in this amaz- in clear. simple language and is devoid problems of thousands of Service ing question and answer book. of the mathematics which is usmdly Men. this bunk deals very carefully with the The tremendously long list of topics confusing. Valuable reference charts and essential stages In the preparat ion better explains the subjects which are for qualifying a characteristic runes of standard anti as Sen lee Man. treated. Here are the titles: special tubes are to he found, also dia- Here are the chapters; The Small In- dependent Service Radio Servicing; Beretse, Design; grams of sockets and pin connect Man; Ath erred Pom- Home Recording; Television; Sound Here d Ions. The enial Aspects ; The Radio Set ; Sent. Technical Considerations; Equipment: Short wasps; Antennas; Edison Effect and The Elel r011 Theory; Advanced Service Operating Notes; Test Equipment; Tubes Electron Emitters and the Ionization Ef- halai Each chattier is again subdivided to bring out in minute l' Itra- Short - Waves ; Police Radio; Repro- fect; The Three - Elect role Tube; Vacuum detail every point ducers; Superheterodynes; Autonot ive Sets; Tube Cho railed st let; Four- and Fl re- of importance. Element Power larks; Automatic and Remote Con- Tubes; Light Sensitive Cells and trol Devices; Aligning Procedure: Photo- Other Special Tubes. Book No. 6 electricity ; Adapters; Measuring Appar- BRINGING ELECTRIC SETS atus; Itand -Selectors; Converters; Public UP TO DATE Address Equipment; Midget Sets; Oscil- lators; Phonograph Pickups. With Pentodes, Book No. 3 Multi -Mus, Dynamic Speakers -Complete Information How to THE Modernize SUPERHETERODYNE BOOK A.C., O.C. and Battery Operated Book No. 9 All About Superheterodyne+ Receiven How They Work. How to Build and How By CLIFFORD E. DENTON AUTOMOBILE RADIO AND to Service Them In this come there are over ten mil - SERVICING By CLYDE FITCH dom lectrically operated receivers that A Complete Treatise en the Subject Cov- could be modernized -by placing in theta ering All Phases from Installing te There is no more fascinating a subjeet new type tubes. n speaker equipment In the large of Servicing and Maintenance array radin circuits than and other modern rvs improvement s. This the fatuous superheterodyne BY LOUIS MARTIN el mull. business of Inmroting old sets cann go in whether yod are a Sen Ire Ilan or experl- the experimenters and Service Men if Automobile radius are out and coning. crnler, first -hand knowledge s about the they will quickly jump into net inn. and eune has to sert ice them properly. of It onstruct tun superheterodyne receivers Read in Ills hook by Mr. Denton. how therefore behoves you lu read this is ten' hnlortant. The book on Super- easily you can modernise immensely Important new book on the gis ny obsolete set. heterodyne. e. un.Ierl'Ing principles and with little additionala rests. art of .automobile Radio. The book is of their construction. right from the i ery If ere are the high lights of this honk: aris, and full of illustrations, photo- ant set made. Tubes Available for Iteplmement.s: Elee- graphs, diagrams and hookups. The (Whet Mg Is a short of - list con Iriling Hatters Itrceiters ; Ilse Here are only a few of some of the tents: Basle of the Principles of the Superheter- New 2- and r, -Volt Tubes; Operating Sets really interesting chapters : Introduction; odyne; The Os,i l later; First Detector; Single 1 A!. . utonot Is e Radio Installations; Complete Single Dial Tuning Systems; Interme- Sets into D.C. Into A.C. ; Re- Descriptions of Commensal Autotraut ive diate Amplifier; Second Detector, Audio placing Output Tubes wit h Higher Output Receiven; Seniring Automotive Receiv- Amplifier am d Power Supply; Commercial Tubes; Intprov I ng Old Supers; Lcd tin - ers; The Ignition System; General Ser- Superheterodyne Revel s ors: Servicing White Amplifiers; Adapters and Three vice Considerations; ERtsts of Tempera - Stqurhelerody ors. Ilse. mre on Power Mace') ; Conclusion. Clip Coupon and MAIL!

GERNSBACK PUBLICATIONS, INC. 96-98 Park Place, New York, N. Y. I have circled below the uumbets of hooka in the RADIO -CRAFT LIBRARY, which you are to send me, and have deducted 2207 for ordering five (5) Imnke or more. I have included my remittance in full, at the price of 50c each, when lens than five books are ordered. l'be amount of my remittance is (Stamps, checks or money orders accepted.) Circle numbers wanted: I 2 3 4 5 0 T 8 9 10 Name Address Cite State RC-10-32

246 RADIO -CRAFT for OCTOBER, 1932 N.R.I. PRACTICAL LABORATORY TRAINING COURSE SPECIAI, 'Phis supplementary laboratory course will prove invaluable to the radio student regardless ¡i4brary of the branch of the business in which he in- "!'ii II- US- i/uii-go.. tends to specialize, as the basic principles un- derlying the fields of servicing. television, sound pictures, aircraft radio and commercial This is perhaps the first real operating are the same- For example, the sound projectionist, just as well as the Service OFFER opportunity that you have ever operation of vacuum Man, must understand the by which you can had to build a radio library of of circuits. and both is a new, practical. plan tubes and the testing HEREstart AT ONCE to become a books that are authentic, right - must have a thorough understanding of the up-to- the- minute and written so generation and control of electricity. TRAINED CHEMIST that they are easily digested and 'l'he course is divided into five sections of clearly understood. Mail coupon on ten experiments each. The first section starts graduated by our Institute, without the obligation the opposite page for your books. with the simple detection of electric currents of signing up in advance for your entire course. by means of an earphone, strid proceeds through By taking only one step ut a time -as your means tests: to show hoe- the permit -you can give yourself the benefit of the Book No. 10 the following further -going, up- tothe- minute edu- force can be di- most complete, thorough presence of an electromotive skilled well- professional work, in HOME RECORDING AND ALL that an has cation for paying tolled iiv the eye: to show e.m.f, the most fascinating of all scientific fields, through ABOUT IT polarity : to show that a magnetic field is our famous always associated with current flow ; to show A Complete Treatise on Instantaneous Re- COURSE IN PRACTICAL CHEMISTRY cordings, Microphones, Recorders, Amplifiers, that a gr'a ter magnetic field is produced by Commercial Machines, Servicing, etc. direct current flowing through a cull wound Our course will give you ale all-around, applied and of Chem- on an iron core than ley the stone current training in both the theory practice By GEORGE J. SALIBA inonWUic and organic Chemistry, an core coil, to show- the istry-including flowing through air quantitative and qualitative analysis. If there is one subject that is fascinating of different materials: different conductivities only for lessons you to every radio man, it is that of Home to effect of electl'o- magnetic In- Under this new plan you pay illustrate the receive at one time. Recording. Of course, this volume is not how electricity- is order and all on "Home" recording, but the information duction; to show generated contained therein is important to commercial by chemical action ; to $how- till' action of the HERE IS THE IDEA: radio men, studio operators, engineers and storage battery ; to show mechanical generation others interested in this phase of radio. of electricity. The art of recording and reproducing The second booklet dents specifically with s 9 C pays for one unit of broadcast selections is becoming more im- vacuum tubes. hoe' to test them and blow to LJ our Practical Chemis- portant everyday to radio men, experi- various conditiuus menters and Service Men. Equipping dance record their behavior under try Course. halls, auditoriums, chu rehm, restaurants and of filament, grid and plate voltage, The con - (lbu entire course comprise, tc;tut y units) homes with public address and amplifiers strue'tiofs of several simple but useful tube brings many extra dollars and often an testing instruments is described and illustrated. excellent income. In the third instalment the student is taken You may order as many units ut a time as your In this book are found such topics as: into the more advanced subjects of the genera- page and your spur time permit. Short of History the Art; Microphones; of )low -frequency oscillations. the contain Recording Amplifiers; Cutting Heads; Types tion of Reconis; Commercial Machines; Adding of frequency. the dy'nat ron oscillator. the modu- Reeonlers to Receivers; Studio Layouts; lated R.F. oscillator, the phenomenon of reson- Mechanical Filters for Turntables. ance. etc. The subject of detection or "demodulation" is treated at length in the fourth booklet. BIG Various types of detectors and detector circuits are considered and the features of each de- DISCOUNT scribed. An excellent modulated oscillator can be made with the apparatus furnished to the student of the course. OFFERED The fifth and last booklet expands generally In order to make it possible for everyone to buy on the subjects covered. 'l'he use- these books the fifty (50) cents price has been previously made uniform for all volumes. You can buy these fulness of the vacuum -tube voltmeter is ex- books separately, but you should take advantage plained. as are numerous methods for using it. of our special offer: 'l'he experiments cover the following subjects: the action of the .t.F. output transformer; When Five (5) Books audio a mplifla t ion with transformer and resistance- capacity coupling; building a regen- Six of Cabinet: Height, 221/4". Length. h7;a "; recei Ver ; It. F, n mpl l U ca ; or More Are Ordered erative adding tier and Weight 25 lbs. the effect of tuning the aerial circuit. Deduct 20% This course is well prepared and clearly Over one hundred Chemicals and Appar tus written, and is altogether devoid of the mathe- When you have completed the first five con ecutive from Your Remittance mattes that confuses many- practical radio units of your course, and order your sixth unit, our workers. valuable chemical experimental laboratory outfit, Simply fill in the ronron below, and mall it to (illustrated alstve) will be sent you free of chary. us together with your remittance. Cheeks, stamps No. 1. or money orders accepted.ted. We suggest that you try out Unit Mail HOME EXPERIMENTS the coupon and start your training as a chemist. (Continued front paw 2:141 You will receive by return mail the first group of which you are conducting the experiment, will lessons of our Course in Practical Chemistry, with All Books Uniform be sufficient to cause n minute elect rival current full two months' service. to flow and register upon the meter. however, The books in the new RADIO - CHEMICAL INSTITUTE OF CRAFT LIBRA 5V are all when the full force of the rays of a flashlight strictly up -to -date. and are flashed on the cell, a decided deflection of NEW YORK, Inc. written by men who be know their subjects. the meter needle will observed. denoting the Founded 1921 The volumes are all fact that due to a chemical action within the HOME EXTENSION DIVISION unlfomh size, ri a 9 cell an has appreciable electrical current been New York, N. Y. inches, and contain on caused photoelectric 19 Park Place an aserage of So to 120 to flow in the cell circuit. illustrations. Sarh ba,k To demonstrate how variations in the size and Is printed on line bead intensity of the beam of light can change the CHEMICAL INSTITUTE OF NEW YORK, Ins. paper, and no expense 19 Y. has been spared to mal, current flow in the cell circuit, it is suggested Park Place. New York, N. It an outstanding vatur. that the experimenter cut vn rions Riled holes Please send me at once Unit No. 1 of your for its editorial contents in a piece of cardboard and then shine the as well as from the Course In rraelleal Chemistry. I shall receive In of my mechanical stand - light from the flashlight through them, noting full two months' service grading exami- 'the while, the change in turrent indicated on nations, and the help of your instructors for the understanding of any problems pertaining to the the meter. Also, pieces of smoked glass of particular lessons. varying density may be hold before the beam Please send me the first unit of your Course of light to cause changes in the flow of cur- C. (1. ii., 1 will pay the postman $0.25 lidos rent. Other experiments will suggest them- postage) upon delivery. selves to the experimenter. The practical AND CANADA, REMIT BY simple FOREIGN knowledge to be gained from this rather INTERNATIONAL MONEY ORDER experiment is lit the parallel which can be drawn between it anal the rather elaborate pro - ceasl's involved in the production of sound Name from film as used in bilking movies. Address Next month : A simple photo cell and amplifier which may be used to demonstrate City Stale variations in sound from an interrupted light RC -10 -32 source. a r

RADIO -CRAFT for OCTOBER, 1 9 3 2 247 MEIRE IT IS: S. W. LABORATORY HMI TO BF( ()ME A\ (C'on t i n a ccl from page 231) : 5,000, 10.000. and 24),000 ohms, thus provid- AMATEUR RADIO OPERATOR ing an excellent reading range of .1- to 20 volts. 'l'he variation of the proper grid volt- We commissioned Lieut. ylynnt P. Eddy, U. S. Navy, 1011 ind, to write u bold: on tlu- age for each resistor Is accomplished by the subject that would answer EVERY possible question in Mach a way as has never he'en done 20,000 -ohm potentiometer lt8. Needless to say, before. We chose Lieut. Eddy because his long years of experituce in the amateur field have the 'acc'uracy of the reading depends upon the made him pre- eminent in this line. For many years he was instructor of radio telegraphy at the R.C.A. Institutes, accuracy of the voltmeter resistors to a large and in this capacity he obtained a vast knowledge and insight on the extent. subject. He is a member of the 1.R.E. (Institute of Radio Engineers), also the Veteran Wireless Operators' Association. Shown with the diagram is the switch S\\'3 If you intend to btrume a licensed ct sir operator, if you wish to hake up phout work whh it is closed during operations. When this eventually, if you wish to prepare yourself fur this itnportaut subject -this is the book you stviteh Is open, terminals 15 and la are used must get. to test fur resistance values. This be ex- This buck covers literally will everything from "soap to nuts' on the subject, in such a clear plained In the following section. and lucid manner that it will be of great value to every student. The 30 -type tubes are used in all the fndi- 5oc. THE COPY tidunl units because of their low plate- and it lamer tem'rent consumption. The "A" bat- 72 Partial List of Contents tery is a 4.5 volt ''C" battery. Resistors of b 11 ohms are In series with each tube filament. Pages CHAPTER 1. Rays and means of learn- Tests and Measurements ing the cote. A system of sending and II4:snsT. \SI'R: 'l'he` usual n'ceiviag with ...bonne, test Is necessary drill words is sup- good for one particular range of resistance. Now to Become plied so that you may go right to work our approved methods. depending on the size of the battery. . 4.5- AM Over 150 volt battery will give useful Indira tlotis up to CHAPTER 2. C'onc'ise, nuthoritat ice 100,000 ohm's, but not above and Illustra- dehti- M that, none tiuus of radio terms, units and lanes, brief below' Lunn ohms. Inrrensing or deereasint AMATEUR tions descriptions of commonly used pieces of radio the battery voltage eplipmetit. will result In different This chapter gives the workitia satisfactory ranges: but for any one terminology of the radio operator. All graphic battery voltage there will be upper and lower limi- ADIOeOPERATOR symbols used to indicate the carious parts and secure a of radio circuits are shown so that they may r tations. U.S. Government License Not be readily' r.cogu trawl when studied in the 'The feature of this unit is that almost any following chapters. range front 50 ohms to 1 megohm can he easily calculated. The potentiometer 113 provides n Sold CHAPTER 3. General milli' theory par- i meal's of obtaining n variable voltage from uwT MOO r a oov. ticularly as it applies to the beginner. , on Tb. 1. to 20 volts. The M. eleclntir theory is briefly given, then waves teeter, i, may be con- PLPe`mtn a, - nected into any range by connecting, for ex- News- their creation, propotat imiti and crept in n. fHORT Fundamental laws f electric ei r'ui, s, ample, the 1t1000-oh0 resistor 10; so that the tieularly those use r in radio, full- scaale deflection of 1(1 WAVE NEW Y0015 stands are explained t1AI is volts, The next and typical basic eirnlits are analyzed). t' ii i l,,ineter CRAFT Pot is now adjusted to give a full - scale deflection. 'l'he resistance testing ter- CHAPTER 4. IL.eript ions of modem e- minals are Nos. 13 15 I sw -O that are brine ised with and It eh S\':; open). sucress br Suppose amateurs. You are told how to build and I that while testing a resistor. the operate these sets, and how they work. meter .IA1 shows a deflection of .5-ma. 'The SHORT WAVE CRAFT, applied potential being 14) volts, the total cir- 98R Park Piece. New CHAPTER 5. York City. amateur transmitters. Dia- cuit resistance is 24),000 ohms. However, i t grams with specificat bunts are Gentlemen: furnished s'- the voltmeter ei rcult there is a resistance of sonstrnetion is made easy. I enclose herewith 50e for which please send I 10,000 ohms flttlI and the value of the re- me prepaid. a copy of your new hook, "How to sistance Become a Radio Amateur and Secure a I'. S. CHAPTER 6. Power equipment that may under test is therefore 20.0(10 minus Government License." the monk to be sent to be used with transmitters and receivers, me- 10,000 or 10.000 ohms. The same procedure me immediately upon publication. (Send )inner titers, filters, batteries, etc. is followed for any range. Select range Order. Check. lash or new U. S. Stamps. Res- the by plugging into the proper resistance. . %djust ister letter If it contains currency or slumps.) CHAPTER 7. Regulations that apply I- the potentiometer 113 amateur operators. to give full -scale deflec- Nana tion at that particular range. Read the scale Address CHAPTER 8. .\ppt'ndi a, which contains rending of MAI in milliamperes when testing. the ianel'amt halal "et" signals, conversion and determine the value of resistance as de- (it) Ct ate tables for reference purpose., etc. serlbed abort. t'.tr.tct't'V: The capacity test is not as simple as the resistance test as it will be necessary to first determine the rapacity of several coudense'ro and then make a permanent record :ID FItTitiF._IE_S"T.S 4)r graph of the readings. rL:i titiiFiEII In this method it will be necessary to know the cell Trent drain of the copper -oxide voltmeter CHEMISTRY MISCELLANEOUS !tow composed of \I.\2 and either Ill1, 1112. RE:, or 1114 I at any point. This may be obtained by dividing the applied BECOME A TRAINED CHEMIST. Thousands SPANISH Representation Executive of .\.C. voltage - New rending at any Point by series of opportunities- fascinating career. Learn at York export house leaves shortly for Spain to the resistance: home. Complete experimental laboratory outfit organize, radio department of their Spanish for example: The A. C. indication is î5 volts. given. Write for big free book. Chemical Insti- branch. Manufacturers of articles that can be If the 150 -volt A.(', range is desired, a series tute, 19 Park Place, Dept. RC, New York. sold in sufficient volume to warrant appointment resistance of 75,0011 ohms is required 1It13I of sales representatives on commission should with the particular reeti tier used; therefore, communicate with Box RC, Radio -Craft. 9i( Park the current taken by INSTRIICTION Place, New York Shipments the voltmeter is City. and payments E 75 can be handled with buyers or through New fork office. I--- -. 001 -ampere 4 MEN-Learn to service Electric Refrigerators. R 75,000 Jobs open. Big opportunity. Write for booklet. RADIO at that point. Tech, 4306 (J. ational Euclid Ave., Cleveland, The voltage drop across the condenser is GUARANTEED MICROPHONE REPAIRS -Any obtained by first reading the line voltage with- EXCELLENT Money in Public Address work - make or model -24 hour service. Stretched dia- out the condenser, then reading the voltage phragm double button repairs, $7.50. system needed in every town -excellent sideline Others with the condenser in series, and finally sub- for radiotricians, electricians. amateurs, etc. Our $3.00. Single button repairs, $1.50. Write for tracting hone study course gives complete training in 1933 Catalog with diagrams. Universal Micro- the second reading from the first theory, construction, and operation of public phone Co., Ltd., Inglewood, Calif. for example, the voltage He across the con- address systems and sound trucks. Special price denser to be tested may be determined from -$3.25 cash, or $1.75 down and $1.00 per month TRANSFORMERS REWOUND. varnished. baked, the ['elation for two months. Complete course sent with first guaranteed, reasonable cost. SPEAKER REPAIR- payment. Lincoln Engineering Company, 855 South ING, magnetic $2.00 -$2.50; dynamic, voice coils, I x 1,000, 000 37th, Lincoln, Nebraska. fields, etc., reasonable charges. Clark Bros. Radio Ec Co., Allia, Iowa. 6.28xf xC INVENTORS and the capacity in rat, equals : RADIO Service Men Attention -Power transformers. rewound or rebuilt. to your requirements. x YOUR Send Meyke Radio Service. 2624 Margaretta, Maple- I 1,000, 000 PATENT INVENTION: for FREE wood, Mo. C book, "IIow to Obtain a Patent." and "Record 6.28 of Invention" blank. Ask us about how to xf XEc rotect your ideas. Deferred payment. Victor LET Us rewind your burned -out magnetic horn where Ec Is the difference in voltage reading: Evans & Co., 620K Vict% Bldg., Washington, and cone units. $1.25 each. Flora Radin Service, f, the line frequency; C, the capacity in mf.: . C. Flora, Indiana. and I, the current at the second reading.

248 RADIO -CRAFT for OCTOBER, 1932 Although so many calculations may seem where tedious, it must be borne in mind that once 91:e.TRANSMITTER UNIT they are made, they are permanent. The capacity is, of course, plotted against the second -with 100 Uses - thousands look to find the rending. This procedure is the same for any e't of frequencies and voltage. The total volt- The Skinderviken latest science news, con- meter resistance is easily known because if the rectifier is self- constructed, the required series Microphone Button resistor can be measured. Where the rectifier structional articles for Is of commercial manufacture, the series resistors are specified for each range. A manu- home work -shop and facturer's curve usually accompanies the rectifier. The particular rectifier used was vade MAKE YOUR OWN so as to utilize the resistances indicated In the LAPEL MIKE money -making ideas . . a wiring diagram. The resistance sizes will vary with each type rectifier, so do not accept the OTHER' USES: values given as standard. RADIO AMPLIFIER PHONOGRAPH AMPLIFIER I N tiPCrAN(r:: having, in all probability. al- DETECTOG RAPH TELEPHONE AMPLIFIER AY ready calculated the current drain of the volt- (Dierogrupl ) LOUD SPEAKER AMPLIFIER cläñeë meter when making the capacity curves. the STETHOSCOPE CRYSTAL SET AMPLIFIER computations for Inductances will be consider- HOME RECORDING OUTFITS ably shortened. The procedure for testing rllachanics : inductances Is the same as that for capacities. :.la Obtain readings before and after inserting the One Unit 95c ; two for $1.75 :: 1:t: the i J difference. In 12 -PAGE INSTRUCTION BOOKLET . choke; then calculate the :-- tn c a l' t '1 4, for innumerable case of inductance, the drop across it is due containing suggestions and diagrams 25c and resistance of the uses, furnished with each Skinderviken Button. to both the reactance !!ensure the D.C. resistance of the The Copy winding. This is the smallest mierophone made. measuring ont choke before testing. The formula used to inches in diameter. It is filled with the finest polished calculate the induitnuCP is carbon grains obtainable. -ULTRA SENSITIVE - EVERY AMATEUR SHOULD HAVE TWO OR THREE OF THESE MICROPHONE- AMPLIFIERS IN HIS LABORATORY Over 450 Illug- EL2-I2 R2 I rat liars L = SEND NO MONEY fio pages - I2Xf2X(6.28)2 \Chen the postman delivers your order you pay him I -t' i r Cover for whatever you have ordered, plus postage. I" Inches voltage tradings. Where EL Is the difference In PRESS GUILD. Int.. RC -10 -32 : 1, the current at any point Ise- 1 rending) 16 Murray St.. New York, N. Y. do not hesitate to say that choke; f, the :\ND MECHANICS is lt, the D.C. resistance of the l'lea,e null me at once as many of the following UAY SCIENCE is 'I, I' Iris 'ken ?Microphone Muttons as 1 lase indicated. l- urecha film! -rou- line frequency ; and L, the inductance the finest seienliflc- technit-a n One for 95e_ zinc in the field. (tight up- henries. for stuctional nuiga made I l'sm $1.75: to- the -minute with news flashes of scientific l'owt:a: Power measurements may be ri Three fer E2.s9; for f runt parts of the world. Lows a known resistance and obtaining 1 l',.ur $3.20 events all by taking still the the cost of the (terms specified of constructional articles for making useful across !t. This is an excel- I Var postman home. the voltage drop plus lest age. things for the shop, garden and way of computing power output of It.l'. you can make things lent Name Many ideas from which A.F. circuits. For example, let us calcu- to sell. and the power output of the modulator: Con- .address late output Get this magazine at your newsstand to- nect a 2,000 -ohm resistor across the City State day. Read about the many cash prizes Connect the input terminals of in terminals. which are offered for simple experiments the V.T. voltniet er across the resistor. Actu- photography, oddities in science. uses of old the resistor. and recipes. ally, then, the A.l'. output, auto parts, radio experiments, input terminals are in parallel. formulas and others. the V.T.V.M. BOOK BARGAIN First adjust the \'.T.V.M, as outlined in in After reading your first issue, you'll agree operation procedure: start the modulator and with its that EVERYDAY SCI ENCE AND then obtain the IL('. voltage change by vary- to be, Special Sale of MECHANICS is all that we claim it ing 113; multiply this by .707 tu get the and better. E2 H.M.S. value. The power output l' equals 2000 It, A Host of Interesting Scientific Subjects- S. GERNSBACK'S where E is the It.\I.S, value of voltage. RADIO CONSTRUCTION RADIO ENCYCLOPEDIA TELEVISION METAL WORKING General Construction ELECTRICITY PHYSICS 1st Edition have been so arranged that ENGINEERING The components PHOTOGRAPHY connections can he math' directly to the have on hand 2000 UNBOUND copies of METALLURGY many this valuable Iwok, and we are disposing of AVIATION on parts themselves. The sockets are WE lugs the a which does not even cover the cost WOODWORKING PUBLIC ADDRESS AND are possible to same at price placed so direct connections of the paper and printing. The books are in first - SOUND EQUIPMENT there are AUTOMOBILES the condensers or resistors. Since class condition. sewed and stitched but unbound. PATENTS AND HOUSEHOLD AND a large untidier of parts within n small space, You can put a cover on ourself or your bookbinder is INVENTIONS SHOP HINTS exact mechanical and physical sparing can do it at a very small expense. 4 ry This indispensable radio reference lank contains AND OTHERS necessary. Take the time and care neces,a NEW DEVICES If the over 1.930 definitions, 549 photo reproductions. to build a good piece of apparatus. the book is t at drawings. and diagrams. The size of copper -oxide rev tiller is to be eons rusted pages, and is and choose 9 by 12 inches. It contains 168 OFFER! home, test the individual Junctions printed on the finest hook paper obtainable. Prac- SPECIAL those having the highest forward-backward re- tically every definition in the book is illustrated. sistance ratio. and all the subjects are arranged in alphabetical 8 MONTHS The simplest manner to make the shouts order with numerous tables and charts distributed RI.i and Itfi is to wind a length of tine, copper throughout the text. I . resistance FOR $ .00 wire. about No. no or No. : the 69 CENTS from wire PRICE PER BOOK, per foot, for which. may be found Po not send any money. we will send you the Clip Coupon and Mail Today! tables. Measure the proper length of wire book and you pay the Isostman 69c plus postage. and wind it on any fors[. (Errors of one or Cut out coupon, paste on postal card, and mail to: two fort in length of wire will be negligible, Inc., 19 Park Place EVERYDAY SCIENCE AND MECOANICS must be absolutely ISKOR PRESS, whereas high -resistance wire N. Y. 100 Park Place, New York, N. Y. RC -l0 calibrated before being used. New York, the I enclose herewith One Dollar for which you Individual shields are placed around am to enter my subscription to EVERYDAY oscillator coil and the tuning condenser. 'fhe BARGAIN ORDER BLANK SCIENCE AND MECHANICS for the next Eight shield for the condenser is short and con ISKOR PRESS, Inc. Rodhs. strutted so as to fit into the case. Roth 19 Park Place "-a terminal. New York, N. Y. shields are grounded to the -" Please mail nie S. Gernsback's Radio be next the Name The output coil should wound to Encyclopedia. 1st Edition; Unbound. I plate end of the oscillatory tank coil. The will pay Postman t9c plus postage. spacings for all coils is not crit lent. being Is'- Address tween !M -in and !rice. Contact to the external Naine test posts can be made only by the bi- polar Address sass...... City State switch. Itefotc testing be certain that the place. (Foreign or Canadian subscriptions not switch is in its proper City. .- State accepted at this rate.) (Conti/turd on following page) t.

RADIO -CRAFT for OCTOBER, 1932 249 REACTIVATOR (Continued groat page 221) In your tube checker. If it is not then O. K., return it to the rejuvenator and flash high HEADQUARTERS voltages to the grid and plate while still using 5 voila on the filament. First flash the grid by pressing switch S\ \'2 a number of times, FOR MATERIALS then flash the plate by pressing switch S\ \'1 a number of times, When the desired color has been produced, press both switches simul- AND PARTS tan,ously a number of times and then test the flew in the tube checker. If the tube does not now show a desired Improvement, then FOR BUILDING flash at higher voltages. 1- 'lashing must be dune by very short, snappy contacts until the desired color is obit ined, hence the need of Electrical and Radio especially quick- acting switches. As a general rule, the Goo -volt tap is used only on type '50 tubes. except after having definitely proven that 490 volts will not do the work: of course, 1.200 volts are used only on '50 tubes. Higher voltages can be used on TREASURE transmitting tubes, front two to three times their maximum plate operating voltages being regnlred, This is being done at some amateur st a flans. LOCATORS If Jiixh ing is continued after the blue-green color has arrived, this color trill grow weaker and so trill the tube. Radio, Audio, Ground Potential measurements, Hughes .\ large percent of '26 tubes will come back Induction Balances and other types; Oscillators and to full life faster than probably any other amplifying systems included. type of tube, and this is well, for they are the We supply all materials needed for building and "weak sister's" among the A.C. tubes. operating any of the recognized treasure finders. 'l'he '12 and '71 tubes will not rejuvenate by The following standard circuits are described in our this method on amount of the type of fila- bulletin: ment, but '12.1. and '71A respond readily. No. 1. Ground Potential, Leap -Frog Method. As may be noted by reference to the pho- No. 2. Hughes Induction Balance Type A tographs. only a single 4 -prong socket is No. 3. Hughes Induction Balance Type B 111011111 141 in the rejuvenator; an additional No. 4. Sensitive Hughes Induction Balance adapter is used for 5 -prang tubes, as shown No. 5. Simple Super-Sensitive Hughes Balance in Fig. 4. The circuit diagram of Fig. 1 Circuit s Iiow-s connections for use of two No. 6. Radio Frequency Oscillator Circuit the sockets. No. 7. Audio Oscillator Circuit Merely leave one out if an adapter is to be Mail Coupon TODAY! No. 8. Single Search Coil Hughes Induction used. Balance with Audio Amplifiers rile following results were obtained in tests GRENPARK COMPANY Io, pt. RC -10 No. 9. Combination Radio Transmitter and Re- conducted by I1.tulo- Ca.t1T 245 Greenwich St., New York, N. Y. ceiver circuit. Before Also accessories such as Frequency After High Buzzers, Practical test of nia.) mn.) Enclosed find Ilk for which kindly send me Audio Oscillators, Differential Current Transform- tin (in pamphlet oit Treasure Finders. ers, Two Stage Audio Amplifiers, etc. 1 'NO 25 50 (one read lower than the other; now, both alike) With all this apparatus you can locate buried treasures, 8 '24 3 -5 5 -10 metal war relics, 1 '12A (not '12) 3.4.5 5-10 Nane mineral deposits, subterranean water veins, buried gas and water pipes, and lost objects, 1 '71A (not'i1) 15-17 20 -Y5 tools and treasures sunken in water, etc. 1 '35 dead 0 -10 .address 4 '20 dead par Write for pamphlet giving history and theory on this specified interesting subject. above (as on a Weston test unit) All circuits are described 6 '45 20 -0 State and explained. List of parts and prices included. 20 -6 (Price of pamphlet 10e.) (par) (average) L 1 '10 40-3 40-8 Two Jewell. type 301, 0 to 1. ma meters, M.a1, S. W. LABORATORY MA 2 ; List of Parts (Continued from preceding page) Two tube shields; One power Four tip jack plugs; transformer, either special wound Parts List or any having 2.i, 5, and 7,5 -volt filament One tip jock ; windings Iwo megohm grid leaks, R1, I110; One carrying handle; and 750 or more volts on the ll.V. one 50 -ohm resistor, 112; cnndary, at 100 ma.; Three type 30 tubes; one four-hole tube socket; One 20.000 -ohm potentiometer, It3; Three 2211/2 -volt 11 batteries; One five -hole tube socket; Iwo 1,000 -ohm resistors, 114, R11; Two 4,5 -volt C batteries; 5.000 -ohm resistor, R5; 're,. four -point rotary switches, SW3 and One One dial and escutcheon; SW4; Iwo 10,000 -ohm resistors, ILO, RS; Twenty- seven binding posts wit h Insult ted top. One .1.C. SW5 ; One 20,000 -ohm resistor, 117 ; toggle switch, One 100,000-ohm resistor, 119; Two special switches S\\'1 and SW2; One resistor, 1110; One A.C. voltmeter, 0.71/2 volts (riot abso- 500.000 -ohm REFLEX RECEIVER lutely necessary); One 0,51N1 -ohm resistor, R12; (Continued front pape Y:UI One 75.000 -ohm resistor, 1113: Two phone tip jacks; One Trutest 4 -prong plug, 26.1 ; One One 3110,0110-Ohm resistor, I0.4 ; metal or wood box; One 'Protest Full- Vision Dial; Five fret of double light -coral nid plug; One .333 -ohm resistor, Ií15; Two Trutest Equalizers, capacity 2 to 35 mmf. 3 1110, 1117; One bakelite panel, 7 x 8 in. Iwo 1/3-ohm resistors, 7, %, 17A : Three 41 -ohm resistors, 1t18, 1120, R21; One 'Protest Binding Post, 1; One 30 -ohm resistor, 1122; One .\mperite Self -Adjusting Line Voltage Con- One 1.- megohm resistor, B23; trol. type 5A -5, 33; TUNING METERS Une audio any make, ratio 3 to transformer, One I.R.C. (Durham) 500 -01m Metallized Re- (font buff grunt pape 2 -101 1, T1 ; sistor. ;¡ watt. type M.l'. 4 .., 14; -pull When us`i in 11.F. or I.F. amplifier circuits. One input push transformer as described; Two I.R.C. I 27011111-011M Durhams Metallized they may Tie isst A,F.1 ; connected in the sketch of Resistors, 1. watt. type 31. F. 4, 13, 24; Fig. 2 They are connected in plate One R.F. choke as described, R.F.C. ; the return Dat' LUX. (I turham i I. 'neg. Metallized Re- lead of One copper -oxide rectifier; sistor, four tribes, the normal plate curent 1, watt, type M.F. 4. 19; of each being about 1. ma. If such One .00000-m f. fixed condenser, Cl ; is the One Arcturus type 50 Tube, 23; case, One .0001 I5 -nit va Hattie condenser, C2: the full scale reading of the meter should tine Arcturus type 55 Tube, 10; be about 5 Three .0091 -mf. fixed condensers, l'3, C4, C5; true ma. so as the signal reduces the Arcturus type 1'Z Pentode Power Output plate current. the pointer travels toward zero. Une .0I12 -mf. fixed condenser, C6; Tube, 4; In One .(12-mf. fixed condenser, C7: other words, the full scale deflection of the One Arcturus type 180 Full Wave Rectifier tarter should equal the One .1105 -mf. fixed condenser, ('N; stint of all the currents Tube. 28 ; of oll Nie tubes which pass through One .2 -mf fixed condenser, el); OHIP the teeter. Aluminum Chassis, 1 /10 -in. material, 10 x In the case of the grid -leak I )ne .1-m f. fixed condenser, ('111: and grid -eon- Ii x 2 -in. high; denser detector, the range of the meter should Ono S.P.II.T. Toggle switch, SW1 ; One Wright- De('oster No. 2 55 Dynamic Repro- be about 1. ma. since the reading decreases as Two S.P.S.T. Toggle switches, SW2, SW3; ducer with 2,500 -ohm field and output trans- the One 10 point bi -polar switch, applied signal increases, similar to the SW4; former to match PZ or '47 Power Tube, 27. case of amplifiers with A.V.C.

250 RADIO -CRAFT for OCTOBER, 1932 OPERATING NOTES Index to Advertisers (Continued from page 2225) i The of a 11 which was covered with rosin. tip MiI hot Iron soon remedied this condition. This ball Joint rendered the control -grid cir- A cuit of the A.V.C. tube open, thus causing the :474-fFUND 242 to pass PRINC1PlEá Alden Mfg. Company tube to draw so much plate current as American Technical Society 240 an excessive control -grid bias on the tubes RADIO Corporation .. 241 producing the effect as Amperite 236 which it controlled, Arco Tube Company described. Autocrat Radio Mfg. Co. 243

1 un4nee 952 sta. B .t large number of General Motors model Burstein -Applebee Co. 242 2:i2 receivers, a ea -tube superheterodyne, have been serviced because of an annoying, inter- C mittent buzz -buzz that rode in, at regular In- Cable Radio Tube Corp. Inside front cover tervals, above the signal level. As the tubes Candler System checked perfectly- nnil the interference ceased L Central Radio Laboratories 240 wires were discon- 247 when the aerial and ground Chemical Institute nected and the local distance switch was set Clarostat Mfg. Company 238 248 nt local, shorting aerial and ground, it op- Classified Section But after 3 Valuable New Books Coast -to -Coast Radio Corp. 243 Reared that the noise was external. 193 build- Coyne Electrical School listening to several receivers in the sane Formulas and Recipes ing. where no interference of this on litre was picked tip, it was evident that the I uzaa. -buzz Radio Mathematics F - .4 was caused by a tube or some part of the set. Presented luir are three brand new beaks, di- 254 and Flanders Hotel was substituted with our from the versified nature, which are most educational Emit tube hook carefully treats a subject the first- detector '24 was re- instructive. Each kit and when in full, and is prepared by an espert in the tield. : orig- G lanced, the in terh'renee was i-ndi.d The The honks are well written and thoroughly illustrat cul responded satisfactorily to all Get these books Corporation. S. 242 lnai litho had to make the contents easily- leamel. Gernsback caused the receiver to coupon below. Gold Seal Mfg. Company 234 meter tots, yet, had promptly -mail Grant Radio Laboratories 243 he noisy. 1. FORMULAS AND RECIPES Grenpark Company 250, 253 Of the four '24 tubes carried in the kit that for the Practical Man were tried in this stage. another was found This book has been compiled by S. Gernsback, a the well -known author of practical instructional manuals H that produced the same noise. Because of helpful a in various scientific fields. It in extremely design of this receiver, it is essential that to save money by making in Hoodwin, Company, Chas. 242 as and will show you how tube of the correct characteristics im used your awn home, at n fraction of the regular cost. the lirst -detector. the hundred and one preparations which you now I buy for use at home or business. Correspondence Schools 239 HERE ARE PARTIAL CONTENTS: International Brunswick 42 I. Adhesives: Glues. Cements. 2. cleansing: Stain Re- International Resistance Company 233 Metal Creft: Coloring. Oxy'dleing. 249 movers, Bleaches. 3. (skor Press, Inc. The automatic mechanism of the phono - Plating. Polishes- 4. Paints: Colors, Stains, Varnishes. r.. Class-Working: rotting, Drilling, Boring. Etching. En- graph part of the Brunswick 42 combination, Arid -proofing. cause graving. 0. wood- Craft: Fireproofing. J though relatively simple, still furnishes etemroofing. Furniture Polishes. 7. Inks: Sympathetic. eases, was found Hectograph. s. Photography: Developers. Emul- 234 for conaplttint. In some it Invisible. J M P Mfg. Company record had been lowered sions. Fixers. 9. Antidotes for Poisons. Remedies for that as soon as the Mans and Scalds. Disinfectants. 10. Preparation. into position and the pickup head had come Manipulation. Handling. 'Rising. Tables of Weights of L down tapon the records, the mechanism re- Measures. Useful Tables. RADIO Lincoln Radio Corporation 200 jected the record before it was played and 2. FUNDAMENTAL PRINCIPLES OF Mfg. Company 238 then another record was lowered, after which Radio Simply Explained-Its Origin, Nature Lynch and Functions this sequence of set ions wens repented. Martin, has been pre- cycle switch, The book, written by Louis M This is usually caused by the pared with special consideration given to young mem- blades or contacts do not open when the who have 237 whose bers in the radin profession, and those McGraw -Hill Book Company to loosen a haphazard fashion. This 199 cycle Is ended. It is only necessary gained their experience in Midwest Radio Corporation is a fundamental aid for "check- 254 the two screw's huldlftg this switch in position radio primer handy Montclair Hotel contacts will ing up" and systematizing your knowledge of radio. and adjust the switch so that the subject. moment. Regardless of how much you know about the disengage at the correct you should reati this book. N defect not permit the phono This same will HERE ARE PARTIAL CONTENTS: National Radio Institute 196, 197 mechanism to be switched off. without pulling Chapter I- Fundamentals of Radio: Electricity. Resistance. New Bismark Hotel 254 ont the line plug and the meeha nism will con- flatteries. The Magnetic Circuit. The Magnetic Field. In- dune. ductance, Condensers. A.C. Clreults, Propagation of Radio tinue to reject until this is Waves; Chapter II -The Simple Radio Set. Single. Two. P On other occasions. the mechanism will not and Three-CBI-tilt Tunen. The Battery Set. Vacuum Tubes, reject the records, Inn repeats the same one. Electric Sets. Loud Speakers; Chapter III -Diagrams. How Peerless Radio Parts Company 242 on to Read Then,: Chapter IV- Amateurs and Broadcast Sta- 240, 248 This is dew to the fact that the contacts Talking Pictures. Television. Popular Book Corporation the tions, Press Guild, Inc. 249, 251 the small switch (that travels along with 3. ELEMENTARY MATHEMATICS tone -arms do not open because they have been for the Technician and Craftsman Here. these. contacts especially prepared for the R set too close together. This manual has been must be so adjusted that when the tone -arm man who wishes to acquire a working knowledge of A com- Receptor Co. 242 head reach the end of the record, the elementary principles of mathematics. Radio and pickup subject by the author. Radio Trading Company 255 plunger or of the switch will open plete treatment of the is given 245 the trigger with special attention to the use Radio Training Association of America engages with the Mr. C. Shainmark, 243 the contacts when the former of mathematics in Radio and other technical work Radolek Company be brought Readrite Meter Works 235 stop. Either the stop will have to for those who employ its formulas daily. Ross, G. Malcom 243 in further by loosening the screw and re-set- HERE ARE PARTAIL CONTENTS: Ross Press 236 ting, or the tension on the spring contact must 1- Arithmetic: Addition, Multiplication. Subtraction. DI- two nuts on the islnn, How to 1se Decimals; Il- Fractions. Percentages. be reduced by loosening the Ratio and Proportions: III -Powers and Roots; IV -The s screw that controls the tension, Metric System; V -How to Reinsure Surfaces end Volumes; VI- Mathcrosties for the Manual and To- hnleal Crafts- Scott Radio Labs.. inc., E. H 195 man; VII -Special Mathematics for the Radio Technician; Shallcross Mfg. Company 245 Automobile Interference VIII -Commercial Calculations. Shortcut Arithmetic. In- Supreme Instruments Corp. Back cover terest Calculation. Discounts; IX-Weights and Measures; Many pa Lucca plis have been written upon X-Useful Tables. T the suppr> -i ii of noise in automotive radio Ali our books are of uniform size, 8 x 9 inches, and cases, where contain 84 pages. The hooks are printed on strong Triad Mfg. Company Inside back cover receivers. but there still arise everything known has been tried with little paper with stiff colored covers. II meccas. It is quite possible that this inter- Clip and Mail Coupon TODAY! ference nets be eliminated by having the motor United Radio Service 238 and all wires and parts beneath the hood thor- PRESS GUILD INC., IS Murray St.. New York City. Lr' -l0 Microphone, Ltd. 242 Universal oughly cleansed and washed, especially the Enclosed find E for which mall me posbald the following books: wires. .lust this. has eliminated noise that No. 1 w for ninny weeks had been combatted without No. Y Williams & Son, J. R. 241 any results, No. 3 'File grease and oil as well as road -dust, cov- 50e each, Postpaid. ering the wires and motor, contain a certain percentage of carbon and graphite which will Name (While every precaution is taken to insure accu- leaks and losses. possibility cause many high-frequency racy, we cannot guarantee against the increasing noise and impairing motor per- Address of an occasional change or omission in the preparation of this index.) formance. City and State

RADIO-CRAFT for OCTOBER, 1 9 3 2 251 V A NEW FREE SERVICE Booklets that will be mailed to you free if you send in coupon below

67. RICH REWARDS IN RADIO chinery in buildings), this arrangement is No one eau read this heavy 64-page INiofaft noticeably quieter than conventional an- book, printed throughout in two colors, tenna systems, and is therefore well worth without realizing that the radio field is installing in notoriously noisy districts. a rich and large one. lt points out in con- Lynch Mfg. Co. vincing fashion that there are many op- READERS' portunities in set servicing, broadcasting, 71. BRUNSWICK REPLACEMENT commercial radio operating, aviation, radio PARTS and television, and it describes the ex- BUREAU Service Men who have occasion to re- cellent courses of home instruction in pair Brunswick receivers, which were these subjects that the National Radio In- On this page are listed booklets, widely distributed at one time, will be glad to learn that stitute has available to ambitious men of catalogs, pamphlets, etc., of Manu- replacement parts for some sixteen models are now available all ages. Dozens of testimonials scattered facturers, Schools, Institutions, and the book indicate that the in- from a reliable organization. This firm throughout other organizations, which may be struction is highly successful in training has published a seven-page list of conveni- of interest capable radio experts. National Radio to readers of "Radio- ently indexed parts, for the following Inst itute. Craft." The list is revised each Brunswick model numbers: 14, 21, 31, month, and it will be kept as up-to- S-14, S-12, S-31, 15, 22, 32, 42, 11, 12, 16, date and accurate as possible. 33, 17, 24 and 25. 58. THE UPPCO A.C. CAR In The number of each part, a GENERATOR all cases the literature has been description of it and its price are selected because of the valuable in- all given. United Radio Service Co. The problem of furnishing power to the formation which the books contain. automobile radio receiver or portable pub- 72. FOX IMPROVED SOUND lic address amplifier has been attacked This Service is absolutely free to EQUIPMENT from several angles by interested manu- all Readers of "Radio-Craft." The three technical bulletins covered by facturers. The general trend seems to be the Fill in and mail the coupon be- name above are of special interest to toward the use of the car's regular stor- individuals or firms low; make sure that your name and engaged in public age battery for filament supply and of "B" address or theatre sound system work. address are included and are plain- batteries, rotary converters and vibrator The first describes a new all-aluminum ly written. Order type power units for plate supply. How- by number only. trumpet horn and an adapter which per- ever, the manufacturers of the Uppco Car mits two or three horns to be used with Generator go a step further and provide one dynamic unit. The second describes a double generator which replaces the standard and cannot be obtained from a heavy duty electro-dynamic speaker unit present charging generator in the car and other sources of supply. Arco Tube having a capacity of 25 watts. The last supplies six volts D.C. for regular auto- Company. bulletin describes various exponential motive purposes and also 110 volts, 60 horns for theatre and other indoor uses. 70. NOISE-REDUCING cycles A.C. for radio purposes. With this ANTENNAS For Electric and Manufacturing Co. power supply, the advantages of standard This four-page reprint of an article on A.C. receivers, amplifiers and associated noise-reducing antennas for short-wave re- 73. AUTO DIAL RADIO equipment may be enjoyed with a mini- ception is very interesting and contains a This folder describes lot of how-to-do-it material that a powerful auto mum of operating trouble and expense. will be radio receiver using a '47 pentode and is in appreciated by practical Service Men and The generator available three models, having an output rating of 21/4 watts. It short-wave fans. It deals with the use of having outputs of 100, 150 and 300 watts, uses regular A.C. tubes of the 24, 35 special aerials of the so-called and respectively. The possibilities and ad- "doublet" 27 varieties, which are easily replacable type, with transposed-wire lead-ins vantages of the arrangement are obvious. or at low cost. The speaker is of the full Upp Electric Company. "feeders" which themselves do not act as dynamic aerials but serve type. The whole outfit is un- only to connect the usually compact and may actual aerial to the be installed with receiver. Since much a minimum of tool work 69. ARCO PHOTO CELLS AND of the noise that affects on the car itself. short-wave recep- J-M-P Manufacturing Company. TELEVISION LAMPS tion is picked up by the ordinary lead-in (because of its proximity The increasing importance being as- to electrical nia- 74. THE LINCOLN DE LUXE 33 sumed by photo-electric cells for a wide Radio men who have become slightly variety of RADIO-CRAFT radio, electrical and industrial "7-74 fed-up on tiny midgets which have applications makes it desirable for Service Readers Bureau just 96-98 Park Place, New enough parts to make them produce sig- Men and experimenters to develop a close York, N. Y. Please nals will read this acquaintance send me free of charge the fol- description of the with them, for eventually lowing booklets indicated by numbers in Lincoln Model 33 receiver the published list above: with relish. they will encounter them in their every- Here is a 12-tube all wave receiver, tuning day work. For this reason the Arco bulle- No. from 15 to 550 meters, with all the fea- tin is worth reading, as it contains sonie tures that advanced radio engineering readable "dope" on the caesium type cell technique has made possible at the pres- and includes a hook-up showing how it is Name ent time. It is a superheterodyne, of used. The back of the sheet also includes course, with automatic volume control, a handy Address reference list of some 60 tubes, visual tuning, twin grid detection, double many City State of which are no longer considered push-pull audio, etc. Lincoln Radio Corp.

252 RADIO-CRAFT for OCTOBER, 1932 "Round the World" Reception! World wide reception with the new " l'inceri one" It'a fine cuustruut inn whirls includes a main .0001

battery operated shortwave w reccicer is an accomplished ilammarluttd cunden.rry gives crin Ci.mplete assurance, fact. Letters front enthusiastic customers verify the of dependable round the world performance throughout fact that they have received mnire distant stati,rus on the years to come. this receiver than on any other two or three tube The tulles used ill this receiver are 1-232 and 1 -233 cceiver. which are used :eh :image n usly aural economically in this It requires no exaggeration t0 create enlhusiusnt for receiver. the new 'Powertone" two tube spurt wave receiver. The toning rang.' of the "Powert une- receiver is The "Powert " short wave receiver handles the broad- from 1-i moms up to brtiaulrast bawl with phtg -in cast band as well as the short -waves. Price which includes four coils RC 504A Our Price $9.95 Price complete w iah set id matched tubes RC 5048 Our Price 12.50 bane -vies for ;those receiver 3.50 T, I of full sii I DYNAMIC SPEAKER POWERTONE DIRECT COUPLED JENSEN DYNAMIC SPEAKER OXFORD CHASSIS CHASSIS AMPLIFIERS l

All the latest features in amplifier design have been incorporated in this direct coupled amplifier. Input terminals for permit) tug phonograph altach- Oxfnnl Speakers are eattstroct eel to give reptndue- menl, and in addü ion, by attaching the proper tion as tirar perfect as pusable -they have long been t rmsformer. also dry cell halt cries, at microphone of are unsur- known to give radio's fittest toue qualities. The mtcnrophuue may he used for public address work. Tho tone and qualiy these reproducers WI II repriJure faithfully under the y Mina most advanced of speaker design for of receiver rant be connected to the input paa.ed. principles Any hype eundlt Ions. These speaker outputs are available s for all banc been in 4ixtr,I Speakers. of loss of energy. These dynamics inrutVur:tied terminals without fear nosai' typo Whet: as well the the old. Those that bear recuguit' are: the thre.._heint amid tfien are for use with dynamic. speakers. A.C. Types. U -7 Jr. Auditorium la.r pictured! uses 250 suspeimion balance; permanenfized (-waits -it l...1 dia - Amplifient supply field current of 2500 ohms to reel Ina tube in conjunction with x odd. electrolytic phrrgm; mnislur-pnwtf roil mountings; :u I inertia dynamic ',lookers. Resist ui-s a tu rnished w ine s .thlea,it which Insures minimum hunt. counteracted roust melba]. D.C. speakers are used. Amplifiers; operate mn flu - 1, st Red filer No. R 84- 514.95 Auditorium Speaker. volts. A.C., GO eyries. \.t' Dry A.C. Models-14" \.e P.'," Jr. Audit Tube Renifler No. R 85.- 9.95 RC 11odiI RC 245 uses 1 -224. 1 -245 and 1 -250 using 250 rectifier No. 177 -$10.00 s C. an. I7 Convert Jr. Tulle Rect No. R 86- 7.50 is at 1 12" Concert Dynamic, using 250 certifier, Output rated watts. if to 'dui Ohm It,('. }yield No. R 87- 6.95 No. RC 178- 8.50 No. RC 245 -Our Price $10.95 (less tubes) i n, ;. - Ohio D'.DA'. Field No. R 88- 7.50 a m 4.75 9" Midget Dynamic, Using 2,.11 rectifier, Exactly the sana' amplifier. but employs power It I 'mu\tl.!alui elhat No. R 89- No. RC 179- 7.50 pentode in place of the 245 tubi'. Output is D.C. Models 14" Speaker, 50110 uhnl rated at 2.5 watts. - (less tubes) field No. RC 180- 8.95 No. RC 246-Our Price $12.95 FARRAND INDUCTOR DYNAMICS 1 and 1 11" Speaker, 2:100 ohm Model RC 250 uses 1 -2_24, -250 -2S1. is S5 watts; maximum undistorted out- field No. RC 181- 4.95 Cousumpl i'arr: n t In bra, dy nitride. the fine .t rated 100 cycles, Sit lb; A.C., 9" Speaker, 2:.011 put, It watts. Cain at -pcaker at a l laid, ant where for rQnusfyRd :j_ ", db; gain at 10,000 cymes, I or hanily nue rated set;. field No. RC 181- 2.45 gain at 1fí00 cycles, ,.t'.. 51..r Input direct t.. 224 control grid; output Will take as murk Ironer and repro- All 9" 1fidgefs are suppli,.d ww it bum balancer. as the tined direr) frtnh 2511 plai-. duce In lone and quality speaker .111. No. RC 250 -Our Price $15.25 (t -a. tuba -st dynamic In buy Ina an FA ItItA ND INul'iTolt 1)l'N.\3IIl' w Olt are makhng a safe hp BALDWIN DYNAMIC CHASSIS e :meat. bee :use these speakers will

output tubes : R.C.A. VICTOR HAND gtrtrh of the n well hall the old r ïyne cutout liait' . MICROPHONE \ teial lea lure of the FAIIIItND INUi i TDit ul'N.\\IIC le that it has a frrtuoatint irae, unir stub w ldrlh tends ti bring barrir the sprrirb natal This microphone is turnidied Iule fidelity. .\b.o hurl)' fill, nut hia.I rr rattle. nrdertng. is Bit the eldest model Radials l'Ita.e state ripe or Iwaer or norther tole . Maurwhen Inch model No. 192 -$5.95 RO !Tonle reconling t;uper- 5.95 12 irate ne,drl No. RC 193 - ILterudcnr R eie i ver and Am- plifier. Do not confuse Unis INPUT PUSH - ntteruphote with the "lily' hype T.C.A. "OVERSIZE" as it can he used for many pro- PULL AUDIO TRANSFORMER fessional and rotnmercial uses. Kn. I ..eI lit 'tills) It is a single button "mike" shielded. highly t attrac- Its tive radudwn plated with at gun metal finish. steel ease. bleat for total Length is fit," and has sub.hanel st ru r t rire mounting. IW Artus of as standard equipment a fou' illy tutu roiling solder toot cord. big terminals - by r ranting col- name n. eel not ployihnR r The Introduction of the BALDWIN No. RC 417 -Our Price $2.75 lars. this unit r also, be further discussed. he reel for ',bread - From the beginning of Radio, Baldwin has been boarl' style hut alla - a pityneer in radin reproducing equipment. We Iion. need no further praise in recommending u Baldwin Franklin Transmit- .\ InartIve Irait - Speaker for any purpose in regard to radio. ting Keys and Buzzers mra:uring Its In: brw x 2's Inri i's x :t inrhe A.C. using 2X0 Tube Rect., Practice Set (all. Actually firigha No. RC 410 -Our Price $6.95 For those maul to prac- ponds: o tice cads. sending and Tel NCindings are rendered lape lots o moisture. This D.C. 2500 Olin -1 l Volts. - n ten conventional all No. RC 411 -Our Price $4.95 Ibis s tail lirartiee set I. recom- also be sel as an Ix-e mended. .\ small well Is -tace An F. transformer. D.C. e oils Field, Le- St rand, dry 2500 ohm -110 r 1 Is ef¡ilent hmaut red to t operate buzzer. We highly ,o vend the it 'ARMY No. RC 412 Price ntp1I11in as well ar for -Our $4.00 t lnn, r.r it I, nnplele. rasa raar ti ionhllr addles. D.('. 2 :,00 Obnh -lin Atolls }yield, 1.. -, thttput No. RC 300 -Key only. 95c ;I :NI:It. SI, Iti :rl.srE :M ENT Pi' Il 'l'ra us No. RC 413 -Our Price $3.25 Nn. RC 301 -Buzzer only. Ittr No RC 900-Our P 're-51.35

All offers are F.O.B. New York, and subject to p rior sale. Terms: A deposit of 20% is required with every order. Balance may be paid on delivery. Or, deduct 2% if full amount is sent with order. Mention catalog number when ordering. Dept. RC., 245 GREENWICH STREET GRENPARK CO., NEW YORK, N. Y.

RADIO -CRAFT for OCTOBER, 1932 253 A HOMEY HOTEL IN THE HOTEL DIRECTORY OF HEART OF NEW YORK THE THE RADIO TRADE NEW FLANDERS The Hotels on this page are patronized by the Radio Trade. 133 W. 47th Street through Make them your Headquarters. to 48th Street One of the Finest Hotels in Times Square Single Rooms with Adjacent Bath 51.50 and up Single Rooms with Bath 2.00 and up Double Rooms with Bath 3.00 and up Suite -2, 3, 4 People 5.00 COMING Special Weekly Rates TO CHICAGO FRED W. BIZEL, Resident Manager

rLURLD'S FAIR SITE

COME this Fall . . . see the Century of Progress in the making. The Plane-

tarium . . . aquarium . . .

Ft. Dearborn . . . and Field Museum are complete. Many more buildings will be finished shortly. Notice how the Bismarck THE HOTEL 1. NEW BISMARCK HOTEL 10. One La Salle Street Bldg. Hotel is centrally located ... Palace Theatre 11. Continental Illinois Bank Metropolitan Office Bldg. Building close to the theatre and 2. Merchandise Mart 12. Central Tr. Co. of Illinois MONTCLAIRTC1LAIR (Marshall Field Wholesale) 13. Board of Trade shopping districts . . . near- 3. Marshall Field Retail 14. Illinois Bell Telephone LEXINGTON AVE., 49th to 50th S'I'S. 4. La Salle- Wacker Building 15. ChicagoCivicOpera Bldg. est hotel to the Merchan- 5. Builder's Building 16. Butler Bros. NEW YORK 6. Chicago Temple 17. Adler Planetarium dise Mart ... and the great 7. City Hall -County Bldg. 18. Shedd Aquarium Directly Opposite the 8. Steuben Building 19. Field Museum Stadium where many con- Waldorf-Astoria 9. Foreman State Bank Bldg. 20. Soldiers' Field ventions are held. I Inviting, outside rooms ... comfortable and quiet. Wonderful beds that 8OO I OOMS lull you to sleep ... silent light signal in your room announces mail .. . Every soft water for your bath ... and food that has a reputation the world over. Room With Bath Cheerful service that invites you back. From $3.00 per day

Rooms with bath, $3.50, $4, $4.50, $5, and $6 Attractive Rates by the Month Rooms without bath, $2.50

Free to those who answer this advertisement . . A RADIO IN EVERY ROOM a map of the Central West together with a map OTTO K. EITEL of downtown Chicago. Manager Short walking distance from Grand Central Terminal HOTE and B. & O. Motor Coach BiSMARCK Station. Ten minutes by taxi Randolph at La Salle Chicago Write for booklet with from Pennsylvania Station. downtown map. American Home Cooking Served in a Notable Restaurant CITY HALL OSCAR W. RICHARDS, Manager

254 RADIO-CRAFT f o r OCTOBER, 1 9 3 2 JUST OUT Nothing Like it in Print 100 New Hook- ups

1000 Illus.

YOU

MUST

HAVE THIS GREAT BOOK

ACTUAL SIZE text book on the subject. Among the found In any radin fol- r technical information listed in this book are the Modernizing old radio sets. -Repairing speakers NEW FROM BEGINNING TO END. lowing: 8"x9 and headphones. -Making superhets out of old T.R.F. re- ENTIRE EDITORIAL SECTION 13 NEW - data for 2.volt battery receivers t'onslderable space ha, been celvers.- Constructional an old w t J remain,. automobile sels. -Constructional data for the tamoul nit ON SHORT WAVES. and to a COMPLETE TREATISE "M EGADYNE "ONE - T UBE LOUDSPEAKER devoted the informa- GERNSBACK at last la the new RADIO AND SHORT WAVE This alone h uvrth its oelgbt In gold. Ail RECEIVER.-Short wave coil winding data. -Discussion TREATISE No. 23. t'o older ably lainer and mom tion necessary for the Short Wave beginner to become a on short wave adapters, converters. receivers and how to instructive than norit No. 24 lsuie. you our is Incoquuael in this excellent Treatise. build them.-Amateur transmitters and how to construct If had regular "hoot" complete Radio Craft Treatise No. 21. you are familiar with the tyep of book No. 25 IS NOT JUST ANOTHER CATALOG. It contains them. -Television recelvers -New can be radio kinks. etc.. eto. we publish; but the N. V.-what a look' ENTIRELY valuable and up -to -date information titan Tube Table- Numerous book. no WRITE TODAY. This honk i. not just another catalog hut a veritable mint of radio Due to great cost of this attention paid to postcards or let- Enclose 4c for postage. information which will be of infinite and everlasting value to . au. Book sent by return mail. ters that do not contain postage. RADIO TRADING CO. 23 WEST BROADWAY NEW YORK Announcing The Pre -Publication Offer of the 1933 Official Radio Service Manual Off ial The importance of the last two OFFICIAL RADIO SERVICE MANUALS to Radio Service those engaged in the Radio Industry has been Manual shown by the fact that over 52,000 copies of both editions have been purchased and are in use by manufacturers, twel.0 pow., jobbers, dealers, Service Men and experimenters. Incessant demands have en- .1 Hall,. !Inc.., couraged us to publish a new and bigger Service Manual for 1933. Fun .4111..- Seen. Gua. The new manual will not contain so many full -page illustrations as in the past for the reason that not as many new sets are being put out at present, but will have in its contents important information that has not yet appeared in print. This new "dope" is invaluable to radio men. Stress has been emphasized on giving only practical material, not complicated theory. It is bound to save time and money for everyone. The simplicity in the makeup of the 1933 Manual makes information easy to find, accurately and quickly. As in the past the size will be 9 x 12 inches, with flexible, looseleaf leatherette cover. Many additional features will be included in the new manual. The FREE QUESTION AND ANSWER SERVICE which was extremely popular in the previous edition will also be maintained. We assure you that the 1933 OFFICIAL RADIO SERVICE MANUAL will be a revelation in radio literature. $4.00 Advanced orders are now being accepted at a most attractive pre -publication price of $4.00. Immediately upon publication of the new Manual this price shall be withdrawn and the Five Dollar sales price shall prevail. Take advantage of this low price -send your order today. Be among the early ones to get a copy from the first printing. Checks or money orders accepted-register letter if it contains THIS SPECIAL cash or unused U. S. Postage Stamps. OFFER IS VOID The following are partial contents of the 1933 Manual: Complete operating notes, and hints from actual experience with radio receivers in AFTER the field, collected by practical Service Men all over the country. Complete actual, pictorial views of hundreds of commercial receivers with addi- SEPTEMBER 24th tional schematic diagrams. Location of parts on the chassis are shown, and where important adjustments must be made. This section alone is worth the price of the book. Values of all intermediate frequencies used in superheterodynes, and a complete OVER 2,000 section of valuable service data on superheterodynes. Values of resistors and condensers, to aid in replacement work. ILLUSTRATIONS Latest information on combination long- and short -wave receivers, short -wave adapters and converters. How to tune and service short -wave receivers for best results. How to use the most modern servicing instruments. Complete section showing how the Service Man can build himself service instru- FREE OVER 700 PAGES ments, oscillators, etc., at very low cost. Complete section on the construction of all test equipment, including high- and QUESTION low- frequency oscillators, tube checkers, ohmmeters, etc. Tube -chart information on all new and old tubes, in handy form for quick AND reference; 9 x 12 indicating socket connections and operating values, thereby pre- INCHES venting confusion. ANSWER An entire section on money- making suggestions for Service Men, written by the SERVICE Service Men themselves who have made a success of the business; giving you short cuts and commercial information on how to get the most out of the In every copy of the servicing game. 1933 Manual, 24 cou- FLEXIBLE pons will be found, Servicing information on interference elimination, with practical data and many which will entitle you LOOSELEAF examples of interference prevention. to 24 thorough and 1 Automobile radio installation and servicing hints on automobile radio in general. complete answers by mail on servicing and LEATHERETTE Complete data on servicing all known, commercial, automobile receivers with operating on any of short cuts to get quickly at the seat of the trouble. the sets or circuits Service kinks, servicing short cuts, and miscellaneous servicing information. mentioned in the COVER manual, as ell as A complete section of various radio tables of every imaginable kind, in constant any others not men- use by up -to -date Service Men. tioned, for which ou A large section giving complete technical data on meters of every kind pertaining might have need. This rvice alone is worth to servicing in general. 56.00. But it is abso- GERNSBACK PUBLICATIONS. Inc. Complete index and cross -index to make it easy for you to find almost lutely free to manual 96 -98 Park Place, New York. N. Y. to service ners. I m nclosing hrrreilh my r nd tta.rm anything pertaining instantly. of $1.00 fur which you are to send me one copy of the 1933 OFFICIAL RADIO SERVICE: MANUAL at the special pre- publication price of $4.00 each. I understand that the price of the 1933 Manual will be Pisa Dollars upon publIeatlon, when this offer will be void. Tlds offer THE OFFICIAL RADIO SERVICE MANUAL Is Void after September 24th. FOR 1933 COMES TO YOU COMPLETE Name Address THIS YEAR -NO SUPPLEMENTS city a,ur 1tC-1032 MAIL COUPON NOW

256 RADIO -CRAFT for OCTOBER, 1932 RADIO -CRAFT OVER -THE -COUNTER SUGGESTIONS By JACK GRAND

The whistles blew and the bells rang, In this department Mr. Grand passes on Here is a good money making idea for the And the door opened with a bang. to RADIO -CRAFT readers many new Service Man who owns an oscillator. Recali- There was I, leaning "Over the Counter" thoughts and ideas he encounters in his brate radio receivers to read in kilocycles or Offering suggestions to an old "Brass with radio meters -as most newspapers and radio mag- daily over- the -counter contact azines list the stations. Thousands of set Pounder." who all over the technicians come from owners, especially those fishing for distance, Anyhow, a customer came in for an '80 tube world to one of New York's oldest retail would like to dial for stations as listed in and I suggested an 82, because the 82 tube radio establishments. these periodicals. is becoming very popular as a replacement a does, if tube for the '80 and '81 types of rectifiers, 82 It gets hot, resistor particularly of these it is placed too close to the base or other ob- as it is more efficient than either 2 MA. two tubes, especially on heavy drain sets, jects that will not allow it to dissipate heat, and is less costly than the latter. However, even if the power rating of the resistor is to obtain best results with this new rectifier, three times what it should be- correct figuring, say some of our good engineers a tube shield is required; also, a small choke To - of about 2 millihenries, with a current ca- FILTER and others. STAGE pacity of 250 ma., must be placed in series ti The flood of the best toned, longest -dist- with the common lead of the power trans- nov, ance getting sets, consisting of four and five former as shown in Fig. 1A. The resistance A.C. tubes "built at a price" as high as $7.95; of the choke must be low; approximately 50 opens the market again for wave- traps. ohms. o f + Some salesman will admit that they are When using the 82 to replace the '80 tube, To a powerful station. ç FILTER slightly broad near I would suggest that an 8 -ohm resistor be STAGE Yes sir! It appears now that all stations used in one of the filament leads to cut the are powerful with this type of set. potential to 0.5 volt. Although the current Mr. S who is connected with one of 82 3 amperes, the fila- requirement of the is the largest untilities in this country dropped in ment winding for the '80 will stand the 2 M.H. , to say "hello" and at the same time to pur- overload. IFA.C.CV' chase a 2 -watt neon tube. We all know that In the case of the '81 type tubes, the you can't read a newspaper by the light of secondary winding must be checked to see a neon lamp so I asked him what he was going that no more than 500 volts is obtained on to use it for. He told me that an inexpensive each half of the winding; then, the filament R the efficiency of STAGE method used to determine winding must be checked. If the transformer various tubes in the detector and audio systems is made by a good manufacturer, then the 7.5- is to use a neon lamp. The neon lamp is con- volt winding will stand the overload; other- nected across the output of the receiver. The wise, I recommend a small 2.5 -volt trans- glow on the plate of the neon lamp will be former rated at 6 amps. at a cost that will greater when the more efficient tube is used. still effect quite a saving. Figure 1B shows In some sets where the amplification is poor, how to connect an 82 to replace one '81; the output transformer should be disconnected 1so v., for this test. This ought to be good sews to and Fig. 1C, two 82's to replace two '81's, A.C. both using 7.5 -volt windings. If a 2.5 -volt some of our thrifty friends. transformer is preferred, the resistors shown Improving the radio -frequency stages, when 1. A (top) is shown the 82 replacing in the filament winding must be omitted. The Fig. At your power tube already overloads, is just like an '80; B (center), the connections for re- when 82 tube, a shield and choke were sold. The recommended adding another load to the old gray mare placing an '81, and; C (bottom), load. smiling report next day was, "O. K., Jack!" wiring for replacing two type '81 rectifiers. she can't even pull the first ------

PLACE PLACE POST CARD POST CARD STAMP STAMP HERE HERE

LABORATORIES. INC. E. H. SCOTT RADIO SUPREME INSTRUMENTS CORPORATIC N Dept. RCI0 1933 Supreme Bldg., 4450 Ravenswood Avenue GREENWOOD, MISS CHICAGO, ILLINOIS

PLACE PLACE POST CARD STAMP POST CARD STAMP HERE HERE

CABLE RADIO TUBE CORP. J. E. SMITH, PRESIDENT

230 -242 North 9th Street National Radio Institute

BROOKLYN, N. Y. Dept. 2KX WASHINGTON, D. C. y 256B RADIO -CRAFT

EASILY BUILT 0 -800 V. PEAK VOLTMETER FOR RECTIFIER WORK By J. S. WILLIAMS* TESTING filter circuits to determine the in Fig. 2, by adding the average D.C. volt- volts, D.C.; 475 volts, peak; 25 volts, R.M.S. correct condenser to use involves a con- age (Vav in Fig. 1B) to the A.C. compon- ripple. sideration of "peak voltages." To measure ent, shown by the ripple voltage -line in the With 135 volts applied to the set, none peak potentials requires either a vacuum same figure. of these voltages should exceed these values. tube, an electrostatic voltmeter, or an os- A D'Arsonval (ordinary D.C.) meter will The peak voltmeter described here is suf- cillograph; these are rarely found outside give the average, or D.C. working voltage. ficiently accurate for all test work of this well- equipped laboratories. Here is a simple The A.C. component, the R.M.S. ripple volt- nature. In addition, it is low in cost, easy means of constructing a peak voltmeter age, is the R. M. S. value of some A.C. volt- to construct, and it is usable on either D.C. which will indicate the peak voltages of the age which will give the waveshape in ques- or A.C. as designed; the range is 0 to 800 entire filter circuit of any standard radio tion (ripple voltage) when it is imposed volts. receiver. upon a smooth D.C. voltage equal to Vav Only five parts are needed, as shown, (Fig. 1B). Its frequency is 120 cycles, for These are: One 7.5 volt center -tap, filament a rectifier operating on a 60 -cycle input. transformer, T; one '81 type tube, V; one 1 Voltages across rectifier circuits naturally mf, 1500 V. condenser, C; one 4 -meg. re- o vary with the line voltages applied to the set. sistor, R; and a Jewel pattern 88, 0 -200 Line potentials reached in service are some- micrometer, M. _ I TIME .-I20 -1 times as high as 135 volts. Because of this, (Since the voltage and current in an A.C. SEC. voltage measurements in condenser tests circuit are continually varying in value and would be made with 135 volts applied to the reversing in direction, it is evident that the B- RIPPLE set. Or, if the measurement is simply to equivalent to an equal unit of steady direct VOLTAGE determine what voltages the condenser must current is really some value between the stand, lower voltages may be increased to maximum and minimum values E of the A.C. Va an equivalent of 135 volts, by multiplying In order to establish the units of alternating O VAV by the following constants: 110 V., 1.227; voltage and current on a common basis with those of D.C., an ampere in an A.C. t TIME f 115 V., 1.174; 120 V., 1.125; 125 V., 1.080; circuit is defined 130 V., 1.038. as that rate of current flow in an A.C. circuit which will produce heat at exactly the same rate Fig. L At A is shown the waveform at the The maximum voltage ratings of, for in- as one ampere of steady D.C. This is the effec- output of the rectifier, and at B the waveshape stance, Mallory -Elkon condensers are: 450 tive or r. m. s. value of the A.C. and is equal to as it might exist on the first condenser of the the maximum or peak value multiplied by 0.707 filter circuit. 7.5V FILAMENT '81 4 MEG5. JEWELL (for a sine -wave potential) ; also, the effective TRANSFORMER PATTERN voltage is equal to 0.707 times the maximum The output of a rectifier is pulsating direct CENTER - 88 voltage (for a sine wave). as A TAPPED 0- 200 The heating effect of D.C. is current, shown at in Fig. 1. The effect MICRO- proportional to of the filter condensers, imposed across the AMPS the square of the current (12R). If we consider output, is to smooth out these wave pulsa- T the instantaneous values of current flowing at various internals during a cycle of A.C., then tions. At B in Fig. 1 is shown a waveform square them (heating effect), then find the aver- such as might exist on the first condenser 110 V. t MF. age of these values (average heating effect) and of a filter circuit. 60 CYCLES 1500 V. then extract the square root ACUNE of this average value, Condensers have a maximum or peak volt- it will be equal to the D.C. that will produce an age rating. This has reference to the maxi- identical heating effect. The effective value of the current obtained in this manner is 0.707 times the mum instantaneous voltage, as Vp P shown by S maximum value. Since it is the "square root of in Fig. IA. The peak voltage of the output the average or mean squares' of several current may be measured by a voltmeter, as shown values during one cycle, it is abbreviated root- Fig. 2. The connections of the peak voltmeter. mean-square. or r. m. s. *Chief Engineer, Mallory -Elkon Division The entire voltmeter is easily mounted in a This subject is very nicely covered in "Radio P. R. Mallory & Co. portable case, with cord, ready for service. Physics Course," by A. A. Gherardi. -Tech. Ed.)

Supreme Instruments Corporation, E. H. Scott Radio Laboratories, Inc., 1933 Supreme Bldg., Dept. RCIO, 4450 Ravenswood Avenue, Greenwood, Miss. Chicago, Illinois. Send me. free of cost or obligation, the 1983 SUPREME SERVICE Send me fully detailed technical description of the new Scott catalog, now ready. Allwave Deluxe. Name

Address Name

City State Address Jobber's Name

Address Town State

Cable Radio Tube Corp., J. E. Smith, President, 230 -242 North 9th Street, National Radio Institute, Brooklyn, New York. Dept. 2KX, Washington, D. C. Dear Mr. Smith: I want to take advantage of your Special Offer. Gentlemen: Please send me current bulletins without charge or Send me your Service Manual "Trouble Shooting in D.C., A.C. and obligation on the items checked: Battery Sets' and your book "Rich Rewards in Radio," which explains Radio's Opportunities for bigger pay and your method of ( ) SPEED Radio Tubes ( ) SPEED Foto- Lectric Tubes aining men at home in spare time. I understand this request does ( ) SPEED Television Tubes ( ) SPEED Triple -Twin Group ot obligate me.

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ddress Address

IL1t7 State City State MY E u I. :if ;44 "HONOR

PRICE BUILT" Some tubes are sold on low -price alone. Where price is the whole consideration, we can't possibly hope to sell Certified TRIADS, the Double- Checked Tubes, with an engineering pedigree accompanying each tube. The TRIAD certification slip assures the purchaser of positive satisfaction and the dealer of a real profit. In quantities, the discount is 50% to TRIAD Dealers and Servicemen. DUALITY Certified TRIAD Tubes are of superior and regular quality. They are all right up to a very high standard. The engineering slip which is sealed in with each tube assures you of absolute satisfaction with a real guarantee. Our story in a nutshell is ''there are no better tubes that Certified TRIADS." PREMIUMS The announcementent made in "ad" last month practically cleaned out our stock of ethe $18.00 Hammond Electric Clocks which we gave free to Certified TRIAD Dealers and Servicemen with their first 50.00 order - $25.00 net. There are a few left. We are now able to make another striking introductory offer. By an arrangement with the publishers we offer a handsome copy of the popular Official Radio Service Manual or Radio Encyclopedia with each Dealer or Serviceman's initial order of 40.00- 520.00 net. No radio organization is complete without copies of all these important books. Read the publishers' advertisements which tell you all about them, then send in your first order for CERTIFIED TPIA i CO. TUBES TRIAD MA UFl TURIRNGI \ly toone order n check for $220. 00 is attached. In return. Isant the CERTIFIED TRIAD TUBES listed front I er regular TRIAD TUBE L1sl amounting to LW. less 50Só dlirount. 1 ant also to ',celte, .UtSOLCTF:LY FREE. the The TRIAD Line isa,,camplete. It includes all types manual rheeked below:

[ 1 1931 OFFICIAL RADIO SERVICE \IANI'.tL. of standard Tubes as well as Photo -Electric Cells [ 1 1932 OFFICIAL 11.AIl10 SERVICE MANUAL.

[ 1 1933 OFFICI.ti. ItAD10 SERVICE MANI'.%L. Television Tubes. [ I S. GEItNSII.%CES RADIO ENCYCLOPEDIA. CERTIFIED TRIAD TUBES are licensed by Nano. Addrr. RCA, and are sold at the same list prices. t'ity State My letterhead or business card is attached the pictorial SUP EME INDEX Testing Instruments to the new 1933 CATALOG now * t

No. 56 Set Analyzer

No. 90 SET ANALYZER No. 66 TUBE -O -METER (Also available with stand) No. 18 Counter Tube Seller

No. 33 Ohmmeter No. 77 No. 88 Universal Leakage Analyzer Tester and Converter D.C. Volt Meter

No. 70 SUPREME DIAGNOMETER Shielded No. 75 Oscillator- Seventeen modern testingAMI instrumensand combina- A.C. -D.C. Output - Volt -Ohm- tions of instruments that speed and simplify the science of radio service! The answer to Mr. Modern Radio- Ohmmeter Milliameter Man's demand for "Supreme" engineering leadership No. 62 in all his equipment ... a demand born of the bril- Tube Testing lian+, indelible way the DIAGNOMETER wrote the Power Unit name SUPREME across the horizon of +he radio service world! No matter when you plan to modernize or add No. 40 to your equipment, send the coupon NOW for the Portable 1933 SUPREME catalog -now ready-and free of cost or obligation. Tube Checker SUPREME INSTRUMENTS CORPORATION H33 Greenwood, Sand Irv. or J. obl7gerion, M. 19U SUPREME SERVICE ca ra,oq,c ady. No. 44 Name D.C. Volt- Addr.ts No. 60 Ohmmeter City Star. Handy ,