A.F.=1(T Research Is Radio's Road to Progress

OVER 125 ILLUSTRATIONS

HUGO GERNSBACK, Editor

`Her Master's Voice" l -by Radio! See Page 73 AMATEUR TELEVISION

RADIO- PILOTED BOAT

/OE SCREEN TELEVISION

BUILD AN F. M. ADAPTER A CONSTANT-OUTPUT rC1'EP. SUPPLY SIGNAL TRACER BOOSTER AMPLIFIER REBUILDING FOP PROFIT A.F.=1(t Research is radio's road to progress

World wide radio communications; national in these three new services are the transmis- and international broadcasting; radio usefulness sion of printed matter and illustrations; the im- in times of peace and in times of national emer- proved transmission of sound services; and the gency, are all the products of scientific research. transmission of sight and sound simultaneously Without such research, the American radio in- through the air. In other words, new and im- dustry would be non-existent.Without it, radio's portant communication services are now out of future usefulness would remain unexplored. the laboratory and ready for use in the interests Radio research has been the keystone of of education and entertainment, and for the ser- RCA's operation since 1919. Today, this vice of industry and commerce. Company, which is engaged in every field of Research continues, however, to explore the radio, is following its consistent policy of im- unknown frontiers of space where additional proving present -day radio services and pioneer- useful radio channels may be created for a thou- ing in the development of the new. sand and one additional services in the interest Three new services in radio now beckon of mankind. those who would expand radio's usefulness to RCA continues with 600 research specialists the public and who would create employment at work constantly improving the old and de- of men and money. They are Facsimile, Fre- veloping the new. Radio's road to the future quency Modulation, and Television. Involved is the research road, the road to progress.

Radio Corporation of America

IN (77,),:, le aRADIOTechnician

Many make $30 a week $40 $ 50

I will train you at home for many Good Spare Time and Full Time Radio Jobs

1. E. SMITH, President, National Mono Institute Radio is a young, growing field with a Sheets--start showing you how ti d.. actual Established 25 years future. It offers ninny good pay spare time Radio repair jobs. Throughout your course I He has directed the training of more men for the Radio and full time job opportunities. And you send plans and directions which have helped Industry than anyone else. don't have give many make $5 to $10 a week in spare time while to up your present job, go learning. I away from home, or send special Radio equipment ; show Set Servicing pays spend a lot of money you how to conduct experiments, build circuits. to become a Radio Technician. I train you My Courso includes Television, too. many Radio Tech- at home nights in your spare time. nicians $30, $40, $50 I Give You This Professional a Servicing Instrument week. Others hold Jobs Like These to their regular jobs Go Men Who Know Radio This instrument makes and make $5 to $10 Radio broadcasting stations employ Radio practically any test you will extra a week in spare Technicians as engineers, operators, Main- be called upon tenance Men and pay well for trained men. to make in Radio serv- time. Radio manufacturers employ testers, in- ice work on both spare spectors, foremen, servicemen in good -pay f time and full time jobs with opportunities for advancement. jobs. It can be used ::e on the test bench, or Broadcasting Stations em- Radio jobbers and dealers employ instal- and servicemen. carried along when out ploy operators, in- lation Many Radio Tech- on calls. It measures stallation, nicians open their own Radio sales and A.C. and D.C. voltages mainte- repair businesses and make $30, $40, $50 and currents; tests resistances : has a multi - nance men and Radio a week. Others hold their regular jobs and Technicians in band oscillator for aligning any set, old or new. other make $5 to $10 a week fixing Radios in You get this instrument to keep as part of your capacities and pay spare time. Automobile, police, aviation, N. R. 1. Course. well. commercial Radio; loudspeaker systems, electronic devices, are newer fields offering Find Out How N. R. I. Teaches good opportunities to qualified men. And my Course includes Television, which Radio and Television Loudspeaker System promises to open many good jobs soon. Act today. Mail coupon nosy for Sample Lesson building, installing, and 64-page Book. They're FREE. They point out Radio's spare time and full time opportuni- servicing and operat- Why Many Radio Technicians Make ties and those coming in Television; tell about ing is another grow- SS/, UN, $51 a Week my course in Radio and Television: show more ing field for well than 100 letters from men I trained. telling trained Radio Tech- Radio is already one of the country's large in- what they are doing and earning. Read my dustries even though it is still young and grow- money nicians. ing. The arrival of Television, the use of Radio back agreement. Find out what Radio principles in industry, are but a few of many offers you. Mail coupon in envelope or paste on recent Radio developments. More than 28,000; penny postcard -NOW. 000 homes have one or more Radios. There are I Trained These Men more Radios than telephones. Every year mil- J. E. SMITH, President, lions of Radios go out of date and are replaced. Dept. OHX, National Radio Institute $10 to $20 a Week in Spare Time Millions more need new tubes, repairs, etc. Over 5,000,000 auto Radios in use Washington, D. I are and C. :epolred nary haino ''r. s,1..1.. I t' tht.u- sentir lesson. I really don't ser hm. u can ands more are being sold every day. In every much for such a small i mnr of branch Radio is offering more opportunities for sso,ey. I made $600 in a year and a hall. amt which I give you the required knowledge of 1 have made an average of y10 to Suit a oe,k Radio at home in your spare time. Yes, few irrst spare time. the THIS .11.1IN Arapahoe St.. hundred $30. $40, $50 a week jobs of 20 years .JERRY, 1129 Denver, Colo. ago have grown to thousands. fpEE BOOK to $60 HELPED Makes $50 a Week If "I am nuking benveen $.:u and $6u a Creek Many Make SS to S10 a Week Extra NAS after all expenses are paid. and I an getting all the Radio mirk I can take care of. thanks in Spare Time While Learning MAKE to N. B. I." H. W. Si'ANGLEIt. 126K S. HMEN Gay St.. Knoxville. Tenn. The day you enroll, in addition to my regular MORE Course, I start you Extra Money sending Job MONEY Operates Public Address System I haro a position with the Los Angeles Civil Service. operating the Public Address System 64 PAGE BOOK In the City hall Council. My salary is $1711 month." It. 11. ROOD, It. 136. City Hall Qoodfoi'Bolh SAMPLE LESSON à' Los Angeles, Calif, ' 0 o J. E. SMITH, President, Dept. OHX s e National Radio Institute, Washington, D. C. ll \t.ithom ample Lesson and 64 page Rork FREE. I l am pari 6 I. branch of Radio checked belmv. (No salesman will call. write plainly.) Radin S vie Business of \ly then G loudspeaker Fgetems. Installations and Sen Ire I want to prove our Course gives practical, money- I Service Technician for Retail Stores Auto Radio installations and Service making is O Spare Time Radio Repair Work Television Station Operator information, that it easy to understand - Broadcasting Station Operator All- around Servicing Technician what you need to master Radio. My sample lesson If you have not derided mild, bra,,lt you prefer -mall coupon now, for Information to help you decide.) text, "Radio Receiver Troubles -Their Cause and I Remedy," covers a long list of Radio receiver troubles in A.C., D.C., battery, universal, auto, T.R.F.. I Name Age superheterodyne, all -wave, and other types of sets. And a cross reference system gives you the probable cause and a quick way to locate and remedy these Address set troubles. A special section is devoted to receiver check -up, alignment, balancing. neutralizing, test- Cil)' State 14X1 ing. Cet this lesson Free by mailing the coupon. EOM =I =I MI =I =I eI1 amIMaataamraataME RADIO -CRAFT for AUGUST. 1940 65 i 9n tha ISSUE! NEXT HUGO GERNSBACK, Editor-in-Chief MicroEhon e N. H. LESSEM THOS. D. PENTI ROBERT EICHBERG Modern Associate Editor t rt Director Trade Digest Editor echniQue ador, the Interference K. U. WAJ11öUKNt, .lanagrng Editor Ground d,o Docun`entorY RoShoP A Model Electro nic Anolting the e Contents AUGUST, 1940 Issue vioiln VOLUME XII -- NUMBER 2

Mailbag 67 Editorial: "The Serviceman's Follies" Hugo Gernsback 71 RADIO DEVELOPMENTS The Radio Month in Review 72 An A.F. Clock! Musical Time Standard 112 Radio -Controlled Boat ... 112 SERVICING Dual -Coaxial Speaker 113

New Circuits in Modern Radio Receivers -No. 35 F. L. Sprayberry 74 Replacing I.F. Transformers L. V. Sorensen 75 DEPARTMENTS, ETC.

Operating Notes 80 Mailbag 67 Rebuilding for Profit Charles R. Leutz 81 The Radio Month in Review 72 Auto -Radio Installations on All 1940 Passenger Cars New Circuits in Modern Radio Receivers Edward H. Barry 86 F L Spraybçrry 74 Fix That Radio Willard Moody 89 Broadcast News Items 79 SERVICE DATA SHEETS: RADIO Operating Notes 80 No. 282- Sentinel Model 217 -P Portable Radio Set 90 RADIO SERVICE DATA SHEETS (see Servicing) 90, 91 No. 283 -Belmont Model 678 Auto -Radio Set 91 Book Reviews 95, 100, 128

Sound Engineering -No. 8 101 TEST INSTRUMENTS Latest Radio Apparatus 114 A Low -Cost Signal Chaser -Plus C. Rask Latimer 93 Some Recent Engineering Developments 121 Radio Trade Digest 123 Shop Notes- Kinks -Circuits 127 S O U N D "Weather 6" Girls Get "Tutor" Records 127 Improved Reflex Speaker R. C. Reinhardt 96 Constant Groove -Speed Recording E. E. Griffin 98 8 101 Sound Engineering -No. ... Published by Radcraff Publications, Inc. Publication office: 29 Worthington for Radio Receivers, Low -Power P.A. Street, Springfield, Mass. Editorial and Advertising Offices: 20 Vesey Street, 20 -Watt Booster Amplifier New York City. Chicago Advertising Office: RADIO- CRAFT, 520 North Systems, Etc. H. T. Ziegler 103 Michigan Avenue. Chicago, III. RADIO -CRAFT is published monthly, on the first of the month preceding that of date; subscription price is $2.00 per year in U. S. and Canada. (In foreign countries, $230 a year to cover additional postage.) Entered at the post TELEVISION office at Springfield as second -class matter under the act of March 3, 1879.

Newest Screen -Size Television 105 Foreign Agents: London-Gorringe's American News Agency, 9A Green St., Leicester Square, W. C. 2 England. Messageries 4 Rue Faubourg, Poissonniere, France. E N G I N E E R I N G Paris- Dawson, Melbourne -McGill's Agency, 179 Elizabeth St., Australia. Dunedin -James Johnston, Ltd., New Zealand. The Fundamentals of Constant- Output D.C. Power Supplies A. C. Shaney 106 * What Causes Echo, Fading, Etc.? 108 Test and illustrations of this magazine are copyright and must not be reproduced without permission of the copyright owners. EXPERIMENTERS *

66 MAILBAG

"DI RECT- COUPLED 10 -W. YOU CAN BECOME A MONEY -MAKING RADIO AMPLI FI ER"- REVISED EXPERT Dear Editor: IN reference to the article, "How to De- sign an Inexpensive All -Push -Pull Direct - p liana113e1 Coupled 10 -Watt Amplifier" in the July, HOME TRAINING 1939, issue of the Radio -Craft magazine, I in would like to know from Mr. A. Shaney if You Learn Easily In it were possible to build the same amplifier Your Spare Hours .... By Doing Many Experiments with with 2 -2A3 tubes in the output stage, and Up -To -Date Equipment a 53 in the driver stage according to the Training Now a Better Job Here's a really fine. up -to -the minute Start for diagram as published. Of course, some Radio and Television Training that's spe- Do you ever sit down and "look your job in the tlxll' designed to give you quick results. changes must be made in the values of the TRAINING face "? Radio plays no favorites the GOOD PREPARES YOU FOR GOOD ... resistors, and I would like to know what RADIO JOBS ... AT EXCELLENT PAY. men get the GOOD jobs. Right now is the time My training values would be used in place of those starts right at the beginning to equip yourself with the technical training that of 11ad10 . unfolds each subject In a will you opportunities listed for the tubes as designed. I do not simplified, logical. understandable style. qualify for the many new You easily learn Television, Electronics. in broadcasting. frequency modulation. facsimile quite understand how you have calculated Faeslmile Radio. Radio Set Repair and and television. The fact that men in more than the values as they are prescribed in the Installation Work, etc. NO PREVIOUS EXPERIENCE NEEDED 300 broadcasting stations selected CREI training article, as my R('A tube manual does not is evidence that it pays dividends in better jobs makes no difference what your education give similar plate and screen -grid currents leas been. I can lit you for a goal -paying and more money. CREI training in Practical Radio job. Your sums. it my full Radio and Television Engineering is available in for the 6SJ7 tubes as you specify in the responsibility. home -study and residence courses. Let us suggest article, i.e., 1.5 ma. and 0.5 -ma., respectively, YOU GET PROFESSIONAL TEST EQUIPMENT PLUS the course best suited for you to keep pace with EXPERIMENTAL OUTFITS etc. The ratings I read are higher. Never- Includes U6 Radio fans (lo build complete Re- Radio. theless, I would like to use the 2.5 volts ceiver), Tools, All-Wave, All -Purpose Analyser. and Ex- perimental Outfits for conducting actual experiments with Write for FREE Book of "A Tested Plan" I have at hand, and would like to know jour men hands. if it is possible, or feasible, and how it I Supply EARN WHILE YOU LEARN To enable us to send you com- My USINESS BUILDERS allow you may be done. 1, put our Equipment to practical plete information, please slate Ill RADIO PARIS 11nw In Money-making PAUL E. Molls, R dio knIeJohs t shortly after o briefly your radio experience, edu- begot training. cation and present position-and Baltimore, .1d. whether you are interested In .a SERVICEMEN home-stud,, or residence trainino. I offer Advanced TralnIng for t15,%e already in Ra. This letter was forwarded to Mr. A. dio. Cet omplete detail. Shaney, whose reply follows: in too FREE 52.page 11a,k. CAPITOL RADIO Nha Sprayberry Course Dear Mr. Rolls: Sold Under a Money- Engineering Institute Your inquiry addressed to Radio- Clujt. RADIO TOOLS bock Aprtrmrnt Dept. PC -8, 3224 16th Street, N. W.,.Washington, D.C. has been referred to me for reply. RUSH COUPON l BIG FREE BOON It is quite possible to design a 2 -2A3 M SPRAYBERRY ACADEMY OF RADIO Direct -Coupled Amplifier. The use of the F. L. Sprayberrt Ps.ri ,. er 320.H University Place. N.W.. NOW! 53 driver, however, is not recommended. Washington, D. C. Please I me FREE. copy of An amplifier of this type is scheduled to HOW TO MAKE: IN RADIO." The great- ALL PURPOSE ANALYSER appear in the August, 1940, issue (on news- importantr Name Age . formula book stands July In print. 1). Address nt The values used for the basis of calcu- r over 10.000 City ...... Stale ..... trade se- lating the resistances in the Direct- Coupled Tear off this cutron, matt In enve- ts. es- lope , ,.te n paany IostraM. Amplifier, utilizing 6SJ7 tubes, were ob- tnheck hero L: J pro° esses frfor nome, rara tained by connecting up a tube with the d work - shop. applied potentials and then measuring the Chock -full money- currents in plate, screen -grid, and cathode making es for circuits. eonst . A. C. SHA:':Y. a n t fume a n t -1,n water p n- D104-maefetaif Gy tngrañhy.I TELEVISION pAg-kaáCTraa.r:l 1 qu er. paiinb. ce- No matter where ments. pres National hasa com plete training plan fr NEW ZEALAND SERVICEMAN you -to fit your circumstances.t Nationals fu migants. Plan Is those seeking immediate shop. insecticides. ANALYZES US as etc. p e t ennoblement and income. Dear Editor: Stall coupon below for FREE: literature. Book ns 1. While looking through your November. lowing im- NATIONAL SCHOOLS portant chapters: Useful Workshop lahorat ry Methods, 1939 issue of Radio -Craft I noticed in fully illustrated. Complete Dover's f:uide, here to buy rNArmNAL SCHOOLS, Dep. Itt' -H materials at wholesale prices: Measuring Mad Easy: Latin the "Mailbag" some opinions. One agree,. Names of Drugs and Chemicals Translated nio English. I .ova Se Ns... s... La Arien. C.r Completely Indexed. In short, Nis a each of another differs with Mr. Moody; well, I Ueluf knowledge! Worm :ta wefeht ini Bold. Pleaae send free teteestere and full detail.. Book 1a p -lo -date and has the newest methods-latest am not going to say which is correct. They discoveries--countless thousands of iacas -w Ìrh you 111 NAME Afe find useful. Remember -there are actually r 10.000 both have their faults and a magazine like clearly described formulae, processes. recipes -MANY NEVER BF.eORF. REVEALED. yours serves not only one class of Service- I MAW.. This huge book has 924 goers, nrtnted n good Mar. Size Is atra man but hundreds. I like Mr. Sprayberry's LrnY_ Send for a ro of this veritable gold min TODAY. You will never regret it. Remember. great forty of are often articles and read them diligently. I have made on formulas.lea to if I want to know all the trick circuits Waned.d0igeil and n inIrea 25er'w fó pos)t- i_ that come out, and although I may never RADIO SERVICE EXPERT Send money order. check, unused U.S. stamps or rash. .i come across one in a year, it improves my (Register all letters containing cas LEARN AT HOME IN SPARE TIME NATIONAL PLANS INSTITUTE mentality for puzzling out those that I do I 'leer. alniple. fascinating lessons New N. come across and which I cannot find in -prac- 246 -R Fifth Avenue York. Y. tiral work with eaperitnentei kits -make my publications. training easy and fast. Up to date R.T.A. .Es Correspondence Courses in methalc tinder personal guidane of The Service Questions & Answers no prominent engineer and educator, highly endorsed by lead- ers In radio hdusl ry. Sp.irir line prontS 11011 pay ' ¡! doubt had good intentions when started for RADIO ELECTRICAL £NGIN££RINC it training. out but such a section always has the Ii, y.,ur ow business ELECTRICAL ENGINEERING;;,(w c WV. START NOW yourself for ,ell Prepare yourself. at Low Cost. for a tendency to lead to the asking of a lot - fit fart )rie,. pnIi',, marins fhufield.re. Modern. simplified. you can understand quickly. of stupid questions; by this I do not mear RADIO ENGINEERING ¡fe áá:e:a.c ÿáú)a éieciaen'w°aai: ;rains you to be uper- service n real vacuum tube that all the questions are stupid. Also T BOOK FREE! per., furnished. Diploma n completion. Tnhnician. kits payment do not agree with Bob Stetler who think . RADIO TRAINING ASS'N. OF AMERICA FREEeCet r fifes of hoot rai tudent magazines, coml leis details. SEND NOW! they are mostly screwdriver mechanics. If 4525 R wood Ave. Dept, RC -110 Chicago, III, the position in America is the same as it LINCOLN ENGINEERING SCHOOL, les 131 -621. LINCOLN, Hilt. is here you find that certain areas have a predominance of one make of set and th RADIO Serviceman may run into trouble if lie RADIO TECHNOLOGY COURSES runs up against an orphan. RCA Institutes offer an Intensive course or Start September high standard embracing all phases of Radio RADIO OPERATING- BROADCASTING Against this, any man who can wait and Television. Practical training with modern RADIO SERVICING a practical murs' probably a whole month for the answer to equipment at New York and Chicago Irhoola. RADIO AMATEUR CODS- TELEVISION Also specialised courses and Rome Study ELECTRONICS yr. day cour.. 2 yea ere. come in your publication, cannot be so hot. l'ourses t der "No obligation- plan. Catalog -I Dept. nay and Evening Classe.. Booklet Upon Rpu..t. He could tear the set to pieces and test RC-40. New York Y.M.C.A. Schools each part a dozen times and probably find RCA INSTITUTES, Inc. w. 64th Street New York City/ A Radio Corporation of America Service it long before he got the answer, (That 75 Varick St.. Nov York, 1154 Merchandise Mart. Chicago

RADIO -CRAFT for AUGUST, 1940 67 MAILBAG

isn't quite the story, Mr. Carlisle. Answers gentle razzing, let me see if I can help you. go directly to inquirers by mail, at once, The wire from the grid -condenser must eslatt RADIO but certain of these questions and answers not run through the probe but must be later are published in Radio- Craft.- attached at one end, leaving 5 or 6 inches and SERVICE Editor) of the probe free, so that there won't be The Radio Kinks are quite interesting, any hand- capacity to short your grid ac- WORK with but only for experimenters in most cases tion. The probe, of course, must be of in- unless one wants to rig up something to sulating material. The gridleak must not be use for a special job and tear it down across the grid -condenser, but from grid to qÁaaaé again when finished as some of them do ground. not meet the standard requirements for a When testing grid circuits in the radio- permanent job or would be unwieldy with frequency end of the set, it is best to detach a lot of unnecessary controls or gadgets. the grid lead from the control -grid cap of The data and articles on the construc- the tube. Do not expect stations to come tion of service equipment I think are ex- exactly on frequency on dial because of the BIG tremely good and I would like to see a large capacity introduced by the long grid lot more of them. In this part of the world wire of the probe. Remember you are merely we do not have the variety of instruments trying to see if there is life there. to choose from and they are a great help What makes this device work, of course, to us in determining which type of instru- is voltage variations. These can be high ment is best for the job and in some cases frequency or audio frequency. Thus, if you RADIO PHYSICS COURSE where constructional details are available have a local station tuned -in you can test I have made quite a number of useful in- the R.F. section as well as the audio or out- BASIC FUNDAMENTALS TC7 P t struments which I should otherwise have put section of the receiver. When a set is Hero's your start in Radio! If you are a beginner, this ono 57ARTP p I5 had to 68 RADIO -CRAFT for AUGUST, 1940

MAILBAG

DEPLORES OMISSION OF "OPERATING NOTES" Dear Editor: I NOTICED in the March issue of Radio- Craft that you left out the Operating Notes section. I would like to see a bigger Operating Notes and Servicing Questions & Answers section, and less of the Radio Trade Digest. I have almost all of the Radio -Craft issues published. S. PINDROH, Pittsburgh, Pa. Dear Mr. Pindroh: We wonder whether you ever sent us any operating notes. We can't keep a department of this nature going without reader support. Send us your operating notes and tell your Servicemen pals to do likewise -we're always glad to publish them if they're considered helpful to others. Editor -

RADIO -CRAFT FOR THE SERVICEMEN Dear Editor: I HAVE been reading Radio -Craft for some time and for the last year or so have been a regular subscriber. Your cater- UTTERLY NEW ! STRANGELY AND BEAUTIFULLY ing to the Serviceman's angle of the in- ANY RADIO RECEPTION dustry is our idea of making a better mag. UNLIKE YOU HAVE EVER HEARD you FREQUENCY MODULATION . . the sen- of the F.M. transmitter. In fact. the most If have articles which aid the Service- sational new man and entirely different system favorable conditions for demonstrating are they help him make more money and of radio broadcasting and reception . . has in the midst of a crashing electrical storm. he will, therefore, wish to continue with been approved and declared "highly per- where the ordinary radio is rendered use- you. Something which, in the end, makes fected" by the Federal Communications less! During pauses between programs or Commission. It is generally predicted that stations there is nothing but deep silence .. the cash register ring -and that is what some 1000 new F.M. transmitters will he only the dial lights tell you the current is on. counts. Articles for the Amateur make it installed at an early date. More than 20 are ring but for money already in full operation. A completely TONE UNEQUALLED IN RADIO HISTORY he's taking out for new new type of receiver is required for this parts or a new rig you've told him about. amazing new Frequency Tone is so utterly realistic it is practically Modulation re- impossible CECIL HARTNESS, ception! Always far ahead, Mr. E. H. Scott to tell the difference between the G. original sound and SCOTT F.M. repro- Hartness Radio Service, has developed a magnificent new SCOTT custom built F.M. Receiver which is caus- duction. Mineral Bluffs, Ca. a ing sensation. It creates a perfection BE FIRST TO OWN THE F.M. SCOTT in radio reception far above any the world has ever known! Don't wait. Ile among the first to own this sensational new home entertainment. The WANTS V. -T. VOLTMETER NO STATIC -NO INTERFERENCE custom built SCOTT is now ready to re- - ceive the new Frequency CIRCUIT NO "NOISE Modulation pro- "! grams on the new F.M. wave band allotted Dear Editor: Frequency modulation reception by the re- by the government. ONLY the SCOTT gives IN your January issue of Radio markable new custom built SCOTT is in- a 5 -year and custom builds -Craft I credibly guarantee to was very interested in Roy Powell's let- beautiful .. like a dream come order, with infinite precision. Newest true! NO STATIC, no interference, no SCOTT offers local broadcast. short wave, ter regarding the home -made instruments, "noise" can he heard within the service area and F.M. reception all on one chassis! and especially, the V.-T. voltmeter. Would Mail The Coupon Now Money you please publish a circuit on a vacuum - -Get Saving Introductory Offer tube voltmeter operating from the line voltage of 110 volts A.C.-D.C. using a 25Z5 and a 6J5 having an input of 15 megs., and having ranges up to 1,000 volts. `'E. H. SCOTT RADIO LABORATORIES, INC. I started reading Radio -Craft about 6 4404 RAVENSW00D AVE., DEPT. 24N40, CHICAGO, ILL. months ago so I have missed many of your Send all facts, special offer, analysis of Scott receivers, and order construction articles. From now on I will ÿ blank. NO obligation. be a constant reader of your magazine. Name DENIS DAVIES, Nanainto, B. C. Address STUDIOS: CHICAGO, NEW YORK, BUFFALO, DETROIT, LOS ANGELES DISLIKES RADIO -CRAFT'S NEW BINDING Drar Editor: IS I HAVE been a regular reader of your LIKES "R. -C." AS V. -T. VOLTMETER ARTICLE magazine ever since it was known as the Dear Editor: GOES OVER BIG Electrical Experimenter and can truthfully AS a steady reader of Radio -Craft I Dear Editor: say that I get more good out of Radio -Craft, wish to inform you that I find the articles MAY we than out of the other 3 radio magazines, written by ('harles R. Leutz very instructive take this opportunity to compli- combined, I and interesting, and look forward ment you on the most excellent article that read. to read- appearing And whenever I have a radio service ing many more articles written by him. in June "R. -C. ", pg. 726, by Mr. Rufus Turner on problem or need a diagram I can Also wish to add that the article written the Universal Direct - be sure Reading Vacuum to find what I need in my Radio -Craft files. by II. S. Manney in the April issue was -Tube Voltmeter. My preference of the articles in the maga- fine, and would like to read many more. This instrument meets exactly, and fills, zines is the Operating Notes, Useful Kinks I find Radio -Craft magazine a good all - a long -felt want among constructors and & Circuits, and constructional articles on around periodical, and recommend it to my Servicemen. radio and test equipment. friends. The circuit is so well engineered and the One thing I don't like about the maga- Hoping you keep Radio -Craft in its pres- constructional data so exceptionally well zine is the new binder. It is not as easy to ent form, I remain written that this most useful unit will un- file the magazines as with the old binder. I. L. FRIEDMAN, doubtedly become an immediate addition to Incidentally, the fewer ham articles you Brooklyn, N. Y. the equipment of many grateful subscribers have in the magazine the better I will to your splendid publication. like it. Your comments are appreciated, Mr. S. I. WELLS, THOS. R. DISSINGER, Friedman -especially that part about rec- Wells Bros. Amusement Co., Chicago, Ill. ommending "R.-C." to your friends! -Editor Toronto, Ont., Can.

RADIO -CRAFT for AUGUST, 1940 69 We Apologize for Order your copy NOW the only the Delay in Delivery: - Due to editorial circumstances beyond our control, the Amplifier Handbook will be ready about July 15th.

P. A. HAND B 00K A Resume of the Contents of the AMPLIFIER HANDBOOK AND PUBLIC ADDRESS GUIDE FOI: I: \C()I I) INTRODUCTIONTION Definitions-decibels, frequency, input, output, impedance, etc. SECTION I-SOURCE Carbon microphones (single- button and double- button) Condenser microphones Velocity (ribbon) microphones Dynamic microphones Crystal microphones (sound -cell types, crystal diaphragm types) Cardioid microphones Contact microphones Phonograph pickups (magnetic types, crystal types) SECTION 11- AMPLIFIERS Voltage Amplification Design of resistance -coupled voltage amplifiers Commercial voltage amplifier The Power Stage Class A amplifiers Class AB amplifiers Class ABs amplifiers Class ABa amplifiers Class B amplifiers When to apply class A, AB, and B amplification Power Supplies Half -wave rectification Full -wave rectification Voltage doublers Filter Circuits Power supply regulation, etc. Practical (lints on Amplifier Con- struction ONLV Microphonism Placement of components Tone compensation Inverse feedback Remote control methods SECTION III -DISTRIBUTION The Loudspeaker Dynamic speakers Speaker performance ( frequency 25 response, efficiency) High- fidelity speakers Speaker Baffles and Housings CENTS Outdoor speaker installations MOST COMPLETE Power cone speakers A copy Radial (360° distribution) speaker AND AUTHENTIC baffles BOOK PUBLISHED SECTION IV- COORDINATION P.A. Input impedance matching THAT no book has yet been published which roscri A MATCHLESS VOLUME Matching speakers to P.A. installa- temamplifiers and sound systems (also kindred As complete as you would expert to find any em.tnerr- tions sl. in complete, authentic volume Is almost Ing handbook -this is how Ihe radio or I'. A. loan believable. Yet. it Is a fact. there Is no tnw,k in AMPLIFIER sAMGBOOhia d c Phasing speakers print eDRESS which cover, Address GUIDE. WitIs technical mp id to o bridge hthis idPublicread RADIO CRAFT 111 from an exceptionally large here of sources. the Effect of mismatching speakers magnificent volume on Public volume covers early hundred different subjects amplifier output Address :1 complete.magnitude-so complete and authorita- ofcoordinating conceivable branch ur sub- division tive-thatAddress t every can even P.A. (in a theoretical and practical knowledgep Public Address, A typical installation and of sound m. The editorial THE CONTENTS rink) f the skating areee so fille i ith ere iswith gIi. To actually show the scope and magnitude that he volume fully Justifies its title AMPI.IFIFR IIANDBOOK AND PUBLIC ADDRESS SECTION 1- USEFUL PUBLIC d 1940 AMPLIFIER HANDBOOK AND PUBLIC AD- GUIDE. an analysis of the contents is 001041 a he IN- DRESS GUIDE. This great HANDBOOK n Public Ad- the material ADDRESS DATA AND dress hot Id he read studied by those who con.e n withiinseahingthe larasetion At reading of build. of file hook. FORMATION 'latently son-ice and sell sound equipment. the contents show. the tccmtdetenens Speaker matching technique Db., Mu, Gm and RADCRAFT PUBLICATIONS 20 VESEY STREET NEW YORK, N. Y. The ABC of VU, Sm Mal Charts and formulas useful to the practical P.A. sound man r RADCRAFT PUBLICATIONS. INC. * 20 VESEY STREET * NEW YORK. N. Y. RCNJO Handy index to important articles Centime, Enclosed find my remittance nf 2ie for nhich send me POSTPAID, one copy of lour NEW on public address and sound 1 1940 AMPLIFIER HANDBOOK AND PUBLIC ADDRESS GUIDE.

Send me Others, for friends, also POSTPAID (4 2.:r each. I I Order Your Copy NOW- Name t ddress City Stale alp &ofcpon and Remit by check nr money Order: register letter if you send cash or unused l'.S. Postage Stamps. 1 /mail Today 70 RADIO -CRAFT for AUGUST, 1940 "RADIO'S GREATEST MAGAZINE" ...."dub" Servicemen can never understand why the "THE successful ones succeed. SERVICEMAN'S FOLLIES" By rho' l ;,ItrHï - HUGO GERNSBACK

you are lying on your sick bed, racked with pain; your eye- extremely poor businessmen. Usually, as Mr. G.O.Getter puts sight doesn't function; you cannot move your legs and your it, "They don't know what it's all about. They are lucky if digestion is they just about completely gone. In short, as far as make $20 to $30 a week and a large percentage of them do not everyone is concerned, you have ceased to function normally. even average this much." In order get to back into circulation once more, you remember My visitor then gave me an example which I really believe is a a certain doctor and you ask the wife to call him up. You are a classic and one which every Serviceman should read carefully. cautious man, however, so you instruct your wife to find out how It appears much he will charge for that in the city in which G.O.Getter lives there is a the call. She informs you that the "Doc" large hall in which a public will charge 50c for the call. This information address system is installed. Not so surprises you and long ago, the system became out of order and proprietors you immediately jump to the conclusion that he must be a cheap the of the hall asked for bids to put it into good repair. A number of quack and you certainly will not put yourself into the hands of bids were received. such a man. Your wife Mr. G.O.Getter, as usual, got the order. A then suggests that you call up a specialist few days thereafter a local Serviceman of whom she has heard. You agree with -let us call him Mr. this quickly and the tele- P.E.Ewee-called upon Mr. G.O.Getter complaining phone call is made. This time the doctor, who is too busy to answer bitterly that G.O.Getter must have underbid him, otherwise how could he have calls himself, does not come to the phone but the nurse answers gotten the order? instead. "Yes, the doctor can come over in the afternoon and his fee for such a call is $20." This strikes you as more in line with Mr. G.O.Cetter drew a sort of pitying sigh, walked over to the your own importance and you ask the doctor to conic as fast filing case and took out a receipted bill. He then asked Mr. as he can. I.E.Ewee what his bid had been, "$5," was the answer. Without a word, Nothing G.O.Getter handed him the receipted bill which was for unusual about all this and it happens hundreds of times exactly $100. At the sight of this, all over the land every day, and whether the little fellow almost passed the patient is a human out and for some time he was too stunned to speak. being or a radio set makes little difference in the psychology of human beings. It is usually a matter of confidence. Believe it or By rights, this should be the end of the story but the best part not -the majority of the Servicemen will not get this simple fact is yet to come. We will, however, let Mr. G.O.Getter tell it to you into their heads; and that is the reason why we have 50c -a -call in his own language. Servicemen -the quacks in the radio service field. "The little 'dub' just sat there and looked at me dazed and un- I have made it a point to tell the above parable, simply because comprehending. Finally, he reached for his hat and as he turned the truth of it is not always apparent, which is the reason that to go, he barked back at me, 'Well, it must be politics.'" thousands of Servicemen bemoan their fate when they cannot This demonstrates clearly what is wrong with "dub" Service- make a living. men who do not know psychology and who can never understand I know that this will bring an outburst from many Service- why the successful man succeeds. Incidentally, Mr. G.O.Getter still men who will write me indignant letters that I know nothing hadn't finished the story, because he confided in me that when about servicing and that I only generalize. What these Service- he got the check for $100, it was given to him most reluctantly men seem to forget, however, is that we are in constant contact because the person for whom the repairs were made has no use with hundreds of Servicemen right along. We see and speak to for the Union to which Mr. G.O.Getter belongs, so rather than them, not only locally, but in our wanderings around the country, having obtained the business through easy politics, he had to and therefore know their problems. Then, quite frequently, we actually fight a hostile customer to get the business! have visiting Servicemen from and out of town -believe it or not Incidentally, Mr. G.O.Getter did not always make money -many of them do come here. Particularly last and nor did year this he make it too easily. During the depression a few years ago, year, they came, and are coming, in droves to see the New York things became so bad in the servicing business World's Fair. Yes, and -the doubting Thomases notwithstanding that he even had - to rig up electric bells to eke out a meagre living. One day he had they stay here for a week at a time and spend quite a bit of money, an inspiration. He printed up a few too. other calling cards with the legend, On the hand, that type of Serviceman is the successful "Expert X -Ray Servicing." Now, Mr. G.O.Getter species -the type who actually makes money money. did not have a -real great deal of experience with X -ray machines but, being a radio All this brings me to the instance of a visiting Ohio radio man, he knew that they probably would be simpler than complex Serviceman who called on us last month. Usually we cannot afford radio sets or public address systems. Ile soon had a telephone call to spend too much time with them, but when -let us call him Mr. from one of the local hospitals. Ile found upon arriving that what G.O.Getter --came in, we spent over one hour and a half with was wrong was a defective cord. The "dub" Serviceman probably him and, as usual, when we talk to a first -class Serviceman of his would have charged 50c for the job. Mr. G.O.Getter charged $3 type, we absorb much knowledge. and got it without a murmur of protest because he had looked Mr. G.O.Getter appears to be a man of acumen and, to boot, a into the X -ray servicing business and found that the big manu- mighty successful radio Serviceman. He has been so successful in facturers of these machines charged exactly that price for cord his community that he is now erecting a good -size brick and replacements. Ile had read through all the literature of the manu- steel building, made from the profits of his business, which com- facturers and knew what the price scale was. In no time he was prises public address systems, stage lighting and talking picture doing the repair work for practically every hospital within the equipment. Mr. G.O.Getter feels sorry for and pities the "dub" county. He still does it today -not personally, of course -but he type of Servicemen and has naught but contempt for them. He has a man broken into the work who now does it for him. maintains that the greatest trouble with them is that -first, they Opportunities? Yes, there are plenty of them in this country are not salesmen; second, they invariably employ the wrong and good money is to be made even today by Servicemen. If they psychology when talking to their prospects; and third, they are don't, it usually is their own fault.

RADIO -CRAFT for AUGUST, 1940 71 THE RADIO MONTH IN REVIEW

The "radio news" paper for busy radio men. An illustrated digest of the important happenings of the month in every branch of the radio field.

"GOLDFISH BOWL" NEWS STUDIOS 4 War and near-war conditions throughout the world, last month speeded completion of N.B.C.'s new Special Events and News Studios here shown under construction. Glass- enclosed, the new speaker -type studios -built in the News Room, 4th floor, RCA Building, N. Y. C.-offer commentators no more privacy than is ordinarily accorded a goldfish. Feeding news bulletins through a slot, from the adjacent teletype and shortwave monitoring rooms. makes it unnecessary to open a door.

Photo-- Hartford Courant HAM -TELEVISION CAMERA -TUBE Amateur radio has won the distinction of being mainly responsible for the introduction, last month. broadcasts from (a) enemy countries, (b) of a comparatively low -cost Iconoscope or tele- ABROAD countries occupied by Germany, or (c) vision image pick -up tube. This makes it possible RADIO plays an indispensable with is forbidden. for the first time for experimenters and shortwave countries allied Germany, enthusiasts to set -up their own experimental tele- part in modern warfare as This calls to mind a recent incident. It vision transmitting stations! Photo shows Mr. Lamb evidenced by the bits of seems that the reprint, in the Radio Month holding the new type 1847 camera tube (right), 1939, and looking at the associated lens system; below is news that censors are passing these days. in Review department of the Nov. smallest previously -available image tube. Items noted last month indicate in various issue of Radio -Craft, of an actual newspaper degrees that this is so. clipping entitled "Nazis Are Warned to Shun Paris. -A U.P. report credits the Official Foreign Radio," aroused the ire of Mr. village of about 1,000 persons, near Basle, Journal with publishing a decree authorizing Josip Sliskovic, of Vienna. Mr. Sliskovic one member of a household would be as- employees of radio stations to arm for pro- wrote to say that "As a neutral foreigner, signed to keep a sharp lookout. The latter tection in the exercise of their duties. living since 18 years in Germany and being idea, of having lookout posted, seems to be Berlin. -Radio stations of Luxemburg and the chief engineer of one of the biggest much the likelier of the two. Brussels have become part of the German Vienna radio firms " *, he felt it his duty to Broadcasting System, A.P. announced. write us the truth. As he puts it, the German A young lady member -Zoe, by name -of London.- British Broadcasting Corp. en- Government never published the item we the Sidney, New South Wales, police, has gineers with the Advanced Air Striking quoted; and he and his German friends been the No. 1 goodwill publicity attraction Force have set up a broadcast studio and everywhere were enjoying unrestricted at various police functions for more than a station on the French battlefront. Discs listening privileges on multi -band receivers. year. Photographs received by Radio -Craft made with an A.A.S.F. recording van permit A short time after Mr. Sliskovic's letter last month from Constable 1st Class Adam dubbing into programs, from the front to was received, the New York Daily News Denholm, trainer of this German shepherd London, recordings made at airdromes and printed a special cable from wholly neutral dog, now 3% years old, show 2 of the more billets. Programs are written, censored and Basle, Switzerland, from which we quote: than 180 tricks this dog has been taught to broadcast all in the same building. This "Despite the severe penalties risked, more perform in response to orders received on technique enabled a French- German en- and more Germans are listening to foreign the portable radio set she carries! These counter on the Maginot Line to be broadcast news broadcasts to find out what really is include drawing water from a well and blow -by -blow. (In similar fashion Berlin going on." One German said a favorite pouring it over an unconscious man (photo subsequently broadcast the account of a method to avoid detection was for listeners on facing page), arresting an armed crimi- German -Belgian fight for an Albert Canal to lie flat on the floor with the radio set and nal, putting on and removing her collar, bridgehead, newspapers stated. Editor) himself covered with several quilts to deaden discharging explosives or a revolver, and un- India. -From Simla comes a U.P. report the sound; another German said that in his furling the Union Jack and then sitting up that all public and commercial radio licenses while the National Anthem is being played! 'Chief Ensiueer, 1:ansell- itadln, Vienna VII/62, Stift- have been canceled; and that listening to gasse 21. How about training "seeing eye" blind -aid dogs to follow radio commands?

ULTRA -SHORTWAVE HORNS! Here's one Ripley may SHORTWAVES spot! Instead of follow- THE 1847, as the newest in ing schoolbook rules, Iconoscope which demands some (image viewing) wire -antenna arrangement tubes announced last month for transmission and re- is designated, was developed by RCA Radio - ception, Mr. A. P. King Mr. of Bell Telephone Lab- tron in cooperation with James J. Lamb, oratories has demon- A.R.R.L. Research Engineer (see photo strated that efficient, above). R. M. in R. suggests that radio highly -directional radia- Servicemen might try hand at making tion of 15- centimter their (3,000-megacycle) waves up a sight- and -sound 2 -Way Inter -Office may be obtained by Television Communication System, by com- using metal horns. As the dash -line in photo bining, in duplicate, a standard television shows, one merely points receiver or adapter with a simple trans- the horn -antenna of one mitter incorporating the low -cost 1847. Use station at the other, for distances within (ordi- ordinary photographic floodlights for illu- narily) the limits of the minating the subjects. The 1897 requires only horizon. The fidelity is 600 anode -volts, has better than 120 -line flat to I db. over a mosaic bandwidth of 250 mega- definition, and has a under 2 ins. in cycles, it is said. dia. Electrostatic deflection is used. 72 RADIO -CRAFT for AUGUST, 1940 THE RADIO MONTH IN REVIEW

TELEVISION HOPS 234 M ILES TO SEA TO BE SEEN Photos received last month show conditions aboard the S. S. President various public rooms. It is estimated that when the DX television record was Roosevelt, en route from Bermuda. when the recent record of television signal made the boat was about 7 miles below the horizon with respect to the top reception aboard the ship, 234 miles at sea, was made. Above, ship passengers of the Empire State Building. First explanation suggested by RCA for this watch images received from the Empire State Building in New York; and, in unorthodox long- distance range was refraction of the ultra -shortwaves from a second photo as picked -up by a mobile unit on deck. Thus this trip between point where a cold layer of air formed a junction with a high warm layer of New York and Bermuda instituted the first "television voyage." Programs orig- air. A second was that the ultra -S.W. signals were reflected from an ionized inating on the ship were piped by coaxial cables to receivers in the ship's layer of the atmosphere.

Memorial Day traffic in New York City Oranges (N. J.). Kiddie programs for a was unsnarled by Police dept. monoplanes, half -hour tangled with police headquarters SOUND 2- way -radio equipped. Instructions from the reports to roving radio police cars. COMMITMENTS keep "The air to headquarters immediately were re- F.C. Commissioner Fly last month handed Voice of Hollywood" from layed to radio -equipped traffic cars... . a bouquet to the Susquehanna Emergency coming East for the broad- Professor Gordon Ferric Dull, former Network for its fine work in past emer- cast series but recordings made in Holly- chief of the ballistic division of the U. S. gencies. The tribute was paid to the S.E.N., wood, and mailed to WOR, solve the problem Army Ordnance Dept. and now a professor a group of Susquehanna Valley and eastern 3 times a week. . . Mobile sound record- of physics at Dartmouth College, last month seaboard radio amateurs affiliated with the ing equipment sent to the San Simeon, Cal., pointed out that ultra -short wavelengths A.R.R.L., by Mr. Fly during a C.B.S. pro- home of veteran American publisher Wil- such as -may be generated by the W.E. gram dramatizing the amateur network's liam Randolph Hearst; later, an air pro- "doorknob" tube (illustrated and described successes, in cooperation with the American gram, over station WMCA in New York, in the May, 1939, issue of Radio- Craft, pg. Red Cross, when rivers inundated large incorporated an extensive "interview" with 658), have extremely important applications areas, snowstorms isolated communities, Mr. Hearst. The "interview" was a trans - in war time. For example, ultra -S.lV. beam epidemics threatened large rural areas, and scription made from the pick -ups by the radio communication between ships, or ships rare medial cures were needed to save dying mobile unit and airmailed to WMCA. and shore, would be almost lnor /r free from persons... . Chiure tones generated by 5 radio tubes interception (or perhaps even from jamming Hobbiests at a Bell Telephone System now clarion the quarter -hours from a loca- -especially with frequency -modulated trans- hobby show in Denver included many radio tion, in a clock, at 7th Ave. and 47th St., missions?- Editor). The advantages of "hamatears" (to quote The New Jersey New York City. A master clock in the N.B.C. transmitting in a searchlight- like beam are Bell) who set up 2 complete 2 -way short- studios regulates the timing. also applicable to war fronts on land, Prof. wave systems, one for phone and one for Most unique recording of 1940, to date, Hull points out... . code. is the "Flight of the Flagship," reports the Signals from N.B.C.'s shortwave station N. Y. Mirror. The discing, by General Rec- W3XAM last month played cops -and- ords, includes sounds heard on a transcon- robbers with the police radio system of the F.M. tinental air flight: greetings of the steward- FREQUENCY Modulation ess, motor warm -up sounds, the dash -dot, seems to have earned for dot -dash buzzes of the radio beams, etc. Itself an almost permanent niche in this department of Radio -Craft. All news of the month of course pales into insignificance alongside the fact that the Federal Communications Commission took a deep breath and then announced the allocation of the full 42 to 50 mc. range to F.M. This necessitated kicking -out a television channel but the decision provides 40 F.31. channels, each 200 Ire. wide; 35 are for commercial stations and 5 for "non- commercial educational" stations. Newest score for frequency modulation reads 130 applications for transmitters pending at Washington. Immediate action is expected.

The new F.M. range clipped -out the No. 1 television band (44 to 50 mc.) which, after "HER MASTER'S VOICE" -BY RADIO! Jan. 1, 1941, will cover the former No. 2 COUNT GEORG VON ARCO -1869 -1940 (Cover Feature) band assignment (50 to 56 mc.); the old The man mainly responsible for the formation of Miss Zoe, German shepherd dog on the staff of the No. 2 band will be given a new yard in the German Telefunken Radio Co., Count Georg Sidney, New South Wales police, has been taught which to play (60 to 66 mc.); 16 other von Arco, died last month in Berlin at the age of do many to tricks via remote control. The photo channels on still higher frequencies continue 71. Often referred -to as a born scientist and said shows this wonder dog receiving instructions - to be a pacifist at heart, he resigned from military from the loudspeaker of the portable radio set to be assigned to television. Now Mr. Serv- service in the Prussian army to devote all of his strapped to her back -to fill a pail with water and iceman can soon go to town on realigning energies to the development of his ideas for radio fo pour the water over an unconscious person! This the approx. 3,000 television sets in the New equipment. New tuning systems, for instance, were is lust one of the more than IBO tricks in her invented by Count von Arco when crystal detectors amazing repertoire. (Story on facing page.) York area. were yet being developed.

RADIO -CRAFT for AUGUST, 1940 73 SERVICING

6H6,2N0: DETECTOR& RECTIFIER FROM P. M. y. I. F. AM PLIFIER ro 1,H5M00 5.G. (EACH) MMF. F.M. (A.M. R LAY AUDIO SECTION) OUTPUT séciiOlb 455 KC 15 MF.

TO RECTIFIER A.V.0 FILAMENT (F M. SECTION) r2 2- TO VOLUME CONTROL MEGS/ AND A.F. AMPLIFIER 0.1- 21.000 MEG. JACK PLUG AUDIO OHMS F.M. (EACH) OUTPUT 0.41- 10.000 TO RECTIFIER -} MEG. OHMS FILAMENT © (A.M. SECTION) 41,000 OHMS O.1 -MF. 5OMMF.(EACH) NEW CIRCUITS I MODERN RADIO RECEIVERS In this series, a well -known technician analyzes each new improvement in radio receiver circuits. A veritable compendium of modern radio engineering developments.

F. L. SPRAYBERRY No. 35

(FIG. I ) 4- POSITION TONE CONTROL HAS frequency modulation in this receiver in 2 result, less failure of input condensers has UNUSUAL CIRCUIT units; each with a separate power supply. been achieved. FADA MODELS 64APC, A66PC, 74APC AND In the amplitude modulation (A.M.) posi- A76PC. -A single switch grounds (a) a tion, as shown in Fig. 2, the regular audio (FIG. 4) CIRCUIT MUTING ACHIEVED BY regular tone control condenser, (b) an in- output is derived from the usual diode rec- OPENING CATHODE CIRCUIT verse feedback circuit, and (e) a bass com- tifier, while the 1st -detector and I.F. screen - CROSLEY MODEL 719. -By meals of push - pensator circuit, in proper combination to grid voltages for the A.M. receiver section button control, a grounded switch lever is achieve the tonal quality desired. are supplied through a relay solenoid. In released front the output cathode circuit, We may see, as in Fig. 1, that when con- carrying this screen -grid current, the relay and connected to the solenoid of the mag- tact 1 is grounded by the switch, the high opens the entire high -voltage supply for the netic tuning coil. frequencies in the audio circuit are pro- frequency -modulation sections of the re- "Magnatune" for operation of the tuning gressively attenuated. The bass compen- ceiver. mechanism. When the tuning operation is sator and inverse feedback circuits function completed, the grounded switch arm is again normally in this position. In position 2, all (FIG. 3) FILTER INPUT CONDENSER PRO- returned to the output cathode circuit and tone control circuits are open. In position TECTION reception is resumed. The circuit is shown in Fig. 4. 3, the bass compensator circuit is made in- Si F. %ARTWARNER MODELS 03.511, 07.58 operative by shorting out the 0.005 -mf. con- AND 03 -SS. -While it has now become gen- denser in the bass compensator circuit. In eral practice to make use of a resistance (FIG. 5) CRYSTAL MICROPHONE AND position 4, both the bass compensator and in the plate circuit of a half -ware rectifier PREAMPLIFIER USED IN RECORDING the inverse feedback circuits are shorted for A.C.-D.C. supply, this has not been WILCOX -GAY MODEL A -70. -Being pro- out. found adequate to protect the input filter vided with complete recording equipment, The effect on the tone of progressing condenser from voltage surges. this receiver makes use of a crystal micro- from points 1 to 4 is to obtain deep, mellow, The plate resistance has taken the form phone and pentode preamplifier. normal and brilliant tones in succession. of a pilot and a section of the rectifier The preamplifier is a 6J7. The signal level filament as in Fig. 3, but did not have all entering the 1st audio grid (6Q7) may be (FIG. 2) PUSHBUTTON AMPLITUDE -FRE- the anticipated advantages with respect to comparable with that from the radio tuner QUENCY MODULATION CHANGEOVER the input filter condenser. Now, a small and crystal pickup also entering at this STBONIBENC -t. 1sLioN Nu. 435. -With a resistance, 33 ohms in this case, has been point. double pole -double throw switch operated by placed between the cathode of the rectifier The circuit of the microphone and its a pushbutton and a relay, reception may and the filter input to limit the peak vol- preamplifier is shown in Fig. 5. It is one of be switched from amplitude modulation to tage on the filter input condenser. As a the 3 inputs selected for the audio channel.

PUSHBUTTON 140 25L6 TO CRYSTAL TO SWITCH OHMS PREAMP?IFIER PICKUP 2ND - OETECTOR

CMICROPHONE

VOLTAGE DOUBLER OUTPUT TRANS. 5W

SPEAKER FIELD

LINE 30 T. M MF. (EACH) OHMS -B +' VOLUME 10 CONTROL O o MF

74 RADIO -CRAFT for A U G U S T , 19 4 0 SERVICING

The June issue of Radio -Craft contained the first article in this valuable series on coils; the title: "Servicing R.F. Coils." The July issue contained the article "Replacing I.F. Coil Windings." In this 3rd, next to concluding article, the author gives Service- men and experimenters information they have long been wanting on the considerations involved in properly replacing manufactured I.F. coils.

4 Fig. I. A- Standard Meissner air-core I.F. transformer; B- iron -core I.F. (increased selectivity); C- new "plastic" I.F. transformer.

REPLACING I. F. TRANSFORMERS L. V. SORENSEN

N the article entitled "Replacing I.F. satisfactory complete Replacement Trans- tubes and 3 I.F. transformers, in a circuit Coil Windings," published in last former is available. There is only one condi- similar to Fig. 2A, the transformer wind- month's issue of Radio -Craft, it was tion when this is not true -when there are ings employed produce comparatively low pointed out that when an I.F. trans- a number of sets of the same model to be gain -per -stage, at least in the 1st and 2nd former fails there are 2 possible courses repaired, in which case the spacing of re- transformers. The last transformer driving to pursue in making the repair: (1) either placement windings may be worked out on the diode usually enables amplification ap- replace only the defective winding; or, (2) one set and then applied to all of the proaching that of a conventional "Output" replace the entire I.F. transformer. The remaining sets. Practically the only occasion I.F. transformer for a set with only 1 I.F. conditions that dictate replacement of the for such a condition to occur is when a tube. coil only were discussed in that article and Serviceman is connected with a large dealer Sets that employ 2 I.F. tubes but only 2 detailed directions were given for making or jobber handling a single line of receivers. I.F. transformers instead of 3. as in Fig. the repair. This next article concerns repair 2B, usually employ a resistance- capacity by replacing the entire transformer. SELECTION OF REPLACEMENT I.F. TRANS- coupling network between the 2 tubes in as a resistance - FORMERS much the sume fashion capacity coupled audio-frequency amplifier. ECONOMICS OF REPLACEMENT By far the greater number of radio re- difference lies in the The Serviceman, like the doctor, has es- ceivers employ only 1 I.F. amplifier tube The only essential sentially only one commodity to sell -his which means that both the input and output values of the resistors and the condenser. knowledge of the operation of a given kind I.F. transformers must have high gain if in the frequency of the signal (I.F.) and is much of device, in this case radio sets, and his the set is to be adequately sensitive. unless in the amplification produced, which ability to correct their malfunctioning. In there is a high -gain stage of R.F. amplifica- lower than that produced by the conven- order to sell the greatest quantity of this tion ahead of the converter (which is com- tional resistance -coupled audio stage. Such commodity, the Serviceman should confine paratively rare). Even in the case of such a sets employ high -gain input and output I.F. his efforts to diagnosing trouble and to set the gain produced by a pair of high -gain transformers and should be considered in checking repaired sets, leaving to an assist- I.F. transformers is seldom objectionable. this discussion as belonging to the type of ant the actual work of repairing. In the few cases where a set may be too sets having only 1 I.F. stage. Returning The installation of a completely engi- sensitive because of the use of a high -gain again to the set with 3 I.F. transformers, neered and factory -made replacement I.F. replacement transformer the sensitivity can it must be realized that at least 1, probably transformer is a task easily done by the always be reduced by a shift in either 2 and possibly all 3 transformers employed least experienced assistant, requiring only cathode bias or screen voltage. It can there- have low gain so that the overall amplifica- checking and aligning by the Serviceman; fore always be assumed that the correct tion will not be too high. If one of these and, in rare cases, the elimination of oscil- replacement I.F. transformer for a set with transformers is replaced with a high -gain it is probable the circuit lation when the factory -made product re- 1 I.F. stage should be of the high -gain transformer that sults in enough greater gain over the type. Replacement I.F. transformers of vari- will oscillate. original transformer to cause oscillation. ous types are shown in Fig. 1; these have 1 It is also probable that such a set has On the other hand, the installation and side of the shield can cut away to clearly a super- abundance of I.F. gain and that :adjustment of replacement I.F. windings show the interior construction. consequently, if the replacement trans- require the knowledge, experience and The air -coil (Fig. 1A) and iron -core (Fig. former happened to have somewhat lower judgment of a qualified Serviceman, and is 1B) I.F. transformers have coils protected gain than the original transformer, the set a task not properly delegated to an assist- by a heavy coating of white wax. Shields are would still be amply sensitive for normal ant. 1% ins. square and 3% ins. long. reception. Following this idea and consider- Replacement Transformers vs. Replace- The "plastic" I.F. transformer (Fig. 1C). ing that the 1st and 2nd I.F. transformers ment Transformer Windings. -As long as is featured by a 1 -piece molded low -loss usually have low gain in sets with 3 I.F. factory -made replacement I.F. transformers trimmer -base and coil form, held in place in transformers, the logical replacement for of good quality are available at attractive the shield can by a novel flat -spring mount- either the 1st or 2nd of these transformers prices the sound -thinking Serviceman will ing arrangement. Coils are protected by is a Meissner "Interstage" transformer realize that he can not afford not to use "Q- Max "; shield is only l',á ins. square and which was purposely designed to have low them, falling back on Replacement I.F. 2% ins. long. gain. The Serviceman, with his signal -gen- Windings only on those occasions where no When radio sets have 2 I.F. amplifier erator and output meter, can quickly tell RADIO -GRAFT for AUGUST, 1940 75 SERVICING

12.. I.F. AMP. 2 9 I.F. AMP 2N0.-DET., A.V. C. y s : COUPLING _ CONDENSER dIP e

A.V.C. "8+" A.V.C.

whether the use of such an "Interstage" INPUT & INTERSTAGE I.F. TRANSFORMER transformer. The length and path of the replacement transformer (low -gain) has COLOR CODE black lead is seldom of any consequence on made the set too insensitive for satisfactory Red = "B +" input or interstage transformers but on service. In those rare cases in which the Blue = Plate output transformers should be short and sensitivity is too poor, it will be necessary Green = Control -Grid direct to the diode load resistance and should to change the "Interstage" transformer for Black = A.V.C. be kept dose to the chassis. an "Input" transformer which has higher When the defective transformer is an gain. If the practice of replacing either the OUTPUT I.F. TRANSFORMER COLOR CODE output transformer with the diode filter and 1st or 2nd I.F. transformer (of a set with perhaps part or all of the diode load re- 3 IF. transformers) by an "Interstage" Red = "B+" Green = Diode sistors and condensers assembled in the transformer is followed, the number of cases same can there arises the problem of what in which it may be necessary to change the Blue = Plate Black = Diode Load to do with these extra parts. If the set is "Interstage" for a higher -gain unit will be large it is recommended that these extra far fewer than the number of cases of oscil- Yellow = Center -Tap (when used) This resistors and condensers be assembled neat- lation or excessive regeneration that it code of connections must be fol- ly on an insulated terminal strip as in would be lowed if proper results are to be necessary to correct if high -gain obtained. Fig. 3 and that the strip then be installed transformers were always installed first. The POSITION of the blue (plate) lead under the chassis close to the replacement In the case of the 3rd I.F. transformer, and the green (diode or control -grid) lead I.F. transformer. This is, of course, not the feeding a diode detector in most instances, should be carefully chosen so as to be as best practice technically which would be to the gain may approach that of the conven- far away from other grid or plate leads as put the parts back into the new transformer, tional "Output" I.F. transformer. It is, ac- possible. Usually the position of the original but is a reasonable procedure in making a cordingly, recommended that an (Meissner) control -grid and plate leads is a reasonable satisfactory repair with a minimum expen- "Output" I.F. transformer be the first choice guide to the best position for the leads of diture of time. as a replacement for this transformer. the replacement transformer, but in cases The arrangement of parts shown in the of oscillation trouble that occasionally figure, is merely a suggestion, as the actual INSTALLATION OF REPLACEMENT I.F.T. develop when the replacement I.F. trans- values and connections depend upon the The replacement former has higher gain than the original original circuit. If the set is congested it is transformer should be transformer, the original lead installed in the defective receiver in as positions may recommended that these extra parts be in- neat not necessarily be best, and a new position a manner as possible because customers stalled in the base of the replacement trans- frequently with greater separation between certain former either on parts removed from the judge the technical quality of "hot" leads may have to repair work by the mechanical appearance be selected. old transformer or on any reasonable sub- of the finished repair. As a rule, the blue and green leads should stitute that can be improvised by the be as short and direct as possible. The Serviceman. In some instarces it may be necessary to length and of drill new holes in path the red lead is seldom of the chassis for mounting any consequence on any (Meissner) SHIELDED LEADS the replacement transformer. A few minutes I.F. The use spent to properly lay out the holes so that of shielded leads should be avoid- the transformer, when mounted, will be ed because close- fitting shielding disturbs appropriately spaced GROUNDED the I.F. transformer characteristics in sev- with reference to LUG adjacent parts and will have its sides par- eral ways. The 1st and most apparent effect allel to or at right- angles to prominent sides of close- fitting shielding on the grid, diode, or edges of adjacent objects is a good in- or plate leads is to add to the circuit capac- vestment. When replacement transformers ity. This requires that the trimmer con- are put on a chassis at odd angles with denser in the transformer be operated at a respect to adjacent parts the customer is correspondingly lower capacity. quite likely to undervalue the technical If the shielded lead is long and the ability of the Serviceman in direct propor- shielding is close fitting it is entirely pos- tion to his apparent lack of care in making sible that the amount of capacity added in the installation of the new parts. the shielding may be more than the amount required to tune the transformer, in which In case that the hole under the original SUGGESTED MOUNTING OF DIODE LOAD case the trimmer will never "peak" but the transformer is too large to permit the re- A.V.C. NETWORK AND BYPASS CONDENSER output will only approach a maximum as placement transformer to be mounted over - FIG.3 the capacity is reduced. In a less a flat metal plate should exag- it, first be installed gerated case, where the capacity added in and the replacement transformer mounted the shielded lead is not enough to prevent on it. In any case, the work should be done the trimmer from "peaking," as possible. the "peak" as neatly may occur at a setting of the trimmer con- The leads on the replacement transformer denser that is too loose for stability when may have a different color code than the the transformer is subjected to vibration. original transformer leads; consequently A convenient check for this fault is to the original color code should not necessarily hammer on the side of the transformer with be followed. The popular I.F. replacement the handle of a screwdriver after the trans- transformers have the following color code former has been aligned. If the output unless otherwise specified: changes materially due to hammering, the 76 RADIO -CRAFT for AUGUST. 1940 SERVICING

INTERMITTENT Quick, now, what are the an- SHORTCIRCUIT swers to the following questions? (1) Under what conditions is it preferable to install a Replacement Trans- former instead of a Replacement Trans- former Winding? (2) How does a "plastic" -type I.F. _._J transformer differ from air -core and iron -core types? (3) What instruments would you use to check for excessive gain caused by an interstage -type replacement I.F.T.? A.V.C. _ AMC.. (4) What are the causes of, and remedies for, Single -Stage Oscillation? TEST FOR SINGLE-STAGE OSCILLATOR (5) What are the causes of, and FIG. 5 remedies for, I.F. circuit oscillation off - resonance? than 2 or 3 inches. It is, in other words, their sets and then wonder why they have Give up? Then, read this article, which a low -capacity shield. so much difficulty making a single I.F. stage answers these questions - and many On experimental or custom -built sets that behave; and why they have to use such ab- more -in detail. have not enjoyed competent engineering, normally high biases on their I.F. amplifier long grid or plate leads have sometimes tubes before stability is attained. The fact been employed without the builder being of the matter is that the grid -to -plate capac- trimmer is probably too loose, and the aware of the troubles that may result. ity of the I.F. amplifier, although it is only shielding should be reduced to permit the When shielding is added to such leads, to 0.01 -mmf. or less, is the limiting factor in trimmers to be worked at a more stable part eliminate troublesome coupling, it should the amount of gain that can be obtained of their capacity curves. be of large diameter such as is used on the from a tube before oscillation results. The 2nd objection to shielding on grid, "lead -ins" of auto -radio sets. In order to obtain high gain from an diode or plate leads is that the insulation amplifier it is necessary that the coupling on the hook -up leads CHANGES CAPAC- ALIGNMENT impedances be very high. To this end, I.F. ITY and POWER -FACTOR (losses) with After the replacement transformer is in- transformers have been built with higher changes in atmospheric humidity. These stalled it should be aligned. It is true that and higher inductance and with better and changes cause the sensitivity of the set to all Meissner replacement I.F. transformers better (higher -"Q ") coils until, when used shift with the weather. These shifts in sen- have been aligned in the factory and tested in an amplifier, the amplifier oscillates. If sitivity can become very bad if excessive for gain and selectivity before shipment, this oscillation persists even after complete- amounts of shielding are used. but installing the transformers in receivers ly shielding the stage and isolating the The 3rd objection to close- fitting shield- in which the circuit wiring has a different screen -grid, "B + ", cathode and A.V.C., the ing is that the insulation on ordinary hook- capacity than that which existed in the test limit of amplification possible with that tube up wire has relatively high R.F. losses, set, coupled with the fact that the inter- and circuit has been reached. Only by neu- lowering the "Q" of any coil to which the mediate frequency of the receivers may be tralizing the grid -to -plate capacity of the shielded wire is connected. some kilocycles different from the frequency tube can circuits of higher gain be used. In A.C.-D.C. to which the transformers were adjusted in What actually occurs is that a part of the sets of the Underwriters - the factory, approved types there is another objection requires that the transformers I.F. voltage appearing in the plate circuit be re- aligned after installation. The meth- of the tube gets back through the grid -plate to shielding on either the diode or diode - ods of aligning are so well known that the capacity of the tube and impresses itself return leads when the shielding is connected details of to the chassis. In such sets the "B-" point that simple process are omitted. on the grid circuit. If the amount of this in the set is isolated from the chassis and feedback voltage is large enough and the is bypassed to it by a condenser whose OSCILLATION AND FEEDBACK impedance of the grid circuit is high enough, will capacity does not exceed 0.25 -mf. Because There will be a few sets in which the sustained oscillation result in much the of the capacity of various parts of the set replacement transformers will result in same fashion as the well -known "Tuned - to chassis, and because the isolating con- enough more amplification than the original Grid- Tuned -Plate" transmitting circuit denser is of limited capacity the chassis is transformer that oscillation will result. The performs. Technically speaking, it is also not at "B -" A.C. potential nor, for that following discussion of the subject of oscil- necessary that the phase relations be cor- matter, is it at the potential of any other lation gives an account of the most impor- rect, but these can so easily be changed point in the set. tant methods by which feedback occurs and by slight adjustments of the trimmer that shows how oscillation caused by the feed- it is a foregone conclusion that the proper Across the isolating condenser appear adjustment for oscillation will be obtained audio frequencies from the filament supply back can be cured. Feedback can be divided roughly into 2 when the impedances are high. The remedies as well as components from the half -wave for single-stage oscillation are: rectified current. When a shield on a diode classes: (1) Single -stage, and (2) Overall. or a diode- return lead is connected to Single -stage feedback is literally what the (1) Use a close- fitting tube shield on the chassis the hum voltages appearing across name signifies, whereas under the heading offending tube. the isolating condenser are impressed by of "Overall Feedback" are considered all (2) Use a tube with lower grid -plate the shield onto the high- impedance diode types of feedback involving more than 1 capacity. circuit, causing an audio hum voltage to tube. (3) Use a tube with lower mutual conduct- appear across the volume control which, ance. of course, is converted by the speaker into SINGLE -STAGE OSCILLATION (4) Raise the bias on the present tube until an audible hum. If the shielding is connected Single -stage oscillation in amplifiers is oscillation stops. to the "B -" point in the chassis, this hum usually the least understood of regen- type (5) Use circuits of lower impedance. will not he present, but it will then be eration trouble. It has frequently baffled necessary to insulate the outside of the Servicemen and experimenters. It is peculiar (6) Neutralize the grid -plate capacity. shielding so that it cannot ever come in in that no amount of filtering applied to If the positions of the grid and plate contact with the coil shield, the chassis, or plate supply, screen, cathode or A.V.C. cir- leads of the I.F. transformer are already any other metallic object attached thereto. cuit, nor any amount of shielding seems to located one above the chassis and the other Unless this is done some one may acciden- make any improvement. This form of below and if the tube has around it a close - tally receive an unpleasant or even danger- trouble is seldom encountered in a set made fitting shield that is grounded to the chassis, ous shock upon touching the chassis and any by a reputable manufacturer if the set is in there is nothing further that can be done grounded object simultaneously. Where its original condition and has the original from this standpoint to improve the situa- flexible -spring shielding such as shown in sets of tubes in the original sockets. Ex- tion. If these conditions are not all fulfilled Fig. 4, has been used on one of the leads perimental sets, custom -built sets and sets some improvement may be made by adding on the original transformer, it is usually that have had new I.F. transformers in- the tube shield or placing leads for lower good practice to use the same shielding on stalled on them are far more likely to coupling. the corresponding lead of the replacement exhibit single -stage oscillation. Concerning lower grid -plate capacity, it transformer. This is permissible because the The enthusiastic amateurs or experimen- can be said that normally this parameter shielding is not tight on the wire and be- ters may select I.F. transformers of the of tubes is quite constant although occa- cause the length of shielding is seldom more highest -possible gain characteristics for sionally there are a few tubes with capac-

RADIO -CRAFT for AUGUST, 1940 77 SERVICING

enon that some Servicemen may have noticed which is that some I.F. amplifiers I oscillate when some of the trimmers are out P__'B',,!Iline to I of adjustment and that as alignment pro- p rofit ceeds the oscillation stops. ' Anti- Resonance Oscillation. - When an Stock the "B" battery that revolutionized the portable radio industry - inductance is shunted by a condenser a "Eveready" "MINI -MAX" 45 volt "B" battery -its light weight means heavy "resonant circuit" is formed whose imped- ' profits ance is very high at the frequency to which for you! the circuit is tuned but the impedance drops "Eveready" "MINI -MAX" means less weight off very rapidly above or below this frequency, soon reaching a low value. The ...less bulk...portable radios that are really impedance at resonance is approximately portable without sacrifice in service life. It equal to the product of frequency times gives twice the service life of 2:t, of inductance, and of the "Q" of the any other "B" circuit. battery of equal size! When 2 similar circuits are separated far Over 30 manufacturers have designed enough so that they have no effect upon portable receivers each other (are not coupled) and they are around the " Eveready" both tuned to the same frequency, they each "MINI -MAX" No. 482. Your customers will have a definite high impedance, but if these demand this mighty midget in the busy sea- circuits are brought progressively closer together (coupled) until "critical coupling" son ahead. Get your order in today! is reached, the magnitude of the impedance 1 of each circuit will drop to approximately NATIONAL CARBON COMPANY, INC. !_ of the original impedance when isolated General Offices: New York, N. Y. from each other. Branches: Chicago and San Francisco When the position of the coils of 2 tuned y of Union Unit Carbide and Carbon Corporation circuits is fixed, as in the conventional I.F. transformer, and the trimmers are adjusted so vastly The words "Eveready" and "Mini -Max" are registered that the circuits are tuned to dif- trade -marks identifying products of National Carbon ferent frequencies (are electrically far Company, Inc. apart), the impedance of each circuit is high at the frequency to which it is tuned. Now if one of these circuits is tuned to the ities up to or even exceeding 10 times their intermediate frequency it will have its high- normal value. It is always recommended est impedance at that frequency when the that several tubes be tried in an oscillating other circuit is tuned to a frequency far I.F. amplifier (realigning each time) before removed from it, but as the frequency of doing much work to determine the cause of the 2nd circuit is brought progressively oscillation or attempting to correct it closer to the intermediate frequency the It can also be said that some G (glass) high impedance of the original tuned cir- or GT (bantam glass) equivalents of metal cuit begins to drop until when both circuits tubes have appreciably more grid -plate are resonant to the same frequency, the capacity than the corresponding metal tubes. impedance of the original tuned circuit Therefore, if the tube giving trouble is a G reaches its lowest value, approaching % of or GT tube and the metal equivalent is the original value if the coils are "critically handy it is wise to try the metal tube, being coupled." When an I.F. amplifier such as is sure however to realign the circuits. shown in Fig. 5, is stable with all circuits Concerning the use of a tube with lower in resonance and oscillates when the 1st and mutual conductance, one might say that 4th circuits are detuned in opposite direc- such a remedy is academic and is included tions, the oscillation is caused by the im- HIGH- CAPACITY only for sake of completeness. It is far more pedance of the 2nd and 3rd circuits reach- practical and logical to raise the bias on ing or exceeding the critical value as the 1st the offending tube until its mutual conduct- and 4th circuits are detuned. LOW- VOLTAGE ance is reduced far enough to establish All competent engineers designing radio stability. sets test their designs for this type of The use of lower- impedance circuits is a trouble so that they will be sure that even DA \DEE'---tho -e popular midget -can very wise procedure for eliminating single - though the I.F. trimmers or coils may drift electrolytics with the very latest refine- stage oscillation and is the method employed a little from exact alignment, the circuit ments -are now available in high- capac- by qualified radio engineers when designing impedances will not rise high enough to ity low -voltage units for special by -pass receivers. When high- impedance circuits are cause single -stage oscillation. Occasionally, and filtering functions. 1000 to 3000 mfd. used and the I.F. amplifier tube is biased -up however, when sets have been pushed to ob- 6, 12 and 15 v. D.C.W. Units are supplied to attain stability, the A.V.C. characteristic tain the maximum sensitivity from average high with mounting straps except for a larger of the receiver suffers, the degree of control tubes, exceptionally -gain tubes may can size unit which has standard mount- becoming less as the minimum fixed bias is cause oscillation with surprisingly little de- ing ring. Ask jobber to show you increased. In (Meissner) replacement I.F. tuning. The usual remedy is to use a tube these units. Ask for latest catalog - transformers the circuit impedances were not quite so good or to raise the bias or write us direct. carefully chosen to prevent single -stage slightly. oscillation in practically all cases. There The most certain check for single -stage will still be found, however, a few sets in oscillation is to connect to the grid of the which the remaining good transformer has suspected tube the I.F. probe of a Meissner a high enough impedance to cause the stage Analyst or similar "Signal Tracing" service to oscillate when a (Meissner) replacement equipment and to watch for indications of transformer is installed. Such sets call for the presence of a strong I.F. signal when CORPORATION increased cathode bias to restore stability. the 1st and 4th circuits are detuned in op- NEW BEDFORD, MASS. ' The use of neutralized circuits in combina- posite directions while the 2nd and 3rd with -grid is are in alignment. If no Analyst IN CANADA: AEROVOX CANADA LimISd Hamilton On,. tion screen tubes academically circuits left interesting and has been of practical inter- or equivalent is available, a milliammeter est in a few special cases but normally connected as shown in Fig. 5, bypassed by a GET this handy Tube Complement Book. such circuits are no longer used to any 0.1 -mf. condenser, can be used to check for . 165 pages of useful tube information you'll use every day. Packed with up-to-the- extent. single -stage oscillation in the following minute data including the tube complements Since a complete understanding of single - manner: and i -f peaks of all the recently announced sets. If you already have the complement stage oscillation involves a knowledge of Detune the 1st and 4th circuits in oppo- book and want only the new 1940 -41 supple- circuit impedances, at least qualitatively, site directions, then watch the milliammeter ment send 10e or if you want both -with the the following explanation of the changes while an intermittent short -circuit is ap- supplement bound in-send 25c to Hygrade Sylvania Corporation, Dept. RCOO. Empor- in circuit impedances is given as a back- plied to the control -grid of the tube, mean- ium, Pa. ground for explaining a peculiar phenom- while slowly shifting the grid trimmer 78 RADIO -CRAFT for AUGUST, 1940 SERVICING

slightly above and below resonance. If the plate current changes when the short -circuit is applied and removed, the circuit is changing from the oscillating to the stable condition, or vice versa. //b/

OVER -ALL REGENERATION Orcr -all oscillation is a familiar complaint on multi -stage T.R.F. receivers, even O of good design, and on I.F. amplifiers of I VOLT-OHM - high gain. On experimental receivers in the process of development it may be produced MILLIAMMETER by any one of a number of causes. Only by / experiment can the offending source of coupling be discovered and removed. It may 25,000 OHMS PER VOLT be of 2 general types, high -impedance or low- impedance; or might be considered voltage feedback and current feedback although all feedback phenomena in radio 17-Atftn;;74 receivers are, strictly speaking, voltage feedback phenomena. MODEL 1600 -E Coupling between antenna and control - grid or plate leads, and couplings between control -grid leads or plate leads, etc., all D.C. scales of the instrument read: of which impress relatively high voltages on the very small capacities existing be- Voltage 0- 10 -50- 250 -1000 ( 25,000 tween the points just mentioned, are classed ohms per volt) ; Current 0 -50 -250 as high -impedance feedbacks. Appropriate microamperes; 0- 1- 10 -50- 250 -500 partition -type shielding quickly stops this milliamperes; Resistance, low ohms, type of feedback. Under the heading of low - impedance feedbacks are placed all oscilla- backup circuit, 1/2 to 500; high tion troubles resulting from the use of ohms, 20,000, 200,000 ohms and 2 MODEL 1600.E common cathode, screen -grid or plate by- megohms at 11/2 volts. Additional pass condensers, common leads in high -fre- resistance measurements available by using 11/2 volts quency circuits, couplings resulting from the common shaft of a gang condenser, etc. of battery for each two megohms. oniy Eliminating oscillation from these sources AC Voltage 0- 10 -50- 250 -1000 at 1000 ohms per volt. requires a study of the receiver and many A plug -in copper -oxide rectifier, easily replaced in case experiments, isolating the various circuits of overload, is used to obtain A.C. readings. that are suspected of causing the feedback, Model $21.00 until finally the real offender is discovered. 1600 -E, less Case, for mounting in panel . . . Sometimes feedbacks are degenerative in- DEALER NET stead of regenerative and the disconcerting Model 1600 -E hi case for portable use ... Dealer Net Price ... S25.50 PRICE fact may be discovered in some cases that isolation of certain circuits increases rather than decreases oscillation troubles. On manufacturer! receivers made by a 3 -WAY VOLT - OHM - MILLIAMMETER reputable company which attempts to keep . 1:1. U. nm- obsn'.. .,rth a Volttil.e. ter anti Fr, I.., \lilli ammeter over -all Model 670 AC .\t' uniform quality, oscillation after Culls II- 111 -50- 260.r,Ú0 -lm in per toll. Ammeter . Free l'oint 'l' some time in service can usually be traced .tolded Case u nit sockets for all to some circuit element changes char- 9e1M1Cun. lobes including Itnnt- that firmer vI Bantam Jr. acteristics with age. For example, if no l'he loue rr nd r Midgets. Tithe 'fester has Inver tri,, paper condenser is used across the electroly- +ai l h permuting in- Dealer Net l dividual switching for tic filter condenser to insure a permanent Price ... 5e.00 every element in tile low -impedance R.F. path to ground, over- tube. all I.F. oscillation can occur when the R.F. resistance of the electrolytic filter condenser MODEL 1183 increases with age. WRITE FOR CATALOG $49.84 In T.R.F. receivers, frequently high - Section 168 Harmon Drive resistance contacts between the gang -con- Dealer Net Price denser shaft and the wipers causes over -all oscillation which can be eliminated by a thorough cleaning of the contacting surfaces. Common bypass condensers also THE TRIPLETT ELECTRICAL INSTRUMENT COMPANY should be suspected as the cause of feedback. Bluffton, Oblo When they are, they are usually found very easily by connecting a known good condenser across each bypass condenser suc- GET A REAL ELECTRIC SHAVER ABSOLUTELY FREE! cessively until the defective unit is found. Complete details as to how it is possible to get a Real Electric Shaver FREE. appear on Page 122 of this issue. TURN TO IT NOW! REGENERATION OF A.C.-D.C. SETS In A.C.-D.C. sets of the Underwriters - WAY TO REPLACE approved types, regeneration is usually a BROADCAST NEWS ITEMS serious design problem because the chassis Says Dr. Raymond B. Fosdick (pre,.. is not solidly connected to the "B -" point Rockefeller Foundation), those who listen, BRLLR5T5 in the receiver but is merely bypassed to most to radio programs find the least inter- 4 STANDARD that point by a capacity not exceeding 0.25 - est in their reading. Hence, "radio listening" TYPES of Amperite mf. This isolation of the chassis from the predominates among those who never Regulators replace "B -" point, which is usually one side of the reached high school, and decreases as the over ZOO types of power line, is done to eliminate the hazard level of literacy rises toward college gradu- AC-DC Ballast Tubes now in use.... Has resistor. attached to a set that has its chassis con- ates.. . Yesterday it was little more than patented automatic starting nected solidly to the power line. For a pile of rocks sticking out of List S1.00 the the water at WRITE FOR REPLACEMENT CHART "S" same reason the capacity allowed between soon will be filled - high tide, but it probably Amperite Co. 561 Broadway, N. Y. C. the chassis and the minus "B" is limited in and made the site of WABC's broadcast to 0.25 -ml. transmitter (now located in Wayne Twp., Since every alternating or pulsating volt- N. J.), for Little Pea Island in Long Island age in the set causes some small current to Sound recently was purchased by Columbia (('outi,,,, ed ort following page) Broadcasting System. AMPERITE

RADIO -CRAFT for AUGUST, 1940 79 SERVICING

(Continued from preceding page) logical remedies possible: the I.F. amplifier until the gain of the tube flow through the capacity of the parts to (1) Reduce the' common impedance across is reduced enough to restore stability. When the chassis, thence through the isolating which the feedback occurs. it is considered that most A.C.-D.C. sets condenser and back to "B- ", there is in (2) Reduce the gain of the I.F. system. are of the very inexpensive type, and that the input circuit of the receiver (which in- As mentioned above, the Underwriters the customers are usually not willing to cludes the isolating condenser) a mixture limit the value of the isolating condenser pay any considerable sum for repair work of frequencies, amplitudes and phases that to 0.25 -mf. to reduce the shock hazard. If (approaching 1/3 to 'h of the original cost) is impossible to predict. Some of the volt- the chassis is well protected from contact, it is usually best practice to correct oscilla- ages are regenerative, some degenerative, the capacity can be increased to some ex- tion troubles by the fastest method -raising some cause trouble at any setting of the tent. However, due care should be exercised the bias -even though perhaps somewhat gang condenser, while others cause trouble to see that the condenser is of good quality better results might possibly be obtained if only over a limited range of positions of and rated at not less than 400 volts more time were to be spent on the repair. the dial (usually at the low- frequency end). (working). When oscillation troubles result after re- A more satisfactory method of eliminat- Look next month for the final article: placing an I.F. transformer there are 2 ing I.F. oscillation is to increase the bias on "Servicing Oscillator Coils."

OPERATING NOTES

. . CANADIAN ROGERS SETS acre, the tuning motor. It is rated for diagram. For a shorted condition the defec- use only and is frequently a tive condenser should of course be discon- 741A. -A rather troublesome intermittent intermittent turned up in a Rogers model 741A receiver. cause for repair. nected but the average are open- circuits This set played for days without any ap- This unit, a 60 -mf. 40 -V. A.C. electrolytic which can be easily bridged by a condenser parent defect, then suddenly would drop in is mounted directly on the tuning motor. of the same size. Cleaning the rotor springs volume accompanied by hum and distortion. Replacement with a manufacturer's part is also a necessity on these models. The type 45 output tubes tested OK as did restores complete operation and smooth, K106, 126. -The 2 models noted here, very all other tubes and condensers. To make even travel of pointer over the face of often break down entirely. The plates of the things worse, the set would often start to the dial. 80 and 5Z3 tubes getting red are an indica- play normally just as I started to make A. W. FREYER, tion of the failure of C36 in the case of some tests. The plate voltage on the 45's Holyoke, Mass. 1(106; and the condenser pack and C32 for would drop about 50 volts whenever the the K126. trouble started. I then disconnected the .... CANADIAN GENERAL ELECTRIC CO. Oscillation can be traced to a failure of 1,200 -ohm bias resistor for the 45's. The . RECEIVERS screen -grid condenser C41. Several cases of set continued to play. The trouble was S22X, S22, 42, 62, S25, S42B.- Receiver poor and intermittent reception were cured caused by an intermittent short at the place oscillation and lack of sensitivity, in these by replacing the antenna coil; however it where the wire from the center -tap of the models, can be corrected on the whole by was later found that the application of a type 45 filaments was soldered to the re- replacing R4 with a 15,000 -ohm, 5 -W. unit; hot iron to the terminals of this coil would sistor. also R1, 8,000, 1 -W. It is good practice to have cured this complaint! 832. -An annoying trouble in the Rogers replace these although they may be in Of the later models bearing the C.G.E. model 832 is intermittent reception due to apparently good condition. Clean and adjust monogram it would be only fair to state poor contacts on the tuning condenser as- the rotor springs. Rebalance the entire unit. that tube troubles caused 85% of set failure sembly. All movable parts should be cleaned R44, 46. -Due to wear the gang condenser and where possible output tubes of the and Russian oil applied, as well as some shaft frequently shifts so that the fixed and metal type were repl -ed by glass tubes. vaseline. movable plates are not centrally located. E Series. -In conclusion, the "E" series 645.-In the Rogers model 645 the input Loosen the holding screws for the 3 sets of have been serviced for oscillation and in a transformer usually gives trouble. I find it fixed plates and if necessary ream the holes number of cases the 6X7 metal tube, while advisable to replace the bypass condenser to obtain greater movement. Then center OK under test will prove to be the offender. from the 10,000 -ohm resistor to chassis. This the 2 sets of plates and tighten holding These should be checked by changing their resistor is in series with the high voltage screws. Clean the shield and tighten the position or by substitution. and the primary of the output transformer. holding springs. A realignment of the set J. HOUGHTON, This condenser usually burns out along with and it performs like new, if not better. Peterborough, Ont., Canada. the resistor so it pays to replace it and H31, 32, 51, 71.-These are large cabinet - save trouble later. type receivers and excellent performers. 951. -A common trouble in the Rogers Poor tone, lack of volume, and sometimes .... CANADIAN WESTINGHOUSE 410 951 chassis is the opening -up of one of the no control of volume can in most cases be Several times recently, in my service windings of the band -pass I.F. assembly. cured by replacing the 4 resistors, 18,000, work I have encountered a number of The can should be removed and the various 10,000, 110,000 and 14,300 ohms, located on Canadian Westinghouse model 410 receivers coils checked. the connection board at back of set; in case which had a rather annoying hum only when Another trouble in this set is caused by you are in doubt, these are located next to tuned to a carrier. This trouble has always dirt on the contacts to the rotor of the the R.F. choke, and are replaced in the been eliminated by connecting two 0.05 -mf. tuning condenser. As the input transformer order given. condensers in series across the power trans- primary is bypassed with a 20,000 -ohm re- In this set, to check audio- frequency former primary and grounding the center sistor, voltage will be present on the plate transformer for continuity it is necessary connection to the receiver chassis. This re- of the type 27 A.F. tube, even though the to disconnect the primary to secure results, ceiver uses a type 6X5 rectifier connected primary winding may be burned -out. otherwise an incorrect reading will be ob- half -wave. ALLAN FORD, tained. STANLEY DAVIS, Portneuf Station, P.Q., Canada. Set the "Local- Distance" control in the Vancouver, B. C., Canada. QUIET position and realign. It is advisable .... FERGUSON MIDGET in most cases to remove the speaker cone PHILCO 800 AUTO -RADIO In Ferguson midget receivers utilizing a and clean the housing as this unit has a A "receiver dead" complaint, in connec- 25A6 output tube, distortion after a few powerful magnet which is liable to scale. tion with one of these sets, can usually be minutes of operation frequently may be This scale will be found obstructing the attributed to defective vibrator points which traced to the grid leak in the 25A6 stage. correct operation of the speaker. are sticking. Replace with a new unit; do Sometimes measures as much as 2 megs. K52, 53, 59, 75, K60, K57. -On these 6 not attempt to file the vibrator points. In Replace this with a ?z- megohm resistor. types, motorboating and oscillation are the replacing, check the buffer condensers for WILLARD MOODY, most common breakdowns. The oscillating shorts or opens. To test them in the pri- New York, N. Y. condition is quite easily checked by touching mary circuit of the power transformer open the cap of the 2A7 and in most cases recep- the transformer case cover. Sometimes of this receiver will throw it out . ... RCA U -30 tion will be obtained. It is advised that the handling This model utilizes automatic motor tun- dual condenser be replaced entirely; it will of alignment, and therefore, realign it as ing. In several models I have discovered that prevent a further call in a month or so. a safety measure. Align first the I.F., then erratic or complete inoperation of the auto- K72, 76, 105, 107, 85, 125, 83, 87. -Hum adjust both the high- and the low- frequency matic mechanism is caused by a leaky or and oscillation obtained on these sets can be padders at 1,500 kc. and 600 kc., respectively. open motor -starting condenser connected cured by a careful survey of the wiring (Author unknown.)

80 RADIO -CRAFT for AUGUST, 1940 SERVICING

REBUILDING FOR PROFIT Servicemen and Servicemen-dealers may find it worthwhile to suggest alterations in an existing receiver in preference to restoring it to obsolete standards. Just what steps to take and how to go about taking them --- thereby turning "nuisance" jobs into profit- makers -is the subject of this article.

CHARLES R. LEUTZ

EVERY technical trade has to contend In view of this unusual condition, it is with "nuisance" jobs and amateur corn- apparent that a- well- informed and skilled petition. The carpenter is called upon radio technician, instead of conducting a to replace a broken picket, the elec- simple repair business, can offer a complete trician to replace a blown fuse, the plumber overhaul; and the new improvements made to fix a leaky faucet, etc. In each case the possible by available new component parts overhead expense and time involved costs and tubes released from time to time. much more than can be properly charged. The radio technician has the same problems, THE REBUILDING MARKET wherein the receiver defect is. due to some Naturally simple these jobs are not applicable trouble, easily located, such as a to low -cost sets. Fortunately, however, there defective tube, dried out electrolytic con- are hundreds of denser or partially thousands of high-quality defective paper con- multiple-tube receivers, a year or more old, denser. However, in the last mentioned that can be substantially examples, improved. This is invariably the customer is unin- not due to lack of designing skill but on formed technically and accordingly a rea- account of the fact sonable that production set de- repair charge is in direct propor- signers are limited by cost considerations. tion to the technician's degree of fairness Technicians who familiarize themselves with and conscience. technical During recent advances in the art can definitely years, radio set owners offer real service which can be readily mar- have begun to realize this state of affairs keted and executed at a profit. and are therefore becoming inclined to give repair jobs to some acquaintance, usually Figure 1 is an elementary diagram of a some young chap with limited technical typical, modern superheterodyne receiver, knowledge but who can be counted upon for showing the circuit divisions and points sub- fair treatment. If the "beginner" is unsuc- ject to possible improvement. It is not the cessful in making the required repairs, the intention of the article to give detailed in- customer turns to an established Service- structions covering every possible improve- man. In the latter case, if the estimate of ment. Past articles in this publication have repairs is low, the job is placed. treated the proper design of different sec- Otherwise, the customer purchases a new tions of a modern receiver including aerial set, invariably some small receiver available systems, radio-frequency amplifiers, dif- at a low cost. Therefore everyone loses. The ferent systems of automatic volume con- repair job is trols, audio -frequency amplifiers, etc. These lost. Neither the dealer or articles manufacturer can make a profit on a low can be referred -to in this connec- cost receiver. Furthermore the customer tion. (See appended list of a few such arti- also loses as the low -cost set can only give cles suggested by the author. -Editor) mediocre service and for a limited time. The most important improvements can The "beginners" giving amateur competi- be summarized as follows: tion cannot be eliminated. As a matter of fact they need encouragement so they can A. AERIAL OR SIGNAL COLLECTOR adjust themselves into established and quali- The prime idea is to provide an aerial fied technicians. In the interval, the estab- system to secure maximum signal energy lished technician needs more business to from the desired stations and minimum survive, and it can only be obtained by eE.T- being in a position OAAERIAL,,oE EEECTUC.üT mFO:óT to offer more value CONTRO,. than can be offered by less skilled and informed "beginners." ORPECTIONAilji A large majority INTERWONI .c Pwo of all radio Service- VIZtpV'GE9 AE t -r wáÉ' .uouriEA.r ScCxr, men are trained to áóçE repair sets by restoring them to their ï Oi original circuit con- LIMIT LA ditions. This means, AL in many cases, res- AEC, . toration to conditions Il.; -.-_ of obsolete engineer- ï ing practice! Some LOOP t t radio repairmen, in AERIAL fear of making mis- takes, go so far as Profitable rebuilding may utilize the following com- to insist on "original i PCPIAP ponents pPEEN., (shown above): ( I ) standard A.C. -D.0 replacement" parts ORIOLES phono oscillator: (2) dual volume control for push although these may eERE CDAi pull audio input circuits; (3) plug -in Type electrolytic; (4) factory -assembled and pre-aligned all. be inferior to modern wave tuner; (5) line- PO ENTIRE POINTS (ON voltage regulator; (6) tabula "universal replace- AE EIVE9 PER.OA..INCE electrolytic; (7) output attenuator for extra loud- ment" equivalents. PRO f speakers; (s) heavy-duty dry electrolytic; and, (9 beat- oscillator transformer and trimmer. RADIO -CRAFT for AUGUST, 1940 BI SERVICING

ESTA F. 6C5 INTERSTAGE A.F R F 65A7 MISER 1ST-1 E. 6.510 2ND'1.F 61-16, 2ND-DETECTORAA.v.0 6C5 1653 65H7 SWL SW2. SWS.SW..4. L IT /1 S0G ANW SI TCHON 1 SHAFT. f SW.T. SW 8. MANG SWITCH-SELEC- ANTENNA WÑ05 TIVITY CONTROL TI ME

50 úJ GNP

COIL leo EACH) 01- INTER- MEG SÁVE 1..i

CI.C2.C3.3- C4NÓLMSER 465 MME L3 05C. LATOR COIL 1953 OSCILLATOR 5.000 PT 5.00.05 x 1 MEG. 6.3V FUSE 3AMF) 1 1 ,T 6 T MF. 520V. M p1.w400 SPEA515 é / FIELD (CAH) e 61.60 o EXTRA Q, PJWERA,F 110 ó 520V. r Y o 0.5 TUNING SEJ MEE e 6L6G OHMS VDiTiGE T3 1 M 1 V,Nf,Er' -"' POWER AF REGULATOR RATEipvA L5A06b000NMS; I DDER a IIV.A.C, TRANSFORMER LIo-NÉMM LOCAL 60TCYCLES/ L-- 5PN R

Where would you start to check up on an existing receiver? And having decided where you wan ed to make changes how would you go about effecting them? are shown in Fig. 2, above. The first of these questions is answered in Fig. I on the facing page; answers to the second question

signal energy from possible interfering sta- pick up but due to inherent capacity high gain, but to secure nearly uniform tions- together with a minimum of local drastically reduces signal energy. gain over the entire frequency spread involved. such transformers will noise pick -up. The different systems avail- (3) Twisted or Transposed Lead -In Furthermore able are as follows: Satisfactory for low -frequency applica- have a "broad top," conducive to high - fidelity reception. (I) Directional Aerial, Electrically controlled tions. The R.F. tube suggested is the single - The use is primarily for long -range (4) Best Rubber -Insulated Coaxial Cable "DX" reception but the application re- Satisfactory for service down to 15 ended 6SK7 for broadcast -band receivers or quires considerable space for erection. megacycles. the 6AB7/1853 for all -wave receivers. These tubes automatically provide stable opera- (2) Omni -directional Aerial (5) Flexible Copper Braid Coaxial Cable in- to re- tion, high uniform gain, and have the The useful application is limited Satisfactory for service down to 30 herent ability to handle unusually strong ceiving locations providing a high signal megacycles. -modulation or modula- from desired stations. signals without cross energy strength (6) Copper Tube Coaxial Cable, Polystyrene tion distortion, due to their remote cut -off (3) Local Loop Insulated characteristics. in adjacent - This is useful eliminating Essential for high- frequency and ultra- For a receiver designed to cover the channel interference but the application high frequency applications. there is little where the local broadcast band exclusively, is limited to locations choice between the use of a converter tube level is low, for example in the Types Nos. 1 and 2 should be eliminated noise mixer -oscillator. In the case of an all - country. in connection with any high -grade radio re- or a ceiver installation. The choice of Nos. 3, 4, wave receiver including the higher frequen- (4) Remote -Controlled Loop 5 or 6 depends entirely on the possible cies, the use of an efficient mixer and (See Fig. 3) expenditure for this item, No. 6 being sug- separate oscillator becomes essential to ob- This application is not only useful in gested for de luxe installations. tain uniform results over a wide range of eliminating adjacent -channel interfer- frequencies. enables removing the loop ence but also R.F. AMPLIFICATION 2 a typical modern all - of local noise inter- Figure illustrates from the field wave superheterodyne receiver circuit ferences. After covering the problem of signal collection, the next point to consider is radio - wherein the 1853 is used for the radio -fre- (5) Loop Aerial frequency amplification. Accordingly the quency amplification, a 6SA7 as a mixer Same as No. 4 but due to the larger - antenna coupling transformer, R.F. tube and another 1853 as the separate oscillator. size loop provides increased signal -to- and R.F. transformer must be given full These tubes are selected due to their favor- noise ratio. consideration. By using properly -designed able noise characteristics, high uniform (6) Directional Dipoles and Reflectors "iron- core" antenna input and R.F. trans- gain, and stability in operation. Used as The advantages are the same as under formers it is not only possible to secure either a converter or mixer, the 6SA7 is No. 4 but the application is suggested for reception of shortwaves of 30 meters REMOTE or less including television and fre- LOOP quency modulation signals (on between 111111.11 111111111 111111111 111111111 I O 5 I I 5 1 0 5 and 10 meters). LOOP TUNING CONDENSER 1 0 5 I I 5 10

1 S 11 5 O B. LEAD -IN ex BEARING The method of connecting the signal col- eLO Ip1OKC. ipOOKC. SSG KC. lector to the receiver is very important. In ROTATABLE a -- - DESIRED CARRIER No. 28 COPPER CENTER Fig. 1, this is designated as item - eiraria PIPE. CONDUCTOR, - -- involves the following methods, given e and y/ BRASS ROD in order of relative efficiency, No. 1 the 987654321 123456769 No. 6 being HIGH- p BEARING being the least desirable and /Z/ 11111111 111111111 111111111 111111 III FREQUENCY the most efficient: INSULATORS : DIRECTIONAL .1 -I CONTROL ( I ) Ordinary Single -Wire Lead -In sig- r r/ I7. I Provides no discrimination between 0ey///. TO 6769 9676 noise collection. RECEIVER ?,010 KC. KC. KC. nal and INPUT 1.000 990 (2) Shielded Single -Wire Lead -In .-- TUNING CONTROL DESIRED CARRIER Eliminates lead -in signal and noise FIG. 48 AUGUST, 1940 82 RADIO -CRAFT for SERVICING

practically free from frequency shift even at high frequencies. Furthermore, due to special structural design, there is a mini- 2 of 22 NEW mum of oscillator detuning by the action SUPREME MODELS of A.V.C. The oscillator can be stabilized to a still higher degree by feeding the oscillator plate and screen -grid voltages from a voltage regulator tube (VR -150) as IN producing Model shown in the schematic diagram. 589 there has been For simplification, the schematic diagram no compromise in the circuit design or shows only 1 band position of - a typical all teriala. The sane wave arrangement. Multiple -contact gang manufacturing meth - switches are available enabling installation ods, a reful inspec- of 5 or more band tion and accurate cal positions. Standard an- ibration are incorpor- tenna input, R.F. transformer and oscillator ated in this instru- coils are available to cover most any speci- ment as in all other fied frequency range. For example one com- Terms: 14.00 rash SUPREME testers. It sad 8 monthly will pay you to inves- bination might consist of Longwave, Broad- payments of $3.63 tigate and see this cast and 3 Shortwave bands. An alternative tester before you could consist of Broadcast and 4 Shortwave buy. Its price is the F R E E lowest at which bands; or any other desired special ar- TUBE SETTING GOOD tube tester rangement. SERVICE can be built. FOR ONE YEAR I.F. AMPLIFICATION The intermediate- frequency amplifier (11) MODEL 5119 TUBE AND BATTERY tester has a MODEL 599 TUBE AND SET TESTER is very completely modernized circuit. The tube test similar in appearance to the Model 589, and in- is one point that can be substantially im- sockets are not wired directly to the circuit. but. cludes all the features and advantages of this proved in a very large percentage of all instead, pass through the patented SUPREME instrument. In addition, it provides the following receivers manufactured. This important re- Double Floating Filament Return Selector sys- ranges: ceiver section must be altered before it tem which automatically re- connects all tube ele- 0.2 TO 1500 D.C. VOLTS -5 carefully selected ments to any possible tube base arrangement. ranges-0/6/15/150/600/1500 volts. 1000 ohms per becomes possible to use a wide -range high - Due to the fact that any or all elements of each volt STANDARD sensitivity. socket can be rotated fidelity audio amplifier. to any desired position, 0.2 TO 600 A.C. only one socket of each type is necessary. VOLTS-4 A.C. ranges -0/6/15/ Assuming the audio amplifier provided Tests 150 /600 volts. Rectifier guaranteed with instru- every type of tube from 1.4 volts to full line volt- ment and fully protected will cover from about 30 cycles to 10,000 age at its correct anode potential under proper from overload damages. cycles with reasonably uniform gain, then load. Tests separate sections in multipurpose 0.2 M.A. TO 600 M.A. -3 direct current ranges tubes. Checks all leakages, shorts. open elements 0/6/60/600 allow measurement of screen, plate, of course, the associated I.F. amplifier must and filament continuity with a neon lamp. A Mr- "B" supply and D.C. filament loads. have a flat -top band -pass of at least 10 kc. cult insert is provided for checking noise. leak- 0.2 TO 600 OUTPUT VOLTS- 0/6/15/150/600- each side of the carrier. Under these con- age. loose and bad connections. ideal for alignment. No button to hold down -no ditions, unless the desired signal is many The battery testing circuit of the Model 589 pro- external condenser necessary. vides the proper load at which each battery is to 0.1 OHM TO 20 MEGOHMS -I ranges 0/200/20.000 times stronger than adjacent- channel sig- operate, plainly marked on the panel. for all 1.5, Ohms, 0/2/20 megohms. A low range at high cur- nals, it is impossible to eliminate inter- 4.5, 6.0. 45 and 90 volt portable radio types. The rent with 3.5 ohms center scale. condition of the battery is indicated on an Eng- ference. Accordingly unless adjacent -chan- lish reading scale. ELECTROSTATIC -ELECTROLYTIC LEAKAGE nel interference is eliminated external to This is the fastest TEST -Sensitive calibrated 20 megohm range and easiest tester to operate. of paper and elec- the receiver, it becomes necessary to sharpen Just "follow the provides excellent leakage test arrows " -you can't trolytic condensers. the I.F. amplifier selectivity down to a go wrong. Roller Just as the 589 is where the band -pass acceptance is your best value in point type tube chart a tube and battery about 4 kc. above and below the desired with brass geared tester, the 599 Is carrier. This automatically limits the audio mechanism lists your best value In tubes in logical nu- a combination tube reproduction to a maximum of 4,000 cycles. merical order. Each tester, battery test- However, an A.F. amplifier that faithfully tester carries a one er and set tester. reproduces from 30 year free tube set- Remember, you a range of about cycles ting service. SU- have all the fea- to 4,000 cycles is by far preferable to a PREME engineer- tures of the 589 PLUS a complete wide -range A.F. amplifier subject to dis- ing and construc- AC, DC volt, ohm, tortion. tion PLUS the best megohm, milliam- materials the mar - meter. at a cost of Figure 4A clearly illustrates the above *eaIrs ket afford,. make only 47c per range. the 589 your big- problem and if the 1,010, 1,000 and 990 kc. Dealer Net Cash hies signals are of equal and gest dollar value. strength all modu- You will be proud $39.50 lating up to 10,000 cycles, it is impossible to own this instru- Term.: 54.50 cash; to properly separate one from another. If ment. 9 payments of $3.33. the adjacent -channel interference can be eliminated by a loop or directional aerial, the desired signal can be received and Illustrated shove is the Model Metal cabinets as illustrated for directed to R.F. and A.F. amplifiers that 589 in a counter type metal case. the Model 589 at left and 599 This model is ailable with op- above are identical-can be used will reproduce the full audio range up to either In a tion of 7" or 9' illuminated SUPREME INSTRUMENTS CORP. horizontal position or 10,000 cycles. GREENWOOD. MISSISSIPPI. U. S. A. vertical position by merely re- m . Has two neon lamps for versing the Instrument panel. Due to the fact that such adjacent -chan- pensitive or super -sensitive tests. Write for information. nel interference cannot always be eliminated external to the receiver, some adjust able I.F. amplifier selectivity control be- A NEW BOOK ON PUBLIC ADDRESS comes necessary. A very satisfactory method An important announcement about the greatest book on the subject of sound and allied subjects calls for the use of adjustable -coupling I.F. appears on Page 70 of this issue. TURN TO THE ANNOUNCEMENT NOW! transformera having 3 different degrees of selectivity. In the sharpest position of such trans- diode detector must be worked at high formers, the band -pass is narrowed to levels. As a matter of fact if the receiver approx. 4 kc.; the result is shown in Fig. is to be used exclusively for reception from FREE! 4B. The desired, received signal (1,000 kc.) a number of different local stations, it is is modulated up to 4,000 cycles. The fre- advisable to eliminate the use of A.V.C. e0 HAMMARLUND quency acceptance from both adjacent chan- altogether. ° NEW "40" nels is limited in each case to the frequen- The _ R.F. and I.F. amplifier circuits in------RADIO CATALOG cies of 6,000 cycles or higher (shown by the clude decoupling filters in the plate- return shaded area). These higher frequencies form and screen -grid leads. The latest Hammarlund catalog with complete data, illustrations, a small part of all musical renditions and Possible useful additions to existing I.F. draw- accordingly ings and curves on the entire Ham - interference is drastically re- circuits include a Lamb noise silencer (30) marlund line. duced. Type Address Department 6SK7 tubes are suggested for and a beat -frequency oscillator (29). The BCs I for your free copy. the I.F. amplifiers. noise limiter is particularly useful in re- HAMMARLUND MFG. CO., INC. It will be noted from the schematic wir- ducing automobile ignition interference en- ing diagram that no A.V.C. is applied to the countered during shortwave reception. The 424.438 West 33rd Street, New York City last I.F. stage. This is very important as a beat -frequency oscillator is useful to locate

RADIO -CRAFT for AUGUST. 1940 83 SERVICING

^+ P1-1ONO- MODULATOR 05CILLATOR^ PHONO-

L 100 1 MEG., How to Become a Fig. 6. "Wireless" Mike PHONO- R.F.0 1.1MF. or Phono Oscillator. VOLUME t)MILLIUV. Here's the diagram and CONTROL all circuit details for CHI 290 HV, that "wireless" micro- ---VVVVv RADIO AMATEUR phone and phono oscilla- 10 MA. tor you have been asking ` for. Nothing to it, is there? Use it with any 05CJ5 radio set; power it from ILLATOR the set or from a sep X X arate A.C.-D.C. supply, as you prefer. 50,000 0.1- OHMS MF. vB+'250V. X X

weak carriers during "DX -ing" tuning oper- lated power supply (24) of ample capacity ations. Figure 5 shows the tremendous, irregular A cathode -ray visual tuning indicator is rush of current involved, using a condenser an essential for any receiver having posi- input rectifier filter circuit, as compared tions of "broad" tuning. For the circuit with a choke input system. The schematic shown, the 6E5 eye is suggested. wiring diagram (Fig. 2) shows a choke in- The 6H6 is suggested as the demodulator put power supply. or 2nd -detector and A.V.C. (12). The Fuse protection (25) is recommended as schematic wiring diagram shows the method a means to prevent serious damage by of using the load resistor as a 1st volume shorted filter condensers or shorted rec- control potentiometer P.1, and associated tifier tubes. In some rural districts, sudden with the 1st A.F. input volume control, P.2. line voltage variations often reach abnor- Adjustment of P.1 results in a loss of gain mally high voltages, strong enough to cause but together with the setting of P.2 enables considerable damage to transformera and maintaining the most favorable conditions tubes. In such locations, line supply fuses for "distortionless" diode detection. are most essential. In the A.F. amplifier (13) a dual volume Less violent voltage variations affect re- THIS IS A FASCINATING TEXTBOOK control, P.3, regulates the input voltage to ception and can be counteracted by install- WHICH TAKES YOU STEPBYSTEP the 2nd or interstage A.F. amplifiers. The ing a line voltage regulator (26). Where an all -wave receiver is used largely THROUGH EVERYTHING YOU NEED TO power audio-frequency amplifier (14) consists of two 6L6G's, self -biased, in push -pull for shortwave reception, interference from KNOW TO BE AN AMATEUR AND HAVE class AB1, with inverse feedback applied, the power line supply is a possibility al- YOUR OWN RADIO STATION: using a split- secondary input transformer. though unusual. Installation of a line noise filter (27) is a solution for this problem. The above arrangement, glance, flow to learn code -how to get your at first The discussion so far has been confined may appear to have excessive A.F. ampli- license theory made under- to the receiver and antenna systems. The -radio fication. However, this is not the case. First, standable-how to build your first sale of useful receiver accessories is in extra A.F. gain must be available to corn- many ways more interesting and profitable transmitter and receiver how to pensate for the loss of gain at P.1 Secondly, than service work. use those same parts in building considerable driving power is required to properly excite the power amplifier tubes, equipment, etc. ACCESSORIES larger after ample inverse feedback has been applied. Phonograph records and players are be- There are 160 pages in the book- coming more popular each day and appar- over 100 illustrations. It is a fine vol- Low -gain triodes (6C5) are suggested for ently the demand will be sustained for some the 1st A.F. stage and interstage A.F. ume, covered and stamped in time Many service customers are good cloth amplifiers. Low -ratio, wide -range high- gold. Any Radio Parts Distributor prospects for a record player and phono- quality audio -frequency coupling transform- oscillator (23). Customers that already ers are essential for maximum can supply you with your copy for results. An have a small player are prospects for a only 75e net. ideal arrangement also calls for triode higher -grade installation including an im- power output tubes, however the proper proved oscillator. Figure 6 shows a con- application of such tubes calls for more stant- current modulated phono- oscillator space ordinarily and power than available which is a little more complicated than in the average set chassis. Push -pull 6LG6's ordinary oscillators, but which will give in class ABI, at 360 volts plate ThORDARSON operated excellent results. One 6C5 and one 6J5 are and 270 volts screen -grid, even with cathode required. ELEC. MFG. CO., CHICAGO bias, will provide an audio -frequency out- This brings us to the subject of record- put of up to 24 watts. ing (19), first regarded as a novelty and By providing high -grade input and out- used principally for entertainment. It is put transformers, the output as reproduced now realized that home recordera are ex- by a high -quality 12 -in. or 18 -in. electro- ceedingly valuable adjuncts in connection dynamic speaker, operated under favorable with studies, viz., foreign languages, dic- acoustical environments, is free from any tion, word pronunciation, public speech, IN NEW YORK noticeable distortion. Where the installation voice culture, elocution, etc. There are many The joy of your New York visit can involves a relatively large room, it is better other applications including the recording be marred or greatly enhanced, de- practice to use two 12 -in. speakers in of favorite programs, important speeches, pending upon the selection of your opposite corners of the room, rather than etc. hotel. 1 large 18 -in. speaker. Where speaker cabi- The sale of a recorder automatically The Victoria has always been the nets are necessary, use of the bass reflex brings the sale for one or more micro- choice of discerning travelers. Friend- principle is suggested. Otherwise, speakers rooms, phones and one or more mixers aside from ly service; bright, cheerful mounted in baffle) each with a radio, tub and shower, right the wall (infinite blank records, cutting needles and other servidor and circulating ice -water. and covered with a thin tapestry will give accessories. excellent results. Extra, remote loudspeak- In suggesting certain types of tubes for Single from $2.50- Double from $4.00 ers (preferably permanent -magnet dynam- the different circuit functions, reference has ics) can be installed using a 500 -ohm line been made to basic types. Equivalents hav- and providing each speaker with a local ing different type numbers can of course be HOTEL VICTORIA remote volume control (17). used. -At Radio City' At the conclusion of this article, refer- 7TH AVENUE AT 51ST STREET, NEW YORK POWER SUPPLY ence is made to a list of articles which have Ronald A. Baker. Manager An essential adjunct for outstanding appeared in the past giving detailed data audio amplifier performance is a well -regu- on some of the subjects covered herein. In

84 RADIO -CRAFT for AUGUST, I 9 4 0 SERVICING

a 500 CONOENSEA ,Yr INPUT ... for the first time ?Ó 250 o Ad a line of TUBES 150 r for Heavy Duty Audio Work

î - 0 150 CNOKE lobes INPUT toI Matched 100 Hunting Hum INliclophonics Replacements

addition to reviewing these articles, it is suggested that the service technician secure SHOP Call a complete set of different manufacturer's and -Back catalogs and technical data sheets covering the following: Antenna Systems, Loops and Transmis- sion Lines or Cables. Iron -Core Antenna, R.F. Oscillator and I.F. Transformers. All -Wave Factory -Assembled Tuning SEE YOUR N. U. DISTRIBUTOR Units. Standard Tube Manual. Audio Transformers. Power Transformers. NOW Loudspeakers. FOR PUBLIC ADDRESS Line Voltage Regulators. DEMONSTRABLY BETTER BROADCASTING STATIONS Line and Other Noise Filters. Thirteen SOUND XTRA types now avail- Phonograph Players. COIN MACHINES Pickups, Microphones and Mixers. able. SOUND XTRA Types can be substi- Recorders. ELECTRIC PHONOGRAPH Resistors, Condensers and Volume Con- tuted for the same type in the regular line. trols. MOTION PICTURE They are DEMONSTRABLY BETTER. AMATEUR REFERENCES Past issues of Radio -Craft contain de- In order to accomplish this outstanding AND EXPERIMENTAL WORK tailed information on the following subjects. performance in SOUND "The 1853 Tube," Nov., 1938. XTRA types modi- "Anti -noise Counterpoise Antenna Sys- fications in construction are incorporated. tem," Oct., 1938. "Ballast Resistor Tubes," Jan., 1939. SOUND specialists have long "The 6SK7 Tube," Dec., 1938. hoped for "Principles of Noise-Reducing Antenna EXTRA QUALITY TUBES engineered Systems," Sept., 1938. "Phonograph Pickups," May and June, specifically for the requirements of SOUND 1938. "All- Direct -Coupled 30 -Watt Push -Pull work ... they're here now in National A.F. Amplifier," Oct. and Nov., 1939. Union SOUND XTRA Types. "A Combination DX Directional Receiving Aerial," Nov., 1939. For More Information Write "Marine -izing Radio Sets," June, 1940. "Amplifier Load -Matching Technique," NATIONAL UNION RADIO CORPORATION March, 1940. 51 STATE STREET, NEWARK, N. J. "Iron -Core 6," Oct., 1939. "Combating Radio Interference," May, 1940. TUBES CONDENSERS BATTERIES SOUND EQUIPMENT "Profits in Recording," May, 1940. "A.C.-D.C. Power Supply for Battery Portables," Oct., 1939. One Meissner phono oscillator coil, type "The ABC of Electronic Automatic A.C. 17 -9373, L4; WRITE TODAY Voltage Regulators," July, 1940. One R.F. choke, 8 millihy., R.F.C.; ABOUT "Specialized A.F. Tubes," July, 1940. One Kenyon choke, type T -155, 290 hy., 10 "A '3 -in -2' A.C.-D.C. Midget ma., Ch. 1; REE. Amplifier," INDIVIDUAL YOUR Jan., 1940. One Kenyon choke, type T -152, 10 hy., 100 ADVICE ON SPECIAL "Frequency- Modulated Programs on Your ohms, Ch. 2; AMPLIFIERS Present OR STANDARD Receiver!," Jan., 1940. One Kenyon push -pull input transformer, AMPLIFIER CO. OF AMERICA Following is a list of a few components type T -58, ratio 1 -to -2, Ti; specified by make and model number which One Kenyon interstage transformer, type 17 WEST 20th STREET, NEW YORK, N. Y. may be used in the positions shown in the T -54, ratio 1 -to -8, T2; schematic circuit, Fig. 2. Makes having One Kenyon output transformer, type equivalent characteristics may be employed. T -317, plate -to -plate load 6,600 ohms (and provided with a 500 -ohm -line secondary), ezo11ED-CA S Sn:.a}rr Dl:meter Electrolytics SUGGESTED COMPONENTS T3. Dry Two Meissner I.F. transformers, type 17- SPEE0°9- 7414, I.F.T. 1, I.F.T. 2; MORE DATA SHEETS! One Meissner I.F. transformer, type 16 -6139, I.F.T. 3; Starting with the September issue, Radio -Craft 14,,e to. Catalog will carry 4 Sheets receiver, One Data on new SOLAR MFG. CORP. oscillator coil (any make), L3; instead of the usual 2 Sheets! Bayonne. New .torsos

RADIO -CRAFT for AUGUST, 1940 85 SERVICING AUTO -RADIO INSTALLATIONS Ou -A!! /940 PPi enyet eats

Knowing just how to go about a job is the hall -mark of the proficient technician. It is these Servicemen who will benefit most from the following article, by the Service Editor of an automotive magazine, on the way to correctly install radio receivers in this season's crop of cars.

EDWARD H. BARRY

WHEN INSTALLING a car radio re- additional places where the installation of The installation of the receiver and speak- ceiver, be sure to select an aerial which a condenser or ground strap may do some er depends upon the make and type of set will give best results with the set be- good. To make a test, connect the lead of a being used. The radio manufacturer's recom- ing used. Automobile radio sets, being bypass condenser with a capacity of 0.5 -mf. mendations should be followed, bearing in very sensitive, often are designed to operate to the "hot" side of the suspected unit. mind, of course, that on almost every car with a certain type of aerial. Some sets Ground the condenser case or the 2nd lead there is some accommodation already in the have separate connections for different on a metal part of the car. When the posi- car for the receiver. types of aerials, while on others an adjust- tion is found where the condenser clears up Buick- Insert a suppressor in the high - ment must be made to compensate the set the interference, make the installation of tension lead to the center of the distributor for the aerial being used. It is also easier the condenser permanent. block. Connect the lead from a condenser to to install some types of aerials on certain When installing a condenser or ground the outside terminal, not the field terminal, cars. Following the manufacturer's recom- strap, all dirt or paint must be cleaned from on the generator and mount it on the gen- mendations will save time in making an the contacting surfaces and the connections erator cable clamp screw. Remove the cover installation. must be tight. When a condenser is installed from the ignition coil by inserting a thin - The recommended locations for installing on a generator, be sure to connect its lead blade tool under the edge of the cover about noise -suppressors, condensers, ground straps to the generator armature terminal. Should 1 -in. to the left of the container seam. Push and static collectors on each car are shown it be connected to the field terminal it will the tool between the lock and the recess, in the table below. After they have been in- cause pitting of the voltage regulator points, twist the end of the cover and lift off the stalled as described, the set should be tested which will prevent the unit from operating cover. Solder one lead of the condenser to to see if they eliminate sufficient interfer- properly. When installing static collectors the case and connect the other lead to the ence. Conditions may vary on 2 cars of the in the front wheels, the inside of the dust terminal inside the cover. Do not attempt same model, and in some cases additional caps and the center of the front -wheel to connect this condenser to the terminal interference eliminators may have to be spindles, to give good results, must be clean on the outside of the coil as it will result installed. The heads of the table suggest and free from grease. in damaging the distributor points and will cause erratic engine performance. Install static collectors in the front -wheel dust caps. The center of the collector supplied CONDENSERS GROUNDS with Buick sets is made of self -lubricating material. To fit the collector in the larger I dust caps used on Buick 80 cars it will be INTERFERENCE Eo # necessary to straighten out perfectly flat ELIMINATION ; the sharp, pointed prongs on the collector. á é Cadillac, LaSalle- Install a suppressor in CHART itIL á : 2S gi : ó the high- tension lead to the center of the $ ú s 3 o O , L., 3 r3 !istributor block. Remove the air scoop from the generator and insert the lead from a Buick N 12 6I >d condenser through the rubber grommet for Cadillac P t2I 1 36 33 the generator wires on the generator and connect the lead to the armature terminal. Chevrolet N 6 11 21 36 zt r- Mount the condenser on the generator Chrysler P 36 6 31 32 ground screw. Install a condenser on the for Buick. Peen DsSoto P 36 16 31 i32 ignition coil as described the distributor rotor insert to lengthen it, Dodge P Sf 16 31 32 or install a radio rotor bar. Install static Ford 7 11 collectors in the front wheels on models 50, 52, 60S, 62, and 72, making sure that Graham s the cotter pin is bent around the nut so that Hudson 2 13 16 it will not interfere with the static collector. Bond the throttle control cable and the oil LaSalle 12 1 x line to the clash with a ground strap and a Lincoln- Zephyr P 16 s 16 10 2s self- tapping screw. Chevrolet elbow suppressor and an Mercury P :d 7 11 -An adapter should be installed in the center Nash P 36 e terminal of the distributor block and at- wire leading to Oldsmobile N 37 6 u tached to the high-tension the terminal. Mount a condenser on the Packard P 3e 6 generator frame and connect its lead to the Plymouth P 36 5 16 generator armature terminal. Mount a condenser on the flange of the instrument panel Pontiac 6 N s7 6 m near the ignition switch and connect its Pontiac 6 N 37 6 26 34 lead to the ignition switch. Connect the lead from another condenser to the spring clip Studebaker MOD. P 36 16 at the end of the fused lead from the dash Studebaker Demo.. P 40 1 unit with a self -tapping screw and attach this clip to the discharge terminal of the Studebaker PNIa.... P 40 ammeter. Ground the free end of the am- Willy' N 30 14 6 meter condenser to a convenient mounting Numbers refer to Illustrations on following pages bolt on the under side of the instrument Stat Indicates unit is used but not illust ated panel. Connect a ground strap from the frame to the muffler tail pipe U -bolt. Install

86 RADIO -CRAFT for AUGUST, 1940 SERVICING

TO RECEIVER f,,, r ,iiIt $1 _ GENERATOR -r

II raLihk,,kt rll CONDENSER CONDENSER MICA CONDENSER GASOLINE GAUGE TANK UNIT CONDENSER GASOLINE CONDENSERS RESISTOR GAUGE CONTACT 11111111 ill 1I Illh COIL

CONNECT RESISTOR TO CLOCK FEED TERMINAL WATER TEMPERATURE UNIT DISTRIBUTOR TERMINAL ,OIL CONDENSER FILTER i,

CONDENSER WATER TEMPERATURE SCOOP TO CONNECT UNIT CONDENSER INSERT CONDENSER OIL WIRE THROUGH RUBBER PRESSURE GROMMET SOLDER TERMINAL UNIT CONDENSER TO CASE TERMINAL CONDENSER GENERATOR \ BROWN CONDENSER

CONDENSER

TO INSTRUMENT SOLDER PRIMARY COIL PANEL OIL TERMINAL GAUGE WIRE COIL CONDENSER VOLTAGE IGNITION CONDENSBR REGULATOR SWITCH

ANTENNA CONDENSER OIL GAUGE VOLTAGE UNIT REGULATOR CONDENSER OVERLOAD / TO RELAY CONDENSER RECEIVER

TO REC. lighting Switch

IGNITION LIGHTING CONDENSER SWITCH SWITCH INSTRUMENT PANEL DASH DASH PANEL MAT FASTENER GROUND GROUND CYLINDER STRAP CYLINDER HEAD HEAD STRAP

u, o

STARTER PEDAL BRACKET STARTER PEDAL GU DE VALVE COVER

RADIO -CRAFT for AUGUST, 1940 87 SERVICING

condenser should be fastened to the voltage TAIL PIPE U-BOLT FRAME GROUND bolt and its lead con- WIRE FRONT OF regulator mounting nected to the "BATT" terminal. Nash- Insert a suppressor in the high - tension lead to the center of the distributor (DASH SELF - L block. On Ambassador cars it will be neces- TAPPING sary to insert a suppressor in both center SCREW leads. Mount a condenser under the gener- GROUND OIL GROUND STRAP LINE ator ground lead screw and connect its lead SPRING to the generator armature terminal. Attach 2 hood clip one torr grounding springs under of the hood lining screws to ground the top and side of the hood to the cowl. GROUND STRAP Oldsmobile -An elbow suppressor and an adapter should be installed in the center ter- STATIC THROTTLE COLLECTOR minal of the distributor block and attached CONTROL CABLE to the high -tension wire leading to the ter- BRACKET STATIC minal. Mount a condenser on the ground SUPPORT ON 6 CYL. COLLECTOR lead screw on the generator frame and con- CARS ONLY nect its lead to the "A" terminal on the i11á81 generator. Attach the lead from another condenser to the ammeter terminal to which the radio set wire is connected and ground DUSTY the condenser with another lead to the CAP upper flange of the instrument panel. In- DUST stall static collectors in the front wheels, COTTER CAP making sure that the cotter pin is bent NOS PIN against the nut so that it will not interfere SUPPRESSOR INDUCTIVE with the collector. SHIELD DISTRIBUTOR SUPPRESSOR Packard -Cut the high tension lead to the ADAPTCR BLOCK center of the distributor and insert a suppressor in it. Mount a condenser under the ground lead screw on the generator and connect its lead to the generator "A" terminal. Mount a condenser on the instrument board flange and connect its lead to the feed line on either the ignition switch or the ammeter, depending upon where it does the DISTRI TUTOR most good. Interference from an electric BLOCK clock can be eliminated by connecting an additional condenser to its ammeter ter- another ground strap from the rear valve the generator under the screw holding the minal. cover nut to the dash. Then install static wiring harness and connect its lead to the Pontiac-An elbow suppressor and an collectors in each front wheel, making sure armature terminal of the generator. Mount adapter should be installed in the center ter- that the cotter pin is bent around the nut another condenser under the screw which minal of the distributor block and attached so that it will not interfere with the static secures the steering column bracket to the to the high- tension wire leading to the ter- collector. instrument panel and connect its lead to minal. Mount a condenser under the head of Chrysler, DeSoto, Dodge, Plymouth - the ignition switch. the ground screw on the side of the gener- Screw a suppressor on the center high - Hudson -Clamp a condenser under the ator case and connect its lead to the gener- tension lead to the distributor block and rear left nut holding the ventilator handle ator armature terminal. Mount another con- plug the suppressor into the distributor cap. guide assembly and connect its lead to the denser under the left -hand instrument Mount a condenser under the generator "AM" terminal of the ignition lock. Attach board mounting stud nut and connect its ground lead screw and connect its lead to the another condenser under one of the gasoline lead to one of the accessory terminal screws "A" terminal on the generator. Remove the gauge tank unit mounting screws. Attach its at the extreme front end of the lighting 3 terminal nuts and wires on the back of lead to the gauge units terminal. Mount switch. Install static collectors in the front - the gasoline gauge dash unit and assemble a another condenser on the upper rear cap wheel inner dust caps, making sure that resistor in place. Then replace the wires and screw in the engine water manifold plate there are no burrs around the center hole nuts. Bond the hand brake cable, heat indi- and connect its lead to the terminal of the in the wheel spindle which would cause ex- cator tube, oil line, throttle, choke, and water temperature gauge unit. Another cessive wear of the contact button. Bolt a speedometer cables where they pass through condenser should be mounted on the rear ground strap to the cylinder head with a the dash. Loosen the grommet holder screws of the generator with a machine screw. Con- special screw and lock washer. On the 6- and fasten a braid around the tubes and nect its lead to the generator armature cylinder cars connect the other end of the screws. Loosen the hood side panel bolts on terminal. Install a suppressor in the high - ground strap to the dash under the upper the left side and pry out the lower hood tension lead to the center of the distributor starter pedal bracket. On the 8- cylinder lacing screw. Attach a hood grounding clip block. Mount a ground strap between the cars drill a 0.199 -in. hole through the dash spring with a self-threading screw using the left rear cylinder head bolt and the dash, 21 -ins. above the upper starter pedal guide hole from which the screw was just removed. fastening it to the dash with a metal screw screw and connect the other end of the Then drill another hole with a No. 29 drill and a lock washer. ground strap to the dash at this point with and insert a screw. This grounds the top a self- tapping screw. Spot face around the Luicoln- Zephyr Install 2 and side of the hood to the cowl. - suppressors hole to obtain a good ground connection. with special brackets on the distributor and If the car is fitted with a "Fore -'n' -aft" Ford, Mercury -Mount a condenser on connect the leads under the terminal nuts. the voltage regulator fastening screw and underseat heater it will be necessary to in- Install a condenser on the overload relay, stall a heater hose shielding. To make an in- connect its lead to the bottom terminal of which is mounted on dash inside the car the stallation, slip 2 pieces of braided metal the regulator. Mount another condenser and over the steering column. Connect its with a special bracket on the distributor and loom over the hose and stretch them length- lead to the saine terminal on the relay as the wise until they are tight on the hose. Re- connect its lead to the distributor terminal battery lead of the radio set is connected. nut. Connect the lead from another con- move the clamp bolt from the double clip Mount a condenser on the rear of the oil which supports the hose at the cylinder head denser under the center terminal on the oil filter bracket and connect its lead to the gauge engine unit and mount it on the and scrape away all paint and dirt from terminal on the oil gauge. Mount another between the support and the clip, and be- line. In some cases it may be necessary to condenser under one of the gasoline gauge move this condenser to the instrument board tween the support and clamp bolt nut to tank unit bolts and connect its lead to the form a good ground. and connect the lead to the bar between the gauge terminal. This is accessible under a oil gauge and the fuel gauge indicators. metal cover beneath the spare tire in the Studebaker Champion -Cut the high -ten- Graham-Cut the high tension lead to the rear compartment. Mount another con- sion lead to the center of the distributor center of the distributor block about 1 in. denser with a special bracket under one block and install a resistor type of sup- from the distributor and insert an inductive of the cylinder head bolts and connect its pressor in it. Mount a condenser under the type of suppressor. Mount a condenser on lead to the water gauge terminal. Another generator ground lead screw and connect its

88 RADIO -CRAFT for AUGUST, 1940 SERVICING lead to the generator armature terminal. Re- move the 3 terminal nuts and wires on the back of the gasoline gauge dash unit and The larger "duplicate" replace: assemble a resistor in place. Then replace ment costs $1.20. Three Atoms com- the wires and nuts. Ground the controls that bined with ST Strap give the same hard -to-get capacities in smaller size pass through the 2 rubber grommets in the for only 96c! dash by using a braided shielding. Place one end of the shield under the screw on one side, make a turn around each cable and fasten the other end of the shielding under the other screw. Drill a s% -in. hole in the steering column jacket just outside the engine bulkhead. Also drill a % -in. hole through the bulkhead just above the steering column and fasten a ground strap between the 2 points with self- tapping screws. CONDENSER Studebaker Commander -Cut the high - tension lead to the center of the distributor REPLACEMENTS and install a resistor type of suppressor in it. Mount a condenser under the generator ground lead screw and connect its lead to Either Way the generator armature terminal. Studebaker President -Cut the high -ten- It pays to try Sprague for any exact duplicate condenser require- NEW MANUAL ON ment. As leading suppliers to the largest set makers, we ran supply of and INTERFERENCE sion lead to the center the distributor almost any needed unit promptly -and identical to the original RADIO of in it. install a resistor type suppressor specifications. Just the book you've been a Mount condenser under the generator looking fur. Complete -fully ground lead screw and connect its lead to But don't forget, you can save on most hard -to-get replacements. illustrated simply by combining several Sprague Atom midget drys. Just strap the generator armature terminal. Connect tells what to one side of a small mica condenser to the 'em together (see picture) with Sprague ST Mounting Straps -supplied free -and you have a smaller, better unit and actually at less do, how to do battery terminal on the distributor and cost than an exact duplicate! Using ST Straps, you can make up it to eliminate ground the other terminal of the condenser almost any combination of capacities and voltages using standard all types of under the distributor condenser mounting Sprague Atoms stocked by every Sprague jobber. Big new man -made ra- screw. catalog of Sprague Condensers and Koolohm Resistors FREE. dio noise. 25e Willys- Install a suppressor in the center net. terminal of the distributor block and connect the high- tension lead to it. Mount a condenser on the generator ground lead screw and connect its lead to the generator CONDENSERS armature terminal. Attach another condenser under a junction block mounting KOOLOHM RESISTORS screw and solder its lead to the terminal TEST EQUIPMENT of the brown wire leading to the oil gauge. SPRAGUE Be sure that the floor board bolt heads are SPRAGUE PRODUCTS CO. NORTH ADAMS. MASS. tight enough to slake a good electrical contact. This article has been reprinted by per- There is now almost pure D.C. on the mission of Motor, the aatomotire business plates of the tubes. But the A.V.C. is "out," magazine, and with the cooperation of and a high -resistance voltmeter indicates an TOPS! P. R. Mallory & Co., Inc. open A.V.C. circuit, which is repaired by in EYE APPEAL! replacing the resistor in the negative line. A glance at the clock, and sigh relievedly EAR APPEAL!! FIX THAT RADIO! -you made it on time! PRICE APPEAL!!! WILLARD MOODY, THE deadline is 2 hours from now . . . New York, N. Y. the set is on the bench , you turn it on, watch the ammeter indicate too much current consumption, flip the receiver FEATURES IN AUGUST switch "off" to prevent damage. You get out the ohmmeter, check the resistance from RADIO & TELEVISION the screen -grid to chassis of the output tube. MAGAZINE and the result indicates a short -circuit. March of Radio Next, you take a look around and see that International Radio Review there is a filter condenser with some white 3 -Tube Loop B.C. Receiver stuff leaking out of the top of it. You put -Chas. R. Lentz the ohmmeter here, with one side of the 5, 10 and 20 Meter Receiver for "Hams" condenser disconnected from the receiver and "Fans" -Harry D. Hooton, WBKPX 2 -Tube wiring. The condenser is shorted, you find, Beginners' Receiver It has everything you herd to sell moree records . quality crystal pickup self silent drive For Hams 21/2 and 5 Meter Transmitter starting rim and another is put in its place. -a motor (also in Ar-DC and 25 eyelet. high Polelity You turn the set on again, and this time -Milton Meyrowitz amplification and speaker and retails at only $14.9 , Dealers wrap for attractive proposition. Servire men the power consumption is not too high, Frequency Modulation -How It Works can tue the PORTABLE \IODEZ. for frequency test is in fact normal. But the tone is none too -Ricardo Munis, E.E. revords. good, being lacking in bass response, which New MUSIC MASTER MFG. CO. F.C.C. Rules for Radio Amateurs 508 S. Dearborn St. Chicago. III. leads you to the conclusion that, since the How to Plan the Radio Amateur Trans- reactance of a condenser varies inversely mitter as the frequency, the opposition to audio Getting the Most from Your "Portable" voltages must be too high at the low fre- Receiver-H.W. Secor IIRECTCBIPLEI AMPLIFIERS quencies, indicating high reactance and too - Television News - low capacity. So you disconnect the other The new RCA 2" Iconoscope Makes Ama- filter condensers and test them by putting teur Television Practical! the ohmmeter on the 100,000 Ohms range, Radio "Hookups " -Including Puzzle Dia- watching the meter needle flip up as the gram condenser takes the charge, watching it Easy Set- Building- gradually recede to zero, if the condenser A Flea- powered Transceiver is a good one. The amount of kick the -H. G. Cisin, M.E. meter needle receives is proportional to the Question Box capacity and the quality of the condenser, Radio Kinks which may be compared with a good one. Latest Radio Patents Write For Complete Details arid Attr e Proposition A new set of condensers, you find, results Newest Radio Apparatus AMPLIFIER COMPANY of AMERICA in improved tone and much less hum. 3545 WEST 20TH STR!. IT NEW YORK CITY NEW YORK

RADIO -CRAFT for AUGUST 1940 89 SERVICING

Radio Service Data Sheet 282

SENTINEL MODEL 217 -P PORTABLE RADIO SET 6 -Tube Superhet.; A.C.-D.C. and Battery Operation; Automatic Volume Control; Built -In Loop Antenna; Sliderule -Type Dial; Under - writefs Approved; Broadcast Band (Range 535 to 1,730 kc.); Inclined -Panel Leather Case Stage of R.F. Amplification; 5-In. P.M. Dynamic Loudspeaker.

ALIGNMENT PROCEDURE through a 0.2 -mf, dummy antenna con- mer, do not connect the test oscillator Remove chassis from cabinet. Place denser. Do not remove the grid cap. directly to the loop. Instead, couple the loop antenna in the same position it Adjust each of the 2nd I.F. transformer test oscillator to receiver loop by making would be when the chassis is in the trimmers for maximum output and each a loop consisting of 5 to 10 turns of No. cabinet. of the 1st I.F. transformer trimmers for 20 to 30 size wire wound on a 3 -in. form maximum output. (See diagram showing and attached across the output of the I.F. STAGES locations of trimmers.) test oscillator. Place this test oscillator loop near the set loop and be sure that Set receiver Glial to any point where neither moves while aligning. no interference signal is received. Feed 1,730 TO 540 KC. BAND a 455 -kc. signal from the test oscillator When adjusting the 1,730 he. oscillator Set the receiver dial to exactly 1,730 to the grid cap of the 1A7GT tube trimmer and the 1,400 kc. antenna trim- kc. and feed a 1,730 he. signal to the loop antenna of the receiver. Adjust the 1,730 kc. oscillator trimmer for maximum output. Then set the receiver dial to approximately 1,400 kc. Feed a 1.400 kc. test signal into the receiver loop antenna and adjust the loop trimmer for maximum output, rocking the gang condenser throughout this operation. Note that this portable, unlike most portables, incorporates a stage of R.F. amplification. When an external aerial is used a good ground connection must be made.

Sentinel model 2174 3 -way portable radio set.

Diagram showing locations of trimmers and Complete schematic diagram a d operating voltages of Sentinel 217 -P receiver. components.

90 RADIO -CRAFT for AUGUST, 1940 SERVICING

283 Radio Service Data Sheet

BELMONT MODEL 678 AUTO -RADIO SET 6 -Tube Superhef.; 6- Buffon Automatic Remote Tuner Unit; Automatic Volume Control; Range 535 kc. to 1,565 kc.; Synchronous -Type Vibrator; Single Stud Mounting. r MMF. -Ili -. RSE, 500 cA, O' ,.11 ATOR 6BV (_ 015- rNT PILOT 4 (LLCM ,HEE 4Eu,EE T .%,r.ÁHOT 40 SFIÉLOR NM3AIF, PUSH- CONTROL , A IL BUTTON 5 MMF, COIL.T3 MICA Oi 5 E I NOTE 1 1, ^,.. 1 1 WN-RJL ((( SO MM pusHet,rroN 1) ÁER 50 AASSEMBLV,T1 MME, rose MICA. 2 01-A= TRIMMER i00Á CONTROL BLACK 500 ^ 00_- n0 O 1- MICA. 6A8 MICA 65K7 3W 601 61(7 NpuT á0COIL CO. SwC 465 C)

MMF. AL. 010 MCA. IMEG ORANSpTRANS LNW.

OHMS. I5. 450V (EACH) 05- I IMF Y L%JW 200V. 40JV 1' L- 600 L 0'S- NOTE 30000 1500 IMF, OHMS WER 1 CONTROL H(AO OHMS. OHMS. MCA 2003/ IE" TRANSFORMER I.F=465KC. min I41EF SURE W. W. OHMS. CHASSIS5515 BLAC wHIrE ( I OUGH ÓUrLS BRAID OF CABLE 100 '15 OHMS. OHMS. z0 fia 411 1.600V (EACH) O 130 -CYCLE - 0 VIBRATOR To 04 SHOWN WITH HOT REVERSE 4.000 3 VIBRATOR OHMS. 01- 1 50 ó 09 HOT SF AF 0 B UE BOTTOM VIEW REDOR BLUE YELLOW, OF ' FLU,

Fig. I. Complete schematic diagram of the Belmont model 678 auto -radio receiver. BOTTOM VIEW OF CHASSIS ALIGNMENT PROCEDURE Turn volume control to maximum for all adjust- VIBRATOR ments. Connect radio chassis to ground post of signal generator with a short, heavy lead. Connect dummy antenna in series with generator output lead;- 0.1 -mf. for the I.F. band and a 125 mmf. for the broadcast band. Use an output meter 6SK7 e It TArtr WALRUS MTK o.. across the wo,tT `IrwA°..u`áO C 00 ás. primary of the output transformer. Allow chassis 6A6 NA1 and signal generator to heat up for several minutes.

NA. WOMNIO. I.F. ALIGNMENT Feed a 465 -kc. signal Fig. 5. Belmont auto -radio mode t ó wT. to the grid of the 6SK7 I.F. 6N7 tube. Set dial at 1,400 kc. Adjust trimmers C19 and 678. Note Remote Tuner at right i.f 0 C20 for maximum output. To align this output I.F. unit without using 34 0 cathode-ray oscilloscope, a (2 10,000 -ohm resistor must be shunted across the diode tuned circuit as indicated by points X and Y on the schematic (Fig. 1) and in Fig. 4. Trimmer C'19 is 0 identified by a red dot on top of the I.F. can. After alignment of these 2 trimmers, remove the Fig. 4. Bottom view of chassis giv- 10,000 -ohm resistor and align trimmer C21 for ing socket voltages. maximum output. Do not readjust trimmer C19 or -615G C20 after the resistor has been removed. Shift the VIBffA signal generator lead to the control -grid of the 6A8 INIronTANT - and adjust trimmers C14 and C15 for maximum 7 /T4 Hvrama. output. i=, SK7 BROADCAST BAND Feed a 1,565 -kc. signal to the antenna lead with Fig 3. Bottom view of remote tuner the set dial adjusted to 1,565 kc. Adjust trimmer C5 for maximum output. Reset the dial to 1,400 kc. and adjust trimmers Cl and C3 for maximum output using a 1.400-kc. test signal. Finally, reset the dial to 600 kc. and adjust trimmer C2 using a 600 -kc. test signal in the antenna lead. Maximum gain for this adjustment depends on the capacity of the antenna system of the car in which the radio receiver is installed. Power consumption is 7.7A. at 6.3V. No suppressors required on the spark plugs; only a distributor suppressor is needed. The output I.F. coil has 3 tuned circuits giving superior band -pass qualities and selectivity as compared to the conventional 2- tuned- CABLE circuit coils. Antenna, R.F. and oscillator circuits are permeability tuned, offering ASSEJ.ELY automatic tuning applications that are both accurate and stable. The entire coil assembly is mounted in the Remote Tuner control head being connected to the oscillator and R.F. circuits by an R.F. transmission cable. The R.F. oscillator, and I.F. and A.F. amplifiers, including the power supply, are Fig. 2. Chassis view showing locations of contained in the speaker case. trimmers and components. This unit has been designed to facilitate servicing.

RADIO -CRAFT for AUGUST, 1940 91 * * * THREE STAR RADIO VALUE Veit receive valuable subscription to RA DIO ffCRAFT

PLUS A FREE COPY oá /940 12adla- lelevlilan J2eóetenee -Pnnua1

1 ITH our compliments. we want to send a ropy of the 1940 RADIO. TELEVISION REFERENCE `r ANNUAL to you FREE. if you will simply take advantage of RADIO -CRAFT magazine's special Read subscription offer NOW. This offer is being made fora limited time only. the summary of contents The 1940 RADIO -TELEVISION REFERENCE ANNUAL has 68 pages. large sire 8S'a x 1IYe, with in FREE over 170 illustrations. The contents of this book has never appeared before in handy book form. Its pages this BOOK! cover practically every branch of radio sound. public address. servicing, television, construction articles for advanced radio men and technicians, time and money saving kinks, wrinkles, useful circuit informa- THE 1940 RADIO- TELEVISION REFERENCE tion, "ham" transmitters and receivers, and a host of other data. ANNUAL contains a collection of the best and The Annuals have always been regarded as a standard reference work for every practical branch of radio most important articles. Covering as they do operation and service. This 1940 edition ably sustains this reputation. Every radio man wants a copy radio, of this valuable book. lust as this book will be of unquestionable value to you. so. too. will every nearly every branch of they form a handy monthly issue of RADIO- CRAFT. This magazine brings you big value every month. It keeps you reference works. In addition, many time and labor- intelligently informed about new developments in radio and television. You want the news, want it saving kinks, circuits and wrinkles, tried and tested fully but concisely, want it first -that is why you should read RADIO -CRAFT regularly. by practicing Servicemen, experimenters and radio This very special offer is made for just one purpose -we want you as a regular subscriber. The Annual, fans have been included. This book cannot be ehose contents appears at the right, is not told, but a COPY is FREE to you if you subscribe now. bought anywhere at any price. Yet It is yours by merely subscribing. Use the convenient coupon SAME SI2E AS below. RADIO -CRAFT BEGINNER'S SIMPLE INEXPENSIVE CONSTRUCTION ARTICLES Beginner's Breadboard Special - a 1 -Tube High -Gain All - Wave Receiver -Wiring Pointers for Radio Beginners -A Watch Charm Size 1 -Tube Set -Beginner's Simple Volt - Milllammeter- Making a 1 -Tube Broadcast Loop Receiver Power Supply for Battery Portables -A 1 -Tube Short -Waver with Band Coll Switching. MORE ADVANCED SET CONSTRUCTION The "High -Seas 4" Broadcast Lamp Radio -How to Build a 8 -Tube 1.4 -Volt Short-Wave Superhet for the "Ham- or Short-Wave Fan -Build the "Lunch Box 5" Super Set - a Broadcast Battery Portable -How to Build a Plug- Together 8 Tube Broadcast Set -The "5 -In -4" All -Wave Radio for A.O. Operation -An Easily -Built 3 -Tubo Midget Broadcast Superheterodyne Receiver. THE SERVICEMEN'S SECTION Base Tone Control -Simplified Variable Selectivity-Prac- tical Servicing Pointers- Servicing Universal A.C. -D.C. Re- ceivers-Killing the "Intermittent" Bug -A Service Shop A.C. -to D.C. lover Supply -Sideline Money for Service- men-Adding A.V.C. to any Screen -Grid T.B.F. Receiver -Iron Particles in Speaker Air Gap. TEST INSTRUMENTS A fleful Neon Lamp Tester-An Inexpensive Output Meter -Making Milllammeter Multipliers- Home -Made Frequency Modulator -The Busy Servicemen's V.T. Volt -Meter. PUBLIC ADDRESS AND AMPLIFIERS Build this Combination A.C. -D.C. Radio and Inter-Com- municator- Speaker Placement in P.A. work -The Design and Construction of an Inexpensive All -Push -Pull 10 -Watt Amplifier- Obscure Sources of Hum In High -Gain Ampli. fiers -How to Build a High -Fidelity 5 -Watt Versatile Amplifier. "HAM" SECTION Ultra-high Frequency Antennas-The Beginner's Low -Cost Emitter -Modulator Meter-Phone Monitor -The Begin- ner's Ham" Recelrer -2% Meter Acorn Transceiver. TELEVISION How to Build 941 Line T.R.F. Television Receiver -Use- ful Notes on Television Antennas. MISCELLANEOUS Simple l'hotoCell Relay Set Up- Making a Burglar Alarm -Bow to Build A.C. -D.C. Capacity Belay -How to Make a lladern Radio Treasure locator. USEFUL KINKS, CIRCUITS AND WRINKLES Making a Flexible Coupler-Two -Timing Chime -A Simple Portable Aerial -An Improvised Non -Slip Screw-Driver. NOTE: The book contains numerous other useful Kinks. Circuits and Wrinkles. not listed here. (approximately) 45 ARTICLES (approximately) 170 ILLUSTRATIONS THIS COUPON BRINGS YOU THE ANNUAL 68 BIG PAGES RADIO -CRAFT 20 VESEY STREET NEW YORK, N. Y. Gentlemen: Enclosed you will find One Dollar for which enter my subscription to RADIO -CRAFT Magazine for Eight Months. Send me ABSOLUTELY FREE and POSTPAID, my copy of 1940 RADIO- TELEVISION REFERENCE ANNUAL. D This is a new order D Extend My Present Subscription RADIO -CRAFT NAME ADDRESS 20 VESEY STREET CITY STATE NEW YORK, N. Y. DON'T DELAY - MAIL TODAY! RC-R40

92 RADIO -CRAFT for AUGUST, 1940 TEST INSTRUMENTS A LOW -COST SIGNAL CHASER - Plus "While the instrument was designed primarily for beginners, and Service- men. who operate on a small scale, the advanced technician will also find this tester capable of promptly locating the trouble in possibly 9O of all ordinary calls." The instrument here described is not only a signal chaser but also functions in. other capacities.

C. RASK LATIDIER

NER' Servicemen are often discouraged and handicapped by not being able to afford a complete set of modern test instruments. Accordingly there is a decided demand for substitute low -cost instruments really capable of useful functions. The instrument to be described in this article can be built at a very reasonable cost. The functions include signal chasing at either radio or audio frequencies, voltage indication, voltage polarity, high- resistance continuity, low- resistance continuity, interference search, hum search and many other applications that will be apparent to re- sourceful technicians.

USES Figure A is a view of the complete instrument which only occupies a space of 10 x 5 x 3 ins. deep, and which is entirely self -contained and -powered. Using the versatile 1D8GT tube, diode detection, triode voltage amplification and pentode power audio amplification are all available within the single tube envelope. The tube requires one 11 -volt "A" cell and two 51 -volt "B" batteries, and there is room for these within the case. Accordingly the instrument is useful at points where ordinary 110 volt 60 cycle A.C. may not be available to operate standard test apparatus. An example would be the field servicing of auto, marine or farm receivers which operate from 6, 12 or 32 volts D.C. or 110 volts D.C. While the instrument was designed primarily for beginners, and Servicemen who operate on a small scale, the advanced technician will also find this tester capable of (A) Front view of the Low -Cost Signal Chaser-Plus. The recessed power -cord receptacle is seen on the left side. To put this "signal chaser -plus' into full operation you need only headphones. (B) The promptly locating the trouble in possibly rear view suggests the ease of construction. 90Ç4 of all ordinary calls. This is especially true if the receiver tubes are first tested. grid is obtained from a series resistor, R10, No. 1 -Audio Test: There are some limitations to the applica- in "B "- negative lead. Tip- jacks, 12 in Input prods at IV and III; tions. The R.F. search cannot be expected the all, are provided to make the necessary Switch at Position 2 for 1A.F., Position to pick up very feeble signals as there is at In addition a 3- circuit 4 -posi- 1 2A.F.; no R.F. amplification. However connections. for the output switch is provided to secure Phones VI from any R.F. or I.F. stage can be detected tion selector at output and VII; and noted. Voltage indication the circuit changes required. Regulate volume at Gain Control. below 65 to low- resistance continuity the 90 volts cannot be For the test, No.. -Hunt Search: secured as the neon lamp headphones and "A" cell are in series with requires that initial voltage before it can Same as above, but connect prods to a the prods. For high- resistance continuity, suitable open -core iron inductance. strike the arc. For R.F. search ordinary with prods leads are suggested, A.C. or D.C., they are in series the No. Radio -Frequency Teat and same being neon lamp In case of D.C. 3- (at any R.F. connected in place, and operator's and prods. the input or output circuit I: the hands the "B" battery is used. In the case of A.C., removed to prevent disturbance of the cir- Input prods at I and II; it is connected to the tester by the recep- cuit. a Switch Position 2 for If desired, coaxial cable type R.F. provided. Using D.C. with the at diode detector prod can be substituted. If tacle plug and 1A.F.; the matter of neon tube, only the negative element glows, circuit unbalance is important, the "hot" Switch at Position 1 for diode detector so gives an indication of polarity. R.F. prod can be connected 100 that and 2A.F.; through a In making an R.F. search, the diode can mmf. condenser or series 1- megohm resistor. Phones at output VI and VII. be used with either 1 or 2 stages of audio In spite of the 2 limitations admitted, the amplification and the audio gain adjusted No. 4- Interference Locator: useful functions are numerous and offset by the volume control. Same as above, but connect a suitable loop the small disadvantages. The instrument is In making an A.F. search, either 1 or antenna and tuning condenser to input not intended to replace precision equipment. 2 audio -frequency stages can be used and terminals I and II. here again the gain is controlled by the No. 5- I'oltage Indication: CIRCUIT input potentiometer. The radio input Prods at VIII and IX; Figure 1 gives the complete schematic (diode) will of course also pick up audio Switch at 1 for up to 500 volts, max.; wiring diagram showing the 1D8GT tube signals (diode to ground). Switch at 2 for up to 330 volts, max.; circuit used which consists of a diode de- Switch at 3 for up to 220 volts, max.; tector, triode 1st A.F. stage (resistance HOW TO USE Switch at 4 for up to 110 volts, max.; coupled), and a pentode 2nd A.F. or power The principal suggested useful tests are (65 to 90 volts min.). output stage. Bias for the pentode control- as follows: The neon tube draws 1 milliampere.

RADIO -CRAFT for AUGUST, 1940 93 TEST INSTRUMENTS

GEOPHYSICAL R9 PROSPECTING OUTFITS MEG. o MF. 1D8GT

(cap)

R1 R6 0.5- Ze MEG.. r OHMS POTEN MEGS. PZ C4 10 MF., RIO 25V. C2 800 .0025- OHMS MF. v Cl BLUE PRINTS and INSTRUCTIONS loo MME Vs For Building the Following Treasure Finders and Prospecting Outfits R7 WTHIS MÉGS. R2 Folder No. 1. The "Radioflector Pilot" --cun- I - ACK T 0.1- IS GROUNDED M EG. '114:10V-AZ "B +" eists of a 2 -tube transmitter and 8 -tube TO THE CASE receiver. Principle: radiated Wave from 90V. 90V. transmitter loop is reflected back to receiver R loop. Emits visual and aural signals. Tubes MEG. used: two IA5G -two 1N5G-one 1H5G. Folder No. 2. The "Harmonic Frequency Lo- R4 cator"-Transmitter radiates low frequency 0.1- wave to receiver. tuned to one of Harmonics MEG. of transmitter. Using regenerative circuit. Ii Emits aural signals. Tubes used: one 166G -one 1NSG. NEON Folder No. 3. The "Beat -Note indicator" -Two LA 05P oscillators so adjusted as to produce beat- note. Emits visual and aural signals. Tubes used: Three type '30. A.C. OR D C. Folder No. 4. The "Radio-Balance Surveyor" INLET -a modulated transmitter and very sensi- FIG.1 tive loop receiver. Principle: Balanced Headphones and test prods complete the Signal Tester -Plus, shown above. The neon tube, in the loop. Emits visual and aural signals. By tri- actual instrument, is protected by a transparent cover. angulation depth of objects in ground can be established. Tubes used: Seven type '30. Felder No. 5. The "Variable Inductance Moni- 6 No. Direct Phone Prods ( for audio test, tor"-a single tube oscillator generating No. -Line Polarity: 9- fixed modulated signals and receiver em- Same as above, negative neon electrode phono pickup output, microphone trans- ploying two stages R.F. amplification. glows. former output, etc.): Works on the inductance principle. Emits Phones at VI and VII; aural signals. Tubes used: six type '30. No. 7 -A.C. Continuity Neon Test (for in- Folder No. 6. The "Hughes Inductance -Bal- dication of condenser capacity, test or Switch at Position 3; ance Explorer "-a single tube Hartley os- open condenser, etc.): Prods at XI and XII. cillator transmitter and sensitive 3 -tube receiver. Principle: Wheatstone bridge. Emits Prods at VIII and X; No. 10- Low- Reaistance Continuity: aural signals. Tubes used: two type '30- Connect 110 volts A.C. to plug receptacle; Switch at Position 4; one type '32 -one type '33. Switch on Position 4. Prods at III and XII; Folder No. 7. The "Radiodyne Prospector" - a completely shielded instrument. Principle: No. 8 -D.C. Continuity Test (for condenser Phones at VI and VII. Balanced loop. Transmitter. receiver and dielectric condenser leakage, No. 11- Lead -in, Transmission Line or batteries enclosed in steel box. Very large strength, field of radiation and depth of penetration. etc.) : Aerial Test: Emits aural signals. Tubes used: two 1N5G Prods at III and VIII; Connect aerial input to primary of R.F. -one 1G4G-- one IH5G -one 1Q5 -one IG4. Connect jumper from V to IX; transformer. With any one of the modern geophysical Switch on Position 4. Connect secondary of the R.F. transform- methods described in the Blue-Print patterns, Radio outfits and instruments can be constructed to locate metal and ore deposits (prospecting) ; finding lost or buried treas- 2 HOLES RILL 2#-{ ures: metal war relics,: sea and land mines R SOCKET

and "duds "; mineral deposits: subterranean g"-H1 I B water veins; oil deposits (under certain circumstances): buried gas and water pines; ]Y m tools or other metallic object. sunken in wa- S ter. etc., etc. AUDIO RADIO1._ GAIN II In _' GAIN 1yNAME Each set of blueprints and Instructions enclosed NAME- ¡'::: heavy envelope (9'.. l l21/2'). Blueprints 22" x PLATE IgF!L+ATE 34 "; eightpage Illustrated 8'/," X 11' fold- COO er of Instructions end construction data . Y'' Add 5e for postage ' '/a "DRILL ,} V:'DRILL The complete set of seven folders I Gí11Ñ 21 I C2NrROL. Shipping weight 2 lbs. (add 25c for ship- $3.00 Fig. 2. Cabinet details. FWI'I _i ping anywhere in U.S.A.) colors MOLDER 41FORRILIU Tip -jack preferred I TO 3P- by the author are: I, red; FUSE RILL1211OLES HOLDER I IN DIA FOR TECH NWí1X Il, black; Ill, purple; IV, SO" TIP -JACKS RC -840 SELECTOR 1917 S. STATE ST. CHICAGO. ILL. dark green; V, slate; VI, NAMEPLATE FLYCUT 3/aORILL I / SPOT 14 HOLES light green; Vil brown; t HOLE 5/16.10 DIA. 1 13/4IN DIA.. I SWITCH FOR NAME- VIII, slate; IX, dark AND SPOT / PLATES. 1917 So. State, Chicago, III, OUTPUT 'TECHNIFAX brown; X, brown; XI, 3 HOLES Ne2T DRILL II' p1NAMEPLATr Xi Enclosed herewith S for which mail to XII, green. FOR A.G. l address below : INLET. V . Ì HONE 1 II NAEPUTE_iI 9 Treasure Finder No. I. 2, 3, 4. 5. 6. 7. ;0 Complete set of seven folders. A.G. INPUT SDI D.C. INPUT NAMEPLATE) I NAMEPLATE __T r. - NAME 2 T

ADDRESS t 2} CITY STATE 5' RC -840 L .1

94 RADIO -CRAFT for AUGUST, 1940 TEST INSTRUMENTS

er to R.F. input I and II, with a parallel Twelve Mallory 400 Series tip -jacks, colors tuning condenser if necessary. as desired; Other connections same as No. 2. Four Mallory No. 15 tip -plugs; No. 12 -Test for Line Power Supply: Two ICA No. 355 test prods; Prods at VIII and IX to power outlet; One General 1%-volt "A" cell No. 2F1; Switch at Positions 1 to 4; Two General 51 -volt "B" batteries No. Note neon indication. V -34 -AAA; 1 Pair Cannonball "Master" headphones; LIST OF PARTS CASE One Littelfuse No. 1075 fuse extractor post One Parmetal case No. B -4508, and bottom and 1- ampere fuse; plate No. BP -4508, black wrinkle finish, One Littelfuse No. 5123 neon holder; 5122 neon size 10 x 5 x 3 ins. deep. One Littelfuse No. tube, 1/20 RESISTORS watt; One Mallory type N, %- megohm potenti- One Amphenol 61M10 male receptacle, flush ometer and switch; mounting; Four IRC, 0.1 -meg., 2 -W., type BT'/s, R2, Seven Crowe nameplates, one each No. 16, R3, R4, R5; A9, I15, G15, J11, D9 and A2; One I.R.C., 50,000 ohms, type BTV2, R6; One triple insulating tie lug; One I.R,C., 10 megs., -W., type BTS, R7; Two hollow spacers, 3 /16 -in. in dia. x 1% 1 ins. long (for socket); One I.R.C., 2 megs., r/e -W., type BT5, R8; Two No. 6 -32 round -head brass screws 1s/a One I.R.C., 1 meg., -W., type BTr , R9; 1 ins. long; One I.R.C., 800 ohms, r/z -W., type BT %, RIO. One Amphenol octal socket No. MIPS; CONDENSERS One grid clip; One Mallory, 100 mmf. mica, Cl; Ten feet Push -hack hook -up wire; One Mallory, 250 mmf., mica, C2; Six feet No. 18 flexible rubber -covered wire; One Mallory, 1 mf., 400 -V. paper, C3; One double and 2 triple connector plugs for One Mallory, 10 mf., 25 V. electrolytic, C4; batteries; One Mallory, 0.01 -mf., 400 V. paper, C5. Four No. 6 -32 round -head brass screws, %- MISCELLANEOUS in. long; One National Union type 1D8GT. Six No. 6-32 hex. brass nuts, lock washers One Mallory 3- circuit 4- position switch No. and soldering lugs; 3234J, with plate and knob; One- quarter lb. rosin -core solder.

BOOK REVIEWS BIG IN VALUE BIG IN PERFORMANCE TELEVISION. by V. K. Zworykin and G. A. Mor- Cuthbert. N.B.C., writes on "The Women ": for- ton (1940). Published by John Wiley & Sons. Inc. eign affairs is John H. Payné s (U. S. Department SENSATIONALLY PRICED AT $11.85 Size, 6 z 9 ins.. cloth cover, profusely illustrated, of Commerce) topic: Orson Welles' topic is "Ra- 646 pgs. Price, $6.00. dio Drama". Frequency modulation, short waves, V. K. Zworykin, E.E., Ph.D., Electronics Re- facsimile, the New York World's Fairs of 1939 Here is an AC -DC Volt- Ohm -Milliam- search Laboratory, RCA Manufacturing Co.. and and 1940, television, and air schools are other meter with all the ranges you want . . - G. A. Morton, Ph.D.. same division, same corn- subjects briefly analyzed. easily readable on the large 7" instru- pany, have collaborated to produce the most up- Another chapter is "Radio History Makers of ment with extra -long 6" scale . .. in a to -date book on electronic television. 1939" with thumbnail illustrations and writeups ; "Television -The Electronics of Image Trans- operations and decisions of the Federal Com- new up -to -date three -tone case you will mission" considers in Part I the fundamental munications Commission are reviewed. be proud to use in your panel, bench or physical phenomena involved in electronic tele- Room does not permit further analysis of the on calls to the home. Check Readrite Big vision. Part II deals broadly with the field of innumerable topics touched upon in this nearly Boy's adaptability for your requirements: television. Part III is an analysis of the corn - 1.000 -pg. book. It may be pointed out however DC V. 0- 10 -50- 250 -500 -1000 at 1000 ponents of the electronic television system. Part that, as with preceding issues of the Annual, there IV describes the entire television system exem- are included an up-to -date listing of the broad- ohms per volt; AC V. 0- 10 -50- 250 -1000 plified in RCA /N.B.C. television operations. cast stations of the United States; Publications at 400 ohms per volt; DC Ma, 0 -I -10- Chapter headings give only a suggestion of the covering the field of radio: advertising agencies 100; Resistance ranges: 0 -500 ohms wealth of detail and ample illustrations in the and radio station representatives ; and, a number shunt type circuit and 0- 100,000 ohms. many subjects treated. of other groupings of lesser extent, but in pro- No person interested in television can afford portion of perhaps equal importance. 1.5 megohms and higher by additional to be without this timely book. Television and facsimile have a 26-pg. section batteries. Maroon case with cream panel, Part I- Fundamental Physical Principles - all to themselves. attached handle . . . Dealer Net Emission of Electrons from Solids ; Fluorescent FLUORESCENCE AND PHOSPHORESCENCE, Price $17.85 Materials ; Electron Optics ; Vacuum Practice. Part II- Principles of Television-The Funda- by E. Hirschlaff (1938). Published by Chemical mentals of Picture Transmission; The Transmis- Publishing Co., Inc. Size, 4 z 6% ins., cloth cover. sion and Reproduction of High -Definition Pic- 41 illustrations, 130 pea. Price, $1.50. * * * We do not know what particular significance. tures : Video Pick -up Devices ; Picture Reproduc- ing Systems. Part III -Component Elements of if any. may attach to the statement that this is an Electronic Television System -The Iconoscope: a "First American Edition- 1939" but you now MODEL 432 -A TUBE TESTER have the quote for whatever it is worth. The Kinescope: The Electron Gun : Video Ampli- Essentially this book is a "monograph" and is fiers ; Scanning and Synchronization ; The Tele- The Outstanding of little interest to any but tube specialists, more vision Transmitter ; The Receiver. Part IV- Tube Tester Value particularly those interested in photoelectric and RCA/N.B.C. Television Project -RCA Television . . . television phenomena to these, this book will be Checks all Project- Studio and Monitoring Equipment ; Em- types including pire State Transmitter Conclusion. an invaluable reference to the most up-to -date information on how and why a' vapor or a liquid Loctals, Single of RADIO ANNUAL 1940, Compiled by the Staff irradiated by light may be able to emit light Ends, Bantam Jr., I:adio Daily. Published by The Radio Daily. Size, (fluorescence), and why this re- emission may con- and the 1.4 -volt Erik x 91/2 ins., cloth cover, 988 pis. Free with I -yr. tinue after the existing radiation has been cut subscription to Radio Daily. Miniatures, Gas- off (phosphorescence). Chemical formulas and eous Rectifier, Bal- It is evident from a review of the third or mathematical equations are included to clarify 1940 Edition of the "Radio Annual" issued to such subjects as the fluorescence of atoms and last, High Voltage Daily lessons been Radio subscribers, that have molecules, the quenching of fluorescence, cathode - Series, etc. Fila- learned from the experiences of the preceding luminescence in gases. liquids and solids ; etc. ment Voltages issues. The march of radio during 1939 is suc- from 1.1 to 110 cinctly portrayed, and the prospects for 1940 THE METEOROLOGICAL GLOSSARY. (3rd volts. Direct Reading GOOD -BAD Meter are analyzed, by a group of specialist,. Edition. 1940). Published by Chemical Publish- Scale. James Lawrence Fly, Chairman, Federal Com- ing Co., Inc. Size, 6 x 9 ins., cloth cover, illustrat- Counter or Portable Case with munications Commission, discusses radio from ed. 251 pgs. Price, $3.00. roomy compartment for tools, etc., the social standpoint: Neville Miller, Pres.. Na- The 3rd Edition of this book will be of interest $ 1 8.85 Dealer Net. In case less 7,85 tional Assoc. of Broadcasters, describes the broad- to those technicians whose business it may be to compartment ...... s casting kaleidoscope of events : David Sarnoff. acquire familiarity with the underlying causes Pres., RCA. presents facts and figures; Elmer of the changes in weather conditions. This group WRITE FOR CATALOG Davis, C.B.S. news analyst, analyzes his field of would include amateurs interested in learning Section 816 College Avenue operations; education is covered by William Dow the whys and wherefores of shortwave perform- Boutwell, U. S. Office of Education ; Margaret ance: and. broadcast technicians. (See Pages 100 and 12t for other book reviews) READRITE METER WORKS, Bluffton, Ohio RADIO -CRAFT for AUGUST, 1940 95 SOUND

IMPROVED REFLEX SPEAKER This article explains the advantages achieved by applying the principle of sound reflection to an exponential horn driven by a horn unit.

R. C. REINHARDT

marine service for the past 5 years. By com- were used, would impose at least 2 very bining this general construction (but with serious objections. improvements which will be described) with First, the source of audio supply for the certain desirable features of a second class flat -baffle type would necessarily be greater of loudspeakers generally referred -to in the than that required for the h?rn type for sound field as the "WX -type marine horn," equivalent acoustic output. This would also driven by a cone -type unit, the attributes indicate (a point which naturally follows) mentioned in the first paragraph of this that higher-powered--and necessarily more article are obtained. costly-amplifiers are necessary. Although the resultant loudspeaker con- Second, and of great consequence, the struction is ideally suited to the rigorous degree of heat produced in the voice coil for demands of continuous outdoor service a pre -set output requirement would nat- under any weather and atmospheric condi- urally be higher in the low- efficiency tions, it is readily adaptable to the require- speaker. The degree of heat production in ments of indoor use, as sound men will the voice coil is one of the most tenacious perceive. problems which confronts the designer of a high -power speaker. For a given size of IMPROVED REFLEX SPEAKER voice coil, the temperature rise is directly All acou -tic transducer systems having to proportional to the power input, and a do with the reproduction of sound fall into precarious limit is reached at relatively low ARROWS 1NDICATF THE 2 broad classifications. The power PATH ASSUMED BV THE most popular of (watts) for conventional speakers. SOUND PCO IN these is the paper -cone dynamic speaker THE LUMN. mounted in a baffle or housing. (See Fig. A.) EXPONENTIAL HORNS It will be generally agreed that the popu- It was originally believed that a horn larity of this assembly is due to the low merely confined the sound pattern within a At top.-"Morning Glory' reflex projector make initial cost and small physical dimensions limited angle with a corresponding increase available in an overall length of 25 ins. an effet of equipment five 6-ff. air column: frequency cut -off. 90 cycles. the together with proper of intensity in this region. Conical -shaped With a bell opening of 29 ins. the projection angle mounting facilities. However, the attendant horns were widely used in the past to in- is 100 °. Note the weatherproof housing for the low acoustic transfer efficiency (that is, P.M. dynamic motor unit. crease radiation from loudspeakers. comparatively low audio output power for Functionally, however, was lelow. -This cross -section illustration of the reflex a given electrical input and poor this most un- projector shows how the long air column is power), satisfactory, inasmuch as a conical horn does achieved in a short horn. articulation, preclude the use of paper -cone not take into consideration the fact that speakers on a system in which the trans- air in motion assumes sharply- defined char- mission of intelligence (voice) is of para- acteristics. More ANEW line of sound projectors, char - importance. recently it was found that acterized by a foreshortened horn mount the true function of a horn is to increase driven by a horn unit, It is this problem of selecting loudspeak- the load on achieves infor application the vibratory system. For a creased transducing efficiency, good ers, in a system where it given throat area, the impedance of the is considered better voice reproduction, and high -intensity pro - engineering to install horn depends on its shape, and it has been jection, in addition to having the mechanical apparatus that will most efficiently transmit found that the exponential rate of expan- advantages of compactness, simplicity of intelligence under the required operating sion creates a greater degree of linear load- mounting, and 100% storm -proof protec- conditions, that is being primarily consid- ing than any other type. (See curve A.) ered in this article. tion. How these desirable qualities have The formulas which show this to be a been obtained is information of interest to PROJECTORS FOR HIGH OUTPUT fact are quite involved, but if any Radio - many sound men. Craft readers wish to delve deeper into the The "Morning Glory," as the new con- To design a loudspeaker for high output subject, an excellent reference is avail- struction has been named, is an adaptation it is almost imperative to use a horn (or able." However it is generally sufficient of the so- called "marine -type reflexed "projector" as it is called). The inherent merely to keep in mind the importance of trumpet," driven by a horn -type unit, which low efficiency of the flat -baffle type, if it "Applied Acoustics," by Olson and Massa. P. has been used for warship and merchant Sro Radio-Craft. June 1935. lilekistou's Son & Co.. Inc.

35 :b-iüiliIIIIPEGi1MINNEíi311111 ....IItriIIIII.....IIIMIIMIN..IC.... 15 Z -_:=Enr^---..e.l.l.E_CI11__... ___ wamosomr M.af =.. eeea=eMi.ii __..a 11.... =M\a11 omura "121N. CONE ll IN IIIIMINIMMlall FUNDAMENTAL FREQUENCY IIIILI II Ile w o Y FLARED CUT Q V .1/"11- BAFFLE III 111111111101 > OJECTOR (140 c.p.s.) - ? aim-._m__n_t_I__III__IIIIIL' w =ate =_ =_ _ =... w u. FUNDAMENTAL FREQUENCY W ..r11 ÌMIÌS..- =MIN -l:UCeaeaeeeaea CUT-OFF L COMPRESSION TYPE PROJECTOR LL ii111EMU UNIT ON REFLEXED .11V O .IIWI\ MORNING GLORY' 11==1111 .I'I111 PROJECTOR _-.1111 11j111 .eel 1 111111ia IIIIIIi_lIIIII(..IIit 40 60 80 loo 500 1.000 10.000 40 60 801-0'0 500 1.000 10.000 0 FREQUENCY 0 FREQUENCY Relative conversion factor of cone speaker in flared baffle vs. compression Theoretical response curve This curve illustrates the fact that the sound unit on exponential cavity. A considerable increase in effet ive output is projection of an exponential horn may be considered uniform over the fre- seen to result with an exponential increase of diaphragm loading. quency range for uniform input from the driving unit, up to cutoff. 96 RADIO -CRAFT for AUGUST, 1940 SOUND

having a horn, the rate of expansion of which is an exponent, in contrast with horn FOR UNMATCHED QUALITY - UNBEATABLE types which frequently are loosely referred - IT'S RCA LOW PRICES/ to as being "exponential" but which in truth are merely patterned to some conical degree of flare. Referring to curve B, note how the exponential horn maintains uniform loading right out to the cut -off point; and that the AERODYNAMIC longer air -path of the larger horn exhibits somewhat greater efficiency. Do not confuse this theoretical curve of horn performance with the overall frequency response. The latter is almost entirely a function of the "MIKE" motor unit (an item which may be discussed in a later article).

REFLEX HORNS In view of the advantages to be gained in the use of exponential horns coupled to Priced right RCA Aerodynamic Mi- compression -type (or, as they are more gen- crophone...Ml -6226D erally called, horn -type) for even the lowest (low impedance) speaker units, the MI.6228B (high concentrically-folded, or "re- entrant" horn cost job! impedance). herein illustrated, was developed, and because of its flower -like shape, was appropriately named the "Morning Glory" horn. These have been made available to replace the straight (long) exponential horns which, by comparison with paper cone speakers, are proving too unwieldy and of too great size for efficient handling and THE RCA Aerodynamic mounting. Microphone is typical of the SOUND COVERAGE world's most complete line of Adverse, or cross -wind conditions, which "mikes "! Its tops in quality, low normally disperse low- intensity sound pro- in cost. Has proved its value jection, have little effect on the sound beam through RCA Uni -Directional emitted by these high -velocity output pro- RCA Junior Velocity splendid performance Microphone Ml -4043, jectors. The sound beam, upon Microphone under the most difficult condi- RCA 3 -Way being directed MI-4036G. Microphone to the area requiring coverage, will produce tions. In the air, on the ground MI -4044. a t "Splash Effect" and thereby cover large areas with uniform -intensity sound. -even in a diver's helmet under The directional characteristics and total water, the quality is outstanding. absence of rear sound generation minimize No matter what kind of in- feedback or acoustic "howl." The flatter frequency response is also of great impor- stallation you make you have tance in eliminating feedback at certain satisfied customers when you use peaked frequencies. RCA microphones. Pressure, PHYSICAL DETAILS velocity, lapel, uni- directional, The "Morning Glory" projector here illus- bi- directional, non - directional trated, in addition to its electrical and -all types are available, for use acoustical advantages mentioned above, presents certain mechanical features that are RCA Pressure outdoors or in. And remember RCA Velocity worth consideration. Microphone prices Microphone The entire construc- MI-4048A. -the are right. tion is of metal, and all details are so pro- MI- 40278. portioned that it can be subjected to severe strain and stress without any appreciable /maw damage. The mounting details are fabricated from malleable iron castings and have unlimited fatigue resistance. The horn proper is built aiimemaal,forotti up of a progressive series of non -resonant RCA Mfg Co Inc aluminum spinnings, of heavy gauge, ade- Camden N.. A Service ofo Radioa Corporationorpora ion o F A merito quately protected against the elements with a 2 -tone battleship gray enamel. All other Any sound system sounds better, equipped with RCA Radio Tubes details, such as the malleable -iron mounting yoke and trunnions, and the hardware, are FILMGRÁP.Fi I sae Page 120 for Important electroplated with a zinc -cadmium alloy to lÿvOlCr AND MUSIC RECDRDINGs Announcement I resist oxidation and ultimate deterioration. on Radio Service Manuals PERFECT SOUND on film recording can now be had Unlike its prototype, the marine -type re- with FILMG RAPH at only 25e per hour (this is cost of flint only -no other espense). Permanent play -back. flexed trumpet, which used an electro- The only device capable of making lengthy recordings dynamic motor unit, the Morning Glory and play -back- Closing out several demonstrator models at AUDIOGRAPH special price. Complete 1940 line now utilizes the more MILES ready modern, permanent -mag- REPRODUCER CO.. INC.. Dept. RC. NE Sound Catalog net dynamic motor, thus eliminating 812 Broadway New York City field AUDIOG "APH Sound pot wiring. This unit is shown, in the photo, Systems repre encased in a weatherproof, streamline sent the atest in Sound Engineering quite as well as a straight or full -length and Desig complete housing. exponential -a line plus pre- Contrary to popular trumpet; requires a fraction of tested accesso belief, the concen- mounting space; and trically- folded re- entrant horn will perform the construction ob- viates the possibility of water or any other NEW LOWE °RICES -Mils term, Inasmuch a, It Is Introduced here for the foreign matter reaching the throat. first time. requires a little explanation. Briefly. It may Outstanding quality and rforrn he The likened to the effect whirl] results when a stream of Morning Glory projectors have a Is once at prices that help you vl Orly water directedlo at high intensity against a solid surface. universal application indoors, outdoors, Just as the eager analogy, when a high Intensity - competition. sound beam strikes a given area, as for Instance a and sound truck. The reflexed construction crowd at a stall , it has been found to "mushroom," results in a considerable reduction in or 'splash," to a much greater extent than Is the caso over- WRITE FOR FREE :OPY e hen a low -intensity sound beam reaches Its objeetle. all length. In fart, In the latter Instance, the sound may be This article has been prepared JOHN MECK INDU RIES entirely absorbed- allowing none of the sound energy to front data 1313 W. Randolph SL, Chicago, III. disperse even within a limited area. supplied by courtesy of Atlas Sound Corp. RADIO -CRAFT for AUGUST, 1940 97 SOUND

A well- known sound specialist describes a method of recording and playback of sound -on -disc said to be new in principle and revolu- tionary in the industry. The result of 4 years' laboratory work, it permits recording a 1/4-hour of music (present recording time, 41 mins.) and 45 mins. of speech (vs. 8 minx. by conventional methods), by embossing on thermo- plastics.

E Fig. 1. The commercial recorder at left was developed by Recordall Mfg. Company for recording and playback of constant groove -speed discs. The same "cutting" head and needle are used for playback of the embossing.

CONSTANT GROOVE -SPEED RECORDING On Ih¢tmo-Pl43tic3 -u9iny the GmGo33ins Aoc¢33 E. E. GRIFFIN

through friction puts excessive wear on the ing stylus and drive wheel remains the ENTIRELY new in principle and revolu- momentary position tionary in the industry, Constant recording stylus and playback needle. sanie, regardless of the -speed an optimum of the head on the record. The rotating of Groove -Speed Recording is one of the At constant groove motor in linear velocity can be selected for the re- the drive wheel by a synchronous most outstanding improvements groove -speed is ob- disc recording since 1926, when Maxfield quired frequency response in each case, and explains how constant velocity being constant, all tained. and Harrison published the results of their this linear has been recording. equalization can be predetermined and per- A drive shaft speed of 90 r.p.m. work on the art of disc for high -fidelity record- This new method in combination with the manently built into the amplifier. No vari- arbitrarily chosen is on Recordall models where embossing process rather than the cutting, able equalization or compensation is re- ing and used The quality, volume level and dis- high- fidelity recording of the wide range in addition to giving the highest fidelity quired. and music most economical tortion percentage remain fixed in quantity, of the audible spectrum of voice possible, results in the Slower drive shaft speeds are method developed since it makes pos- regardless of the momentary diameter of is desired. yet on business and conference models, sible the recording of a full % -hour of music the record at any recording position. used the record This feature of the constant groove -speed where their use requires the intelligibility on one side of a standard -size -as of the speaker only, on the conventional makes the use of the embossing process and recognizability against 4% minutes slower speeds are used on the disc 45 minutes of speech practical, since excessive high- frequency while still phonograph -or communication models where intelligibility as compared to 8 minutes on the present attenuation -caused by the damping effect to bur- only is required. Figures 2 and 3 show the conventional dictating machine. of the record material's resistance for nishing be equalized by proper tilting time available on different -size discs -can models. FIXED LINEAR SPEED of the amplifier's frequency response curve recording on the various Constant groove -speed, as the words im- -for a uniform linear velocity. of the The building -up of high- frequency re- EMBOSSING ply, means that the linear speed or burnishing was used almost recording track in inches per second is sponse, on the other hand, is made possible Embossing in the embossing exclusively in recording on aluminum blanks fixed, independently of the record diameter. by qualities inherent recent, yet fixed process (outlined subsequently) without -the first and comparatively In the conventional phonograph a form of "instantaneous" 78 or 331/3 r.p.m. is bringing surface noise to an objectionable already outmoded, angular velocity of The crystalline structure of all used, and this results in an excessive groove - level. recording. process causes aluminum alloys used made this imperative speed at the outside and a too -slow groove - Also, since the embossing in Taking practically no wear on the polished round -since cutting exposed such granularity speed at the inside of the record. the increased surface noise disc, the groove -speed at point of the embossing stylus, its life is the material that a 12 -in. diameter created an entirely unsatisfactory signal - '78 r.p.m. will change continuously from 48 practically limitless, a decidedly economical -noise ratio. The embossing process on 12 ins. per second as the stylus moves advantage over sharp -edged styli as used to to aluminum, on the other hand, required very from the largest to the smallest diameter. in the cutting method. cutting head variation of much greater power, since the The same size disc will give a weighted and the cutting arma- approximately from 21 to 5 EQUIPMENT had to be groove- speeds damped, "stiffened," to overcome the second 33 1/3 r.p.m. Figure 1 illustrates how constant groove - ture ins. per at of the metal and its high resis- It is at once obvious that it is not pos- speed is accomplished in Recordall equip- resilience ment. The relative position of cutting head, tance to burnishing. rible to have the same quality of recording added up in creat- for all of these different speeds -without recording stylus and the patented drive All these requirements through the plate -glass ing all kinds of frequency distortion and continuously- variable compensation and wheel is visible function of for the resultant distortion being a equalization, in addition to correction turntable. groove speed, equal- varying amounts of distortion. The exces- This drive -wheel and shaft are integrally the momentary linear the head carriage mechanism, ization was extremely difficult. A well - sive linear velocity near the outside of the mounted with recording engineer disc reaches a point where the heat created so that the relative position of the record- trained, experienced for AUGUST, 1940 98 RADIO -CRAFT SOUND

Figs. 4 and 5. Unrefouched microphotographs of recording on thermo -plas tics Fig. 4, cutting creates a source of high noise level; Fig. 5, embossing offers a high signal -to -noise ratio.

could produce satisfactory results on care- more stable to temperature changes than the unmodulated groove. At the same time fully- designed equipment -but even the wax, and so eliminate the necessity of tem- comparatively best larger grains are exposed, as records were comparatively short -lived, perature- controlled storage and recording, is plainly visible if the dull structure of the deteriorated with age and had to be played in combination with simplified mechanical sidewalls, "B;" is compared with the shiny, with special equipment, and non -metallic construction and the instantaneous play- undisturbed land, "C," between grooves. It needles to maintain their quality, even dur- back feature makes their use in profes- should be apparent faithful ing that reproduc- this short life. Thus embossing on sional recording advantageous. tion of this groove will result in some sur- aluminum has gradually gone into the dis- Constant groove -speed - as mentioned face noise ( "scratch "). card and with it, apparently, its outstand- above -made the return to embossing pos- ing one good feature, overlooked Let us now examine the microphotograph either or sible. Several features of this process in of an purposely disregarded by recording en- combination embossed section of the same record, with acetates and other plas- Fig. 5. (The photographs, gineers, but retained by the present method tics make it desirable. by the way, were of embossing on thereto- taken under identical conditions with the plastics. The atomic structure of these materials same magnification shows and are unretouched.) a combination of hydrocarbons and The cut was recorded on a THERMO -PLASTICS crystalline substances, standard pro- and the "floating" fessional recorder with a new sapphire The introduction of "acetate" coating on process used in the manufacture of records, stylus by a competent brings recording engineer aluminum recording discs caused the return the finest grain to the surface. The and the embossing on a standard Recordall to cutting instead of embossing-since cut- coating and hardening of the substance machine. Note that the "skin" was creates a not dis- ting was at the time a much better de- surface tension. The combined turbed on the embossed record. Edges, "A," veloped art and without any doubt had result is a shiny "skin," the thickness of of which the unmodulated groove show absolutely quite a few advantages. It didn't require is a function of (a) the chemical no tear, no raggedness, and the structure excessive weight on the cutting head or too structure. (b) the thickness of the entire of the sidewalls and bottom much equalization coating, and (c) the speed the of the -at average speeds -and employed in the grooves, "B," is just as smooth and shiny could well be played back with most any drying process. Considering the fact that as the undisturbed kind of pickup total land, "C," between and most any kind of needle. thickness of coating seldom exceeds grooves. Approximately 100 diem. The fine 0.0065 -in. enlarge- -grained structure of most ni- (for cutting), it is easy to see ment does not show any source of surface trates used to make these "acetate discs" that the skin can be measured in microns noise here. reduced only. surface noise to a satisfactory Analyzing the embossing process it was minimum and with a little training even "SCRATCH" found that the triple action of burnishing the uninitiated layman could learn to pro- results in the best groove obtainable duce records comparable in many respects Cutting disturbs the continuity of the -if skin, unbalancing used in combination with constant groove - to commercial pressings. These facts ac- the surface- tension. The speed. A blunt stylus under great pressure count for the increasing popularity of in- microphotograph, Fig. 4 *, clearly shows at (between "A" 75,000 and 125,000 lbs. per sq. in.) stantaneous recorders. the resulting "tear," ragged edges on compresses the recording substance, the The fact that acetate records are much courtesy. Dr. Gordon Laboratories, lb- lbwood, Cali'. heat created by friction followed by rapid

13 iI'IPPIPMPRMNBNIPMEMIEMPS/ .2111 16" i START 16-RECORD, ____MNiNNIpirlMEMI 12 III . ß.EO . SN s.o !iiIIII a1 :i 5 + ,411111111111 O 13 -MIMEM soE.t/1111 ° t7 WEel ' ó 9.I.d1i1ii11i11i w g ;o i :íiiiiiiiiiiiiiiii ó

1111111N1IeÍ11111111111111111 . 8111111111í1111111111111 w g-.iI1II1111AIIIIIIIIIU111III1111I 11P1:i1111111llm11 Q , ,.iiIliiilïiiil1ii1 0 6.111111I111MIIMINIIIIIflIIIIIInMIII 41:iI1f1I111III111111111111111111 4- r4..M...... I...I 0 10 20 30 40 50 60 70 80 90 100 110 120 0 2 4 6 8 10 12 14 16 18 20 24 28 32 40 46 36 44 RECORDING TIME IN MINUTES ® RECORDING TIME IN MINUTES MEE Fig. 2, playing fine for discs recorded at consta t groove- speed. High -fidelity speed at 10 ins per second; conference speed, 7y= ins. per econd. Fig. 3, playing time at rate of S ins per second, as used on communication models. RADIO -CRAFT for AUGUST, 1940 99 SOUND to be eliminated to correct the signal -to- noise ratio in playback? DIRECT - COUPLED AMPLIFIERS The damping effect of the plastic on the embossing stylus attenuates the high fre- "The Ultimate in Design" quencies-as we pointed out above. The These new ID. 20 and 30 Watt Direct -Coupled (Push - constant groove -speed on the other hand Pull Loftin- White) Amplifiers a now available with of 14 optional features.1 including makes permanent predetermined equaliza- Variable Speed Non.Overloadin Push -Pull Expander, High Frequency Accentuation iand Attenuation, Low tion for this diminished high- frequency re- Frequency Boost and Cut Control. Push -Pull Automatic Volume Compressor. Push -Pull Automatic Volume Lim. sponse possible and the absence of inherent iter, Push -Pull Automatic Volume Control, Non -ree. fluencyn y Discriminating Scratch Suppressor. Low -Cain noise in the embossed groove makes this Ended Input. High-Cain Single Ended Input, Low -Gain Push -Pull Input, Nigh -Gain Push -Pull Input, equalization practical with very little effect audio Spectrum Control. Calibrated Volume Indicator. and Push -Pull Remote Control. on the signal -to -noise ratio. Boosting the Write or Wire Today for Complete Details high frequencies as much as 30 db. at 7,000 and Unnenally Attractive Prises. cycles was found to be quite permissible, the noise level of the resultant record, when AMPLIFIER CO. of AMERICA played -back without equalization being still 17 WEST 20th STREET NEW YORIL N. Y. lower than that of any cut record.

RECORDING -PLAYBACK STYLUS cooling-uniform at constant groove -speed The fact that constant groove -speed em- -hardens the groove by "heat -treatment" bossed records can be played back with the -while the blunt, smooth nose of the stylus same stylus they were recorded with, at the polishes the recorded surface by burnishing. same angle, makes it possible to reproduce The result is a hardened, durable and all there is on the record. Another glance smooth groove with an excellent signal - at the microphotographs (Figs. 4 and 5) to -noise ratio. will show at "D" that the groove -width remains constant in the modulated track FIDELITY on the embossed record, but undergoes sub- Examining the frequency- distortion char- stantial variations in the cut record. acteristics of the same 2 kinds of recording, This is caused by the chisel -point shape the cutting process has an undisputed of the cutting stylus in combination with superiority -in recording. A sharper stylus the pivoting of the armature as usually under less weight, with less damping can employed, causing a vertical shift of the more faithfully follow high- frequency modu- momentary periphery of the point doing lation. But the necessity of using a dif- the actual cutting. The blunt nose of the ferent- shaped playback needle point and playback needle will have a noticeable up equalization necessitated by the inherent and down motion as it is squeezed out of surface noise features of the cut groove, the groove where it contracts -adding to practically eliminate these advantages. the distortion as it increases the danger of The fundamental defect existing in all jumping grooves. This necessitates a deeper disc recording systems where a sharp- edged, groove in the cut than in embossing. chisel -shaped cutting tool is used to form Thus more lines per inch can be used the groove, and a round -nosed needle is with the embossing system without endan- used in playback, is the fact that these 2 of playback needle different. The groove gering the tracking the shapes are entirely in the groove -while the reduced depth also so cut will couple to the round -point play- of the re- is un- reduces the required thickness back needle so long as the groove cording substance on the metallic backing. modulated; as soon as modulation takes place, the cut groove becomes narrower as All these factors tremendously increase A TRIAL WILL PROVE it deviates from a straight line, resulting in the economy of this system in addition to improper coupling to the playback needle appreciably improving the quality of repro- you in reproduction. duction and simplify the process to enable it payshto use This condition is overcome in the em- the operation of such equipment by laymen bossing method since the recording stylus -and we think it justifies the contention is used in playback exactly the same as it that it is the most outstanding improvement WRIGHT VERIFIED SPEAKERS is in recording, thus resulting in the best in disc recording since 1926. possible coupling and resultant minimum This article has been prepared from data Catalogue mailed on request distortion. What good does a "high- fidelity" supplied by courtesy of Recordall 3Ifg. Co., New York: No. 17 West 60th Street recording do if the higher frequencies have Inc. Los Angeles: 1101 W. Olympic Blvd. WRIGHT, Inc. St. Paul, Minn. BOOK REVIEWS

...I.P.111111111111111II111111111111111111111I111I1111e111111I1101111111111I111tlitt FREE 711111111111111111111IIIIIIIIIIIIIIIIIIIIIII:IIIIIIIIIII11111111111111111111111CIIIIII". IALL RADIO NEEDS CATALOG Here in this OF TECHNICAL TERMS. by DO YOU WANT TO GET INTO RADIO? by one big book you DICTIONARY will hod y Frederic S. Crispin (3rd Edition. 1940). Published Frank A. Arnold (1940). Published by Frederick m You need radio . . Co. 6 x 8 ins., cloth A. Stokes Co. Size, S x 8 ins.. cloth cover. 140 supplies seta, parts and by The Bruce Publishing Size. . - , pgs. Price. eYsteau public address cover, illustrated, 327 pgs. Price, 82.25. 81.50. .. amateur e The revised and enlarged edition of "Dictionary For each type of radio work, the author states moon ... testers swp- your and w.- of Technical Terms" is an exceptionally compre- definitely what temperament. education and ex- nationally known . an - hensive compilation, taking in as it does the perience is required of the applicant and what al lowestwest possible big Write today nomenclature of about 70 fields. kind of work and surroundings the beginner may big for this more 1,000 new words, expect to encounter. to get into the respective doable catalog and The book features than save money, various tables of weights and measures. and many fields of radio. classifications PROMPT new illustrations. Included in the A chapter is devoted to personal aptitudes for SERVICE are radio, electricity. physics. science, ceramics radio work in general. and whether college train- and the plastic art. The dictionary is for the ing is essential. An appendix lists those colleges use of students. draftsmen, mechanics, builders, which regularly give courses in radio. author BURSTEIN- APPLEBEE COMPANY electricians and workmen generally. The States the author in his preface: "I am writing has made the scope broad rather than detailed this volume for the hundreds of young men and 1012 -14 McGEE STREET KANSAS CITY, MISSOURI and hence has not included all the technical women who would like to get into radio but do terms in any field of endeavor. not know how to go about it. It is intended not as a textbook or a study in psychology: rather HOW TO USE THE CATHODE -RAY TUBE, by as the story of radio broadcasting from the J. H. Reyner (1940). Published by Furzehill standpoint of its career possibilities, bearing al- RADIO DIAGRAMS Laboratories, England. Size. 5 x 71 ins.. paper ways in mind the training and aptitudes required Any circuit diagram for all radio cover. 33 illustrations, 40 pgs- Price, 1 shilling book lets. To help you service radios. for success in this field." This non -technical Specify manufacturer and model (about 35c, including postage). analyzes business possibilities in broadcasting and number. Only 25e each. Guar- This booklet may be considered a primer on television. anteed immediate shipment. cathode-ray tube operation for technicians who (Turn to Pages 95 and lE8 for other Book SUPREME PUBLICATIONSIT,F=IngtPUBLICATIONS are otherwise "up" on their radio theory. Reviews.)

100 RADIO -CRAFT for AUGUST. 1940 SOUND SOUND ENGINEERING Tree !7¢3i9n and -adviioty Setv[ce `Tor Jadio - eraP SuGscziGeri

Conducted by A. C. SHANEY

This department is bring conducted for the benefit of RADIO-CRAFT subscribers. All design, engineering, or theoretical questions relative to P.A. installations, sound equipment, audio amplifier design, etc., will be answered in this section. (Note: when questions refer to circuit diagrams published in past issues of technical literature, the original, or a copy of the circuit should be supplied in order to facilitate reply.)

R FC 15.000 15.000 No. 8 0K m5 03. OHMS LEACH) .F. (EACH)) 20 -WATT AMPLIFIER WITH completely isolated from its adjoining chan- FOUR 6B5'S nel, and no cross -talk will be prevalent. Furthermore, the placement of the volume The Question F . . control after the 1st stage, will provide I have a 30 -watt amplifier which I wish higher -level mixing. to rebuild to one of higher gain and more Two 6SC7's are employed as electronic inputs without adding too many transform- mixers. These in turn feed through the ers. Will you kindly send me a sketch cover- high- and low- frequency equalizers into a C-` ...... X03 ing this. i wish to have 3 microphone inputs 6SC7 inverter. A balanced inverter circuit MF. and 1 phono, and would like to use two 6SC7 of the type you require was diagrammed in FIG _2 'MA.REINER.5 AMPLIFIERJ -OUTPUT CIRCUIT, tubes in the input stage, followed by a the April, 1940, issue of Radio -Craft (see O1'. 6SC7 used for electronic mixer, and 6SC7 page 531). The inverter circuit of Fig. 1, MF 6C5 for balanced inverter. The final stage should however, is of a conventional type and 6A3 utilize four 6B5's. For the power supply I easily constructed and checked. The 7,000 - 15.000 would like to use a 5Z3 rectifier. Please ohm resistor, though, should be made vari- furnish high- and low- frequency control able for critical adjustments, if perfect in- ISSOO circuits. version is desired. This can best be checked I l LEACH) JAMES MOY, by connecting an oscilloscope to each of Chicago, Ill. the control -grids of the push -pull output stage and adjusting the 7,000 -ohm resistor The Answer .. . until equal potentials are applied to the 'B+ A schematic diagram of the type of am- push -pull grids. 15.000 OHMS / plifier you is 1. O.1- desire given in Fig. Your The power supply should be capable of AIR 6A3 suggested tube line -up would not provide delivering 220 ma. at 300 volts. The power

sufficient gain for low -level microphones. I transformer should deliver about 330 volts E FEEDBACK CIRCUIT TOBE INCORPORATED have therefore suggested a 4 -stage amplifier under full load. The 1st choke, Ch.l, should CM^'TNI THE AMPLIFIER-OUTPUTCIRCUIT OF FIO2.' instead of 3 stages. be of capable carrying the full output of INPUT Because of the interelectrode capacities the supply. The 2nd choke should be capable OUTPUT between the plates and grids of the 6SC7, of handling 50 ma. The output transformer this tube is not recommended as a dual - should, of course, be properly matched to channel input, unless the gain controls are the push -pull parallel output stage. You connected ahead of the input grid. This will note that 4 R.F. chokes are inserted in .` circuit arrangement, however, would be par- each plate circuit to suppress parasitic FIG 4A CONVENTIONAL TUBE CIRCUIT. ticularly susceptible to volume control noise, oscillations. These, however, may not be OUTPUT and is therefore not recommended. By using necessary. Your preliminary tests will indi- INPUT 6SF5's, however, the preamplifier stage is cate whether or not they should be used. Ex E5F5 ^-20-WATT 6B5 6E5 a+ AAIPLIFIERti OF FI646 VOOLTAGE INDICATTEDAT.5''..

OUTPUT SOO INPUT Ol. ii-CD,. 0: kif í "( B; C5F5 05- FIG. 4C ''PARALLEL FEEDBACK~

OUTPUT INPUT /

/ 1 B +"

FEEDBACK~ FIG. 4D ,'SERIES

OUTPUT INPUT L l C_ P w oi ti FIG 4E FIXEDBIASCRCUITTA,

RADIO -CRAFT for AUGUST, 1940 101 SOUND

You can construct these inductances by which I wish to acid inverse feedback. Will point where it is applied, is known as the winding 500 turns of x30 wire on a form you kindly add to my sketch such an ar- feedback loop. 1/2-in. in dia, and 11 ins. long. rangement. (I am not too strong on the Figure 4A shows a conventional tube All resistors are of the 1k -watt type, ex- theory of such arrangements.) circuit. If a voltage -dividing network is cepting those marked for higher power. I am, and have been, a Radio -Craft sub- connected from plate -to- ground, as in Fig. scriber for years. I came across a circuit 4B, a small portion of its total voltage will PRACTICAL APPLICATION OF similar to Fig. 3. which has inverse feed- appear at X. This voltage can then be INVERSE FEEDBACK back. I am not certain, however, about applied to the grid of the tube in parallel being able to adapt this feedback arrange- with its original incoming signal, as illus- The Question .. . ment to my resistance - capacity coupled trated in Fig. 4C, or in series, as indicated I have an amplifier, as per Fig. 2, to amplifier. I am trying to get the best pos- in Fig. 4D. If a bias is to be applied to this sible hi -fi quality. stage, the bias resistor is removed from I thank you for whatever help you can ground and bias voltage is applied through The NEW give me. the bias network, as indicated in Fig. 4E. L. F. REIHER, It is important, however, that the low end Horn Miami, Fla. of the resistance network be bypassed to DOENUT ground, so as not to affect the feedback The Answer .. . arrangement. In applying these feedback Provides Inverse feedback can easily be added to circuits, it is of course important not to your amplifier. There are many ways of excessively shunt either the grid or plate Wi der doing this, which will present themselves to circuit of the amplifier itself. you after reading the following description Feedback is applied for any one or all following reasons: (1) Reduce dis- Angl e of how to apply inverse feedback. of the Unfortunately, most discussions involv- tortion; (2) reduce noise and hum within ing the theory of inverse feedback have the feedback loop; (3) reduce frequency Coverage been steeped in mathematics, and are be- discrimination within the feedback loop; or, yond the scope of the average Serviceman. (4) reduce plate resistance of the stage This has undoubtedly seriously hampered from which the feedback loop is taken. the application of this type of circuit to From the above, it may be seen that if many amplifiers. the feedback loop embraces the output Model transformer, it will compensate for fre- DX8B SINGLE -ENDED AMPLIFIER quency discrimination and distortion intro- Inverse feedback evolves from the prin- duced by this element. If feedback does loop ciple of taking some voltage from some the output transformer, it is important that An entirely new development in point in an amplifier and coupling it back the transformer be designed for minimum exponential horns which provides into a previous section of the amplifier, so variation of phase shift with frequency. unique features never obtainable arranged as to partially buck -out the before. original signal. This is technically known DOUBLE -ENDED AMPLIFIER as feeding the signal back out -of- phase. The Up to now, we have only considered a Spreads high frequencies over a wide angle. NV1MMhh 0.1- Weatherproof. 0.3- MF RI Ji MF 0.75- 8 Wide frequency range. MEG. OHM l'EAHER No metallic sound. Write for complete details

WRIGHT -DECOSTER, Inc. Fig. S. Balanced inverse feedback applied from '75.000 2251 University Ave.. St. Paul. Minn. balanced output trans- OHMS Export Dept.: M. Simons & Son Co.. Neo York (EACH) Cable Address: "SImontrlee" former to push -pull stage. Note I. - The 0.3- OHMS Canadian Representatives: amount of feedback may Wm. F. Kelly Co.. 1207 Bay St.. Toronto. Ontario be varied by varying the (EACH) Taylor & Pearson. Ltd.. Edmonton, Alberta 0.75 -meg. resistors (RI -B+ and R2). Note 2.- Values of RI and R2 to be ad bjutted fo provide proper 7OHMS ias for output stage. (EACH) Balanced tubes should be used in parallel output circuits.

R2 0.3- / MF. ¡ MEG 7 - I rr 0.1- MF.

trick in its application is to make sure that single -ended amplifier. If feedback is to be the signal which is fed back, is out of phase. applied to a push -pull amplifier, it may be When this is done, a loss of gain should be done through one of 2 ways, either (1) from noted. If, however, the signal is fed back a single -ended signal (as a grounded out- YOUR BEST in- phase, then we have a condition of put transformer secondary) back to a regeneration, which usually produces sus- single -ended input stage (as the input of ELECTION BET! may be applied Cor.,pkde tained oscillations. the inverter); or, (2) it "MORNING GLORY" For ideal performance, the signal that is from a push -pull signal (as through a Projector, Unit, Bracket fed back should be exactly 180° out -of- balanced output transformer) back to a cir- push -pull stage, as illustrated in Fig. 5, 40 DEALERS phase with the input signal. In many $29Y NET PRICE EVERYTHING you can ask cuits the feedback signal is exactly 180° which is the recommended method for apply- for in a highpowered out -of -phase at only one frequency. At other ing inverse feedback to your amplifier. P. M. speaker for Election sountl k ... 1000'. Weather and Mechanical Protection . . High Acoustic Transfer frequencies it gradually shifts around to an The value of R1 and R2 should be ad- Efficiency . . Super -Power Projection Qualities. Its for a compromise between the ruggedly built for sound truck application . sturdy in -phase condition. This type of circuit pro- justed mounting bracket supplied. There's no doubt ... this duces sustained oscillations. usually at some amount of feedback desired and the re- speaker will win your vote! See your jobber or send for FREE CATALOG F.40 describing 101 types of speakers very high frequency and is always indica- quired stability for the amplifier. The phase and accessories. tive of varying phase shift within the loop of the feedback voltage may be easily re- ATLAS SOUND CORPORATION of the feedback circuit. The point from versed by reversing the plate connections 1446 39TH STREET BROOKLYN. NEW YORK where the feedback voltage is taken to the of the output transformer.

102 RADIO -CRAFT for AUGUST, 1940 SOUND

TO CI SPEAKER 0.5- MF. INPUT 500 TERMINALS T2 O -I 15 8 -t Ow,.

; f 5w. SHIELD P2 A VOLUME CONTROL B 4 OHMS OHMS SWITCH T ON T3 M' `6ROl ND P2 +CHASS15 CONTROL SET AT 250V. A.0 RADIQ e RECEIVER

rRS 20.000 5CAHIEriDED OHMS LE C3 BMF A RADIO CH At P 5V RECEIVER

CA BMF. BMF. ,,foro ERH A

FIG. 1 ^ 20-wATT BOOSTER ^+ TO CHASSIS OF BOOSTER Diagram of the 20.W. output stage. (See NOTICE at end of article.) The completed Booster Amplifier. Power in a small bund e! 20 -WATT BOOSTER AMPLIFIER `Tor radio ) QCQ[vQti, Jow -Power Iv. {. _7yit¢ms, Ltc. This article describes the construction of an easily-built power output stage which may be added to the "'Transitional' P.A. System" described last month. Connected to a $10 A.C.-D.C. midget, delivering 3 W. with appreciable distortion, this power stage afforded an output of 28 W. with no audible distortion!

H. T. ZIEGLER

SOMETIMES additional power is re- The overall height, with tubes inserted, is We then connected the stage to a good A.C. quired for radio reception, especially in only 8!4 ins. superhet. and were surprised at the high public places such as restaurants, clubs, The small size of the amplifier permits it quality of reproduction and enormous taverns, etc. With this Booster Ampli- to be mounted in the cabinet of console - power. fier even the smallest A.C. /D.C. midget will model radio sets. When used with table - Finally, we connected it to a frequency - supply sufficient volume for an audience of model receivers it can be installed in a modulated receiver just to make sure that 5,000 persons! Phonograph music or carbon separate cabinet or concealed in any con- we could handle the high -frequency re- mike programs which are fed through the venient place. sponse. radio set can be amplified also.* Inverse feedback was used to obtain a It is necessary, of course, to use good This power stage can be used also to flat frequency response and to reduce hum P.M. speakers with the Booster Amplifier increase the output of small A.F. amplifiers. and distortion. This was accomplished by if good tone quality is desired. If the full connecting 100,000 -ohm Modern radio receivers have from 3 to 5 the resistor from output is to be used, select speakers which watts output, which is sufficient for all the secondary of the output transformer to will handle the 20 watts. That is, one 20- ordinary installations. But where a radio the secondary of the input transformer. watt speaker, two 10 -watt speakers, etc. set is operated in a public place, additional All the first experiments were made with Speakers rated higher than this will be amplification is necessary. the unit connected to a low -price A.C./D.C. even better, such as one 30 -watt speaker, superhet. The tone was really excellent and two 20 -watt speakers, etc. Do not attempt There are many radio receivers which are the hum and other distortion were inaudible. to use the radio receiver speaker. It will be furnishing inadequate volume where crowds damaged in a short time. gather to dance or listen to sports reports such as baseball and football games, prize PARTS REQUIRED fights, etc. Building this Booster Amplifier OUTPUT and installing it in such places should add N¡MMER In the laboratory sample we used the considerably to the income of any radio 7 parts recommended in the list at the end Serviceman. of this article. This list need not be fol- ROARER i lowed religiously. Any parts of equal elec- TRANS DESIGN EM trical rating may be substituted. Because All unessential parts were left out of the the average Serviceman will have some of Booster so that it would be the necessary parts, we decided to give the installed eco- specifications nomically. Fundamentally it is a pair of on all parts which require 6L6G tubes in push -pull, with power sup- special explanations. The plied from a 5Z3. The entire unit is mounted input transformer, Ti, has a 10,000 - J ohm primary and a 90,000 on a chassis only 10% ins. x 7 VOLTER-- tapped -ohm sec- long ins. wide. CRONE TRANS- FORMER ondary. Sea the article "'Transitional' P.A. System" In the The push -pull output transformer, T2, is uty issue of Radio -Craft for adding a mike to CONTROL TONE any CONTROL radio receiver. Add this Booster to hare a complete, the heavy -duty type to match a pair of powerful sound system. OEM ^CHASSIS LAVOUT^. 6L6G tubes, having an 8,000 -ohm primary, RADIO -CRAFT for AUGUST, 1940 I 03 SOUND

25 W., R3; 4 -S -15 -500 ohms. and the reproduction will become distorted; One voltage divider, 20,000 ohms, and a secondary tapped at with switch, If the amplifier is to be used with a specific at the other point the volume may drop One Centralab potentiometer or set of speakers, the tapped slightly, but reproduction will be improved. No. 62 -116, 1 meg., Pl; speaker No. 72 -121, secondary is not necessary, permitting the One Centralab potentiometer, use of a lower priced transformer, one 0.25 -meg., P2; OPERATION sockets, S -8; which will directly match the speaker sys- Two Amphenol octal Only a single shielded wire is required to One Amphenol 4- contact socket, S -4; tem used. connect the Booster Amplifier to the re- The power transformer, T3, must have One Amphenol receptacle, 61 -F; ceiver for A.C. sets. (Connecting to A.C./ One Amphenol polarized plug, 61- 9íP11; a 5 -volt secondary winding for thé filament D.C. radio sets is explained later.) The cen- switch marked 4 -8 -15- of 5Z3; a 6.3 -V. secondary for the One Amphenol tap the ter conductor is terminated in a clip which 36 -1, Sw. 1; 6L6G filaments, and an 800 -volt center - 250 -500, slips onto the plate prong of the output One line cord with plug; tapped secondary winding for "B" current. tube in the receiver. The shield is connected should be capable Misc. (nameplates, knobs, etc.). The high -voltage winding to the radio receiver chassis. When the answer any in- of delivering at least 180 ma. (The author offers to receiver uses push -pull tubes, connect the quiries regarding the building or adapta- wire to either plate. tion of the 20 -Watt Booster Amplifier to CHASSIS LAYOUT For A.C. /1/.('. radio sets 2 -wire shielded any radio set. If a particular radio receiver On the top of the chassis are all the cables must be used to connect the set and is referred to, please give make, model num- transformers, a 4- contact socket for the amplifier. One wire is connected to the plate ber and tube line up. An addressed, stamped 5Z3, and 2 octal sockets for the 6L6G tubes. of the output tube and the other to the envelope will be appreciated.) front of the chassis are 2 poten- The shield is connected to the On the cathode. error, caught too late to 1 for the tone control and 1 for Booster. NOTICE. -An tiometers, chassis of the exists in the volume control. If there is any grid noise present be- permit changing the illustration, and B in lower -right of On the back of the chassis is a tap switch of the leads between the receiver and detail drawings A cause of complete 20 -W. for matching the unit to the speakers. the amplifier, connect one side of the power the schematic diagram the (Note: The only tap switch available was transformer primary to the Booster Amplifier. In sketch A a single - stage input is used for connect- 4 If the transformer, conductor shielded cable marked -8-15 -250 -500. chassis. Center like ours, has no 250 -ohm tap, this point ing the Booster to an A.C. receiver. is connected from "A" on the switch is simply left Unwired.) conductor of cable LIST OF PARTS of Booster to plate of receiver out- A 2 -pole A.C. receptacle is installed on One Thordarson input transformer No. terminal the back of the chassis for connecting the T67A40, Tl; put tube. speakers. Two such receptacles can .be used, One Thordarson output transformer, No. In sketch B a 2-conductor shielded cable if desired, wired in parallel. T65S94, T2; is used to connect the Booster to any A.C. Also on the back of the chassis is a 2 -post One Thordarson power transformer. No. D.C. receiver. Wire "A" connects plate of terminal strip as the connection for the T92R21, T3; receiver output tube to terminal "A" in the radio receiver wires. One Thordarson choke. No. T1TCOO-B. ch.; Booster. Wire "B" connects to cathode of incoming is con- No special wiring instructions are neces- One paper condenser, 0.5 -mf.. Cl; output tube (or any terminal which Simply follow the wiring diagram. Use One paper condenser. 0.05 -mf.. C2; nected to "B -"). This wire "A" connects to sary. The cable a shielded lead from the terminal strip to One Mallory electrolytic condenser. No. CS- terminal "B" of the Booster. the primary of the input transformer. 133, 8 mf., 450 V.. r':1; shield is not connected to the receiver The wire marked "X" should be tried at One Mallory electrolytic condenser, No. CN- chassis, but it is connected to the Booster after the unit is com- 152, 8 -8 ntf.. 450 V., ('4; chassis. points "Y" and "Z" data pletely assembled and is in operation. At One resistor, 0.1 -meg., '; -W.. R1; This article has been prepared from one point regeneration will be introduced One resistor, 200 ohm;. In W.. R2; supplied by courtesy of Allied Radio Corp.

J7L t. Nadia Setviceman: A NEW SEASON BEGINS - MOVE FORWARD WITH RSA! Plans announced at the Radio Parts Trade Show make it more imperative than ever that you belong to RSA. All the new developments planned by manufacturers place increased responsibility on trained top -flight servicemen. Join other good servicemen in RSA. Send the Coupon Today!

=I um MAIL THIS COUPON NOW ! IIImmsio . 71 Let's Grow Together RADIO SERVICEMEN OF AMERICA, INC. in 1940! 30 Dearborn St., Chicago, III. I 1 Name Address I RADIO SERVICEMEN i City State II am interested in RSA Membership. Tell me about it OF AMERICA, Inc. $4.00 National dues and initiation. Covers ducs I am enclosing for JOE MARTY, JR., EXECUTIVE SECRETARY up to Jan. 1, 1941 I(Does not include Local Chapter dues where Local Chapters are 304 S. DEARBORN STREET, CHICAGO, U.S.A. IM-organized.) I- MM--- I-- I___EMuIRC -41n 104 RADIO -CRAFT for AUGUST, 1940 TELEVISION

view of RCA projection -television apparatus. N.S.C.'s Ray Monfort, and projection Kinescope; left, projection lens. NEWEST SCREEN -SIZE TELEVISION Not yet on the market, is the newest type of projection television receiver here described, which permits viewing by 150 persons. A feature of the system is the use of an enlarging mirror in place of the lens system ordinarily used!

ANEW large- screen television system voltage power supply, and the 3rd houses unit has an effective numerical aperture of the type designed for use in the electrical circuits, amplifiers, and con- of F:0.7, or more than 4 times the speed of theaters and before large audiences trols. All 3 are assembled on a single mobile the best available projection lenses. This was demonstrated last month at the platform. The overall dimensions are: means an increase in screen brightness of annual stockholders' meeting of the Radio length, 6 ft., width, 2 ft., and height, 5% ft. more than 4 times. Corporation of America in the RCA Build- 56,000 VOLTS. -The new kinescope uses The brightly- illuminated image on the ing, Radio City, New York. 56,000 volts as compared with the 6,000 or surface of the kinescope, which faces in the The demonstration, first public showing 7,000 volts used by the kinescope in the opposite direction to that of the finally proof the unit, was featured by an outstanding ordinary home -type television receiver. The jected picture, is thrown upon a concave program of entertainment. Among those actual size of the image on the face of the mirror surface measuring 16 inches in diam- who appeared on the television screen were kinescope projection tube is 2.4 by 3.2 eter. The mirror collects the light and mag- Madame Kerstin Thorborg, distinguished inches. The television signals are brought to nifies the image 22% times. The image is contralto of the Metropolitan Opera Com- the kinescope by either an antenna system, then projected back through a glass lens pany; Lowell Thomas, 4 1st -chair men of which takes them off the air, or by a direct surrounding the neck of the kinescope, and the NBC Symphony Orchestra, and other wire line from the source of the program. thence 20 ft. through space to a screen well -known artists. In the demonstration, the signals were mounted on a wall. The system effectively WALL -SIZE IMAGES.- Although the RCA taken off the air as broadcast by the Na- utilizes the industry television transmis- Laboratories have been working several tional Broadcasting Company's transmitter, sion standards formulated by the Radio years in the field of large- screen television, W2XBS, atop the Empire State Building. Manufacturers Association: 491 -line defini- the particular system shown was completed MIRROR LENS.-The optical system of the tion and 30 frames pas ?cond. early this year. A laboratory model, it projects images 4sá x 6 feet in size onto an ordinary beaded motion picture screen. The LENS projected pictures compare in brightness DEFLECTING YOKE with motion pictures and are considered to The new RCA large -screen television system, here PROJECTION have definite entertainment possibilities. shown in cross -section, KINESCOPE TUBE The unit was built as an intermediate is based on projection CONCAVE MIRROR step in the development of apparatus for optics of extremely wide the projection of much larger images, but aperture, a kinescope capable of high -voltage - it has already become apparent that the operation, and apparatus 9% x 6 foot image has interesting possibili- suited fo these conditions. Most essential ele- ties for use in clubs, schools and other ments are the new kine- similar places where the viewing group scope projection tube numbers from 100 to 150 persons. The Com- and the optical system. These provide more light pany has no immediate plans for marketing and utilize it more effec- this apparatus. At least 12 months would be tively than ever before, needed to develop it commercially. so that large- screen tele vision becomes practical. 3 -UNIT CONSTRUCTION. -The apparatus consists of 3 parts. One contains the newly developed kinescope projection tube and the optical system. Another contains the high- RI1r0-y0t14G1 IIRMINßI

RADIO -CRAFT for AUGUST, 1940 I05 ENGINEERING -

PLATE TRANS -6L6 PUSH -PULL OPERATION CHARACTERISTICS ETYPI AT GRID-CURRENT POINT Ef.: 6.3 VOLTS ZERO-SIGNAL PLATE-SUPPLY VOLTS . 300 SCREEN -SUPPLY VOLTS .300 CATHODE MILLIAMPERES. 800 IFEEL4 POWERSUPPLY BIAS CURVE RESISTANCE (OHMS) METHOD Controlling the degree of saturation in an in- 1.000 SELF * genious magnetic -circuit rn. O FIXED arrangement makes pos- C 335 OHMS BYPASSED BY 16MF sible a power supply FILAMENT CONDENSER having automatic regu- TRANS lation within wide limits. ÌI RL 11 2 5 moo===m WTCUT 117V.,AC i, (Sr) SATURABLE CONTROLLED 1- REGULATOR 1214[111 SATURABLE REACTOR 4 Zv O cr DIn a,11, IS áá Da< IS The Tundamentali o 3 10,l0 Ó i-C CONSTANT -OUTPUT 5 S °_ DISTORTION O D.C. POWER SUPPLIES 4,000 6.000 8.000 10,000 types of regulated PLATE -TO-PLATE LOAD This article describes conventional 11[4111 RESISTANCEI - OHMS power supplies; and concludes with the engineering details Distortion vs. power output of push -pull 6L6 stage of a D.C. power supply unit capable of regulating the output with zero -ohm and 1,100 -ohm res,stance power supplies. within 1 per cent under a load change of 300 per cent! A. C. SHANEY THE need for a stabilized constant vol- supply regulation is usually overlooked by it naturally would have "O regulation." The tage power supply has undoubtedly been many amplifier design engineers. term "regulation" does not always give a felt by many laboratory technicians Figure 1 shows the power output versus true picture of the operating characteristics who are constantly developing new total distortion of a class Al, GLfs amplifier of the power supply, unless the changes in electronic devices for accurate measure- operating with a power supply having per- current are taken into consideration. The ments. A constant voltage supply is also fect regulation (or 0 internal resistance:, regulation of a power supply may also be necessary for stable operation of communi- as against the same circuit with a more or expressed as a function of its internal re- cation systems involving the use of oscil- less standard power supply having an in- sistance. For example, a power supply which lators, which are subject to frequency drift ternal resistance of 1,000 ohms. A careful delivers 200 volts under no load, and 195 with variations in voltage. In addition to examination of the (lotted curves (which is volts under the full load, would be said to these, many precision electronic instruments the condition obtained with a 0- resistance 200 -195 require a constant voltage under all condi- power supply) will disclose that approxi- have a regulation of X 100= 2/ %'c. .tiops of operation. mately 23 watts is available at 1.5'- of total 200 High -power amplifiers operating in Al, distortion. An output of 25 watts is avail- Its internal resistance, however, can be cal- 'All:, All2 or class B similarly require a able at 3.5'/c distortion. The solid curves culated from the following formula: show with a conventional power supply, stabilized voltage supply for attainment of that EA maximum power output with minimum dis- this same circuit, under optimum conditions. tortion. In fact, the importance of power will produce only 16.5 watts at 6.7rí total R1 - (2) distortion. These characteristics should not IJ be construed as applying to a 6L6 amplifier where R1 = internal resistance OPERATION CMARACIERI$IICS - only. In fact, the 2A3 tube is subject to the same detrimental effects of poor regulation. EA = change in output voltage I = change in output current Figure 2 indicates power output versus For example, a power supply which de- distortion curves for various types of sup- livers 205 volts at a load current of 100 plies for a push -pull 2A3 amplifier. It will milliamperes, and 200 volts at a load current be noted that a plate and bias supply having of 125 ma., would have an internal resist - 0 (see curve 1) will enable the resistance -200 attainment of 16.6 watts at 1.4', whereas 205 a plate and bias supply, having internal ance of which is equal to .125 -.100 resistance of 780 ohms, will attain only 11 at 2% distortion. Naturally, poorer 5 watts will be power supplies will produce more distortion 200 ohms. It noted that at equivalent power levels. .025 the internal resistance of a power supply REGULATION combines in one term, the ratio of voltage current change. \iAm^ Regulation of a power supply may be regulation to expressed as the ratio of the change in out- m D.C. REGULATED Z 12 1.LIl»m=m.....1 put voltage to the highest output voltage. CLASSIFICATION OF DN Expressed mathematically, this ratio may- POWER SUPPLIES CyVIIrWiiis Regulated D.C. power supplies may be EA broadly classified into 3 groups. Group No. 1 ^ be written as . Percentage of regula- 3:IDNr c .nploys a cowl- cathode glow discharge tube : F E 1JI- similar to the ordinary neon lamps, or other aU1. 611111111111111111 tion can be calculated from the following radio versions of the Sylvania VR90, VR150. iC 4 formula: and the RCA 874. uNciommommmi EA Group No. 2 employs a grid- control 2 imminimeirmomm % R = X 100 (1) vacuum tube, the exact type, depending ? ° - í`cE E upon the control range desired. 2000 4.000 6000 8.00ó where Group No. 3 employs a saturable reactor LOAD RESISTANCE - E = Highest voltage output in series with the plate supply transformer. PLATE T PLATE - OHMS ® EA = Output voltage change It will be noted that all 3 are of the elec- a power supply produces no voltage tronic type and employ no moving parts. Distortion vs. power output of push -pull 2A3 ampli- If fier with various types of power supply. change under full- and no -load conditions. A discussion of the fundamental circuits and

106 RADIO -CRAFT for AUGUST, 1940 ENGINEERING

operating principles, as well as limitations GRID -CONTROLLED VACUUM TUBE of application of these 3 types follow: REGULATOR RBA Ed I To simplify the explanation of the oper- COLD -CATHODE GLOW DISCHARGE R RL-. ating principles of this type of regulator, C EÓ I. REGULATORS let us refer to Fig. 6, wherein Rr is con- EQUIVREGUL DISCHARGE To best understand the operating char- nected in series of RL. The voltmeter Eo is [ú`A7 ATRORGLOW acteristics of this type of a regulator, let connected across RL and an ammeter, Io, us refer to Fig. 3, which shows a D.C. gen- connected in series with RL. Under this con- RB' erator in place of the conventional power dition of operation, it can readily be seen RL GRID- GLDw -, supply filter network feeding a resistor, Rs, that if the load current increases (RL de- TUBE y in series with the load RL, having an addi- creases), the voltage across RL (E0) may be - BASIC GRID -GLOW REGULATOR CIRCUIT - tional variable resistor R,. connected across brought back to its original value by de- ®. it. If a milliammeter is inserted in the load creasing R,.. Similarly, if the load current IO Rp f G/ circuit, and if the load is varied, so as to decreases (RL increases) then the voltage CONTROL draw more or less current, it can be seen Eo may be decreased by increasing R. 1.1 L-v. E I p that an appropriate adjustment of R,. will If R. is now supplanted by a tube, as -EQUIVALENT CONTROLLED TUBE I always maintain a constant voltage across illustrated in Fig. 7, the plate resistance of FIG.FIG 6 REGULATOR RL within the operating limits of the circuit. the tube (from plate to filament) may be When the load draws more current, it controlled by the bias applied to the con- CONTRO RL means TUBE that its internal resistance is de- trolled grid. Figure 8 shows such a circuit. TO CONTROL creased. Now, if the control resistor R,. is To increase the sensitivity of the control : VOLTAGE increased, by a compensatory amount, the voltage, a voltage amplifier (6F5) is em- -BASIC CUUM -TUBE voltage EG across the load will remain con- ployed to amplify the variation in line volt- FIG.7 REGuLATORRIO-CON-rROOLCIRCUIT stant. Resistor Rb is inserted into the circuit age. This, in turn, changes the bias in the 1 2A3 to act as a "ballast" so that excessive vol- regulator tube, which increases or decreases REGULATOR tage may be "absorbed." If a grid -glow dis- its plate resistance. charge tube is inserted in place of RV., Fig. 4 It will be noted that a number of grid - :'2MEGS. results. This is a characteristic grid -glow glow discharge tubes are used in this circuit O /\ discharge circuit. to maintain / MF a constant voltage across MEG J A casual study of critical points. (These grid glow discharge regulating character- 6F5 LJ istics of both the Sylvania VR90 VR150 tubes may be the small 2 -watt neon lamps 7 and (see Fig. 5), will disclose that a practically with their internal resistors removed.) For constant drop is maintained across these example, 1 tube is employed in series with regulators under wide conditions of varia- the cathode of the 6F5. This insures a con- i tions of current through them. Another way stant cathode voltage. Three additional of looking at the regulating characteristic tubes are connected in series from the high -GRID- CONTROLLED VACUUM -TUBE of this type of tube, is to view the regulator side of the supply directly to the grid. This F G.8 REGULATOR CIRCUIT- as being able to maintain a constant voltage arrangement insures that the total voltage 2A3 drop across itself. change at the output is applied to the grid of the voltage control It is to be noted, however, that these amplifier. a If we assume that the output voltage RL tubes operate in comparatively limited MEG range. In other words, more than 30 ma. should drop from 300 to 290 volts, this 10- should never be passed through them. It will volt total change is applied to the grid of " also be noted that the operating range of the 6F5 because the voltage drop across the VR150 is from 5 to 30 ma., which gives the 3 series neon tubes remains 180 volts us an effective range of 25 milliamperes. at all times. This 10 -volt change decreases the bias on 6F5 (the neon in \\Y , IEAcm Under these conditions of operation, the the tube the t voltage across the tube will change from cathode circuit keeps the cathode potential approximately 146 to 150. If this tube is constant under all conditions of voltage placed across the output of a regulated sup- variation of the output circuit), which in- VACUUM- TUBE-COMROLLED REGULATOR EN- ply, the internal resistance of the supply creases the plate current through the con- ( GLOIINGA PENLOOE(OMNOLLEO VOLTAGE A...URER- (within the operating range of the regula- trol amplifier, this in turn, increases the tor) will be according to formula (2) drop across the 1 -meg. series resistor of Epp the control tube. This increase in drop EAC `F 150 -158 decreases the bias of the control tube, which A_/ = 80 ohms. in turn decreases its plate resistance, and CONTROL 30 -5 enables more current to flow through it to . REACTOR f RC The internal resistance of a power supply compensate for the increased current of the utilizing VR90 would be approximately 300 output, so as to bring the voltage back to - EQUIVALENT SATURABLE REACTOR. ohms. its normal point. MregM CONTROL CIRCUIT - The advantage of this type of circuit is The type of control tube employed, de- SATURATING COIL that it compensates for variation in line pends upon the amount of current desired voltage, as well as for variations in load from the regulated supply. A 2A3 is nor- current. The effective control range is mate- mally employed to control changes in cur- rially reduced, if large variations in power rent up to 60 milliamperes. The normal volt- REACTOR REACTOR line supply voltage occur. The disadvantage age drop from plate to heater of the control of this type of regulator is that it operates tube, should be adjusted so that maximum over a comparatively limited range, wastes plate dissipation is not exceeded under any an condition of operation. The maximum regu- appreciable amount of power in the rtern -SATURABLE REACTOR. CONSTRUCTION-ONSTRUCTION - series resistor (Rb), and it can only be lating range of a single 2A3 tube is approxi- applied to supplies that are to deliver 90 mately 60 milliamperes. A fixed resistor volts, 150 volts or multiples of these vol- across the controlled tube will increase the approximately 41.7 ohms. With two 2A3's tages. available current, but will not increase the connected in parallel, this same circuit de- regulating range. Where increased regula- livers 205 volts at 20 ma., and 200 volts at tion is essential, 2 more control tubes may 140 ma. Its internal resistance remains the be connected in parallel. An experimental same. u''''''-11111111111111111 model employing a single regulator tube The advantage of this type of circuit is with a shunt resistor across it, delivers that it provides regulation for variations Y-,°, 400.5 volts at 230 ma. and 399.7 volts at in load current and variations in line volt- ,,,,,,Ei, 280 ma. This would indicate an internal age. Its disadvantage, however, is its com- resistance of 16 ohms. Another variation paratively limited operating range, appreci- O O of this circuit employing a 6.17 pentode able waste of power across the controlled â á 11.11.3111111111. voltage control amplifier tube is given in tube, and the necessity to stabilize the 25 30 O OPERATING CURRENT THROUGH Fig. 9. This circuit employing a single 2A3 operation of the neon tubes. REGULATOR IN MA.,D.C. FIG 5 is capable of delivering 202 volts at 10 ma., This type of regulated power supply has 199.5 ma., which Fig. 5. Typical regulation characteristics of cold - and volts at 70 is equiva- become very popular because of its com- cathode glow discharge tubes. lent to having an internal resistance of parative simplicity and economy.

RADIO -CRAFT for AUGUST, 1940 107 ENGINEERING

SATURABLE REACTOR VOLTAGE series with the primary of the plate trans- 100 to 300 201-200.5 2.5 REGULATOR former, any decrease across the saturable 0 to 300 200-197 10.0 The saturable reactor type of regulator reactor appears as an increase across the With slight variations in circuit design, employs a distinctive principle of operation. primary of the plate transformer. This in the power supply can be made to have a The fundamentals involved can easily be turn increases the plate voltage supplied to negative resistance characteristic. In other understood by referring to Fig. 10, wherein the rectifier which raises the output of the words, the output voltage may be made to an A.C. supply, Eac, is connected in series power supply. rise with an increase of load current. with the control reactor, Rc, and a rotary This control action can be made entirely of still pro- by a portion of the out- Characteristics another type converter, Edc, which produces direct cur- automatic passing duces the following rise in voltage with an rent for the load Re. If the current through put current through the saturating coil. increase of current: Ile is increased, the voltage across Edc will Referring back to Fig. 11, it will be noted naturally decrease. However, a decrease in that the center -tap of the high -voltage A.C. Output Output the control reactor will increase the A.C. winding is connected through the saturable Current Voltage Current Voltage potential across the rotary converter, so as coil into the load. Resistor R1 is placed 20 140 180 173 to increase its output back to its original across the output of the rectifier, but in 40 143 200 175 value. Similarly, a decrease in load current series with the saturable coil so as to set 60 148 220 176 will tend to increase the output of the the permeability of the saturable reactor at 80 154 240 176.5 rotary converter. However, by increasing its correct operating point on its perme- 100 158 260 177 Rc, the voltage applied to the converter ability curve. If the load current through 120 164 280 177.5 would be decreased and its output would Ra, is increased, an increase in voltage drop 140 168 300 178 be likewise affected. If we now substitute takes place in the filter choke Chl, Ch2. 160 170 however, a conventional power supply for Edc and The increased current, saturates This type of regulation characteristic is a saturable reactor Sr for Rc, as dia- the series reactor, decreases the voltage only available with power supplies having a grammed in Fig. 11, we have the funda- drop across the reactor coils, increases the negative internal The voltage of plate resistance. actual mental circuit of a saturable reactor volt- across the primary the negative resistance can be calculated from age regulated supply. transformer, and across the rectifier plates, (2) as follows: which in turn appears as increased voltage The operation of the saturable reactor, 140 -178 -38 Sr, can best be understood by referring to at the input of the filter, to cancel the normal drop across the filter chokes. R = - - 136 ohms (approx.) Fig. 12, wherein it will be noted that 3 .300 -.020 .280 coils are wound on the 3 legs of a standard The range of this type of reactor is type EI lamination. The outer 2 coils, limited only by the type of rectifier tube A great advantage of this circuit is that known as the reactors, are connected in employed. It can easily be extended up to no power is dissipated. The voltage drop series- aiding. The drop across the reactors many amperes. It likewise operates effi- which appears across the saturating coils, will be proportional to the permeability of ciently at currents commonly encountered is not in phase with its current, because the core. in laboratory equipment or commercial am- the load is of an inductive nature. The dis- This in turn, however, is controlled by plifiers. Typical regulation characteristics of advantage of this supply, however, is that the amount of current passing through the experimental models follow: it does not compensate for line voltage center winding, called the saturating coil. Regulation Internal fluctuations. This condition may be cor- The more D.C. that flows through this coil, Current Range Voltage Resistance rected by using a conventional A.C. voltage the lower will be the permeability of the (in Ma.) Output (in Ohms) regulator ahead of the power supply. entire core. As this permeability decreases, 20 to 140 206 -204 33.4 The author will be pleased to answer any the inductance of the reactors decreases, and 0 to 80 169 -168 12.5 questions relative to this article, if a the voltage drop across them decreases. 120 to 240 212 -210 16.7 stamped addressed envelope is enclosed. As the saturable reactor is connected in 140 to 300 204 -202 12.5 Simply address inquiries c/o Radio -Craft.

WHAT CAUSES ECHO, FADING? NEXT time your customer waxes irate at if a news bulletin, for example, is being be received from both directions. Since the the results he gets on his allwave radio read, and conditions bring about the echo 2 paths are of unequal length, the time receiver, let him see this item, which tells effect described, then the distortion pro- taken for the signal to arrive will not be in the words of the Engineering Division of duced may make the program practically the same from both directions, and echo the British Broadcasting Corp. some of the unintelligible. Although, as is shown below, may again be produced, the time interval reasons why listeners may sometimes expe- certain types of echo may be overcome by being determined by the difference in the rience echo, fading, distortion and other the use of reflectors at the receiving end, 2 path lengths. effects when listening to, let us say, one of the type referred to here cannot be sup- This effect can also be produced even the B.B.C.'s Overseas Stations. pressed in this way. when the radiating aerials are equipped "Echo" effect is rarely to be observed on A 2nd form of echo, sometimes called with reflectors, for it would be both diffi- waves longer than those in the 19 -meter "backward echo," takes place when the cult and costly so to design them that the (15 megacycles) band, which means, usual- transmitting aerial used is not equipped whole of the energy radiated would be con- ly, that on transmissions from one of the with a reflector. From such aerials energy centrated in the one direction. With the B.B.C.'s Overseas Stations the effect is most is radiated in equal amounts in opposite arrays actually used by the B.B.C., a small likely to be observed by listeners in India, directions. If the point of reception is not amount of energy escapes in the direction Malaya, and Australia -and possibly the equi- distant from the transmitter over both opposite to the line of maximum radiation. West Indies -during Transmissions 2 and 3. paths, and if conditions are well suited to When conditions are suitable, as, for in- (The same principles apply in receiving the frequency concerned, then signals may stance, on 13 meters and 16 meters in short -wave programs in America, of course. Transmissions 2 and 3, serving India, this -Ed.) small amount of escaping energy is suffi- All the aerials used at the B.B.C. short- cient to provide useful signals at relatively wave station for wavelengths below 20 great distances from the transmitters. The meters are fitted with reflectors, the effect of MORE BROADCASTING "Great- Circle" route from Britain to the which is to concentrate the radiated energy HI'RE'S a toast to folk like Mickey West Indies happens to be almost exactly in one direction when it leaves the aerial. Rooney, a fellow of simple tastes, who in the opposite direction to the route to When propagation conditions are particu- has 15 "radios" in his 18 -room man- India, and listeners in the West Indies will, larly favorable, it may happen that a fre- sion.... Listen -in for Morton Gould's series no doubt, be well aware that frequencies quency in, say, the 13 -meter band, such as of compositions, "Experiments for Radio GSJ and GSG often provide useful signals GSJ, may provide strong signals in India, Orchestra." This young composer-conductor there when primarily intended to serve and still be of sufficient strength to travel plans to air over WOR- Mutual a series of India. onward, until, having completely encircled 2- minute "experiments" which "emphasize It may be possible, when propagation con- the globe, it provides a second signal at the tonal configurations that previously ditions are particularly suited to those fre- the same point of reception. served only as a lace -like fillet" (my, my). quencies, for listeners in the West Indies When such "round- the -world" or "for- Such compositions as "4 Flutes and a Filter - to observe the effect of echo due to the ward" echo takes place, the interval between Mike," and "Bassoon, Viola and Echo -Mike signals' arriving by the shorter route direct successive signals is of the order of 1/7- Study," he hopes will aid young composers from Britain, and also by the long path second -there are authentic accounts on who are studying effects possible in radio. across India and so round the globe. This record of as many as 5 or 6 separate repeti- The heretofore background sounds will be type of echo may be reduced by the use of tions of a single signal. It will be seen that acoustically spotlighted.. . reflectors on the receiving aerials.

108 RADIO -CRAFT for AUGUST, 1940 THIS óOFS( $0,)çÇUL x TR,4

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RADIO -CRAFT for AUGUST, 1940 109 EXPERIMENTERS

TUNING LL DIAL V6 C5

-CI-4.1

--V7

The neat and compact construction of this new F.M. Adapter h Must ated in photo A. Even an underview, photo B, will not scars the constructor. BUILD THIS PRACTICAL F. M. ADAPTER Complete directions make it easy for any constructor to build and align this Fre- quency Modulation Adapter. Use it with any radio set or P.A. system. Add headphones and it functions as a complete F.M. receiver. ARTHUR H. LYNCH

tures, the circuit diagram and the List of Parts, it should be a simple matter to identify the location of all the component parts. The construction and the circuit are entirely straightforward and adjustment of the completed receiver follows normal practice. It been made from WITH the advent of Summer. the value of programs over the will be observed that a view of the receiver has new frequency -modulated broadcasting stations will become the bottom, so as to enable the constructor to see those parts which more and more apparent. Our own investigation of this new would otherwise be obscured by a portion of the cabinet. field bears out the statements which have been made by the Considerably better performance is provided where an 1852 engineers of several of the large companies which now have fre- (6AC7) tube is employed in place of the 6SK7 in the radio frequency modulation receivers and frequency modulation adapters quency stage. The improvement is found in much better gain and for use with regular broadcast receivers available. results in considerably better limiter action. Another 1852, The claim, of course, which seems most important with Summer (6AC7) may be used in place of 6SK7V4 as indicated in the is found this changeover and the thunderstorm season coming on, is that frequency - circuit diagram but it sometimes that it is worth a modulated broadcasts can be received through the most severe results in oscillation. In any event, trial. thunderstorm with no interference whatever. Here's an interesting story that illustrates this feature, which ALIGNMENT Frank Gunther, the Chief Engineer of Radio Engineering Labo- The materials needed for aligning the completed F.M. Adapter ratories, the organization which has built most of the equipment are a service oscillator and a 200 -microamp. galvanometer. For for Major Armstrong, as well as for many other frequency modula- aligning the discriminator, T4, a 0.1 -meg. resistor must be in- tion broadcast stations, told us that one day last Summer. serted in series with the meter. With meter and series resistor When a crowd of visitors had climbed the mountain to the loca- connected across R23 apply a signal to control -grid of the 6SJ7. tion of the Yankee Network's station at Paxton, Mass., a very Using 2,100 kc. as the frequency of the I.F., and modulating with severe lightning storm came up. The children of the group were 400 -cycle note, adjust the primary of T4 for maximum reading of obviously frightened. The engineer in charge connected an extra, the galvanometer. remote loudspeaker to the F.M. receiver used to pick up the The meter with its series resistor should now be connected to transmissions of the relay station, which was sending onward to both cathodes of the 6116. Apply an unmodulated signal to the Paxton the program from Boston, and raised the output volume control -grid of the 65J7 and adjust the secondary trimmer of T4 of the loudspeakers to a point where it overshadowed the thunder. for zero reading on the galvanometer. Rock the oscillator back While the storm was going on, the visitors enjoyed the music and and forth 100 kc. each side of 2.100 kc. and note that the galva- paid little or no attention to the conditions outside, while previous nometer should show an equal deflection either side of zero as the to that time their attention was all on the outside. frequency is changed. There should be a change of voltage propor- tionate to the change in frequency either side of the "center" CONSTRUCTION frequency. From the accompanying photographs and drawings it will be Now remove the series resistor and insert n meter in series with possible for the experienced constructor to duplicate the Frequency RIS at the point marked X. Apply an unmodulated signal to the Modulation Adapter which we have built. By comparing the pic- control -grid of V4. Set the oscillator to 2,150 kc. and adjust the

I10 RADIO -CRAFT for AUGUST, 1940 EXPERIMENTERS

65HT. 1852 ONO. ANT GACTOR IB52(1/1) 65H1 (1/3) GAClOd1652(1/4) Li V ER(V5)

E2 MME

3 -30 MME C21 C9- RIS 5 M` MMP. L2 R12 15.000 ÌIX1 X % TI OHMS,OHOnJO MMF. pOIaQS 1/1V1 CB Rp4pp //a w 72 MIF. -i-,r hN! C10 i T

I i ó1Z O Á6 R 1.000. - e9 OHM yyII oMs I/i I/iW. 75 e5 digo R15/ WÑGÉDO 60000 OHMS. 1W. OHM9. I/LW. VDT. I W. t250V R24' I )y C26 50.000 13 3V TO W MMF. MMF. AMPLIFIER e R2 2 1 L1.L2.L3- 5TURN5 ON P/Ie FORM. SPACED 1 /e 5W.1 EG. WOUND WITH Nt IB TINNED COPPER WIRE. /LW. ¡1 PRIMARY- WOUND WITH Ne 24 055 WIRE 22Ñ URN S. C25 OSCILLATOR TAPPED IHl TURNS FROM BOTTOM. R25 .M0f- SMC.I.F USED. MÉG.-1 84 O1p EG. T IAw. This F.M. Adapter may be used with headphones as a complete receiver; or it may be used to drive the A.F. section of any radio receiver or P.A. system.

primary trimmer of T3 for maximum deflec- such a unit will give him an insight into Three Cornell- Dubilier, type 5W -5T1, 100 tion of the meter. Next set the oscillator to the operation of the receivers of this nature mmf., C22, C23, C24; 2,050 kc. and adjust the secondary trimmer and will be very beneficial to him in han- One Cornell -Dubilier type, 1W -5D1, 0.001 - for maximum reading. The oscillator should dling service problems on the various F.M. mf., C25; now be rocked 100 kc. either side of 2,100 sets now on the market. Connect a doublet One Cornell- Dubilier, type DT -4S1, 0.05 -mf., kc., and meter readings taken at various antenna to terminals Ant. and Gnd. 600 V., C26; positions, to make sure the transformer The author desires to express apprecia- One Cornell -Dubilier, type BR -845, 8 mf., shows a symmetrical resonance curve. It is tion for the assistance given him by Messrs. 450 V., C27; not necessary that the transformer have a Shaughnessy, Day and Stiles, of Major One Cornell -Dubilier, type BR -1645, 16 mf., flat top (of 200 kc.) but that it should be Armstrong's laboratory. 450 V., C28; symmetrical. It is desirable that the signal The actual building of this receiver was RESISTORS should attenuate rapidly beyond the 2,000 done for the writer by Mr. Anton Schmitt, kc. and 2,200 kc. points. W2KWY, Two I.R.C., type BT1/z, 300 ohms, R1, R14; of the Harvey Radio Company of I.R.C., Apply a signal to the control -grid of V3 New York City; and Four type BT%, 1,000 ohms, R3, R6, the receiver has been R11, R16; and proceed as above. thoroughly tested not only in the labora- Short the oscillator coil to V2, apply a tory of Two I.R.C., type BTsfz, 20,000 ohms, R4, the National Company at Malden, R21; signal to the control -grid of V2, and adjust Mass., but also in the laboratory of Major T2 as before. Next disconnect the short on Armstrong at Columbia Four I.R.C., type BT%, 40,000 ohms, R7, University in New R12, M7, R18; the oscillator coil and apply a modulated, York City, and in the Radio Engineering Two I.R.C., type BT1, 15,000 ohms, R8, 43 -mc. signal to V2 and turn C4 until the Laboratories. Long Island City, N. Y. meter in the control -grid circuit of V5 R13; ' registers a reading. Now adjust trimmer LIST OF PARTS One I.R.C., type BT %, 200 ohms, R9; Two I.R.C., 0.1 -meg., C6 for maximum reading. Finally, apply a CONDENSERS type BT%, R22, R23; One I.R.C., type BT1/2, 50,000 ohms, R24; 43 -mc. signal to the antenna terminal and Three National Co., type UM -15, Cl, C2, adjust C5 to maximum. The band -width of C3; Three I.R.C., type BT1, 60,000 ohms, R2, RIO, R15; R.F. is sufficient to pass the broad band. One National Co., type UM -50, C4; One I.R.C., BT1, 20,000 ohms, R5; When using a 6AC7/1852 in place of the Two National Co., type 3 -30, C5, C6; type I.R.C., 1 6SK7 more care must be taken in the Fourteen Cornell -Dubilier, DT -6S1, One type BT1, 0- -meg., R19; type One I.R.C., placement of parts and in the laying of 0.01 -mf., 600 V., C7, to C19 type BT1, 50,000 ohms, R20; (incl.), C29; I.R.C. ground wires. Each circuit must be ground- Two Cornell -Dubilier, 5W -5Q5, 50 One potentiometer, type 13 -133, 0.5- type meg., ed at the socket to chassis and all points on mmf., C20, C21 (erroneously indicated in R25; the chassis connected together with 1/.a -in. diagram as 5 mmf.); TUBES braid. It may be desirable to use braid to One Sylvania or RCA 6SK7, or 1852 (see ground the shield of the tube as wire has a text), V1; roLESq higher R.F. resistance. I- One Sylvania or RCA 6SA7, V2; IP,wA 8:1'I1-.:: It may be necessary to insert a 15- to One Sylvania or RCA 1852 (see text), V3; 25 -ohm resistor in series with the control - One Sylvania or RCA 6SK7, or 1852 (see grid of V2, at point X, to suppress parasitic text), V4; oscillation. i 4L One Sylvania or RCA GSJ7, V5; Coil construction: Ll, L2, L3 -5 turns, One Sylvania or RCA 6H6, V6; IR on 9/16 -in. form, spaced % -in. and wound A One Sylvania or RCA 84, V7; with No. 18 tinned wire. Primary -2 turns TiNSEÓRMÉÑ I 0 MISCELLANEOUS wound with No. 28 D.S.S. on lower end. . o D o Three National Co. I.F. transformers, Tl, Oscillator tapped 1% turns from bottom. T2, T3; An I.F. of 2.1 mc. is used. le o' n Lo --13' One National Co. discriminator L là'i í4 transform- {4D---P-- 4o y er, T4; CREDITS ° 1 One United Transformer, A.F. transformer It was our purpose in providing D --- this de- tl+iï type R -54, T5; sign to make the advantages of frequency 1 One Thordarson choke, Chi; modulation reception available to the more I in One Hart & Hegeman roto switch, Sw. 1; experienced constructor. It will be recog- One National Co. steel cabinet, type C5W -3 nized that the receiver has been designed (the subpanel comes with this cabinet); to use items which will be found in stock 4e-o-4r0 One National Co. dial, type 0, with No. 2 in most of the leading radio stores. The - -t scale; Serviceman should find this design extreme- 1-(}+I-I1+-2' 2-T 1l One National Co. dial drive, type ODD; ly interesting because the construction of 9' Two National Co. knobs, type HRP. RADIO -CRAFT for AUGUST, 1940 III RADIO DEVELOPMENTS

SUSPENSION SUPPORT

DRIVING PERMANENT ELECTROMAGNETS MAGNET 4 The "singing- string" secondary time standard, and its originator Mr. Henry E. Wilson. TO PLATE GRID CIRCUIT, CIRCUIT

AL LOY WIRE

The voltage gener- ÿ WEIGHT ated in a magnetic (L(RISES circuit by a vibrating FALLS alloy wire helps keep the COILS) wire humming.

CONTROL VOLTAGE AN A.F. CLOCK! /%lui ica l 7íme S'tandatd

by several expedients. A dual -wire string, consisting of a nickel - steel alloy and a beryllium- copper alloy, maintains uniform length. CLOCKS are "accurate" only to the extent that they remain and hence frequency. with changing temperature. Any slight exactly in step with some known frequency reference or changes that remain are ironed -out by placing a light spring at "time standard." A time standard, remember, is the basis of the lower end to aid or oppose the gravity force exerted by a our computations of the frequencies of radio channels, the speed heavy weight (used for major tuning of the string). Coils which of radio propagation, etc. project into an alnico magnet set in the base of the weight, and The earth revolving on its axis constitutes our primary or which connect to a voltage source, establish a magnetic pull or astronomical standard. Secondary standards include the pendulum push on the weight to further tune the string. (accurate to about 1 sec. /yr.); the vibrating quartz crystal Now that we have a string capable of vibrating, it only remains (accurate to about 1/6-sec./yr.); the tuning fork (accurate to to drive it. This is conveniently accomplished in somewhat the about 1/10-sec./day); and, the news singing string, with an manner utilized in tuning -fork oscillators (t). In the case of accuracy about equivalent to the tuning fork. Virtually a vibrating the musical- string oscillator, a cobalt -steel bar -magnet is rigidly violin string, it sets up and maintains oscillations, in a vacuum - fastened to the center of the string. One pole projects into a tube circuit, at a predetermined frequency. pick -up coil connected to the grid of a triode, and the other, into conditions The first consideration is the string. Under ordinary a driver coil in the plate circuit of the same tube. The A.F. output, it would be impossible to keep it in tune, as anyone familiar which is nearly sub -audible, is then amplified to any desired problem was solved with string instruments will attest, but this degree; 2 watts, for example, will run a Telechron clock motor. by Henry E. Warren, Assoc.. A.L}:.E. (Pre.. Seo "A New Time Standard," "Oscillators at Work," by John Eider. wattcn Telechron Co. l: this paper was presented at a meeting of the A. I. E.E. TSee

RADIO -CONTROLLED BOAT

(Rudy Arnold Photos lust A "jam session" would not the performance of the 6 -ft. radio -controlled A flotilla of such radio -controlled boats, arranged to travel silently disturb in it boat shown above. Due to its extreme selectivity the ultra -shortwave receiver below the surface of the water and each carrying a contact bomb is practically immune to interference (jamming); however, any transmitter, snout would seem to be a coastal defense weapon well worth developing - knowing the combination, may pick up control and put the boat through its NOW. An airplane beyond effective range of anti -aircraft guns still could to its objective a torpedo -boat of this design. The 2nd photo maneuvers at 5 m.p.h., up to a range of I I miles, says its designer, Henry W. unerringly direct receiver has a rod antenna. A storage Wickes, a Lieutenant in the U. S. Naval Reserve, stationed at Floyd Bennett shows the "works" in close -up. The 3 hours. Field, Brooklyn, N. Y. Will the United States Navy take over this robot craft? battery powers set and boat for

112 RADIO -CRAFT for AUGUST, 1940 RADIO DEVELOPMENTS

DUAL - COAXIAL SPEAKER

The Armstrong Wide -Swing Frequency Modulation System, which has made practical for the first tinte utilization of the full audible range in broadcasting, has created a desire by broadcasting stations for an exceptionally wide- range Monitor Speaker. To meet these requirements, the Dual Coaxial Loudspeaker, here described, was developed. The speaker, although essentially for F.M. Monitoring, too, is excellent for A.M. Monitoring.

THE model 35 Dual -Coaxial Monitor COVERAGE Speaker, here described, is probably the The most recent attempt to solve in con- angular distribution is exceptionally venient, wide, the response at 6,000 cycles, for ex- economical fashion, the problem ample, of high- fidelity reproduction as afforded in at an angle of 50 degrees to the axis being clown "F.M." reception. This reproducer employs only 3 db. from that on the axis. The apparent Front view of the Stromberg- Carlson No. 35 car - a new dual loudspeaker system which has an efficiency of the system is from 4 to 6 db. higher than of pinchoe- leather Monitor Speaker in the new duel exceptionally wide frequency that the coaxial design. range. Both usual radio loudspeaker. The speaker units are of the direct cone input imped- -radiator ance is 24 and type, the small, high- frequency be- ohms the power -handling speaker capacity on speech and ing mounted coaxially with low -fre- music is adequate the for, as example, the home rooms. quency speaker and within the hollow of its largest cone, the 2 thus closely simulating a unit The No. 35 monitor speaker is designed source. A marked increase in naturalness is to handle the output of a 15 -watt audio - thereby attained over the reproduction frequency amplifier. However the apparent afforded by the usual side -by -side arrange- power output of the complete loudspeaker ment having a comparable cross -over fre- assembly (loudspeakers and baffle) will be quency. The cones of both loudspeakers are greater than the apparent output of a single equipped with carpinchoe -leather edge sup- speaker and baffle assembly operated at the ports to control diaphragm resonances. same power because of the increased fre- The high- frequency radiator is only 2!a quency range made possible by the use of ins. in dia., providing. not only desirably 2 loudspeakers arranged for wide frequency small mass but also wide -angle radiation response. Although the frequency range re- over an extended frequency range. quired for voice re production ordinarily is considered to be quite narrow, this is true CROSS -OVER AND RESPONSE only for the fundamental voice frequencies; it is It is caused to function the harmonics which serve to set one adequately down voice apart from another and these har- to the cross -over frequency of 1,500 cycles monics may by broadly resonating at an appropriate extend to quite high frequencies. Exceptional naturalness in voice repro- frequency the mass of the moving system duction with the stiffness of the in a therefore may be expected from a air tight -back sound reproducing such enclosure. This stiffness also serves as a system as the dual coaxial speaker having wide frequency re- Cut -away view protective feature in preventing acoustic sponse. of the new No. 35 Monitor Speak. driving of the high- frequency This is actually the case. Add to hawing the location of the dual -coaxial speakers speaker by this n relation to the patented labyrinth (to aid low the adjacent low- characteristic of voice realism the ad- frequency speaker. vantage of still wider requency reproduction) enclosed in the cabinet The presence of the high- frequency frequency response in cavity. speak- the reproduction of music together with er structure in front of the 8 -in. low -fre- the almost complete lack of background FIG quency cone acts as a spreader for the noise, .0 in startling contrast with ordinary A.M. radiation of the latter in its upper frequency reception, range, where concentration around the axis which characterizes the per- a°:a. formance of F.M. receivers and you have a 1 otherwise would become effective. The back ' new merchandising possibility. of the low -frequency cone works into an acoustical labyrinth, which In the No. 35 Monitor Speaker the appa- *tp effectively ex- /`:` tends the low- frequency response, prevents ratus complete with dividing network and 4,448314*- y'* resonance in the enclosing cabinet, and field supply rectifiers is housed in an attrac- m°-. w tive modernistic cabinet finished in metallic 1 provides a suitable acoustic load for the - Qa ° beige 1 diaphragm. lacquer with black trim. Height, 29'4 N10 -20 -30 -30 20 -IO 0 The response ins.; width, 27'ía ins.; depth, 15'Fa ins. RES7ON5=1N of this speaker is substan- DB.RELAT..í' VE TO THAT ON AXIS tially uniform from 70 cycles to 10,000 This article has been prepared from data Directional characteristic of the Dual -Coaxial Loud- cycles, and significant response is obtained supplied by courtesy of Stromberg- Carlson speaker (A) at 6,000 cycles compared with that of below 65 cycles and above 15,000 cycles. a single 8 -in. cone speaker (B). Measurements made Telephone Manufacturing Company. on I8 -in. radius.

1111 1_A111111!MN11II 80i . 80 .mat NI :irw'Irt1N:*:' m iìll/iiu D 70 N IIIMrM11111Ï1 =111111 `:ri111 70 =M1111 WI 1111 111111111 EMI= =MIMI 1111 111111 W 1111 60 111 M 111 111111111111111 111111.111111 11111=111111 cj 1.111.1.1111111CC:1M11111 50 M111111111111 5 50 M1.11I 1111 -M11111 . ,,111 1111M11111111111I1 MEMO' 40 30 50 100 500 1.000 5,000 10.000 300 500 1,000 5,000 10,000 FREQUENCY IN FIG. A CYCLES PER SECOND FIG. B FREQUENCY IN CYCLES PER SECOND Response of the Dual -Coaxial Loudspeaker measured in a damped room at Response of only the high -frequency 10 ft. loudspeaker, of the No. 35 assembly, average ilstance, and with the microphone rotated on an 8 -ft. radius. measured on axis at 18 ins. distance. (The 2 -unit assembly handles 15 -W.) RADIO -CRAFT for AUGUST, 1940 113 LATEST RADIO APPARATUS

HIGH -VOLTAGE WET Designed to operate on 110 V. A.C. line, earphones but also all bone conductors). ELECTROLYTICS 50 to 60 cycles. Also available in D.C. Small -size "A" cell and 30 -V. "B" battery models. are in a separate, compact case. Radio - Aerovox Corp. Craft New Bedford, Mass. 30 -W. AMPLIFIER WITH AUTO- NEW RELAYS MATIC RECORD CHANGER Standard Electrical Products Co. Allied Radio Corp. 317 Sibley St., St. Paul, Minn. 833 W. Jackson Blvd., Chicago, III.

THESE units are available in 4, 8 an I 16 mf. capacities, with a 600 -V. D.C. surge rating as compared with 350 and 500 V. ratings heretofore available. Units are self - ILLUSTRATED is a new healing. Can sizes are 1% and 1% in. dia., one of series of relays designed especially for radio fre- and 37/16, 47/16 and 415/16 ins. high. quency and high -voltage applications. Types BBA (for use up to 15 mc.) and BMA (for ADJUSTABLE -LINK OSCILLA- THIS unit features an RCA record changer which operates from 6 V. D.C. or 110 V. use up to 60 mc.), illustrated, are the break - TOR AND BUFFER COILS A.C. Features of the amplifier are 37 W. in type known more commonly as the push - Bud Radio, Inc. undistorted (37 W. peak), output imped- to -talk relays. The amateur radio operator 5205 Cedar Ave., Cleveland, Ohio ances of 2, 4, 6, 8, 16 and 500 ohms avail- merely presses a pushbutton while transmit- able on a selector switch. Four input chan- ting and releases it when receiving. The re- COILS are delay has 4- ampere, 3/16 -in. pure silver con- signed for use nels, namely, 2 for use with high -impedance mikes (each with .individual volume contacts. Available with 110 V. A.C. or 6 V. D.C. in circuits where it coils. insulation is Mycalex, on type BMA. is desirable to ad- trols), 2 for phono inputs with wider control; 2 tone controls of the attenuator type, Other types of relays are available for inter- just excitation or communication units, remote -control cir- 1 for treble and 1 for bass. The gain for antenna loading by cuits, and antenna change -over. varying the link microphone is 135 db., and phono, 80 db. coupling. Each coil Frequency response is 30 to 12,000 cycles is individually per second (for the amplifier). Standby THIN -CASE PORTABLE linked and coupling switch helps reduce power consumption. Philco Radio & Television Corp. is varied by push- Tioga & C Sts., Philadelphia, Pa. ing the link in or out of the main 3 -TUBE SMALL -SIZE winding. All coils HEARING -AID in this series fit TayBern Equipment Co., Inc. standard 5 -prong sockets and are designed York, N. Y. for stages where the input power does not 135 Liberty St., New exceed 50 W. Coils are available for all amateur bands. NEW MIKE STAND Eastern Mike -Stand Co. 56 Christopher Ave., Brooklyn, N. Y. THIS new -type mike stand has a hollow base made of die -cast metal to which a highly polished chromium finish is applied instead of the usual method of using a thin metal shell around an iron casting. The edge of the base is fitted with a rubber link which acts as a base guard and shock ILLUSTRATED is one of a new line of absorber. The stand weighs 6 lbs. but its l'hilco 1941 portables. It is model 81 -T weight can be increased when desired by having self -contained batteries. Other fea- filling the hollow base with sand, buckshot, tures include 4 tubes, built -in loop antenna, etc. Light to carry, it may be weighted "on lightweight full -vision dial and slender case. location." NEW PHOTOELECTRIC VARIABLE CRYSTAL CONTROL OSCILLATOR United Cinephone Corp. Bliley Electric Co. 43 -37 33 St., Long Island City, N. Y. Union Station Bldg., Erie, Pa. controls are THIS "Vari -X" in- THESEhoused in compact NOW N as the "1.ltra -Ear" this compac strument is a vari- (9 x 6'6 x 4!a ins.) en- I< hearing -aid is easily concealed on both able frequency exciter closures having knock- men and women. Although measuring bu with self- excited oscil- outs in the bottom for 4% ins. long, 214 ins. wide and 15/16 -in. lator which affords ex- power connections and thick, it incorporates a 3 -tube high -gain cellent frequency flex- a knockout on top for audio amplifier and crystal microphone; this ibility with full quartz wiring -in external design assures adequate sensitivity, fidelity crystal stability flexi- photocells. Various and volume. bility for the amateur's models are available, Sensitivity is said to be sufficient for nor- transmitter. Its power some with external mal conversation up to 30 feet. Its fre- output is 2% W. at either 40 or 80 meters. photocells, others with quency response is so designed as to benefit It is worked from the station operating collector lenses. All 80 per cent of the hard -of- hearing cases. position and is easily installed. Pentode. units utilize a type 6J5 amplifier tube; the Power output better than 50 milliwatts tetrode and low -power triode tubes cus- photocell-tube life is about 10,000 hours. (ample for properly actuating not only tomarily employed in the normal oscillator

114 RADIO- CRAFT for AUGUST, 1940 LATEST RADIO APPARATUS

stage will be easily driven as an amplifier claimed to reproduce low frequencies with a impregnated. Three general types -KF, KS, by the Vari -X. Either one of the 2 crystal fidelity never before obtainable with a small KW- available to fit all standard wiring units plugged into the socket on the Vari -X speaker in a small cabinet. Its frequency channels and in capacity values to satisfy panel is instantly chosen by a convenient response is from 80 to 7,000 cycles. Its diam- the power factor correction requirements of selector switch. Total adjustable frequency eter, 7 ins.; weight, 3 lbs. Handles 3 W. any installation. range at 80 meters, about 12 kc.; frequency continuously.-Radio-Craf t doubling (40 meters), about 24 kc.; quad- rupling (20 meters), about 48 kc. Metal MIDGET PLUG -IN -SHAFT cabinet is 8 ins. sq. PORTABLE RECORDING STUDIO POTENTIOMETERS Speak -O -Phone & Recording Equipment Co. International Resistance Co. 23 W. 60th St. RADIO NOISE METER 401 N. Broad St., Philadelphia, Pa. New York, N. Y. RCA Mfg. Co., Inc. Camden, N. J. NOW available is a complete Recording Studio incorporating a collapsible booth and recording equipment. Booth measures 57 x 30 x 78 ins. high; easily assembled; soundproof; accommodates 2 persons in recording section; has 2 -way interphone between customer and technician; easily carried by cur. Has built -in P.A. system for ballyhoo. Conies wired complete with lights and recording equipment.- Radio -Craft MANUFACTURER recommends these for universal use in volume control re- MULTITESTER MODEL 414 placements. Installation is simplified through Radio City Products the use of plug -in type shafts making a Co. small 88 Park Pl., New York, stock of these units handle a large N. Y. variety of receivers. 312. Built around a superhet. re- TYPEceiver. Its principal uses include measur- RUNS PHONOS ON D.C. ing the noise levels of transmission lines American Television Si Radio Co. and electrical apparatus, and field strength 300 E. 4th St., St. Paul, Minn. of radio signals in comparison with noise levels. When equipped with a directive loop MODELS PCP, -F, antenna it indicates the direction of signals and - R Phono- and interfering noises. Size, 13% ins. high, graph Inverter per- 13% ins. wide and 9'4 ins. deep.-Radio- mits the operation of Craft 110 -V. A.C. phono motors on 110 -V. NEWEST 3 -WAY PORTABLE D.C. Used primarily in phono -radio com- Allied Radio Corp. binations and port- 833 W. Jackson Blvd. ables of the A.C: Chicago, III. D.C. variety. A good item for Servicemen MODEL 414 Universal Deluxe Multitester to sell to owners of A.C.-D.C. sets. Size, is now available in 4 additional series. 2% x 2% x 2 5/16 ins.; weight, less than 1 lb. Series V7 has a large 7% in. bakelite square -Radio -Cra f t meter, jewel indicating light, and front - panel fuse holder. Series V9 is the same except that meter is 9 -in. jumbo round type. 3 -UNIT ANALYZER KIT -SET Series RP7 is similar to V7 except that the Simpson Electric Co. panel is arranged horizontally for rack 5216 W. Kinzie St., Chicago, III. mounting and has no case; meter is instantly removable for use at a remote point. Series RP9 is identical to series RP7 with the exception of the meter which is a 9 -in. round type.

NEWEST portable radio set merchandised FLUORESCENT -LAMP by this company incorporates automatic CONDENSERS change -over from battery to electric (A.C: Cornell -Dubilier Electric Corp. D.C.) operation, and vice- versa. Tuning S. Plainfield, N. J. range, 540 -1,550 kc.; has 5 tubes, A.V.C., and sliderule dial; wgt., 15 lbs.- Radio- Craft NEW CONE LOUDSPEAKER RCA Mfg. Co., Inc. Camden, N. J.

COMPRISES 3 small matched meters, in a single carrying case, per kit; 3 different kits (9 meters) are available. The meters are available in combinations to measure current, voltage and resistance for all requirements. This grouping of in- MODEL M1 -0233. A new P.M. dynamic dividual meters it is claimed increases loudspeaker which makes effective use flexibility, reduces cost and makes readings of a folded or "accordion edge" cone sup- easier. All meters may be used separately. port principle. This permits the cone to DESIGNED especially for power factor Each meter is the same (uniform) size, 5?. move more freely when driven by the correction which is necessary when ins. x 2% ins. x 1% ins. and none weighs permanent- magnet speaker mechanism. It is using the new fluorescent lamps. "Dykanol" more than 20 ozs.- Radio -Craft

RADIO -CRAFT for AUGUST, 1940 I15 LATEST RADIO APPARATUS

NEW OSCILLOSCOPE radio set is a 12 -tube, 3 -band chassis, including 6- button station selection, built -in Allen B. Du Mont Labs., Inc. broadcast and shortwave loop antennas, 2 Main Ave., Passaic, N. J. tuning indicator. Recordings may be made of radio programs and local talent via a FREE- microphone. Entire combination may also be used as a public- address system.- Radio- RE4L Craft 10 -W. AMPLIFIER fLfC1R0P1llT/NG Terminal Radio Corp. ovrrrr 68 W. 45 St., New York, N. Y.

TYI'E 208. Designed with sufficient flexibility, associated circuits and controls to MODEL T -8. A neat 8- to 10 -W. amplifier facilitate its application to the great ma- for public -address work or for use in Now - jority of laboratory requirements. Utilizes homes with good record players and fre- an intensifier -type cathode -ray tube with quency modulation tuners. Has 2 high - You Can ELECTROPLATE electrostatic focusing and orthogonal elec- impedance input channels for microphone trodynamic deflection. Its amplifiers are flat and record player, and provides for compact Its mixing and fading operations. -Radio -Craft A BRUSH to 100,000 sinusoidal cycles per second. EASILY WITH sweep frequency range is 2 to 50,000 cycles per second. These response ratings are en- BX CUTTER tirely independent of attentuator settings. SOMETHING new for radio men- Ideal Commutator Dresser Co. Li which gives you the Incorporates many other new features.- Radio -Cra f t 3067 Park Ave. opportunity to make additional prof - Sycamore, III. its-or to improve your type of service. Here's an ELECTROPLATING NEW SOUND PROJECTORS KIT amazingly simple to operate - Jensen Radio Mfg. Co. you just Electroplate with a Brush! 6601 S. Laramie Ave., Chicago, Ill. TYPE "S" peri- dynamic projector. Em- ploys a heavy -duty P.M. speaker capable of handling 15 to 25 W. of input power. The NOT A TOY! speaker is sealed within an enclosure and profit. hundreds utilizes the peri- dynamic principle, result- household-ashtrays.t fau"ei..lnworn brackets. door knobs. usical instruments. Jewelry ing in a sharp improvement in the middle and sllvenvare and other articles. an india articlesit' in frequency response. Lack of radiation from apatntoffuildg.te, hatoutfi(ulrice biniand pledc dn a frme. - the back of projector helps eliminate feed- aiglaboratories.used ProfessionallyollyM1es THE time- and labor -saving BX Armor eectiins,ltrcaft radiobt service es automobile re- back troubles. -Radio -Craft hops, etc. Requires one single dryf cell I t a- Cutter here illustrated has jaws that fit pairolt battery to nitrate. BX cable of any make, and 2- or 3 -wire No. You can electroplate tarnished receiver pans. escutcheons. contacts. worn radio n and . "RADIOCORDER" 12 or No. 14. Cutting blade is removable. merles. and display chassis. Put this REAI. EI.F.C TROPI.ATING KIT to use immediately -make It the Radio Wire Television, Inc. Does not nick wire. Eliminates waste. - most useful article in yourv shop or laboratory. And. you can get It absolutely FREE (except for slight Radio -Cra f t mailing cost). 100 Sixth Ave., New York, N. Y. Subscribe today to RADIO-CRAFT for One Year (12 Issues) absolutely FREE ccepteddF.or TROPLATINOII KIT. New accepted "CHEST MIKE" extend r present subscription twelve Mail remittance of $2.00 (Plus 10c for shipping Universal Microphone Co. charge on kit) to the publishers. iCanada 1 foreign receive UsRco Inglewood, Calif. OUTFIT returnmaRE pen below to enter subscription.

RADIO -CRAFT 20 Vesay Street New York, N. Y

ì RADIO -CRAFT RC -840 20 Vesay Street, New York, N. Y. Gentlemen:ee subs remittance for e `tEnclosedr subscription RADIÓ CI AFT for One Year (12 Issues). Send me FREE. ELEC. TROPLATING OUTFIT (Canada and $2.851. In SOC additional to coy shipping ryes óaddi only

O New Subscriber O Extend Present Subsertetton

Name

Address

City State (Send reittnce money un- model BB -96. A combina- usedus U. S mPostage btamps.k Register letter if YOu LAFAYETTE cash or Memos.)emos.) tion which includes a high -fidelity radio, resembles the breastplate ar- recorder and playback equipment. The CLOSELYrangement used by telephone operators.

116 RADIO -CRAFT for AUGUST, 1940 LATEST RADIO APPARATUS

Enables the operator to have both hands "BREAK -IN" SWITCH free. Adapted for sound trucks, mobile transmitters, etc. Its frequency response is Atlas Sound Corp. ample for all usual requirements; the out- 1447 39 St., Brooklyn, N. Y. put is 48 db. below 1 V. per bar. Known as model N -3. Weighs less than sfs- lb.- Radio- Craft A WHOLE BOOKFUL

F.M. -A.M. MASTER ANTENNA ÌuN THE BIG NEW Technical Appliance Corp. 17 E. 16 St., New York, N. Y. LAFAYETTE CATALOG

It:".. MYSTERY Oscillator with hand microphone Now - enjoy your record player through your rodio without a wired connection! Simply plug in output of crystal pick -up to the oscillator. HIS switch This 'broadcasts" to the radio offers in a single unit both which picks up and reproduces the music with all its original 11"on-off" and press -to -talk operation. The tone and brilliance. To conduct a "broadcast" of your button is pressed to talk; and turned, to own, connect to oscillator the hand mike offered with the shut off the mike. Designed to modernize complete unit. For 110 volts AC and DC. Complete with ALTHOUGH usable A.M. (12A71 for receivers, mikes which do not have close -at -hand tube and hand mr'k e a t this.a specs I low price :2,95 this system provides for an expanded switches.-Radio-Craf t frequency range to include F.M. reception. The use of iron -dust cores permits full Complete Battery Kits for POCKET MULTIMETER isolation of primary and secondary trans- Popular Portable Radios former windings without loss in signal Supreme Instruments Corp. strength; 15 to 25 receiver coupler units Greenwood, Miss. Exact duplicate replace. may be fed from 1 master antenna.-Radio- ment battery kits for the Craft most popular portable battery radio sets on the market today. Replace the NEW SQUARE METER originals exactly; both Burton- Rogers Co. physically and electrically. Offered at new low prices! 857 Boylston St., Boston, Mass. You save on every purchase. Shpg. wt., each kit, 7 lbs. K20173 -KIT "A" SALE PRICE ..,.sZeS K20174 -KIT "B" K20175 -KIT "C" K20176 -KIT "D" ANY ABOVE, SALE PRICE EACH :2.49 K20177 -KIT "E" SALE PRICE ._...sje %5 KIT "A" FOR FOLLOWING SETS: Emerson CE259: Philco 39. 71T, 72T, 74, 504; Pilot TH I I, THI2; RCA 948P80, 94871, 94BP4, 94BP64, 948P1, 966A. 94BP66; Zenith 4K400D, L, M. S, Y, 5416. MODEL 543. A small -size pocket multi - KIT "8" FOR FOLLOWING SETS: Emerson C263. C1275, CX263, meter using a 3 -in., 1 -ma. meter. Single CX283, CX284, CX305, rotary selector switch provides functions DC308. CE265, CE275, Pilot H11, H12; General Elec. and ranges of: Resistance trie GB400, HB408. -0 /2,000/200,000 KIT "C" FOR ohms; D.C. -0/6/60/600 ma.; FOLLOWING SETS: A.C.- 0/15/- General Electric JB515, JB508, HB412: Pilot T 1351, 150/600/3,000 V.; D.C. TYPE 600. A 4% -in. square molded case -0/15/150/600/3,000 11451. TI452, X1451, X1452; RCA BP55, 56, 85. meter which provides for illumination if V. Batteries are self -contained. Ranges at KIT "D" FOR FOLLOWING SETS: desired. The face is open, the corners are 1,000 ohms /volt (standard) sensitivity.- Emerson DF306, DF302, DJ3I0, DJ3 I I, DJ312, EA338, Radio -Craft EA339, EÁ340, EÁ357. rounded. Circular back is 2% ins. in dia., KIT "E" FOR FOLLOWING SET: 11/16 ins. deep. The movement has an Majestic 130. accuracy of 2 per cent; sensitivity 42 mc. at DOUBLE -TUNED 1 ma. Scale is 3',F ins. long.-Radio -Craft I.F. TRANSFORMERS BUY BY MAIL OR IN PERSON At one of our 7 convenient stores. Either way you're Rades Corp. sure to get better service- grooter value. DELUXE "TEL- OHMIKE" 1733 Milwaukee Ave., Chicago, III. Sprague Products Co. 100%11h Ave., New York, N. Y. 901 W. Jackson Blvd., Chicago, North Adams, Mass. Ill. 265 Peachtree St., Atlanta, Ga. 110 Federal St., Boston, Ness. 24 Central Are., Newark, N. J.

542 E. fordham Rd., Bronx, N. Y. 90 -08

166th St, Jamaica, E. I.

THE instrument includes a built -in volt- DEPT. 3H -100 SIXTH AVE.,NEW YORK, N.Y. meter and milliammeter with switch and I ENCLOSE f RUSH ATTACHED ORDER pin -jacks for external measurements. Meter ranges, selected through an 8- position PLEASE RUSH NEW FREE CATALOG Na. 80 switch, are 15, 150, 500, 1,500 V., D.C.; and, 1.5, 15 and 50 ma., D.C. The instrument NAME tests all condensers and resistors, and indicates "intermittent -open" condensers and THESE units duplicate electrically I.F. ADDRESS resistors. Balance is indicated on an "eye" transformers used in the majority of CITY ._.. . STATE tube. -Radio -Cra f t receivers. Provisions are made to bring the RADIO -CRAFT for AUGUST, 1940 I17 LATEST RADIO APPARATUS

gridleak out from either the bottom or top PLUG -IN ELECTROLYTICS OPPORTUNITY AD-LETS may be mounted of the shield can. The unit Aerovox Corp. Advertisements in this section cost L. trot, either by the top or bottom of the can. Only for each insertion. Name, address and initials must New Bedford, Mass. be included at the above rate. Cash should accmn- 3 different units are required to cover prac- pony ail clmlfied advertisements unless placed by an accredited advertising agency. No advertisement tically all intermediate frequencies. Type A for less than ten words accepted. Ten percent di- has a range of 150 to 250 kc.; type B, 240 count for via luuw, twenty percent for twelve lettres Objectionehle or misleading advertisements not a to 300 kc.; type C, 430 to 500 kc. Radio - rented. Advertisements to' August. 1910, issue mo., reach us not later than June 7th. Craft Radio -Craft 20 Vesey St. New York. N. Y. PORTABLE RADIO BATTERIES AGENTS WANTED Bright Star Battery Co. 300% PROFIT SELLING GOLD LEAF LETTERS FOR Clifton, N. J. store windows: Free samples. Metallic Company, 451 North Clark, Chicago. SEVEN new types AMPLIFIER DIAGRAMS of portable "A" und "B" batteries 10 MODERN CIRCUITS OF 8 TO 84 WATT EASY to -build high -fidelity amplifiers. All tor 20e. Send coin are added to this or stamps. Amplifier Company of America. 17 West 20th Street. New Vont City, N. Y. company's line which now 4 BOOKS AND MAGAZINES comprises types of 45 -V. "B" ASSURE YOURSELF OF GREATER PROFITS BY and the fol- doing radio service Jobs more quickly. Authentic service batteries guides show lorate and correct troubles lowing "A" cells and any radioy receiver. Official adio Sice Manuals show you how to complete more repair Jobe to batteries: 6 types of lass time -how to earn more money by faster servicing. 1';4 V., 1 type, 4'z Read the advertisement which appears on page 120 of thls V.; 4 types of 6 V. PERMITS electrolytic to be instantly re- WE HAVE A FEW HUNDRED RADIO ENCYCLO- and 1 type of 7% V.- providing replace- moved without tools or trouble, for test- lwdias, by S. Gernsback. second edition, originally said ments for a good percentage of portable ing and replacement. Now used extensively at $3.95. Book has 332 pages, weight 3 tbs.. tine 9 a 12 Inches. Red morocco- keratol flexible binding. Send radio receivers.-Radio-Craf t by the U.S. Signal Corps and for aircraft $2.411 in stamps, rash or money order and book will be police radio and sound system equipment forwarded express collect. Terhnlfax, 1911 So. State Street. Chicago, Illinois. DYNAMIC CUTTING HEAD where continuity of service is important. Available in etched foil and plain foil, in 2 BUSINESS OPPORTUNITIES Sound Apparatus Co. can diameters, 1 -3/8 and 1 -5/32 ins., and AMBITIOUS? EXTRA MONEY SHOWING TALKIES 150 W. 46 St., New York, N. Y. -home or neighboring towns -no im- estment -snund equip- by the U.S. Signal Corps and for aircraft, ment- Ilims rented reasonably B100 -$300 monthly possible DESPITE its small size of 1 x ltz x 2 in heights from 2% to 4% ins.-Radio- -wonderful opportunity. 512 State Theatre Building. Pittsburgh. Pennsylvania. ins. and its light weight of 7 ozs., this Craft EDUCATIONAL COURSES cutting head, designed on the dynamic principle, has comparatively high efficiency NON -INDUCTIVE RESISTORS USED CORRESPONDENCE COURSES AND EDUCA- (1 -W. Its damping is obtained en- tlonal books bought, sold, rented. exchanged, catalog tree. driving). Mfg. Co., Inc. V. W. Vernon, Reneger. Alabama. tirely by air which results in extended f re- Clucci's, 285 N. Sixth St., Brooklyn, N. Y. CORRESPONDENCE COURSES BAND EDUCATIONAL quency range which is claimed to be 9,000

Jette. eatlafacllon guaranteed. Cash paid for used courses. cycles. Its impedance is 6 ohms and can be Complete details and bargain catalog FREE. 3 \rite Nelson readily connected to any loudspeaker (low - Company, 500 Sherman. Dept. II -2242, Chicago. impedance output). The impedance does not ELECTRICAL SUPPLIES vary with frequency which is said to elim- FLUORESCENT AC DAYLIGHT LIGHTING FOR inate matching problems.- Radio -Craft desk; office; windows; home. latest sensation. 5O ' dis - count. Literature FREE. McGee Radio. F-2073. Kansas City . 31n. REPAIR KIT MANUSCRIPTS WANTED "FLOCKING" Stromberg-Carlson Telephone Mfg. Co. WANTED -MANUSCRIPTS, POEMS. SONGS FOR Publication. Portnoy's. 87 Fifth Ave.. New York. Rochester, N. Y. PRINTING LOCK" is the fuzzy. suède -like finish 125 - 81/ax11 BONO LETTERHEADS AND 125-4% I used on many phono turntables and in envelopes. $1.00 postpaid. Letterheads, envelopes, state- Carlson receivers (in the in- ments: 300 -$1,00. Itennesille, 907 Rest Roosevelt, Phila- Stromberg- delphia. teriors of cabinets), partly to act as a ERIES Z. These are wire -wound units noise RADIO finish and partly to help absorb the S -necessary in many special applications that comes directly from the needle. This -available in the following values: 10 W., RADIO TESTING EOUIP- WE BUY AND SELL USED ( gun, jar of binder. brush, a 25 W., ment. Time payments If desired. Harold Davis. Inc., kit "flocking" maximum resistance 3,000 ohms; Jackson. Miss. supply of green and brown flock, and in- 7,500 ohms; 50 W., 12,500 ohms; 100 W., DO YOU WANT A GOOD CAR -RADIO SET? HERE'S structions) is designed for the repair of 25,000 ohms. For Iii these power ratings chance to get an Arvin. List, about $80; sell for $21. "flock ". It is known as Push -pull output affords high quality and power; set I. damaged or worn multiply the maximum resistance available selective and very sen,itive. It. Bernard. 40 Manning Ave.. No. SD- 210. -Radio -Craft by 4.-Radio-Craft No. Plainfield. N. J. ATTENTION DEALERS, SELL WRIGHT SPEAKERS. WARD -LEONARD relays, reaiaors. CONSOLIDATED VIBRATOR POWER SUPPLY POWER TAP SWITCHES YOLl'MF; CONTROL:. SUPREME INSTRUMENTS. Illinois CONDENSERS. Gernsback, Manuals, Sentinel FOR PORTABLES Ohmite Mfg. Co. Radios. Send for catalog. Anchor Radio Distributing. Dryden ltd.. lutera, New York. Electro Products Labs. 4835 Flournoy St., Chicago, Ill. 549 W. Randolph St., Chicago, Ill. HARD -TO -GET RADIO DIAGRAMS. TRY USUAL7- sourees tiret. If you can't get then, try us. Price, to $1.50 if w succeed: no charge it we don't. You lose nothing! Send no money-write first giving fullest information. Enclose return -addressed, stamped envelope We have helped many Servicemen, experimenters ano radio fans. We nmay Iwlp you. Allan Stuart. P.O. Box 56. Teaneck. N. J. STAMPS

THREE SCARCE SETS. NOW OBSOLETE. 25e. WITH new customer, gift; Box III, Malden. Mass. TECHNICAL ART SERVICE DRAFTING AND ART SERVICE -A COMPLETE Service for tilo Indutrlal and Commercial Marketers. If your business or plant can't afford a designing or drafting staff, don't let this stop you from going ahead THE Synchro model Q (model R, for 2 -V. with that new product you intend marketing. or that catalog of mechanical or electrical items which needs sets) "A -B" power supply operates from fine detailed drawings and highly retouched photographs. Any mechanical, electrical or radio problem can be solved any 6 -V. D.C. power source (drain, 0.75 -A.). for you by our associated staff of designers. draftsmen Supplies "A" and "B" voltages to 1% -V. and artists, and technical copywriters. write for any additional information as to methods and price for this receivers of 4, 5 and 6 tubes -without cir- service. Tee-Art Drafting Service. 228 Charlotte Terrace, 51b. x 5 x 2% Roselle Park, N. J. cuit changes. Measures ins. Separate plug-in sockets provide correct HIGHER ratings have been set for each SCHEMATIC DIAGRAMS -DRAFTING-SEND US A 5 current tap switches re- rough sketch of your circuit. Estimates by return mail. filament voltages for the receivers; 90 V. of the high- Our prices are moderate; our work guaranteed. No jobs of "B" at 18 milliamperes are provided. - cently announced. Model 111 is rated at 10 inn big or small. Vm. Kadierek, Jr., 440 East 8511h St., 15 A., 150 V. New York, N. Y. Radio -Craft A., 150 V. A.C.; model 212 at

118 RADIO -CRAFT for AUGUST, 1940 LATEST RADIO APPARATUS A.C.; model 312, 25 A., 300 V. A.C.; model cuits result in exceptional performance. - 412, 50 A., 300 V. A.C.; model 608, 100 A., Radio -Cra f t 300 V. A.C. These ratings apply to A.C. VeaL circuits operating at any power factor. MARINE RADIO TELEPHONE v Units are single -pole rotary selectors, txtW multi -point, load- break, and non- shorting.- Jefferson -Travis Radio Mfg. Corp. Radio -Cra f t 198 Milburn Ave., Baldwin, N. Y. 0 ' ' tG III TILITY" mod- Plaices ' "B "- BATTERY -LESS el 80. A crys- 4tiowee.t tal- controlled 5 to NEED THIS ttBOOK "4 -WAY" PORTABLE 7 W. marine radio YOU wituttater Setchell Carlson, Inc. telephone for use you au't alt ird to be Serviceman. . If y'Ú11 re a 2233 University Place, St. Paul, Minn. on all types of P.A. Man. AmateuoOs blggea rnmplrtr small sail and pow- n's the today -your it"' Catalog mn er boats. Designed Guide to real matey-aarinee. nullo hits - for short -range so New Sets. Beal .t'smeri and ann service on a sin- Europe reception new . nI,pact!: plastic phonons;et gle, fixed -frequency comblnbtions: etc. h, Ine recorder sys channel such as 18 New Sound New P.A. watts Ele;- ship -to -ship. Nor- tents -7 to 75 -for tal ?. O cheatras. tioueering. R idea,. mal range, 25 miles. Churches. etc. New Schools. new Consists of a radio transmitter, receiver, - new applications- prices -Time l5Ylnert Offer. etc. power pack, loudspeaker and microphone.- - Pay Trial Teel Fquip- Radio -Cra f t Servicemen. New niire trot000nVualitYtre- than $perlai placemente parts. 31g CUTTING NEEDLES Section. APORTABLE radio receiver, model 66, Bargain for Builders. Count on AI.LIF.D which operates from (1) a self -con- Recoton Corp. new kits and builders' tug all the yourlepnnO tained "A" battery (as a portable on out- 178 Prince St., New York, N. Y. p11Ì1EDoa8c Sp p F.D ings, etc.); (2) 110 V., A.C. (home or cot- Headquarters because Aid.i . tage); (3) 110 V., D.C. (office or hotel); is the. 1 0 1 1 ' or (4) 6 to 8 V., D.C. (car or boat). No "B" batteries of any kind are used; vibrator unit furnishes "B" power from the "A" supply.-Radio-Craftt WIND -UP AUTO ANTENNA MADE of Swedish steel alloy, and dia- mond -dust polished to a perfect cut- ALLIED RADIO Radiart Corp. CORP. ting edge, these needles give exceptionally 833 W. Jackson Blvd., Dept. 2 -H -0 Shaw Ave., at East 133 St., Cleveland, Ohio quiet performance. Each needle has a flat Chicago, Illinois KNOWN as the Ro -Tenna this auto -radio portion on the shank, making it impossible Send your FREE 1945 Radio Supply Catalog. antenna is a mechanical wind -up aerial to insert it at the wrong angle.-Radio- Name which is controlled entirely from inside the Craft Address car. A handy knob raises or lowers the Lefty aerial to the exact height desired for peak NEW ACORN SOCKET State reception or for clearing overhead obstacles. Hammarlund Mfg. Co., Inc. -Cra f t -Radio 424 W. 33 St., New York, N. Y. MOD EL ELEMENTARY 5 -10 METER CONVERTER U H S -900. These sockets Browning Laboratories, Inc. MATHEMATICS 750 Main St., Winchester, Mass. are designed to clamp the acorn MODEL BL- tubes so they EASY - SIMPLIFIED - PRACTICAL 510. A com- do not work pact 5 -10 meter HERE is a book for the business man, the tech- loose. Contacts nician and craftsman explaining and answering converter for re- are silverplated every operation and meaning with Interpreting ceiving 2 bands Illustrations and examples. beryllium. Sock- It Is the key to a simple understanding of many o f frequencies et has a metal perplexing problems in daily life. when In clear. positive and definite language. the author used in shield for use popularizes and clarifies every subject and helps the conjunction with reader to overcome any apparent difficulty in the study with the pen- ofmmathematics. any mobile, home, tode -type acorn A real home study -course in mathematics for the or aviation re- student or the man who nts to achieve proficiency tube. The base is made of super- Isolantite, or desires to brush -up on whis knowledge. ceiver; 4 separate called "Iso -Q". Size, 1 -9/16 ins. dia., 1 -3/16 Entiire (hop r n Speriof Math. O_ ties nor tfehe Radio low -loss tuned cir- ins. mounting centers.- Radio -Craft Technician CONTENTS OF BOOK CHAPTER I. Aran metic- Addition- Subta'action- llultlpll to CXq -DPet ma sn Percentage-Ratio-and rPoporionettone III. The MetriceaN system. A Radio "Harn" Writes to Radio -Croft CHAPTER IV. now Geumet.l to Measure Surfaces and Capacity CHAPTER V Powers and Involution -Roots and lion. Snobs. CHAPTER I. Mathematics /or the Man. d T rte Tit r thms-Ua Curve1ePlotconversionsi o[arlihma -Uw of onte Fenton, Michigan the Slide Rute special for 105 Pine Street CHAPhER.Radio csnathematics Calculations- íoe "Dave," a member CawiIIn do Curlat POSTPAID of Arithmetic.eetCisouaCSt-Dcnts the Short Wave League, CHAPTER IX. W Wit d M is i d in radio sets Useful Tables. that 'Practical Muthemalic." M, rarried Cradi! you parka. will enable him fo Send use some of those older Stamps, Cash or Money ' Order. tubes he has on hand, we SWL should judge from his TEC HNIfA\X card. However, back is- 1917 S. State St. RC -840 Chicago, III. sues of Radio -Craft con- Date 4.1.._a2,44o tain circuits using older stati equipment; most readers YOU ARE WELCOME prefer to learn how to Your Report foR, wean[ . . .tt A.Q -s+`^ - -tee. .tyA apply the new tubes as to one of our fine Illinois Time -Tested rapidly as they appear Tubular Paper Condensers, free and -or sooner! My Receiver _ , 4PI- 6c6 -70 postpaid, if you'll just send us the name of your jobber. Write NOW I QSL ße David Stiff I/41vr ILLINOIS CONDENSER CO., Inc. 1160 N. Howe St. Chicago, III. RADIO -CRAFT for AUGUST, 1940 119 Tot ßtt - ` of ßiqet Ptc t ti - USE GERNSBACK MANUALS AND BOOKS!

3ERVICUV(a W9TM SlrANAMFZF. v eL- °!T1it0eJ

SINCE 1931 Servicemen have been buying RADIO -CRAFT LIBRARY SERIES more GERNSBACK OFFICIAL RADIO Get into the swing of reading instructive, authoritative books on technical SERVICE MANUALS year after year. The au- subjects-radio. air conditioning and refrigeration. It's the easiest, quickest thentic material, easily accessible diagrams and and most inexpensive way to improve your knowledge on these topics. In this series, popularly known as the RADIO -CRAFT LIBRARY SERIES. complete service data make them invaluable are all the titles necessary to your personal advancement. Only by careful to dealers and radio Servicemen. Without a study of these enlightening books, can you gain adequate experience in and refrigeration. Each book is uniform. at the job, there's time fields of radio, air conditioning Gernsback Service Manual repair The volumes measure 6 x 9 inches -contain 64 pages. and have stiff. and profit lost. Your service kit or laboratory is incom- flexible covers. PRICE 50c PER BOOK. All books are sent to you postpaid. plete without all the GERNSBACK OFFICIAL RADIO SERVICE MANUALS. There are GERNSBACK MAN. UALS for servicing auto- radios, also refrigeration and Here Are The Titles: air conditioning equipment. Book No. 2 Book No. 16 MODERN VACUUM TUBES PRACTICAL RADIO CIRCUITS

VOLUME 1 OFFICIAL RADIO SERVICE MANUAL `.neOI tXU12'i Net fiián Book No. 3 Book No. 17 0lle. LóOgleafg cor.rover ire z le at ANALYZERS 104j tbs. e' THE SUPERHETERODYNE BOOK SERVICING WITH SET

Book N- o. 18 Book No. 6 POINT -TO -POINT RESISTANCE BRINGING ELECTRIC SETS 1936 OFFICIAL RADIO SERVICE MANUAL ANALYSIS Over 1,200 reges e :vor 2. 500 llluslrationa e c iff. Leather- $7.00 UP-TO-DATE ette. Looseleaf Coeerx tee .t x 12 loche. e Net Weight S Ibs. Book N- o. 19 Book No. 9 PRACTICAL RADIO KINKS AUTOMOBILE RADIO ANO AND SHORT CUTS 1935 OFFICIAL AUTO -RADIO SERVICE MANUAL SERVICING tUr Loe eCoer eSS°0 xIeh e l $2 .50 Book N- o. 20 Book N- o. 10 THE CATHODE -RAY OSCILLOSCOPE HOME RECORDING AND ALL ABOUT IT Rook No. 21 RADIO SERVICE MANUAL 1934 OFFICIAL Book N- o. 13 BREAKING INTO RADIO SERVICING Over 400 rage% Over 2.000 Illustrations Flexll.le. leather. Leeseleaf Covers Size 0 a 12 Inches Net Weight $3.50 ABC OF AIR CONDITIONING ttte.y tbs. Book No. 22 Bonk No. IS NEW RADIO QUESTIONS POCKET RADIO GUIDE AND ANSWERS 1932 OFFICIAL RADIO SERVICE MANUAL Over 1,000 Pages 2.000 Illustrations FIexn\e. Wete. LooselefaOver rovers. size . Book No. IS Book No. 23 Weight lbs. ABC OF REFRIGERATION PRACTICAL PUBLIC ADDRESS

OFFICIAL REFRIGERATION SERVICE MANUAL EACH BOOK IN THIS SERIES -50c IVolume Ill r 952 rage. e Over aun Il lnxtrato,ii. Flexible. Loather. $5.00 elle. Looseleaf Covers. Site 0 X 12 Inc bese Net Weight Ily Ibs. I- RADCRAFT PUBLICATIONS. Inc., 20 VESEY ST., NEW YORK. N. Y. I Gentlemen: Enclosed find my remittance of E for which send me. POSTPAID, t the Manuals or Books indicated below by a cross Ix) In the panel. OFFICIAL AIR CONDITIONING SERVICE MANUAL Volume 7 @ 610.00 ( ) 1936 Manual @ $7.00 ( ) 1934 Manual @ $3.50 el. ?.. OXII12 a Ñiiglci 21 ) 1935 Auto - Manual @ $2.50 ( ) 1932 Manual @ 65.10 senee. 14,0teleafco e nchtx Net íl bs. $5.00 '( Manual (1 Relri ion Manual (Vol. 2) @ $5.00 1 ) Air Conditioning @ 65.00 I famous Manuals, see or Write to '( To order these RADIO -CRAFT LIBRARY SERIES @ 50c EACH ' your jobber or favorite mail order house. If more Circle hook numbers baffled: 2 3 Ii 9 10 13 11 13 I.I 17 15 19 20 21 22 23 convenient, mail coupon directly to publishers. IName Address I I Cl,y State ' RADCRAFT PUBLICATIONS, Inc. (Send re ittanee in form ef cheek or money order: register year letter Stamps.) RC.s4n NEW YORK, N. Y it you send euh or unused U. S. Postage 20 VESEY STREET a L

1 9 4 0 120 RADIO -CRAFT for AUGUST, ENGINEERING

SOME RECENT ENGINEERING DEVELOPMENTS MOST difficult to appraise are contribu- SUPER BARGAINS tions of research to any one year's Practically all of the attractive items listed here are brand new, others are reconditioned like new: but ALL are advances. Major in PERFECT WORKING ORDER. In many cases, the parts alone total snore than the price we are asking. advances from the labora- 100% satisfaction guaranteed or your clones refunded. tory may be reflected in a product commer- ORDER FROM THIS PAGE. Use the convenient coupon below. Include sufficient extra remittance for parcel cially introduced during the same year, post charges, else order shipped express, collect. Any excess will be refunded. C.O.D. shipments require 20% but deposit. If full remittance accompanies order, deduct 2 °ó discount. Send money order, certified check, new U. S. it is much more likely that the research and stamps. No C.O.D. to foreign countries. fundamental engineering will be more ap- ORDER TODAY LIMITED QUANTITIES PROMPT SHIPMENTS ASSURED parent in the products of future years. In the research and other laboratories and in G.E. INDUCTION DISC MOTOR FOR RECORD- AMAZING BLACK LIGHT!! the engineering departments, investigations ING PLAYBACK AND DISPLAY PURPOSES Powerful 300 -Watt Ultra -Violet Bulb continue unabated- investigations in some Sobs( ant ally constructed The best and most prac- cases reflected in a product commercially by General Electric, this tical source of ultra-violet ball -bearing notor is light for general experi- introduced during the year, but most com- high-quality mental and entertainment phonograph se. Makes all fluorescent monly apparent in technical- society papers unit. Its power and smooth - tinningting make excellent home substances brilliantly lumi- and presentations and, for the moment at work. speed. nescent. No transformers of Its any kind needed. least, more quickly recognized as pure or governor -controlled. Is vari- Fits any able both below and ¡those .tandarrl lamp socket. Made with special glans unapplied science. 78 r.p.m. For 110 sollo. GO filter Per- Sold less mitting o n l y ultra- violet To describe all in cycles, A.C. turn- rays of these developments table and Cheft. diame- to cane through. Brings 74' out beautiful opalescent hues a single field, or even a few in a number ter x 5%. high. Shp. Wt. il serious lbs. Packed In Original Box. in types of mate- of related fields, would consume more space rials. Swell for amateur ITEM NO. 81 parties, play's. etc., to ob- than is here available. However it is possible YOUR PRICE $3.95 tain unique lighting effee s. Bulb only. Size of bulb. to brief some of the most interesting en- Shp. Wt. I lb. ITEM NO. 87 gineering developments made during a lim- SUPER SPECIAL YOUR PRICE $2.00 ited period by a single research group. 3%2 R.P.M. SYNCHRONOUS MOTOR Description of the unusual photoelectric 110 Volt, 60 Cycle There are 101 uses for a eyn- A.O. only SUPER MAGNET tube here illustrated therefore affords an chronous motor making only 31/2 revolutions per minute. Ideal for LIFTS MORE THAN 20 TIMES opportunity to mention, for such interest as crowil-catching store-window dis- ITS OWN WEIGHT it may hold for technicians, comparatively plays, agitating filin-dcveluping tanks. as an electric winch on recent developments of General Electric model motor boats, as derrick LITTLE GIANT MAGNET. Lifts motor In erector sets. etc. Built- 5 lbs. easily. Weighs 4 oz. Made Company. of new high -magnetic in high -ratio step-down gears ALNICO provide amazing amount Of steel. Complete with keeper. power. Made by !Milton Mfg. World's most powerful magnet ever t'o. of Waterbury. made. The experimenter and hob- r In diameter z a" x 1" thick of overall. Shp. Wt. 2 lbs. byist will find hundreds cellent uses for this high quality ITEM NO. 76 permanent magnet. Measures lei" YOUR PRICE $1.95 z '!4 ". Shp. Wt. 3a Iba.

ITEM NO. 86 A.C. "SQUIRREL CAGE" SYNCHRON. MOTOR YOUR PRICE $1.00 Stif -st arting shaded polo motor designed for radio classic for l'usi, Mutton 'riming. 111gh speed, power- BRAND NEW! ful. One lubrication lasts lifetime. BATTERYLESS BIKE -LITE Excellent for model railroad trains. small boats. humidifier water PUMPS. rte. !4' long shaft, 3/16" diameter. Complete with brass amounting posts. 2'4" a 2' a 2i1" overall. For 110 volts, 60 cycles, A.C. only. Shp. Wt. 4 lbs. ITEM NO. 77 YOUR PRICE $1.35

MECHANICAL FLASHLIGHT l'an be InstalLd i .e f.w This batter ^Ire. flash - minutes on any ',5 , 111kr- light generates Its a Llte throws an ieusise brain power merely Cry Drees of light when bike Is in m log handle. Gives strong lion. Absolutely no batteries light whenever needed. needed -- to replace. Coal, nothing to main- Cats nothing to Operate! tain. Amazing new Bmall, built -in generator, turned by the bike wheel miniature dynamo op- subpar -s lug current. Most economical headlight erate, liar hl ight. Pocket yet. Guaranteed for lasting performance. All metal size. a 4%" 2" a 1" Shp. wt. 2 lbs. constructionc netrnctlmr wltli beautiful silver finish and polished ITEM NO. 88 cbrom tum- plated reflector. Armature operate. with a YOUR PRICE $1.70 powerful Alnico General Meetric permanent magnet. Measures 4' a 5'0'. Umplete with bulb and Instruc- wt., 3 FOR tions, ready to attach. Ship. lbs. MOTOR ROTATING RADIO ITEM No. 90 BEAM ANTENNA YOUR PRICE $2.10 One Revolution tar Minute (luis by Honeywell a temperature reg- SEWING MACHINE MOTOR ulator for coal fired For electtuying foot -trea- Window "bubble" passes U.-V. rays to sodium furnaces but ideal for dle sew hie machines cathode. manyany ther unes. replacing burned -out molars especially for rotating on electrified machines. Pow- beam antennae on the erful and high- speed: nu- uof for directional toeraps Other uses. Ideal as Electronics.-To start, we analyze the beaming and recep- handy grinder -polisher mo- outstanding feature of the bubble -window tion of radio signals. tor. Small, compact, flat on Built - in commutator 1550 sides, requiring a mint - tube here illustrated. The window which is switching permits mum of space. Speed con- turning antenna from trollable by foot-pedal rheo- only 0.002-in.-thick is made of special ultra- north -smith to east- stat )available optionally for violet- transmitting glass which passes light, west ti ieet.. i remote point. Constructed for hard 83.75). Its !4" diem. shaft sere. IL, d ,hafts geared down to about one Is available with or without 110 Volts -A. C. or D.C. at wavelengths up to 2,500 A.U., to a sodium revolution her r note. Ideal for window displays and Pulley (pulley Ile extra). cathode. A tube of this construction re- other simv a. mechanical motions. 110 sotte. 60 Completely enclosed and dirt proof. Measures 3!e" x 5' x cycles. A.C. may. C'¢" a G'z" a 4'4'. Shp. Wt. Ill lbs. Y overall. Shp. Wt. 7 lb,. places a more expensive quartz -bulb tube. ITEM NO. 82 The new tube may be used in mercury - YOUR PRICE $5 97 5 YOUR PRICE (motor only) $3.75 vapor detection, and the measurement of low -pressure mercury germicidal lamps. HUDSON SPECIALTIES CO., 40 West Broadway, N. Y. C. Metals. -By utilizing a steel sheath, to WE HAYE NO CATALOG. IT'S EASY TO ORDER -CLIP COUPON -MAIL NOW ORDER FROM THIS PAGE direct the magnetic flux against the keeper, around an alnico pellet using a new grade HUDSON SPECIALTIES CO., 40 West Broadway, Dept. RC -840, New York, N. Y. of alloy called Alnico IV, made by the I haro circled below the numbers of the Items I'm ordering. My full remittance of 8 (Include powder shinning charges) is enrhoe,I. process, it is possible to lift a weight OR my deposit of 8 is enclosed (220'2 required). ship order C.O.D. for balance. (New U. te. stamps. approximately 1,500 times heavier than the check or money order accepted.) magnet. Circle Item No. wanted: 76, 77, 79, 81, 82. 86. 87, 88, 90

Printing. -There was produced a photo- Name Address electric system of color register control whereby registration of 4 colors can be CIIy State maintained automatically within the toler- Send remittance by abed k. stamps or money order; register letter if you send rash or statnie.

RADIO -CRAFT for AUGUST, 1940 121 ENGINEERING

ance permissible in Intaglio or rotogravure coil system. printing when operating at web speeds of This feature of design, together with the 1 approximately 1,000 feet -per- minute. Paper use of freon gas as an insulating medium, Signal loss is greatly reduced and the quality of results in a big saving in size and weight. the product is considerably improved by this Diagnostic X- Ray. -An important addi- use of the "electric eye." tion to the family of G -E Coolidge X -ray Chaser The control system incorporates 2 photo- tubes is a diagnostic unit. Shockproof and electric scanning heads for each color unit. oil-immersed, this tube unit is much more One head is aligned to scan the margin of compact and lighter in weight than its A 1.D \\ acti- ril !rm.! that flits the web, on which equally -spaced register predecessors. It is the first diagnostic tube servicing liulr and coat. or index marks are printed simultaneously to incorporate an oil- cooled cathode for ton ran: make stage analysis tests (signal with the 1st color impression. The 2nd head rapid removal of heat from this structure, chasing) of all RF. IF is arranged to scan a disk attached to the thereby eliminating cathode -gas problems to and AF stages; voltage. resistor and con- printing cylinder. Should the printing improve tube performance and increase denser tests; locate cylinder be back of working men -made interference; slightly ahead of or capacity. check for polarity. hum, true register position, the impulses from new X -ray AC and DC trwdinuity. Fluoroscopic X -Ray. -The and many, many other one head will be correspondingly ahead or Tire -o -scope shows the car owner where tests. May be used on back of the impulse from the other head, all sets, including tele- and why a "puncture" or "blow -out" may rislon and frequency causing an unbalanced condition in a "mix- occur. Without removing the tires from the plmlulat ion. ing panel." A correction is then automati- automobile, a service station or garage cally applied by a reversible pilot motor in operator now may, by X -ray, look into the LOCATES MAJORITY OF ALL response to the corrective impulses from tire to detect breaks, bruises, cord separa- ORDINARY SERVICING TROUBLES the "mixing panel" relayed through close - Employs ta tions that are otherwise hidden, and such 101., /II la i e. foc l -r f ONLY coupled thyratron power tubes. foreign material as tacks, nails, wire, a ts make n usable anywhere. screws, glass, and stones imbedded in headphone (audio, and neo $14.9 5 Therapeutic X- Ray. -A new gas-insu- the tube Comc(visual. indication uses lated 1,000,000 -volt X -ray therapy apparatus casing. The driver is assured that his tires teats. light weight. batteries: es s potable: 10 x3t x3 Ins. Ano nes. utilizes a transformer designed to operate at are safe, or is given warning with definite resonance, thus eliminating the iron core proof that tires are unsafe and should be ALLAN STUART and permitting the multisection X -ray tube replaced or repaired to provide safe riding. P. 0. Box 56 Teaneck. N. 1 6 to be placed in the center of the transformer Varnished Cambric Insulation. - Heavier loads may be used, higher voltages WARNING TO RADIO -CRAFT READERS withstood, and more severe operating conditions met with a new varnished cambric Radio -Craft has no representatives in the field soliciting subscrip- for cable insulation. Similar in appearance tions, in the "door to door" fashion. Pay no money to any person who to the black (or "Empire " -Ed.) cloth pre - comes to your home, store or service shop and represents himself as %iously used, the new high- temperature being an agent for Radio -Craft. Subscriptions may be safely obtained varnished cloth permits cable to be operated only from authorized subscription agencies, whose names we shall at a maximum copper temperature approxi- be glad to furnish, or directly from us by mail. Address your letter to mately 10° C. higher than the old cloth. It Subscription Dept., Radio -Craft, 20 Vesey St., New York, N. Y. also has lower dielectric losses, and is as good or better in all other respects than the old type of cloth. Llecttic l7tyS'havet Carrier Current-Communication. - get In the standard line of single- frequency simplex and 2- frequency duplex communication equipment the incorporation of auto- ABSOLUTELY FREE! matic modulation control has not only increased the range of communication by raising the strength of weak modulating signals JUST THINK OF IT -you can get absolutely but also prevented cross -modulation on FREE, the useful DRY ELECTRIC SHAVER closely -adjacent channels. which is shown at the left. This ELECTRIC DRY SHAVER is sent to you by the publishers Need for expensive dial- calling methods with a one -year subscription to RADIO- CRAFT. was reduced by the introduction of a 60- cycle code -bell calling system, similar in Han Are the Features of The performance to standard metallic magneto ELECTRIC DRY SHAVER calling and employed in place of loudspeaker Constructed of metal with attractive red bronze voice -calling. finish. Scientifically constructed to give a perfectly clean shave. 5 -foot rubber insulated cord and plug. Carrier Current Trans- Constructed to Relaying. - last for many years. - mitters and receivers were developed to Operates from I10 -volt. 60 -cycle A.C. elec. for trie line. Carries a two -year manufacturer's facilitate use of the same channel sim- guarantee. A fine quality. self sharpening plex point -to -point communication, control, toilet necessity. or telemetering in addition to relaying, with Send your subscription to RADIO -CRAFT increased receiver selectivity and higher fur One Year (12 issues) and receive absolutely FREE one of these remarkable transmitter output when operating from Electric Dry Shavers. New subscribers are accepted or you may extend your pres- station control batteries. ent subscription another twelve months. Carrier Current -Control. -New cir- OPERATES ON Man your remittance of 22.00 (plus 25c 110 -VOLT. 60-CYCLE for shipping charges on Shaver) to the cuits and mechanical arrangements were publishers. (Canada and foreign developed to provide fixed audio -tone modu- A.C. LINE sr.15.) You will receive your DRY ELECTRIC SILVER Im- lation of essentially standard telephone mediately by return mall. Use coupon below to enter your transmitters and receivers up to a maximum subscription. of 4 simultaneous impulses, for telemeter - ing, control, and indication, thus greatly RADIO -CRAFT expanding the services available over a 20 Vesey Street, New York. N. V, single power -line carrier channel. A medium- frequency transmitter and re- Ir ceiver was developed to provide telemeter- RADIO -CRAFT, 20 Vesey Street, New York, N. Y. ing and similar services over suitable tele- Gentlemen: Enclosed find my remittance of 22.00 for which enter my phone circuits where the absence of power subscription to RADIO -CRAFT for one year (12 Issues). Send nie lines or unusual conditions prevent the use Immediately FREE. ELECTRIC DRY SHAVER (Canada and foreign $2.75). In U. S. add only 25c additional to cover shipping charges on of a power -line channel. WE SHIP ELECTRIC DRY Shaver. Investigations into New Subscriber Extend Present Subscription Accessories. - the SHAVER THE SAME DAY dielectric properties and propagation char- YOUR SUBSCRIPTION Name acteristics of concentric (coaxial) cable led ORDER IS RECEIVED. to the adoption of a tellurium compound- Address covered cable suitable for overhead or under- Ctty State ground construction, and possessing a new CLIP (Send remittance by check, money order or unused U.S. Postage Stamps concentric dielectric of great permanence, COUPON - Register letter if you send cash or stamps.) RC -8 -40 AND MAIL! L stability, and low losses.

122 RADIO -CRAFT for AUGUST, 1940 All the worthwhile A PLEDGE: - To print the important Radio Trade News news of the radio of the past Month - industry; to review Digested for busy major news events; radio men. to help point a path rdielhei fo radio profits. IMPORTANT HAPPENINGS OF THE MONTH IN THE RADIO INDUSTRY

No. 24 AUGUST, 1940 No. 24

F.C.C. AUTHORIZES WAR SITUATION FORCES F.C.C. COMMERCIAL F.M. TO RESTRICT Forty 1.'.I1.F. Channels I..igned for "HAM" BROADCASTS the New Broadcasting frt. Five Sales of Amateur Radio Equipment Expected to Take Sharp Drop. Channels :Ire Non -Commercial Contacts Limited to U.S.A. and Possessions Only Acting with unusual speed the Fed- Stringent new regulations governing eral Communications Commission has ham activities have just been announced given frequency modulation the green by the F.C.C. These are commercially light to go ahead with commercial oper- PHILCO GOES PUBLIC important in that they may cut into ation. Forty U.H.F. channels have been sales of radio equipment & components. assigned this type of broadcasting and Philco stockholders have cleared the At press time the regulations were two- only 5 of them are retained for non- way for public participation in the fold: (a) Contacts with hams outside ownership of corporation's securi- commercial work. The Commission does the of U.S.A. and possessions were banned; ties. ( Heretofore Philco has been a not feel that present -day radio sets will privately -owned company.) As a result, (b) the use of portable rigs was re- be made obsolete at least for a period par value of the outstanding common stricted to frequencies above 56 mc. ex- of years. stock has been changed from $100 to $3. cept for special emergency service. The major portion of the radioindus- Each share of present common stock has It hardly need be stressed that the try was highly elated at the news and been exchanged for 331/3 shares of new greater the transmission distance and some spokesmen foresaw a "life- saving common stock. Outstanding shares of the more equipment the amateur is per- boom." collusion stock now become 1,221,100 in mitted to use, the greater will be his number, plus 28,385 shares of $100 par A prominent consultant to purchases. The fact that his contacts will the trade value $5 preference stock, but no bonds, foresees a great opportunity for sales mortgages or funded indebtedness of any be limited, for the most part, to this in South America. Most manufacturers, kind. hemisphere means that he will be less he points out, will be concentrating on Present stockholders agreed to sell, inclined to buy the apparatus needed to the domestic market. However, he through a public offering, part of their construct high -power transmitters and stresses that South America with its holdings of the reclassified common super -sensitive receivers. Simpler, less heavy static is an ideal spot for the stock. Plans have also been made for a costly, apparatus will probably serve his sale of F.M. transmitters and receivers, public offering of sufficient additional purpose during the emergency. Similar- as these are less affected by electrical common stock to obtain funds to retire ly he will be less likely to construct a and magnetic disturbances. all outstanding preference stock. Upon portable post since his use of it will be completion of these plans, the common limited to equipment able to reach only With the European and patent situa- stock will represent the only outstand- tions as they are, he suggests that now ing security of Philco Corporation, and to the horizon. A ray of hope exists in is the time for American mfrs. to intro- applications will be made to list this the fact that the war may soon be over. duce F.M. to the Western Hemisphere stock on the New York Stock Exchange. Until then all loyal Americans will co- and absorb the market. operate uncomplainino:ly.

NEW G.E. INSTITUTE ENTRANCE THE MUSIC GOES 'ROUND & AROUND

Visitors to General Electric in Bridgeport must inter this door & pass through a New "Roto Base" on RCA Little Nipper model 46X23 permits it to be turned reception lounge & display of appliances in order to reach factory E offices i any direction, thus permitting the built -in loop antenna to be aimed direct- beyond. Building also houses testing lab & meeting room. ly at the wanted station thereby increasing signal strength. RADIO -CRAFT for AUGUST, 1940 123 ' AUGUST RADIO TRADE DIGEST 1940

DEMONSTRATES F.M.'S STATIC ELIMINATION TIMELY TELLY TRENDS The N.Y. Police Dept. was given a Farnsworth television receiver when mem- bers of its police athletic league won a box- ing contest locally promoted for youngsters. Du Mont has abandoned production on all GEN ERAL)ELECIRIC receivers smaller than those using 14- or 20 -in. C.R. tubes. FREQUENCY MODULATION Thomas F. Joyce, v.p. of RCA Mfg. Co. predicts that within a yr. after the F.C.C. Demonstrator for G.E. OK's commercial telly 25,000 receivers will F.M. sets, permits dealer be sold in the N.Y. area alone. He also to show how this trans. mission - reception oper- thinks that Americans will buy 1,000,000 ates free from man -made telly sets within 5 yrs. (Recent check -up static, by playing record of sales figures in N. Y. weekly on wireless record player shows sales through F.M. and A.M. not 100 sets per wk. but 160.) sets. Electric razor, well - known "static generator" Miss RCA Television at N.Y. World's is also feature of Fair was partly selected by votes of tele- demonstration. vision audience who saw dozen damsels demonstrate pulchritude & talent over the air. Typical home comment was "Ah, the high school elocution class!" The newly organized Television Institute of America in Hollywood, Calif., does not have a technically impressive board. Arthur A. Stern, Hollywood business man, is secretary-treasurer; Edna Williams, "prominent in the motion picture industry "; and G. H. Seward, of Hollywood Television Art- ists & Writers Guild, is founder -president. Du Mont Labs. have just issued a special Vs & N°-'s FCC THREATENS NETWORKS bulletin covering new C.-R. tube type desig- $328,202 NET PROFIT for the first 3 The FCC (which does not stand for nations. A letter contained in the type num- months of 1940 is the record of Stewart - Fifth Column Cohorts), having slipped ber designates the screen: A-medium -per- Warner Corp. Equivalent to extra earnings the dagger between the shoulderblades sistence green; B- long -persistence green; of 26c per share, after provision for Federal of television, is now whetting its knife C- short- persistence blue; D- medium -per- income tax and Canadian exchange. Equiva- for the networks. sistence white. lent period of 1939 produced only $146,275. A Commission triumvirate held that Despite trade paper survey showing 100 Gross profits were $1,364,595. contracts signed between major nets and their outlets were unfair to the latter, in television receivers sold weekly in N.Y. DIVIDEND OF 871/2c per share on first that they tie the outlet exclusively to area correct figures are more than 50% preferred stock and $1.25 per share on one net, refuse to let it sell time for greater. "B" preferred stock was declared by RCA. less than the network rate, and are for These dividends are for the period from excessively long periods. Shift in television channels due to April 1, 1940 to June 30, 1940 and were The 3 -man committee, however, failed FCC's commercialization of F.M. has tele- paid on July 1, 1940 to stockholders of to charge that men with guns and whips vision mfrs. worried about possible changes in record at the close of business June 7, 1940. compelled the outlets to sign the con- necessitated television receivers in area tracts. serviced by W2XBS whose channel would 189 IS THE TOTAL number of affiliated be wiped out. stations of the National Broadcasting Com- pany with the addition of KRBM, Bozeman, Mont.; and WSJS, Winston Salem, N. C. The former operates full time on 1,420 kc. the full time on Personal with 250 watts; latter, new 1,310 kc. with 250 watts. LOUIS A. McNABB is dir. of the award from the Franklin Institute of the electronics div. of 13e11 & Howell. This lead- State of Pa. "in consideration of the inven- $1,073,925 WORTH of radio receiving sets ing movie camera co. is planning entry into tive skill displayed in the development of were exported in March, 1940, as compared the sound equipment & television fields. the Hammond organ." with $730,417 worth in February, 1940, and GEORGE W. RUSSELL, Sentinel Radio STEPHEN NESTER, sales mgr. of $875,746 worth in March, 1939. The United sales mgr., reports situation in South indi- Recoton Corp. won the Advertising Club's with 60,682 Kingdom was biggest customer, cates this will be banner yr. silver medal in the Selling & Advertising sets valued at $440,182. Other major mar- PHILIP D. REED was reelected chair- essay competition. worth; Mex- kets included Brazil, $77,059 man of the G.E. board & CHARLES E. ALLAN R. ROYALE succeeds Clifford J. ico, $60,810; Union of South Africa, $56,375; WILSON pres. All other officers were also Hunt as sales rep. in the Phila., Balto. and and Venezuela, British India, Chile and the reelected. D.C. districts. Hunt has become mgr. of Philippine Islands, all of which took ship- WALTER R. JONES, Hygrade Sylvania the co.'s distributor div. ments ranging from $50,000 down to commercial eng., is back from a radio JACK CLUNE, Nat'l Union's office mgr., $38,000. service lecture tour in the Central South has graduated with a B.S. degree from $2,567,042 WORTH OF PENSIONS was & reports especially lively interest in oscil- Fordham U. He took the course in his paid out by General Electric during 1939. lator circuits and battery receivers as far spare time. On December 31, 1939, 3,410 pensioners as Servicemen are concerned. GUY FLAIG has been made mgr. of the were on the rolls with an average age of P. A. TILLEY (no relation to Eustace) Crowley Distrib. Corp. of Cincinnati. Mr. 69.3 years, an average continuous service has been appointed ass't mgr. of G.E.'s Flaig has been a distrib. & mfrs.' rep. in of 29.3 years, and an average annual pen- radio & television dept. with hq. in Bridge- Cinci for 15 yrs. sion of $756.00. port, Conn. L. MARTIN KRAUTTER for 4 yrs. copy $2,945,244 is the consolidated earned sur- CHARLIE GOLENPAUL has celebrated chief of the Cramer -Krasselt Adv. Agy. has plus of Zenith Radio Corp. for the yr. ended his 10th yr. with Aerovox. Prior to that he been made adv. & sales promotion mgr. of April 30, 1940. Its net profit for the yr. was with Clarostat. the Crowley Corp. In the same co. WILLIAM ended April 30, 1940 after depreciation, Changes in the FCC include TELFORD M. SHIPLEY has been made mgr. of ac- taxes and prior yr. adjustments was TAYLOR succeeding W. J. Dempsey as gen. count sales. $738,083. The co.'s cash & cash resources, counsel, & JOS. L. RAUH, JR., succeeding ANTHONY G. SCHIFINO who formerly according to its annual report just re- W. C. Koplovitz as ass't gen. counsel. operated the Rochester Radio Supply Co. leased, is $1,775,265 including $500,000 in LAURENS HAMMOND, the big elec- has taken charge of sound system engineer- U. S. government treasury bills. tronic organ man, received a 1940 medal ing at Stromberg- Carlson.

124 RADIO -CRAFT for AUGUST, 1940 AUGUST RADIO TRADE DIGEST 1940 EDITORIAL NEW DEAL ON TEST INSTRUMENTS AN By Artie Dee The Consolidated Edison Co., as you know from seeing the figures on the sales derived on some of their deals, are no dopes. Radio -Craft received additional proof thereof a couple weeks after moving to its new address. It also received an idea which should help you National Union. now put - ting out branded A" make money. and "8" bath, offers a A letter signed by the v.p. of Con- deal on counter-model Triumph Mfg. Co. bat- solidated Edison says: "Now that you tery tester. Dealer can have had time to 'size up' your new use it to demonstrate condition of old & new place, perhaps you have found things batteries. that need attention ..." and goes on to say that maybe we could use better lighting, a new ventilating system, etc. An enclosed postcard invites us to have a representative call to give us free advice on our lighting, air conditioning, etc. You know when moving day is in your town. You know the leading rental agencies and moving companies. Have you been to see them? They can give you information as to persons who have moved into new quar- ters. These persons are natural cus- dr- tomers for antenna installations, if nothing more. They are potential customers for alteration of receivers from Servicemen are invited to enter Allen B. Du Mont Labs.' "Cathode -Ray Tube Applica- A.C. to D.C., or D.C. to A.C. They are tion Contest" which runs for a yr. beginning June 1, 1940. Get the dope straight from Du Mont.... 5 new models in the G.E. line include an auto -radio & 4 portables... . also possibilities for sales of new and Stewart better radio equipment. (Old furniture -Warner has introduced a special de luxe line. . . Harold Davis, Inc., Miss. parts house, will run its post -graduate radio course in Jackson, Miss., 15 always looks at its worst in a new July -27. G.E. has built & equipped an Institute home.) Talk -up office interphones! of Electrical Living in Bridgeport, Conn. A postcard -a letter -a personal visit Stromberg- Carlson is marketing a com- Changes & New Addresses from you or your salesman may mean plete kit for repairing damaged or worn more than an initial sale. It may mean "flock" (whatever that is) on radio- phono- Where to Reach Old and New Companies establishing a contact for long and graphs. . . Nat'l Union has become ex- UNITED CINEPHONE profitable service connections. A logical clusive U.S. sales agent for sound systems CORP. has moved its offices & plant to Torrington, made by Erwood Sound Equipment Co... . method is to send out a letter specifically Conn., taking over more space. You be DeJur -Amsco Corp. is now putting out a aimed at the new resident. may complete line of able to sell an annual service contract ammeters, milliammeters, RADEX CORP. is in new & larger quar- microammeters & voltmeters in 2, 3, & 4 in. ters at 1733 N. Milwaukee Ave., in conjunction with a special -rate in- Chicago, sizes, round and square cases. Aims par- Ill. stallation fee. You will certainly be able ticularly mfrs. at ALFRED CROSSLEY, 549 W. Randolph to let him know of a good reliable Farnsworth Tel. & Radio Corp. held its in St., Chicago, Ill., will give sales engineering Serviceman his neighborhood, ready 2nd annua! internat'l sales conference at service on Allen B. Du Mont cathode -ray to dash to the rescue when his set goes the Edgewater Beach Hotel in Chi.; about equipment in that territory. sour. 300 reps. from U.S. & S.A. saw the new NATIONAL RECORDING SUPPLY CO. Stop saying that business has gone to line. . . G.E.'s new wireless record player is non -directional; there is also a new is a new firm at 1065 N. Vine St., Holly- Sheol. Even if it has-go after business. wood, Calif., acting as exclusive wired job. . . Same co. now tests appara- local sales tus by giving it thorough shaking.... reps. for Universal Microphone Co.'s prod- Stromberg- Carlson believes that F.M. "will ucts. Glenn Walliebs & F. H. Brown, well - Sales Helps and Deals revitalize the entire industry." known in that area, are associated in the enterprise. WILLARD STORAGE BATTERY CO. Flash! Place no faith in rumors that NBC has run off a series of 27 electrical tran- will abandon television if forced to make CALLITE TUNGSTEN CORP. is the scriptions featuring air and screen stars costly chamges in W'XBS transmitter. Fact new name of the old Eisler Electric Corp. for local radio station use. A commercial is that so many RCA television receivers The co. is situated in Union City, N. J. have been sold on time, with payment de- provides for local dealer tie -in. THE MAY CO. in Cleveland & the Punchboards are being used to push the ferred over 18 -mo. period, that co. must RUDOLPH WURLITZER CO. in Buffalo sale of KENT A.C.-D.C. portables. continue to supply programs in order to have been made exclusive outlets for Ansley PHILCO'S 4-in. square aerial demonstra- insure payoff. Dynaphones in their respective cities. tor generates terrific static causing terrible THE BENJAMIN T. CRUMP CO. of reception until "super loop" in receiver is Richmond, Va., and the CHARLES S. MAR- adjusted. Co.'s parts sales mgr. says demon- CORRECTION TIN DISTRIB. CO. of Atlanta (with a stration is more convincing than star sales- Your Trade Digest editor has been branch at Athens, Ga.) have been appointed man's best spiel. informed that the Trymo Copycraft & Farnsworth distribs. Cut prices up to 90% on surplus stock Supply Company is a company separate PARMETAL PRODUCTS CORP. has of guaranteed genuine parts & new P.D. and distinct from Trymo Radio Co., Inc., ice -cube tray are 2 PHILCO deal offers. moved to 32 -62 49 St., Long Island City, and does not supersede it, as our write - N. Y., affording greatly expanded facilities. WQXR, hi -fi station in N.Y., sells com- up on page 764 of the June 1940 issue plete printed programs for $1 per yr. and inferred. Both companies are in the C. G. PYLE, gen. sales mgr. of lamp has a nice sideline from including ads in field doing business- Sorry. operations for Hygrade Sylvania has moved the booklet and stuffers in the envelope. his hq. from Chi. to N.Y.C.

RADIO -CRAFT for AUGUST, 1940 125 AUGUST RADIO TRADE DIGEST 1940

THIS SET WAS NOT G.W.T.W. Salesman $am Says:- Data issued by U. S. Gov't. Far more de. tailed information is available from the Bureau of Foreign & Domestic Commerce. Washington, D. C. Publications to request are: World Radio Markets covering coun- When a tornado struck tries wanted & The Electrical & Radio Albany. Ga., Will An- World Trade News. derson's house collapsed and the set, pictured at left, flew away together URUGUAY -About 150,000 sets in use with most of his furniture. The set was recov- by 2,000,000 population, 1/3 of which re- ered and returned to the side in the capital, Montevideo. The an- Morrow -Cook Furniture nual market has been about 20,000 receivers, Store for repairs. Acci- dentally plugged in be- but growing restrictions of import caused fore work started, it op- by exchange control, seem to be gradually erated perfectly and thus cutting down this figure. Both socket power won fame. and battery receivers are in demand. Most of the receivers sold are of the 5- to 6 -tube table model type, with all -band reception, and selling at moderate prices. The electric supply is 220 volts, 50 cycles, A.C. There are no demands for phonograph combinations or television receivers. Portable sets are not selling well because of the difficulty THE PRESS of securing suitable dry batteries. OFF SWITZERLAND. 500,250 sets in use by FOLDER. Cornell-Dubilier Elec. Corp., filter units, new plug -in type transformers. population of 4,000,000. The annual market South Plainfield, N. J. Complete listing of Contains a variety of "Ken- o- graf " 's. is estimated at 40,000 domestic and 9,300 condensers for power factor correction of CATALOG. General Rotary Antenna Co., imported receivers. The War has boomed the new fluorescent lamps. Includes circuit Coral Gables, Fla. 8 pages. Lists rotary the radio market, which will probably re- and data on calculations of line current for beam antenna equipment and accessories. main good if Switzerland is able to remain the standard lamp. FOLDER. J.F.D. Mfg. Co., Brooklyn, neutral. Over 99% of the sets sold are of PAMPHLET. Sprague Specialties Co., N. Y. Lists a variety of frequency modula- the A.C. variety, A.C.-D.C. sets without a North Adams, Mass. 8 pages. Specifications tion and television antennas, including special transformer are prohibited. Five - and technical descriptions of coaxial tuning brackets and accessories. tube receivers are most popular-these should be preferably of the all -wave variety. units. FOLDER. Triplett Elec. Instrument Co., CATALOG. Presto Recording Corp., New Bluffton, Ohio. Describes complete line of U.S.S.R. 450,000 sets in use by popula- York, N. Y. 52 pages. Complete line of portable and panel -mounting meters. recording equipment, amplifiers, pre- ampli- tion of 165,000,000. The purchase of many other ac- CATALOG. Radio Wire Television, Inc., items, including radio sets, is very re- fiers, radio tuners, needles, and The Soviet has em- cessories. New York, N. Y. 120 pages. Everything in stricted. government radio, public address, amateur radio equip- phasized the development of central re- CATALOG. Atlas Sound Corp., Brooklyn, ment, portablé, parts, etc. ceiver systems. Outlets are estimated to N. Y. 8 pages. Describes complete line of 5,500,000 with 460,000 CATALOG. Crowe Name Plate & Mfg. number as compared sound projectors, exponential horns, trum- individual receiving sets. pet units, speakers, baffles, microphone Co., Chicago, Ill. Complete listing of remote stands and connectors. control units and matching plates for all auto radios. FOLDER. Ideal Commutator Dresser Co., "PREFERRED TYPES" Sycamore, Ill. 4 pages. Describes all types CATALOG. Terminal Radio Corp., New of hand- and machine- operated wire strip- York, N. Y. 12 pages. Lists complete line pers, DX cable cutters and other electrical of public address equipment, microphones, accessories. speakers, phono pickups, phono motors, radio tuners, recorders, etc. FOLDER. RCA Mfg. Co., Aviation Radio Section, Camden, N. J. Gives complete CATALOG. National Carbon Co., Inc., physical and technical description of model New York, N. Y. 8 pages. Lists complete line AVR -20 Aircraft Communication Receiver. of drycells and batteries for portables and other applications. Features the new "Mini - BOOKLET. Hygrade - Sylvania Corp., Max" "B" batteries for longer life. Salem, Mass. 18 pages. Describes in detail the advantages of the new fluorescent lamps RADIO BUILDERS' HANDBOOK. Allied and lists a variety of models and reflectors Radio Corp., Chicago, Ill. 36 pages. Con- Co. tains complete constructional data, plans CATALOG. Kenyon Transformer a variety of Y. Lists com- and parts lists for building Inc., New York, N. 24 pages. amplifiers, photo- line of replacements receivers, transmitters, plete transformers, cell equipment, etc. Send 10c to Allied Radio for it. NEW TUBE BOOSTS HAM BIZ CATALOG. Burton Rogers Co., Boston, "Ikey ", the baby iconoscope just made Mass. 8 pages. Describes a complete line available by RCA, should prove to be the of portable and panel -mounting meters, sold under the trade -name "Hoyt." heart of a flock of sales to the hams who always like to be the chaps who put the VOLUME CONTROL GUIDE. Interna- Co., Pa. 48 "van" in advance. Designed for amateur tional Resistance Philadelphia, pages. Gives a complete listing of volume experimental use, the new television control replacements for all commercial re- pick -up tube can be used for ham trans- ceivers, besides listing the various types mission of indoor or outdoor pick -ups. of controls available, including the various It has the advantage of operating on tapers, etc. voltages available from most xmtr power SHEET. Ideal Commutator Dresser Co., supplies, and requiring but a cheap lens. Sycamore, Ill. Describes new instant -heating Other components will be required with soldering tool operating from transformer it to build sweep circuits and video am- on 110 -V. line. A similar tool is described T e above title applies to both the RCA Victor tubes for heating metal conduits where joints are and the personable person presented with them. plifier to hook into the UHF rig. T e display in 10 colors is 42 ins. high á 25 ins. soldered. wide, designed for promotion via window or wall.

126 RADIO -CRAFT for AUGUST, 1940 SHOP NOTES -KINKS -CIRCUITS

HOME -MADE PANEL BRACKET STAGE ANALYZING WITHOUT A STAGE ANALYSIS TESTER! EVERY LATEST ENDS FLATTENED Y2' COPPER TUBING AND DRILLED PROFIT GUIDE (ANY STAGE CAN BE ELIMINATED THIS WAY) CUT -OUT >- / \' IST. COPPER ( - IFr. RADIO! TUBING \/j / BRACKET V -I- COMMON COMPLETE SELECTIONS GROUND BETWEEN °0. GUARANTEED QUAUTY BOTH Faster Delivery CHASSIS Diuxt complete tocks of CM- SETO I versa! and Exact Duplicate Re- placement and Repair Parts, SET FOR ALIGN I F's TO THE Radio Sets, and Amateur Sup- R F STAGES REOURED FREOVENc plies. ..HEC.ED AFTER WIRES TO BE CONNECTING P. A. EQUIPMENT Separate amplifiers or complete ,ystems with any desired assort- ment of .speakers, horns, bates and microphones. Everything IT IS sometimes very difficult to check from 5 to 100 Watts. Prices that save FOR supporting panels I found that a set if one has not a channel tester or money for you. ELECTRICAL APPLIANCES brackets made from 'Fs -in. copper tubing some similar instrument. I have been using the following trick for Extra pruh!s for you! Standard Brand Electric Irons, were light, strong and inexpensive. The a long time. Grills, Toasters, Percolators, Wattle Irons, Vacuum tubing is flattened with a hammer for an To check I.F. stages I remove the 1st - Cleaners, (Mocks, Mixers, etc., at lowest prices. inch or so at each end, and then drilled and detector tube and solder a wire (as short as bent as shown. possible) to the plate of the 1st- detector 'MAIL THIS COUPON TODAY DAVID BIRNBAUM, tube socket; the other end is soldered to The RADOLEK Co. Brookline, Masa. the plate of a radio set which is quite OK. 601 W. ltandelph St., Chicago, Peps. G41 Now remove the 1st I.F. primary lead from Send the latent Radio Profit Guide FREE. the socket, connect a common ground to same both the chassis, and turn them "on." By Address Dealer? 2- CHANNEL MIXER using this kink one can easily find out Experimentor? Serviceman? Amateur?..... many faults which cannot be traced out so Ti, MME TRANSFORMER very 56 OR easily such as defective I.F. trans- 16 formers, crackles, intermittent reception, TO MINE fading, etc. PATENTS -TRADE MARKS R. J. ANTlA, .ttirzapter, Booklet concerning Inventions & Patents T2, Forty, "Evidence of Conception" with PICKUP Ahmedabad, India. netrvetions for we and Schedule of TRANSFORMER R2 Government and Attorneys Fees' -Free 2.000 ONMS LANCASTER, ALLWINE & ROMMEL / TRANSFORMER AS Rectstered Patent Attorneys OUTPUT 436 Bowen Bldg. Washington, D. C. TO PICKUP FILAMENT TRANSFORMER ós- MF OUTPUT TRANSFORMER

TOFS I WANTED a mixing system for 2 chan- OF DATAI'RINTS nels but did not want to go to the VOLTAGE If// TESLA -O -FREQ. expense of buying attenuators. I have de- COILSDIN111 ¡Yf 20e Ea. in order for 10 signed a mixer (see diagram) that will mix r (Data and Drawings only.) 2 channels without requiring LOW - 86" Tesla -Oudin Coil 40e the usual ex- RESISTANCE Sp'k pensive attenuators. The works 1100 WINDING (1 K.W. Exc. Trf. Data, system quite .a,C, included FREE!) well and yet is inexpensive. The value of 8" Sp'k Tesla -Oudin Coil 40e the potentiometer will depend a great deal 04 K.W. Exc. Trf. Data. on the transformers used. With a little = = included FREE!) experimenting the correct value to suit in- SOMETIMES experimenters find a need 8" Sp'k Oudin; 110 Vt. for small filament 1 'f "Kick Coil" type 40c dividual cases can be found. It should be at transformers. These 3" Sp'k Tesla Works on least 0.1 -meg.; in most cases it will have are hard to find in the ordinary junk box. Ford Sp'k Coil 40e to be more. An old universal output transformer, how- 1" Sp'k Violetta Hi-Freq. Coil 4oc Model WINNIE NEAL, ever, will do the job nicely. The transformer Warships -Get List of Plans Huntsville, Ala. need not be of the "universal" type but it is preferred as the taps of the low- voltage Induction PIPE & winding will give you outputs ranging from ORE LOCATOR 2 to 10 volts; and approximately 1 ampere. Induction Type, Data 40e STEADIES LINE VOLTAGE FOR To use the output a transformer as fila- B,110 Type 40e TEST INSTRUMENTS, ETC. ment transformer the 110 -V. A.C. line is connected to the high- resistance winding. BOOSTER TRANSFORMER The filament voltage will be taken from the More DATAPRINTS 40c each! "low" winding which is more commonly 5 Meter Superhet. Electric Refrigerator called the voice coil 14. r winding. The trans- Meter Tr. & Rec. Resistance Measuring 90 v. 115V. former 25 & Ans. PRIMARY- SECONDARY connected this way can also be used A.C. Probs. Bridge TO 20 Telephone Hook -ups (ISOLA.) SEFVICING for ringing doorbells and buzzers. Weld. Transf. 2 K.W. APB IN TFVMENTS 100 Mech. Movements BALLAST GEORGE PLATCO, 20 Motor Hook -ups Rewinding Armatures Brockway, Pa. Television Hook-up String Galvanometer 20 Elec. Party Tricks 20 Simple Bell Circuits Solenoids and Magnets Steel Wire Recorder! -get list. Water Wh e e l s or 90- 130v,A C UNE "WEATHER 6" GIRLS Fry Eggs on Ice! Turbines GET "TUTOR" RECORDS Experimental Photo- Photo Cell and Relay phone Ring 4 bells: 2 Wires Control An innovation in training girls to handle Radio for 20 Tesla Tricks I HAD trouble with my test instruments the job of recording on steel -tape, in making Models on account of the line voltage fluctuating Diathermy Apparatus Polarized Relay recordings for the Bell Telephone Co.'s Inductor Organ Induction Balance from 90 to 120 volts. A Thordarson Booster Weather Forecast service, is the use of Transformer type T -6107, and a ballast phonograph records which demonstrate the Special Prices: 4 10 resistor from an old Majestic 8P6 power perfect way to give a weather forecast prints 81.00; for $2.00: pack, did the trick. This idea may be of bulletin, showing -up all the subtle problems Single, 40e each. Get New Catalog 100 A. value to others who may be experiencing in its delivery. This will enable the girls to listen over and over again, and study each the same trouble. point as much as they like. The recordings The DATAPRINT Co. AUBREY V. SCHROEDER, were made at the Bell Labs. by some of the Lock Box 322C, Ramsey, N. J. Loyalton, Calif. weather service girls.

RADIO -CRAFT for AUGUST, 1940 2 7 BOOK REVIEWS

RADIO AT t'LTRA -HIGH FREQUENCIES (1940). Published by RCA Institutes Technical Press. Heavy paper cover, 6 x 9 ins., profusely il- JHdRK A4 4dAMlLt%i1PAa. lustrated, 456 pgs. Frequency Modulation-toddy's No. 1 topic -is extensively discussed in the newest publication of BROADCASTING RCA Institutes Technical Press. In "Radio at Ultra -High Frequencies" technical papers by RCA Radio Corp. of America..Inside Front Cover engineers also present the newest information on the propagation, relaying, measurement and re- PUBLIC ADDRESS EQUIPMENT ception of signals on frequencies above 30 megacycles. Amplifier Co. of America 85, 89, 1(0 The book is divided into 2 sections as follows: Atlas Sound Corporation 102 PAPERS PUBLISHED IN FULL: Part I- Ultra- John Meck Industries 97 high frequencies below 300 me.; Part II- Ultra- Miles Reproducer Co. 97 300 mc. PUB- high frequencies above PAPERS Music Master Mfg. Co 89 LISHED IN SUMMARY FORM: Part Ultra- I- RCA Mfg. Co., Inc 97 high frequencies below 300 mc.: Part II- Ultra- Wright- DeCoster, 102 high frequencies above 300 mc. Inc We could go to great lengths in reviewing this Wright, Inc 100 Extra Profits for book, pointing out in detail the important articles it contains on television. frequency and phase PUBLISHERS modulation, new transmitting and receiving tubes Data Radio Men Selling and the various other subjects of interest to short- Print Co ..127 wave specialists, but we would still fall short of National Plans Inst 67 Electric Humidifiers conveying the importance of this book. We can Raderait Publications, Inc. 70, 120 only say it is a "must" for every advanced radio Radio & Technical Pub. Co 68 IT doesn't take a salesman to sell this Humidifier. technician. Note that there is no price set on the Supreme Publications 100 You can do it on single demonstration. The volume and no copies are to be sold. Its sole talks for itself. This electric Fountain Technifax 94. 119 unit Humidi- will be no a with the 3rd fier is 14- in diameter and sprays into the air distribution premium year of a new or old subscription to RCA Re- eight streams of water which rise 5 above fountain RADIO PARTS head and then fall hack into the pond. The Humidi- view (quarterly). fier Is of spun -proof made heavy aluminum (scratch Aerovox Corporation 78 surface) and is available in five different attractive NEW CONSTRUCTION BLUEPRINT SERIES. colors -Bronze. Chrome. Copper. Red and Oreen. Amperite Co 79 Construction Pattern Series, Folders Nos. 1 to 7. No water connections are needed -merely plug into Hammarlund Mfg. Co 83 the 110 -Volt, 60 -Cycle A.C. line and turn the switch; incl. Published by Technifax. Price. 50e each. -no pipes. no rubber connections. no messy fitting -. This series of construction patterns is a set of Illinois Condenser Co 119 Complete evaporation does not damage the mech- show how to make various types National Carbon Company. Inc "8 anism. blueprints that of metal locators or so-called treasure finders. Solar Mfg. Corp 86 In winter, the Fountain Humidifier adds healthful moisture to the air, evaporating as much as a elm The Patterns are complete with construction de- Sprague Products Co 89 it Is a charmille. of water In 24 hours. In summer. tails. List of Parts and a 22 x 34 in. blueprint Thordarson Electric Mfg, Co 84 useful attraction and provides the pleasant, trickling schematic working plan. sounds of falling water which suggests comfort and diagram and construction coolness. A drop M perfume added to the water will The different Patterns are identified as follows: any room odor. Operating cost is only a free RADIO SETS diffuse No. "Radioflector Pilot" : No. "Harmonic cents monthly. 1- 2- Frequency Locator "; No. 3 -"Beat -Note Indica- E. H. Scott Radio Lab., Inc 69 le ft. Silkcomplete.r and switch on bale tor "; No. 4- "Radio-Balance Surveyor " - No. 5 (F.O.B. N.Y.C.) shipping weight 9 lbs. Inductance Monitor No. .95 -- "Variable "; 6- RADIO SUPPLY HOUSES Distributors, jobbers and dealers strife "Hughes Inductance -Balance Explorer "; No. 7- for prices "Rudiodyne Prospector". Allied Radio Corp 119 JOSEPH H. KRAUS COMPANY Burstein -Applebee Co 100 FREQUENCY MODULATION. by John F. Rider 123 Liberty Street New York. N. Y Hudson Specialties Co 121 (1940). Published by John P. Rider Publisher, Lafayette Radio Corp 117 JOSEPH Inc. Size. 5% x 8% ins., cloth cover, profusely il. H. KRAUS COMPANY 127 123 Liberty St., New York, N. Y. lustrated. Price, $1.00. Radolek Co i entlemen: Enclosed you will find my remittance of Servicemen throughout the country are evincing 614.95 for which ship me one ELECTRIC FOUN- interest in frequency modulation. For TAIN HUMIDIFIER (F. O. B. New York Cilia exceptional SCHOOLS Send me details for this reason, "FM -An Introduction to Frequency Capitol Radio Eng. Inst 67 JOBBERS and DISTRIBUTORS Modulation" should receive wide acceptance if ID DEALERS and SERVICEMEN only because it is the first published description Lincoln Engineering School 6" in detail of frequency modulation as seen through National Radio Institute 65 Name the eyes of the Serviceman. This reviewer predicts National Schools 67 Address Rider's newest book will be a sell -out. New York YMCA Schools 67 The chapters cover: Frequency Modulation: Radio Assoc. 67 City State Training What Happens at the Transmitter and Receiver; RCA Institutes 67 (Remit by cheek or money order; register letter Transmission of F.M.; F.M. Receiving Antennas: if you send rash) RC -840 Spray-berry Academy of Radio 67 and. Servicing F.M. Receivers. For the theorist there is appended an amazingly extensive bibliography which should meet the TEST EQUIPMENT needs of anyone who wishes additional informa- Radio City Products Company....Bark Cover tion not strictly related to servicing. Readrite Meter Works 95 CENTRAL SOUND SYSTEMS FOR SCHOOLS Stuart, Allan 122 (1940). Published by Committee on Scientific Aids Superior Instruments to Learning. Size, 6 x 9 ins.. paper cover. illustrat- Company Inside Back Cover ed, 69 pgs. Supreme Instruments Corp 84 Here is a practical manual dealing with the Triplett Electrical Instruments 79 installation of sound equipment in schools which the Serviceman and sound technician will find useful. Sound systems and components are de- TUBES SWINGS INTO ACTION scribed in sufficient detail as to enable sound men Hygrade Sylvania Corp "8 to readily apply the information to practically all National Union Radio Corp 85 makes of apparatus. Write for this publication Primarily the aim of the Association is fo on your company letterhead. return to the Distributor, the Dealer and Table of Contents: The Functions of Central MISCELLANEOUS Provided by the Serviceman the profits which are Sound Systems in Schools: Facilities Classified Section 118 Sound Systems; Technical Characteris- Central Joseph H. Kraus & Company 126 legitimately HIS! This can only be ac- tics of 'Sound Systems: Sample Specifications for Lancaster, Allwine & Rommel 127 complished by raising the standards a School Sound System. National Radio Parts Distributors Assoc 128 of ethics of merchandising within the THINGS A BOY CAN DO WITH CHEMISTRY. Radio Servicemen of America 104 Industry. by Alfred Morgan (1940). Published by D. Apple- Remington Rand, Inc 109 Co.. Size 5% x 8% ins., cloth ton- Century Inc. Victoria, Hotel 81 Names of Member Jobbers in your ter- cover, profusely illustrated, 288 pgs. Price. $2.50. Radio and electronic experimenters will be par- ritory will be supplied if you will address ticularly interested in at least 4 of the chapters the Executive Secretary of the Asso- in this book. viz.: The Two Great Divisions of is taken to insure Chemistry. Atoms and Molecules, Chemical Short- (While every precaution ciation. accuracy. we cannot guarantee against the hand -The Tools of the Chemist ; Metals. Alloys. Iron and Steel: Experiments with Metals; Elec- possibility of an occasional change or omis- Office of the Executive Secretary trochemistry. sion' in the preparation of this index.) S West 86th Street New York, N. Y. Mr. Morgan is an old hand at making descriptions of things technical easy to read.

Printed in the U.S.A. I2B RADIO -CRAFT for AUGUST, 1940 Buy Direct From the Manufacturer and Save Buy Direct From the Manufacturer and Save THE NEW MODEL 1230 THE NEW Combines t Models 1240 SIGNAL GENERATOR M°80 SET- TESTER and 1250 WITH 5 STEPS OF SINE -WAVE AUDIO

A complete testing laboratory in one unit, the Model 1280 combines the Models 1250 Multitester and 1240 Tube Tester. (See specifications of each below.) * Instantaneous Snap Switches Reduce Actual Testing Time to Absolute Minimum. * Spare Socket and e Filament Voltages Up to 120 Volts, Make the Model 1280 Obsolescence Proof. * Latest Design 4l// D'Arsonval Type Meter. * Works on 90 to 125 Volts 60 Cycles A.C. SPECIFICATIONS: Esen 1. Combination IL F. and A.F. Signal Generator, R.F. -100 KC. to 90 those servicemen who through past purchases know they can always get SUPER- VALUES from - \legarycles, A.F.- -200 to 7501 cycles: S ine-Wave.--W ITII Ol'TI'l'T OF Superior, will be amazed and delighted when they read the specifications of this all purpose Instrument D'Arsonval OVER 1 VOLT. All direct reading. all by front panel switch manipu- and then note the unbelievably low price. The Model 1280 features pe lation. U'pe meter for easy reading of the various scales. and In line with our new policy of stressing a 1200 our 12811 0 2. R.F. and A.F. output Independently obtainable, alone or with A.F. appearance well as serviceability in our new line of test equipment. Model utilizes an aluminum etched designed for beauty as well as ruggedness. The prlmar, t any frequcoryI modulating 11 F. Del, tb function of an instrument Is. of course, to make measurements accurately and when designing 3. Latest design full - range attenuator used for controlling either t ho we the Important part the pure or modulated R.?. test equipment this is our first thought. However, also appreciate appearance of an instrument plays in the impression a servIceman makes on Ills customers. I. Accuracy Is within V1 on I.F. and broadcast bands: 2ç4 one higher outward design of all rrequenries. especially on home calls. We have, therefore, paid special attention to the O of our new the of Model 1280 is made of heavy -gauge 5. Giant dial etched directly on front panel, using a new mechanically instruments. For instance, panel this aluminum and by a radically new which results in a beautiful. confidence drive for v control. etched process perfected perfect appearance. A h. Operates on 90 to 130 V. A. or D.C. (any frequency). inspiring with w The Malrl esx0 comes with tubes, shielded ApC Model 1200 comes complete test leads, tabular Bala and Inatrue. $ 19 95 -bees, mildest carrying handle and instructions. Sfzo `85 lions. Shippltg aright I+ pounds. Size 13' s I1' x c:n5 ". Ilor net price .. weight 15 Only I 1's,ï sl1 ". Shipping pounds. Portable cover $1.00 additional THE NEW MODEL 1250 THE NEW MODEL 1240 M U LTITESTER TUBE TESTER SLOPING PANEL FOR PRECISE RAPID Instantaneous snap SERVICING switches reduceac- tual testing time to absolute minimum.

Tests all tubes 1.4 to 117 volts.

Specially designed electronic rectifier enables Sockets for all linear A.C. scale, tubes - high stability and No adapters. little or no temperature drift. 0 Here is an opportunity to acquire a Multi- Service. Precision Engineered m Instrument, for less than you would have to pay for an ordinary Volt - n Ohm Milliammeter. Besides making the usual volt, resistance and current measurements (both A.C. and D.C.) this unit accurately measures the condensers, Superior is proud to offer the CAPACITIES of mica, paper anti electrolytic INDUC- newest and most practical tube TANCE of rails, chokes and transformers, DECIBEL gain or loss, of tester everr designed. Unbeliev- power amplifiers and public address systems, WATTS output of am- ably low in price -unbelievably plifiers, receivers, etc. high in performance.

* Tests all times. 1.4 bs I 17 vous, including I. 5 6. T. TL. °tats, loci :as. SPECIFICATIONS Bantam Jr.. Peanut. single ended. floating Illumeni, Mercury Vapor Certifiers. Complete A.C. and D.C. Voltage High and Low Capacity Scales t he neww S series. In fart es-cry tube designed In date. and Current Ranges .0(105 to I mfd. and .05 to 50 mfd. * Spare socket inclnled on front Panel for a s fume tubes. missinn fur tube directly read on D.C. Voltage: -0 -15, 0.150, 0 -750 3 Decibel Ranges * Tests by the well . est ahl i shed method quality. volts the GOOD t Ittl) scale of the meter. Jewel n o t A.C. Voltage: -15, 0- 150, 0 -750 _ * protected -0 10 to +19, -10 to +38, -10 to * Tests shorts anti Ir .rkages up to 2 mecoiuns in all t ubes. volts 53 * Tests leakages and shore. in all elements AGAINST all elements In all tubes. D.C. Current :-0-1. 0 -15, 0-150. * Tests BOTH palles in metiitrn,. 0 -750 ma. * Tests Individual sections such as diodes, triodes, pentodes. etc., in multi tithes. A.C. Current: -0 -15, 0 -150, 0 -750 Inductance: 1 to 700 Henries purpose ma. * latest type voltage r gel :our. * Features a au votive ..trued aluminumi panel. 2 Resistance Ranges Watts: Based on 6 mw, at O D.B. * Works on Mt to 125 volts nu rimes A.O. 0 -500 ohms. 500 -5 megohms in 500 ohms .006000 to 600 Watts Model 1210 r complete with worm.? inns and tabular date Model 12:o works on 90-120 volts CO cycles A.C. COW'S for I ».nn pr t,,. td,

136 LIBERTY ST., DEPT. RCS fn SUPERIOR INSTRUMENTS CO NEW YORK, N. Y. al Buy Direct From the Manufacturer and Save Buy Direct From the Manufacturer and Save TUBE TESTER -SET ANALYZER Model 801M WHERE COULD YOU BUY these two essential instruments individually, and get the same high quality -at the same low price? And RCP has added, at no extra cost, miniature tube testing and self- contained battery power supply (for ohmmeter range below I megohm)-new features built on the basic advantages owners have long enjoyed in Combination Model 801. Here's the biggest test instrument value low price ever bought! Model 801 has every worthwhile modern feature . . and it opens a whole new era in test equipment profit. Extra- money- making features like these make RCP Combination Model 801 something to see your nearest jobber about TODAY- Meter is fused -line is double fused New miniature tube tests Tests all new and old tubes . . . Four range AC voltmeter All ballast tubes 0 10.50 500'1000 Noise test . . . meter reversing DC milliammeter 0'1,10'100,1000. witch DC Ammeter 0 10 AC voltage measurements have linear Ohmmeter 0 500,5000 1.000.000/ scales to coincide with DC 40.000.000-butt -in power supply. DC voltmeter 0 10/50/500/1000 D.B. Meter -0 -15 15 to 29 29 to ohms per volt 49 32 to 55 decibels

RCP MODEL 801 $27.95

GENERATOR Famous DYNOPTIMUM MODEL 102 TUBE TESTER An even finer performing test instrument than RCP's famous former Signal MODEL 308 Generator. and it costs 30 0b less! All latest improvements in circuit and mechanical design. Extremely wide all - Tests all new miniature tubes wave coverage continuously variable from 95 Kilocycles to 100 Megacycles. ... all ballast tubes. Noise Output modulated at will. 30 °'e mods lotion at 400 cycles, sine wave from and hum test for tubes self- contained independent 400 cycle showing otherwise good. circuit. Attenuation approximate microvolt cal ibrat on by means of five step !ulcer $22.95 Sensitive neon tests for attenuators. Highly attractive appearance. shorts and leaks. Spare socket for future tube developments. Checks pilot lights, headlights, miniature lights. Rapid, accurate. Individual AC -DC MULTITESTER check of sections of rectifiers and multipurpose tubes. MODEL 445 It's Tomorrow's Tube Checker today! . . . amazingly It's in a class with testers selling versatile, handsomely finished, sensationally low- priced! at twice the prix! Actually, it i the equivalent of 25 different instru-

D'Arsonval meter accuratements. within 2 °b. DC voltmeter 0 5 50 250500/2500. DC Ammeter 0,10. Counter Type Model 308 $16.95 AC voltmeter 0 /10 100 500 1000. Three range ohmmeter 0 500 100.- ' 000,1 Meg. Combination Portable Meter sensitivity 1 - Milliampere or 1000 ohms per volt. Selector swatch Counter Type Model 308P $18.95 operated, complete with batteries. $9.95

JOBBER OR if he cannot write to desire, you the SEE YOUR Test Instrument describing with the RCP catalog Line. Test EquiPmenT dpet penny VALrd) Cost BIG VALUE-Low complete RCP