Radio-Craft 1942 10.Pdf

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Woce w aox; t at you stetting . now a modern re of ne It you're en r alto 9airbu t Votintter of Warn of end in on your interest in Radio the suse rsgecircuits You can begin cashing olpinR ap Operator.Rodio You QUICK YOU ACT NOW! The Radio repair nevi mr- -IF my business, booming because of the shortage of new sets. baffled xtrs knowledgeaa be f promotiooa' home and auto Radios, offers more opportunities than ever to make $30, $40, $50 a week in full -time extra jobs, or $5, $10 extra a week if you hold your pres- eq r buymely saKe. ent job and fix Radio sets in spare time. Practically all branches of Radio need Technicians, Operators. Radio training can win extra rank, pay in Army, Navy. Find out how I train you at home in spare J. E. SMITH, President time for Radio's opportunities. MAIL THE COU- NATIONAL RADIO INSTITUTE PON BELOW -NOW! Established 27 years IMO He has directed the training of more men for Radio than anyone else. He has helped men already in Radio to get ahead, and men not in Radio to get into Radio and win SUCCESS. Make Me Prove I Can Train You at Home to Be a RADIO TECHNICIAN or OPERATOR

CRp. tho coupon and mail lt. Cm certain I con tram pa,a Ili n.ury. ()there, in the Array or Nary. r w rig you at home i 1 your spare time to be a RadloTTechni- pi woolaxl, extra pay, because of their Radio s training. cian. I want to send you a sample lesson free; to exam- Government orders for Radio Equipment have opened new ine. read. See how clear my Course Is to understand jobs for moly In Radio Factories, while many have good EXTRA PAY IN ARMY. See how my Course is planned to help you get a good Civilian Government lobs as Radio Technicians. Open - lob In Radio, a young growing field with a future. You lors. NAVY TOO un't have to give up your present Jean- or spend a In: Of My Course Is Thorough and Practical money to become a Studio Technician. I train you at terne nights In your spare time. I give you a thorough basic training in Paolo Theory and Men likely to go Into military service, soldiers, Charles F. Helmuth. 16 Hobart Ave., Absecon, N. J.. l'ractire whleh enables yin to understood the operation sailors, marines, should mail the Coupon Nowt of every type of Radio e:qu I nnlrnt. I Send writes, "1 tertal Radio in the Marines. Later 1 took practically men got extra rank. extra G hui Learning Radio helps the N. It, 1. Course. Now 1 am my you Rig Kits of Radio Parts with which you hl own boas and get prestige, more interesting duties, much higher P.Y. lobs over other. who thought they had them. I owe Radio circuits and testing equipment. copluct tests and plenty N. It. James Peb- experiments which give you practical experience. That's Also prepares for goat Radio lobe after servire end,. ble er. Mang write., "I was working Ina why many men I train begin to make more money quick- IT'S SMART TO TRAIN FOR RADIO NOW! mirage when I enrolled with N. R. I. I am now Radio ly awi get and hold good jobs. Serviee Manager for the Furniture Co. for their four store.. M- Beginners Quickly Learn to Earn S5 to $10 a Week Extra In Spare Time MAIL THE COUPON -get my FREE Lesson anti 64-page Why Many Radio Technicians I Trained Nearly erery neighborhood offers opportunities for a good book. "Rich Rewards in Radio," at once. See what Itadh at Horne Make $30, $40. SSO a Week part-time Itadio Technician to nicke extra money fixing offers' you as a skilled Radio Technician. Learn how practical my Course really Is. head letters from more The up-to- the -minute Itadlo Technician Radio sets, I give you special training to show you hoar or Operator must in start cashing in on these opportunities early. You get than IGO men I have trained so you can see what they have BOTH a thorough knowledge of Radio. and experi- are doing and earning. atoll Ille Coupon NOW -in an ence working with Radio parts and Radio parts and Instructions for building test equipment such as nient. for conducting experiments that you valuable envelope or paste It on a penny postal. my training gives you. That is why men I trained are give taking advantage of the booming practical wls method Itadlo re,air business with its -senxd yea, half J. E. SMITH, President, Dept. 2KX to get better jobs, to make more money In spare time, sudying my Lessens- or makes Irarn'.ng Itadio at Inner in,t rrvtü.g. fair iva ln¡;, National Radio institute to open their own Radio repair hustnenea. Others fill good -nay Jobe in many of the country's 882 Broadcasting toadied Washington, D. C. Stations, and in Aviation, Police. Commercial, yterine and Government Radio. Loud- Speaker Systems gire g MIA TRAINING MEN FOR VITAL RADIO JOBS

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RADIO -CRAFT for OCTOBER 1942 THEE IN TT SSVE , lrerv,r,rrntinr: w¡11 NEXT issue November ¡tied list HUGO GERNSBACK The diversified Editor- in- Chief contain a for of0 selected HARRY CONVISER G. ALIQUO the 1lnna 'ing Editor Circulation Manager RA010 BBEGINNER, usual o the ¡n addition Contents OCTOBER, 1942 Issue features.

VOLUME XIV -- NUMBER 1

Mailbag 4 Editorial: Deadly Radio Transmission. by Hugo Gernsback 7 DEPARTMENTS, ETC. The Radio Month in Review 8 Mailbag 4 The Radio Month in Review 8

SERVICING RADIO SERVICE DATA SHEET (See Servicing) 16

Practical Transformer Design by Fred Shunaman IO Operating Notes 19 Latest Radio Apparatus 37 Analysis d Alteration of an Analyzer... by Ted Powell 12 Book Reviews 63 Tracking Down Grid Emission 14

Testing Small Power Transformers by H. R. Heap 15 RADIO & TELEVISION How to Make a 23/4"s 4" Receiver by Irving Minton 39 RADIO SERVICE DATA SHEET: Egg- Fertility Radio Tester 40 No. 326 Emerson Model 436 High - Fidelity A.C. Superheterodyne 16 II -Tube Frequency Modulation Receiver by George Francis Baptiste 42 Low -Capacitance A -C Power Supplies Getting Started in Radio by C. W. Palmer 46 by G d Mountjoy and Charles W. Finnigan 18 Which Regeneration Scheme? by M. Harvey Gernsback 43 Receiving Tube Charts 20 Radio Kinks 53 Making A Voltmeter Read Watts. by W. G. Lofstrom 22 Radio Patents Digest 63

B- and C. Battery Eliminator for Service Test Bench by Russell E. Powers 23

Transformerless Power Supplies -Part I. 24 Published by Radcraft Publications. Inc. Publication office: 29 Worthington Street, Springfield, Mass. Editorial and Advertising Offices: 25 West Broadway, New York City. Chicago Advertising Office: RADIO -CRAFT, 520 North Michigan Avenue, Chicago, Ill. RADIO INSTRUCTION RADIO -CRAFT is published monthly, on the first of the month preceding that of date; subscription price is 32.50 per year in V. S. (In foreign countries. Flight Radio School Trains Enlisted Men 26 7Sc additional per year to cover postage; Canada, 50c additional.) Entered at the post office at Springfield as secondclass matter under the act of Signal Corps Training Begun at Illinois Tech 27 March 3, 1879. All communications about subscriptions should be addressed to: 29 Worthington Street, Springfield, Mass., or Director of Circulation. 25 West Broadwa,, New York, N. Y. SOUND * Factors Contributing to Good Recording. by R. A. Lynn 28 Foreign Agents: Sound as an Aid to Navigation by Willard Moody 30 London- Gorringe's American News Agency, 9A Green St., Leicester Square. W. C. 2, England. Devices for Air Raid Warnings 30 Paris -Messageries Dawson, 4 Rue Faubourg, Poissonniere, France. Wide -Range Film Recording Developed for Home Use Melbourne -McGill's Agency, 179 Elizabeth St., Australia. by H. W. Knettell 32 Dunedin-James Johnston, Ltd., New Zealand. ENGINEERING * Text end illustrations of this magazine are copyright and must not be Radio Direction Finders by Willard Moody 34 reproduced without permission of the copyright owners.

2 Selected for Dependability

The lives of America's fighting men -the winning of America's battles depend on swift, sure radio communications. Army radio equipment must be completely dependable. Exacting Army specifications make sure it will be. -flurdock The Air Corps and Signal Corps test, approve, and use Murdock RADIO Radio Phones. PHONES MURDOCK MANUFACTURING COMPANY-Chelsea, Mass.

RADIO -CRAFT for OCTOBER, 1942 3 MAILBAG

2.5 -VOLT TUBES SERVICING DOPE Dear Editor: Dear Editor: I am but a beginner in radio although i like R -C. I've read it since Hector was The name is new very much interested in it. I find the cost a pup. Even before Buck and Moody started of parts very high, and so I salvage most grabbing more free space than Victor of mine from old sets. The tubes of most Mature. of these sets use two and a half volts in I have my own shop, located here 4 years, Purpose the heaters and the power transformer and I am doing very nicely. I have plenty ...the produces this. To build many sets illus- of good equipment, try to do a good, honest trated in your magazine six -volt tubes and job and treat people squarely. I am proud transformers with six -volt filament wind- of the fact that most of my first customers ings must be used. are still my customers and friends. This is is not Changed Could you not publish suitable circuit a small town, 1,600 inhabitants, with closely diagrams using these parts? I believe there populated surrounding country, and news, are others who would appreciate such cir- good or bad, travels fast. In addition to cuits. my own business, I do work for six garages DONALD MILLER, and two electric stores on a wholesale basis. Parry 30, 1942i Sound, Ontario, Canada Of course, all work is done in my own en gay shop. I find this wholesale business a steady (Most of the general -purpose tubes are and substantial portion of my gross busi- lite atockA°lde.t° available in 2.5 -volt filaments as well as 6.3- ness. I also take care of two locally owned ç}Ll ANIA volt filaments. These include triodes, pen- P.A. outfits. I like articles concerning unusual servic- RV GROW. todes and output tubes whose characteris- ORPORAT tics are either similar or very nearly simi- ing problems, equipment and P.A.; real, CORPORATION lar in both types of filaments. Substitu- meaty dope that helps pay the rent and la cltartge tions of 2.5 -volt tubes can be selected from keeps customers satisfied. How about some :teood any manufacturer's tube manual by com- additional articles on aircraft detectors and name paring the characteristics data. Of course, related subjects. I've gotten plenty of good the cont/terety metal tubes and some of the more recent dope, advice and ideas from R-C in the /t special- purpose tubes can be obtained only past, and I look for plenty more in the for 6.3 volts. Where simple revisions for future. 2.5 -volt tubes can not be made, a separate BURNIE ADAMS, 6.3-volt transformer can be wound for the Fortuna, Calif. core of an old audio transformer by following the practical design data given by (Most of our service articles Shunaman in are written Mr. this issue.- Fditor) by men like yourself -servicemen. We are eager to publish the "meaty dope" but we POCKET -SIZE RADIO are almost wholly dependent on readers for this material, since most of our former Dear Editor. "specialists" are busy aiding in the war I had noticed in a recent issue of your effort. You might try to relate some of your magazine your asking the readers to state own service -problem solutions, or describe the kind of articles they desire. any unusual equipment you may have. - I look on this as a grand opportunity, Editor) being somewhat a novice on set building. AS of July 30, 1942, the Hygrade I do have in my mind what I would like Sylvania Corporation became and hope to see it in your magazine in some COOKE'S SLIDE RULE Electric future issue. Dear Editor: Sylvania Products Inc. I would truly appreciate your publishing For three years now I have been read- say, is my desires in the Mailbag! Hoping there Needless to the change one are beginners, in ing your magazine and have found it not uniform or otherwise, who only interesting but also very educational. in name only. will find the article I want to be what they want, too! Now that I wish to write in for informa- There is no change in the high tion I can find no instructions as to who or I would like to see an article on a truly write. quality of our products, no turning pocket -size radio, a set that could be truly where to I have mathematical from our purpose to bring forth a "vest- pocket companion" for the soldier the Cooke's book on the march, etc. for radio repairmen and electricians and I the finest lighting and radio equip- wish to know where I can buy a Cooke's ment our skill and For the sake of keeping the set small as experience can possible, why not use In Gordon's sug- slide rule. create. gestion in your June issue and use the C. MC HENRY, popular midget "hearing aid" type of tube. Canon City, Colo. And that means we will continue I would like the set to be a "one- tuber "! to provide you with an incompar- And using the crystal detector as well (We know of this slide rule only from able line of radio would be dandy. the book recently published. We tried to tubes, backed by all The type of set in question would prove buy one at several stores but were unable to find one. Perhaps some of our readers the technical assis- a real traveling companion. PVT. CYRIL COWPER, can furnish the information.- Editor) tance and promo- Toronto, Canada tional help you need RADIO IN THE ARMY to do a first -rate -COIL DATA selling job. OSCILLATOR Dear Editor: Dear Editor: I am a subscriber of Radio -Craft maga- In reference to Mr. William F. Santel- zine and like it very much. I am taking a mann's letter in the July issue of Radio- correspondence course in Radio Electronics Craft regarding the design of superhetero- from the National School of Electronics of dyne oscillator coils, the desired informa- Minneapolis, and I am very much inter- tion can be found in Terman's "Radio En- ested in radio. I am thinking about joining SYLVAN IA gineering," in the "Radiotron Designers the Army Signal Corps sometime before I am drafted into the Army. Why don't ELECTRIC PRODUCTS INC. Handbook," and undoubtedly in many other similar texts. While the derivation of these you have articles in your magazine about formerly equations is beyond the scope of the aver- radio in the Army and give us a writeup age experimenter, it requires no great about the Signal Corps? HYGRADE SYLVANIA CORPORATION knowledge of mathematics to be able to RAY JEAN BATTS, Emporium, Pa. substitute into these formulas for the value Thorntourrt, Ind. of the unknown component. Also makers of Incandescent Lamps, JOHN L BELFn, (We can not publish information that Fluorescent Lamps and Fixtures New York, N. Y. might be useful to the enemy.Editor)

4 RADIO- CRAFT for OCTOBER, 1942 MAILBAG

THE AMATEUR AND THE WAR Dear Editor: thing. I am very unhappy. I suppose a lot I feel that I have been cheated by the of other amateurs arc, too. Japanese. or Germans, or the F.C.C. or The government claims it uses the ama- someone. To explain this I will have to teur bands for aviation and army use. 1 give you some of my past history. have a good communication receiver and I search all over the amateur bands and I I became interested in radio in the win- can't hear anything. Not even a telegraph ter of 1939. I listened_to amateurs on the signal. N'hy can't the F.C.C. give us ama- short -wave end of my broadcast receiver. teurs just a little space to operate. For in- I also read radio books here and there for stance, they could give us back the 160 - a year. I got set about a telegraph and meter band and not let us use over 40 watts to send up about 12 w.p.m. it. learned to on input and operate only during a certain I got Then a key and buzzer. In May of period of the day. 1941 I built a two -tube battery radio and There are a lot of amateurs in the army had it. I much trouble with did not get it and on defense jobs, but there are still some to operate until July, 1941. Also in May license left, like the ones under 17 and over 64, I bought a manual and radio ama- or blind, deaf, or disabled, who love teur's handbook, and rented a Teleplex in- the strument. It was two months before the amateur radio. I am 14 years old. w'll be at least Teleplex came, because of war needs. I It three studied in all of my spare time until Sep- years before I can go to war. If I could get on the and Use radio equipment and tember 22, 1941. That day I went 165 miles air become experienced enough, I would be able to Dallas and took my examination. I to in I have my passed the code exam swell and I figure operate a radio the army.' licenses, but I have never been on the air, that I made about 85 on the questions. and have not studied radio since December From then until December 6, 1941, the of '41. day when my licenses came through the Isn't there some way for us to get on mail, 1 built my station. I bought a Sky the air, at least to learn? Buddy receiver and built a 25 -watt trans- GILES EASLEY, mitter and a lot of other equipment. The Calvcat, Texas. only thing was that my antenna was broken by a high wind and replacement had to wait (Your letter stresses the nuisance of war several days before I could get some more but fails to consider the seriousness of war. of the right kind of wire. On December 8, If an amateur band were opened it would Send for FREE Ohmite 'I finished it and was ready to go on the require constant vigilance to see whether Stock -Unit Catalog air for the first time in my life. I was advantage were not taken of this liberty No. 18. Very handy excited all over. I had been waiting for by enemy agents, and the F.C.C. is too busy for quick ref this hour for two years. Then I heard over for that. Undoubtedly you can find other the broadcast receiver about the F.C.C. amateurs in your vicinity who may be able closing all amateur stations. You can to meet with you for occasional code prac- The extras built into Ohmite Re- imagine how 1 felt. tice -even if its only on an audio oscilla- sistance Units make them elec- Between December and February, 1942, tor. You should have more time now to I did not see a R & T. magazine. Without study the technical phases of radio and to trically and physically fit for the it, I could not read about what was hap- do some experimental work which will be toughest service. Ohmite units, pening in the radio field. Now I have for- valuable to you later on. Perhaps your local gotten nearly all I knew; I can't send or Civilian Defense group will find use for for instance, were on the planes receive over about 10 w.p.m.; I have for- your services, either for constructing or that bombed Tokyo. They're gotten most of the ham slang and every- operating emergency transceivers. -Editor) widely used in ships and tanks, too communications and WANTS SIMPLE SUPERHET in the summer it is nice to have a portable -in Dear Editor: phonograph to take to the beach, and I electronic equipment -in re- Your magazine is unbeatable in its field. would appreciate it very much if you would search and production -in train- I would like to see some circuits, using give me some information on how to metal tubes. for a simple two or three -tube counteract this fault without going to more ing centers and industrial plants. superhet with regeneration. After a pleas- expense, as the phonograph is one of the It's well worth remembering, ant while of building the one- and two- manufacturer's most expensive portables tube regenerative sets, a lot of fellows and has already cost me a great deal of when you build original equip- would like to build a simple "super." money. ment or make vital replace- HERBERT WOLFF, More power to your good magazine 1 GEORGE P. BLACKBURN, Brooklyn, N. Y. ments -today and tomorrow. Tyler, Tex. (Assuming that the phonograph is prop- WON'T STAY IN THE GROOVE erly leveled -two small spirit levels placed Dear Editor: at right angles may be permanently mount- I have a portable phonograph which has ed adjacent to the turntable-the fault could been giving me a great deal of trouble, and be due to some mechanical defect that does for that reason am writing you for some not permit the sound head to rest freely on information. the record. If the trouble you encounter is It has the old type of sound -box, that is, characteristic of the phonograph you have, Send lOc for handy Ohmite Ohm's with the diaphragm type pickup, which as the manufacturer's service department Law Calculator. Helps you figure you know is quite heavy. It has cost me a would be sure to know about it.- Editor) ohms, watts, volts, amperes- quickly, lot of money as I have had quite a few easily. records of value ruined. HELP WANTED This is what happens: When the record Dear Editor: OHMITE MANUFACTURING COMPANY is put on the turn -table and the arm put 4894 Flournoy Street, Chicago, U.S.A. on the record, it jumps grooves in the Having read your magazine for quite record whenever the arm strikes a heavily some time I have seen you help a good many %GHT recorded portion of the record, and as you people with their problems. I would like to Wpl know, the recordings today are being made know if anyone has a diagram of the * ti with extremely high volume so as to Howard "Neutrodyne," Type A, five -tube counteract surface noise. Because of this, receiver. I believe it was manufactured in it has been necessary for me to put a great 1924. I will be more than glad to pay for the (DEAD TIE information. deal of money into needles and replacement RheostatsResistors of records which I have had ruined. Dur- WILLIAM M. REYNOLDS, ing the winter months I did not mind it 301 W. Laurel Ave., Top Switches because I do not use it quite as much but Lake Forest, 111. RADIO -CRAFT for OCTOBE R, 1942 QUALIFY-AT HOME - QUICKLY for your pick of the 200,000 RADIO JOBS in the Armed Forces, Commercial Broadcasting & Industry. Use this Standard New Home Course in BASIC RADIO COMMUNICATIONS to brush up and meet today's requirements

I- you want to prepare yourself for a radio post in advance of induction or enlistment in the military services -if you want to get into radio broadcasting or into the radio industry -here is the book that will give you the basic training you need. FUNDAMENTALS OF RADIO trains you in the entire field of basic radio communications, from the simplest circuits right through FM transmission. No previous experience is necessary. This easy -to -grasp home course is written not for engineers, but for student technicians who must know how to maintain and operate all types of radio apparatus, and have only a limited time in which to master the required essentials. "The One Book Unique In The Radio Field" "With this one volume alone, men with no previous radio experience or knowledge can . obtain a thorough grounding in radio principles. In thoroughness, this book is outstanding . in the authors' appreciation of the reader's outlook and problems . .. the one hook unique in the radio field." -Scientific American. "For many years, I've sought an adequate answer to the oft -repeated question, 'Where can I find a hook 'which, in one volume, will teach me the fundamentals of radio?' This TRY book is the answer I've waited years to have." FOR INDUS -E. N. Cohan, Director of Engineering, C.B.S. FOI2Cf5 A TECHNICIANSTHE ARMED "Anyone mastering the contents of FUNDAMENTALS OF RADIO should postures all the TO T AND preliminary requirements of radio men and technicians for military and naval service." BROADCASTING. -E. E. Tierney, Chief Instructor, Eastern Radio Institute, Boston, Maas.

Concise Review of Radio Mathematics-A. C. and D. C. tors -Transmitter Circuit -Radio Frequency Section - Circuits- Power, Energy. Fuses, Batteries. Electro- Amplitude Modulation Radio Receivers - Frequency COMPLETE magnetism. Generators, Meters, Transformers, Recti- Modulation, General Principles, Wide -Band FM and fiers, Resonance Testing, Voice and Music Waves - Static Eliminators -FM Systems for Communication TRAINING FOR TODAY'S Electronic Principles- Rectified Power Supplies -Sound Services -FM Transmitters and Receivers -Radio Wave and Electrical Transmission- Sound, Distortion, Micro- Propagation - Polarization - Static and Man -Made phones- Reo roducters Telephone Loudspeakers - Noise -Ultra -High- Frequency Propagation -Diffraction . . - , - IMMEDIATE NEEDS Audio Amplifiers -Public Address Systems- Vacuum- -Refraction -Functions of Radio Antennas- Types- Tube Instruments-Oscillators- Electromagnetic Waves Directional Antenna Systems -Radio Beacons- Direc- Here is a glimpse of your -Radiation and Reception - Antenna Structures - tion Finders and Radio Compasses. Transmission-Radio Frequency Amplifiers and Detec- instruction in basic tors -Input and Output Circuits- Amplitude Modula- tion Radio Transmitters- Radio, Audio Frequency Sec- OVER 300 WORKING DIAGRAMS radio communications tion- Crystal Oscillators -Buffer Amplifiers-Moduln- from the simplest circuit to FM transmission

With any sort of past interest in radio as a background, your chances of landing a big -pay, big -opportunity job were never so bright. In the Let land and naval forces, in aviation, commercial broadcasting, police these experts airways and the manufacturing industry, the shortage of radio tech- rapidly fit you nicians is acute, the rewards exceptional. Now is the time to give your- for big pay self the rapid basic training in radio communications which qualifies now_ and you without delay. FUNDAMENTALS OF RADIO provides exactly that fora post training -at home -in your spare time -without wasting effort on non- war future in essentials- without omitting any of the essentials required in actual radio. William practice. In one handy, easy -to- master volume, written by six high - L. Everitt, Senior Consultant Ph.D., everything on Editor. ranking instructora, FUNDAMENTALS OF RADIO covers tion and Director Air Comn.unica- search Section of ODerat¡onel you need to know about basic radio communications. in Re- Army; Professor Signal Corps gineering of U.S, Ohio Electrical En- _eeM AIEE State University Fellad of and IRE: member FREE 5 -DAY OFFER Editor Directors and of the Institute Board of MONEY -BACK GUARANTEE I Every minute counts! Engineers f 1 of Radio Don't postpone your op- Signal Consultant PRENTICE -HALL, Inc. Corps; on portunity for good Job 9 for orps; Army; formerly Air Communication, Dc pt. PR-6, 70 Fifth Ave., N.Y.C. now and the foundation of Board U.S.Association Director. of Editors of Broadcasting; eerr I for a highly successful of Institute o-Emember Please rush copy of FUNDAMENTALS OF RADIO. I enclose William of Radio future in radio. Get start- Carl Engines. 15, toe 5 days. I decide net keep Ostarbrock plus postage. If, within to 9, University Professor this book, I am free to return it for refund of the purchase ed by mailing the coupon of of Electrical Fred Cincinnati, En- Price. at once on our 5.DAY- H. Pumphray, I I U.S. Army Curriculum MONEY -BACK- OFFER. Professor Ad NAME ing, Rutgers Head viser, Signal I Read, study, examine gars Universitynd of Electrical or Ps, Paul 9 near ADDRESS FUNDAMENTALS OF H. Nelson, I RADIO for five days- Sor Westinghouse otherperfirm Electric. formerly radio CITY & STATE tree. Return the book for IfCA Victor refund if you do not find Edward C and SEND C.0.0., plus few cents postage work Jordan, charges. it the easiest way to in C.,fantennas Ohio LI (Same refund guarantee.) I consultant ándand impedance University; qualify, at home, quickly on matching research IClip this coupon or order by lee:.r% addreuing Dept. FR -6, for one of the 200,000 radiating systems; as above. ' systems. radio lobs now waiting gM MM MMMI =we ma a wpm mel for men to MI them. 6 RADIO -CRAFT for OCTOBER, 1942 THE RADIO MONTH IN REVIEW

CIVILIAN DEFENSE RADIO LICENSES GRANTED The first licenses to be granted by the Federal Communications Commission under newly- established regulations for civilian defense radio systems have been issued by the Commission to the City of Akron, Ohio, and the City of Lawrence, Massachu- setts. Classified as War Emergency Radio Service, these stations extend the organized civilian units functioning under the Office of Civilian Defense. In event of air raids or other enemy action which destroy other forms of communications, the emergency radio will be available to co- ordinate rescue and repair work. Under the terms of the licenses granted, Akron will have a two-way low -powered radio system of sixteen receiver- transmit- ters. Some of these will be in fixed locations, others will be mobile and a few will be of the type known as "walkie- talkies," because the operator may use it while moving aboùt. Lawrence, Massachusetts, has been licensed for a system of eleven two - way radios. Applications of many other cities are now pending at the F.C.C. and requests from the different communities vary to fit local conditions. Fort Wayne, Ind., has plans for more than one hundred such sets, while Mrs. James Marglin, first woman radio Dayton, Ohio, indicates that forty radios operator to receive an appointment to the Signal Corps, conducting a code class at the American Women's Voluntary will serve its needs. Some applications are Services school in New York City. being returned to municipalities because the forms fail to indicate what arrangements exist for liaison with Defense Command - ers for the purpose of receiving orders of SIGNAL CORPS WOMAN TEACHES AWVS GROUP radio silence when conditions dictate. Regu- A series of special code classes for a special lations of the F.C.C. require "mill" typewriter used for com- that the li- selected group of students from the Amer- munications work. Mrs. censes be issued to the municipal govern- Marglin believes ican Women's Voluntary Services code that advanced AWVS code students ments proper rather than to any of the who course, aimed to bring these students up have a departments. speed of 25 words a minute or over to sufficient code speed to qualify them can be brought up to the required speed of Formation of the War Emergency Radio for service in communications work with between 30 and 35 words a minute in a Service was announced jointly by the the Armed Forces, was begun last month month's intensive training. F.C.C. and the O.C.D. last June 13, at at AWVS Greater New York Headquar- Mrs. Marglin was invited to give the which time it was explained that radio ama- ters, in New York City. teurs, repairmen special courses for advanced students at and others having suffi- The classes are being directed by Mrs. the request cient experience would of Mrs. Lenore Kingston Conn, be asked to volun- James Marglin, of Fort Knox, Kentucky, Director of AWVS Instruction teer and serve in the operation of the civil Code for the first woman radio operator to receive Greater New York, is defense radio systems. The two-way radios and conducting these an appointment to the United States Army classes during her five operate on short waves weeks' stay in New ultra with power Signal Corps during the present war. Mrs. York. She sufficiently low limit range entered the field of radio a few to their to ap- Marglin, who, though only 24 years of age, ago proximately ten miles. Spare years because of a challenge that parts lying is said to be one of the fastest operators - "women were not sufficiently around radio repair shops are considered intelligent to man or woman-in the Signal Corps, hav- master the art of radio." Deciding to sufficient to construct these radios. ing a speed of 50 words a minute on the "show" her doubting male friends, she took up the study of code and within three weeks was sufficiently proficient to send and receive 18 words a minute. Within a relatively short time she. earned her Federal Communications Commission Amateur Radio Operator's License and established her own "ham" station (W9ZTU) at Fort Knox. It was over this station that she first talked with her present husband, James Marglin (W9THS), who is an instructor in communications at the Armored Force School at Fort Knox and who is now in New York with her. Although they lived only a block apart for six years, he in the army barracks, she at home, it took the air waves to bring them together. Their court- ship was carried on for six months over the air before they actually saw each other face to face. During this period Mrs. Marglin had been doing volunteer service for the government by maintaining communications on a four -times -a -day schedule between service men from Fort Knox who were out on maneuvers and their families at home. She says that it was in recognition of this service that she received her special appointment to the Army Signal Corps. Her work at Fort Knox involves handling War Chief Metalsmith Ed Regan (U. S. Navy) receives detailed instructions on a new and Department traffic, with a bit of teletype secret tube -welding process from an employee of National Union Radio Corporation. operation on the side.

RADIO -CRAFT for OCTOBER. 1942 9 SERVICING Practical Transformer Design By FRED SHUNAMAN

This is the second of a series of articles on wartime transformer rewinding by Mr. Shunaman, whose work as a serviceman in China frequently made it necessary for him to rewind transformers for the different filament and plate voltages encountered there. His article last month described how to make coil -winding machines and gave essential information for the serviceman to follow.

MOST articles on transformers are we're looking for, so bear in mind that too FIG. II theoretical. They deal with voltage big a core will- within limits -both improve SIZE OF TRANSFORMER CORE and impedance ratios, flux fields and the performance and make winding easier. FOR OUTPUT WATTAGE iron and copper losses. The would -be A bigger core requires less wire and has Volt -amps Core size designer of a small transformer looks in a larger window, so if wire of the correct Output (Sq. In.) vain for an answer to the question, "How size can not be found, a larger size can be 25 1.0 many turns of what size wire on how big used, again with an improvement in per- 50 1.5 a core do I need to do such a job ?" This formance. Too small a core invites disaster. 75 1.75 article will attempt to answer just that 100 2.0 question, and will leave ont all theoretical SQUARE CORE IS PREFERABLE 150 2.5 angles. Let us assume we had a large trans- 200 3.0 Let us consider a transformer needed to former with a core 13 inches wide (the 250 3.5 supply a small amplifier. The plate supply width of the center bar of the "E" piece), 350 3.75 requires 100 mils at 250 volts, the filament enough laminations are taken to make a 500 4.0 windings 1.7 amps at 6.3 volts and 2 am- core 13 inches square. This is a little bigger These sizes are generously calculated peres. at 5 volts. The drop through the than we need, but the square core, besides and allow ample regulation. filter choke (or speaker field) is 100 volts, being preferable electrically, is the easiest and as condenser input is used, the input for which to wind a coil. The window is rounded up for convenience and to help filter voltage at 100 mils will be about the 2% by 11/16 inches. It now remains to de- overcome any voltage drops due to re- same as the R.M.S. voltage of the trans- termine if we can get the necessary wire sistance. It is also well to add about 5% to former secondary. onto it. all filament windings; in our case one turn First, we must have a large enough added to each low -voltage winding should DETERMINING DESIGN FACTORS number of primary turns properly to mag- be enough to compensate for the resistance The first step is to make a diagram of netize the core. The usual rule for this drop (voltage loss due to the ohmic re- the proposed transformer, putting down the size transformer is sistance of the wire). voltages and amperages of each winding, and filling in other facts as we find them. 7.5 X voltage CURRENT RATING GOVERNS WIRE SIZE (See Fig. 1.) So far, we know the number Figure 3 shows us the correct size of of windings and the voltages and currents core area (sq. in.) wire for each current rating. As almost required from each one. If we multiply all transformers of this type are wound volts and amperes together we arrive at commonly stated "7.5 turns per volt." Our with enamel- covered wire, it was thought the number of watts we expect our trans- core is almost 2 square inches in area, unnecessary to show figures for other kinds former to put out-in this case about SS therefore the turns ratio is 3.75 per volt. of insulation. For intermittent use-as in watts. Now we can proceed to fill in our diagram radios -the rule is to allow 1,000 circular The core material is our first problem. further. 110 x 3.75 gives us 412.5 turns. mils to each ampere. We find that the half - Fig. 2 says we need a core a little bigger Similarly, the secondary will need roughly ampere drain in the primary requires No. than lr/2 inches in cross -section. As our 1350-1350 turns, the 6.3 -volt filament 24 and 23, the secondary No. 30 and the two fila- Work must be done with junked material, the 5 -volt filament 19 turns. The figures as ment windings Nos. 18 and 17, respectively. we can not expect always to get just what calculated are 1312.5, 18.75 and 23.6, being (In transformers designed to run 24 hours per day, 1,500 circular mils per ampere may be allowed.) Since only half the secondary is carrying l' current at any time, we can cut down the Fy 1 wire size. We will use No. 31, a cut of 20% F75-1/ 20 t in the carrying capacity, though we could ?amp cut it as much as 1/3 if necessary. Eco- n #18 nomics can also be made on the filament core- 111 le windings, for being near the outside they have a better opportunity to dissipate heat 6.3 V _25t than the primary or secondary. We will use No. 18 instead of No. 17 for the recti- 1. Jamp #1.9 fier filament. It is rated at only 1.6 amperes at 1,000 C.M. per ampere, but can carry 6 amperes in open air. The filament winding 411110 just inside it can be cut down a little, too. 350V 1,350t using No. 19, rated at 1.3 instead of 1.7 1731 amperes. 111111, SIZE C T. CHECKING FOR WINDOW 100 I77113 rs Now that we know just about what we I/O f12t 411110 can use, we have to find if we can get this V` C. T amount of wire in the window. 41110 /,350t Referring to Fig. 3 under "Turns per 0.5a p 423 square inch" we find: 4111. 412 turns of No. 23 occupy 0.24 sq. in. 350V #31 2700 turns of No. 31 occupy .26 sq. in. Filament windings .22 sq. in. The filament windings in this case were calculated by allowing 1/16 inch for each 1942 10 RADIO -CRAFT for OCTOBER. Incorporating RADIO & TELEVISION

"RADIO'S GREATEST MAGAZINE"

The Axis Radio Agents must be elimi- DEADLY RADIO nated.. . TRANSMISSIONS

By the Editor - HUGO GERNSBACK

WE have found it necessary to speak from time to time of the It often takes quite a while before a mobile transmitter can be real peril confronting the United States, due to the activity run down, but we believe that sooner or later the majority of of Axis agents, who operate secret radio transmitters in them will be apprehended. the United States and its territories. The F.C.C. recently reported that approximately 100 monitoring This is all quite ancient stuff and, as often before, history merely stations have been set up during the last few years in order to repeats itself. stamp out the illegal short -wave transmissions from the United I probably was one of the first to point this out, even before States. These stations not only search out the illegal stations the First World War got under way, when the then Imperial themselves, but they analyze suspicious communications and un- German Government -even before the United States entered World known sounds as well. But we should realize that the monitoring War No. 1-succeeded in sending valuable information from the of all the multitude of wavelengths day and night is a tremendous United States to Germany. undertaking. and while recordings are made of every transmitter At that time, the German Telefunken Company had erected on on the air -located not only in the United States but of every Long Island a transmitter known as the Sayville Station. transmitter in the entire world (which can be heard in this In my former publication THE ELECTRICAL EXPERIMENTER, country) -I believe also that something more is needed, if we are (August 1915 number), I pointed out that secret messages to cope successfully with the menace. could no doubt be sent out over this station, violating the neu- It has been suggested many times that amateurs should monitor trality of the United States. It will be remembered that the director as many wave lengths as possible and report immediately any of the station went to great pains to denounce me, in no uncertain suspicious- sounding transmission to the proper authorities. terms, for the publishing of such a "fantastic story." Yet before The trouble with this plan is, that so far such listening posts the ink was dry, . phonograph records had been made showing to the best of our knowledge have not been organized in such a that the station actually had sent out high -speed signals, inter- manner that every section of the country would be under con- spersed with the regular signals, which could not be detected by stant surveillance 24 hours a day. In each section of the country the normal ear ; but by recording these signals on a phonograph there should be listening posts monitoring continuously certain record and then slowing up the record, the secret messages became wavelengths and no others. This in itself would be a huge under- clear. Subsequently, the United States Government took over the taking but it is believed that only in this manner full safety can Sayville Station and thus prevented secret messages from going be realized during the long war which we are certain to have. out over that channel. Nor will it be satisfactory to have even expert amateurs and In the present War, when there is a super -abundance of radio listeners just "listen in ". It is more important that there be a stations and facilities all over the country, it becomes much simpler record of each emission, and this means high -grade equipment for the Axis agents to use their ingenuity in trying to get informa- which few amateurs possess. tion out of the United States. Instead of only 100 F.C.C. monitoring units, we really need Troop and ship movements particularly, in the very nature of between 1,000 and 3,000 such posts, scattered all over the country things, must be transmitted speedily if the enemy is to get any and in our territorial possessions as well. In my estimation. trained advantage. The telegraph, telephone and cables are pretty closely radio amateurs, of which there are many thousands, and par- watched. and such slow means as the mails cannot be considered. ticularly men above 40 years who have been amateurs, could be The agents who are charged with the transmission of important sworn in by the Government for a listening -monitoring net- information must be resourceful; they also must be good radio work with only one purpose in mind to account for all illegal technicians, if they are to succeed at all. This makes the problem transmissions that may emanate from the United States. The all the more complicated for our authorities. No foreign agent problem is further complicated by what is known as the skip - would be foolhardy enough to operate a fixed transmitter. distance effect, whereby short -wave emissions are not heard at Taking a leaf from the book of our own bootleggers -who all in the immediate vicinity, and for that reason such stations operated mobile transmitters during prohibition -Axis agents are best monitored from a distant point, or points. With such a necessarily will use only such mobile transmitters. When located listening -monitoring network, mobile enemy transmitters could in automobiles or trucks they can be moved rapidly from point be watched and located much more readily than is the case now. to point and it becomes a problem of the greatest magnitude to The principle that it is easier to catch a fox with a dozen dogs, locate and apprehend the men who operate such transmitters. As than with two: holds good in radio as well. the agents for obvious reasons, use short waves almost exclusively. Finally, I wish to go on record once more and repeat what I their problem is simplified too. because such equipment weighs little have said numerous times -that I believe illegal messages can and can be readily concealed in an automobile, truck or motorboat. readily be sent out over our small foreign -language stations of There has been a movement in this country to prohibit the sales which there are too many in this country and territories now. The of all radio parts and accessories because it was thought that possibility of sending out secret intelligence through the means this would stop the assembly and manufacture of such illegal of an innocent violin or piano or other music solo should be spy- transmitters. apparent to every one. Such a course would he the height of foolishness, because The foreign -language stations are a powerful magnet to every any radio man, even without being a brilliant technician, can Axis agent who would like to try his hand on a new and fanciful easily assemble a good transmitter from junk radio receivers. It code, that can be sent out easily by radio performers without too thus becomes not only impossible but quite impractical to stop much danger of being apprehended. It is here that our greatest any wilful agent from plying his trade if he so chooses. vigilance should be centered for the duration. RADIO-CRAFT fqr QÇT9Bp, i,4942

THE RADIO MONTH IN REVIEW

NEWS FROM FM CENTERS CHICAGO -Some of FM's best tributes A Digest of have come from some of the nation's finest News Events of Interest musicians. Stravinsky, Koussevitzky, Deems Taylor, Stokowski and others have com- to the Radio Craftsman mented on the tonal qualities of FM. Among the latest laurel wreaths is a re- mark by Felix Borowski, one of the country's top musicians and composers who is also professor of music at Northwestern University. After hearing a piano concerto over \V59C, The Chicago Tribune's FM outlet, Dr. Borowski declared: "Frequency modulation is an answer to the prayer of music lovers who have longed -and many of them have spent years in longing -to hear musical instruments as they really are. "The greater fidelity of certain instruments under the new system has to be heard to be believed. This, it appears to me, is particularly noticeable in the case of the piano, whose tone with frequency modulation is not only a true reproduction of the original sound but often takes on a well- rounded singing quality that may not have been present in the performance that is broadcast. Altogether, I am convinced that the new system has a great future before it."

MILWAUKEE -FM is becoming quite a husky youngster in the radio world around these parts. According to figures obtained by W55M, The Milwaukee Jour- nal's 50,000 -watt FM outlet, following a recent comprehensive study, there were - as of June 1 -a total of 16,230 FM receivers in the 8,540 square miles which make up the W55M service area. These figures tally closely with those issued by FM Broad- casters, Inc., FM's national trade associa- RADIO EQUIPMENT FOR THE WAR AT SEA tion, which indicate 13,000 FM sets in the Long rows of radio transmitting equipment for the Navy are shown here in one of the vastly expanded city of Milwaukee alone. This amounts to factories of General Electric's radio, television and erectronics department. Many warships have not one but a number of transmitters and receivers of various frequencies and power. They carry also equip- an increase of more than 75% over totals ment for detecting enemy planes and ships as well as portable radio equipment for various uses. Besides shown in a similar study made last Fall. making radio equipment for the armed services General Electric is conducting courses in its care and use for many military and civilian technicians in government service. PHILADELPHIA -The unique color and sound film -"Listen! It's FM1"-pro- "TEMPORARY" FM STATIONS TO GET WARTIME LICENSES duced last fall by the General Electric Company to explain and illustrate the merits Because war conditions have caused connect with station transmitters would of frequency -modulation broadcasting, is great shortages in materials, equipment and come under the policy. Applicants for new now making the rounds of Philadelphia skilled personnel necessary to radio broad- facilities, however, are barred, except un- schools as an educational feature. Roger W. casting, the Federal Communications Com- der special circumstances, by an earlier Clipp, general manager of W53PH (oper- mission has announced that holders of con- "freeze" policy announced in April, which ated by WFIL), was so impressed recently struction permits for new f requency-modu- recognized the necessity for conserving with the instructive qualities of the film that lation (FM) radio stations may obtain li- critical materials and banned new grants he invited the entire Philadelphia Board censes during the war to operate presently for FM as well as most other types of of Education to view it. They concurred existing facilities, provided construction has broadcast radio. with his opinion, and Philadelphia school reached a point where the transmitter is The commission observed that the Coin- children are now learning what FM means presently capable of being operated to ren- munications Act does not contemplate ex- in terms of better radio reception. der a substantial public service. FM broad - tensions of time within which to complete casters obtaining licenses under this policy construction unless it appears that con- COLUMBUS, Ohio -W45CM in this will have to show that additional construc- struction can be completed within a reason- city, Ohio's pioneer FM outlet, has encoun- tion is not possible at this time and they able length of time. Nor is it desirable to tered what it believes to be the ultimate in must assure the Commission that construc- continue the issuance of special temporary listener loyalty. The owner of a new FM tion will be completed according to the authorizations upon a short -term basis. receiver, so pleased with the purity of FM rules, regulations and standards of the FCC However, it is desirable to encourage such reception, called up the station and offered as soon as the required materials and en- service as is now possible to listeners having to donate money if it should ever be needed gineering personnel become available. FM receivers. Accordingly, the commission to keep W45CM on the air! The gentle- According to FCC records there are 5 will give consideration to applications for man's generosity was politely declined, of licensed FM stations now in operation. licenses to cover partial construction of course, but W45CM says the incident shows Twenty -three stations are operating under FM and ST (studio transmitter) stations how much the public appreciates and ap- special temporary authorization pending where such construction has proceeded to proves of noise -free, full -fidelity broad- completion of construction in accordance the point where it is possible to provide a casting. with the construction permits. Upon ap- limited but satisfactory FM service. The propriate application these would receive commission will also consider applications licenses to replace the special temporary where construction has been completed and authorizations. An additional 7 stations are the permittee has been unable to obtain CBS MOBILE TELEVISION now conducting program tests and have equipment and technical personnel to make PERMIT filed applications for operating licenses. measurements, required as a prerequisite to The new policy under which the FCC will issuance of a license. Such licenses will be Columbia Broadcasting System was consider applications for operating licenses granted on the definite understanding that granted modification of its construction on the basis of partial construction proba- as soon as the required materials and per- permit for a new portable mobile television bly will affect also 21 other holders of FM sonnel are available steps will be taken to relay broadcast station, W2XCB. Comple- construction permits. Six permittees now comply fully with the original construction tion date was extended from July 7, 1942, to building studio transmitter links, which permit. January 7, 1943. 8 RADIO- CRAFT for OCTOBER, 1942 SERVICING

COPPER WIRE TABLE -ENAMEL INSULATED WIRE Fig. 3 Carrying Capacity B. & S. Diameter Diameter Circular Mils Turns Turns per Feet per W. Ohms per (amperes) Nearest (A.W.G.) M.M. Mils (Bare) per in. sq. in. 1000 ft. 1000 C.M /amp. 1500 C.M /amp. S.W.G. 14 1.67 65.9 4107 14 182 69.4 2.575 4.1 2.7 16 15 1.49 58.8 3257 16 240 100 3.247 3.3 22 17

16 1.33 52.4 2583 18 310 126 4.094 2.6 1.7 18 17 1.19 46.9 2048 21 397 159 5.163 2.0 1.3 18

18 1.06 41.8 1624 24 493 201 6.510 1.6 LI 19 19 .95 37.4 1288 26 592 253 8.210 1.3 0.86 20

20 .848 33.4 1022 29 825 319 10.35 1.0 .68 21 21 .76 29.9 810 33 1100 402 13.05 .81 .54 22

22 .678 26.7 642 37 1380 507 16.46 .64 .43 23 23 .605 23.8 510 41 1725 639 20.76 .51 .34 24

24 .54 21.3 404 46 2160 805 26.17 .41 .27 25 25 .482 19.0 320 52 2715 1010 33.00 .32 21 26

26 .431 17.0 254 58 3425 1280 41.62 25 .17 27 27 .386 15.2 202 64 4300 1610 52.48 20 .13 29

28 .35 13.6 160 72 5410 2030 66.17 .16 .11 30 29 .309 12.2 127 82 6730 2550 83.44 .13 .084 31

30 274 10.8 101 91 8475 3220 105.20 .10 .067 33 31 246 9.7 80 100 10425 4050 132.70 .079 .053 34

32 223 8.8 63 113 13000 5120 167.30 .063 .042 36 33 .198 7.8 50 127 16550 5430 211. .050 .033 37

34 .175 6.9 40 143 20500 8160 266 .039 .026 38 35 .155 6.1 32 158 25500 10200 335 .032 .021 38-39

36 .140 5.5 25 175 31800 12850 423 .025 .017 39-40 37 .124 4.9 20 198 39800 12690 533 .020 .013 31

38 .112 4.4 16 224 49200 20500 673 .016 .010 42 39 .0965 3.8 12 248 62500 25800 848 .012 .008 42

40 .0862 3.4 10 282 77000 32573 1069 .009 .006 44

All figures with the exception of Circular Mils. are given for Plain Enamelled copper wire. M.M. stands for millimeters, mil for I /1000 inch. S.W.G. is British Standard Wire Gauge. for the full length of the winding, as each down to 13,, by 7/16 inch, or just a trifle volt, which should give him plenty of extra will take up one layer in this job. over a square inch, and leaves us a clear- space. How to do the winding was described If we add 25% for insulating paper, the ance of 10 %. in the previous article, which appeared in total area of our winding will be about 0.90 If the winder lias already tried his hand Aug.-Sept. Radio - Craft. sq. in. The core window is 2,4 by 11/16 at a few old transformers, he can go ahead, Output and audio transformers are wound inches -at first glance amply large. But we certain that his windings will be smaller to a different set of rules. Generally the must allow rjb inch for the core piece and than estimated above. Otherwise he would design is based not on watts output and volt- to insure ample clearance around the core, be well advised to increase his 10% leeway age ratios, but rather on such factors as and at least 3/16 inches at each end, so to about 25% by using a few more lamina- impedance matching, frequency response that our windings may be short enough to tions, and cutting down the number of turns and core losses. Should Radio -Craft read- permit insulation and clearance at the win- per volt. For example, if he makes his ers be interested, a future article will be dow ends. This brings our window size core 114 x 13y he can wind at 3 turns per printed to cover this subject.

OHMITE EXPANDS FACILITIES FOR STANDARD PRODUCTS WORLD WAR II found Ohmite Mfg. industry-all have received the increased in training, especially in Signal Corps and Co. producing units of vital importance output of this company's expanded facil- aviation schools, at a nominal price of ten to industry and the Armed .Forces-rheo- ities. Devoted exclusively to the manufac- cents. From all reports, this calculator is stats, resistors, and rotary tap switches. ture of rheostats, resistors, tap switches and doing its part well in the war effort. unnecessary. Conversion was Increased chokes, Ohmite is well able to supply the its production, however, was imperative. needs of industrial, aviation, radio, elec- This company and employees are The completion of a large addition to the tronic, and scientific manufacturers, radio proud to have a vital part in the arming of In still factory doubled the production space avail- jobbers and others. Everything possible is our country. another way these The moving whole workers have shown their patriotism -the able. of departments at being done under present conditions to work flag more than 90% a time into the new building was worked with jobbers in promoting present markets. Minute Man showing transfer cooperation in the War Bond drive, flies out in advance so as to permit the Jobbers in many areas are serving industrial over the factory. without the loss of a single production day. experimental, development, and mainten- Recently another nearby building was ac- ance needs. Also, they are serving essential Ohmite has not forgotten the future. quired which added fifty percent more pro- requirements of local training centers and When the war is won, its products will duction space. Besides utilizing the addi- schools. again serve every need of industry and indi- tional space to sten up production, a night A most unusual aid to the war effort has viduals. Present development work and en- shift has kept the windows of the plant been provided by the Ohmite Ohm's Law larged facilities are expected to permit even blazing with light for many months past. Calculator. This handy little device has better service in the future than the note- Planes, tanks, ships, communications and been distributed in large quantities to men worthy service it has provided in the past.

RADIO -CRAFT for OCTOBER, 1942 II SERVICING Analysis and Alteration or.agliffilk4 of an Analyzer

By TED POWELL

THE owner of high -grade test equip- sign suggestions were prompted by the type ment generally is reluctant to make any of service work the writer has been en- constructional or wiring changes in his gaged in, and the circuit analysis is given equipment because of the voiding in the belief that other servicemen might clauses contained in the manufacturer's use it as a guide either for alterations or guaranty. for a better understanding of the same or The chances of failures directly attrib- similar instruments. utable to any possible manufacturing de- The first operation consisted of some fects, however, are small indeed, and the cabinet -making work. The analyzer comes radio man who finds need for expensive in an enclosed type of portable case typical equipment usually can take care of these of laboratory equipment. While this style occurrences himself or can afford special- of case has its advantages where portability cut saw. The cut was made as close to the ized factory repairs where necessary. There- is concerned, it is something of a handicap partition wall as possible so that the saw fore his desire to make revisions for the in bench -work testing. The inconvenience teeth just cleared it. The three -walled ridge purpose of increasing the utility of his in- lies in its cumbersome size and the greater that was left was then planed down and fin- strument carries with it only the slight ele- handling effort required, a point which must ished off flush with the partition wall with ment of chance regarding the guaranty. be seriously considered where continuous a fine rasp and sandpaper. The wood sur- Analyzers of the class to be described are day -long checks must be made. face was touched up with thin coats of engineering developments, and the sugges- The panel which supports all the analyzer shellac and lacquer, each rubbed down and tions for changes should not be interpreted components (except the C batteries) was polished when dry. as criticism of the original design. Rather, removed from the case and the small com- This partition wall was made to serve as it should be understood that the alterations partment above the meter panel was un- the new bottom of the analyzer case. The -in this case on the Weston 772 -and de- ceremoniously amputated with a fine cross- manufacturer's tag and all the hardward was removed. Wood screws were replaced 000v 1[ where necessary to fill up 10 AMP 10 AMP 5.000 old screw holes. a C . A.[. The case handle was mounted at the new 9$954000 4,63151 OHMS O O 0rns top of the case and the manufacturer's tag 'TELlv1n.- screwed down into place in the center be- neath it. The eight rubber toes were reset i o at the corners of the new ' a(. VOLTS o.e.e.-o..i a bottom and the OHMS. M.A new shortened back. The toes on the bottom 23i' A C. VOLTS are for rapid readings in a vertical meter position and those at the back are for more O O accurate checks in a horizontal position. A 026 meter's zero set and general accuracy is 2yr somewhat better in a horizontal position be- o o cause of better meter movement assembly balance in this position. The old case cover was discarded. o The photograph shows the simple case alteration plainly enough SOYA 2500'0C so as to obviate 25 VOLTS IMAC OUTPUT the necessity for any diagrams. The result 26.313' METEO is a trim -looking, open - faced, bench -type analyzer.

DECK In the writer's short experience with in- NEAREST dustrial and radio analyzers which have PANEL had to withstand constant and hard usage Moo 2.51E O.- (various industrial and radio analyzers 7500. 150.000; 10 v. O aboard U.S. Naval warcraft, for instance) ONU. ADJ 400oM 600.000. the small potentiometer tvoe wire -wound 50V 0 AC. VO ITS resistor used for zero-setting the ohmeter 2040 4MEG. ONLY 15.000 250V 0 R ranges for variations in battery voltage were 754 15M L 1.0006 0 found to be too light to stand up under punishment. The designers apparently figure 250rÁ0 O o NORMAL - A212' ac volTS the resistor size on a wattage basis rather 50M --0 than on a mechanical -wear basis. The net 1.32 2104. S 101AA O result is worn shafts, shaft bushings, R 4000 276.760 rheostat contact arms and resistance ele- O ments. This results in a wobbly knob and 0.210000 o -o erratic control over the meter needle when A110 O O- attempting to zero-set the ohmeter ranges. This can be a considerable time- wasting R O o nuisance where many accurate low- ohmage readings must be taken on more than one range. As a result, the small 15,000 ohm potentiometer was replaced by a heavier 2 -watt unit which just cleared the case's inner wall. The shaft bearing surface was FIG. 1 oiled lightly to prevent excessive wear. The analyzer wiring, as is the case with Sc.rr.Mc Op nearly all such equipment, was laced with beeswaxed cord in the familiar "roll" and

12 RADIO -CRAFT for OCTOBER, I 9 4 2 'SERVICING

"lock" stitches. The lacing was drawn SIMPLIFIED CIRCUIT ANALYSIS ohms would be required to obtain this range, tightly as is the best practice in order to It is interesting to break down the vari- since 500 volts divided by 500,000 ohms produce neat looking forms. Although this ous analyzer circuits in an elementary equals 1 ma. This total resistance would may look pretty, it is not very beneficial fashion, analyze the methods by which they be distributed between the meter circuit from an insulation point of view. The meter are obtained, and attempt to set up theo- and multiplier sections : 497,500 ohms in movement is a highly sensitive 50 µa. unit retical values of circuit components neces- the multipliers and 2,500 ohms in the meter and its readings will be appreciably effected sary for new ranges not incorporated in the circuit. This would be obtained in a 250,000, by small leakage currents. The thinly in- analyzer. We might begin with the voltage 200,000, 40,000, 7,500, and 2,500 ohm sulated hook -up wire pulled tightly to- ranges since they are the least involved. (meter) arrangement. The 1,000 -volt range gether by the lacing can cause trouble The D.-C. ranges when isolated and re- would then have its own sectional multi- where moisture -laden air or chemical fumes plier of 500,000 ohms instead of 750,000 ship or arranged a bit, become the equivalent of are present, salt -sea air aboard the circuit shown in Fig. 2. If we check the ohms to maintain the necessary total multi- fumes in industrial plant. All lacing plier resistance 1 megohm. In an 2.5 -volt range, we find a series of resistors of other was carefully clipped away with a pair of whose 26,313, 21,187 and 2,500 words, the 1,000 -volt sectional multiplier manicuring scissors. The formed wires values are has in (meters) ohms for a total of 50,000 ohms. effect been tapped at 250,000 ohms held their shape fairly well without the the -volt The meter is rated at 50 µa at .125 volts to obtain extra 500 range and this supporting lacing cord anyway. with an internal resistance of 2,500 ohms. tap has been obtained by replacing the The A.C.-D.C. switch was replaced by a According law, 750,000 -ohm unit with two equivalent re- to Ohm's we get a check 250,000 high -voltage rotary switch and a knob was on our circuit tracing operations. Thus, 2.5 sistors of and 500,000 ohms each. The 1,000 range purchased from \Veston to match the volts divided by 50,000 ohms gives us 50 new circuit for the -volt ohmeter zero -set knob. The knob was set would be 500,000, 250,000, 40,000, 7,500 and so that the white indicator on the knob 2,500 ohms for the required total of 1 swung to equidistant positions from the megohm (1 megohm divided into 1,000 A.C.-D.C. markings on the panel. This too volts equals 1 ma.). See diagram 3. is a minor alteration but it results in an In a similar fashion a 500 -volt D. -C. improvement in the appearance of the ange can be set up in 5 megohms, 4 meg- analyzer. ohms, 800,000 ohms, 150,(00 ohms, 21,187 Since the analyzer was to be used as ohms, 2,500 ohms (meter) and 26,313 ohms laboratory equipment (although strictly for the necessary 10 megohms. (500 volts speaking it is not), some minor resistor divided by 10 megs equals 50 µa.) The new replacements were made. Looking at the 1,000 -volt D. -C. range would then be in wiring diagram (Fig. 1), it can be seen a 10- megohm, 5- megohm, 4-megohm, 800,- that the two banks of resistors starting 000 -ohm, 150,000 -ohm, 21,187 -ohm, 2,500 - with the 7,500- and 150,000 -ohm pair and ohm (meter and 26,313 -ohm set -up for the ending with the 750,000-ohm and 15- required 20- megohm total. (1,000 volts megohm pair, constitute the voltage -range divided by 20 megs equals 50 µa.) See multiplier section. The left bank is the diagram 2. A.-C. µa, which is what the meter should draw section and the right the D.-C. sec- at Thus by applying Ohm's law we can set tion. The 200,000, 750,000, 800,000, 4 meg- full -scale deflection. Making up a sim- ranges. ple chart for the D.-C. volt ranges we get up any desired volt ohm and 15 megohm units are carbon re- Figure 4 shows the D.-C. current ranges sistors. The 200,000, 750,000 and 800,000 the result shown in the chart, which includes all the analyzer ranges. rearranged and simplified a bit. The process ohm units were replaced with IRC Pre- these is The A. -C. volt ranges are shown in Fig. of isolating current ranges compli- cision 1% wire -wound resistors. Wire - cated slightly by the fact that the lighter wound units in the 4- and 15- megohm sizes 3, in which are drawn the complete meter ranges circuits omitted in the analyzer circuit dia- current are selected by the selector are impractical because of the excessive switch and the heavier current ranges by size, insulation difficulties and great costs gram for the sake of clarity. Resistor A is a series adjusting spool for accurately the jacks and two smallest current are involved. Besides, such resistors would selected by jacks, rather inconsistently. have to be specially made and this is out setting the total meter circuit resistance to 2,500 ohms. Resistor B is sensi- However, upon some simplification, we get of the question in times such as these with a current- the simple series -shunt affair shown in a war to be won and priorities governing tivity and temperature -compensating spool Fig. 4A. nearly all production. Therefore, metallized for controlling the over -all A. -C. tem- Type F IRC resistors were ordered in a perature characteristics of the meter cir- If we take the 1 ma. range for an ex- 1% tolerance rating for these two ranges. cuit. Resistor C is a full -scale adjustment ample and set up a still further simplified network, we get a shunt leg containing a One tenth of 1% precision resistors were spool adjusted at the 2.5 volt range for exact full -scale deflection at 50 µa. Resistors D, E meter resistance of 2,500 ohms, a resistance considered, but since the meter calibrations of 2,500 ohms in series with it and a and the various resistors in the analyzer and F are the rectifier load units and also auxiliary temperature-compensating resis- paralleling shunt leg of 262.787 ohms in are held to within one or two per cent parallel with it. Remembering that a full- limits, this is unnecessary. tors. Each analyzer's meter circuit is carefully adjusted at the factory under tempera- The 7,500 -ohm resistor in the zero -set ture- control conditions by means of spools leg in the ohmeter circuit was replaced with A, B and C and therefore the exact values a 1% wire -wound unit, but this change of these resistance spools will vary some- AIOA IA +2SOMAtSOMA 1011A MA 100,LLA what. However, in analyzing the A.-C. volt ranges, the effects of the rectifier and other resistances will be ignored except for the fact that the meter sensitivity is only 1,000 ohms per volt at these ranges. This is a point that must be borne in mind since we now have a rectifier circuit included in the meter circuit. Meter sensi- F16.4A tivity no longer is 20,000 ohms per volt but 2,500a QG CURRENT RANGES is 1,000 ohms per volt. The total meter current drawn now is 1 ma for full -scale deflection instead of 50 µa. Ignoring the FIG.18 effects of the various compensating re- 01. CURRENT RANGE sistors, which are minor in their nature, FOR 1 MA RANGE we can set up a simple chart for the A.-C. (SIMPLIFIED) volt ranges similar to the D.-C. ranges. (At 2,500n these A.C. ranges the meter "resistance" is still 2,500 ohms but at a sensitivity of (262,187nIN SHUNT) 1,000 ohms per volt at 1 ma at 2.5 volts.) (2,500 n IN SERIES) Both volt -range charts can be used to make simple alterations of the analyzer circuits. Suppose a 500 -volt A.-C. range were obviously is not essential. One happened desired (one used in radio service work scale meter deflection requires 500a. or to be on hand (it sells for about 60c) and with some frequency), and a rotary switch .125 volts, we know that a voltage drop it was installed, leaving only two resistors with more than 12 positions were avail- of 25 takes place across the meter- resistor in the analyzer which were not wire- wound. able. A total circuit resistance of 500,000 (Continued on page 58) RADIO -CRAFT for OCTOBER, 1942 13, SERVICING TRACKING DOWN GRID EMISSION Causes and Cures for a Trouble -Making "Bug"

AMONG the many "bugs" that find graphite is sprayed on plates and bulbs to their way into a radio circuit, there increase the heat radiation to the outside Is one that has caused untold grief away from the grid, -all to keep the in- and confusion to the serviceman. Its ternal tube structure cool. common name is GRID EMISSION We conclude, therefore, that excessive Although it starts life as a tiny electron, heat is the factor that must be avoided if it soon grows to huge proportions. It is we are to keep away from grid emission. elusive in its ways, and much valuable time More recent tube types are of higher may be lost merely in determining its pres- mutual conductance than those of the earlier ence. After that, more time is consumed in days and in order to obtain this increase in solving the serious problems that it creates. mutual, the spacing between the grid and No doubt, you are familiar with some of cathode has been greatly reduced. As a re- the following complaints: blocking, loss of sult, the grid is close enough to the cathode sensitivity, lack of selectivity, distortion, so that excessive heater voltage, or cathode burned out plate and screen resistors, low current will heat the grid to the emission emission rectifier and power tubes, and hum. point. These are a few of the problems of grid Another recent factor aiding the evil of emission and they are generally reported to grid emission is the trend toward the zero - take place after the receiver has been in bias type of receiver operation. In this type operation long enough to become over- of circuit the DC resistance in the grid re- heated. turns are generally very high. This results Perhaps you have tested tubes, conden- in a higher disturbing -voltage drop, and at sers and resistors, yet you found every- the same time fails to produce a negative thing to be normal. Try though you may, bias voltage which would be helpful in you have never located the cause of these opposing the disturbing voltage. drop is the HARMFUL factor. Current complaints, although you may have effected The r -f circuit shown in Fig. 1 represents flowing from the diode to the grid produces a cure by the cut and try method. Of course, a typical zero-bias arrangement which we a negative voltage at point X, but current you know that the cathode of a radio tube will use to follow the actions of grid emis- going from the grid to ground produces a is designed to emit electrons; but this is sion. positive voltage. Therefore, at point X we not true of the grid. Grid emission, as the Let us assume that the initial bias on the have +3 volts developed by the grid cur- name implies, means that the GRID gives tubes derived from the contact potential of rent flow, minus the -1 volt of bias caused off or emits electrons. When electrons flow the diode is -I volt. We will also assume by contact potential, leaving a +2 volts. there is also a flow of current, (as can that the receiver has been in operation long This means that at the grid of each tube be seen if we place a milliammeter in series enough to become sufficiently over -heated to on the A.V.C. string, there are 2 volts of with the cathode) and current flowing stimulate grid emission. The excessive heat positive voltage'. You and I know that we through coils and high value resistors in may be caused by improper ventilation, high cannot use positive voltage on control grids. the grid return circuit, will produce a volt- line voltage, or the exceeding of the voltage It must be negative! age drop detrimental to good circuit per- ratings of the tubes. With positive voltage on the grid, the formance. The grid of any one of the tubes, being plate current increases, causing more heat Why do we have grid emission? Well, overheated, will now give off electrons and within the tube, thus liberating more elec- during the process of evacuation of a radia current will flow. To start with, this cur- trons from the grid. This continues in a tube a small portion of the cathode emit- rent is very very small, being only about vicious circle until the positive voltage at ting material is sometimes unavoidably one microampere. However small though the grid becomes high enough to block the splashed on to the grid with the result that it may be, it must return to ground. There- tube. Plate and screen resistors may burn should the grid become sufficiently heated fore, it flows through the r -f coil, through out, rectifier tubes are overloaded, and during operation, it will emit electrons. the A.V.C. resistor R, on through the sensitivity falls off, due to the change of To reduce this disturbing effect every volume control to ground. During its course characteristics brought about by grid emis- precaution is taken in the design of Syl- to ground the current had to pass through sion. vania radio tubes to keep the grid as cool the A.V.C. resistor R whose value is three possible. Fig. 2 represents a typical power output as Copper grid supports are used megohms, and, according to Ohm's law, stage. Here grid emission is more trouble- because copper, being a good heat conductor, current flowing through a resistance must carries the heat away from produce some, clue to the greater amount of heat the grid. Grid a voltage drop. As E = IR we generated within the power tube. The grid radiators are attached to the grid to give then have a voltage developed across R radiation current flowing in R. can become sufficiently a greater heat area. Colloidal equal to 3 volts. The polarity of this voltage high to cause enough positive voltage to cancel out the negative bias thereby producing bad distortion. At the same time the resultant heavy plate current will in a short time liberate gases from the over -heated elements. With the ionization of the gas the cathode is bombarded by positive ions and its emission is destroyed. To prevent the possibility of such de- structive effects, tube manufacturers issue specifications as to the maximum permissible voltage ratings that may be applied to each tube. also the values of permissible DC resistance in the grid -cathode circuit. These values must be adhered to at all times for satisfactory tube operation. The effects of grid emission are to some extent minimized by the employment of automatic or self -bias in which grid bias is derived from a resistance in the cathode "r filament return. An increase in plate current tends to increase the effective negative bias applied to the grid, thus opposing the cumulative effects of the positive voltage caused by grid emission. (Continued on page 50) 14 RADIO -CRAFT for OCTOBER, 1942 SERVICING

TESTING SMALL POWER TRANSFORMERS By H. R. HEAP

THE following simple tests can be car - Power Factor: ried out by the average amateur with- Watts out the use of complicated apparatus. P.F. = Volts X Amps (1) Voltage ratio (4) Iron loss The power loss in the core, due to eddy- (2) Temperature (5) Copper loss currents and hysteresis, are obtained by'di- rise (6) Regulation viding the power, as read on the wattmeter, (3) Polarity (7) Flash test by the voltage across the primary.

VOLTAGE RATIO COPPER LOSS Fig. 1 show, the connections for check- The copper -loss test is carried out in the ing the voltage ratio, when the secondary same way as the iron -loss test, except that voltage is known annroximately and is the secondary is shorted. The voltage ap- within the range of an available voltmeter. The meter should preferably be of the electrostatic type or a moving -coil instrument and rectifier with a resistance of at least 1,000 ohms per volt. because in actual operation the transformer If the output of the secondary is not is usually inside a closed cabinet and the known or is not within the range of an cooling will not be so effective. When conducting tests, a piece of plasticine should be used to bed the thermometer on to the windings. If the test is run for a considerable time the temperature of the core can he measured. The tests should be taken with full -load currents in all windings. 4 POLARITY Sometimes it is useful to know the polarity of transformers, such as when connecting them in parallel. This may be deter- Fig. 5 O

available voltmeter, it is safer to connect A.C. the A -C line across the secondary and measure the primary volts. An obvious exception is a filament transformer or a plied in this case s::ould b¢ vc p much less model -railway transformer, but these types than the normal line voltage so that the of transformer can easily be identified by current flowing in the secondary is limited the fact that the secondary winding has a to its normal full -load value (which can very low D.C. resistance. whereas the pri- be measured with a meter in series with mary has a medium resistance. The com- the winding). Alternatively, the primary parison of resistances can be made with the voltage can be arranged to give the calcu- aid of a battery and flash -lamp bulb. The lated primary current on full load. lamp will light to about half brilliance with Whereas the iron loss is practically con- the primary in series, but will light to full stant for all loads (being roughly propor- brilliancy when a low- voltage secondary is tional to the square of the voltage). the connected in series. This method can be used copper loss increases with the square of the to identify the windings of a power pack current. The copper loss is given by the transformer, as the high -voltage secondary mined, if the primary and secondary are wattmeter reading. is usually of such a high resistance that connected in series and placed across the the lamp will not light at all. A -C supply as shown in Fig. 3. The volt- REGULATION AND EFFICIENCY age across the secondary will be smaller Fig. 5 shows the connections for regula- TEMPERATURE RISE than the line voltage when the windings are of the same polarity. When the polari- tion test. The secondaries are loaded up to Although this may not seem to be very their full value with resistances of a non- important, the temperature rise of a trans- ties are reversed, the secondary voltage will be greater than the line voltage. inductive type, and switches arranged so former should be checked. The reason is that the transformer may be tested with in ordinary insulating materials that using IRON LOSS and without load. The voltage of the wind- it is necessary to limit the maximum tem- ing to be checked is measured first on no perature at any spot inside the coil to about Fig. 4 shows the connections for an iron loss test. The voltmeter and ammeter give load and then on full load and the regula- 90° C. (190 °F.), this being the maximum tion percentage obtained from the expres- temperature to which normal insulation ion: should be allowed to be heated. Except by inserting thermocouples inside the wind- 100 (No load Volts -Full discover load Volts). ings, it is not easy to the actual Regulation = "hot spot" temperature of the transformer, Full load Volts. consequently it is usual to measure the tem- Total secondary Watts x perature on the surface of the windings by means of a thermometer (Fig. 2). 100 The efficiency = Another method is to measure the varia- primary Watts. tion in the resistance of the windings as the transformer heats up, but this is not always FLASH TEST convenient or necessary. With a thermometer it is usual to limit the rise above room To check the insulation between windings temperature to 30° C. (86 °F.), so that as- the V.A. (Volts -Amps) of the primary and from copper to ground a flash test is suming the room is at 20° C. (68 °F.), this and the wattmeter gives the actual watts necessary. For ordinary small transformers allows for an actual surface temperature consumed. Except for unity power factor with 250 volts secondary a flash test at of 50° C. (122° F.). This figure should nev- these values will not be equal and when about 800 volts is all that is necessary. er be exceeded when testing in the open measured give an approximation of the -Radio Society of Great Britain Bulletin .p4A,DIOr;9FT., fofvt .,:..13V 15 SERVICING

Radio Service Data Sheet 326

EMERSON MODEL 436 HIGH -FIDELITY A.C. SUPERHETERODYNE

the screw entirely. Loose screws are a sure sponse. Realign at 1600 kc. source of noise. drifting, and microphonism. To align the loop, set the dial pointer at 160. Set the signal generator at 1600 kc and Location of Coils and Trimmers feed its output into a loop of wire about 12 The two triple -tuned I -F transformers are inches in diameter. Hold this radiating loop mounted in cans on the top of the chassis. about 12 inches from and parallel to the re- The trimmers are available through holes in ceiver loop antenna. Advance the output of the tops of the cans. The copper colored screw the signal generator until deflection is ob- -is for the tertiary coil. The first I -F trans- tained on the output meter and then adjust former is next to the 6L6 tube. trimmer on loop for maximum response. The broadcast antenna coil is the open coil on the top of the chassis between the 6SA7G and the 6K7GT I -F tube. The trimmer for the RECORD -CHANGER MODEL coil in mounted on top of the coil. The Emerson Model 372, housed in the The interstage coil is the larger of the two Georgian period console, contains the same coils underneath the chassis. Its trimmer is chassis as the high fidelity receiver but has located on the right end section of the variable in addition an automatic record changer. cdndenser. For this model the following notes apply: The trimmer for the loop is mounted on the Before servicing the automatic record loop board. changer, inspect the assembly to see that all This Emerson 8 -tube High -Fidelity receiver levers, parts, gears, springs, etc.. are in good order and are correctly assembled. has an output rating of 20 watts. 1 -F Alignment A bind or jam in the mechanism can Push the switch at the rear of the chassis to usually be relieved by rotating the turntable "external antenna" and feed 455 kc through in the reverse direction. GENERAL NOTES 6K7 a .01 mf condenser to the grid of the The changer can be conveniently rotated The receiver should never be turned on I -F tube. Unscrew the copper colored screw through its change cycle by pushing the index with either the speaker plug or the 6L6G of the second I -F transformer as far as possi- lever to "Reject" and revolving the turntable tubes out of their respective sockets, since ble and then align the other trimmers of this by hand. Six turntable revolutions are re- the rapid rise in rectifier voltage will damage transformer for maximum response. Shift the quired for one change cycle. the to the electrolytic condenser. input to the grid of 6SAT (clip input If the record changer or cabinet is not section When replacing the chassis in the cabinet stator lug of right end of variable perfectly level, normal operation is likely to take precautions to keep any part of the dial condenser) and repeat the same procedure on be affected. the the and condenser assembly from touching the first I -F transformer. Do not disturb The 10 and 12 inch records must be abso- cabinet, otherwise microphonism will result. alignment of the second I -F transformer. lutely flat for smooth operation when using The color coding of the I -F transformers is as Feed the signal again to the 6K7GT I -F tube. a mixture of the two sizes. follows: shunt the and secondary of the sec- primary Incorrect adjustment of a particular mech- Plate 25,000 ohm resis- Grid -green -blue. ond I -F transformer with anism of the changer is generally exhibited B plus -red Grid return -black tors, and adjust the tertiary (copper color) in a specific mode of improper operation. The The color coding of the power transformer is trimmer for maximum response. Again feed following relations between effects on opera- ns follows: the grid . f the 6SA7, shunt the primary and tion and the usual misadjuatments will enable Primary-two black leads secondary of the first I -F transformer with ready adjustment in most cases. High -voltage secondary -two red leads resistors and then, without removing the For any irregularity of operation, the ad- High -voltage secondary center tap -red and shunting resistors from the second transform- justment of the main lever should be checked yellow lead er, adjust the first transformer tertiary for first. 6.8 volt secondary leads maximum response. Do not disturb the align- -two green If needle does not land properly on 12 inch 5 volt leads ment of the second -F trimmers. Re- secondary-two yellow of any I record but correct on 10 inch -Effect adjust- The switch located at the rear of the chassis move the resistors and sweep the signal gen- ment "E ". is provided to allow the use of either the en- erator through the band. The response should On failure to trip at end of record -In- closed loop antenna or an external antenna. be quite flat with a slight peak in the middle, crease clutch friction by means of screw. Push the switch to width the left for use of external with a band of about 10-12 kilocycles. Also, see that levers are free to move with- antenna. Visual alignment may be used in which case out touching each other. receiver The has a self-contained antenna a similar procedure should be followed ex- If pickup strikes lower record of stack or loop and normally does cept that will be not require additional it unnecessary to shunt the drags across top record on turntable -Adjust antenna or ground connection. However, in lo- transformers ' with resistors. With either lift cable. cations far removed from broadcast stations method of adjustment, however, the align- If needle does not track after landing or. in shielded locations, ment should be repented - an outside antenna until a satisfactory, Friction clutch adjustment may be too tight; may be used to improve reception of weak broad response curve is obtained or the fidelity there may be a bind in tone arm vertical stations. of reception will be seriously impaired. bearing levers fouled; or pickup output cable twisted. ADJUSTMENTS R -F Alignment If cycle commences before record is com- An oscillator with frequencies of 455. 600 With the switch at the rear of the chassis in plete-Record is defective, or adjustment of and 1600 kc should be used. the position marked "external antenna" set friction clutch is too tight. An output meter should be used across the the pointer at 60 and feed 600 kc to the ex- A wow in record reproduction indicates voice coil or speaker output transformer for ternal antenna lead through a standard dum- that the record is defective. observing maximum response. my antenna or a 0.0002 mf mica condenser. If record knives strike edge of records- Use a standard dummy antenna or a .0002 Adjust the series padder (located at the left Records warped; record edges are rough; or mf condenser for aligning the antenna coil. of the variable condenser, on the top of the knife adjustments are incorrect. Always use as weak a test signal as possi- chassis) for maximum response. Move the Record not released properly -Adjust record ble during alignment. pointer to 160, feed 1600 ke and align first the ehelt assemblies in respect to shaft. The last motion in adjusting trimmers oscillator trimmer (right end condenser sec- Needle lands in 10 -inch position on 12 -inch should always be a tightening one, not a tion) and then the interstage and antenna record or misses record when playing both loosening one. trimmers (see preceding for location) for types intermixed-Increase tension of pickup Never leave the trimmer with the outside maximum response. Return to 600 he and ad- locating lever spring. plate so loose that there is no tension on the just the series padder (while rocking the screw. Either bend the plate up or remove variable back and forth) for maximum re-

VOLTAGE ANALYSIS Readings should be taken with a 1000 ohms- per -volt meter. Voltages listed below are from point indicated to ground (chassis) with the volume control turned on full and no signal. Line voltage for these readings was 117 volts, 60 cycles, a.c. All readings except B plus at rectifier. heaters, and cathode voltages were taken on 800 volt scale. Tube Plate Screen Cathode Heaters 1 6K7GT 245 70 6.3 6SA7GI 245 70 6.3 6K7GT 235 70 6.9 6SQ7GT (det.) 125 6.9 6SQ7GT (P.I.) 150 6.9 6L6 (2) 275 285 1 .5 6.3 Voltage drop across field -65 volts. Voltage at 5Z3 filament to ground -850 volts.

6 RADIO -CRAFT for OCTOBER, 1942 SERVICING

Radio Service Data Sheet 326

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RADIO -CRAFT for OCTOBER, 1942 17 SERVICING LOW -CAPACITANCE A-C POWER SUPPLIES By GARRARD MOUNTJOY and CHARLES W. FINNIGAN*

ACCEPTABLE HUM INTENSITIES SUMMARY -Wilk the curtailment of A is 1.6 volts. This produced 17 microwatts MOVULATION hum may be meas- strategic materials, particularly aluminum, of hum in the voice coil of substantially ured in decibels below 100 per cent the design of power filters with a minimum 120 -cycle tone. The speaker used was of modulation for full undistorted of capacitance is of increasing importance. the light six -inch type having a 700 -ohm signal output. Reduction in hum to If aluminum for electrolytic: is to be 2 -henry field utilizing 0.2 pound of copper provide a 40 -db discrepancy may be con- available in restricted quantity, the use of in the winding. The capacitors used were: sidered acceptable for some low -priced de- low- capacitance sections, say 1/3 the size signs, with 50 db considered excellent and of previous liberal design practice, is indi- C, -1µf 60 db superlative. Zero signal hum levels cated. If, however, aluminum is to be re- C, =2µf may be measured directly in intensity. With stricted totally, then paper capacitors are C, =1µf a medium sized dynamic speaker of aver- the logical substitute. This paper describes age sensitivity the consumer used to be a few filter systems which employ sufficient- Increasing C. to 2 µf reduced the zero satisfied with as much as 100 microwatts ly low -capacitance filter sections to permit signal hum to 5 microwatts. The capacitors of hum. However, within the last few years the use of paper capacitors in lieu of alumi- used were paper. If electrolytics were used the economy of high capacitance electro- num, or of very small electrolytic: if alumi- the sections could be of comparable values lytics has enabled the ready reduction of num is available. with C, increased to say 3µf and the tap hum to 5 microwatts or so. This reduction The systems described herein take into omitted from the field. This would permit is definitely too conservative and it is doubt- account the importance of copper and steel, wider capacitance drift. This type of bal- ful that the majority of consumers will dis- and hence consider comparable systems with ance is not very critical, however, permitting criminate between no hum and say, 20 and without filter chokes. The systems do C, to vary from 0.5 to 2µf without impor- a microwatts, other commercial factors being not require dynamic speaker fields larger tant change in hum level. satisfactory. While electrolytics are still than those commonly associated with small available the 5 microwatt level may easily receivers. be achieved, even with reduction of capaci- The number of "filter circuits" conceiv- tance below the values now being used in able is unlimited, and the systems discussed practice. However, if the curtailment of herein are merely those of the many tried aluminum forces the use of paper con- in this development which permit the use densers or electrolytics of comparable of Paper capacitors of moderate size and capacitance values then consideration should number. be given to higher hum output levels. In Doubtless there are other systems which the event of a critical shortage some uni- will produce comparable or Perhaps even versal sacrifice in hum level should be better results. The systems below are hence made to enable the production of the offered for comparison as well as for their largest number of sets from the available own merit. Nevertheless it is believed that materials. they require something We a minimum of capacitance where criticality is a factor. POWER FACTOR OF CAPACITORS The balance between voice coil and The power factor of electrolytics is usu- bucking coil was found satisfactory, limit - ally higher than that of paper capacitors, wherein two large electrolytics were used ing the induced hum power from field to but in any usual application the resistance in conjunction with a speaker field or filter voice coil to a negligible level. The neces- resistor. Economy in mocrofarads of ca- sity for exact increases somewhat component of either may be neglected. pacitance, balance Hence, in the systems described electro- however, is indicated by the use with the magnitude of ripple volts across lytics may be used in place of paper wher- of several sections of lower capacitance. the field and imposes this precaution in ever capacitance drift inherent with elec- For example, three 3 -µf sections of ca- manufacture. Filter systems using large trolytics is not a disturbi factor. pacitance may produce a lower hum level electrolytic input or choke input will per- in the speaker than two 12 -µf sections, with mit wider variation in bucking -coil balance HUM REDUCTION IN A -C RECEIVERS a marked reduction in aluminum. Very as the hum intensity in the field is much probably the future technique of filter de- In the past, with aluminum available in less. In the case shown in Figure 1 the sign will be directed toward the reduction ripple voltage was 80 r -m -s volts. any desired quantity, the price of electro- of materials and away from the reduction lytics increased very little with increase in of filter sections. Labor costs may be in- capacitance above a certain base price. This creased by this trend, yet indications are led to the then economical filter design that labor will be more available than material. One of the most simple and economical expedients for the reduction of hum is to employ cathode degeneration in a single - tube power output stage. This produces an improvement in zero signal hum of some 6 db, reducing hum derived from plate, screen, and driver tube, end minimizing the effect of inaccuracy in speaker bucking -coil Its Power -supply ripple may appear on the balance. use also conserves the grid of the output tube through capacitor usually used as a cathode by- the plate circuit of the driver as 2. pass. The loss in audio gain may be tol- shown by Figure erated in most designs. The portion of the ripple which is impressed on the grid is determined by the Since the power -tube screen circuit is voltage divider formed by Re, R and R. more susceptible to hum than the plate cir- of Figure 3. R, increases somewhat as the cuit a separate screen filter usually proves value of R. is increased as shown in Fig- more economical of material than the use ure 4. The rate of increase of R. is not of a common voltage point for screen and commensurate with that of Re, however, plate. so that the greatest reduction of hum is A system which follows this plan is obtained by making Re as large as possible. shown in Now with Stromberg- Carlson Telephone Man- Figure 1. A tapped field to min- The limiting value of Ra will then be de- ufacturing Company, Rochester, N. Y. imize hum at point B is indicated. The termined by the size of R. which may be RCA License Laboratory, New York, N. Y. hum voltage at B is 3.5 r-m -s volts and at increased up to the limit imposed by gas le RADIO -CRAFT for OCTOBER, 1942 SERVICING current conditions in the power -tube grid order of 0.3 volts. Ia the "straight A.C.» circuit. From this standpoint self bias op- type of set an appreciable drop in D.C. Operating Notes eration of the power tube is to be preferred voltage from B+ to screen is required. to fixed bias since a much higher value of The dropping resistor serves as one leg 1touUUa in . . . Rr is then nermissible. The hum may be of a filter which may be terminated by a still further reduced, if necessary, by a capacitance from these screens to ground. .... MOTOROLA AUTO RADIOS resistance capacitance filter in series with A capacitor in the order of 0.5 µf is ade- 1940 -41 -42 MODELS R5. The filter may be of high resistance, quate. The A.C.-D.C. type circuits do not These sets may have a great deal of back- low capacitance, if Re is also high, with a lend themselves readily to filtering with ground hiss at high volume setting and resulting economy. A section comprising low capacitance values, since high storage litte or no signal. Customer usually objects capacity of the first capacitor is required to this, especially in remote from station to maintain a good D.C. output. areas. Here is a good remedy : Cut R.F. and This may be illustrated by the following I.F. tube cathodes from ground. To R.F. measurements which were obtained using cathode, connect 20,000 ohm 4 -watt resistor an A.C.-D.C. receiver having a current and .05 600 -volt condenser, ground other end drain of 45 milliamperes. Using an A.C. of each resistor and condenser. To I. F. RP line voltage of 120 volts the following cathode connect 500 to 5,000 ohm Y2 watt relation was established between the filter resistor (resistance according to set model input capacitance and the rectified voltage and amount of suppression required in your developed : particular 'locality). Ground this resistor and by pass with .01 600 -volt condenser. A Capacitance D.C. Voltage slight loss of sensitivity will result, but 20 µf 116 Volts background noise will be reduced 75% or 10 " 107 better, actually resulting in better daytime 8 " 103 " reception. 6 " 98 " ....FORD- MERCURY AUTO RADIO a 150,000-ohm resistor and a 0.05 -µf ca- 1940.41-42 pacitor is indicated in Figure 1. This pre- Less than 12 -µf sections will cause ob- To repair antenna connector plug on top vented any contribution to hum from the jectionable hum. It would seem therefore of chassis damaged by backing car out of driver tube. that A.C.-D.C. operation is dependent upon low garage door with antenna extended. The use of a filter choke will permit the clectrolytics for its utility, with something This gives antenna a violent snap usually deletion of a filter section, as shown in like two 20 -pf sections working in con- breaking the little fibre wafers that hold an- Figure 5. Only if the choke is tuned may junction with a speaker field as the prob- tenna plug in place. Repair : After removing the inductance be small. The type used ably desirable minimum. Tapped field cir- set from car and removing side plates, work cuits and other balancing systems may re- a stiff wire, with small hook on end, through duce this estimate considerably although plug sleeve from top, hook on sleeve and balancing systems are only effective when pull up into place, lining it up in center of the balance is not critical and when the casting so antenna end will properly engage hum level resulting from unbalance is not it. Then bend wire over a nail or small stick intolerable. so it holds sleeve tightly. Then fill casting If the A.C.-D.C. size of chassis is still around sleeve with good cement (I use Duco desirable in the event electrolytics are not Household cement) and let harden 24 to 48 available the voltage- doubler system may hours. I have found it best to leave broken fibre wafers in place if at all possible as cement works between them and forms a esma.. solid contact. This is generally stronger than the original connection. The plastic nut Ac.sY aw^ t.Mr IA dtlM[ f/F!D that tightens antenna to set is also usually Br broken, and I put the pieces together and Por.D.e. wrap them with 2 or 3 turns of ordinary was 4- henry, 200 -ohm, using 0.085 pound surgical gauze soaked with Le Page's glue. of copper and 0.42 pound of steel. I-T, R.nv.-Milt ortr! I 1` When this dries I trim out top hole with a The speaker of Figure 1 was used with- knife and smooth up with tine sandpaper. out the tap as the use of the tap in this Keep glue out of threads on inside of nut. case introduced too many harmonics. Fig. 7 I have found the above repai s satisfactory The choke was of little value until it =111.0n in every way and they come in handy, as was tuned. The tuning is not critical, and replacement of the damaged parts are diffi- most acceptable hum output, tone consid- have merit, as these systems may be built cult and parts are not readily obtainable. ered, was obtained when the tuning ca- with less total capacitance than the A.C. - On small Pushbutton sets with mechanical pacitor C: was made small, say 80 per D.C. type for the same D.C. voltage output. P. B. Tuning, the dial scale is usually fas- cent of its resonating value. The resulting The following D.C. voltages were meas- tened permanently in the cabinet. Before harmonic content of the hum was then ured at the filter input of a voltage- doubler removing chassis, I set a button on each of of the choke filter greatly reduced. The use system operating from a 120 -volt line with the alignment frequencies : 1500 kc.; 600 requires in addition to the choke and tun- a current drain of 55 milliamperes. The kc.; and 1200 kc. The latter is only neces- ing capacitor an increase in secondary filter input was composed in each case of sary to push the right button to get each two condensers of the capacitance indi- exact dial setting. cated, connected in series. To help locate noisy resistors, I have a

short length of rubber- covered wire with . Capacitance D.C. Voltage ends skinned and momentarily short out sus- 8 pf 224 Volts pected resistors. Usually does not upset a 4 " 163 circuit that a noisy resistor, generally in 2 " 136 " screen or cathode circuit, will not show up. Caution : keep off filament or coil shunting Also the voltage- doubler system has as resistors. However, these are seldom at its fundamental frequency 120 cycles in- fault. stead of the more difficultly filtered 60. B. F. ADAMS, The 120 -cycle pulse may also be pro- Fortuna, Calif. duced by a low- voltage transformer and . SILVERTONE MODEL 2541 full -wave rectification. Unfortunately the Complaint: Battery fails sooner than it screens of the converter R -F and I -F tubes should ; on checking the battery I find that voltage on the power transformer with re- are not easily filtered by RC networks unit is dead. Trouble: Shorted 10-mf. 100- sulting increase in copper. The ultimate less an appreciable D.C. voltage differen- volt condenser connected between the desirability of choke input may be deter- tial is produced. The circuit and constants ground on chassis and the B + on the plates mined by considering the availability and of Figure 6 produced low zero-signal hum, and screens of the 1N5, lA7 and 1A5. Re- costs of copper and steel vs. the materials but had considerable modulation hum. The place with 10 mf. condenser having a higher for paper or electrolytic capacitors. choke input method illustrated in Figure 7 working voltage. In some cases it can be Acceptable modulation hum requires a is capable of further reduction in zero - left out entirely. low- ripple voltage on the screens of the signal hum with considerable reduction in JOHN W. BURGER, carrier and I -F frequency tubes, in the (Continued on page 55) Westphalia, Kansas RADIO -CRAFT for OCTOBER, 1942 19 SERVICING RECEIVING -TUBE CHARTS

The radio serviceman as well as the radio ceivmg tubes for other than war use. The and -identified by the term "special purpose." experimenter will find a considerable chart showing tubes discontinued and RCA These tubes are particularly of interest for amount of useful information in the new direct and possible replacements appeared applications involving special performance RCA Receiving Tube booklet, just off the in Radio -Craft for July 'on page 657. It requirements. press, the tube- classification charts of which will be noted from the classification chart The beginner in servicing and the new- are reproduced here. shown here that the GTs and Gs are now comer in radio experimenting should find The receiving tube characteristic charts represented by a single tube designated as the reproduced classification charts in- in the booklet contain 327 types arranged GT /G. structive because of the groupings of tubes in numerical- alphabetical sequence. The The booklet contains another chart on into classes of specific functions and the tube listings take into account replacements special purpose tubes giving information on listings of filament voltages in which these for types discontinued by the War Produc- certain tubes closely allied to receiving tubes are available. Obsolete types of tubes tion Board order on manufacture of re- tubes but customarily tabulated separately are not listed in the charts.

Cathode Volts 1.4 2.0 2.5 to 12.6 to 5.0 117 DIODE DETECTORS & RECTIFIERS single Detector 1 A3 {twin (6H6, 6H6- GT /G), 7A6 12H6

'half -wave 1 -v 12Z3, 35Z3, 35Z4 -GT/. 35Z5- GT /`i, 45Z3 45Z5 -GT holf -wave, with beam power amplifier 32L7 -GT, 70L7 -GT 117L /M7 -GT, 117N7 -GT, 11 7P7-GT Rectifers< half -wave, with power pentode 12A7 25A7 -GÌ /G vacuum (5T4/. (6X5, 6X5 -GT /G 84) 5U4 -á, 6Y5, 6Z5, 6ZY5 -Ci,7Y4 5X4 -G, 5Z3), (5W4 5W4 -Gr/G, 5Y3 -GT /G, , full -way 5Z4, 5Y4 -G, 80), (5V4 -G, 83 -v) mercury 82, 83 as Cold- Cathode Types: OZ4, OZ4 -G. Rectifier-Doublers (25Z6, 25Z5, 25Y5), 50Z7 -G, 11 7Z6-GT/G DIODE DETECTORS with AMPLIFIERS with high -mu triode (1 H5 -G 1 H 5 -GT) , 1 LH4 One Diode with high -mu triode, r -f pentode 3A8 -GT with medium -mu triode, power pentode 1D8 -GT with pentode 155

with power pentode 1 N6 -G with medium mu- triode (1B5, 55 (6SR7, 6R7, 6R7 -G, 6R7 -GT 12SR7 1H6 -G) 6ST7, 6V7 -G, 85), 6C7, 7E6 Two with high -mu triode 2A6 (6S07, 6507 -GT /G 607, (12507, Diodes 607 -G 607 -GT, 6B6 -G, 12507 -GT /G, 6T7 -(, 75), 766, 7(6 1207 -GT) with pentodo (1 F7 -G, 287 (6B8, 6B8 -G, 687, 6B7 -S), 12(8, 12S-F7 1F6) 6SF7, 7E7 CONVERTERS a MIXERS Pentagrid Converters (1A7 -G, (1C7 -G, 2A7 (6SA7 6SA7-GT /G 6A8, (12SA7, 1 A7 -GT), IRS, 106), 6A8 -6, 6A8 -GT 6b812SA7 -G, -GT /G, 1 B7 -GT, 1 LA6 (1 D7 -G, 6A7, 6A7S), 7B8, 707 12A8 -GT) 1 A6) Triode -Hexode Converters (61(8, 6K8 -G, 6K8 -GT), 12K8 Triode -Heptode Converters 6J8 -G, 7J7 Octode Zonverters 7A8 Pentagrid Mixers (6L7, 6L7 -G)

20 RADIO -CRAFT for OCTOBER, 1942 SERVICING

2.5 to Cathode Volts 1.4 2.0 6.3 12.6 to 5.0 117 VOLTAGE AMPLIFIERS, DETECTORS, OSCILLATORS single unit 1G4 -GT /G (1H4-G, 27, (6C5, 6C5-GT/G), (6J5, 12J5 -GT 30) 56, 6J5 -GT /G 7A4) (6P5 -GT /G, 485 76), 6L5 -G, 6AE5-GT/G, 37 twin unit 3A5 6C8 -G, 2AH7 -GT medium -mu 6J6, 6SN7 -G 125N7 -GT twin plate 6AE6 -G twin input 6AE7 -GT Triodes with power pentode 6AD7 -G with diode, power pentode 1 D8 -GT single unit 6SF5, 6SF5 -GT, 6F5, (12SF5, 6F5 -G, 6F5 -GT), 6K5 -G, 12SF5 -GT, 7B4 high -mu 12F5 -GT) twin unit (6SC7, 7F7), 6SL7 -GT 125C7 12SL7 -G`T with diode, r -f pentode 3A8 -GT cut -off 1D5-GT Tetrodes 35 sharp cut -off 32 24 -A 36 'remote cut -off 1T4, 1P5 -GT (1D5 -GP, 58 6SS7,(6SK7 6SK7 -GT, G,6K7, (12SK7 1A4-P), 6K7 -G, 6K7-GT, 78), (6S7 12SK7 -G`T, 34 6S7 -G), (6U7 -G, 6D6, 6E7), 12K7 -GT), 6W7 -G, 39/44, 7A7 14A7/ 6A87, 6AC7, 7H7, 787 12B7 remote Pemodes< cut-off, with triode 6F7, 6P7 -G 1288 -GT, 25B8-GT semi- remote cut -off 6SG7 12SG7 sharp cut -off (1N5-G, (1E5-GP, 57 6AG5, 65H7, (6S 7, 14SH7, 1 NS -GT), 1B4-P), 6SJ7- GT`6J7,6J7- G,6 -GT, (12SJ7 1L4, 15 6D7); 77, 6C6, 7C57, 12 7 -dT 1LN5 7G7/1232 12J7-GT)5 cut -off, with diode, high -mu triode 3A8 -GT' POWER AMPLIFIERS single unit 31 2A3, 6A3, 684-G 45 low -mu 183/483 Triodes twin unit 6E6 single unit 49 46 6AC5 -GT /G, 6C4 h igh -mu 25AC5 -GT/G {twin unit 1G6 -GT /G (1J6-G, 53 (6N7, 6N7 -GT /G 6A6), 19) (6Y7 -G, 79), 6±7-G without rectifier (1 Q5 -GT /G (6L6, 6L6 -G), (6V6, (25L6, 305- GT /G), 6V6- GT /G), 6Y6-G, 25L6- GT /G), 1T5 -GT Beam 7A5, 7C5 25C6 -G, Tubes 35A5, 35L6-GT /G, 50L6 -GT with rectifier 32L7 -GT, 70L7 -GT 117L /M7 -GT 117N7 -GT, 117P7 -GT single unit 1A5-GT/G, (1F5-G, 2A5, (6F6, 6F6-G, 42), 12A5, (1 S4, 3S4), 1F4), 47, (6K6 -GT /G, 41), 6G, (45A6 1C5-GT/G, (1G5-G, 59 38, 6A4, 89, 7B5 25A6 -GT /G, 1 LA4, 1 LB4, 1 J5 -G), 43), (3A4, 304) 33 25B6 -G Pentodes twin unit 1E7 -G* with diode 8 triode 1 D8 -GT with medium -mu triode 6AD7 -G with rectifier 12A7 25A7 -Gl/G video 6AC7 Direct- Coupled Amplifiers 6B5, 6N6-G (2585 25N6-G) ELECTRON -RAY TUBES remote cut -off triode Single {with 6AB5/6N5. 6U5 /6G5 with sharp cut -off triode 2E5 as Twin, without triode 6AD6 -G, 6AF6 G GAS -TRIODES 2A4 -G

* Two 1F5-G's in one bulb. Filament arranged for either 1.4 volt or 2.8 -volt operation,

NOTE: The above classification does not include the following old types: 00 -A, 0I -A, 10, II, 12, 20, 22, 26, 40, 48, 50, 7I -A, 81, 99, 112 -A, 876, and 886.

RADIO -CRAFT for OCTOBER, 1942 21 SERVICING Making a Voltmeter Read Watts By WILLIAM G. LOFSTROM

TiHERE probably are many radio serv- set is drawing abnormal current and you ce shops that do not have a wattmeter. can be sure that somewhere within the This is because many servicemen do set a short exists. The power supply is to not think that such a unit is essential be suspected first. to the radio shop. Others believe that a Although the wattmeter to be described wattmeter is too expensive a piece of test can be mounted on the shop test panel as a equipment for them to own. But they are permanent fixture in the shop, I decided to wrong on both counts. You need not worry build this one in a metal cabinet, making it about the expense, if you desire a watt- a portable unit. This enabled me to bring meter. It need not be the expensive dynamo- it into the customer's home when needed. meter -type meter. You can construct your Do you wonder why I would want to bring own wattmeter right in your own shop in a wattmeter in the home of a customer ? On your spare time, using odd parts which now several occasions I have had customers in- are lying around your shop accumulating quire if I could tell them how much elec- dust. When you will have constructed this tricity their radio set was using. Of course, wattmeter and put it into operation you will I could have looked it up in the manual, wonder how and why you ever got along but there is nothing more convincing to a without one. customer than to let him see the answer with All that you need to construct this watt- his own eyes. With a portable wattmeter meter is an old power transformer which the shop. It will save time in your service you can do that, and even though the trip still possesses a good 110 -volt primary work. to the customer's home does not net you winding, a low -range A -C voltmeter, a Nearly all radio schematics specify the any cash, it will help to build up the cus- female receptacle and some wire. normal wattage consumption of the set be- tomer's faith in you. All of us have at one time or another had ing serviced, and by comparing the watt- a set on our bench that started smoking The metal case that I selected to house meter reading with the specified wattage the this wattmeter is a 6 x 6 x 6 -inch black soon after it was switched on. If you had following conclusions can be drawn. a wattmeter in shop on crackle -finish cabinet, which can be pur- your this occasion 1. If the reading obtained on the wattmeter chased from any radio supply house. The and had checked this set first for wattage is lower than that specified by the manu- consumption, you would handle on the top of the cabinet can be pur- not have had to facturer, the set is drawing less than its in any five- and ten -cent store. The wait for the set to start smoking. The normal current, and you can be certain chased wattmeter that I used on this particular unit meter would have registered excess power that somewhere within the set there is consumption when was a 0-4 A -C voltmeter, but any other the set was turned on. an open circuit or circuits. low -range A -C voltmeter will do. A piece Once you have added a wattmeter to your 2. Ift on the other hand, the reading ob- you should of plain paper, white in color, is pasted over shop, train yourself to use this tained on the wattmeter is higher than old dial scale for the new scale be instrument first on every set into 'hat specified by the manufacturer, the to that comes the calibrated in watts. The meter hole in the upper center of the front panel will have to be cut to fit the meter which you plan to use. The hole in the lower left hand corner of the front panel is a r/z inch hole Tg. 1A into which is placed a rubber grommet. The A.C. lead wire feeds through this rubber Load Line grommet. The hole in the lower right -hand corner of the front panel is cut to hold a female receptacle. Select an old power transformer that .till has a good 110 -volt primary winding. Remove all the laminations and take off all the secondary windings, leaving only the primary winding, which is usually found e on the bottom. Wrap a piece of Empire cloth or Kraft paper over this winding to Feinale Receptacle serve as insulation. A new winding is wound over this insulation, but before pro- Metal ceeding it will be necessary for you to Original Case decide whether the wattmeter you are to construct will be for 125, 250 or 500 watts I/O Volt Primary full -scale reading. The number of turns and the size of wire depend on the range you desire to cover. Following are the three sizes of wattmeters together with the number of turns required and the size of wire to be used : 125 watts full scale-36 turns -16 DCC wire 250 watts full scale-16 turns-16 DCC wire /Yew Windig Low Range 500 watts full scale- 8 turns -14 DCC wire Select the size of wattmeter best suited to A.C. Voltmeter }our needs and, using the correct wire size, wind the proper amount of turns over the insulation which now covers the old 110 -volt primary winding. When this winding is completed wrap a piece of Kraft paper over it and fasten it with medical tape. The laminations are now placed into position and clamped tightly together. This com- 18 pletes the transformer. (For details on transformer rewinding see Fred Shuna- man's article in Aug. -Sept. issue of Radio - Craft, page 726. (Continued on page 54) 22 RADIO -CRAFT for OCTOBER, 1942 SERVICING

B- AND C- BATTERY ELIMINATOR c' FOR SERVICE TEST BENCH By RUSSELL E. POWERS

URING my spare time I constructed condenser in the set is disconnected the set that other sets using a tapped C supply will a B- and C-battery eliminator mostly oscillates. If too high a resistance is used work satisfactorily with the eliminator even D from discarded parts that each serv- the set will have poor tone quality. though the proportion of total C voltage to iceman has in his junk box. I believe The tap on the bleeder resistor, R3, for the tap is not exactly 3 to 1. With an that servicemen who have occasion to serv- the adjustable B+ should be adjusted so average -sized power transformer and re- ice many battery radios will find it quite that an output of 15 ma. may be obtained at sistances as indicated on the diagram, the useful and economical, due to the fact that about 125 volts. The voltage with no load total C voltage may be varied from zero to it eliminates the necessity for keeping B at this tap will be between 165 and 170 volts. about 21 vòlts. It is necessary to have this and C batteries around the shop to use while The tap for screen voltage should be set so range, as some battery radios use 22.5 volts servicing sets. The unit should cost no more that it delivers 67% volts under normal load. of C. than one set of B batteries. It has been Even though some sets use 135 volts of B The most desirable feature of the elimi- suitable for every battery radio I have had with a tap of 90, while others are tapped at nator I have saved until last. Probably there occasion to service, as it supplies voltages 45, it will be found that 67% is satisfactory. is no serviceman who has done an appre- comparable to those of the batteries used Voltage output is obtained through six pin ciable amount of work on battery radios to operate the radio. jacks on the front panel. who has not at some time accidentally The unit first was built without a trans- A jack is provided for the full voltage shorted the B batteries across the tube fila- former, using a 117Z6GT as a half -wave output. This may be substituted for the B ments. This usually has a detrimental effect rectifier, since it was intended primarily supply in A -C receivers and is otherwise on tube life, especially if the tube filaments for use in servicing 1.4 -volt radios. It handy to have around the shop. Sockets are 1.4 volts and the B supply is 90. With would also work for 2 -volt radios which may be salvaged from dead A -B and B -C this eliminator tube burnouts cannot happen required no C batteries and did not have packs so that the radio may be plugged in from this cause, because the eliminator will the B batteries tapped for screen voltage. I with the regular battery plug. I f marked not deliver sufficient current to do the found, however, that more complete isola- wires are attached to these sockets, connec- job. The total filament drain of a 1.4 -volt tion from the line was necessary than tions may be made with a minimum of set with four 50 ma. tubes is 200 ma. The the AC -DC arrangement gave. With some trouble. I use a 2 -volt storage battery with current which can be delivered by the ad- radios it was impossible to eliminate hum a 10-ohm rheostat in series adjusted to 1.4 justable B+ voltage tap does not even even though all test equipment was A -C volts for my filament supply to 1.4 -volt bat- approach this figure. The voltage under load operated. Also, shocks were plentiful be- tery radios. at the adjustable B+ tap may be varied tween it and almost any other metal object The hum level of radios operated from from 90 volts on up to about 125 volts pro- one might touch. In view of these objections the eliminator will be found to be low. Re- vided current requirements do not exceed it is recommended that anyone who con- sistances have been selected so that one- 15 to 18 ma by adjusting R+. The minimum templates building any such instrument third of the C voltage appears at the C tap. current at which the voltage output can be should consider using a transformer and a This proportion is the one most widely used ; held to 90 volts is 7 ma. Battery radios full -wave rectifier. for example, the sets using a total of 9 don't happen along which draw less than Since layout of parts may suit one's taste, volts of C with a tap at 3. It will be found this. none is given here. Possibly an explanation of some of the parts, construction, and operation would prove helpful, however. A filament -type rectifier tube such as the 80, 5W4, etc., will eliminate the nuisance of having to wait for a rectifier cathode to reach operating temperature. J The unconventional hook -up of -the re- SW) ,P2 sistor in series with the 8 -mf filter condenser from the adjustable B+ to B- is I/O VaT not a mistake. Battery radios use a con- P/LOT denser from B+ to ground to keep R.F. out of the power supply. If this condenser in a radio is open, and a good condenser which G + ru has loW impedance to R.F. is used in the TEXT power supply, the set will operate perfectly R3 from the eliminator and not from batteries. An ideal condenser to use in this place is lP/-7.500-ONMW/RE-WOUND2S-Hs9TTQES/STOR ç;+ one in which the R.F. resistance has in- WTN 4al!/.fTAdIIE.WEDS --- creased due to age. If no such condenser is R2-7.000 -TO /gOgp-ONMW/.aE-Kamp RWEOSTAT 02 available one may be by plac- constructed R3-500-01/41 - WI'( WOUND POTENT/OMáT6V "" 11 + ing a resistance of 200 to 400 ohms in /4-/a0a0-ayN/ series with a good condenser. The exact it PaTTQES/SR74 R5 ,04 value desired may be determined by dis- RS-20.000 . . .. connecting the by -pass condenser from B+ C/-8 -MF 45V-VOLT ELECJAa[YT/C COAOENSER to ground in a battery radio which is in good CI-10-MF 50 .. " . OO operating © o condition, then experimenting L- 30- HENRY CNOKE with different values of resistors. A resist- CI C/- 74P) B- ance should be selected so that when the C+ ,0.u3.1.c190

CRITICAL OCCUPATIONS LISTED FOR COMMUNICATIONS INDUSTRIES M\KING no recommendations of its classes for telegraph firms, 51 classes for tun: of positions and the principles applied own, the Board of War Communica- telephone organizations, 48 classes in the in the inclusion or exclusion of positions tions announced last month that lists of various sub -divisions of commercial radio have been different in the various branches critical occupations in the communications communications services, 15 classes 'in in- of the industry." industries have been forwarded to the War ternational short -wave broadcasting and in industry Manpower Commission, the Selective Serv- standard broadcasting there are 6 classes of It was suggested that the and ice System and the United States Employ- technical workers and 3 classes of skilled labor representatives on the Board's Joint ment Service for such use as these agencies personnel in program departments. Labor- Industry Subcommittee should con- may find. The agencies were told "The Board does sult directly with the Government agencies Separate lists for each of the different not feel that it is in a position to consolidate in supplying detailed information on the types of communications show 23 classes of these lists for the entire communications functions performed by persons in the listed critical occupations for cable companies, 45 industry due to the fact that the nomencla- positions. RADIO -CRAFT for OCTOBER. 1942 23 3( ,ot tiA)i :.CIUAi SS SERVICING TRANSFORMERLESS POWER SUPPLIES By THE ENGINEERING DEPARTMENT, Aerovox Corporation

PART I

RANSFORMERLESS power -supply to set up any one of these circuits with the to exceed the voltage across the capacitor. units are not new in principle. The so- best components for desired operation. The tube passes current into both the called "line rectifier" and voltage input filter capacitor and the resistor. Total doubler first attracted somewhat wide- HALF -WAVE CIRCUIT current through the rectifier is the sum of spread attention among radio set builders The simplest transformerless power sup- the charging current flowing into the ca- in 1933 when the 25Z5, first of the high - ply is the half -wave line rectifier shown in pacitor, and the load- circuit current. For a voltage heater -cathode dual rectifiers, ap- Figure 1. This is the so-called A.C. -D.C. given tube, this total must not exceed a peared. The gradual increase in distribu- power unit. The general design and operat- certain value stated by the tube manufac- tion and application of the several types of ing principles of half -wave rectifiers apply turer. The tube table included in this article transformerless power supplies has been in full to this circuit. shows the peak plate current which may concurrent with growth of the midget Operation of the circuit is weal under- safely be handled by the various tubes de- A.C.-D.C. radio receiver. stood. The diode -type tube, V, conducts signed for transformerless power supplies. Aside from the well -known radio appli- only on positive half -cycles of line voltage, From a study of the capacitor and resis- cation, transformerless power supplies are and during those intervals the filter capacitor current magnitudes, it may be seen that applicable to test instruments and othe- the average D.C. load current is always electrical apparatus in which space is lim- only a traction of the peak plate current ited or magnetic fields, such as might arise flowing through the rectifier. If the filter 'from transformers, undesirable. New at- capacitance permits a rectifier current tention is centered upon this type of power LINE higher than the manufacturer's rated peak unit at this writing because the war emer- value to flow through a tube, small safety gency has made it increasingly difficult to resistors must be installed in each plate obtain certain transformers. lead to limit the total current to a safe - All of the high -voltage- heater tubes de- value. The value of these tube -protecting signed expressly for use in transformerless resistors may be obtained from the manu- power supplies are of small size. The same facturer's data. However they are generally is true of modern high -capacitance elec- of the order of 30 to 50 ohms and do not trolytic filter capacitors. For certain ap- introduce too great a voltage drop in the plications; the transformerless unit is de- circuit. sirable over other types for inclusion in a C Since the half -wave line rectifier utilizes small space with other apparatus. only alternate half -cycles of line voltage, Transformerless units can deliver D.C. the ripple frequency present in the rectifier power at high voltages or at the line volt- output will be identical with the low line age.' The voltage multiplier circuits, while frequency. This means that the half -wave providing the potential step -up, do not T transformerless circuit is not as easily fil- possess the voltage regulation provided by tered as full -wave rectifiers. The supply transformer circuits. However, the current HALF -WAVE RECTIFIER frequency, input filter capacitance, and load output and regulation may be improved by FIG. I resistance determine the ripple voltage and methods which will be discussed later in ripple current magnitudes. the text. One of the leading virtues of the Choke input is rarely ever used with the simple. .transformerless circuit-the line tor, C, is charged to a voltage equal to the half -wave transformerless power supply; rectifier-is its ability to operate from peak line voltage less the small drop capacitor input has been, found to be su- either an A.C. or D.C. line. through the tube. On negative half -cycles, perior in this circuit. The half -wave unit The usefulness of the transformerless the plate of the tube is negative with respect gives best results when high -capacitance rectifier circuit in certain applications has to its cathode and it cannot conduct fur- capacitors are used. The 40 -mfd. electro- been slowly recognized. An understanding ther. The capacitor cannot discharge back lytic capacitor has been designed principally of the operation of the transformerless through the tube and into the line, so it for this application. A large input capaci- voltage multiplier circuits is not possessed discharges through the load resistance. R. tance is necessary to maintain the output by sufficient radio men who are called upon For the usual values of filter capacitance voltage at a reasonable level. High- resis- to work with this equipment. and load resistance, the capacitor will not tance filter chokes are not recommended This article will describe the various get rid of its entire charge before the tube for use in the half -wave circuit, since the transformerless power supply circuits which plate again becomes positive and charging output voltage is already low- somewhat have been adapted to radio receivers, elec- current again flows. Consequently, it is seen less than the effective value of the line trical test instruments, photoelectric and that the charging current on each succeed- voltage -and in most cases cannot be dras- electronic equipment, and small radio trans- ing positive half -cycle will find the capaci- tically reduced. mitters. Sufficient information will be given tor still partially charged, and no charging to impart to the reader an understanding current will flow into the capacitor until VOLTAGE DOUBLER CIRCUITS of the circuit operation and to enable him the instantaneous line voltage is sufficient The transformerless voltage multiplier

CHARACTERISTICS OF TRANSFORMERLESS POWER- SUPPLY TUBES Peak Plate Max. D.C. Max. A.C. Max. Max. Peak Current Heater- Plate Output Heater Heater Inverse (Per plate) Cathode Voltage (Per Current Type Voltage Current Voltage 1).0 Ma. Voltage plate) RMS D.C. Ma. Style 12Z3 12.6. 0.3 700 330 350 235 55 Half -Wave 25Y5 25Z5 25Z6 25 0.3 700 450 350 235 75 Full -Wave 25Z6-G Per plate 25Z6-GT 3523-LT 35 0.15 700 600 350 250 100 Half -Wave

35Z4;GT . 35 0.15 720 600 350 250 100 Half -Wave 35Z5-GT 35 0.15 700 600 350 235 100 Half -Wave 45Z3 45 0.075 350 390 175 117 65 Half -Wave 45Z5-GT 45 0.15 700 600 350 250 100 Half -Wave 50Y6-GT 50 0.15 700 450 350 235 75 Per plate Full -Wave 50Z7-G 50 0.15 700 400 350 235 65 Per plate Full -Wave 117Z6-GT 117 0.075 700 360 350 235 60 Per plate Full -Wave 24 RADIO -CRAFT for OCTOBER, 1942 SERVICING

circuits make it possible ta obtain a higlr vokage less the-drop in-V,, and its polarity Operation of this circuit may be described D.C. voltage without a step -up trans- is as indicated in the diagram. in the following manner : When the plate former. Explained briefly,. this is accom- Note that the two sides of the capacitors of diode V. is positive, this tube passes cur- plished by alternately charging two or more that are joined together are of opposite rent, charging C. with the polarity indicated capacitors to the peak line voltage, or very polarity, which means that if the capacitors and to a voltage equal to the peak line volt- nearly so, and allowing them to discharge did not discharge into the load circuit the age less the tube drop. in series so that the total voltage will be voltage now appearing across C. and C, in When the line polarity reverses at the the sum of the voltages appearing across series would be equal to twice the peak line end of the half -cycle, the voltage due to individual capacitors. This action is achieved voltage less the small drops through the the charge in C. will be added to the line automatically by two or more diode -type two tubes. Hence, the term voltage doubler. voltage: V. passes current and C, is charged rectifier tubes which perform the switching Cl really discharges through the load re- to a voltage equal to the line peak (less the operation electronically. sistance R while C, is charging. But the drop through V.) plus the voltage across The most familiar transformerless volt- capacitor charge is not entirely dissipated C.. C, begins discharging into the load re- age multiplier circuit is the voltage doubler. in the load in the short interval before the sistance as soon as V, begins conducting and The doubler is employed widely in A.C. polarity of the line returns to positive, a consequently does not quite receive the full operated midget radio receivers to obtain residual charge remaining in the capacitor. charge which would be equal to twice the plate voltages approximately equal to twice Consequently, the charging of each capaci- line peak. the line voltage. Figures 2 and 3 show tor on subsequent positive half -cycles begins The "reservoir capacitor C. is never sub- voltage- doubler circuits. only at that instant when the instantaneous jected to higher voltage than the sum of The circuit of Figure 2 is a full -wave line voltage exceeds the capacitor terminal the line peak and ripple voltages. Therefore, voltage due to the residual charge. The its voltage rating may be the same as the charging then continues until a value is reached equal to the line peak less the tube drop. The capacitor then discharges ex- UN, ponentially through the load, while the other rt capacitor is charging, until the drop across 6 the load resistance (due to the capacitor discharge) exceeds the instantaneous line voltage. The voltage presented to the filter is the weA mil potential difference between the posi- MPGE 1004,0 actual r0.10 CSMACI1 , MAX VOLTAGE, tive terminal of C. and the negative terminal CCE, UNS VOLTAGE X M. C. LINE VOLTAIS X ,.M I FULL-WAVE DOUBLER of C,. This value would have a possible F19.2 maximum, under conditions of no load or low value permissible for half -wave transformerless operation. C,, on the contrary, receives approximately twice the peak line arrangement, also termed the symmetrical voltage plus the ripple voltage and must be doubler circuit. This circuit operates in the rated to withstand this totaL C. may have following manner: When the plate of the reversed current flow, depending upon the diode V. is positive, current flows through capacitance and load resistance. that tube and charges the capacitor C, to C2 For the same value of load resistance, a voltage equal to the peak value of the line the half -wave doubler output is lower than voltage less the small drop through V.. The R that of the full -wave circuit. Likewise, the polarity of the charged capacitor is then as half -wave doubler, like the simple half - indicated in the diagram. During this half - wave rectifier, is more difficult to filter, since cycle of line voltage, the plate of V, is nega- in this circuit the ripple frequency cor- tive and that tube can pass no current. responds to the low line frequency.

Gy VOLTAGE TRIPLER CIRCUITS T Extending the principle of voltage mul- tiplication still further, we show two voltage CAPACITOR PEAK VOLTAGES tripler circuits as Figures 4 and S. The cir- G., Cy LINE VOLTAGE X 1.01 cuit of Figure 4 is essentially that of a con- G2 LINE VOLTAGE X 2.82 ventional half -wave doubler and half -wave VOLTAGE TRIPLER rectifier in series. FIG.4 How this circuit supplies D.C. at three times the line voltage may be explained in this manner : When the lower side of the extremely light load, of double the line peak. supply line is positive, diodes V, and V, The actual value, however, will depend upon pass current, charging capacitors C. and Ca how much current is being drawn by the to the line peak less the drops in the two load resistance. tubes. When the input cycle reverses, the Due to.the Separate discharge of C. and C, voltage across C. combines with the peak on successive half -cycles, both sides of the line voltage and charges C, through V, to line -voltage cycle are utilized by this cir- this total value. The voltage across C, is cuit The voltage pulsations are accordingly then very nearly equal to twice the line peak, at twice the line frequency although the (Continued on page 49) ripple across each individual capacitor is at the line frequency. In this respect, the output of the full -wave voltage doubler re- VOLTAGE TRIPLER INPUT II V. RUS sembles that of the full -wave rectifier. The TUB S 2 25 6G

full -wave doubler is therefore much easier r CIRCUIT IN FIG 5 F to filter than the half -wave transformerless supply. 500 Cl and C, are usually of the same capaci- CAPACITOR PEAK VOLTAGES tance for best results, although this is not IOo C1, LINE VOLTAGE X 1.41 an imperative requirement for circuit opera- C2, Cy, LINE VOLTAGE X 2.82 tion. These two capacitors are charged by separate diode units in the same manner as °> 300 HALF -WAVE DOUBLER in the full -wave rectifier, and the increased a5 FIG.3 output voltage afforded by the doubler cir- 200 cuit is obtained from the two capacitor o voltages in series. Hence, the capacitor volt- 100 When the line polarity reverses. how- ages, due to charging. never exceed the line ever, current will flow from the lower side peak and their voltage rating may be the of the line, is 0 1 0 0 which now positive, through same as recommended by the capacitor 0 , 00 o o o o g o$ ñ the circuit containing V, and C, and back manufacturer for half -wave service at line to the upper side of the line. C, is then voltage. LOAD MILLIAMPERES S charged to a voltage equal to the peak line Figure 3 shows a half-suave doubler. FIG.6 RADIO -CRAFT for OCTOBER, 1942 25 RADIO INSTRUCTION FLIGHT RADIO SCHOOL TRAINS ENLISTED MEN

HUNDREDS of enlisted men are now being trained in ground and flight radio operation and in radio maintenance for the U. S. Army Signal Corps, the Navy, the Coast Guard, the merchant marine and the airlines at the Melville Aeronautical Radio School, in New York City. These trained men, in the opinion of a high- ranking officer of the Signal Corps, are the types needed for the Officers Training School. Enlisted students remain on inactive duty while training and are sent to the various branches of service upon completion of a training period of from four to eight months. Frank Melville, founder of the school, has passed the greater part of his life in radio work. He received his first radio license when he was thirteen years old. Now, at the age of thirty -one, he is one of the leading transoceanic flight radio operators, traveling to Ireland each month. In addition, he is directing what probably is one of the most specialized radio schools in the country. This school has been accepted as the standard for the training of high -speed radiotelegraph and radiotelephone operators by the U. S. Army Signal Corps. It is also the official apprentice school for training employees of the major airlines. Only those holding amateur radio licenses may make application for connection with these airlines through advanced radio training at the school. Mr. Melville believes that the future of aviation, which, in his opinion, will expand to almost unlimited horizons, depends to a large extent on the thoroughness with which men are trained in the principles of safety in operation, which in turn depends upon complete knowledge and mastery of essential equipment in flight use. Therefore he has planned the type of training, equipment and facilities for this highly specialized field accordingly. Instead of using "make - believe" equipment, he uses actual operation equipment such as are standard in the airlines. That actual operation of the equipment is the best way to learn aeronautical communications is Mr. Melville's firm belief. In building up this plan, the school has taken over the equipment of one of the leading wireless companies and has also been aided by other branches of aviation-companies that believe in these methods of preparing men for this type of radio work. Instructors are top -notch men with years of experience in radio communications-several of them are also connected with leading airlines -and they are teaching high -speed telegraphy, airline radiotelephone, teletype, radio maintenance, radio theory, meteorology, and a number of inter -related subjects deemed essential for a thorough training course in aeronautical radio. On any of the four large floors occupied by the school one hears the continual hum of activity. Radio receivers, transmitters, radiotelephones, teletype and maintenance departments are going at full speed day and night. A student learning to operate a radio station is giving orders to planes in flight, ultra-high-f requency receiver and precision monitor combined with a microphone on his desk. His 250 -watt transmitter is similar to the latest airline ground station -its frequency is crystal controlled. A young man, training for radio service with the Army Signal Corps gets basic instruction on direction - finders (see front cover), one of the most important phases of the flight operator's work. In another section of the building one finds a group of students - the Airline Procedure Class- operating radiotelephone and radiotelegraph circuits simultaneously. All reports are copied directly on the telegrapher's mill. The instructor acts as the pilot in flight, giving orders to each station. Each student is assigned a station. The pilot reports his position and receives instructions from the different stations, just as is carried on in airline communications. The microphones, we noticed, are (Top) Students wiring a control panel; (center) trainee giving flight orders from operated by pressing a foot pedal, similar to stations a simulated ground station, and (bottom) an instructor inspecting tape at the at the airports. Melville Aeronautical Radio School. (Continued on page 57) 26 RADIO -CRAFT for OCTOBER, 1942 RADIO INSTRUCTORS SIGNAL CORPS TRAINING BEGUN AT ILLINOIS TECH LITERALLY making Illinois Institute waves work is compulsory. Like the special code school will be opened by the Institute of Technology, Chicago, the elec- trainees, they will be eligible for Signal about September 15, to train a continuous trical war- training headquarters of Corps commissions. enrollment of hundreds of men. the Midwest, thousands of men -the In addition to these groups -whose en- All these various classifications together largest such group at any private school rollments are expected to double within the will add up to a continuous enrollment of in the nation -arc studying electronics, ra- .next month -a new radio operator's and (Continued on paye 57) dio, fundamentals of electricity and micro- wave techniques at that school. This program is so important to the war effort that the United States Signal Corps is awarding commissions to all men who complete the most advanced phases of the work. Some of the best power company engineers in the Chicago area have come back to school for special courses at Illinois Tech. The training is considered so important that Illinois Tech is making some phases of the work compulsory for its electrical engineering seniors. Seven courses or types of work make up the complete program. Keynote of the whole setup is the training in the principles and operation of micro -wave or ultra- high- frequency techniques recently announced by Secretary of War Henry L. Stimson as the newest and most effective of the Armed Forces' secret communications and detection apparatus. United States Signal Corps radio and electronics engineers, operators and technicians "by the thousands" will be trained annually at Illinois Tech for the duration, Major -General George Grunert, in command of the Sixth Service Command, said. The program, which features the most complete electronics work being given anywhere in the Sixth Service Command - including the ultra -high frequency tech - niques-is rapidly reaching full operation. One of the several hundred Signal Corps enlisted reserves receiving special radio studies at this Midwest Already students in all the various levels school. He is working with Instructor J. C. Abener. The two pieces of apparatus with which they are of radio study at the Chicago school are working are a signal generator and a vedolyzer. (Above) figured in ternis of four digits. When the A student records the data supplied to him by a piece of test apparatus in the $100.000 laboratory built program reaches top capacity, at about the by Illinois Tech staff members especially for the micro -waves courses. This multivibrator measures the middle of the month, the continuous en- frequency of oscillations of the ultra -high -frequency waves. (Below) rollment will be in the thousands, more than double the present number. The phenomenal growth of this technical training program is especially significant in view of the fact that it is a new type of work, developed almost entirely since the Signal Corps began its expansion program. All of the course of study had to be planned and designed by Col. C. N. Saw- yer, of the Signal Corps, and Illinois Tech faculty members, under thé direction of Dr. Jesse E. Hobson, head of the department of electrical engineering, himself a young electrical engineer who finished his own graduate work only a few years ago, since never before had ultra -high frequencies been a part of the standard engineering curriculum. In addition to the micro -waves study -in which several hundred men are currently enrolled -the Illinois Tech program includes every phase of radio work from fundamentals on up to the advanced studies. Other groups now studying include an even larger number in "elementary radio engineering"-which precedes the ultra- high- frequency work -and several hundred others in part -time evening elementary study. Also listed among the radio "war trainees" are Illinois Tech's electrical engineering seniors, for whom the micro - RADIO -CRAFT for OCTOBER, 1942 27 SOUND FACTORS CONTRIBUTING TO GOOD RECORDING By R. A. LYNN

MMANY variables are encountered in Engineering Department, National Broadcasting 500 region Company, York cps is so "peaked" by the use recording and reproducing tran- New of corrective electrical networks that the scriptions. Certain of these varia- cutter characteristic is altered to be rea- bles can be controlled by the setting SUMMARY is the desire, in the tran- sonably close to the ideal characteristic. 1,1 standards. Others can be controlled by -/t scription fold, that the reproduced This electrical correction can be made a realization of the variables and conse- quality be a facsimile of the original program. The anywhere in the channel equipment, pro- quent employment of a technique which vided it is always associated with a par- reduces recording unit, the disc, and the reproduc- their magnitude. ing unit play important parts in ticular cutter. Under normal circumstances, It is the purpose of this paper describe achieving to the desired results. A a all cutter heads of a given manufacture the operating characteristics of certain re- discussion of few of the operating characteristics of these require similar compensators for the basic cording and reproducing components, and correction of the crossover point. How- give a few items and their effect on record quality is to suggestions pertaining to the presented. ever, minor irregularities in the form of employment of good engineering practice high -frequency peaks are sometimes en- in their use. countered which are not the same for all curve will be one which steadily diminishes heads. Such irregularities can be corrected THE CUTTER HEAD in the region starting at 500 cps and pro- in the compensator. It is for this reason There is no particular problem with gresses down to 50 cps. Furthermore, the that it is advisable to avoid the use of a present -day equipment in obtaining the de- characteristic must fall at the rate of 6 db compensator with any cutter head other sired electrical and distortion -free charac- per octave correctly to convert the expres- than that for which its circuit elements teristics in the amplifier chain from the sion from an amplitude basis to a velocity were adjusted. microphone up to the input terminals of basis. the cutter head. The cutter head, on the The existing characteristic of the cutter METHOD OF MEASUREMENT other hand, represents an item which is head is first determined and a comparison The characteristic of a recording head subject to great variation dependent upon to the ideal characteristic is made. The its manufacture and manner of use. is measured by engraving various single - frequency tones through the spectrum on The first step necessary in placing a a disc. The pattern, when observed in visually cutter operation is to have it engrave under proper light conditions is generally the desired frequency characteristic on the referred as disc. to a "Christmas Tree" pattern. This characteristic should not be an Since the frequencies in the region arbitrary one, but iKC from should follow some set i 1000 cps to 10,000 cps are to be of constant of standards. The analysis of practically velocity, any KC the observed tone bands in this standard frequency characteristic which section should give rise to a light- diffrac- has ever been proposed will show that it sKc tion pattern equal may of band spreads. The be broken down to certain basic sec- 78 RPM departure from this condition is an indi- tions. The one 7 KC to be discussed has, as a _ cation of the variation of the recording- foundation, a constant amplitude section head characteristic extending from : 9 KC from normal. The the lowest frequency of amount of change in level of the recording 50 cps to 500 cps and a constant velocity ixi amplifier that is necessary to establish the section from 500 cps to 10,000 cps. The flat condition is a measure of the original frequency 500 cps is therefore called the deviation. "cross -over frequency" indicating the Frequencies t -ansition from "constant amplitude" to below 1000 cps are more "constant velocity." With this characteristic conveniently measured by reproducing them through a pickup head as a basis, any desired pre- emphasis curve which has been cali- may be added. brated previously by means of a known tone record. (Several such It may records are be well at this point to mention available on the market -RCA T- 2485 -2, that the characteristic curves which are :a' !KC etc.) to follow have been plotted on a velocity jjYi A Figure 2 is a photographic basis. In the region from 500 cps 10,000 5 reproduction to RPM 7 KC of a recorded cps we will encounter a curve which fol- tone disc. It will be noted .t'^' 8 KC that the flat -top section is the high -fre- lows, let us say? the zero axis for the ¡KC . quency portion ideal condition since this is the vim of the spectrum. It is more constant satisfactory to use 78 velocity section. Below 500 cps is encoun- rpm for recording the tered the constant amplitude section; tone patterns due to the resulting sharper how- picture of the higher frequencies. The pho-

amount of correction to be applied Trill be apparent. Such a comparison is shown in Figure 1 -a and Figure 1 -b. Figure 1 -a is the ideal characteristic shown with a sharp re corner at 500 cps for the sake of clarity. 11111111_111111111111E11111111111 In actual practice, e 1111111=Mu1111111111ç- I II I X all such transition points ., 1n1R1NM1un11.1111117i11 lu Ro are permitted to "round off" to the 11 .! extent e 111111 1111111.111 III of approximately 1.5 db to avoid the un- e 11111111111111MMIl 1111111111111 I desirable use of complicated multi -section 11I111MIMIER IIMIMUlli I I II 1u111í 111111mim1111Il hum 20 compensators. Figure 1 -b shows the char- 1uH111mm111111111lmoI111II1 our acteristic of a particular present -day lateral recording head of the magnetic variety PROPOSED STANDARD RECORD NG CHARACTERISTIC designed for FOR LATERAL TRANSCRIPTION transcription service. It is TOLERANCE ± 2 D B seen that the cross -over frequency is not well defined, but is located at approxi- 1 11111111 1 1 1111111 1/1111111) las ,ee gas woe suss 11 mately 1000 cps. Furthermore, a departure Ro SOO t 0000 ,opOQ cose Ks ateo from constant amplitude is present below a

The relationship between the diffraction frequencies. Likewise, this characteristic pattern and the engraved characteristic has represents a present -day standard for those been established mathematically by others organizations now making vertical record- and has been accepted by the art for many ings. years. It is sufficient here to say that the band spread can be considered equivalent THE RECORDING STYLUS to voltage. Therefore, should a band spread Present -day recording styli are sapphire be encountered for a particular frequency jewel points in practically all cases. They which has twice the linear dimension of are ground into a wedge shape in such a the patterns generated by other frequencies, manner that a shaving of lacquer (in the it is to be considered as being 6 db greater case of "instantaneous" recording) is re- than the reference frequencies. moved from the disc. It is essential that The term "band spread" as here used the resulting groove be quiet upon repro- refers to the total width of the diffraction duction. Sharpness of the point is there- pattern created when modulation is ap- fore necessary. It is found from experience plied, measured at right angles to a radial that if a burnishing edge is ground on a axis of the disc. It should not be confused sapphire, a quiet groove results. This bur- with the thickness or duration of the band, nishing edge, however, if carried to ex- which latter is purely a function of the extreme, will cause a loss of high frequencies due to the fact that a "bull -dozing" action tent of time the modulation is applied to echoes from the cutter head. results in the displacement or flow of the either the adjacent grooves lacquer rather than its removal. will be heard, or in extreme cases the reproducing stylus will break through into APPLICATION OF PRE -EMPHASIS As will be seen later in the discussion of one of the adjacent grooves. The proper After the basic recording characteristic reproducers, the groove size is of utmost groove depth is obtained when the ratio importance. A good fit must be is determined, it is then relatively easy to obtained of the groove width to the "land" width apply the particular pre_ emphasis curve re- is 60 -40 (at a pitch of 136 lines per inch). quired by the standards. Figure 3 shows a proposed lateral- record- TiiE RECORDING DISC ing characteristic. It follows basically the The disc used for recording plays a very construction outlined in the foregoing dis- important part in the eventual result. Un- cussion. There is one difference, however ; fortunately beyond selecting discs for op- that is, a compromise has been made to timum hardness (that is, discs not so soft accommodate simplified compensator de- as to permit the loss of high frequencies, sign, especially for the playback circuit. It nor so hard that high scratch levels ensue), is noticed that no attempt has been made and employing careful handling there is to preserve the sharp corner at the cross- very little the consumer can do to vary over frequency of 500 cps. The tolerance the results as far as the finished recording of ±2 db permits the use of several fre- is concerned. The manufacturer holds a quency characteristics that are in use today. great responsibility for such items which These represent standards for different or- pertain to the disc dimensions, and to the ganizations which account for a very large lacquer coating. Many requirements could percentage of lateral recordings. The toler- be mentioned which go into the fabricating ance of ±2 db appears, at first glance, to be of a good instantaneous transcription disc, excessively liberal, but it must be realized but it should suffice to say that lacquer -disc manufacturing has made great strides in and the past few years and, consequently, the between the side walls of the groove now offers products. the reproducer point, in the case of laterally market satisfactory recorded discs, to avoid a chattering effect THE REPRODUCER and consequent distortion. The tendency An otherwise today is to use a stylus with a 70° included good recording can be angle for the face. The radius of the bottom ruined easily by a faulty reproducer. Pres- 1 ent -day reproducers, of the transcription 11111 1111111111111111111111111111111 is approximately 0.002 inch. Figure 5 shows " 1111 IIIMMIIIIIIIIfi1III!íIIllII the essential dimensions of a cutting stylus variety, are a great improvement over 11111 111111111111111111111111111:í111111111 which is in use for lateral -transcription those of even a few years ago. Neverthe- ° 1111111 IIIIIIIIIIIIIItIIII less, they still lack several desirable fea- 111111 11IIIIIIIIIIItIIIItII11Ill11illlliII work. These dimensions may be changed slightly upon further investigation by the tures. The stylus and its associated vibra- 1111 Pram1111111111111111It tory system must have stiff- N min twluuii .unum 1 N.A.B. Standards Committee. unfortunately 111111 ME111111111111M11111III11 ness and mass. However, these elements In the case of vertical recording, it is now have been reduced to small values. PROPOSED STANDARD RECORD NG CHARACTERISTIC preferable to use different dimensions since At high frequencies, conditions are such FOR VERTICAL TRANSCRIPTION upon reproduction it is desired that the TOLERANCE 2 2 Da that it takes considerable force to swing playback stylus track firmly on the bottom the stylus. The coupling between the groove side only 1 11111111 1 11111111 1 1111111111 of the groove. utilizing the walls .m and the stylus, and also the hardness of Soo low 8818 W4.10 as a guide in following the pitch of the the disc is insufficient to make the stylus cana, n sw grooves. If separate vertical and lateral Fig. perform a faithful excursion of the groove 4 reproducers are to be used, both vertical contours. It is probable that the groove and lateral systems could independently have their own standards. However, with (Continued on page 56) that this is the final recorded characteristic the present tendency of using a combina- and, consequently, must absorb the various tion reproducer with a fixed -dimensioned irregularities in the entire recording chan- stylus, it is seen that the two systems will nel. The particular pre- emphasis as shown have to employ coordinated standards for in this case is a 100- microsecond curve for the recording groove sizes. (This means the treble section. The curve is essentially that the vertical groove should be larger constant amplitude below 500 cps and in than the lateral to permit bottom tracking addition there is a slight amount of pre - in the case of vertical and to permit tight emphasis below 100 cps. sidewall coupling in the case of lateral. 14'DIA. 78 RPM III 13'013 33i RPM The pre- emphasis curve just mentioned This problem is also under consideration 9 01A is normally obtained from an electrical cir- by the N.A.B. Standards Committees.) -,1 7'DIA. III cuit consisting of L and R in series, said The groove depth is important in that if components having a time constant of 100 too shallow, the reproducer will not be 111111 microseconds. The formula is L RESPONSE CNARACTERIST C OF DEVELOPMENTAL /R=0.0001, tightly coupled to the disc and either dis- REPRODUCER AT VARIOUS DIAMETERS OF A where L is expressed in henries and R is tortion will result, or in extreme cases the LACQUER DISC. expressed in ohms. reproducer stylus will actually "skip out"

Figure 4 shows I the proposed standard of the groove and slide across the face of 111wo1111 111111 1 IIIIIII recording characteristic for vertical record- the disc. On the other hand, if the groove iP 000 yo pow ing. It differs from the lateral primarily depth is too great, the groove sidewalls will CYCLE] ss, in having a crossover frequency at 300 cps tend to be deformed or actually disappear Fig 7 and a different rate of increase at the high on peak modulation with the result that RADIO -CRAFT for OCTOBER, 1942 29 SOUND SOUND AS AN AID TO NAVIGATION By WILLARD MOODY

ONE of the most interesting properties a.. A simpler formula, where the distance is of sound is its relation to practical velocity or .nand .n dry ae at a in feet is: teenperat of degrees determination of distance by taking into 70 1>. Fahrenheit a 1.127 ft/x d account the difference between sound veloc- t ity light velocity. T d f rege.ed between =- and sg.& d heo reeve eve V The velocity of sound varies according ...rig light `"9: eeond, or t.m. difference 6,nß., U: Penn ' rodeos where t is time in seconds, d is distance in to the medium through which the sound is hearing gnat and fog ,li :i:11 ft. and is in passed. Even air has a variable transmission pyet horn is given in terms of it I v velocity ft. /sec. A curve for characteristic since the temperature of air C datante xporot ng the a velocity of 1127 ft. per sec., showing changes the character of the air and hence transmitter and receive : relation between time and distance for this 0 e.. velocity, is given in Fig. 2. the velocity of sound. e : : At 0° Fahrenheit, the velocity of sound 44 Because of reflection and refraction from .0 I in air is 1,050 feet a second and it increases strata of air of different temperatures, or 1.1 ft. per sec. for each 1° F. rise in tem- F;g.2 from foggy layers, the sound of a fog horn perature. At 0° Centigrade, the velocity of um env.: may be entirely unheard by a vessel near sound in dry air is 331 meters a second and 3:11:0'4 ::: the shore and in danger. If the lower por- it increases 0.609 meters per sec. for each e.:: ::...... tion of a horizontally moving sound wave degree on the Centigrade scale. in Fig. 1, is in warmer air than the upper part, it will a curve is drawn which shows the velocity travel faster and cause the wave front to . s 34 ., change its direction, possibly causing it to Time D ((erence .n Seconds curve upward. Also, currents of air, causing Fig.1 one part of a wave front to move at a different rate than other part, wi :l distort the Velocity of 'Sound in Dry Ai wave form and consequently the direction GS a function of temperature. sound 111 air is independent of the pressure in which it advances will be altered. of air. Assuming that the temperature is Greater accuracy would he obtained if 70° Fahrenheit, which would be normal for the sound wave were transmitted from the many conditions, the relation between the shore station through the water instead of time difference of arrival of sound and through the air. The character of the water light, or sound and radio signals, is given in would not possess the uncertain properties Fig. 2. Of course, radio signals like light, of the air and better reliability should re- travel at approximately 186,Oó0 miles a sult. This principle of water transmission puma second and from a practical standpoint are is used for determining depth in the fatho- instantaneous. The important point is l :ow meter. In this instrument, which works on much later after seeing the light or hearing the echo principle, or sound -reflection effect. the radio signal, the audio or sound signal a powerful audio oscillator sends out sound takes to come through the air. A practical waves which go down to the sea bottom. case would be that of a lighthouse sending At the start of the cycle of operation, a out a beam of light and following the flash pointer passes a zero mark on a dial. The of light with a blast on a fog horn. In some pointer is revolving at a known rate and cases a radio signal is sent out, picked up Ve oc ty increase,' at the rate carries a small neon tube on its tip. The by a receiver and a stop watch is used to depth in fathoms is read directly on the I. for each -degree of ft/sec check the time difference between the radio - calibrated dial. The on the hydrophone picks up 1..I..r. ... rise in temperature wave signal and the sound -wave signal. the reflected signal and makes the neon v4oeNW/AM Fahrenheit cale. Both signals start out simultaneously, the lamp glow, giving the indication. A lateral sound signal taking a longer time than the audio signal in the water, originating at the radio or light signal to arrive at the obser- lighthouse or beacon station would be most vation point. useful. If the distance separating the two points The intensity of sound depends on the is in miles, the following formula may be medium that carries it. The ticking of a used : watch can be heard two and a half times as in terms of Fahrenheit temperatures. tv far under water as in the air. Loudness The freezing point of ice on the Fahren- d= depends on the intensity of sound produced heit scale is 32 degrees and the boiling 5,280 by the sonorous body. The explosion of a point is 212 degrees. Temperature at any volcano has been heard as far as 300 miles. given place on the earth's surface varies where d is the distance, t is the time differ- In fresh water the velocity of sound is with the time of day, season and the latitude ence in seconds, y is the velocity in ft./sec. 4,700 ft. /sec. and in salt water it is 4,765 -to mention a few factors. The velocity of and 5,280 is a constant. ft. /sec. Devices for Air Raid Warnings AS a result of the war, civilian authorities ber of facts which have been listed under that as the frequency is decreased the sound are eager to obtain information concern- the following headings: energy which is lost becomes smaller. Rea- ing devices suitable for air -raid warnings. soning along these lines would indicate that Many requests for such information have 1. Frequency the lower the frequency of the signal, the been addressed to the National Bureau of 2. Quality of sound better would be its transmission. Standards. In response to this demand, the 3. Loudness However, the frequency of a warning bureau has undertaken a study of such 4. Ease of coding signal signal should be such as to stimulate the devices and has tried to collect as much 5. Type of device nerve terminals in the ear. Work by information as possible about the most de- 6. Effects of weather Fletcher and many others has shown that sirable type of signal. at lower frequencies the ear becomes less 1. Frequency sensitive, hence a signal having a frequency This work has not been completed, but In deciding on the type of signal that is as the need is urgent, all of the information too low is not satisfactory. to be used for air -raid warnings, one of the For these reasons it is necessary and data which have been obtained up to first considerations should be its frequency to com- the present time are presented in Letter promise between loss due to air absorption characteristics. and loss in sensitivity of the ear. Circular LC -685. As fast as additional data Experiments by Knudsen and others show are obtained, supplements will be issued. that there is a decided absorption .of sound Experimental work by the bureau in co- To aid in deciding on the type of warn- at frequencies above 1,000 cycles per second, operation with the former Bureau of Light- - ing device that should be used in any lo- and as -a result these higher frequencies are houses .indicated that the most desirable fre- cality, it seems desirable to discuss a num- attenuated quite rapidly. This would indicate (Continued an page 38) 30 RADIO -CRAFT for OCTOBER, 1942 _ p10 KITS RAD D uTy CORPS.C ARS THEIR y SIGNAl. DOING ARMY WITH THE 7de4 rffilf449

know the Corps Schools engineeredo the Signalge aCie -built and Army sponsoreder {its Se Merssn Signal Corps ' ' instruction. spo nsored faster basic radio in Arno value of resultsstraining in instruction Distributor give better Radio Meissn to of actual earest illustration See your

ILLINOIS Mi. CARMEL,tt .T ' t VUC,rs'e

RADIO -CRAFT for OCTOBER. 1942 SOUND Wide -Range Film Recording Developed for Home Use By H. W. KNETTELL A new tape, 7 mm. wide, that carries two sound tracks, gives continuous two -hour distortion -free reproduction and is capable of extending the upper frequency limit to 16,000 cycles can be manufactured at sufficiently low cost to bring its use within the reach of the music lover.

ÀNEW type of recording for home use speakers will have to be materially im- needle scratch, uninterrupted by pauses for that literally pushes the upper fre- proved in frequency range and in distortion - change of records or needles and with a quency limit beyond any frequency free performance before anything approach- crystal -clear quality equal in every respect previously achieved commercially has ing the amazing qualities of this method can to concert -hall performance -will be grati- been developed in an upstate New York be realized. fied to learn that his dream has at last be- laboratory. The music -lover who has longed for home come commercially feasible. A series of tests conducted on this method recordings that would enable him to listen Famous musicians who have listened to indicates that existing amplifiers and loud- to a full -length symphonv- unmarred by their own and other artists' recordings ad- mitted they could not detect the difference between the real and recorded music. "It's perfect! they said. When Fritz Kreisler Sound Frequency Characteristics was unable to determine which of his two Stradivarius violins he liked better, he asked that recordings of his playing be made by this method. The method utilizes sound -on -film reproduction, which is similar to talking- picture equipment but for the superior qualities of ._s a new type of film. The process was developed by Andre Schoen, research engineer for the Ozalid Products Division of General Analine Film Corporation, and utilizes a product of the company known as Oza- pl(ColO- Flu phane. WIND Ozaphane made its first public appear- IM114YIY1 ERfNCMMOON ance at a dinner which was held last month 445 CI co ME at and was by about OA the Waldorf attended srYIYOJI YLTTII 300 guests. To demonstrate the reproduc- MINK VIOL CEIIO ing fidelity of the new sound track, the 101 1¡ L YlS3 r-- I most difficult of piano selections and modern 4r ÿUIC[N 1 --`--itM4 ÖNFF---- I i orchestral compositions were played. A li recording and reproducing system was built

s D 6 A A ^. !( If OO O If 6 IL O II 6 IC D If 6 ' II t for it by J. A. Maurer, of New York. Al- though the sound film is capable of being saes s :á reproduced to 16,000, the demonstration iRg 31 :á R ó.áá " (rCIES 5E0 WOW) --- s NIDOIE C ^ was given with the upper limit at 12,000.

I! But even this was a distinct advance over `-Po. I at .kmN s...s. N hung 4ryns, Oe/o.e sense 04 Mw.n3 other systems. Although Ozaphane is similar in principle WIRE TRANSMISSION CIRCUITS to the 'conventional sound film, there are Tkn..n < I1 ON10.000<,eM pe sw .d) many significant exceptions. The most basic M.y..+ <4. e I 4 4...d<.d...3 ( íU 1 4.0001 of these is that the sound -track image, in- 4.. O.d,roey ., ".00.. D...Awe..y ISO Seo 5,000) stead of being reproduced in a silver emul- te/spheve ..ü.o4 M,l f o.e,ne.y < (1<0 4.1150) -+ sion coating on the film, is embedded within .ir..n weenu k4pken,< calk (300 N 7,300 ) - SloG.e telephone ,n,rn,nenl (WIN 000).. the base material itself. ta.1,1.4pN.w 1.,es1500 fa WOE ve. The base material is a cellophane tape treated with diazo compounds, which are RADIO BROADCASTING ANO RECEPTION light- sensitive organic dye substances. The

Sadr b..á I. 4 .Ml (30 s 1,000) dye is not a coating, but actually impreg- 0 oaks 1.y .Ielan Ir.q_dbw3 ckon per., NO 1. 5.000) - nates the tape. N 31r 10..6 /p red. set (50 to 5.500 ) 04650. w peer .od. ses (156.01.100) .. The process of recording essentially is no different from that used in sound -on -film SOUND REPRODUCERS theater recording, but the quality of the A.40 add ysl (60 re 5,300) Dye0 < k d sp. k.e (40 0. 5,500 recording must be considerably better to be I. pore 4.61 I..O *peek.. (10 N 3.500 ) able to take advantage of the particular 14sí 3 I,< p 4 /160 ro S.(00) properties of Ozaphane. The recording means utilized gives the variable -width SOUND RECORDINGS FOR RADIO AND FILMS double-track sound film such as is used in 4 SNes1 1,p. .k

THE radio direction finder is useful in cuts the conductor L,, inducing a voltage ample, the first detector of a superhetero- navigation of ships on the sea and E.., proceeds further to cut conductor dc, dyne), the output meter on the direction planes in the air, but in addition it has inducing a second voltage which lags be- finder will have deflections proportional to important duties to perform in obtain- hind the first by the phase angle 0. The the square of the terminal voltage at the ing bearings of unlicensed transmitters that amount of this lag is proportional to the loop. If a readable deflection is obtained may be used by enemy aliens. It is worth- length of L,. The voltage induced in the when the loop is displaced 10 degrees from while, therefore, to review some of the loop is then represented by the vector dia- the zero position, the theoretical accuracy simple properties of the loop antenna and gram and is given by the formula, is less than .2 degrees when taking the to draw attention to certain principles and mean of the angular position for the same practices associated with direction- finding output -meter reading, the positions being equipment. 2n EA not greater than 10 degrees on either side The direction finder is based on the prin- V= volts (1) of the null, or zero, point. A highly sensi- ciple that radio waves from a transmitter tive and selective receiver is desirable for will travel in an essentially straight line gaining sharp bearings. and that the loop where field will pick up a minimum E = strength in volts per meter The presence of a sky wave will detract signal if the plane of the loop is perpendicu- A = area of the loop from the accuracy of the measurements. lar or at right angles to the incident wave This is encountered when tvorking with front, with the possible exception of fixed (provided ff is small) compass installations in aircraft which employ the basic Department of Commerce l' = induced voltage in loop radio compass. This system depends for its ). = wave length in meters operation on a cardioid pattern derived by means of a fixed loop and vertical antenna. The phase angle between E.. and Fe,, i.. In Fig. 1, a rectangular loop is illustrated. -7C A radio wave of direction indicated in the be 1. drawing, has an electromagnetic flux which 8 = (2) ).

Zero The induced voltage is proportional to the field strength multiplied by the area of the loop and is inversely proportional to r the wavelength. The induced voltage for n F.3. 8 i Maximum turns will be n times as great, if it is assumed Reception the loop dimensions are small in comparison with the wave -length. This means standing waves will not be present. high frequencies and is also observed The preceding formula assumes that the on lower frequencies due to "night wave direction is incident to the plane of effect." The effect of stray capacitance due an- Zero the loop. Where this is not the case to and tennas on board ship or metal objects the angle of direction of the loop is on m with board plane, productive of spurious reradi- respect to the line of true minimum bear- ation effects which subtract from accuracy Q- ing, the phase difference will not be so } is, of course, well known. For this reason large as is indicated by formula (2). In- the loops are carefully balanced to ground stead, it will be given by the following relation, by using a split stator condenser and, in addition, are shielded electrostatically. In navigation aboard shin, it is necessary to 271 1, cos 9 take into account that due allowance must 8 = (3) be made for chart distortion before the navigator can plot the bearings obtained by a::d the induced voltage will be, radio, since radio bearings are true great - 2n NEA circle bearings. Before the navigator takes V = cos q' (4) the plot from the regular compass rose of a Mercator Chart, a correction factor must be applied. Where the distance does not inhere V = induced voltage in millivolts exceed 50 miles, this correction can be dis- C regarded. The position of the ship obtained E = field strength in millivolts/ by dead reckoning and the position obtained meter by the radio direction finder result in a dif- A = loop area in square meters ference, between which, in the middle, is a V n = number of turns on the loop new bearing called the middle latitude or ). = wavelength of the signal middle longitude. The tangent correction qr = angle between direction in is, which loop is pointing and bearing of station. (tan cliff. long.) X (sin middle lat.) tan - (5) If the loop is not square, equation 4 con- correction 2 tinues to hold true, provided that the areas How a bearing may be taken is illustrated Fig. 2. The transmitter is 2n nA located at Eab point A and the ship takes a ire identical in all cases. The term bearing at B, proceeds a definite and known distance in X a straight line, B-C, and a second bearing is taken at C. Then, the distance b is given L. known as the "effective height" since it by the formula, letermines the ratio of effective induced voltage to the field strength, when the loop sin B is a in line with the station or incident wave. b = At right angles to the loop, at a point of sin A minimum signal pick -up, the cosine ofgt is zero. Assuming a square -law detector is To obtain the "sense" of the bearing, I nstrucwr, commercial operator. used in the antenna input circuit (for ex- since in a loop the pick -up may be recipro- 34 RADIO -CRAFT for OCTOBER, 1942 .4I 1 /. / . / 4,4 /+ A J- ENGINEERING cal, a vertical antenna is used. After first must fly in a curved path, deviation being obtaining a null, tue sense antenna is con- dependent on cross -wind velocity. nected to the loop or input circuit of the re- Compasses of the rotating loop type RADOIEX- ceiver and the signal will immediately gain aboard ship and aircraft are used princi- in strength, if the direction of the incident pally by the Coast Guard and Navy. The wave is favorable. The pattern obtained is Navy has about 50 stations at entrances to adqUartes illustrated in Fig. 3. The result is heart - principal harbors on both coasts. On the shaped, often termed cardioid. large planes equipped with a navigator, the rotating loop is practical. In loops of the sort described, with cardioid pattern and switching, serious errors For Essential pfcA up due to a dephasing action occur, and while ..- the fault was properly corrected, it was, nevertheless, required that precise gang tuning of loop and antenna be achieved. A system which effectively eliminates this PARTS drawback is one employing a cathode ray REPAIR tube. The directional and non -directional independently and I voltages are amplified ser- C3 then combined at the cathode -ray tube. The Thousands of progressive Fig. 3 its own R.F., vicemen rely on Radolek for vertical antenna works into of mixer and I.F. system and the loop antenna their complete requirements similar channel. The loop volt- repair materials. Make Radolek has its own source for es- age when amplified results in a variation or your dependable This cardioid pattern principle makes it beam of the sential replacement and repair deflection of the horizontal vol- possible to employ a simple scheme for di- the vertical antenna voltage parts -tubes, condensers, can be in- scope, while resistors, trans- rection finding purposes. A loop acts on the vertical beam. With the loop ume controls, stalled in aircraft with the loop plane set at pick -up, the horizon- formers. etc. -all at lowest with adjusted for minimum right angles to the fuselage or parallel line on the screen of the cathode -ray prices. is flying tal the wings. Then, when the pilot tube becomes a point and expands as the Radolek understands service the ship in the direction of an incident for increased signal pick- problems -gets delivery to you bearing will loop is adjusted wave or station, a minimum up. Signals between maximum and mini- in double -quick time. Buying be obtained. It is necessary that he swing effects in from Radolek means Greater to mum limits produce proportional the nose of the ship slightly off course the case of Vertical antenna or loop pick -up. Values. Better Service and left or right from time to time in order The resultant effect is, of course, the vec- More Profits. The big Radolek that the bearing be checked. tor sum of the voltages acting on the plates Radio Service Guide is FREE Send for your A novel modification of this scheme was of the tube. for the asking. developed prior to 1927 by Dieckman and The trace produced by the vertical an- copy today ! Hell in Germany and a practical version of tenna inclines to right or left, depending on it was exemplified by a Department of magnitude and phase of the voltage in- RADOLEK P. A. SYSTEM: Commerce instrument. The cardioid pat- duced in the vertical antenna. The amount tern is alternately switched back and forth of inclination will be governed by the rela- FOR EVERY REQU(REMEÑ in direction. This system is employed in tive intensity of the voltage due to loop aircraft fixed loops. The audio rate of re- pick -up. When on the course, a vertical versal of the pattern is about 1,500 cycles line is observed, but a left bearing will per second. The figure 8 pattern of the loop produce a left incline on the cathode -ray is stationary, as far as the indicating meter tube trace ; a right bearing produces an in- is concerned, but the difference in output clination to the right on the screen. The from the two cardioid patterns which are figure may be changed to a straight line reversed in polarity, operates a balanced by adjusting a trimmer. The pattern ob- vacuum -tube voltmeter circuit which moves tained when directly over a transmitter is the zero-center meter pointer to the left circular and would be obtained by an air- Thousands of successful Radolek or right, depending on the line of flight flying directly above a radio station. P.A. installations are proof of craft quality, superior design and top with respect to the radio wave and the The loop antenna has a voltage 90 degrees performance. Complete systems transmitter on which a bearing is being out of phase with the vertical antenna re- for permanent, portable or mobile taken. Should the plane be heading oppo- sulting in the circular pattern. use -wide choice of microphones, at by speakers and related equipment. site to the true course, or variance The Simon Radio Guide direction finder Radolek P.A. Systems give you 180 degrees, a left indication would be ob- loops mounted at right angles. more for your money in Perform- employs two Dependability and tained on the meter, and the opposite effect in essentially the same way as ance, Styling. does not Operating Reserve Power. Select the P.A. would also obtain. The compass a radio range, except for the fact that the apparatus you need from Rad- operate on the principle of a minimum sig- instrument is aboard the plane, this type olek's big FREE catalog. nal, in contrast to most others, which means of finder unfortunately has not only 180 is and the signal -to- RADOLEK REPAIR SERVICE that the range greater degree ambiguity but two 90 degree ambi- Let Radolek repair your damaged or noise ratio better. Once set on a station it burned out transformers, coils. speakers, guities as well. It is necessary to employ a etc. Many items cannot within 1 or 2 degrees. test equipment. indicates continuously sense antenna for ambiguity determination. now be replaced and therefore repairing Is Trained crafts The Kreusi Compass, developed by the This sense antenna is switched in or out of sing precisioftn otools and factors needed. The receiver is a dual methais, assure perfect Jobs equal b, Army, uses a similar idea except that re- the circuit, as new. Write for of phase switching takes place in type employing two sections of substantially prigs or better versal still, send in any the vertical antenna at an audio rate. A dis- equal sensitivity. Occasionally, it is required article to be re- is it can not be used for that the sensitivity be adjusted when ap- paired. It will be advantage that bandied promptly. voice broadcasts since switching is at audio proaching or leaving a station. frequency. Indication of direction is provided by a reversing cardi- two crossed needles at the intersection of In the Navy Compass, is right, the SEND FOR NEW FREE oid field pattern is also employed but aural these needles. If the indication rather than visual indication is used. The needles cross to the right ; if left, the RADIO SERVICE GUIDE needles cross to the left. The center refer- signals are an interlocked A and N pro- The duced by a commutator geared to the en- ence line is equivalent to "on- course." gine tachometer shaft. The commutator al- instrument is calibrated so that the station's RADOLEK CO., Dept. C -11 direction in degrees of the plane's bearing 601 W. Randolph SL,Chiago, III ternately works two relays in the R.F. I causing superimposition in may, be read up to about fifty degrees on coupling unit, installations the dual antenna either side. In some Please send the BIO FREE Radio Service Guide. alternate phases of the vertical means of a suitable pick up on the loop pick -up. Thus, to the type loop is rotatable by left of true bearing an A will be heard, to wheel. Name the right an N. On course, signals are long Any radio operator who has had experi- and ence aboard ship with direction finders Address dashes composed of the interlocked N O SERVICEMAN O SOUND ENG A. In the case of cross winds, this and knows that changes in the metal in the vi- Cl DEALER similar types of direction finding instru- cinity of the loop will seriously affect the AT RADOLEK ments are at a disadvantage since the plane (Continued on page 41) SAVE RADIO -CRAFT for OCTOBER, 1942 ENGINEERING IN -PHASE AMPLIFIER Designing a Non -Phase -Reversing Stage

By R. C. WHITEHEAD

THE ordinary resistance-capacity amplifying stage has an output voltage which is 180 degrees out of phase with Output respect to the input voltage. In the design of vision-frequency amplifiers, Cl pulse-generators, multi -tube oscillators, etc., it is sometimes found that, while sufficient gain can be obtained with a given number R of tubes, this combination produces the wrong number of phase reversals. To avoid adding a tube, the gain of which is not required, one of the stages can be made into a non -phase -reversing stage. C3 Fig. 1 shows the fundamental circuit of a non- phase- reversing stage: Instead of the RS cathode being connected to ground and the input being applied between grid and ground, the grid is grounded and the input is applied between cathode and ground.

INPUT AND OUTPUT VOLTAGES ARE IN PHASE In Fig. 2 is shown the circuit of a practical non -phase- reversing stage. Because the input and output voltages are in phase, and because the grid acts as a grounded screen between input and output,* a triode tube can ground potential by generally be used in the sane amount, less second) may also lind their way to the cases where otherwise the amount of grid bias required it would be necessary to use a pentode. for nor- cathode and these are not entirely removed mal operation. This is most conveniently by C. and R.. If these are troublesome they The condenser Ca and the resistance R. done by connecting the lower end of the grid may be reduced by reducing C. or C,. Re- have been introduced in order to avoid leak to a tapping on R.. The grid condenser duction of passing the former will increase the bass the DC component of plate current C_ and the grid leak R. can have normal response, reduction of the latter will de- through the source resistance R,. If R. is values. crease the bass response. high in value and a wide frequency band In this circuit the plate filter condenser The grid leak of the succeeding stage is to be covered, then C. and Ra cause de- is sign Ca shown connected to the cathode. The (R,) should have a value which is high difficulties, and they should not be alternating component of plate included unless absolutely necessary. current does compared with R, multiplied by the stage If Ra not therefore pass through the source re- gain. is made high then the voltage available for sistance R,, operation of the tube and negative feed -back and is reduced. If Ra consequent reduction of gain are avoided. is made low, then C. must have a low re- TUBE MAY REQUIRE actance at the lowest working frequency, When selecting a condenser for the Ca SEPARATE HEATER WINDING and if this frequency is in the neighborhood position an electrolytic type should be If the cathode chosen only if the normal -ground volts exceed about of 50 cycles, then, as both sides of C. are leakage current 30, the tube should normally have its own at high signal potential, the stray capacity will not upset the performance of the circuit. heater winding. A compromise may, how- between it and ground will influence the ever, be effected by connecting a common design and performance at very high fre- Examination of Fig. 2 reveals that both heater winding to a potentiometer across quencies (e.g., 3 megacycles). Rs and R. are effectively in parallel with the B supply, and arranging for the poten- R.. Normally R. should be equal to R.. tial of the heaters to be midway between the DESIGN CONSIDERATIONS The load resistance R: and the filter re- extreme values of cathode -ground poten- sistance R, should be made as high as is tials of the various tubes. Since the cathode has been taken up consistent other above ground potential (as regards with requirements in order The input capacity of the stage comprises DC). that the capacity of Ca may be kept so also must the grid be taken up above to a the following :-(a) Cathode- heater capaci- minimum because the stray capacity of Ca to ty. (b) Cathode -grid capacity. (c) C, and "Journal of the Institution of Electrical En- ground is effectively across R.. Ca stray capacities to ground. (d) Stray gineers" (London), September 1939. Description Supposing that the B supply voltage wiring capacities. of Series Amplifier in the Standard Telephones con- transmitter. tains some residual hum, and for the mo- It will be seen that the input capacity of ment ignore the components .shown dotted this stage is higher than that of a normal in Fig. 2. In an ordinary amplifier the re- stage. sistor- condenser circuit acts also as a filter circuit. Finally a successful design can be best Output achieved by arranging the circuit as follows. However, in the circuit of Fig. 2 this is These notes apply particularly when cover- not so. If the reactance of Cs at the hum ing a very wide frequency band. (a) Insert frequency is small compared with R, plus the non- phase -reversing stage at a point R., then the hum volts present in the plate - where the output impedance R. and the out- R2 supply system are only reduced in the pro- put voltage of the previous stage are both L portion R, / (R. + R5) and these hum volts low. (b) Avoid use the of C, if possible. are applied to the cathode or input of the This can be done if the previous stage is a stage and are thereby subject to its full cathode -follower. (c) Make R, as high as amplification. The remedy is to ensure that possible without encountering loss the hum at the voltage is small at the top end of highest operating frequency. (d) Make Ra R.. This is done by adding C. and R.. and R. as high as possible without allowing the tube to be overloaded. (e) Make C. REDUCING PLATE -VOLTAGE VARIATIONS and Ca as low as possible without encounter- Variations in plate voltage occurring at ing loss at the lowest operating frequency. very low frequencies (a few cycles per -Wireless World, London. 36 RADIO- CRAFT for OCTOBER, 1942 LATEST RADIO APPARATUS

AIR -RAID SIGNALLING 3 -IN -ONE MULTITESTER HAS WIDE RANGE OF CONTROLLER APPLICATIONS Automatic Temperature Control Co., Inc. 34 East Logan Street, Philadelphia, Pa. Radio City Products Co. 127 W. 26th St., New York City DESIGNED to supplant manual methods for sounding "Alert" and "All Clear" MAXIMUM sensitivity, flexibility and air -raid signals, this new unit will auto- utility are combined in this new matically control operations of motor sirens, vacuum -tube multitester. This instrument, air or steam sirens, bells, lights, or any designated as Model No. 662, is an electronic standard signal device in compliance with voltmeter, ohmmeter and capacitymeter in official civilian defense standards. Housed one, with an extremely wide and useful in a dust -tight, sheet steel case, 14 ins. x 14 range of applications in laboratory and pro- ins. x 5 ins., and is supplied for either flush duction -line tests, service work, etc. or surface mounting positions, the controller It is a vacuum -tube voltmeter on AC embodies the following construction fea- readings -not a copper oxide rectifier type tures: Indicator lights show whether and it furnishes capacity readings directly in micrufara ds. with a measurement ration amperes are available for D -C measurement. Self -contained ammeters to 100 amperes, D -C and A -C, and voltmeters up to and D -C are also available. 500 volts A -C INSTRUCTIONS Higher ratings may be obtained by using resistors, shunts, or transformers. On rectifier instruments the dial is calibrated in root- mean -square values with a sensitivity of from 1,000 to 5,000 ohms per volt. These are used for measuring A -C values when low energy consumption is important. Thermocouple styles are available with either self- contained or external thermocouples developed for maximum overload and stability and are used for measuring radio -frequency currents. Frequency errors have been reduced to a minimum, and the overall design is balanced to give the minimum capacity or inductive errors. "Alert" or "All Clear" signal is in effect; Features common to all instruments in a 3 -pole contactor used in the standard con- this classification are permanent white dials, struction will handle siren loads up to 25 high torque to white ratio, and Moldarta Amperes at 110 Volts, A.C. non -inductive; cases. a toggle switch provides manual operation may be obtained Additional information when desired ; it is rated for operation from from the company. -Radio -Craft 110 or 220 volts, 25, 50, or 60 cycles, and it can be supplied with an automatic throw - EXTRA -HEAVY DUTY 50 -WATT over inverter and stand -by battery for in- POWER RHEOSTAT suring operating in the event of A.C. power failure. An instruction plate is mounted on Mfg. Co. case. -Craft of 40,000,000 to 1. In designing this mu ti- Clarostat the front of -Radio purpose instrument, RCP engineers elim- 285 North Sixth St., Brooklyn, New York inated danger of shock on low -capacity FERRULE RESISTORS 50 -watt rheostat is virtually There are no test leads to THISHIS new measurements. to the previously introduced 25- Ohmite Manufacturing Company and no resetting is necessary when 3M short, unit, except for its larger size. The 4835 Flournoy Street, Department ranges. The meter cannot be dam- watt changing is wound on an insulated Chicago, III. accidental connection across a live resistance wire aged by metal core which distributes the heat at resistor or by using a low range on high THESE Ohmite ferrule resistors were due to line voltage fluctua- designed for easy interchangeability with- readings. Error of tion is eliminated by a VR105 -30 regulator out any need for tools. An even winding core is pro- tube and associated circuits. resistance wire on a ceramic enamel coating. The wire This model employs a sloping panel and tected by vitreous hands, or ferrules, a 45/2-inch meter but an upright -style com- is terminated on metal in fuse clips. Fer- panion model (No. 662 -V -7) with a large which permit mounting 8% rectangular meter is also available. rules are cup, sleeve, or cartridge type. -inch coating are Both instruments have similar performance Ceramic cores with special characteristics and are furnished with leads available which will withstand temperature immersions alter- and large, readily accessible batteries, tubes shock tests of repeated and hot water. Pro- and pilot light. The case is finished in nately in ice -cold water crystalline gray.- Radio -Craft tective coatings which will pass salt water immersion tests are also available. The ferrule type of resistor is particularly THREE AND ONE -HALF INCH METERS The resist- Westinghouse Meter Division, intermediate rotational settings. imbedded in a Newark, N. J. ance element is firmly ceramic housing with an inorganic cement, FOR radio transmitters, control panels, resulting in a solid thermal mass. A gra- industrial test units and general test phited- copper contact shoe rides the collec- work in electrical laboratories a new line tor ring and the winding, assuring two posi- of miniature panel instruments is announced tive sliding contacts. Contact pressure is by Westinghouse Electric and Manufactur- provided, by a helical spring concentrically ing Company. mounted around the shaft, the action of Direct and alternating current, thermo- which is evenly distributed by use of a couple and rectifier types of the three and tripod -type contact carrier. The contact is one -half -inch class for indicating volts and insulated from the metal shaft by a center amperes are made with a chassis construc- ceramic insulator, thus providing a "dead" tion permitting only a change in cover to shaft and mounting bushing. These rheo- applicable for use in the Navy, in the Signal make up square, circular, flush or projection stats are available in any resistance values Corps, on Army aircraft and on railroads. type instruments. up to and including 10,000 ohms.-Radio- Units may be obtained in a wide range of Full -scale readings as low as 20 micro - Craft sizes. -Radio -Cra f t RADIO -CRAFT for OCTOBER, 1942 ENGINEERING

DEVICES FOR AIR RAID WARNINGS (Continued from page 30) quency range for warning signals lay be- such signals will penetrate rooms in the in- tween 200 and 500 cycles per second. More terior of a building. recent work, which has been done on this To obtain signals of this level present program, where shorter distances will require are involved, a considerable acoustic output, and it be- indicates that this upper limit comes necessary to consider might be raised the economic to 700 cycles. (A 200 -cycle side of the question so note is about 2 as to decide whether tones below middle C, and a large number of small signals placed close a 500 -cycle note is about an octave above together would be more economical than a Radio Laboratory middle C.) Surveys of signals in Boston few large Northern Street and signals spaced considerably East Lake by the Northern Electric Company, farther apart. The answer to this question 3927 Minn. Ltd., in Canada, confirm the bureau's Minneapolis, prod-o- find- might be very different in different locali- using N.U. ings that signals in this frequency range "Tie ties. This subject be have been They carry better will discussed further inception. than those having frequencies under parts 5 and 6. since their merchaealers outside this range. ucts It is the bureau's belief that in have an aggressive all Another reason for choosing a signal with a down- we feel of. a comparatively town section, where the buildings are con- ing plan themselves low frequency is that the avail bus- signal should be heard inside tinuous and high and the streets are narrow, should buildings. relatively 22 years in he Union's Studies made by the bureau on sound trans- small signaling devices, placed at "After find r set street intersections, might give the best we n mission through different types of building iness, always b O sLFE coverage. The number of intersections be- helps have W Construction indicate that the average transmission loss of sound through such tween signaling devices would depend on the to us. struc- size tures is about 8 decibels less at 200 cycles of the signaling device, and whether locations could be worked WHERE YOU FIND than at 1,000 cycles, and therefore a low- out so as to give frequency sound is more likely to be heard uniform sound coverage for all streets. inside a building than one of high frequency. For other locations where a uniform cov- NATIONAL union Low -frequency sounds also give a better erage is desired in all directions, it is be- YOU FIND coverage within a definite area, as buildings lieved that a device which will give a signal BETTER and natural obstacles produce less of a level of approximately 110 decibels at 100 shielding effect than when a higher fre- feet will give, on the average, a satisfactory RRD10 SERVICE quency is used. Also, directive effects caused warning signal up to a distance of one -quar- by horns and other radiating surfaces are ter mile if the average noise level does not considerably less when a low frequency exceed 80 decibels, and up to one -half mile sound is used. if the average noise level does not exceed 70 decibels. If the signal strength is 100 2. Quality of Sound decibels at 100 feet, these distances will be Having chosen the band of frequencies about one -half as great, and for a level of which is most likely to be heard, considera- 120 decibels at 100 feet the distances could tion should be given to the quality of the be doubled, but the uncertainty due to weather conditions will tone ; that is, should it be a pure tone or be somewhat greater should it be a complex tone made up of at these longer distances. This point will be inharmonic components. Tests again show discussed further under 6. that an inharmonic combination of tones or The above statements are rather general a pure tone which is being constantly varied and may not apply exactly to any given in frequency arrests the attention more location. The distribution of signaling de- quickly than a pure tone or a tone with vices in any city is an individual problem, overtones which are exact harmonics of the and it may be necessary to make trial in- fundamental. Also, a combination of tones stallations at some points before the best which are separated by a half octave or results can be obtained. more can be selected which will sound BATTERIES louder than a pure tone which has the sanie 4. Ease of coding signals amount of uwooii. pr. energy. If, in addition to the use A signaling device should be chosen of two tones, these tones can be varied in which can be easily operated so as to give oEwSEt{ , frequency the signal becomes very dis- coded signals. tinctive. CONDENSERS The character of the signal should also 5. Type of device Transmitting he such that it cannot be confused with the tubes, panel signals used by fire trucks, ambulances. In considering the type of device which tau lamps, cathode ray tubes, should be used, it is exciter Moreover, it should not be similar to sur- desirable to make a lamps, sound rounding noises, since these would mask survey of existing facilities. An attempt equipment, photo electric the warning signal. should be made to lay out a warning sys- cells, sound accessories, dry tem which will require the purchase of a batteries, flashlight bulbs. 3. Loudness minimum amount of new equipment and still give an efficient warning. For instance, NATIONAL UNION . invites .. To be heard above other noises, it is nec- if there are essary that the signal steam plants which have steam All be sufficiently loud. up all of the time, a steam whistle or steam radio service dealers to enjoy There is very little information to indicate the benefits of the N. U. siren might be used. In many cases a fac- Shop how loud a signal should be, but it would tory might Equipment seem have a whistle or siren, and it Plan. The latest in desirable that the loudness level of the would not be necessary signal should be to purchase addi- tube testers and test equipment at least equal to the loud- tional equipment for that locality. In many ness level of the- noise at a point where are available to you .. . the other locations it might be signal is to possible to use act as a warning. (In very quiet air horns. The necessary air to blow such More than 60,000 completed areas, the signal, of course, should be louder horns might than the surrounding be obtained at a filling station deals prove the success of this noise.) In areas where or a bus terminal, provided an extra air plan. Investigate now. there is considerable traffic the average noise tank were installed. There level is 80 might also be decibels or more. In a residential other factors which could be I1 area, off arterial taken advan- Ask Your N. highways. the average tage of in any given city to lessen the or Write noise level is approximately 60 to 70 decibels Distributor amount of equipment which it would be in Washington, although in some very quiet necessary to buy. areas this level may he as low as 50 decibels. If a signal level of 80 decibels is chosen nATIOnALunion as a minimum level for noisy locatións and 6. Effects of weather 70 decibels as the minimum level for resi- One of the most important factors in the RADIO. dential districts, there will be a positive propagation of acoustic signals over large warning to persons -of -doors distances is the weather, or more specifically 57 STATE ST..IIEUTARR.f. J. out and probably to anyone located in an outer room the humidity, wind and temperature varia - with windows. It is unlikely, however; that (Continned on page 53). 38 RADIO -CRAFT for OCTOBER, 1942 )2adio eondtzuction Radio 7tzlavisioa HOW TO MAKE

A 23/4 x 4" RECEIVER

By IRVING MINTON

GONE are the days when experimenters battery. The A battery is fastened by a sought to make sets larger and more clamp to the back of the panel. elaborate. The tendency today -based The microtubes have no bases and pins on scarcity of parts, among other as do larger tubes, and therefore have their factors -is to make sets smaller and bet- leads connected to the necessary terminals. ter, using, of course, only currently avail- Two of these tubes (one M74 and M54 able materials. audio tubes) are held in place by the wir- Until the introduction of microtubes, ing. To prevent possible breakage of term- which were introduced principally for hear- inals or shorting of terminals, I used two ing -aid devices, tubes required so much strips of celluloid, one on each side of the should be left between primary and second- space that anything resembling vest -pocket tube wires, cementing them together with ary windings. receivers couldn't possibly be accomplished. acetone into one solid piece. The soldered For aerial and ground terminals I used The last issue of Radio -Craft (Aug. - joints were made below the point where pin jacks to avoid having bulky binding Sept., page 723) disclosed that a miniature the wires project. posts on the panel. It was necessary to cut four -tube receiver was described at the The detector stage required shielding. down the excess insulated portion of the recent I.R.E. convention. Although I have This was done by wrapping a piece of thin two-pin -jack assembly a bit to make it fit not seen this receiver, I believe that Radio - sheet copper around the M74 detector tube between the A battery and the antenna coil. feature I be Craft readers will be interested in knowing to a fairly tight fit, sliding the shield away The which believe to the that I was able to construct a complete re- from the tube and soldering it to form a most novel is the improvised loudspeaker. ceiver using three microtubes and an im- cylinder, leaving a small amount of cop- This was made from a single Trimm ear- provised loudspeaker, all of which, includ- per extending beyond the joint to be able phone. I removed the cap and made a corre- to solder a connection for the ground. This spondingly sized washer, 1/16 inch in thick- tube was placed adjacent to the trimmer ness, out of celluloid and placed it between condenser, which in this case serves as the the earphone and the back of the panel. tuning condenser. This permits free movement of the dia- The wiring presented no great difficulty, phragm, while holding its outer periphery the only necessary precaution having been securely to the panel. A number of holes to keep the terminals relatively short. This drilled in the panel exposed a sufficient meant that most of the condenser and re- amount of the diaphragm disc so as not sistor leads had to be shortened. seriously to impede the sound. I found that by changing the coil from The on- and -off switch is a miniature the one used by Mr. Dezettel, I could ob- rotary which I happened to pick up some- tain greater selectivity. I made up a tube where. Only a locking nut and two wires by rolling up some gummed paper tape protrude in back of the panel. into a half -inch coil form, that is, one - The tuning condenser is a small Meissner half inch in diameter and one -half inch trimmer which varies in capacity from 125 long. About 75 turns of No. 32 enameled to 350 mmf. This trimmer has a ceramic wire make a good primary. The secondary casing and has the usual slotted screw pro- consists of 25 turns of the same size wire. jecting from the top. Although originally The experimenter should make up several I placed the trimmer behind the panel, I coils, varying the number of turns, and found that this caused too much cramping select the one best suited for radio recep- of the parts and therefore I mounted the tion in his locality. The turns can be random whole trimmer on the front of the panel, wound, but a space of at least inch (Continued on page 55)

bg an A battery and a 45 -volt B battery, fits into a single box measuring 234 x 4 inches. Lest there be any misunderstanding, I should like to state that the circuit diagram did not originate with me. In fact, it was designed by L. M. Dezettel, whose instructive articles are familiar to Radio-Craft reaflers. Whereas, Mr. Dezettel's receiver (described in Popular Mechanics) was built in a box measuring 3 x 3 x 21/2 inches. the A and B batteries and earphones were not incorporated within the box, the belief that the complete receiver, including all SWITCH accessories, could be made even smaller o prompted me to undertake the mechanical -A IXV. +A +845V. redesign of his miniature portable. ANT. COIL CI- TRIMMER COND. 125 -350 HMI -B As be seen from the photograph, the will C2-.0001 MF MICA TYPE COND. 400 V. complete receiver that I built fits into the C3-.01 MF 500V. palm of the hand and requires only that R1 -IMEG. X WATT. it be held near the ear to enjoy a broadcast R2 -SMEG. program. R 3 -21MEG. The complete receiver was assembled on ONE A- BATTERY 14V. ONE (MACAO). Ne.555 45 VOLTS) a 234 x 4 inch panel, with all parts and the B BATTERY A securely mounted to the panel to permit ease of wiring and future removal from I 2 5 5 the case for battery replacement. The case measures 2 inches deep and houses the B RADIO -CRAFT for OCTOBER, 1942 39 Gxpatim¢nt¢t!

EGG-FERTILITY RADIO TESTER

High-frequency oscillator and resonant tank. serve the effects on maximum current and resonant frequency in the radio circuit by introducing an egg into the coil. These EGG Coll A METHOD of measuring conductivity effects depend upon the and conductivity of the dielectric effects without the use egg which reduces the current, and upon of electrodes in contact with the material III LICO its dielectric constant which by increasing Il/il'/'ll coCOIL being measured has been developed at Cor- the coil capacity lowers the resonant f re- 4111 nell University Agricultural Experiment quency. Station, Ithaca, New York. These Utilizing a high- frequency oscillator and studies indicated that at these f re- a resonant tank circuit quencies the conductivity was lower and Dr. Alexis L. Ro- the dielectric manoff and Karl Frank, of the effect higher in fresh fertile Depart- hens' eggs than in ment of Poultry Husbandry, have been infertile. In view of D' ERMO- these results the Cornell experimenters de- AMMETER TO RADIO able to apply this method in their studies GENERATOR of detection of .fertility of fresh cided to extend the study of the intact egg eggs. to wider range Observations previously made by Dr. a of frequencies. Romanoff and an associate, using an audio - To cover the range between 2 and 60 0 frequency bridge, showed that the elec- megacycles two separate oscillators were trical conductivity of yolk and albumen of used. The source for the lower frequency fertile range of from 2 15 VARIABLE eggs increased from the beginning to megacycles was the flG.l of incubation. This suggested the possibility oscillator shown in Fig. 1. For the 15 to 60 CONDENSER of observations on the whole egg showing megacycle range a special oscillator (Fig. differences between fertile and infertile 2) was constructed. The power supplies RADIO FREQUENCY CIRCUIT eggs if a radio -frequency circuit were used for both oscillators were fed from a 60- and effects due to eddy current losses ob- watt voltage regulator and there was served. negligible frequency drift or detuning on The test apparatus is shown in Fig. 1. A loading. radio-frequency with egg coil or dielectric cell. circuit consisting of a Figure 2 shows the circuits of power sup- The oscillators were coupled inductively variable condenser, inductance coil and ply, high -frequency oscillator and resonant thermoammeter to the resonant tank circuit which was con- was driven by a link - tank. The 450 -volt power supply feeds a nected in parallel with a pair of circular coupled stable 5 -watt generator at fre- tuned -plate tuned -grid type oscillator using plates forming the dielectric cell. The 3 to quencies ranging from 14 to 14.4 mega- two 210 -Ts in push -pull mounted base to 15µµf variable cycles. The method tank condenser was pro- followed was to oh- hase, which in turn drives the resonant tank vided with a very accurate micrometer

B NIGH FREQUENCY OSCILLATOR RESONANT TANK

PHOTO iELL M.t(tn CALL V Polt te M AI

n. tw..er .ut

.--. AEWMaM rOtlt

5 1.575 175 7.5 13 30 60 LOG, FREQUENCY pow( R SUPPLY FIG. 2 EGG HOLDER IN MEGACYCLES

RADIO -CRAFT for OCTOBER, 1942 LXjletimentet9 Radio g eevleion

worm drive and dial permitting settings of electric effects on several lots of intact eggs the condenser capacity to an accuracy of at frequencies of 54.6 and 27.3 megacycles SPRAYBERRY ±0.0021.4µf. In the center of the tank coil showed tendencies in relative values of fer- was mounted a small 2.3 -volt flashlight tile and infertile eggs very similar to those RADIO TRAINING bulb above which was a photronic cell pro- previously observed at lower frequencies. includes tected by a copper sulphate heat filter. A There was greater separation in conduc- galvanometer shunted to critical damping tivity in favor of infertile eggs. The di- FULL EQUIPMENT registered the intensity of the light from electric effect was less consistent, although Experience Easily Acquired the bulb. again showing higher values for fertile than at Home for infertile eggs. was placed in a The entire apparatus The measurements of the conductivity You Do Practice- Giving shielded cage and operated by remote con- and dielectric effect of the egg components Experiments. Many Soeclai oscilla- Features , .. ALL Designed trol. The power output from the yolk and albumen were then made to locate to Help You Make Fast Progress tors showed a long period drift of less principal differences FUIT the region where the ing starts naht at thee beginning lta- than 1 cm galvanometer scale reading per eggs occur. di,,. You ily learn Television. E- between fertile and infertile guency Modulation,dulation, Signal Trac,mr, hour for the ultra -high frequency oscil- 2 -B) Mobile Radio tAUto- Tank), Aviation Ra- Curves on relative conductivity (Fig. dio, Electronics. Facsimile Radio. Hadi,, lator and somewhat more for the lower fre- shows that the values for various parts set Repair and Installation work. quency oscillator. of the egg were maximum at about 15 Training Prepares You for a Business of Your Own ... or Good Radio lobs- .. 1t. When measurements on whole eggs were megacycles. The difference in power ab- Civilian or Military of between high and Today, Radio offers mnrkable l,nOrtu, dies to the man being made the egg was mounted inside sorption any sample who wants to get head. My Training will help YOU in but the per- quick promotion In tae Army or Navy ill lit You for the resonant tank coil by means of an egg - low frequencies was large, a bright Civilian r. Your Training will not interfere holder sliding on a track and consisting of centage difference between 2 different sam- with your present domes. No previous a perience is needed. You Get Dual -Purdue Radio Bet two opposing glass cups pulled together by ples remained almost constant over the en- I supply you with Radio Parts which you use to gam u,ed aas Modern Signal Generatorand for Signal Tracing, etc. You'll rind my Course and Equipment fully described In the catalog offered below. Hut in addition to this Catalog. I am going to send you a valuable new manual. YOUR'S FREE! Just Off The Press! Big 80 -Page Book RADIO SERVICE SHORT CUTS" t,n, -t rt:ice It, It's a rich storehouse of pp - r.il tips and information. Tel how Radio -downs o . how to spot these defer..dreak how to correct them quickly and efficiently. If you ACT now, u can along with Catalog 0c coupon drivurEbelow! THE COURSE UNDERR trinNERY,rg NT

RUSH COUPON A., BOTH FREE BOOKS SPRAYBERRY ACADEMY OF RADIO F. L. bprayberry, President 520 -K University Plaee. N. W. Washington. D. C. Please rush my FREE copies of HOW TO MAKE MONEY IN RADIO" and luable 80 -page RADIO SERVICE SHORT COTS." Name Address (Mall in envelope or paste on penny postcard)

Dr. Alexis L Romanoff, right, and Karl Frank, of Cornell University Agricultural Experiment Station, Ithaca, N. Y., shown at the high -frequency conductivity testing apparatus.

a spring. The long axis of the egg was tire frequency range employed. The ob- thus automatically made to coincide with servations on the dielectric effect showed the principal axis of the coil. By this that there was little increase in values method the effect of position of the egg was and a gradual levelling off toward lower reduced to a minimum and readings on an frequency. individual egg could be repeated very pre- The relative conductivity and dielectric cisely. The coupling between the oscillator effect of the intact egg at frequencies of and the resonant tank was standardized by 27.3 and 54.6 megacycles gave results in- means of a glass egg filled with egg al- dicating that fresh infertile eggs have a bumen. higher conductivity and ...tendency towards The readings on v -ieiniddle dense lower dielectric constant than fertile eggs. albumen eré made alternately on fertile The conductivity values for various parts and rtile individual eggs. Outer and of the egg were maximum at about 15 die fluid layers of albumen, owing to megacycles. There was no frequency de- the small amounts available, from each egg, pendence for the percentage separation be- samples only. tween yolk and albumen over the range were studied from composite Performance . . Eye Appeal ' Priced Measurements of conductivity and di- from 2 to 60 megacycles. Value . . Sensationally - "- et SI 265. Dealer Net Price. iCaK

Here Is an AC -DG Vol Ohm- Milliammeter with all the ranges You want . easily readable on the large T' instrument with extra-long 6" scale, in a upto-tho- minute three -tone case. DC RADIO DIRECTION FINDERS loop once it has been installed. Volts 0,10 -50- 250- 500 -10x0 at 5010 Ohms per volt One way of doing this is to fly the plane DC: 1000 ohms per volt AC. AC Volts 0-10-50 - (Cautioned from page 35) miles from a station 255 -I003 at 400 ohms per volt: DC Ma. 0 -I -10 -100; a distance of about 50 Resistance ranges: 0 -1500 Low Ohms; 0- 150,000 calibration. For example, a guard rail torn whose location is definitely known. The Ohms and 0 -7.5 and 0 -I5 Megohma. Maroon case down by a storm may throw the loop "off," directional gyro can then be set for a with red and silver panel. attached handle. or a correction factor must be applied to straight course and the loop adjusted for Dealer Net Price, Sl0.65 into presence ob- calibration or a calibration disc made up. 1f take account the of metal College Drive jects in the field of the loop. In the case a gyro is not at hand, a straight road call Inr Catalog writo Section 1117. a flying above the straight of a plane, similar deviation is to be ex- be used, the plane READRITE METER WORKS, Bluffton, Ohio pected and it is necessary to calibrate the road. RADIO -CRAFT for OCTOBER, 1942 4! Radio %alavieion Xadio eonetruction

11 - Tube Frequency Modulation Receiver

By GEORGE FRANCIS BAPTISTE

FREQUENCY- MODULATION sets A 6SC7 is used as an amplifier to operate mounting the type -6SC7 tuning -indicator no longer are manufactured for con- a type of 6AD6 dual tuning indicator, which amplifier tube. An Amphenol above- chassis sumer sale, and except for some dealer tube offers the advantage that the F -M socket is preferable here because the side stocks that may be gone by the time receiver can be tuned to the center fre- holes simplify the problem of carrying you inquire about them, there are none to quency (mid -frequency) by noting the in- wiring from below the chassis to the tuning be had. The experimenter who has some dications of the tuning -ray shadow angle. indicator, which is well above the chassis suitable parts on hand and is willing and A 6SFS is used as the first audio stage level. able to purchase what he needs to fill in (see Fig. 2) and this is followed by a e'*gure 3 and the photograph should be the gaps in his equipment need not be dis- 6F6G output pentode. A type 80 rectifier cotsulted for the placement of these tubes couraged. The receiver built by the writer furnishes ample current for the power - as well as for the layout of the various tube may be duplicated by the experimenter by supply requirements. Dual speakers or a sockets and I.F. transformers, power sup- using the parts listed in the article, or he single speaker can be connected to the out- ply, etc. The installation of the power trans- can make necessary substitutions if he keeps put transformer, since it is of the universal former used requires that its chassis hole sufficiently close to the constructional plan type. be made larger. This transformer is of the outlined here. The complete frequency -modulation re- half -shell type and has a rating of at least The schematic diagrams illustrate the ceiver is mounted on a Browning chassis 125 milliamperes. Keep the power trans -. general wiring plan of the U -tube F -M (see part list), the speaker or speakers former as close to the corner of the chassis receiver. One preselector stage of radio - being placed in a cabinet to suit one's own as possible. You can construct your own frequency, utilizing a type 1852/6AC7 tele- taste and pocketbook. The size of the F -M F-M tuner, amplifier and power supply as vision -type R.F. pentode for high -gain am- receiver in the cabinet is 12 inches wide by separate tut interconnected units, depend- plification, feeds the signal to a 6SA7 com- 9 inches high by 12 inches deep. The F -M ing upon available materials rather than bined first detector and oscillator, which range is from 40 to 50 mcs. on strict adherence to the plan described. oscillator tube was found to have a low If a Browning tuning unit (described by frequency drift. This is followed by three CONSTRUCTION the author in the Jan. -Feb. issue of Radio - I.F. stages the first two using single -ended The construction of this receiver should Craft, p. 382) is not available, suitable. 1852 pentode tubes, which also have low not be difficult if a few precautionary parts may be obtained from Wholesale frequency drift, and the third stage, called measures consistent with good wiring prac- Radio Service Company. The, parts list at a limiter, using a 6SJ7. tice are observed. The Browning chassis the end of this article gives the part num- The second detector is a type 6H6 tube. must have a few holes added to permit bers. The Lafayette F -M tuning condenser

40,000A 11 i5N

100po0n .01 n MN! Ìo0n 0501' 5,000 o ISO,00On

100000 104,000A

M- nNy

104 nrs TTT 5.3 I nn .mnr w-ñi IMO. :w MIT NIxER 3 FIG. I COIL co1L

42 / RADIO -CRAFT for OCTOBER, 1942 Radio COnittuct4on %2adio /Qlttivi9ion

is 2% inches long by 15/16 high by 134 into the grid (this must be a three mega- kñs wide. The antenna coil, R.F. coils and mixer cycle signal) ; then adjust each I.F. trans- coil are one inch long. The antenna and former for maximum gain, adjusting the oscillator coils are mounted to the right and third I.F. transformer first. Maximum gain on the side of the tuning condensers above will be indicated by the dual tuning- indica- ev the chassis and the radio-frequency coil on tor shadow angle, which will narrow more the left side of the gang condenser or un- as each stage is tracked properly at its derneath it, at right angles. Leads from correct resonance frequency. In the align- the various coils are taken through the ment process the tuning indicator may over- naZA chassis to the tubes socket connections. Be lap considerably and if such is the case all AVOW -MVUMA sure to keep all grid and plate leads as far that is necessary is to -reduce the signal and recheck. With a sig- apart as possible. Wire all tube heater generator output toni connections first, then wire in the power nal of about one millivolt from the signal 23 V supply and bleeder system, leaving the B ' generator the tuning indicator should com- e. supply connections to the various points pletely close. The final step is to adjust t$0-300 V for the last operation. the detection transformer. Do not change but use 30- the setting of the signal generator, 300v a high- sensitivity voltmeter of 5,000 ohms CONSTRUCTION per volt or better. If the meter is of the The power supply (Fig. 2B) is standard center -zero type so much the better ; con- ts,0OO and requires no explanation. The audio nect this between cathode number four of 20 W,TT3 system (Fig. 2A) can be varied to suit the 6H6 tube and the ground (chassis) and - proceed to align the transformer with the 110 one's own requirements. A separate high A. C. fidelity amplifying may seem desirable but three -megacycle signal feeding into the grid was found unnecessary, judging from the of the 6SA7 tube. Adjust the secondary .0tnr transformer (this rate excellent results obtained with this audio trimmer of the detection POWER 4VVPLY system. will be the trimmer nearest the 6H6 tube) The choke and universal output trans- until zero voltage is obtained, as indicated former are mounted under the chassis in on the voltmeter. Now change the signal frequency to 2.90 and 3.10 mc. the rear near the dual 8mf filter condenser, generator 3-D a -a 606 ample room being provided for the trans- alternately and adjust the primary trimmer OIßCRI- Aro ORT formers given in the parts list. so that equal and opposite voltages are de- MATOR The photographs show a front view of veloped. Next readjust the signal genera- and check to see the complete F -M receiver, a general view tor to three megacycles t 1852 mega- *um of the top chassis and a bottom view of the if zero voltage is obtained at three srs t.r. same chassis, parts and wiring. The I.F. cycles. If it is not obtained, readjust the secondary trimmer slightly to obtain the transformers and tube socket should be 3,11 mounted with their terminals and connec- zero voltage. When this result is obtained A ' . the complete I.F. System is properly 6Sí7 tions in such positions that all plate and ANT. grid leads are as direct and as short as aligned. Be sure that your alignment tool possible. Bypass condensers should be has no metal in it, as this will detune the POWER due to the capacitance being intro- 1652 1352 mounted on their ends, as this gives a circuit TRANS- R.F. R.r shielding effect, and they should be placed duced into the circuit. With this operation FORMER between grid and plate, adding to the shield complete disconnect the signal generator and reconnect ose. i3A7 3 -n of the plates and grids, at the same time from the 6SA7 tube grid Ott making all leads as short as possible. Rigid the grid wire back to the grid of the 6SA7 oso. 1r I.F. wire should be used wherever possible. The tube, making sure that it is soldered prop- circuit diagram looks similar to the usual erly. FIG.3- CHASSIS LAYOUT TOP VIEW) superheterodyne, except that all the I.F. The next step is to align the R.F., detec- transformers have resistors placed across tor and oscillator stages. You can feed a them to damp out transient oscillations 45- megacycle signal into the antenna sys- Frequency Modulation Parts List use an F -M station that is around which otherwise would cause fuzzy fre- tem or RESISTORS 1/2 -WATT VALUE, IRC quencies in the output. These resistors also this frequency. First adjust the antenna Two 200 ohm trimmer, then the detector trimmer and Two 400 ohm widen the band pass of the I.F. trans- Foor 1000 ohm formers, and in this case, where the I.F. finally the oscillator trimmer. This process One 5000 ohm is 3 megacycles, the band width is approxi- may have to be repeated to have the dial One 10,000 ohm pointer track properly. Sometimes a slight Five 50.000 ohm mately 150 kc. Such an I.F. system is made Three 15,000 ohm broad instead of selective as in the regular readjustment of the antenna trimmer will Four 40,000 ohm I.F. stages in amplitude modulation sys- bring signal more into the resonance fre- One 20,000 ohm quency. This can finally be checked by ob- One 90,000 ohm tems. The limiter or third stage of I.F. Six 100,000 ohm uses a 6SJ7 tube, which has a sharp cut -off, serving the dual tuning tube for equal One 2500 ohm no bias being employed on this tube so shadow angles in a horizontal position. It Two 250.000 ohm Two 500,000 ohm it can operate at the point of satura- may be well to state that these stages tune that right One 600.000 ohm tion. The detection transformer is similar rather broadly, but this is perfectly One 2 megohm with switch to the type used in so- called discriminator for the damped circuits. One .6 megohm volume control One 1 megohm tone control in automatic frequency -controlled circuits, The speakers used with this receiver One 15,000-ohm 20 -watt resistor for bleeder its is quite different, this trans- were a Jensen high -frequency tweeter five - but function -AEROVOX 600- VOLT TYPE former being designed so that when the inch P.M. and one Jensen twelve -inch low - CONDENSERS is Both speakers had Fourteen .01 mt. signal frequency varied at an auc}iPíate- frequency P.M. woofer. Three .05 mf. the audio volts es.--at -developed in the eight -ohm voice coils, and as connected in Three 100 mmf. mica the 50 mmf, mica diode s of the 6H6 tube, which volt- parallel, present an impedance load to One of four ohms. Any One 1000 mmf. mica are fed to the audio amplifier system. transformer winding One 80 mf. 450 volte network of condensers and resistors other combination, such as two four -ohm One 8-8 mf. dual electrolytic condenser, 460 The volts ,_ used in this tube circuit arc necessary be- voice coils will give a load impedance of volts. 550 peak combinations were One .002 mf. mica cause frequency modulation stations pre - two ohms, etc. Other One .0005 mf. mica emphasize the high frequencies -this is tried and all worked out successfully, with Two 10 mf., 50 volts, electrolytic power to spare. standard practice- to obtain a flat audio - ample audio BROWNING LAB. PARTS at the loud speaker of be sure to tune frequency response In tuning the receiver, One 3D I.F. transformer the receiver, and it is necessary to com- for a horizontal rattern with equal shadow Three 3M I.F. transformer pensate for this and "deemphasize" in the on both sides of the 6AD6 tuning - One 100C chassis angles slide rule tuning dial receiver. indicator tube. As a final note, there are One 6D three points on the dial where you can tune TRANSFORMER THORDARSON your F -M station; the center one is the One T -13S42 Universal output transformer ALIGNMENT DATA by correct one and this can be noticed PHILCO indicator -tube shadow TRANSFORMER When the F -M receiver has been com- observing the tuning No. 82 -7440 flush be able Power transformer part pletely wired and carefully checked pro- angles. On either side you will not mounting, 123 ma. 125 ma. or ceed as follows for correct alignment: Dis- to equalize the shadow angles and this One filter choke. part No. 32 -7116, that it is off tune. When they are similar 20 henry choke connect the grid wire from the 6SA7 tube shows (Contracted on puje 64) and feed a signal from a signal generator equal it is properly tuned. 43 RADIO -CRAFT for OCTOBER, 1942 FOR VICTORY TODAY

AND SOUK i $INE$S TOMORROW

Get This Flag Flgu ig Now!

This War Savings Flag which flies today Think what 10% of the national income, over companies, large and small, all across saved in War Bonds now, month after month, the land means business. It means, first, can buy when the war ends! that 10% of the company's gross pay roll is being invested in War Bonds by the workers For Victory today ... and prosperity tomor- voluntarily. row, keep the War Bond Pay -roll Savings Plan rolling It also means that the employees of all these in your firm. Get that flag flying companies are doing their part for Victory now! Your State War Savings Staff Ad- ministrator ... by helping to buy the guns, tanks, and will gladly explain how you may so. planes that America and her allies must have do to win. If your firm has not already installed the Pay- It means that billions of dollars are being roll Savings Plan, now is the time to do so. diverted from "bidding" for the constantly For full details, plus samples of result- getting shrinking stock of goods available, thus put- literature and promotional helps, write or ting a brake on inflation. And it means that wire: War Savings Staff, Section F, Treasury billions of dollars will be held in readiness Department, 709 Twelfth Street NW., for post-war readjustment. Washington, D. C.

Save With War Savings Bonds

This Space Is a Contribution to America's All -Out War Program by RADIO CRAFT

44 RADIO -CRAFT for OCTOBER, 1942 THIS is a war of speed -a radio war. Com- mands and messages must go through like lightning. Never have communications been so vital to victory, or have new devices meant so much. The "Nerve Center of the Army" The whole responsibility for "getting the message through" is in the hands of the U. S. Army Signal Corps. Hands that install and TODAY! maintain countless thousands of radio sending needs your skilled hands and receiving sets - hands that adjust the marvelous mechanisms of America's newest and most secret weapons - hands that flash the orders to attack! Now - today- the Signal Corps needs your skill in this thrilling branch of service. You may already be an expert in radio or another communications field. If so, there is no more worth -while service you can render your nation than as a Signal Corps soldier. You may have no more than ambition and a love of mechanics and electricity. In that case the Signal Corps is ready to give you thorough train. ing - at good pay! It's the opportunity of a lifetime to serve your country and prepare for a future career. US.ARMY 4. tn4L `saw

HOW YOU CAN GET IN NOW tKEEP'EgN FLYING!" I. ENLISTMENT

If you are 18 to 45 a gstcally 1 t, you may apply for enlistment in the Signal rps or in the Signal Corps Enlisted Reserve. E. S. Army DIRECT F ISTMENT: Experience as a licensed radio operator, a trained radio ref' rman. a telephone or telegraph worker. will qualify you for active duty at FOR FURTHER INFORMATION REGARDING ENLISTMENT - Call as earn higher technical ce. From Private's pay you can dvance rapidly you and talk this over of the nearest Army Recruiting and Induction to $138 month, with board, shelter and uniforms. ratings -up Station. Or write fo: "The Commanding General," of the Service ENLISTED RESERVE: If you are skilled with tools but lack qualifying experience, you may enter the Enlisted Reserve. You will be given training, with pay, in one Command f you: to active duty when you have of the many Signal Corps schools, and ordered Massachusetts the course. First Service Command.. _.... Boston, completed Governors Island, New York may apply for immediate commission. Second Service Command COMMISSIONS: Graduate Electrical Engineers Baltimore, Maryland in the Signal Corps. And special opportunities for training and commissions are Third Service Command open to Juniors and Seniors in electrical engineering colleges. Fourth Service Command . . .._.Atlanta, Georgia Fifth Service Command Fort Hayes, Columbus, Ohio CIVILIAN TRAINING Sixth Service Command Chicago, Illinois 2. Seventh Service Command Omaha, Nebraska If you are over 16 years of age, and even though registered for Selective Service, order to repon for induction. the Signal Corps offers you Eighth Service Command Fort Sam Houston, Texas have not received your Douglas, an outstanding opportunity. Ninth Service Command Fon Utah you want to secure training in the vitally impor- If you have ability with tools -if Enlisted Branch, AK -1. A.G.O., Washington, D. C. tant field of communications-you may attend a school in or near your home city. Or write fo: You will be paid not less than $1020 per year while learning. And when you have finished your training-in 9 months or less -you can advance to higher pay as your technical skill incr . FOR CIVILIAN TRAINING INFORMATION - Call at any oMee of you have a minor handicap, Signal Corps Civilian Training may Even if physical or U. S. Employment Bureau. give you the chance you've wanted to serve the Army of the United States. the U. S. Civil Service RADIO -CRAFT for OCTOBER, 1942 45 radio & "ra1eviiion llayinnQtJ

ELECTRON GETTING STARTED

IF+ PROTONS

ELECTRON IN RADIO ORBIT

By C. W. PALMER FIG.1 AN ATOM OF HELIUM.

OUTER INNER FOR the benefit of those who have a very learn that two like charges repel (the CR817 - pith ORBIT limited knowledge of radio, we will ball and the glass rod were both positive ORBITS OF assume the FREE VIC that reader is entirely un- when they were allowed to touch) and un- IRONS MOT familiar with the subject. Therefore, like charges attract (the positively charged IN SAME we beg those more fortunate readers with pith ball was attracted by the negative rub- PLANE some S o o past experience to be patient if we ber rod) . spend undue time in explaining every tech- o o nical word and expression. CONDUCTORS AND NON -CONDUCTORS o o To understand how radio signals are re- Some materials, such as gold, copper, ceived, it is necessary to have a knowledge silver, brass, aluminum, etc., present very PROTONS- z 1 ELECTRON of electricity -the basis of radio. Suppose, little opposition to the passage of electric then, we start by considering the subject currents. Others, such as cotton, silk, rubber, NUCLEUS from the very beginning. wood, mica, etc., will not readily pass a current. The first class of substances is FIG. 2 AN ATOM OF CARBON. ELECTRONS called conductors. The atoms of most metals Matter is any substance having weight apparently do not have a very strong hold and volume. The air we breathe, the water on the electrons which make up their nega- SILK we drink and the earth on which we live tive charge. An external force can easily PITH THREAD are all forms of matter. Matter of all kinds remove some electrons or add some to the BALL /1 is composed of tiny specks which have normal number. The second class of sub-. been called atoms. These atoms, in turn, are stances mentioned is known as non- conduc- l,iSì made up of a number of still smaller par- tors. They have a strong hold on the elec- j i ticles of two kinds, and in order to start trons and will not readily change from their / x` out with the right foot, we will give these neutral state. t / particles their correct names -e lectrons and i L `x protons. The electrons are tiny charges of POTENTIAL negative electricity, and the protons are We have learned that like charges repel charges of positive electricity. Do not make each other and unlike charges have an at- e-, the mistake made by some people when traction for each other. If we translate this `r - ;P thinking about í/ electrons and protons. They into terms of electrons, it will read : elec- `/v °íi co not carry the electricity. they are the trons repel each other but attract protons, /`J.. , electric charges. If a negative charge of and similarly, protons repel each other but 44// WOODEN electricity were divided into many attract electrons. STAND small Apparently the feeling of `'`. charges, eventually a minute charge would the protons and electrons is mutual. be reached that could no longer be divided. If we charge a body with negative elec- This final division would be an electron. So tricity (add electrons) a stress or strained much for the electron and proton. condition is set up in that body FIG.3 A STATIC EXPERIMENT. by the elec- Normally, each atom contains a definite trons repelling each other. Some of these number of electrons and protons, in such a "free" electrons move to the surface of the combination NEGATIVE POSITIVE that the charges just equal body to get away from the others. The more CHARGE CHARGE each other. The atom is then said to be un- electrons we put into the body, the greater charged or neutral. Figures 1 and 2 show becomes the force of the electrons trying - -- + ++ examples or normal atoms. However, if a to escape. This force which tends to return - - - -__ FLOW force is applied to the atom, some of the a body to neutral is called a "potential." electrons will be pulled away from it and it The same effect is noticed in a -- - OF ELECTRONS body from it \viii have an excess of positive electricity which electrons are removed. compared to the remaining negative charges. To illustrate the effect described, suppose EXCESS DEFICIT Conversely, if a force is applied in the op- we refer to Fig. 4. The two balls shown OF ELECTRONS OF ELECTRONS posite manner, too many electrons are pres- are charged, one negatively and the other ent in the atom and it is said to have a positively. we touch FIG.4 TRANSFER OF SURPLUS ELECTRONS. If these halls together, negative charge. the excess electrons in the negative one will We can perform an interesting experi- rush to the positive one. It follows directly HIGH LOW ment at this time, to illustrate the effect NEGATIVE NEGATIVE of from this-that a- current will flow, as we CHARGE CHARGE charging a body. For this experiment we already explained that electrons are electric need a rod of hard rubber (some fountain charges. Several other examples of current pens are made of this material), a glass rod, flow are shown in Fig. 5. A, the -__-_ FLOW At -left - - - - - a piece of silk cloth and a small piece of copper ball has a higher negative charge OF ELECTRONS - - - -- pith from a corn cob. We suspend the pith than the right one, causing a current to flow on a silk -_ - -A- - - thread, as shown in Fig. 3. Then from left to right. At B, the left copper we rub the glass rod vigorously with the baH has a higher positive charge than the silk cloth and hriig it near the pith ball. right one and a current will flow right to HIGH LOW It will be found that the pith ball POSITIVE POSITIVE will follow left -the right ball has more electrons than CHARGE CHARGE the glass rod -it is attracted by it. Then the left one. we allow the rod to touch the pith ball and It will be noticed that the electrons move +++ notice that it + + + ++ + + now repels it. Now rub the from negative to positive and since we know ++t ++ _+ I- + rubber rod and bring it near the pith hall - that electrons are electricity, it follows that it attracts it. the current is also from negative to posi- i +t ++ + + The _B_ glass rod receives a positive charge tive. A number of years ago, before we when rubbed and the rubber rod receives knew as much about electricity as we do a negative charge. This is FIG. 5 EXAMPLES OF ELECTRON FLOW. the reason why now. physicists experimenting with it de- we notice the difference in their actions on cided that the current flowed from positive the pith ball. From this experiment, we to negative and this illusion has been passed 4S RADIO -CRAFT for OCTOBER, 1942 l{syinnats Radio 7alavieion down to the present time and is still com- countered the effects of induction when we monly used. We must keep this discrepancy noted that the pith ball was attracted by in mtndas it is important in understanding the glass rod, even though it was not touch- the operation of vacuum tubes and other ing it in any way. Inductive actions are very ow is Your electric devices. important in radio, in tuning coils, trans- The difference in potential, as that shown formers, etc. Chance! in Figs. 4 and 5, is measured in volts. Be- cause a difference in potential always causes MAGNETISM before in our history pas NEVERthere been such a demand for a current to flow, we sometimes call it an When a current flows through a con- be noticed. RADIO CODE OPERATORS! . electro- motive force (E.M.F.). Current ductor, two principal effects can You may never again have this oppor- strength, that is, the number of electrons The first is that heat is produced. The cur- tunity! ... Army, Navy, Merchant passing through an electric conductor per rent encounters a certain opposition (re- Marine and Industry need trained second, is measured in amperes. sistance) in the conductor and part of the Radio Code Operators now! ... this electric energy is used up in overcoming is your chance to train right in your resistance. The energy own home, with the same training RESISTANCE this "frictional" thousands of code oper- in makes itself evident that has put We have found that the current flowing used up this manner ators into good paying positions.. . through an electric circuit is dependent on in the form of heat. The Candler System can train you the potential. We also learned that some The second effect is known as magnetism with their easy, practical method that will give you unlimited opportunities materials will carry a current (lose and and we can best illustrate this by consider- ... no expensive practice sets needed gain electrons) more easily than others. ing Fig. 7. This illustration shows a coil of -costs you nothing to investigate .. . The opposition that a conductor offers to wire wound around a bar of soft iron. A no salesman will call... . the passage of a current is known as re- current from a battery is flowing through WRITE TODAY! sistance. The resistance depends on the kind the coil. While the current is flowing, the FREE QOOK! Bend oat have card today of material, the length of the conductor and iron bar will be found to the power for The Candler free BOOK OF the cross -sectional area. To be exact, the of attracting small pieces of iron and steel. FACTS ... tells you all the facts is not about being a radio cads operator. resistance increases directly as the length When the current from the battery Your copy Is waiting for you - of the conductor. A standard unit of re- flowing, the iron bar no longer attracts the WRITE FOR IT TODAY! sistance has been set up and is called the iron pieces. Thus we can see that the cur- CANDLER ohm, in honor of the noted German physi- rent passing through the coil of wire has Bllilknl cist, Simon Ohm. given it a new property which we call mag- SYSTEM CO. George 928 netism, and since it has this property only BOX If we analyze the above information, we Dept. S -10, Denver, Colorado learn that the current depends on the volts when the electric current flows, we call it and also on the resistance. In 1827, George an electromagnet, Simon Ohm put this relationship into terms Now, if we replace the soft iron bar with of arithmetic and it is known as Ohm's one of hard steel and allow the current to Law. There are three forms of Ohm's Law. flow for some time, we will find that the READ and SEND CODE Easily at Mont. This Quicker Way The first tells us that the current in a dr- steel will attract the pieces of iron even No when current flow has stopped. We have r is ad cuit is equal to the potential (volts) divided the code au kly pplyy :(y the resistance (ohms). The second tells now made a permanent magnet. A careful leiis,.eeldr preagy .act; us that the resistance in a circuit is equal examination of the soft iron bar will show m with als Wßä Master Telenlen Code to the potential (volts) divided by the cur- that it also retains a small amount of mag- 'reacher. Only ried which records rent (amperes), and the third tells us that netism, although in a smaller degree than In visible d t, sanl°d dsselÌb the volts equal the amperes times the ohms. the steel. The steel is said to have a higher specially prepared Pa- per to sends We will learn the application of these three degree of retentivity than the iron. oack your ey work at any speed formulas as we progress further into the If we drop a permanent magnet into a wish. NO PERFORATIONS --NO INK. Far Superior to any. thing ever developed . marvel of simplIClty. subject of short -wave radio. box of iron filings, we will notice that there Paw foolproof-gets because you learn !WARING ass wel EING.i That N' ds are two places on the magnet to which the la rest and quickest. While not matthiss..ared Standard equipment. Tele°IOX Is used at OF ELECTRIC CURRENT most filings cling. See Fig. 8. These places many O. S. Army Posts. Naval Tlnin Stations. We PRODUCTION AN furnish Complete Course. lend you the New All Electric In the foregoing discussion, we have re- near the ends of the steel bar are called the Matter Teleples, and personal instruction with MONEY -BA( OPARANTEE. Low cost, easy tens ](a ferred to a force (E.M.F.) that would cause poles of the magnet. One pole is called the for folder ' 9: obligatln' north pole and the other the south pole, or 107 HUDN ST. electrons to be separated from atoms and TE LEPLEA CÖ, JERSEY CITY, N. J. move through a conductor to other atoms. more accurately the north -seeking pole and This E.M.F. can be maintained by means the south -seeking pole, for if we suspend of a battery or a generator. The former the magnet from a thread, it will swing Do you need consists of plates of certain materials im- around until the north- seeking pole faces mersed in certain solutions that cause a the north and the south -seeking pole faces BINDING POSTS? chemical action, resulting in the production the south. This is the effect used in the mag- XL with Action assuuaN C%n.tant and of free electrons at one of the plates. We netic compass. ilrk connection. will not into the details of these chemical Manufactured in All Aluminum Tyne M go Magnets and magnetism are used in a .( 12c each. actions at this time. The interested radio number of different ways in radio receivers. Aluminum Body, Bakelite Top Type SI rt SSc Seen. fan can find this information in books on Headphones and loud speakers contain mag- Types CI or NP. ALL BRASS -STAIN. LESS STEEL SPRING A PIN. PROVEN by electricity or batteries. Several common nets. The transformers used in radio ampli- 240 M R. SALT SPRAY TEST NON. types batteries are shown in Fig. 6. CORROSIVE at 2Sc each. of fiers depend on magnetism. Even the actual Manufacturera ana Dealers Liberal The other common source of E.M.F. is transmission and reception of the radio D. scount, a generator which depends on the effect of waves depends on magnetic principles. X. L. RADIO LABORATORIES Ave.. Chicago, III. induction and magnetism. We already en- (Continued on page 52) 420 West Chicago

LES Correspondence Courses In COIL IRON MAGNET' ` RADIOS dELECTRICAL ENGINEERING ati DRY CELL --- BATTERY c...I creel , __ , ELECTRICAL ENGINEERINGO eher i -- atal riel. Pre pare yourself, a HLow Coetsfl. fore - fUto,e Modem, Im lifted, you understa nd 1' yam, ava t,; RADIOENGINEERING °4;(á'y1 ' ,,i, ', IRON Trains you to be per real vacua tube 11 \ technician. Emir kits furnished. Diploma on rn pletlan. S /,s FILINGS / (.Li.. 1A A14 Tuition. (Get course. School payment plan. Get tines. of School catalogs..o SE student NORTH SOUTH ES2E maPSlnu, CwmpÌete details. SEND NOW! ` f \\ _ / I t LINCOLN ENGINEERING SCHOOL Ihm I31448,LINCOIN, NEBR. STORAGE 1 \ ___ / BATTERY `?'L¡r \, f - Zi(4ir 'l MAGNETIC FIELD i -, ', ,t COMMERCIAL RAD1O INSTITUTE A radio training center for over twenty years. Well equipped. Excellent faculty. Practical resi- `,.. BATTERY dent (unmet.+ in Defense. Radio Telegraphy, Broad- cast. Serviclna, Tednetrial. Television. Aero- wJ BOX OF IRON FILINrS nautical D-acting. Mathematics and Studio Tech- ' "' `it BATTERYl / FIGS nique. Placement bureau. Fall classes now form- 5. Catalog upon request. FIG. 6 TYPES OF BATTERIES. FIG 7 ELECTROMAGNET DEMONSTRATING POLES OF A MAGNET. ing for October Dept. D. 58 West Biddle Street, Baltimore, Mi. RADIO -CRAFT for OCTOBER. 1942 47 Radio g 7aiavbios &yinnazi

REGEN CONTROL 0 FIG 2 (VAR CONDENSER)

500000 OHMS \-. WHICH REGENERATION 1 SCHEME? litir1 By M. HARVEY GERNSBACK - - .0002-MF .001- I ONE of the most important factors In ' MF V<<1 RE short-wave receiver design is regeneration control. Unless a set has an efficient FIG 7 method for controlling regeneration it is well nigh useless. A discussion of various methods of control and their advantages .0001-MF. and disadvantages will be undertaken in this _ article. L Detector systems using three -element 30,000 tubes will first be discussed. For simplicity, OHMS all diagrams will show grid returns to cathode, which is equivalent to A -minus filament in battery sets. Figure 1 shows the \ simplest system of control, by mechanical movement of the tickler coil with respect to the grid coil. This method is now obsolete, as it is very critical in adjustment and l-MF causes quite a noticeable detuning effect on the detector tuning control. Figure 2 shows +90V a method that was once considered the best FIG.8 possible for short -wave work. It is used but 50.000 OHMS little at present, as it also is fairly critical in adjustment and causes detuning. It is simply a parallel plate feed system similar in principle to the method of isolating the plate current from an A.F. transformer primary in audio amplifiers. The control shown in Fig. 3 merely varies the voltage applied to the detector plate by < means of a variable resistor. This control }3 is likely to be very noisy and in addition it gives only rough control, together with detuning effects, all of which makes it unsatis- factory for high efficiency. In Fig. 4 is shown a method which, although it has negligible detuning effects, is not very satisfactory because of its critical and not always 5V noiseless operation. Figure 3 illustrates what + 90- t80 is probably the most generally used form IIIIIII of control. 50,000 v.+ If carefully designed it will It OHMS usually prove a FIG.9 very quiet and smooth form (POT OPTIONAL) of control. Noisy variable condensers cause trouble frequently and in addition there is 5000 TO a pronounced detuning effect. 50,000 OHMS Figures 6 and 7 illustrate two entirely different methods of control. The exponents ... 27- of the scheme shown in Fig. 6 claim that it is free from detuning effects, is very quiet in operation and gives a very smooth control of regeneration. The method of control illustrated in Fig. 7 also gives very satisfactory results, according to reports. We have not yet experimented with it, however, so we are not able to give definite statements as to its merits, but it is certainly FIG 10 - worth a trial. ' ' 'e+- Recently quite a number of set builders 48 RADIO-CRA FT for OCTOBER, 1942 Qa9innat5 naáit, a idavieioa

From the first SUPREME instrument. AO)-Mr .01-MF. OR LARGER and through the fourteen years since, the acceptance. loyalty and coopera- 5 THANKS S-- tion of servicemen everywhere are largely responsible for the excellence IINmIII R of SUPREME instruments today -and : our ability to produce them in quan- 0 TO YOU, tity for our armed forces. If you could not get the new equipment you FlG.lt -04- no 13 wanted this year. just remember that MISTER it is now doing duty for us in some spot on the globe and l00.000 0NMS represents part of your OIIr,.ARGER contribution to Victory. r.02-MF Bet 00000f--OFRI. p SERVICEMAN Q100000fi1_o Many Jobb.rt ,r,!! burr er_ SUPREME Instruments in J SEC Stock. Tell as the instru- SUPREME C10 14 ment you want. We'll do INSTRUMCNTSCORP. Our best to get it for you. MISSISSIPPI, U. S. A. F16.12 - t-ioZ MtG GREENWOOD, have advocated the use of screen -grid and ucnin ju,t beture the receiver goes into WHY GROPE? RF. pentodes in the detector stage. These oscillation. As the period just before oscil- tubes, when properly used, give much lation is the most sensitive of operation, stronger signals than triodes and offer much threshold howl effectively ruins a receiver's You Can Get That more efficient methods of controlling re- efficiency. The reasons for threshold howl generation. All of the methods of control are not very well understood, but there are discussed under three -element tubes may be several methods of eliminating it. Figures BETTER, used with these tubes and will give much Io and 11 illustrate methods of curing this stronger signals. There is a much better condition when a transformer is used for RADIO JOB system of control for these tubes, by vary- coupling to the audio amplifier. Both of ing the potential applied to the screen -grid. these methods result in reduction of volume, -insure your present position with the This method gives very fine control with but they are necessary if the receiver is to help of CREI home study training in none of the objectionable features of the function properly. Practical Radio Engineering! methods of control described above. Figure If resistance or impedance coupling is shows how the screen voltage is varied system, Don't play "blind man's buff" with your futureI 8 used between detector and audio Take advantage of today's opportunities to in- by a potentiometer. A variable -mu tube used threshold 1towol is not present. This is the crease your technical ability not only to as detector in this circuit will give even bet- most satisfactory method, as the systems meet the demande of your present job, but to better There are good tech- ter control than an ordinary screen -grid or in 10 and 11 affect the rise to a still job. illustrated Figs. nical positions for experienced. trained radio- pentode tube. audio response. Figure 12 shows a resistance men in manufacturing, broadcasting, aviation The use of the R.F. pentode as detector coupling system. It is necessary to apply and governmental fields. CREI home Study courses can help you acquire the necessary tech- has only recently been considered, because at least 180 volts to the plate of the detector, nical knowledge to hold on to that new job you of lack of R.F. pentodes in the open market. due to the drop in the resistance. Figure 13 now have -and to quality for the better, higher- This tube should prove even more efficient is a form of impedance coupling. This is the paying positions that await you. Act now. as a detector than the screen -grid tube, best method for all- around use, as the volt- WRITE FOR FACTS TODAY! especially when provision is made for vary- age drop through the plate impedance is Our free booklet and personal ing the potential on the suppressor grid as very slight and a fairly low plate voltage recommendations may hold the be applied to the detector. When using answer to your success. In your well as. on the screen grid. The suppressor may inquiry, please state briefly grid potential should be adjustable so that a screen -grid or pentode tube as detector, your background of experience. positive as well as negative potential may it is almost imperative to use the impedance education and present position. be applied. This control need only be ad- method, duc to the high plate impedance justed when first operating a receiver, as of these tubes. By connecting the primary CAPITOL RADIO once the best point is found there is no and secondary of an A.F. transformer in Engineering Institute further need of adjustment unless tubes or series as shown in Fig. 14, a satisfactory Dept. RC-11, 1224 16th Street, N. W., Walmiene, D.C. the circuit is changed. We would like to plate impedance may he secured. It may be hear front experimenters as to what results necessary to shunt this impedance with a they have had using these new tubes. (See - resistance in series with condenser, as LEARN RADIO Fig 9.) shown by the dotted lines in Fig. 13. This TELEVISION One of the most troublesome things in a is to cut the high note response. It is also regenerative detector system is threshold possible to use a high impedance choke coil 600 LICENSED graduates placed in howl-a strong audio frequency howl which in place of the audio transformer. past 7 years in shipping, broadcasting, aviation, police, etc.; we also teach radio servicing and repairing; new beginners' TRANSFORMERLESS POWER cuit. Constants given in the diagram are class forming Sept. 8th; 60 -page catalog those employed by the editors in an experi- free; oldest, largest and best equipped. SUPPLIES mental set -up. An output voltage -load current curve for this circuit is given in Fig- MASS. RADIO SCHOOL from page 25) Est. 1899 (Continued ure 6. 18 BOYLSTON ST., BOSTON, MASS., while that across G is very nearly equal to the line peak. HALLICRAFTERS AWARDED RADIO TECHNOLOGY These discharge in series, ü'tAn1 two-year two capacitors ARMY AND NAVY "E" f t high standardalembracingintensive all phases affording combined voltage drops. of 'I Radio and Television. Practical training their with Modern equipment. Also shorter spe- Thus, the voltage presented to the load re- The Hallicrafters Company was notified cialised rouses In Commercial Radio Operat- last month by Under Secretary of War ing. Radio and Television Servicing, and sistance R is the sum of the voltages appear- Aviation Communications. For Free estates ing across C, and Ce- approximately three Robert P. Patterson that it has been award- -rite Dept. ILC -42. times the line peak. ed the Army and Navy "E" Banner, accord- RCA INSTITUTES, Inc. In the tripler circuits, the ripple fre- ing to an announcement by W. J. Halligan, A Radin Corporation of America Service quency corresponds to that of the line be- president of Hallicrafters. 75 VARI'K STREET - NEW YORK cause of the asymmetry of the arrangement. The company was complimented in Mr. Filtering procedure is therefore the same as Patterson's notification letter for the "high RADIO COURSES for the simple half -wave transformerless achievement attained in the production of war equipment. The high and practical Start Sept.. Day and Evening Classes circuit. RADIO OPERATING RADIO In the second voltage tripler circuit, patriotism of the men and women of The AMATEUR CODE RADIO SERV- shown in Figure 5, the four diodes of the Hallicrafters Company is inspiring. Their ICING RADIO TECHNICIANS two tubes are connected in a full -wave record will be difficult to surpass, yet the New York Y.M.C. A. Schools doubler- full -wave rectifier circuit in a man- Army and Navy have confidence that it was W. 64th Street New York City %j ner somewhat similar to the foregoing dr- made only to be broken." i 49 RADIO -CRAFT for OCTOBER , 1942 %2adic g 7alQVieioa 'Vadits knáa

NEUTRALIZING CONDENSER the holes so that the coil form is held intact rAMPLIFIERS Kink number one is a lhuncmadc neu- to the plug. Then wind your coil and solder tralizing condenser for small tubes such as the ends of the wires to the prongs of the AND PARTS 6L6, 2AS, etc. Take a piece of copper plug. In the case of Eveready plugs, the tubing of 3116" size as one plate and use a prongs are hollowed. Since GUARANTEED IN ABSOLUTE PERFECT there are three piece of well insulated wire for the other prongs, the terminal leading to the antenna MECHANICAL AND ELECTRICAL CONDI- plate. The copper tutte is about 4 inches can be left hanging as in Fig. 3. ALTHOUGH SLIGHTLY USED. TION, long, and the capacity can be varied by The socket may be used like an ordinary Photo shows30 watt pushing the wire into the tube or pulling socket to suit the purpose. Cut off the metal amps. # 104A it out. strips as in Fig. 5, and mount on the chassis. The terminal of the socket would serve as the terminals for the corresponding N2.1 TO BOTTOM OF WELL INSULATED WIRE leads TNAT FITS CLOSELY as in Fig. 4-A. Locilio. PLATE COIL IN TUBE B.F.O. CODE -PRACTICE KINK COPPER TUBE It is common practice to turn on the b.f.o. TO GRID of a receiver so that it makes OF TUBE a whistle with a station, connect a key in series with the STANDOFF INSULA rap earphones, and practice code. Very frequently, however, this is not satisfactory COPPER TUBE as All amp?. shipped there is so much capacity between key com- Ready to operate ponents and earphone wires that the station * 102A -12 WATT PUSH -PULL 2A3 AMPLIFIER can be heard fairly well even with the key Frequency response plue or minus 2DR. from 30 15.000 to up. This of course makes code practice diffi- CPR. bass and treble boat. Inputs for phono Pick-up or radio tuner. Output impedance 8 or 16 cult as the keying is liard to read. ohms to P.M. or Electro-Dynamic speakers. supplies With the field eurent for one or tien 2500 ohm apesker fields circuit illustrated the phones An excellent amplifier for FM or re- are shorted out when cording. the key is up so that $18.45 there is no sound in the phones until the 1102-12 WATT PUSH -PULL 2A3 AMPLIFIER key is pressed down, unshorting the phones. without Schematic furnished to I.tal otage.. change ofn ver to these 8* STANDOFF To be used with one or two 2500 ohm dynamic speak INSULATORS ers 16 ohm voire roil. May be changed over to u. Phones P.M. speakers. Input for magnetic pickup. Variable tone control. Kink number two is the use of two coil Phone PPlug Shipping Weight 25 lb.. for either of above mounts for one stage in a Xmitter. The idea came to me when I found that I could ' 5103A -20 WATT PUSH -PULL 6L6 AMPLIFIER get much more output on 10 meters with a Input for one crystal or dynamic 0 microphone. Input self -supporting for one crystal or magnetic phono pick -up. Full range copper tube coil, than with tone control. Frequency response 30 to 10.000 a coil wound on a coil form of the plug CPS. Output Impedance 8 or 16 ohms to PSI or Electric -Dynamic speakers. supplies field in variety. I use a T -40 as the final on 10 fcurrent for one or two 2500 ohms sp.aker Re/ay norma//y I . elds. $15.95 meters but when operating on the other bands the T-40 stage becomes Closed *103 -20 WATT PUSH -PULL 6L6 AMPLIFIER a buffer amp. Same bove. but without saga off crystal pica and crystal microphone. Schematic -up and feeds a 203A final. As the 203A is link III furnished to ñange unit over to these stage.. coupled to the -40, To be used with one or two 2500 ohm dynamic T a coil of the plug -in speakers 18 ohm voice coil. May be changed over to variety was found to be the best suited use P.M. speakers. Input for magnetic to The keying is very clean therefore and is pickup. Variable tone control. .$9.85 the case. I wired in a coil socket for the easily readable, being sharp. Be sure Shipping Weight 24 very lbs. for either of above plug -in coils in parallel with the standoff you have the right type of relay for this insulators, which have large jacks for the circuit, one that is normally closed.- Frank- :104A-303O WATT PUSH-PULL 01.6 AMPLIFIER copper tube coil.- George Levensalor, lin Williams, W6ULF. Glendale, Calif. Input for two cryst. dynamic or velocity microphones individually controlled. Input for crystal or high WJDPJ. impedance phono pick -up. Full range tone control. Frequency response 30 to 10.000 CPS. Output Im- TRACKING DOWN GRID pedance 2.8.3.2.4.5.3.8 and IB ohms to P.M. or 15ertro- Dynamic speakers. supplies field current PLUG -IN COIL EMISSION for aie or two 2500 $21.45 ohm speaker fields. Here is an economy for radio beginners (Continued from page 14) who have PUSH-PULL AMPLIFIER bought plenty of 45 volt "B" bat- ae abov The presence a6e bu t wit uMf8 o crystalta lSmes teries of the plug -in type. I use of grid emission is usually and crystal. dynamic or Velocity Microphone. Schematic a plug and furnished free to change unit over to these n indicated by distortion, increase in hum, Ilas input for magnetic pickup. volume control. and excessive plate current. It is some- variable tone control. Supplies field current to one or two 2500 ohm dynamic speakers. output titi times difficult to detect the presence of podance 2.6, 3.2, 4, 5.3. 8, and 16 ohms. Full T-To Anf wells output. 3u excessive plate current unless the rilete( is $12.05 permanently in the circuit during tests, as Co1 CvI the switching -off of the tube may allow it Shipping Weight 211 lbs. for either of above to cool sufficiently to restore normal opera-

AU Amplifiers Less Tubes & Speakers. Fit , tion. For this same reason grid emission cannot be detected on tube checkers. JENSEN IO INCH In performing tests to determine grid ELECTRODYNAMIC emission the receiver should be thoroughly heated, not by applying excessive line volt- SPEAKER age which might damage condensers and 2500 OHM F.y3 other parts, but by placing a box over the FIELD F;g 2 chassis so that ventilation is cut off. li OHM VOICE -COIL A microameter, having a 0 -10 scale, connected in series with the grid return circuit EACH $2.95 Cut Cu, I SocFc/ y is the most practical method of measure- Shipping Weight 7 lbs. Charra Chows ment. However, this instrument is expen- Pi 5 4 sive and delicate and is not easily obtainable. Fi A milliammeter, which we all have, per- ORDERS SHIPPED SAME DAY AS RECEIVED. Socket All goods are sent Express collect if no money for manently connected in the plate circuit will Parcel Post is included In rem.ttange. Customers in show a rise in is Foreign countries are requested to remit in U. S. current after the receiver Currency or International Money Orders and Include sufficiently heated if grid emission is present. enough money to ship a socket taken from a useless 45 volt "B" goods prepaid. Order from this ad. Practical cures for this ailment may be 251/4 deposit required on all C.O.D. orders. battery. From the plug, I cut off the clips (Fig. 1) leaving only the hook straight- effected by a diode gate, a resistor on series with the filament to slightly reduce the fila- PEERLESS RADIO ened up as in Fig. 2. Now take a cardboard ment voltage, proper ventilation, automatic AND SOUND CORP. tube of one inch diameter and make three bias. Above all, make sure that the values small holes near the base to suit 11 So. Desplaines St., Dept. 1042 CHICAGO, ILL. the loca- of voltages and grid resistors are within tion of the hooks. Bend the hooks through the ratings of the tubes. -Sylvania News 50 H40,10-çR'ttFT .,or OCT9Ai.. { mew "Type oj Set vice A't'anual/ RADIO CIRCUIT MANUAL -1941 The Only EDITED Manual Ever Published !

DIRECTORY OF RECEIVERS MANUFAC- TURED IN 1940 AND UP TO JUNE, 1941

MORE INFORMATION IN HALF THE NUMBER OF PAGES

The value of a service manual is measured not by the number of pages but by the amount of useful information. Thus. In only 736 pages this Radio Circuit Manual covers over 200 receiver models MORE than does any other c mpetitive manual in twice the number of pages.

HOW DID o WE DO IT7 .

. . . By increasing the size of our page; by discarding non-essential data and editing the balance; by listing only those receivers which the Service Engineer will definitely have to repair (no c munications or export receivers, no shortwave sets or amplifiers, no electronic devices, etc.); by many months of hard work based on a definite plan of procedure and a clear understanding of the actual requirements of the Service Engi- neer. There is no "dead weight'' information to add bulk to this Manual. Every word counts. Every minute of reading timo Is well spent. OUTSTANDING FEATURES Contains data on more than 1800 receiver models! -more than any other radio service manual. Only 738 pages1 Cé less than half tho bulk of any other manual and more than I/3 lighter. All information is EDITEDI -all non- essential data deleted and the balance checked and correlated with the schematics and sketches. on one 40°,'larger page permits listing of all information page. (A few excepted.) I.F. peaks afor all superhet aro boldly displayed in black Locos; -none missing, all accurate. No space wasted on communications and export receivers. amplifiers. electronic musical instruments, etc. -a 100 °'o Servloe Engi- neer's Manual.

A "CUSTOM -TAILORED" MANUAL FOR SERVICE ENGINEERS THE OLD TYPE MANUALS -Bulky. handle. apace consults- E^ heavy. hard to Here. at last, is a Servitor Manual deliberately PLANNED for the Strome Ira. less USEFUL a ate despite greater of service data, an of pages. Engineer. Instead of a mere hodge-podge collection manuals have been in the past, this RADIO CIRCUIT MANUAL is an orderly compilation of essential radio diagrams and service information, carefully edited and uniformly presented for the maximum convenience of the busy Service Engineer. All time -consuming, non -essential data have been weeded out, and the remaining information. vitally important to the rapid and efficient servicing of modern radio receivers, has been laid out in a logical, easy -reading style which cuts time from the day's work. Because of features which are self- evident upon first observation. it has this and other model on been possible to list all information pertaining to a given single page. 1800 receiver In 736 pages this Manual presents essential service data on over models; --more than any other existing service manual on the market! ONLY ONE MANUAL PER YEAR! The new technique used in compiling this RADIO CIRCUIT MANUAL - com- OUR NEW MANUAL -Lighter, 1941 makes it possible to include in a single book all the new receiver part, easy to handle. takes half as which the radio industry can produce in a single year. This factor much room on the shelf, more USEFUL models Engineers. Informat.on despite fewer number of alone represents an important saving to all Service Dago,. MANUAL MANUALS NOW READY! ORDER YOUR A PERMANENT r IMMEDIATELY -NOW! INSTITUTION RADCRAFT PUBLICATIONS, INC.. New York, N. Y. Get ymailingur copy direct from us by filling This Radio Circuit antuay 9 <11.r^ NOT a one- 25 West Broadway, convenient out ONLY time M be a for the the following Gentlemen: Enclosed find nay remittance U 510.00. loi, t your favorite çsE aYmralx194T. RADIO ectfront Manua4 t!.` which send me. POSTPAID, my copy of the distributor.

$$$$$$$$HALLICRAFTERS$$$$$$$$ GETTING STARTED IN RADIO $ $ (continued iron page 47) $ INDUCTION $ WANTED! One of the greatest discoveries in elec- $ tricity was the fact that a magnetic field in $ (notion will cause a movement of electrons $ which we know as an electric current. If $ we connect a coil of wire across an indicat- HALLICRAFTERS ing instrument (such as a galvanometer, H H which indicates the presence of current) and run a permanent magnet through the A RECEIVERS AND TRANSMITTERS! A end of the coil, the needle of the galva- L nometer will move, indicating the presence L of current in the coil. The needle of the me- L Do Your Part! If you have any modem apparatus, L ter will quickly return to the zero position don't put it away in moth balls for the duration. Put it when the magnet is at rest in the coil. Then I I if we draw it out again quickly, the galva- to work for VICTORY! nometer needle will again move, but this C time in the opposite direction. It will be Send a detailed description of your station to HARRISON found that the faster the magnet is moved, -day! Give age, condition and photographs (if avail- R the greater will be the deflection. A We pay Ií we substitute a piece of unmagnetised Ato will you immediate cash! Remember! A steel for the magnet there is no current in- Development dicated. The difference between the magnet F of new radio equipment is being rapidly and the steel is the presence of the magnetic T accelerated under the pressure of military requirements. T lines of force surrounding the former. This experiment shows that whenever a conduc- E All signs point to radically different gear when this war is E tor is placed in the presence of a moving over. Don't be magnetic field, a current is produced. This R an antique collector! R current is caused by induction. S You can buy Defense Bonds with the money! S $ $ CURRENT PRODUCES SIMILAR EFFECT A similar action can be obtained if the $ RADIO $ /magnetic field is produced by a current in- $ HARRISON stead of a permanent magnet. Suppose we 12 WEST BROADWAY - NEW YORK CITY wind two coils and place them end to end closely together, one coil being connected $ to the galvanometer and the other to the $ $ battery, with a switch to open the battery circuit. When we close the switch, the gal- $$$$$$$$HALLICRAFTERS$$$$$$$$ vanometer indicates a momentary current. Then open the switch again and the galvanometer needle shows another current, op- Complete two-way wireless loud speaking posite to the first. LAST CHANCE system. Perfect performance. Plug into any 110 volt house socket A.C. or D.C. Equipped If the insert a piece of soft iron through that you will have to buy with Call- Listen -Talk switch and volume the coils, the action is the same as before, control. but much stronger. This is the principle of No installation charges. Modulated carrier the tuning coils and transformers used in signal travels over the electric light lines. IDEAL FOR OFFICES. STORES. FACTO- radio reception. It will be noticed that we RIES, SCHOOLS. LIBRARIES, HOMES did not move the coil as we did the magnet. AND WHEREVER INTERCOMMUNICA- The magnetic field, building up in the coil TION IS DESIRED. EXCELLENT SPEECH CHARACTERISTICS. when we closed the switch, gave the necessary "moving" field to induce the current in Each unit is housed in beautiful 2 tone veneered cabinet with grilled speaker front. the second coil or the secondary, as it is called. This Coupon is worth 12.00 if mailed to us with order BEFORE Oct. 15/42. Name DIRECT AND ALTERNATING CURRENT Up to this time, we have limited our dis- Address , cussion to currents flowing in one direction . -J in a conductor. This type of current is Crosley known as direct current. It will be remem- C H AT TA B O X bered that when the magnet was plunged INTERCOMMUNICATION KORROL MFG. CO. into the coil and withdrawn, the current re- T M OF TWO UNITS FOR $24.75 350 GREENWICH ST. (DEPT. RC8) versed its direction when the magnet was LIST PRICE-159.50 A PAIR NEW YORK CITY withdrawn. To state this in another way, we ï can say that the direction of the current was alternating in one direction and then in the other. This type of current is known as an EVERYTHING If It's a CANNON -BALL alternating current. It Alternating currents are used extensive- IN RADIO is a ly in radio. In fact, the radio waves them- Sir Su iris. public address systems, amateur GOOD HEADSET selves are alternating currents which re- ments stersm kits and fluores-equip- verse very fast, in the neighborhood of cent lighting at lowest prices. For clarity of use Huge stocks, bought months ago tone 1,000,000 times per second or even more. Cannon - Ball ready for shipment the same sensitive Currents which have a frequency day your order is receivedeived The phones. Assure depend- (reverse Defense Program big their direction of flow) of less than 10,000 demands on our industry but be. able performance. Guar- cause of our advance buying we anteed to give absolute cycles (complete reversals) per second are prare able to fill your orders satisfaction. Write known as audio frequencies, and those over omptly and efficiently. Scientifically Built Headset Headquarters 10,000 cycles per second as radio frequencies. Heavy har g- for folder C -9 illustrat- BURSTEIN -APPLEBEE neta greatlyIn- It is suggested that the reader perform .e their em. ing complete line. COMPANY cleney. the various experiments in this discussion 1012 -14 MGR, KANSAS CITY, MO. C. F. CANNON COMPANY in order to fix the facts firmly in mind, as SPRINGWATER, N.Y. these principles are all directly applicable to the operation of radio apparatus. 52 RADIO -CRAFT for OCTOBER, 1942 SOUND

WIDE RANGE FILM RECORDING (Continued front page 33) ' Headquarters for quite expensive if the recording involved a symphony. One of the problems encountered by the Ozaphane developers was the distortion in HALLICRAFTERS EQUIPMENT loudspeakers. This fact, coupled to the difficulty of obtaining suitable microphones, caused them to decide on an upper range for commercial reproductions of 12,000 cycles. It will be noted from the sound - frequency characteristics chart that modern WE CAN ALL HELP WIN THIS WAR! electrically recorded discs for home phono- graphs are capable of going only to 5,000 WE ARE busy supplying our government with new and used commu- cycles. The fact that such recording are nications receivers and transmitters urgently needed. to 60 cycles assumed to be able to go down That is why we are paying highest cash prices for used communica- is of little value, because the lower fre- to avoid over - tions equipment. quencies must be attenuated us at once if you are will- cutting in the recording process. With Oza- You can help win this war by contacting phane, however, the lower limit is governed ing to convert your equipment into cash. principally by the reproducing amplifier and Remember -after the war, you will want speakers. a new receiver. And you can buy a new and At a private demonstration given recently COMPLETE STOCKS better receiver with what we will pay you. Ozaphane We still have large before a group of musicians, the stocks of receivers, 21/2 Write, telephone or telegraph us descrip- process was compared with a high -priced meter equipment, meters, tion of your used communications receivers phonograph radio combination. The reac- tubes, transformers, re- and transmitters of standard make; you will listened to this sistors, condensers, pan- tion of the persons who els, chassis, and radio be paid cash immediately without bother or demonstration was that some trickery was parts of all sorts. We sell red tape. resorted to-so great was the difference. and rent code teaching equipment. Your orders a 2335 Westwood Blvd., The photo-electric mechanism is no dif- and inquiries invited. We also have store at ferent from any similarly used equipment, West Los Angeles, Calif. except of course that the amplifier needs to have an exceptionally wide frequency response and must be relatively low in distor- W9ARA tion. This will be understood when it is Bob Henry, realized that any distortion generated in the HENRY RADIO SHOP amplifying process creates harmonics -generally second and third harmonics -and BUTLER, MISSOURI since these harmonic frequencies extend into RECEIVERS" the'higher range, they will alter the quality "WORLD'S LARGEST DISTRIBUTOR OF COMMUNICATIONS of the reproduced music by giving spurious , overtones. The use of negative feedback to reduce amplifier distortion will be necessary in the amplifiers for the new system. The recent developments in loudspeakers, brought about by the introduction of frequency modulation, would indicate that the two speaker systems -the woofer and tweeter-will be necessary, and it is hoped that speaker manufacturers will be able to lower the distortion of present designs or provide new designs which could be used for the new type cif htimr equipment. SOLVES EVERYDAY PROBLEMS-HELPS YOU GET IN TI AHEAD VERTICAL DEVICES FOR AIR RAID Now many times have you lost money because of mis- know how InnNst °ate. WARNINGS okr,eetly?guCangyouonÑrc lytaxeai ADJUSTABLE AlltenllÁ$ and all the other calculations you meet up with In your trom rage 38) daily life? For Defense and War installations (Continued AM14eavung trouble lif ing for pro- not up on mathematic.?ONeer -standard or special designs de- tions in the atmosphere. The amount of in Here Is the book that gives you good background aluminum and temperature, the mathematics: that takes all the irritation and anger, veloped in monel, moisture in the air, the out of It. You don't need to be seed of themac.. frills, us your requirements direction and velocity of the wind, the here' the subject explained without With- steel. Tell out useless computations. for Bulletin of standard presence of ascending or descending air cur- the forces: for hostile.. or write Herl the designs. rents, the existence or absence of stratified everyday matci problems in ea..to-undnd erst htechnicianswordsg math layers, all affect the transmission of sound understanding mane. Yes. le the key to simple of It' I home -study ire through the air. the man who's alert to the importance of r'~nathem.aira in 13" e /17 CI X / rocìlucfs It has been observed that under favorable the world today. atmospheric conditions a powerful signal DIV. CHISHOLMRYDER CO INC. Falls, N. Y. may be heard many miles. In fact, some of ELEMENTARY MATHEMATICS 1292 Highland Ave. Niagara on which the bureau is report- the devices EASY -SIMPLIFIED PRACTICAL ing have been heard for distances up to 8 - OPPORTVNlTy AD-LETS miles, yet under some of the urífavorable .CONTENTS OF BOOK. ta.etu.enbnt in stir rectlen emu 1s eqta a I. Arithmetic-Addition-Subtraction-Multi- for each Insertlou. Name. aadreee ant hound t :.::;',,.: conditions mentioned above they have not Sheet ion-Division. be included at the above rate. Cash should aceom- unie.. placed by been heard for one -quarter of a mile. On DeecimalsR-Pei ntagge-Inttatioo -a dnProportioncuon- pang all advertisements CHAPTER III. The Metric System. an accredited advertising annex. No advertisement account of these atmospheric vagaries it CHAPTER IV. How to Measure Surfaces and Capacity for less than ten words accepted. Ten percent dis- number of medium -sized iGeometrv). Involution -Roots and Eco- count as loues, twenty percent for te baues . would seem that a CHAPTER V. Powers and Objectionable or misleading advertisements not ac- signaling devices, spaced in some form of cuaPTER VI. Mathematics for the cepted. Advertisements for November, 1912, issue must Technical ONLY reach us not later than October Ill, 1942. a grid pattern, would give a more positive emome conversions-Graphs or ler -Use or Radio-Craft 2S W. S'way New York. N. Y. coverage than a few very large devices the Plottin -Loarithm. cu e nYathertutla 50c spaced relatively far apart. for AthegRaa of Technician. POSTPAID III. Commercial Calcula. lions -interest- Dinounta -shoe Cut RADIO SERVICEMEN AND EXPERIMENTERS SEND Arithmetic. for our giant radio catalogue. Save dollars. United Radio IX. Weighta and Measures -U.4 w Tables. TUBE DIVISION NAME CHAPTER Co.. II000PI Newark. N. J. Send Stampe. Cash or Money Order. OUTDATED MAGAZINES. CATALOG IOa CHANGED York. N. Y. Sand Haas Cicerone's, 902 First Ave.. New a w The Vacuum -Tube Division of the General adeeprnouwp«dispel.. t MEMORIZE CODE EASILY WITH COPYRIGHTED Electric Radio, Television and Electronics De- KolorKards. New, Practical, Complete- 81.00. Kolar - partment will henceforth be known as the Elec- Kards, Dept. RC. Bluffton. Ohio. Tube Division, according to a recent T EI:NNIFA\ USED CORRESPONDENCE+. COURSES AND 17CEI- tronic Free announcement by Dr. W. R. G. Raker, vice - 1917 S. State St.. RC -1042. Chicago, III. NICAL Baoka Bought. Sold, Rented, Catalog president in charge of the Department. a Educational Exchange, Renegar. Ala. RADIO -CRAFT for OCTOBER, 1942 53 SERVICING

WORLD -TIME CLOCK MAKING A VOLTMETER READ DELSCO The Only Clock for Universal Use WATTS FILTERSTAT Throughout the Entire World! (Continued from page 22) Eliminates radio disturbances caused by A REGULAR The transformer is now mounted on the motors, fans, refrigerators, lights, etc. CLOCK base of with A.M. and the metal cabinet, and with the Protects radio from line voltage surges. P.M. divided dial female receptacle, the meter and the rubber A REAL NOISE grommet mounted on the front panel, we FILTER A WORLD-TIME are ready to wire the unit. No trouble CLOCK should be encountered Manufactured By in making the con- instantly indicat nections if Fig. lb is followed. Ins time in all When all DELSON RADIO CO. 24 zones connections are completed the panel is fast- 2324 Broadway New York City ened to the cabinet and the meter is ready INTERNATIONAL for calibration. List Price $7.50 CLOCK Before we start to calibrate this watt- Write prices. with A.M. and for Very large discounts. P.M. 24 hour dial meter it will be necessary for us to construct a load line. See Fig. la. This load Pere is really the first new clock advancement In line consists of four light 200 years-three clocks in o a world-time lark. It sockets connected is rye It is years The Sky Pilot in parallel WORLD- ThMR CLOCK is with a short lead which has a 'Amazing hew "WALSCO" d. p. rly Imrt eslfans this male plug on chock offers great convenience-it is educationalw and the end of it. This load is at the same time Indicates world time differences. In simple to make, and upon completion, o few one you cana determine the correct time the STAPLE DRIVER London, Moscow, ky,, Buenos Aire.. male plug is inserted into the female Lllfax- anywhere. American de-it Is exceptionally re- n. end asy to operate. It carries guarantee of ninety days ceptacle of the wattmeter and the operation eebleedo , ' Fo, Md1.11 the time. material n Inn epled in c n b. .d p molding.-We ,r,tist c design, it is 140 of rl,ru.,ed brass- measures of calibrating the instrument 514- high by rrygal. begun. With men. r -ell,,ible -ill, e hem end ordinety .tepk,. Dr,. defile, 43/4" wide -and has convex even brick, mer Meg the wattmeter plugged into the A.C. screw c. Y, ne err .tom cc ty and Electric (for A.C. 110.120 volts, 60 cycles) $9.95 Add.'.hip, GI c epk..hick come in I colon. All Yew jobber a 25 -watt lamp into one of the light sockets. for demo.....Ao, and cetelogue 41.0 of .e WALSCO PRODUCTS Spring Modal $8.95 The wattmeter should now register a read- or write WALTER L. SCHOTT CO. . prepaid Remit by Check order; register letter If ing. With a fine pen point mark the dial face 5264 W. Pico Boulevard. Los Angeles, California you send GOLD SHIELD PRODUCTSits. at this point 25 watts. 350 Greenwich St. Dept. RC -10 New York City At any time in the future that we have an occasion to measure the wattage consumption of any electrical device that has PATENTS - TRADE MARKS a wattage consumption of 25 watts the Booklet concerning Inventions & Patents needle of the meter should come to a stop Form "Evidence of Conception" with at the point which you have just cali- Vol hare been successfully telling Inventions, instructions for use and 'Schedlde of patented and unpatented. since 1924. Write u Government brated and marked as 25 watts. If you hee s practical. useful Idea for sale. and Attorneys Fees" -Free CHARTERED INSTITUTE LANCASTER. ALLWINE & ROMMEL Now if we should screw another 25 watt Registered Patent Attorneys lamp into one of AMERICAN INVENTORS 436 Bowen Bldg. Washington. D. C. of the other sockets, making Dept. 109 Barrister Building. Washlnoton, D.C. a total of 50 watts, the meter will register a new reading and this new point on the dial can be marked as 50 watts. If we should add a 50 watt lamp to another socket get 1Z s ¿lash« Pty S'havet we would have a total of 100 watts being consumed and this new reading can be marked on the dial as 100 watts. By screw- ABSOLUTELY FREE! ing different sizes of lamps into the sockets various wattages can be obtained and marked on the dial. Undoubtedly you have recog- JUST THINK OF IT -you can get absolutely nized the fact now that you have marked FREE, the useful DRY ELECTRIC SHAVER the dial in accordance with known stand- which is shown ar the left. This ELECTRIC ards. In the future whenever you make a DRY SHAVER is sent to you by the publishers wattage with a one -year consumption test on any electrical subscription to RADIO -CRAFT. device you are in reality comparing the watt- Han Are the natured of The age consumption of that device with given ELECTRIC DRY SHAVER standards which you have marked on the Constructed of metal with attractive red bronze dial. When the wattmeter is completed I finish. Scientifically constructed to give a oerleetly suggest that you try it on clean shave. 5 -10ot rubber insulated cord and out your radio plug. Constructed to last for many years. sets, your soldering iron and any other electrical devices that you have on hand. Operates from 110 -volt, G0 -cycle A.C. elec. trie line. Carries a two -year manufacturer's Do not attempt to measure the wattage guarantee. A fine quality. self -sharpening toilet necessity. consumption of any device that has a larger wattage consumption than the full -scale Send your aubecrlptlon to RADIO-CRAFT reading of the wattmeter. for One Year (12 blares) and receive absolutely FREE one of these remarkable On completing this wattmeter you may Ifleetrle Dry Sharers. New subscribers find that the reading OPERATES ON are accepted or you may eilend your pres- you desired for full ent subscription another twelve mantle. scale reading is not at its correct location 110 -VOLT. 60 -CYCLE Marl your remittance of 92.00 (plus 25c on for shipping charges on Shaver) to the the dial. This can be remedied by juggling A.C. LINE publishers. (Canada and foreign $2.75.1 You will receive your the turns of the new winding, of the trans- DRY ELECTRIC SHAVER Im- former. If you wish to move your dial read- mediately by return mall. Vie Coupon below to enter your ings up scale remove one or two turns from suborn pt in n. the new winding. On the other hand if you desire to move your dial readings down RADIO -CRAFT scale, add one or two turns to the new wind- 25 W. B'way.. New York. N. Y. ing. When adding or subtracting turns to this new winding it is advisable to take a reading of a known standard after each RADIO-CRAFT, 25 W. BROADWAY, New York, N. Y. change and in this way you will be success- Gentlemen: Enclosed find my remittance of $2.00 for which enter nu' subscription to RADIO -CRAFT for one Year (12 Issues). Send me ful in getting your full -scale reading at Immediately FRER EI-E(TRIC DRY SHAVTID (Canada and foreign the correct location. $2.75). In U. 8. odd only 25o additional to cover shipping charges on WE SHIP ELECTRIC DRY Sharer. SHAVER THE SAME DAY D New Subscriber Extend Present Subscription YOURSUBSCRIPTION Name ORDER IS RECEIVED. COMPLETION DATE CHANGED Address F \I station, \V71S13 (South Bend Trib- une), South Bend, Ind., was granted modi- city State fication of its construction permit, extend- CLIP COUPON (Send remittance by check. money order or unused U.R. Postage Stomps Register letter If you send cash or stampe.I RC -1042 ing completion date for the period of 6 . AND MAIL I. J months from June 25. 54 RADIO -CRAFT for OCTOBER. 1942 Radio eonsttuetion Nadia lelevision

HOW TO MAKE A 23/4x4" RECEIVER WHILE THEY LAST Page 39) ( Continued from All of the attractive items listed here are brand new. ALL are in PERFECT WORKING ORDER. In many cases, the parts alone total more than the price we are asking. 100 °6 satisfaction guaranteed or your money using the lock nut to hold it in place. The refunded. ORDER FROM THIS PAGE. Use the convenient coupon below. Include sufficient extra remittance for pares) wires pass the Bakelite panel through two post charges, else order shipped express, collect. Any excess will be refunded. C.O.D. shipments require 20 °. Since the deposit. If full remittance accompanies order, deduct 2% discount. Send money order, certified check, new U. S. small holes drilled in the panel. stamps. No C.O.D. to foreign countries. condenser has no knob, I used an old binding post cap, soldering its metal center to ORDER TODAY LIMITED QUANTITIES PROMPT SHIPMENTS ASSURED the condenser shaft. HANDY WORKSHOP OUTFIT WESTERN ELECTRIC BREAST MIKE The case was assembled from scrap pieces light .weight Loon. - aircraft carrbone of Bakelite put together by small L angles It weighs only I lb. Mike come. with breast- fastened by screws. Some of these screws plate S- way swiveling adjustment had to be removed and replaced by rivets It ca be adjusted tothatany desired position. to permit the battery (No. 455 Eveready, 45 There are 2 woven traps; isle goes around the volts) to slide into the back of the case. other around chest. St ps cann be snapped on and off Although some form of aerial was re- by an ingenious ar- quired for reception, I found a ground con- rangement. beTada pee foe nhomek broad. unnecessary. Here i. a marvelous article dint to the hest of our d nection Id t such low price. This casting or private ro . knowledgeledge has never delivers the Precautions should be taken in wiring outfit must be seen r tobe appreciated. It dismounting brreeastplate. Blt can used microtubes. A bead to one side of the for dt10'`v ltn' A.C.` or D.0 ieMadespeediiginally for dicta- as desk the phone chines by Gramophone Co. Motor cnd lt with - other font rd hard rubber tube's terminals should be used as a guide !. reconditioned and in excellent condition: h plut. Finished in sherardised are Special control permits plate, non- for determining the numbering of the wires. various sup to 3000prp uses px 3h/ table. Man, overall. THIS IS A BRAND NEW nearest the bead is the No. 1 Included in the outfit are the following Items, as MIRE. IT HAS NEVER The wire d BFFN SOLD AT SUCH A Illustrated: 1 excellent chuck which takes drills o LOW PRICE BEFORE. ORIG- terminal, as can be seen from the illustra- other tools -chuck In easily screwed motor shaft: standard emery wheel. diameter: One steel rotary INAL LIST PRICE. 815.00. tion, which in addition shows the actual 4 diameter: wire scratch brush. 4, diameter; Shipping weight. 2 ins. Mandard cloth buffer, 3e diameter. Total Wt. 9 ms. ITEM NO. tSa 00 size of the microtube when compared to an YOUR PRICE . `r ITEM NO. 149 $1 average small -sized paper clip. Complete outfit, Including motor. $5.45 Two L brackets fastened to the sides of YOUR PRICE METAL CUTTING SAW case serve as "stops" to hold the B Hero Is an Ideal metal-cutting saw the VARIABLE SPEED UNIVERSAL MOTOR made of fine tool steel specially designed battery in place. The battery has snap -on FON 110 VOLTS, A.C. OR O.C. to cut metal. Teeth are set at a special terminals and the wires are electrically Made for Dictaphone machines by American Gramophone double angle for metal -cutting work. Saw Co. )d,/sa but In fa lient t. specially hardened for long and ex- connected to the L brackets. Thus the o dition. Special lever control permits variable speeds tended use; measures 3%. diameter; front panel can easily be removed by up tO l/ center hole Is %- aqua,.; thiclnus shaft extends 42/1000 (42 mils.) 3/94 -. loosening two 6-32 1 -inch long screws, aides of 'rMeasÑ Try, 31/4- diam. overall. NO. 151 93/4 ITEM which in addition disconnect the B battery Shp. Wt. me. YOUR PRICE 50c for replacement. ". . °a "... $2.45 The back cover is a thin piece of Bake- POWER ADJUSTABLE RHEOSTAT Here excellent lite cut to fit snugly so it will snap into WESTON MODEL 562 used especially place. A.C. -D.C. A M M ET E to regulate speeds of Designed by Weston for the East- r' Handy Workshop out. ma Co. It a preciion St. This rheostat can be bilt magn.Oie..ane type ammeter used in connection with which. with suitable shunts. can be motors up to h.p. used milliameter too. It le 1/20 3, in a diameter and designed for mounting. Bakelite bane n.l rnswoud on prceiwire-orcelan cover. Shit. 2 insulation. bnetlack- enameled Wt l steel easing is perforat ed for ventilation. Ad- LOW CAPACITANCE AC POWER lbs Instable handle regulates speed of motor easily and ITEM NO. 35 $1.25 smoothly. Size 5.x23/4. overall. Ship. Wt. 2 lbs. YOUR PRICE P ITUM SUPPLIES 14. .1" $1.20 (Continued from page 19) POWERFUL ALL -PURPOSE INDUCTION MOTOR IDEAL FOR EXPERIMENTERS -101 USES AMAZING BLACK LIGHT!! Powerful 230 -Watt Ultra.Vlalet modulation hum. Specific converter and Sturdily constructed to precision Source standard., thin self - starting The best and most prac- 1 -F circuit design intended to reduce modu- shaded pole A.C. Induction tical source of aura - foist to is powerful enough for a light for general experi- lation hum may be carried out provide laaorrge variety of uses. Some of mental and entertainment tolerable hum levels with these low voltage [bare Automatic Timing Lakes all fluorescent Devices, Current Interrupters, substances brilliantly loon - systems. Economy of copper and steel will Electric Fans. Electric Chimes. Ileactnt. No transformers of result with the use of an auto transformer Window Displays. Photocell Con. any kind needed. Fits any Oral Devices. Electric Vibrators. standard lamp socket. Made instead of the primary coupled type pro- Small Grinders. Buffers and with special filter Klass per- Polishers. Miniature Pumps. mitting o n l y ultra -violet viding the two A.C. plate voltages are Mechanical Models, Sirens. and rays to come through. Brings balanced in phase. Other applications. out beautiful opalescent hue/ Consumes about 15 watts of in various types of iota, power d has speed of 3.000 dale. Swell for uateur parr I..s. etc.. e to ob- CONCLUSIONS r.p.m. aWhen Seared dawn, this 1,1.5s sturdy unit will conshuttly oper- tain unique lighting effects. Bulb only. Shp. The utility of multi - sectioned filters in loaded ate an 18 -Inch turntable ITEM NO. 07 $2.00 minimizing total capacitance necessary for with 200 lbs. dead weight- THAT'S POWER! YOUR PRICE t. Dimensions. 3- high by 2- wide by 131- deep; has 4 acceptable hum levels has been demon- convenient mounting studs; shaft is Toe long by 3 /188 WATTHOUR METER oil- retatning prove diameter, and runs In eeU- aligning bear- and strated. This procedure should Designed 110-20 50 -60 cycles, A C. only. Completely overhauled for wit,. o mmediate economical in materials at the possible ex- ITEM NO. 147 regular YOUR PRICE $1.45 volt. 60 eyrie 2.Wi pense of labor and manufacturing costs. trcuit. Servicemen use It in their show to - An A.C. receiver with pentode output current consumption Of sets. 100 POWER TELESCOPE KIT Irons. etc. 1, 1 tube may be filtered with (say) 2 and costa do . dimted Make GaLENS4 thecor' parts alone would itf of paper capacitors without the use of Now y ou can tilt ill O brine the price. The lab - trainercoOuld be filter choke or large field. If elec- to a loeeup view of the worlds gear a speaker Bee the rin:;! oratteneed In stare. chines f various kinds. trolytics of small capacitance are developed around Saturn. Ont n dais ,.. Simple to install: 2 wires gs diam.. f wires the moon! Kit gth. the to meet the material shortage now becoming au.'. then Sturdily fool focal length. ground to metal acute, then comparable capacitance values polished objective 1.1,1 and Size, 8Lÿ, nigh. complete full strum .n 50: and lait:. Gen. are likely to prove permissible. Complete kit Ilh full lnstructlone. Electric. Shp. Wt h 14 Ibs. ITEM NO. 123 ITEM NO. 33 Paper capacitors or extremely low-capaci- PRICE $1.95 YOUR PRICE $4.95 tance electro'.ytics do not appear feasible for A.C. /D.C. operation. Small A.C. re- HUDSON SPECIALTIES CO., 40 West Broadway, N.Y.C. ceivers of this size may be developed using IT'S EASY TO ORDER -CLIP COUPON -MAIL NOW ORDER FROM THIS PAGE. A.C. /D.C. connection of heaters, but a low - voltage transformer to permit full -wave HUDSON SPECIALTIES CO., 40 West Broadway, Dept. RC-1042, New York, N. Y. D.C. voltage of 3 (laded* rectification and satisfactory T here circled below the numbers of the Items I'm ordering. Sfy full remittance output. This type of receiver has small econ- shipping charges; is eslelosed. OR my deposit of 5 is enclosed (20% required), ship order C.O.D. for balance. N. C.O.D. omy over the described higher -voltage type order for less than 32.00. (New D. 8. stamps. check or money order accepted.) and should find utility only in the event Circle Item No. wanted: II, 33, 35. 07, 123, 147, 149, 151, 152. 159 electrolytics for A.C. /D.C. use are completely curtailed. In the event of partial cur- Name Address tailment, voltage doubling circuits give City State promise of replacing A.C. /D.C. circuits. Send remittance by check, stamp. or money order: register letter if you send ash or stamps. -R. C. A. Review. RADIO -CRAFT for OCTOBER. 1942 55 SOUND

FACTORS CONTRIBUTING the center of the disc is very apparent. TO GOOD RECORDING The rise of the high frequencies due to resonant conditions at the higher groove TECHNICAL (Continued front page 29) velocities may also be seen. Superior performance has been obtained walls compress, permitting the stylus tip in specially to "short built reproducers. Such units cut" around the peaks of modula- have been classified as BULLETINS tion, particularly at the inner diameters laboratory models. of In general, they are extremely light in lacquer discs. In the case of pressings, weight which and are sufficiently delicate to cause Technical bulletins give reliable information in are a harder medium, the effect is their use in the not so pronounced commercial transcription easy -to-follow form, and save valuable time and, consequently, the field to be somewhat hazardous. With the otherwise spent in laborious reading of numerous reproduction of more high, frequencies is incorporation apparent. of a little more ruggedness books. Every subject is treated briefly and con- However, with the harder press- in the construction of these laboratory -type cisely. yet completely. No complicated math- ing, appreciable driving forces are still reproducers, involved and after and with the proper educa- ematics, chemistry, electricity, or theory. Each a certain number of tion of the user, it is reasonable to believe bulletin written playings the high -frequency is in simple language. peaks are that additional advances will take place in worn off, with resultant loss of frequency reproducer range the field in the near future. PRICE $1.00 EACH POSTPAID and an increase in distortion. Figure 6 -b shows This loss the translation losses ORDER of high frequencies is not a encountered in a fairly rugged laboratory BY NUMBER constant throughout the disc. The outer circumference model reproducer. It is seen to be an im- of a disc is traveling at a provement over previous ELECTRICAL DESIGN & CONSTRUCTION greater relative linear the curve. velocity than is the Figure 7 shows a family of character- D- 111 -DESIGNING AND BUILDING TRANSFORM - innermost recorded groove. This means ERS.- Simple, nonmathematical methods for designing istics obtained at various disc diameters. transformers of all kind.. Also special transformer. such that for a given frequency and amplitude, as are It conveys essentially the used for ultraviolet lamps, Neon tubes, etc. the physical wavelength of same informa- the engraved tion given in Figure 6 -b, but in a more O .112- DESIGNING ELECTRO- MAGNETS. -The sub pattern is longer and, consequently, better useful form. lent of electromagnet design is so clearly explained that defined than that of the innermost anyone can design and build magnets for practically engrav- The improvement in reproducers lies in every purpose. Complete, practical data covering both ing. The recording and reproducing and D.C. styli the hands A.C. magnets. have finite dimensions, of the manufacturers and also so that because of is contingent upon the demands imposed 13-I13-HOW TO DESIGN SOLENOIDS AND PLUN- the finite size and the use of the burnished GER MAGNETS. -Anyone who to interested in solenoids by the field. The user can contribute his Of edge on the recording plunger magnets cannot afford to be without this non - stylus mentioned part at the moment by insisting mathemetical, simple and practical information. previously, a deterioration of upon using the wave the best the market has to offer. In any O -101 shape takes place toward -USING NICHROME RESISTANCE WIRE.- the central por- event, if high fidelity is demanded, Explains how to repair electrlo Sal Irma. toasters. rheo- tion of the disc. The loss of high frequen- there stat., resistors and other electric heating devices. Simpli- is no excuse in transcription work for the fied methods of figuring lengths and sixes of wire for cies thus incurred is generally referred to any use of the heavy reproducer job. as "translation loss." with its mas- Strangely enough, sive steel stylus, which was in vogue only DI00- REWINDING ELECTRIC MOTORS.-Complete there is an opposite effect which occurs un- a few years ago. Information. diagrams. sketchs, tables. etc.- to enable der any shop man. mechanic, electrician. experimenter. etc.. some conditions; that is, the high -fre- to rewind A.C. and D.C. motors and generators of all quency response tends types. to rise with increase CONCLUSION in frequency on reproduction over that The mention of other than a D- 144-A. C. CURRENT CONTROLLED WITH EASILY which was recorded. This effect is encoun- very few MADE CHOKE COILS. -How to dealen and construct specific dimensions has been purposely How tered at the higher groove chop coils. to determine Sae and amount of wire velocities and avoided in this paper. This is required, how to And the core eta.. Full details on is especially pronounced at the outer di- to avoid wembly and coil winding. . possible ameters of a 78 confusion, since it is to be expected rpm recording. The reason that the results of the 0.148- DESIGNING AND USING ELECTRIC RELAYS. for this is that the vibratory system of the standards commit- -Simple practical instructions for designing, building. tees will be published in the near future. and using A.C. and D.C. relaya; also thermo- eleetrle reproducer and the material in which it relays. Includes The use practical relay control systems for motors is working set up a resonant of standardized recording and and machinery. condition. In reproducing techniques by certain organi- the case of relatively soft lacquer, the res- zations D127 -SMALL ELECTRIC LIGHT PLANTS. DESIGN onant frequency may well has provided excellent operating AND CONSTRUCTION. Tells how to design and build appear within experience to help in the establishment small electric light plants for cottages. camp or country the working range of the system, while of homes at small cost. Covers construction of a 110 -volt what is hoped will be the use of the same system to light six 30.watt lamps. how to build a with the harder pressings, it may appear 8 -volt system using an auto -generator, with or without standards by all. The use of the same battery, beyond the pass band of the system, pro- a and how to convert a Ford model T' gen- standards and the employment of good en- erator to 110 -volt. A.C, generator. ducing the same effects, but to a lesser de- gineering practice gree within the working frequency range. will permit a coordina- 13- 134 -ELECTRICAL EXPERIMENTS WITH SIMPLE tion between the recording and reproduc- MATERIALS,-How anyone without previous knowledge Figure 6 -a shows translation of electricity can perform harmless. Interesting, and curves for tion of the records with resultant improved educational experiments with simple. inexpensive ma- a typical good reproducer and a lacquer terials. performance. disc. The loss of high frequencies toward -R.C.A. Review D- 131 -MODEL MAKERS 6 INVENTORS GUIDE TO REMOTECONTROL SWITCHIND,- Controlling electrical devices, train morels, equipment of all types at dis- The books listed below have never been sold by us before. The tance by means of a telephone dial. value of each book Is 50e. They are exactly the same as RADIO d TELEVISION'S 50e blue books which have been on the market D -137- ELECTRICAL METERS EASILY BUILT. -In- SPECIAL for years. formation that will enable students to build experimental For a short time only we are selling these at a speelel reduce electrical meters to n alternating or direct cur- price of only 75e for the 3 books. rent.. Including meteru, voltmeters and wattmeters All of the books contain merous photographic Illustre- sufficiently accurate r for experimental purposes (ions and diagrams and shave stiff flexible cover.

Each Bulletin consists of a set of large sheets, assembled In one packet- sire 9x l4' -'; weight lb. Numerous illustrations, diagrams, charts to g ßp00K supplement text. S'Q.w' is "' transmtt¿s Ì f CF INIE1áX 1817 S. STATE ST. (DEPT. 1042) CHICAGO, ILL, r DEPT. 1042 TECHNIFAX 1917 So. State- Chicano, III. Enclosed rind $ for which please send me postpaid the following Technical Bulletins: r RADIO A TELEVISION Nee. 25 W. Broadway. New York, N. Y. Gentlemen: Incised you will find remittance for 75c Icaah. new 11 S. stamps or money order accepted) for which please send me at once your 3 books Name ABC OF TELEVISION SHORT WAVE GUIDE SHORT WAVE RADIO QUIZ BOOK Street and Number Name Address City and State City State RC -10.43 a. ..1 56 RADIO -CRAFT for OCTOBER, 1942 RADIO INSTRUCTION

FLIGHT RADIO SCHOOL TRAINS ENLISTED MEN "THE !SERVICEMEN! (Continued from page 26) r 'Get Handy New In another room is a Pan -American student- employee (in uniform) operating a INDUCTANCE RADIO LABORATORY Vibroplex-a semi -automatic transmitting key. He is hooked up on a circuit with GENERAL G CEMENT similar operators and they are exchanging AUTHORITY" ' messages. Other students can be seen tran- R, D10 CHEMICAL LA8ORATORY scribing actual airline traffic on their "mills." By EDWARD M. SHIEPE, B.S., M.E.E. A battery of code machines greets us. [A NEW BOOK] Creeds. and Kleinschmidts- automatic tape - ONLY BOOK OF ITS KIND IN THE THEWORLD, "The Inductance Authority" entirely perforating machines which can store up dispenses with any and all computation for the traffic that can be fed to a transmitter and construction of solenoid coils for tuning with out on the air as fast as 180 words a min- variable or Axed condensers of any capacity. covering from ultra frequencies to the borderline ute. Students are checking messages they of audio frequencies. All one has to do is to read received against the tape. Nearby instruc- the charts. Accuracy to 1 per cent may be attained. tion work is being given in teletype "punch- It is the first time that any system dispensing with calculations and correction factors has been ing," another phase of communications presented. work. There are thirty -eight charts, of which thirty - In the Code Room is a novel panel board. six cover the numbers of turns and inductive I Instead the results for the various wire sizes used in commer- of old- fashioned patch cords, cial practice (Nos. Id to 32), as well as the differ- switches are used. By turning a single - ent types of covering (single silk, cotton -double SAVES TIME- MONEY- TROUBLE , Brushes,: gang, 12- position rotary switch, any one of silk, double cotton and enamel) and diameters of twelve channels may be fed into any 3, %. 1. 1%, 154, 1%, 11ií2, 1%, 2, 21/, 2%, 2?,i Repair Old Parts with single 3 inches. to table or any combination of tables, includ- and Chemicals Each turns chart for a given wire has a sepa- A real professional outfit! Contain every , CetS ing audio receivers. Through a unique tie- rate curve for each of the thirteen form diameters. essential radio chemical and ement- The book contains all the necessary information everything you used for instant service back arrangement the instructor can moni- on spemers, coils, contacts, dials. vo.ume the any individual to give the final word on coil construction to serv- controls, cabinets, eta Permanent Indexed tor progress of student ice men engaged in replacement work, home ex- rack for easy use on bench or wall. Every or give instructions right on the circuit perimenters, short -wave enthusiasts, amateurs, efficient radto man should have this com- without leaving his position at his desk. engineers, teachers, students, etc. plete Inlaxatory. There are ten pages of textual discussion by Contains 20 Most Needed The maintenance class, one of the best Mr. Shiepe, graduate of the Massachu,etts Insti- Radio Cements and Chemicals liked courses, gives the student an oppor- tute of Technology and of the Polytechnic Insti- Twenty large 2 m. bottles contain ce- tute of Brooklyn, in which the considerations for menu, solvents, contact cleauen, uen -alto tunity to work on the latest types of ultra - dial chemical,. lubricants, insulating accuracy in attaining inductive values are set varnish, cabinet stains, glue, liquldope. short -wave transmitters and receivers. forth. grafotlne, etc., etc. use it a week and* Modern test equipment is used here. The The book has a flexible fiber black cover, the You'll wonder how you ever got along page size is 9 x 12 inches and the legibility of all without it. Get one today! Dealer net students adjust, repair, replace parts and curves (black lines on white field) is excellent. cost Only 14.90 with FREE RACK. go through the whole gamut of emergency ORDER FROM YOUR RADIO JOBBER repair of modern airline equipment. Price at your dealer or direct -$2.50 Passing along the corridor, some strange GOLD SHIELD PRODUCTS GENERAL CEMENT MFG. CO. sounds were heard which seemed to be Rockford, coming from behind a closed door. Inquiry 350 Greenwich St. (Dept. RCIO) Illinois, U.S.A. brought the information that the sounds New York City were the real and reproduced voices of students being trained in voice culture and diction. The instructor was recording the students' voices for criticism. Your Money Back-

. If the RADIO AMATEUR MdiMMINIMINIWINMENNIMMONININOIMMall COURSE does not represent SIGNAL CORPS TRAINING the greatest book value ever BEGUN AT ILLINOIS TECH offered to the radio C ®C (Continued from page 27) "fans" for "several thousand." Most of the courses T`O convince you that there isn't a are pf either a 10- or 12 -week duration, al- 11 better book buy today, the pub- lowing four or five complete turnovers an- lishers of the RADIO AMATEUR nually. COURSE make the sensational Like the courses of study themselves. offer of a money -back guarantee on laboratory equipment -which is now valued such a low-priced book. Stop in at at a minimum of $100,000 -had to be de- any of the many dealers handling signed and built largely by Illinois Tech this book and examine it. See for engineers, since much of the apparatus yourself if the RADIO AMATEUR needed was too new in principle to be G.W.Shuárt COURSE isn't just the book you've manufactured by standard electrical com- RADIO& 'W2Ah1N' always wanted. panies. Printed on the finest coated paper Apparatus built at Illinois Tech includes TELEVISION -well illustrated attractive 4 -color numerous wave guide facilities, designed cover -complete with radio information you must have. It contains a especially for use with the micro -waves; step -by -step program for obtaining Lecher -wire systems for the measurement short-wave radio education. of wave lengths; coupling and tuning units, Written by George W. Shuart, and numerous types of tube equipment. WSAMN foremost short -wave authority Most of the equipment consists of new adap- PRICE SOP tations of older principles modified for use with the ultra -high frequencies. RADIO AND TELEVISION Also included in the laboratory equip- 25 West Broadway, New York, N. Y. ment complete .ent)emen: t enclose herewith my remittance of are the facilities of the old Fifty Cents 150e) for Which picase a POST- PAID. my cd of tae RADIO AMATEUR COURSE. RCA Institute in Chicago, acquired by 148 PAGES (Remit by check or order; register If you Illinois Tech in June and now unused tas! set up with 6 x 9 INCHES other equipment to form one of the most complete electronics laboratories available OVER 160 RADIO DIAGRAMS Nnn,e - anywhere. The RCA facilities include some of the finest equipment available for work and TECHNICAL PHOTOGRAPHS in radio, electronics, code and television, Address direction finders and eleven standard trans- RADIO AND TELEVISION mitters ranging from tiny 15 -watt stations 25 West Broadway New York, N. Y. Wish . tic -1042 to the largest commercial types. city

RADIO -CRAFT for OCTOBER, 1942 57 SERVICING

ANALYSIS AND ALTERATION used is an unknown under actual operating OF AN ANALYZER conditions since it depends upon the make, MELVILLE -TRAINED MEN age and loading of the particular unit being ARE "POUNDING BRASS" (Continued from pagé 13) used. Therefore, the variable zero-setting resistor's setting is an unknown and must FOR VICTORY leg. Since the 262.787 -ohm leg is in parallel be determined in one way or another. This -resistance is the 15,000 ohm wire -wound potentiom- Behind communications equipment of every with the meter leg, then a drop of 25 volts must be across it. Therefore, eter). type - Government and Commercial - hun- a' current of .0009513 amps must flow in Figure 6A shows the R- times -10 range dreds of Melville- trained radio operators and this 262.787 -ohm leg, since .25 volts divided rearranged still further to simplify calcula- -scale technicians throughout the world are busy day by 262.787 ohms equals .0009513 amps. tion for full meter deflection when the resistance under test is zero. This is to and night, doing their part for Victory. And Since 50 µa. already is flowing in the meter leg, the total analyzer current flowing for obtain the value of the variable zero -set when peace comes, many of these men will the 1 ma range is .001013 amps, an error potentiometer when the battery voltage is continue the climb to greater engineering of about 1.3%, assuming that the ele- responsibilities. mentary circuit analysis is generally correct and ignoring various averaging and com- On the land, on and under the sea, in the pensating factors in the analyzer. A simple air-everywhere radio equipment must be op- chart can be set for the D.-C. current erated with speed, precision, and courage- ranges. there you find men who began their radio With the aid of a chart and Ohm's lam, some additional ranges can be calculated. careers at Melville Aeronautical Radio School. Remembering that the total resistance loop Their outstanding performance is the reason must remain constant at 5262.787 ohms and why so many leading airlines of the world look resorting to some simple algebra, we can to Melville for new men -why the Army, Navy, calculate for the required values for a 500 - ma range, for instance. \t e would have to Merchant Marine and Coast Guard seek the discard the .773 -ohm resistor between the cooperation they from are getting Melville for 250 ma. and 1 ma. ranges and substitute the instruction of young men from all parts of two resistors equal to .773 ohms. In other America. The management of this school is words we would have to tap the .773 ohm resistor at an appropriate value to get the proud of every Melville graduate who is now 500 -ma. range, as in the case of the volt "doing his stuff' in the service of the United ranges. Setting up the analyzer current cir- Nations and in Commercial radio aboard the cuit with these two substitute resistors in ships and planes of the world. place of the .773-ohm unit, we can call one x ohms and the other .773 -x ohms. Thus we have a total of .262 + x ohms in one MELVILLE shunt leg and a total of 5262.525 -x ohms AERONAUTICAL RADIO SCHOOL, INC. in the meter -shunt leg. We know that at assumed to be its full 1.5 volts. Fig. 63 is 45 West 45th St. New York full -scale deflection we have 50 pa. flowing City arranged for a test resistor of 1,000 ohms Train...g .sre.. for Rodlo in the .,-r;, e of in the meter -shunt leg, or a voltage drop of (one tenth of one per cent) which gives a NINLINE6- E11MT- NANI- MENCNLNT WINE-COW 611116- Ie6USINT (26312625- .00005x) volts. Since we are meter 10 µa, since the 100 mark,- creating a 500 -ma. range, we must have a current of ing on the ohmmeter scale coincides total analyzer current of 500 ma. at full scale with 10 marking on scale. deflection. Since we already have .00005 in the the volts -mils In the meter leg, then a current of .5 - .00005 or .49995 amp. flows in the other shunt leg. have Therefore we a voltage drop of 1.5V [(.262 + x) times .499951 volts in this shunt leg or (.1309738 - .49995 x) volts. Since these two legs are in shunt, the volt- 2s6.Sa age drops across them must be equal and therefore we can equate the two quantities IE representing the voltage drops and we get I, 1, .00005 t, 4 STANDARD TYPES the following: 18.15A 21,1e7A 2,500A On of Amperite Regulators replace over (METER) Rx types of AC -DC Ballast Tubes now in u .1309 + .4999x = 2631 - .00005.E .49995x .1322 F16.6A. Rx10 RANGE REARRANGED FOR CAL- Amperites are real = REGULATORS ... ha x = .264 ohms CULATING VALUE OF ZERO -SET RESISTOR patented Automatic Starting WHEN BATTERY IS AT 1.5 VOLTS Resistor whi .773 -x = .509 ohms MAXIMUM AND 15 events initial surge and saves pilot lug Check -.264 + .509 = .773 ohms TEST RESISTOR ZERO OHMS, METER .. Ask Your Jobber. DEFLECTION IS FULL-SCALE AT SOJUA WITH ZERO-SET RESISTOR ADJUSTED4ORCHOFF'S Therefore we replace the .773 -ohm re- LAWS ARE APPLIED IN THIS CASE) sistor with the two equivalent .264- and .509 -ohm units to get the extra 500 -ma. 1.5 V range. In other words, since the 500 -ma. range is about one third the way between the 250 and 1,000 ma. (1 amp.) range, by tapping the .773 -ohm resistor about one third the way down (at .264 ohms) we obtain the new 500 -ma. range. Similarly, we can calculate for any other current range within the 100 -µa. and 10 -amp. range limits 18.15a 21,1870 2,500n. 1,000n MI(METER) Rx of the analyzer. THE il When we get to the ohmmeter ranges, TIG. 6B. RYIO RANGE SET UP TO CHECK TEST we get into more complications. (See Fig. ON 1041AANO100-SCALE MARKINGS ON A 5). This rather elaborate circuit is no doubt 1,000A TEST RESISTOR. OHM'S LAW ISAR WAY TO REPLACE familiar to test -circuit and insulation -test PLIED IN THIS CASE. workers. The circuit has been rearranged and simplified somewhat. BALLA5'T5 A chart of resistor values for these the former case we use Kirchoff's laws ranges can be set up but is not of much and in the latter case we may use Ohm's WRITE FOR REPLACEMENT CHART value where a full understanding of altera- law and the parallel -resistance formula. tion or addition to these circuits is con- The use of Kirchoff's laws are advisable AMPERITEC s61 uonowr.. NEW TO. cerned. A further complication lies in the here since the circuit in 6A is a bit too in- fact that the actual voltage of the battery (Continued on page 62)

58 RADIO - CRAFT for OCTOBER, 1942

- p Y ' OFF THE PRESS!

MODERN RADIO SERVICING TECHNIQU

Aa Aid re O,.i.Lo, Mora PrehNb'

S.r,, iea Tl.wrb nk. Apph..d,e. ef Medoa M.rbod.

New RADIO -CRAFT Library Books

E four latest books of our well -known RADIO -CRAFT Red Books- Outline of Contents: Elementary Servicing Technique -Correct Procedure Nos. 25, 26, 27 and 2N -have just cane off the press. for the Servicing Beginner -Elementary Procedure for Servicing Radio Sets- - These four books are all on timely subjects and we recommend every A.F.C. Alignment Made Easy-Dynamic Servicing -Dynamic Testing S.mpliees ono of them to you strongly. Servicing- Modern Receiver Test Requirements -Servicing Universal A.C. -D.C. Now, more than ever, radio education has helwme a burning question. Receivers-Servicing "Orphans' and Private -Brand Sets -Emergency Servie no If you are to be in the National Service; in the Army. Navy or Air h ree- Without Test Meters-Servicing Coils -Servicing R.F. Coils -Servicing Oscil- praetleal radio knowledge is of paramount importance. YOU CAN GET BETTER lator Coils -General Information -RMA Transformer Color Code -What Causes RATINGS AND ADVANCE QUICKER IF YOU HAVE A GOOD RADIO Echo, Fading ? -Radio Service Puzzlers. BACKGROUND. Conversely, if you are not with the armed forres. there is whale of a job No. 28 -ALL ABOUT FREQUENCY MODULATION to be done at home. With more and more men going into tie service. the Ilene Is a complete compilation M pertinent data on the entire subject of demand for practical servicemenvicemen becomes greater each day. Therefore say the hew d ung art of Frequency Modulation. PROFIT BY THESE UNIQUE BOOKS. WHICH ARE PRICED SO B LOW There is du nn question but that Frequency Modulation is already revolution- THAT THEY ARE WITHIN THE REACH OF EVERYONE'S PURSE. ising radio broadk-ast big in this country. Were it not for the war. there would now be a tremcn,ions boom in this new art -yet. even with war restric- No. 25-HOME -MADE RADIO TEST INSTRUMENTS tions imposedpod upon it. Pregheory Modulation le still .jumping ahead by and bounds. This book Includes articles covering a wide range of Mat apparatus of live leap. of stations Interest to every radio n . Seroirrme, will find many circuits in this book With Frequency Sfalul :.lion no longer a Theory -with bundreelo come to make their work snore m profitable. New Ideas in test equipment make It already dotting the land and with countless hundreds M others to possible to service radio receiseri more prickly. when Mace is achieved once owe- -every radio matt should read up and know Laboratory worker. and experimenters will find many articles whirl. describe all there is Io know on this most Important stibievl. In detail construction and use of all essential radio test units- multi-meters. Tide particular handbook is chuck -full with a tremendous ount of oscillators. stage-analysis testers, oseillmcope equipment. V. -T. voltmeters, ele. inforationinformation which you obably will not find hl may similar honks in print. Even advanced technicians will be Interested in the circuit arrangements showing Outline of C : The ABC of F.M. -Frequency vs. Amplitude Modula- the new and improved variations of well -known, basic test equinuwnt. A MUST tion -Basic Facts About F.M. Breedeasting- Conatructioo -Build This Prac- for every serviceman. This book contains A6 Illustrations. tical F.M. Adapter -Audio Amplification-F.M. Audio Amplifier, Part I- FM. Audio Amplifier, Part 2-F.M. Audio Amplifier Part 3-F.M. Service Outline Of Contents: A low -Cost Signal Chaser -- Signal Tracer Test Unit - Tube -Part 1, Antenna Installation and Servie. -Part 2. Receiver Alignment and Simplified Practical Signal Tracer -A Home -Made Infinite - Resistance 3, Test Equipment for F.M. Servicing. Engineering I. Make a Modern Diagnosis-Part -Part Checker-Build This D 'rest- Reading V. -T. Voltmeter -How to of 2. The How and Why of F.M.-Theory V. -T. Voltage and Current With a The How and Why F.M.-Part Voltmeter -Measuring High Values of A.C. and Design ConsideratIons of R.F. and I.F. Coils in F.M. Receivers. Low -Range Meter -How to Make a Meter -Range Extender -Haw to Build a Practical Tube Tester and Set -Analyzer Adapter-The Beginners' Simple Volt - Milliammeter -Build This Simplified Neon -Type Test Unit -Midget Oscillo- SPECIAL SEND -NO -MONEY OFFER scope -How to Make and Use a Frequency Webbler- Double Tracing Your It Is not necessary that you send money with order. if YOU wleh to take Osoilloste:s -Home -Made Frequency Modulator. advantage M our C.O.D. plan, simply 'rut out the coupon. Paste It on post tad and send It to us. Books will be sent to yet immediately. No. 26- MODERN BATTERY RADIO SETS All four books are listed uniformly at 50e each. No discount on less than Whether you are a radio man or a beginner. the articles in this book give three books. you basic circuit arraneetnerus or elementary radio receivers which serve the If you wish to take advantage of our special 01ftr, ordering three books or dual role of teaching the elements M radio reception. as well as making more, wo make an unusual low price to you as follows: perfectly- operating 1- and 2-tube radio receivers. Picture diagrams and bread- 3 books-61.25 board layouts galore. 4 books -41.50 Advanced radio set builders are offered more complicatedplicated arrangements. Do not fall to send coupon today! Laboratory workers and engineers will find In many the articles circuit and RAl)CRArr PUBLICATIONS. INC. constructional features Whirh have become commercial practice. Many entirely 25 West Broadway. New York. N. Y. new ideas are given in thin book. One of the most important volumes we recently Issued. This beck contains 76 Illustrations. r Radcraft Publications, lac.. 1042 Outline of Contents: Beginner's 1 -Tube High -Gain All -Wave Receiver- 25 West Broadway. Beginners -Build This 1 -Tube Loop Receiver -A "3 -in -I" Battery Portable-An New York. N. V. Easily -Built 'Shovelling Superregenerative" 2 -in -1 "Card File" Battery Set -

RADIO -CRAFT for OCTOBER, 1942 59 Radio a 7elevieion Radio Paten ti

Electron Discharge Device No. 2,244,733 issued to Andrew V. Haeff, East Radio Patents Digest Orange, N. J. An electron discharge tube including means for projecting a beam of electrons, means for modulating said beam of electrons, an accelerat- Antenna Rotator Arrangement for the Transmission ing electrode for said beam of electrons and a No. 2.284,672 issued to Bernard J. Merkle, Chi- of Intelligence collecting electrode for collecting the electrons cago, Ill. after their passage past said accelerating elec- No. 2,284,706 issued to Wiessner Alfred and trode, all said means being in said tube Wolfgang Hagen, Berlin, Germany. in the A two -way carrier frequency station in which a plurality of different signal messages are transmitted and received by use of doubly modulated carrier channels, the signal messages being trans. mitted on different respective frequencies as sin gle sidebands, the transmitting branch compris ins: a single carrier wave generator, a plurality of first modulators, means for applying to each of said first modulators carrier waves from said single generator and signal waves constituting one of said plurality of different signal messages, means for selecting a single rideband from the output of each of said first modulators, means for order named, said collecting electrode compris- deriving higher frequencies from said carrier ing an elongated cup -shaped member with its wave generator, a plurality of second modulators. open end in position to receive the beam of elec- means for applying to each of said second modu- trons. and a ring -like electrode within said cup - lators one of said derived higher frequencies and shaped member and adjacent the open end thereof field modulated energy comprising a single sideband for providing a at a lower potential than selected from the output of a different first modu- that of said collecting electrode. lator, means for selecting a single sideband from the output of each of said second modulators, and Sound Recording In a rotatable support, a hollow vertical shell No. 2,284,744 issued to Edward W. Kellogg. with a support at the top, a base into which the Moorestown, N. J. lower end of the shell is inserted, bearing means for supporting the lower end of the shell com- The signal recording method which comprises prising a circular shoulder extending inwardly actuating a recording element in accordance with below the end of the shell, an anti- friction ring said signals to effect movement thereof corre- bearing interposed between the shell and shoul- sponding to said signals, and simultaneously der, and an oil retaining sleeve secured to the causing said element to be displaced from its inside of the shoulder and extending upwardly normal movement by an amount proportional to above the bearing within the shell, and means for the slope of the curve being recorded. rotating the shell in either direction.

Electric Phonograph No. 2,284,678 issued to Lucius P. Petroaehell. Stratford, Conn. common transmitter for transmitting said selected single sidebands, and the receiving branch comprising a common receiver for receiving a plurality of single sideband waves. means for segregating said received single sideband waves. first demodulators for said received sidebands, means for applying said derived higher frequencies to said first demodulators, second demodulators and means for applying energy from said single generator and from said first demodulators to said second demodulators to derive the Amplifier Circuits received signal messages therefrom, the modu- No. 2.284,855 issued to Julian M. West, Ridge lated energy applied to said second modulators wood. N. J. and the modulated energy applied to said second demodulators occupying the same frequency bands.

Television System No. 2,284.714 issued to Alda V. Bedford, Collings- wood, N. J. In a picture transmitting system, the method of synchronizing scanning at the receiver with r. 2,284,855 scanning at the transmitter which comprises transmitting one group of synchronizing impulses each having a steep front side and having a A wave amplifying system comprising a plu- In an electric phonograph, in combination. a gradually sloping back aide and transmitting rality of vacuum tube amplifying devices, im- plurality of record supporting units each having another group of synchronizing impulses each pedance networks coupling said devices in tan- a translating device mounted for traversing having a steep back side and a gradually sloping dem, a feedback path coupling the output circuit movement in relation thereto, driving means for of the last of said tandem connected devices with each of said units, means adapted to effect se- the input circuit of the first of said devices and quential operation of said units, an electrical an impedance network included in said feedback power supply for said driving means, control path. said impedance networks each comprising a means for controlling the supply of power to plate circuit branch and a grid circuit branch. said driving means, a plurality of indicating de- said networks having a combined attenuation vices connected with raid power supply and which is substantially constant and small relative located with said control means remotely from to the combined gain of said amplifying devices said phonograph and adapted to indicate which at frequencies in an assigned operating range. of said phonograph units has been in operation. which increases with the decrease of frequency switch means for controlling the operation of just below said operating range, and which has a each of said indicating devices, and operating progressively changing phase as the frequency is mechanism for each of said switch means oper- still further lowered, means for delaying the atively associated with one of said translating building up of phase shift with decreasing fre- devices and adapted to actuate said switch means 2.284.9J4 quencies, said means comprising capacitance when the respective translating devices occupies shunting a portion of the grid circuit branch of an initial position from which it moves during one of said coupling impedances, the magnitude its traversing movement whereby said indicating of the capacitance being such as to delay the devices are rendered inoperative when said trans- front aide, intercepting said impulses at the re- building up of phase shift with decreasing fre- lating devices are in their initial positions and ceiver and substantially differentiating them, and quencies until a frequency -level is reached at rendered operative when the translating devices utilizing the differentiated signals for synchroniz- which the net gain around the feedback loop is have departed from their initial positions. ing the scanning at the receiver. less than unity. 60 RADIO -CRAFT for OCTOBER, 1942 Radio Patents )2adio 7alavision

Beacon to emit secondary electrons, and an anode, means Navigation Aiding Radio for simultaneously impressing both carrier fre- NOW: System quencies upon the control grid, a local oscillator No. 2,284,873 issued to Roland John Kemp. You can get the math Chelmsford, England. A navigation aiding radio beacon transmitter ray you need for solving installation of the television type comprising means for radiating alternately and periodically two radiations representable by similar but oppo- everyday radio sitely disposed intersecting polar diagrams which together produce an equi- signal zone along the and electrical line of intersection, the rate of alternation of being above the rate of persistence said diagrams s cf vision, means for rotating the alternated dia- problems grams about the transmitter, picture modulating means for modulating the radiations correspond- with signals corre- ing to both diagrams picture Radiomen and electricians know sponding to a scanned picture indicative of the that the language and the momentary direction of the equi- signal zone. habit of mathematics are es- means for also modulating said radiations with sential for real progress in scanning line synchronising impulses and means their chosen field. They know for also modulating the radiation corresponding mathematics is a tool that they to of said diagrams with a framing synchro- are helpless without. one grid for impressing NOW out of the U.S. Navy nising signal so that a framing synchronising loosely, coupled to the control a pair of Radio Materiel School at the is included with the signals sent out on a heterodyne frequency thereon, and signal the cir- Naval Research Laboratory comes a complete on the other of the two diagrams. impedances each included respectively in and so de- one but not of the home =study book that is so thorough cuit of the auxiliary cathode and in that can perform arith- a high value tailed that any reader "who anode and each having respectively metical computations rapidly and accurately is Electric Wave Amplifier for one of the intermediate frequencies resulting capable of mastering the principles laid down the interaction between the heterodyne fre- .1. Burger, South from in this teat." No. 2,284,894 issued to Michael of the signal- modulated carrier Park, N. Y. quency and each Ozone frequencies. MATHEMATICS for A push -pull amplifier, a driver amplifier for one side of said - RADIOMEN supplying oscillations to push Electric Musical ELECTRICIANS and pull amplifier and having circuit elements of such Combination By N. M. COOKE, Chief Radio Electrician, as to a definite ratio of even constants produce Instrument U. S. Navy order distortion to the fundamental of products No. issued to Paul Weathers, Audubon, 9, the applied oscillations, an inverter amplifier 2,285,132 604 pages 6x $4.00 and William L. Rothenb , Merchantville, elementary al- having an input connected to the output of said This book teaches you mathematics from N..1. gebra through quadratic equations, logarithms, trlgonen- driver amplifier and an output connected to the ary. plane vectors and elementary vector algebra with of push amplifier and having acoustical electric trans- applications to electrical and radio problems. lt other side said -pull In an electric piano, direct kowledge in such constants as to produce audio amplifier connected to teaches you how to apply this mathematical circuit elements of lating means, an the solutions of radio and circuit problems. In other even order distortion products of the applied said translating means, a loudspeaker connected word., It gives you the grasp of mathematics you need oscillations of such magnitude and phase as to to said amplifier, manually controlled means in- and then shows you how to use your knowledge. Based on over 8 yearé experience teaching mathe- substantially neutralize the even order distortion dependent of the piano mechani :m for regulating matic. to U.P. Navy electrician. and radio operators, the products supplied by said driver amplifier to said volume from all of said translating means, book gives you 600 illustrative problems worked out In the with answers so means independent of the piano detail and over 3000 practice problems push -pull amplifier. and pedal control you can check your work. mechanism and supplemental to said manually controlled means for regulating the volume from DAYS' FREE EXAMINATION'"'" i be- all of said translating means over the range McGraw-Hill Book Co., 330 W. 42nd St., New York I which the manual vol- tween the maximum for Send me Cooke'. Mathematics for Electricians and ume control is set to the maximum output of Radiomen for 10 days' examination on approval. In means. 10 days I will send you $4.00 plus few cents postage. I said translating or return book postpaid. (We pay pottage If remit- I tance accompanies order.) Name Addreu City and State ®J r Position Company RC. 10-42 T..w,v,..e.. wowww=wwwwwww..=ww= =w=ww=w= Piezoelectric Crystal Apparatus taken from said cell for placing all of said means television scanning circuit is no Erie. in an electrical No. 2,284,968 issued to John M. Wolfakill, greater than the number of leads required to Pa. place one of said laminar means in said circuit. Piezo electric crystal apparatus, comprising: a piezo electric crystal having a pair of major Radio Vision Transmitting, Re- faces, electrodes for said major faces, one of and Reproducing said electrodes being adjustable with respect to cording, the corresponding one of said faces to provide Apparatus and Method an air -gap therebetween, and means for sub- No. 2,289,427 issued to Karl Robert Hoyt, Los An- stantially preventing the movement of said crys- geles, Calif. tal toward or away from at least one of said electrodes during vibration of the apparatus, said Television System and Method In a system of the class set forth, light beans controlling means including a source of light, a means comprising adjustable members extending issued to John N. M. Howells, No. 2;289,363 cylindrically bored shell part having a light slot to and almost touching face portions of said crys- Kittery, Maine. tal to define and substantially prevent movement through its bore wall and a barrel part movably of said crystal toward or away from the afore- A unitary scanning cell adapted to be mechan- fitting in and close to the shell and having in its said electrode but not affect operation thereof. ically moved for scanning, said cell comprising a cylinder wall a series of light slots; the shell and plurality of closely spaced linearly aligned electrically insulated elemental photo-responsive areas and a plurality of laminar electrical means, each having a characteristic frequency, each of said areas having a different laminar means electrical- 3 ly associated therewith, said laminar means being so connected that the number of external leads

Receiving System No. 2,285,030 issued to Johan Haantjes, Adelbert van Weel, Maximiliaan Julius Otto Strutt, and Aldert van der Ziel, Eindhoven, Netherland.. A frequency changing circuit for heterodyning and separating two signal -modulated carriers of and slots different frequencies, comprising an electron dis- the barrel being relatively movable the as to the slot of the charge tube having at least a main cathode, a of one part being angular to form a travel- control an auxiliary cathode in the form other and cooperating therewith grid, for light from said source to of a solid plate impervious to electrons adapted ling light aperture upon impact of electrons from the main cathode the exterior of the shell. RADIO -CRAFT for OCTOBER, 61 SERVICING

ANALYSIS AND ALTERATION aG'c{unA.t pJiíced OF AN ANALYZER (Continued from page PuGlic`cfc;cfszi jot expertisre,nÍeru 58) volved to be handled readily by the simple Ohm's law. They state that : (1) The sum FOR of all currents entering any one junction in 10 SOC any network must equal the sum of cur- Here is a large number of radio, short -wave, and me- PLEASE ORDER EACH PROJECT BY ITS PUBLICA- rents rhanical "how -to- make -it" designs. TION NUMBER, and use the special coupon below. leaving that junction. (Algebraic in Each is a special publication originated by masters in We accept money- orders, cash. checks or new U. S. the case of D. -C. and unity power factor their respective fields. stamps. (No lore.gn stamps.) If you send cash or stamps. For the low price of 50 CENTS, you buy TEN complete register your letter. A.-C. currents and vectorial in the case of pamphlets with photographic reproductions, complets me- Money refunded if you are not satisfied. reactive A.C. currents.) (2) The sum of chanical layout, and full description to make it possible ANY TWENTY -FOUR PUBLICATIONS FOR ONE for anyone to build the project in question. DOLLAR. potential gradients about any closed loop in any network must total zero. (Algebraic SHORT -WAVE in the case of D.-C. and vectorial in the RECEIVER PUBLICATIONS case of A. -C.). NOW TO MAKE THE "OSCIL- HOW TO MAKE THE I -TUBE- HOW TO BUILD THE "DUAL - LODYNE" I TUBE WONDER SET. ALL- ELECTRIC OSCILLODYNE. WAVE" SHORT -WAVE BATTERY The unknown currents are set up as al- No. 101 No. 106 RECEIVER No. 112 gebraic quantities and their direction of flow HOW TO MAKE THE 2 TO 5 NOW TO MAKE THE "19" TWIN - METER HOW TO BUILD THE I -TUBE are assumed in a logical PLE% (ONE TUBE PERFORMS TWO -TUBE LOUDSPEAK- RECEIVER. and consistent ER SET No. 107 "53" TWINPLEX" AS TWO) RECEIVER No- 102 113 fashion, of course, HOW TO MAKE THE 3 -TUBE No, and the various al- HOW TO MAKE THE WIZARD- 1 BATTERY SHORT -WAVE RECEIV- HOW TO BUILD THE PORTABLE gebraic equations are set up to represent TUBE 50 -WATT TRANSMITTER. ER No. 106 MINIDYNE SHORT -WAVE BAT- the various voltage drop and current No. 103 THE BRIEF -CASE SHORT -WAVE TERY SET No. 114 condi- RECEIVER AND HOW TO BUILD tions according to these laws. These equa- HOW TO MAKE THE IMPROVED IT No. 109 HOW TO BUILD THE HAMBAND 3 -TUBE DOERLE SET FOR BAT- HOW TO BUILD THE POCKET "PEE -WEE" 2- TUBER No. 115 tions are then set up as appropriate simul- TERY OPERATION No. 104 SNORT -WAVE RECEIVER HOW TO BUILD THE DUO -AM- taneous equations and solved by a series No. 110 PLIDYNE No. 116 HOW TO MAKE THE "60 -GET MOW TO BUILD THE CIGAR - of substitutions and further simultaneous EM 2" RECEIVER FOR THE BE- BOX 1 -TUBE "CATCH ALL" RE- HOW TO BUILD THE "MONO - etc., GINNER No. 106 CEIVER No. 111 COIL 2." No. equations, until all the unknowns are 117 solved. The trick to applying these laws lies in the consistency and intelligence with RADIO BROADCAST RECEIVER AND SPECIAL RADIO PUBLICATIONS which the choice of equations and substitu- NOW TO MAKE THE A.C. -D.C. HOW TO BUILD THE 2 -TUBE HOW TO BUILD A 6 -TUBE BAT- tions are made. "CASH BOX" RECEIVER, 118 No. "PENTODE PORTABLE" BROAD- TERY ALL -WAVE "FARM PORT- Suppose we wanted an HOW TO MAKE BEGINNER'S 2- CAST SET No. 122 ABLE" SET No. 126 R-times -I00 re- TUBE ALL -WAVE SET No. 119 HOW TO BUILD THE RADIO HOW TO MAKE AN A C.D.C. sistance range. We can set up the R- times- "TREASURE" FINDER No. 123 ONETUBE "DEAF AID." Na. 127 HOW TO BUILD THE "RADIO - HOW TO BUILD A PIANOTRON. 10 range with an assumed full battery volt- LAMP" 4 -TUBE TABLE HOW TO BUILD THE GERNS- RECEIV- BACK ONE No. 128 age of 1.5 volts and with a short ER No. 120 -TUBE PENTODE HOW TO BUILD THE ONE -DOL- circuit LOUDSPEAKER SET No. 124 LAR RADIO No. 129 across the test leads for a full -scale meter HOW TO BUILD A SUPER-SEN. HOW TO BUILD THE WORLD'S HOW TO MAKE A VARIABLE - deflection of 50 VE ALL -WAVE CRYSTAL SMALLEST ONE TUBE BATTERY TONE CODE PRACTICE SET. µa. We can then solve for SIT No. 121 RADIO No. 125 No. 130 the correct setting of the zero-setting potentiometer with a full 1.5 -volt battery poten- MECHANICAL PROJECTS PUBLICATIONS tial. We can also theoretically insert a test resistor of exactly 1,000 ohms across the HOW TO MAKE A SOUTH SEA HOW TO BUILD A SIMPLE PORT- HOW OUTRIGGER TO MAKE YOUR OWN test leads and 100 CANOE. No. 131 ABLE REFRIGERATOR... No. 138 MICROSCOPE No. 144 since this mark on the HOW TO BUILD A PEE -WEE HOW TO BUILD A XYLOPHONE. HOW TO MAKE A WIMSHURST ohms scale corresponds to the 10 marking AUTOMOBILE No. 132 ELECTROSTATIC MACHINE No. 139 on the volts -mils scale, we know HOW TO BUILD A DUAL -CON- No. 145 we must HOW TO TO TROL GLIDER No. 133 BUILD THE ROWMO- HOW MAKE A POWER DRILL have a meter current of 10 .ta for this test BILE No. 140 PRESS FROM SCRAP PARTS. HOW TO BUILD A HOUSEBOAT No- 146 resistor. Thus we have a second method ON PONTOONS No. 134 HOW TO BUILD LARGE TESLA HOW TO AND OUDIN COILS !B- BUILD A GOOD LATHE and a cheek for finding set- HOW TO MAKE GIVING FOR $1.00 No. 147 the theoretical A BAND SAW IRCH SPARKS No. 141 FROM OLD AUTO PARTS. No. 135 HOW TO MAKE AND EXPERI- ting for the zero-set resistor with a full- HOW TO BUILD A REAL LATHE HOW TO MAKE AN ARC WELD- MENT WITH AN ELECTROPHOR- voltage battery. Having found this value FOR $5.00 No. ER No. 142 OUS No. 148 136 HOW TO MAKE AN ELECTRIC (using Ohm's law and the parallel- resist- HOW TO BUILD A SAIL CAT- HOW TO USE AN A.C. ARC ARC WELDER FROM AN AUTO - BOAT No. 137 WELDER No. 143 MOBILE GENERATOR... .No. 149 ance formula), we can then set up a simple chart showing the various ohms ranges RADIO PUBLICATIONS, 25 West Broadway, NEW YORK, N. Y. RC 1042 and their resistances (see diagram 7). We find that the two sets of resistors I enclose 4 for the publications listed by number, at 101 102 103 104 105 106 that vary right. at the rate of 50e FOR ANY TEN PUBLICATIONS. NO 107 108 109 110 with the ranges change roughly in ORDER FOR LESS 111 112 direct THAN 50e ACCEI'TIOI. 41.00 for 24 Dublin- 113 114 Ume. These publications are to be sent to me have 115 116 117 118 proportion to the R multiplier. that is, the postpaid. I 119 placed a circle around each number which I want. 120 121 122 123 124 resistors increase 11 times 10 125 126 127 128 129 130 to for the R 131 132 133 134 135 136 multiplier. Thus, if we assume a value of Name Address 137 138 139 140 141 142 about 185 ohms for our new series resistor 143 144 145 146 147 148 City State 149 for our new R-times -100 range, we can solve for our new shunt resistor by assuming the same zero -set resistor value as was 10 BEST RADIO BOOKS found for the R- times-10 range and using 10 CENTS EACH Kirchoff's law RADIO FANS EVERYWHERE--these fine amazed at the wealth of information con - and some elementary al- ten cent text books give you an excellent tained in these handy books. Excellent for gebra- We will finally arrive at a value of foundation for the study of RADIO. They are reference -ideal for every technical library. about 2,255 ohms for the new shunt re- clearly written, profusely illustrated and con- YOUR MONEY RACK if you are not satisfied. tain over 15,000 words in each book- You'll be PROMPT SHIPMENTS sistor. This is close to the approximate value of about 2,300 NI. 1 -NOW TO BUILD FOUR DOERLE SHORT No. 5- BEGINNERS' RADIO ohms we would expect WAVE DICTIONARY SETS No. 6-HOW TO HAVE FUN WITH RADIO from an inspection of the chart of the other Mo 2-HOW TO MAKE THE MOST POPULAR No. ALL -WAVE 7 -HOW TO READ RADIO DIAGRAMS ohms ranges. 1- AND 2 -TUBE RECEIVERS No. 8 -RADIO Ne. 3- ALTERNATING CURRENT FOR BEGIN FOR BEGINNERS PIERS No. 9- SIMPLE ELECTRICAL EXPERIMENTS It must be remembered that we assumed No. 4 -ALL ABOUT AERIALS No. 10- TELEVISION a full battery voltage of 1,5 volts. For BOOKS ARE ALL UNIFORM accurate calculations we would have to ob- Aron book to the OERNSBACK EDUCATIONAL. LIBRARY has 32 pages tain volts -age -load curves for the particular 30 to 66 in number. Each volume -with illustrations varying front title oontains over 15,000 worde . Positively radios book do not think these !woks worth greabst boys' If you battery being employed in the the price asked, return thorn In 24 hours and your money will be instantly refunded. analyzer. Obviously, the best and RADIO PUBLICATIONS 25 WEST simplest pro- BROADWAY NEW YORK, N. Y. cedure would be to employ a variable re- RADIO PUBLICATIONS. Dept. RC -1042 sistor of 2,500 ohms for the shunt leg and 25 WEST BROADWAY, NEW YORK. N. Y. a variable unit of 200 ohms for the series Gentlemen, Please send Immediately. POSTPAID, the book numbers circled below, I am enclosing reni, -each book being 10e. leg temporarily. Then using a set of one - I 2 3 4 5 6 7 8 9 In tenth of one per cent precision wire -wound NEW NEW Q Send PRIM listing of 48 now 10o publication,. resistors as test standards across the leads, we can juggle our two variable legs till we Name Addrose obtain the most accurate meter readings. City gists Obviously, the general circuit as used for Remit by deck or money order -register letter If you send cash or unused U. S. meters stamp. .MAIL COUPON TODAY!. (Continued on page 64) 62 RADIO -CRAFT for OCTOBER, 1942 200,C RevieW Ï2adio Gr %.ebeviiion BOOK REVIEWS

VACUUM TUBE VOLTMETERS by John finish his course, resorts to cramming. The Radio Code Manual contains twenty les- F. Rider. Published by John F. Rider Pub- data on electro-acoustics, therefore, is brief sons in learning the code, gives instructions lisher, Inc. Stiff cloth covers, size 5% x13 and to the point, and is almost non- mathe- for building code- practice equipment and ins., 179 pages. Price $1.50. matical. contains a lot of useful information for Because the application of acoustics is so the beginner. The author's intention is that John Rider places the inception of the dependent on measurements, emphasis is the beginner learn not only to send and vacuum -tube voltmeter in 1895. While this given to laboratory test methods, and many read code, but also that he be able to date coincides with the invention of the diagrams and sketches are used to illustrate handle commercial messages and press mat- Fleming valve (the diode), the reference the text. An enormous amount of informa- ter. Various abbreviations and tricks of the is not strictly correct. Nor is a second ob- tion is contained in its pages. Experiments trade that have grown up with the art of servation any more accurate that with the long conducted and long since forgotten radio code are given so that the trainee invention of the triode in 1907 "engineers will be quizzically examined. will be able to understand the use of the were quick to realize the improvement Gauze tones, using a piece of gauze and advanced methods practiced by operators. which could be made by using it in v -t Special information required for ship-to- voltmeters." The mere use of a meter in a flame, or oscillations maintained by electrical heating are to be found. The data shore communications as well as commer- combination with a tube does not make a cial operating are included. vacuum -tube voltmeter -not any more than once published by an English physicist on coil make production of sound by solidified carbon This book is recommended to radio code a horseshoe magnet and a pivoted instructors of the numerous code classes a meter. dioxide (dry ice) didn't show up here (if memory serves us right, the description begun since our entrance into the war, since Vacuum -tube voltmeters as we know them was written by a woman and appeared in its use would help to standardize teaching today are of relatively recent development. the Journal of Scientific Instruments), but methods. The few isolated developments prior to it is undoubtedly contained elsewhere in 1920 are, of course, not to be belittled, but the text. their use was extremely limited principally the The classical controversies on combina- AMERICAN STANDARD DEFINITIONS because of their erratic behavior. Even OF ELECTRICAL TERMS. Published by c -t voltmeters of the early 'Twenties. begin- tion tones that have been carried on for more than a century (as probably the the American Institute of Electrical Engi- ning with the work of E. B. Moullin, who cloth covers, size 7% x 11 ins. has probably done more than any other analogous side -band theories or the ex- neers. Stiff 311 pages. Price $1.00. single investigator for such instruments, re- istence of ether will be) are described. A mained temperamental laboratory tools. It drawing, however, shows quite a modern The American Institute of Electrical is significant that Mr. Rider's own book, method and apparatus for demonstrating Engineers, acting with the approval of the Practical Testing Systems (published in combination tones, using a "piezoelectric" American Standards Association, under - 1930), which contained a chapter on v -t (probably a Rochelle -salt crystal) micro- took, in 1928, the project of preparing "defi- voltmeters, said: "To safeguard against phone, an amplifier and several other pieces nitions of technical terms used in electrical errors, the voltmeter should be checked for of equipment. engineering, including correlation of defini- calibration at two or three points every day There is information on supersonics, tions and terms in existing standards." that it is used." sound -ranging (for locating enemy guns) Forty -three Institute members, represent- Mr. Rider in his current book is more and, of course, binaural listening for air- ing thirty -three organizations, including na- concerned with the practical rather than craft detection, and so many other subjects tional engineering, scientific and professional historical aspects of v -t voltmeters, and he that this book undoubtedly will become - societies, trade associations, government de- is content with his inclusion of a fairly if it has not already become -a reference partments and miscellaneous groups were complete bibliography at the end of the source for reference sources. organized under this plan. Eighteen subcom- book for historians. mittees, with personnel of about 120, divided The analysis is practical, there being the work, consulting also non -member experts. More than 300 men in all fields helped almost complete absence of formulas. The RADIO CODE MANUAL, by Arthur R. amount of laboratory work done in the prepare the definitions. Nilson, published by McGraw-Hill Book and preparation of the book made it unnecessary Inc., Flexible covers, special The reports were widely publicized the Company, for criticism and revision both to include equations, according to wire binding, size 5 x 7% inches, 170 pages. circulated field of v -t voltmeters in and out of the AIEE. This work was author. The whole Price $2. is discussed rather thoroughly and values carried on until 1941, when final changes for component parts are given where they Anyone who has worked with radio code were made and the completed report sub- were available to the author. knows there is more to it than learning the mitted to the members for approval. Amer - The reader may find interest in reading alphabet and numerals in terms of dits and icon Standard Definitions of Electrical about the principles and practices of v -t dabs. Hams can tell whether you're a sea- Terms, now published in a bound volume, voltmeters, but by and large, he will get his soned veteran or a neophyte before you can received official approval by the AIEE and money's worth from the working diagrams say Jack Robinson. ASA. which he can use for constructing such It is a pleasure to listen to clear, sharp The definitions give the meaning gener- instruments. signals as they cut the air, giving as much ally associated with each term in electrical significance to spaces as to characters. engineering work in this country, with the jerky, jumbly sending tires the ear to the greatest weight given to strictly engineering point of unwillingness to listen. It is, after applications. Since it was planned so that a ACOUSTICS, by Alexander Wood, M.A., all, the transmission of intelligence we are preferred definition be a simple one, the D.Sc. (Glas.). Published by Interscience after, and the burden falls upon the sender tendency is toward the simple statement of Publishers, Inc. Stiff cloth covers, size to make himself understood. function rather than to the explicit descrip- 53/ x ins., 8% 588 pages. Price $7.00. Because the process of code learning re- tion of all the properties to which a term Dr. Wood is a lecturer in experimental quires memorizing the sounds of individual refers. Because of similarity of terminology physics at Cambridge University. Perhaps letters, which later become a function of in the many branches of electrical engineer- it is characteristic of English lecturers to the subconscious mind, it is essential that ing, the index refers to numbers which give delve thoroughly -and leisurely -into such the learning process be correct. The neces- the key to the section in which each term a subject as acoustics and to describe in sity for learning from an able instructor is to be found. Cross- indexing is used to minute detail all the analytical aspects that can not, therefore, be too strongly empha- avoid unnecessary duplication. fit into its pattern. The result, in Acoustics, sized. Where individual instruction can not Electrocommunication, including radio is a comprehensive text suitable for the be arranged, a book such as Radio Code and television, takes up 28 pages, and five advanced student possessed of sufficient Manual is the next best thing. pages are allotted to electronics, but num- mathematical background to digest its The author, Arthur R. Nilson, is an old erous terms generally believed to belong to contents. hand at training radio students. He is chief radio but which actually have had prior use Although the author presents practical instructor of the Nilson Radio School and in other electrical branches are listed in material, it is outweighed by the amount is a retired lieutenant of the U. S. Naval various sections of the book. of theoretical discussion in the beginning Reserve. He is co-author, with J. L. Hor- Mathematical expressions were used only of the book. But as the book progresses, nung, of such well known books as "Prac- where they were considered to be essential the balance shifts the other way. Towards tical Radio Communications" and "Radio to the simplest description. Only two illus- the end the professor, apparently eager to Operating Questions and Answers." trations were found in the book. RADIO -CRAFT for OCTOBER, 1942 63 Azdio ialavigioR ilool /aviaw

ANALYSIS AND ALTERATION NIGH EFFICIENCY results VDE LUXE GENUINE OF AN ANALYZER Sonnd Notionar Defense page that is why (Continued from 62) NATIONAL DE. FENSE SOUND IBROPLE all the ohms ranges in this analyzer can SYSTEMS are World's Finest Semi -Automatic Key not be used for an R times one tenth or an University Relies R times one hundredth range since the shunt NIGH POWER The LOUDSPEAKERS smartest looking, smoothest action, easi- resistor becomes so small as to draw a ruin- UNIVERSITY LABS c;t to operate Vibroplex 'Bug" has ever ous current from the battery. Some sort of 195 CNIISTIE ST. R.T.C. produced. Has Patented Jewel Movement found only in De Luxe Vibroplex Keys. Pre- shunt type of ohmmeter circuit is advisable cision construction including DIE CUT con- for such low- reading ranges as well as tact and main spring. colorful red switch heavy low- resistance test leads. knob, finger and thumb pieces and silk cora (To he in RADIO To and wedge. Large contacta. An outstanding concluded next issue) KITS-Ready Wire key in smartness, signal quality, speed and Tremendous quantity of standard parts. ease of operation, users say. Vibroplex keys HOME RECORDER ARTICLE suitable for kits. Complete in every detail. give quality performance -insist on Vibro- All hardware. tubes, parts. Diagrams fur- plea. Three De Luxe Vibroplexes . . . . IN 'the article "Construct a Home Record- nished. Latest parts catalog-FREE.

Lightning Bug, Original and . Blue Racer. ' er" which appeared in the June 1942 issue, McGEE RADIO. R-2055, Kansas City, Mo. The finest semi-automatic keys money can page 602 some of the values were not indi buy. Place your order NOW l Money order cated. In response to the numerous queries registered mail. Write or for catalog of we obtained required information from Vibroplex keys priced from $9.95 to $19.50. the Mr. LeKashman, the author of the article, Send for Free Catalog who adds also the correction for the speaker The Vibroplex Co., Inc. field D.C. resistance. Amperite Corp 58 C1 -16 mf.. 450V Audel & Co., Theo. Bac!.: Cover 933 BROADWAY NEW YORK. N. Y. C2 -10 mf., 25V C3 -.Ol, 600V Audiograph 64 C4 -.006, 600V Burstein -App :ebee Co. 52 C5 -10 mf.. 50V R1- -.25 meg.. y watt Candler System Co 47 R2- -.5 meg., potentiometer Cannon Co., C. H 52 R,i 2 nleg., % watt Capitol Radio Engineering, Inc. 49 The 100 -ohm Speaker Field should be Chartered Institute 1000 In cf America 54 changed to ohms. case a magnetic Commercial cutter is used the grid resistor of all the Radio Institute 47 tubes should be reduced to give less bass Delson Radio Co. 54 and more intelligible speech. General Cement Mfg. Co. 57

Gold Shield Products . 54, 57 Hallicrafters, Inc...Inside Back Cover 'NEW CATALOG 11 -TUBE FREQUENCY Harrison Radio 52 MODULATION RECEIVER Henry Radio 53 OF SOUND AMPLIFYING SYSTEMS (Continued front paye 43) Hudson Specialties Company 55 AUDIOGRAPH Sound Systems represent the Hygrade Sylvania Corp. 4 latest in Public Address equipment -a com- AMPHENOL SOCKETS Korrol Mfg. Co. Nine Octal sockets 52 plete line plus pre -tested accessories. One Amphenol above chassis octal socket Lafayette Radio Co. 64 Une tuning eye indicator for eight prong socket Lancaster, Allwine & Rommel 54 NEW LOWER PRICES Lincoln Engineering School 47 Outstanding quality and performance at TUBES; RCA OR SIMILAR Mass. Radio School Three 6AC7 or 1862 tubes 49 prices that help you meet any competition. One 6SA7 McGee Radio 64 WRITE FOR YOUR FREE COPY One 68.17 McGraw -Hill Book Co 61 One 6116 Une 80 Meissner Manufacturing Co. 31 une 6SC7 Melville Aeronautical School ure 6SF5 AUDIOGRAPH of Radio 58 6F6G THE FIRST NAME IN SOUND One 6AD6 dual tuning indicator tube Murdock Mfg. Co 3 Nits Sink loslateries-tAierly e hanutaw a A',a nrwwS. M. MISCELLANEOUS PARTS National Radio Institute 1 sine CRL single pole double throw switch. for National Union Corp. 38 tone control Soldering terminals Nelson Co. 64 No. 16 copper wire, covered for wiring N.Y. -YMCA Schools 49 See text, or use One tuning unit three gang. Ohmite Manufacturing Co. 5 Browning unit rewound or one wholesale radio condenser part. No. K10332, three gang F/M Opportunity -Adlets 53 One K10327 antenna coil Peerless Sound & Radio Co. 50 One K10928 RF mixer coil Premax Products 53 One 1(10329 oscillator coil Solder, nuts, bolts. etc., and tuning indication Prentice -Hall (l holder and socket, Amphenol Radcraft Publications, Inc.: ..51, 54, 59 FAST SYLVANIA TUBES RCA Institutes 49 book - Three type 6AC7/1852 Radio Publications Standard Radio and .test 62 nt. thousands of parts for Radio. One type 6116 Radio -Television Institute Electrical and Electronic assem- One type 6SJ7 33 blies. Nsl wide service swith Teletype connections for speed 4a d One type 80 Radio & Television 57 dendability. Engineers. laboratory work- One type 6SA7 Radolek WRITE ers, rvicemen and Industrial plants ook Co. 35 everything in radio. Write One type 6SF5 Readrite TODAY torfaÌetteRfor One type 6SC7 Meter Works 41 One type 6F6G Schott Co., Walter L 54 One type 6AD6 tuning indicator. dual type Solar Manufacturing Co 64 0RADIO CORP. 12 6 wire cable for tuning inches eye indicator Sprague Products Co. 33 901 W.JACK SON, CHICAGO TRIMMERS 265 PEACHTREE ST. ATLANTA -CONDENSERS Sprayberry Academy of Radio 41 3 30 mmf. Three -25 or trimmers Supreme Instruments Corp 49 New, Technifax 53, 56 MANUAL ON G.E. RECEIVING Teleplex Company 47 UNIVERSAL Treasury Department 44 r4. TUBES Triplett Electric Instruments . A 24 -page technical manual on G.E. radio Co., Inside Front Cover Wrl,e REPLACEMENT receiving tubes, prepared to assist those U.S. Army Recruiting Induction who work or experiment with radio tubes Service 45 Catalot$ 4 'NM 7 and circuits, has been released by the Re- University Laboratories 64 newal Tube Sales Section of the General Vibroplex Co 64 NOME- Electric Radio Television and Electronics STUDYSTUDY COOURses X. L. Laboratories 47 IUeational honks, Dept., Bridgeport, Conn. The manual can ED ce slightly used. Sold. on be obtained by radio Servicemen, radio tech- (While every precaution is taken to insure milderie s. Money backlk esPCo r es guarantee. Cash paid for nicians, experimenters, radio amateurs, and accuracy, we cannot guarantee against the Co" de. possibility of an occasional change or omis- tails and illustrated - others technically interested in radio tubes page bargain catalog FREE. Write tda,l sion in the preparation of this index.) NELSON COMPANY. 300 Sherman. Dept. KSEO. Chiale by writing to the G.E. department.

64 Printed in the U.S.A. RADIO -CRAFT for OCTOBER, 1942

PIIIPARCIP CAI6

wanmakiroo INI Including Frequency Modulation-Television, etc. Inside Information for all Service- men- Aircraft Pilots, Students. 772 PAGES, 400 DIAGRAMS is complete -gives Authentic Principles & Practices in Con - Struction, Operation, Service & Repairs. Covers clearly and con- cisely Radio fundamentals - Ohm's Law-Physics of sound as . related to radio science- Measur- ing instruments -Power supply Resistors- Inductors Condens-- ers- Transformers and- examples Telephony-Receivers-Dia-- Broadcasting stations -Radio grams-Construction-Control systems -Loud speakers- Anten- nas -Auto Radio- Phonograph pickups -Public Address Systems -Aircraft & Marine Radio -Ra- dio Compass Beacons Auto- matic Radio Alarms- -Short- Wave -Coil Calculations- Testing- Cathode ray oscillographs- Static Elimination-Trouble Pointers Underwriter's standards -Units- &tables. REVIEW QUESTIONS -Ready Reference Index. COMPLETE PAY $1 A MO. To get this practical information in handy form -Fill in and MAIL COUPON TODAY. AUDEL Publishers- 49 West 23rd St., New York Mail AUDELS NEW RADIOMAN'S GUIDE for free examination. If O. K. I will send you $1 in 7 days; then remit $1 monthly until $4 is paid. Otherwise I will return it. Name _

Address _ Please Note: Occupation_ _ If you do not wish to mar this page by clipping coupon - send Reference letter or penny postcard instead.