A Practical Neutrodne Receiver by ALLAN T

Radio News for January, 1924 899 A Practical Neutrodne Receiver By ALLAN T. HANSCOM This article explains the action of the neutrodyne circuit in a manner which can be grasped by the novice. Its formation is described stage by stage, followed by complete constructional details for the building of a receiver of this type. on which the secondary coil is wound. It is difficult to buy one tube to fit inside another in this manner, but it can be overcome by sawing a piece of tube /" wide length- wise from the same tubing. Then when it is wound, the wire will draw it to a smaller diameter whereupon it may be slid into place inside the full sized tube. It is very important that these transformers be mounted

Insulated wire fig. 2 /w/sted together A One -Stage Radio Frequency Amplifier and a Non- Regenerative Detector, the Respective Secondary Circuits of Which Are Tuned by Means of Variable Condensers.

IT is unfortunate that so many good cir- the neutrodyne after we add the neutralizing cuits are labeled with such formidable condensers which will be considered later. titles. The name "neutrodyne" is usu- In Fig. 3, there are two stages of radio ally enough to scare the average radio frequency amplification and the detector, fan. A neutrodyne circuit, as commer- each stage being tuned by a variable conden- cially developed, is, however, a great deal ser in the grid circuit. This circuit would more simple to understand than the regen- give wonderful results if it were not for the erative or reflex circuit. internal capacity coupling between the plate and the grid circuit of each radio frequency Bus wire Meta/ frbe tube. This internal capacity is neutralized by the combination of capacity and inductance; the inductance being the windings of the air core radio frequency transformers R. fig. d The capacity necessary for the average vacuum tube is very small and is usually Several Ways of Making the Neutralizing Capac- about equal to two circular plates /" in ities. diameter separated by 3/32 of an inch. This is only approximate and the proper value may at least 6" apart and at such an angle that easily be found. Other types of condensers a line drawn at right angles to the axis at for this purpose are shown in Fig. 4. the end of the winding does not intersect The radio frequency transformers can be the winding of the adjoining transformer. made by winding 80 turns of wire on 3" tubes See Fig. 6. Note the relative position of Two -Circuit Non -Regenerative Receiver Having a Tuned Secondary Circuit. with a tap taken off at the 20th turn. It is primary and secondary windings.

The average fan is not interested in the higher mathematics of a circuit but he does like to know the size of the parts so that he can put one together to obtain results. Fig. 1 represents a simple type of non -regenerative hook -up. By varying the condenser the natural wave -length of the set can be altered. This is exactly the diagram of the first stage of the neutrodyne. In Fig. 2, another stage exactly like the first has been added. In this case the first tube acts as a radio frequency amplifier and the second tube as a detector. fig 3 It will be noticed that the plate circuit of Two Stages of Tuned Radio Frequency Amplification and Detector. These Circuits Are Free to the first tube is not tuned, but that the grid Oscillate Due to Feed Back Through the Internal Capacity of the Tubes. circuit of the second tube, as well as the grid circuit of the first tube, are both tuned and preferable to use cardboard because it is an NEUTRALIZING CONDENSERS in reality make the two stage filter through advantage to have a close coupling between Since the variable condensers used are con- which the incoming signal must pass. this coil and the primary, which is inserted nected between the grid and the filament, it Fig. 3 represents three stages exactly as inside. The primary consists of 20 turns of is possible to connect the grid to the fixed outlined above and this is the scheme of wire on a tube which will just clear the tube plates and then mount the other small mov- able plate on the back insulated portion of .002 M.f the condenser. By this means a very small change of capacity can be made in the neu- Vh0rIe5 tralizing circuit. See Fig. 7. t meg0lim After the proper value of this capacity is I found, it need never be disturbed unless tubes 1.1222 are changed. It is likewise advantageous to + 5in shield the set, although it is absolutely im- M.f possible to make this set oscillate if it is .005 properly constructed. To find the proper value of the neutralizing condensers it is necessary to tune the set -B to a very powerful signal. The Flewelling .0005 A "screamer" makes an excellent oscillator for o this case. A paper may be inserted in the socket to cover the filament connections but fig. 8 leaving the plate and the grid free. Then the tube is inserted and the signal is still Complete Circuit Diagram of a Neutrodyne Receiver Having Two Stages of Tuned Radio Frequency heard. Amplification and Detector. The Circuit is Kept from Oscillating by Means of Small Condensers Which Neutralize the Capacity of the Tubes (Continued on page 914)

www.americanradiohistory.com 914 Radio News for January, 1924

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upreme sharply with the single and multiple turn upreme switches of the tuner. This is in effect an LOUD SPEAKER. air core transformer coupled amplifier and HEAD SETS is equally effective over the entire range of the tuner. The resultant complete circuit is shown in Fig. 2. ADAPTED TO SINGLE CIRCUIT TUNERS For single circuit tuners the amplifier shown in Fig. 3 has proven very effective. As in the first case the output of the amplifier is connected to the input of the tuner. When a receiver such as an R.C. is used where the tuning elements are in one cabinet and the tubes in another, busses connect the two. The post marked "G" in Fig. 3 con- nects to the post marked "Grid" on the tuner. When the tuner has no outside connections, such as in an Aeriola Senior, a separate wire is run from the grid lead inside the tuner to "G ". On some sets it is necessary to re- move the grid leak when it is connected around the grid condenser instead of to the filament. This arrangement makes a tuned imped- ence coupling between the first two tubes

No extra Batteries The Head Set required. that is Always Ahead Finely and as accurately made as a high -priced watch and fig. 4 there you have the whole A Regenerative Circuit Employing One Stage story of Tuned Radio Frequency Amplification to In- crease Selectivity and Distance and to Prevent Re- of BERWICK Headset su- At LAST. radiation. premacy. and is shown below with the detector in Fig. 4. Every BERWICK Headset A Perfect Loud It is not necessary to install this apparatus is perfectly matched for tone Speaker With a in a cabinet, as very excellent table mounted instruments are available. The parts used - TESTED in ACTUAL MICROMETER are : 1 Variometer use for clarity and reproduc- Adjuster and Tuner 1 Potentiometer tivity, and sold with an uncon- 1 Rheostat This remarkably powerful special Unit with the marvelous MICROMETER Adjuster, gives 1 Socket ditional guarantee, or your you -with just the turn of a little knob -maxi- 1 .00025 M.F. Fixed Condenser mum clearness, and a ready ability to meet 1 Amplifier Tube. money back. every individual condition as easily, as simply as you would adjust a pair of opera glasses to I feel confident that any reader who will suit your own vision. spend the few dollars necessary to install 2200 ohms-$5.00 FIBRE HORN, non -resonant, non -breakable, either of the amplifiers will be well paid by damp- proof. TWICE TESTED in actual radio the in his I know 3000 ohms -$6,00 reception before it reaches your hands. improvement set and will SEALED to prevent tampering. UNCON- be blessed by his neighbors. DITIONALLY GUARANTEED FOR A BUY A BERWICK Su- YEAR against any defects. t,.1,,,11,111111111111,111,,,,,,,,,,n,11.,m11M1,,,,,,,,1,1,11,,,,11,M7M,.,1,7M. ,,,M1,11111111, Here indeed is the Loud Speaker that brings preme Headset TODAY you everything you want to hear - clearly, - faithfully -from the most delicate shadings of A Practical Neutrodvne and note the difference. the human voice to the rich, full blare of a great brass band. É Receiver At All Reliable Dealers Convince Yourself- (Continued from page 899) =- Get Yours TODAY. Sold Through Jobbers If your dealer cannot supply you, get in touch with us direct. This is done for the first stage and second DEALERS: Ask your jobbers for information. stage separately, adjusting each condenser TRIANGLE until the signal is no longer heard. I have found it possible to adjust these condensers Electro Trading Co., Inca TRIANGLE without going to this trouble by simply set- Manufacturers Co., Inc. ting them at the greatest capacity which 632 -634 Broadway, New York Electro Trading would not cause the set to go into an oscillat- Manufacturers New York Chicago Minneapolis ing condition. The action of these conden- _ 632 -634 Broadway, New York sers is similar to that of the potentiometer San Francisco in the original radio frequency circuit with

www.americanradiohistory.com 'PI6 Radio News for January, 1924

Top- 20turns, OW! Tube arawn -together YOU CAN LEARN ÉLECTRAD NEWSPAPER PRODUCTS WORK Experienced Editor Will Teach You The NEW DIODE How to Become a A revelation for all reflex r Reporter work. Replaces the crystal Primary 20 /eras and overcomes all former 1. ,I difficulties of reflex cir- 3 FASCINATING WORK- -GOOD PAY cuits. Requires no adjust- 5ecoadory fig 5 ments for change of wave lengths. Gives you the Constructional Details of the Primary and Sec- Only a Few Months' Work Required clear reproductions of a ondary Coils of the Neutroformers crystal with the sturdi- To Qualify You for a ness and reliability of a tube. No "B" batteries the exception of the fact that they need never Better Position required. Operates on less than % ampere from sin- he changed for different wave -lengths or sig- 2 gle dry cell. Easily adapt- nal strengths. The complete circuit of the Regular reporters earn from $40 to $125 ed to Fria and all other neutrodyne receiver is shown in Fig. 8. a week. Good deskmen on a daily paper Socket 50c circuits. If this set is constructed properly it will are paid from $60 to $100 a week. A give results in clearness and sharpness which "Star" Reporter can command his own are superior to any other type of set which salary. Hundreds of ambitious men and has come to my attention. The volume is women enhance their income materially by not extremely loud but audio frequency can corresponding for newspapers or writing for be added in the usual manner. magazines in their spare time. As seen, there are two stages of radio frequency amplification and a detector. The We Will. Teach You at Home radio frequency transformers, unlike the iron We can develop your talent for writing core type, have untuned primary circuits and and lead you into this well paying profes- tuned secondary circuits. The tuning sys- sion. Our Practical Course in Journalism tem likewise has an untuned antenna circuit was personally prepared by Henry J. Brock - and a tuned secondary circuit. All adjust- meyer, Assistant City Editor of the New The NEW VARIOHM ments are made by the three variable con- York Evening Post. Mr. Brockmeyer has densers and maximum volume of any one trained hundreds of men and women, many The latest invention in variable grid leaks. Each movement gives a defi- signal will not be obtained until these three of whom have, under his guidance, developed nite new resistance. Positively does into front rank reporters or feature writers. the work where others fail. A gradual Mr. Brockmeyer's course will teach you resistance over entire range of % to what it would take years of actual news- 10 megohms. Eliminates circuit noises, is moisture proof and non -microphonic. paper work to learn. It consists of six Ideal for use in Miloplex and other cir- comprehensive lessons just brimful of every- cuits. Guaranteed. thing a reporter must learn. The following are only a few of the subjects covered. Starting in Journalism. What is a News- paper? What is News? Start and Finish 75c of a News Story. Technical Terms. The Type Point System. Styles of Type, Proof It Is Important That the Radio Frequency Trans- formers Be Mounted as Shown in the Above Reading. Capitalization and Punctuation. Illustration. A Late Fire Bulletin. Court Stories. Libel Laws, Copyright. Hints to Reporters. Per- The LEAD-IN sonal Conduct. Re- Writing and Condensing circuits are tuned to the same values. This Stories. Fits right under closed should Paragraphs and Short Items. Good window. Can be bent be kept in mind when operating a and Bad Styles. Broadening the Vocabu- into any shape to fit neutrodyne receiver. The simplest way for ledges. Covered lary. Aids to Good Style. Special Stories. with hunting stations on various wave -lengths is Suggestions for Stories. Rhetoric. Prepar- fire -proof insulating ma- to start at zero on all and terial which prevents dials slowly work ing Your Story. Don'ts for Writers. Office grounding of circuits on towards 180 degrees moving the right hand Organization. Syndicated Matter. Business wet window sills. Takes condenser dial a few degrees first, followed Office. Mechanical Department. Hints for the place of ungainly by a corresponding adjustment porcelain tubes a n d of the second Headline Writers. The Make -Up. The holes in the window and first dials. Keep progressing until a Country Correspondent, etc., etc. sash. Always presents a station is heard. At this point, a fine adjust- neat appearance. ment of all three dials will be necessary to This Complete Course For $10 obtain maximum volume. The price for the entire course is only If it is desired to add the regenerative $10, and entitles the student to full consult- feature to this receiver a variometer should ing services which are directed by Mr. 40c be connected in series with the plate of the Brockmeyer personally, including any ques- detector tube and the head-phones. This tions in connection with journalistic work. variometer will allow as well the placing of All products at your dealers, otherwise the detector circuit in an oscillating con- Five Days' Trial send purchase price and you will dition for the reception of C.W. signals and Just pin a check, money be supplied postpaid. order or ten dol- without a chance of re- radiation. lar bill to the coupon below and mail. Then take five days after the course arrives to Small condenser plate decide whether you want to keep it. If not, Write for FREE Cockaday -Diode return it at our expense and your money Reflex Circuit. will be immediately refunded. Or Write For Free Circular "R" THE PRESS GUILD, Inc., 66 -R West Broadway, N. Y. r r THE PRESS GUILD, Inc., 66.R -West Broadway, New York City ELECTRAD, Inc 1 Enclosed find $10 for which you are to ship ma at once, prepaid, Henry J. Brockmeyer's complete course in 428 -H Broadway Practical Journalism with the distinct understanding that if I return the course in five days my full $10 will New York be refunded and no questions asked. fig. 7 (Name) (Address) A Small Metal Plate Mounted. as Shown Well Serves the Purpose as the Neutralizing Capacity. (City) (State)