Radio Digest (July 1924-Apr 1925)

'fitly 19, 1924 RADIO DIGES T^ -Illustrated England's New Unidyne Radio Receiver Part II — Amplifier Hook-Up and Two-Tube Set By Harry J. Marx THE introduction of the new unidyne circuit in conjunction -with its use of the four electrode tube to the Radiophans of England, has been the direct cause of considerable controversy between the various English magazines on the subject of the practicability of the scheme and its relative merits. Since both inventors, Mr. G. V. Dowding and type — about three to one. The one used In the English circuit has 4500 turns of 40 gauge enameled wire in the primary and 11,000 turns of the same wire in the secondary winding and is equivalent to about 2% to 1 ratio. The core should be made of good laminated steel about 5 mils in thickness. Each lamination should be shellaced so as to reduce eddy current Output (j Figure 3 Mr. K. D. Rogers, are members of the staff of the English magazine Popular Wireless "Weekly, which is presenting the details and developments to the fans, competing publications have been running series of articles and comments by recognized authorities on the subject. Although the invention of the circuit has been disparaged and even claimed old stuff, yet all appear to have room for conviction in order to be on the safe side. Then again, tests by other authorities indicate that tube for tube the circuit compares favorably with any using B batteries. It must be remembered that the claim is the elimination of the plate batteries. As has been said, there undoubtedly will be considerabe experimental development of new circuits in connection with this tube. In the next article of this series, a Radio frequency amplifier will be presented. English fans are able to devote considerable time to experimenting with the circuit due to their opportunity of purchasing these tubes. In this country we are more or less compelled to look on and wait patiently, although efforts are being made to either import the tubes from England or to get American manufacturers to produce them. It may be anticipated that the success of this circuit will immediately lead to the development of a lamp socket device that will automatically take care of the antenna, ground, and filament battery connections. This would be applicable to sets of any number tubes. Audio Frequency Amplifier The first impression appeared to be that the tube could only be used in detector circuits, but experimentation has proven numerous obvious advantages as amplifiers. Figure 3 presents the hookup diagram of a single-tube audio frequency amplifier. This amplifier circuit can be followed for as many stages as desired. There are a number of points to be emphasized in connection with this amplifier circuit. The audio frequency transformer used must be of the low ratio losses to a minimum. A .001 microfarad condenser is inserted in the grid return side of the secondary of the transformer. This is done so as to avoid putting too much of a negative potential on the outer grid. The inner grid is the one connected to the positive filament terminal. A two megohm grid leak is connected across the blocking condenser. Two-Tube Circuit Since a further development in the form of a two-tube circuit showed some slight variations from the original as presented in the last article, it is shown in Figure mn-iTi Sets a NewCrystal Standard Star-ite •'Loud All Over" Crystals are distinctly a new, big step in the Kadio World. The present Kadio Era began with the crystal set which fell behind because the more important part of the set — the crystal — had fallen in quality due to cheapening of the product. Star-ite is doing much to re-standardize crystal set performance and with the coming of re-broadcasting, when your crystal set will enable you to hear concerts and speeches from New York and Washington you will not hesitate to pay even $5.00 for a crystal like Star-ite. Sold by all live, wide-awake dealers who are fast stocking Star-ite, but should your dealer not be able to supply you send $1.00 to us for one of these great crystals, sent post-paid and your $1.00 back if you are not satisfied. Dealers please write for our special offer. They're like 1 Buckin' i|J Bronchos iS, —YOU CANT BREAK 'EM A new Walnart Socket free for every one that breaks or fails in any way! You write your own ticket. Leading set manufacturers use them because they don't break and have lower dielectric losses than bakelite, fibre or composition sockets. WALNART SENSIBLE SOCKETS Approved by Radio News Laboratories. Over half a million doing duty. Features: Bakelite insulation;' heavy, genuine phosphor bronze contact springs; low resistance; high elasticity (to insure perfect contacts). Nickel or dull black enamel finish. For base or panel mounting. Unconditionally guaranteed by world's largest producer of unbreakable sockets. Trial will convince. Ask your dealer first, please. "Makers of good /#,=0»v goods only" tIC MFG. CO. WALNART E Sept. 444 Chicago i. This hook-up has the detector and one stage of audio frequency amplification with a switch to permit the use of the detector stage only if desired. The only real change from the original circuit is the elimination of the high ratio transformer which was used to add a second regenerative feature. It will be recalled that in describing this feedback it was for tuning but the vernier type is recommended. A variable grid leak is an important requirement for the outer grid circuit of the first tube. The same recommendations as given for the transformer in the amplifier unit described above, apply for the audio frequency transformer used in this circuit. One rheostat is used for the Q Output Q Figure 4 anticipated that the difficulty of control would necessitate the elimination of this second form of regeneration. This circuit uses two honeycomb coils with a double coil mount. The main coil can be a 50 or 75 turn coil depending on the length of the antenna. Although a 100 turn coil is indicated for the tickler, it will be found advisable in some cases to increase the number of turns to 125. A .0005 mfd. variable condenser is used S. HAMMER RADIO CO. 303 Atkins Ave., Brooklyn, N. Y. TUBE COCKADAY 6.70 80 80 *3 Pour Circuit Tuner Precision Coil $ *'!J2 Amsco 26 PI. Condenser Dubilier .00025 Fixed Condenser Amplex Grid Denser Bradleyleak ]■'» Melco Sockets '■*■> Pacent Double Jack "> Pacent Single Jack ••>•} Amertran Transformers Jc Amsco Switch Lever 25 Amsco Kheostat, 6 ohms 85 2 Amsco Rheostats. 20 ohms 2.00 7 Switch Points, 2 Switch Stops 15 1 Dubilier .0005 .40 1 Bradleyohm '•«? 1 Panel 2.25 1 Baseboard 60 Wire, Diagram, etc.. SPECIAL KIT PRICE Wired Complete in Mahogany 4C^ A A Cabinet «pDO.UU The Above Parts Can Be Bought Separately $3500 sIantduabed SUPERDYNE I — Superdyne Coupler 2 — 23Plate Variable Condensers. I—Variable Grid-Leak. I— .00025 mfd. Fixed Condenser. 3 — Rheostats. 4 — V. T. Sockets. 2 — Acme Audio Transformers KNOCKDOWN COMPLETE PARTS I — Single Circuit Jack. I — Double Circuit Jack. 7x24 in. Panel, Drilled. 7x24 in. Baseboard. Bus Wires, Spaghetti and Diagram, etc. PRICE ^ SP" i •D\) Wired" Complete in $4X OO Genuine Mahogany Cabinet «p-««J.w/ Orders over $5.00 will be shipped prepaid. Money orders or C. 0. D. Not insured unless insurance charges included. Write for Price List control of the filament lighting of both tubes. The blocking condenser (.001 mfd.) with the two megohm grid leak is inserted in the grid return of the secondary circuit of the amplifier stage. (In the next article a Radio frequency amplifier will be described. — Editor's Note.) 2&ABIO AjPjPAMATHJS THE MOST STURDY of the New Type LOW LOSS CONDENSERS flUELL MANUFACTURING QO. Z977 Cottage Grove Ave., CHICAGO A^:2rOO,ooo.oo Company d'S /j/* Stands Squarely Back Ml* y Every ^ Phone (Plus a /cut cents postage Send No Monev Order by mail if your dealer cannot supply you and we will ship immediately. Written 5-day money back Guarantee with each «el. Our next year's production schedule of two million phones UNDOUBTEDLY places us as the Worlds Largest Headset Makers THE TOWER MFG. CO. 98 Brookline Ave. Boston Mass. WORLDS GREATEST HEADSET VALUE Five-Day Money-Back Guarantee 11 Not Fully Satisfied. 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