Radio Digest (July 1924-Apr 1925)

August 2, 1924 RADIO DICES T— Illustrated n 30 Minute A-B-C Lessons for Radio Beginners Chapter XIX, Part 1 — What Is Doing in Complicated Circuits By P. E. Edelman IN THIS series of articles the story of Radio is told in so simple a manner that the uninitiated can follow theory and practice whether or not he knows anything1 about electricity or its application to Radiocasting' and reception. The series consists of twenty-five chapters, of which the five next will he: Chapter XX — How Tar Can I Hear? Chapter XXI — Choosing a Radio outfit. Chapter XXII — Making Your Own Radio. Chapter XXIII — Fixing Tip the Radio Set. Chapter XXIV — The Radiocast listener's Brief History. Stabilizing Radio Frequency Circuits Radio frequency amplifying circuits require some means of stabilizing. Several ways in which this is done in modern circuits will now be shown. Some forms require an adjustment. Thus in Figure T HE aim of the designers for listenapparatus is to please the Radio cast listener. The general aims are simplify operation, economize initial Figure 185 cost and upkeep, extend the range of reception, increase selectivity, mitigate interference, reduce distortion, and improve appearance. Figure 189 184, grid current is initially passed between the grid and filament for stabilizing purposes. This is accomplished by means of a potentiometer. Sometimes a small condenser C is used to by pass the lesistance of the potentiometer to Radio Figure 193 current, sistance Figure 190 Figure 185 shows series re Figure one of the circuits to limit obtained Reflex (Latoue. Ee-Cesu^n) Figure 186 Many circuits pointed out as single tube arrangements can have Radio amplification added ahead or audio amplification Figure 187 aftc-rvrards to make the usual forms of multi-tube machines. PEVEE5EO SOPERPYNE Figure 191 the current and prevent oscillations building up. 186 shows how stabilization is without the potentiometer in some reflex circuits. An audio input circuit feeds back into the first tube from the plate circuit of the second tube. The transformer used for this audio input into the first plate has capacity in each winding and capacity between its windings — condenser effect. In such a circuit, the potential distribution and coupling of proper value can stabilize the Radio amplifier against self oscillation. Some circuits use a draw-off circuit or wavetrap number 1, Figure 187 to take energy from the circuit and stabilize operation. Figures 188 and 189 are examples of coupling stabilization. Sometimes two or more stabilizing means are combined. Figure 190 shows a very stable form of circuit, automatic in operation. (Continuned on page 16) A^ocooo.oo Company 5 i|£ Stands Squarely Back iJV of Every^Phone GREATEST H EADSET VALUE (Plus a /cut cents postage Send No Money Order by mail if your dealer cannot supply you and we will ship immediately. Written 5-day money back Guarantee with each set. Our next year'* production schedule of two million phones UNDOUBTEDLY places us as the Worlds Largest Headset Makers THE TOWER MFGiXO. 98 Brookline Ave. Boston Mass. Five-Day Money-Back Guarantee If Not Fully Satisfied. We Guarantee the Scientific to be 1 . One of the finest phones on Ihe market regardless of price. 2. The most comfortable -weight only 8 oz. 3. Perfect tone mates. 4. Made of ttandard double pole construction (no single pole nonsense to save expense.) 5. Made of the best materials money can buy. Powerful magnets, genuine tinsel cords, aluminum cases. Manufactured under ideal working conditions. THE LOW LOSS GENERAL INSTRUMENT CORPORATION GROUNDED ROTOR CONDENSER STARTLING SUMMER TESTS Actual tests have proved that dielectric losses have been practically eliminated. This means new power for your receiving set — a special consideration in the summer. Small wonder that laboratories use this ingenious low loss condenser. RECOMMENDED BY A PROFESSOR A Professor of Radio Engineering in instructing his pupils said that" to attain results such as no other variable condenser will produce you must use the Low Loss General Instrument Grounded Rotor condenser. HEAR THE DIFFERENCE The proof is very simple. If you are really after greater selectivity, more distance and a remarkable increase in volume replace your old condenser with the New Low Loss General Instrument Grounded Rotor Condenser. You will hear the difference. Minimum Maximum Type 4631 11 Plate 5 MMFD. .00025 MFD $4.50 Type 46A 13 Plate 6 MMFD. .0003 MFD 4.50 Type 46D 21 Plate 9 MMFD. .0005 MFD 5.00 Type 46F 43 Plate 15 MMFD. .001 MFD 5.50 AT YOUR DEALER Otherwise send purchase price direct to us and you will be supplied. General Instrument Corp. 423 Broome Street NEW YORK CITY rin