Radio age (Jan-Dec 1925)

RADIO AGE for January, 1925 The Magazine of the Hour 11 FIG. 1 SCHEMATIC CIRCUIT D1/>GR*M FOUR TUBS NEUTRODYNE REFLEjC RECEIVER. Simplifying Reception With A REFLEXED Neutrodyne WITH the ever increasing demand for a receiver that will not only reach out to far distant points, but which will bring in the distant stations with sufficient volume to operate a loud speaker, popularity has shifted around from the single circuit regenerative receiver of a few years ago to the super-regenerative set and then to the multitube radio fiequency circuits, and so on down the line to the more recently improved circuits. After reflexing most of last Winter, the neutrodyne circuit gradually took its place in the public favor and it is perhaps the most popular receiver today among broadcast fans. But as time goes on, we find that each has its limits. While the super-heterodyne great possibilities for vanced fan, it becomes too expensive with its maze of tubes and other equipment and is beyond the reach of the average fan, so he naturally looks to less expensive equipment that will produce exploring qualities and volume sufficient to boast about with the best of them. The set described in this article may be just what the fan has been looking for, as it was constructed with the desire to get the best A Four-Tube Receiver That Gives Regular Six-Tube Volume; Can Be Built at Small Cost receiver shows the more ad By H. FRANK HOPKINS A. E. E. results possible without great complication and for the least possible investment, combining the popular neutrodyne circuit with the reflex amplifying features. Simple Problem In describing the how and why of the set, let us take the two features separately, so as to better understand why each circuit was designed and how it will function as a single unit. Then it will be a simple problem to put the two circuits together and understand the principle THE PARTS FOR THIS SET 1 — Fixed Mica condenser. .0015 mf. — F 1 — Fixed Mica condenser. .002 mf. — H 1 — Grid leak condenser .00025 mf. \ ff 1 — Grid leak resistance 1 megohm / ** 4 — Vacuum tube sockets. — M1.M2.M3, M4 2 — Neutralizing condensers. Variable — •N, Nl 3 — Radio frequency transformers^*Rl, R2, R3 2 — Audio frequency amplifying transformers. Ratio 5 or 6 to 1 — T, Tl. 1 — Cutoff jack (If required). — X 1 — Phone jack. — Y 7 — Binding posts. — A, Al, A2, B, Bl, B2, G 1 — Composition Panel. 1 — Composition Shelf. 1 — Cabinet. (If required). Brass screws, nuts, wire, solder, terminals and miscellaneous raw materials used in the construction of the parts described in this article. 1 — Loop' aerial. (If required). 3 — Variable condensers. — .0005 mf. CI, C2, C3 3 — Composition dials for condensers. — CD1, CD2, CD3 1 — Tube control rheostat. — 9 to 16 Ohms.— D 1 — Composition dial for rheostat. — DD 1 — Fixed Mica condenser. — .001 mf. E •Construction of articles marked with asterisk is detailed in this account. They can be purchased from any reliable dealer if desired. of the set described. We will start with the neutrodyne circuit, which is of the tuned radio frequency type. A radio frequency circuit amplifies the incoming signal before it reaches the detector tube, much the same as a regenerative type of circuit amplifies the signal after it has been passed through the detector tube. This is accomplished by inserting one or more electron tubes between the tuning element and the detector tube, which amplifies the weak signal currents received on the antenna and passed through the tuning element, before it reaches the detector tube, the same as a regenerative circuit amplifies them by regeneration. The only exception is that the circuit is free from the objectionable oscillation or regeneration which is the cause of howls and squeals in the set when regeneration is pushed beyond its critical stage. By connecting the output side of each radio frequency tube to a tuned circuit, great selectivity is obtained and interference is eliminated. The neutralizing or balancing of the regenerative effect makes possible a simplified means of tuning, eliminates oscillation noises and reproduces better. (Turn the page)