Radio Broadcast (Nov 1926-Apr 1927)

A Single-Tube Receiver That Won't THE PANEL LAYOUT Of the one-tube non-radiating receiver is well balanced despite its simplicity. The single condenser dial, rheostat knob, filament switch, and jack are the only visible pieces of apparatus on the front of the panel Constructional Details for an Ideal Beginners7 Receiver Employing the "Ecfruamatic" Principle — Tickler Coil Coupling Is Automatically Varied as Condenser Knob Is Turned — Coil Data Are Presented By ZEH BOUCK IT IS the author's experience and belief that there exists a very definite demand for a "perfect" beginners' home-made receiver. Though the last few years have seen many receivers placed on the market which, ultimately, could be purchased far more cheaply than the average enthusiast could build a similar set, these receivers have by no means filled this particular bill. The amazing cheapness of these sets has generally been due to the inability to dispose of them at higher prices in competition with better equipment. The ideal beginners' receiver for home construction should comply with the following requirements: I. It should be a simple receiver, particularly in reference to wiring. There is nothing more discouraging to the incipient experimenter than the failure of his first attempt — and ninety per cent, of these unhappy trials are due to wiring complications. Consideration of this recommends a one-tube receiver for the fan's first efforts. The receiver also should present no great mechanical complications (though this is a less important consideration because the radio beginner is often an experienced mechanic), which postulates the possibility of obtaining the various coils and sundry parts especiallyprepared for use in the circuit he will employ. And with final but consistent simplicity, the set should be easily tuned, a factor that favors one-dial control. 2. The receiver should be inexpensive to construct — a condition that runs more or less hand-in-hand with the idea of simplicity. 3. The receiver must be non-oscillating. An oscillating single-tube set (and most multi-tube sets for that matter) radiates interfering signals, which are annoying at all times, yet rendered more so when the offending set is operated by a beginner. 4. The receiver should be a permanent one. It should exhibit such qualities of selectivity and sensitivity that it need never be discarded. When the enthusiast desires more elaborate equipment, he should need only to add an audio amplifier (and perhaps a stage of r.f., if he craves dx) to have a thoroughly satisfactory receiver. The once very popular three-circuit regenera • The Facts About This Receiver tive tuner filled these requirements with the exception of that very important commandment — "Thou shalt not oscillate"; and these sets were not always so easy to tune. Until recently, the three-circuit tuner was indubitably the most selective and sensitive of one-tube receivers, and it gained wide popularity before propaganda exposed the iniquities of its oscillations. In the last two years, various reflex and other circuits have been offered as substitutes for the threeand single-circuit arrangements. However, while these substitutes were non-radiating, they fell down on one or more of the other points outlined above, and never attained the popularity of the receiver whose place they would usurp. WILL NOT RADIATE THE beginners' receiver we have undertaken to describe fulfills every stipulation, above outlined, imposed upon the ideal set. This receiver is nothing more than a three-circuit regenerative tuner that will not radiate, and it is controlled by a single dial (the coupling between the tuning and tickler controls being automatically varied). Regeneration is automatically maintained at close to the optimum degree over the entire tuning range (the optimum degree being that amount of feedback that will give maximum signal strength and selectivity without distor ?iame of Receiver King "Equamatic." Type of circuit Single-tube regenerative receiver. dumber of Tubes One uv-199; other types of tubes may be used. Frequency range 545 kc. to 1 500 kc. (200 to 550 meters). This receiver is excellent for local reception. It uses regeneration but if correctly adjusted, cannot oscillate and cause interference. The amount of regeneration is automatically controlled by a movable coil mounted on the shaft of the condenser. In this way the circuit is maintained at a point of high sensitivity throughout the entire broadcast band. It is an ideal singlecontrol receiver.