English: An early vacuum tube regenerative radio receiver from 1922. The regenerative receiver, invented by Edwin Armstrong in 1913, was widely used during the "radio craze" of the early 1920s to listen to the first radio broadcasts, until it was superseded by Neutrodyne and superheterodyne receivers around 1930. This set is made in two sections: the tuner section (left) and the amplifier section (right) which contains the three triode tubes: one regenerative detector followed by two audio amplifier stages which amplified the audio signal so it could drive a horn loudspeaker. Three holes in the front panel allow the operator to see the filaments glowing to make sure the tubes are operating. The set uses the common Armstrong or "tickler" circuit, in which some of the signal from the plate circuit of the detector tube is fed back into the grid (input) circuit using two magnetically coupled coils of wire, to increase the gain and selectivity of the receiver. This is accomplished by the "honeycomb coil vario-coupler" mounted on the top of the receiver. This consists of two coils of wire; one is part of the input en:tuned circuit connected to the grid, and the other is the "tickler" coil attached to the plate circuit. The coils are mounted on hinges so they can be swung closer or further away, to adjust the coupling and thus the amount of feedback. The two large knobs on the lefthand section tuned the primary and secondary of the inductively coupled tuned circuit. The three knobs of the righhand section controlled filament current to the three tubes.
Caption: Receiving set in which three compact inductance coils, adjustably mounted on top of cabinet, permit of variable coupling and regenerative action. The unit at right is the vacuum tube detector and two-stage amplifier