One Valve Radio Regeneration Coil

Reaction/regeneration occurs when we feed a tiny amount of the amplified signal from the output of the valve back to the input of the valve for a second time amplification. It enables the valve to amplify the signal two to three times thereby making it very cost-effective. Regeneration is a very difficult balancing act to achieve, especially for hobbyists, and first-time constructors, because if you feed too much of the signal back, then you get oscillation type squealing noises, on the other hand, too little signal fed back does nothing. Even worse, the amount of feedback required varies depending upon the signal strength of the original signal. Hence, I have created this "fixed" type regeneration that operates on its own.

The regeneration apparatus consists of a pair of open-ended coils. The coil wire is the same as that used for the tank circuit; it is the familiar CAT5e solid core. We use a standard BIC pen casing, and require 10 turns of the wire secured by tape. I am using clear tape so you can see the wire. Leave exactly 1 cm distance and wind another coil in the same direction that is also 10 turns. The coils are not connected. Only one end of the coil connects to the circuit whilst the other end remains unconnected (floating). One end of one coil connects to the input terminal where the antenna connects, whilst one end of the other coil connects to the output after the 0.47 µF capacitor. We require an extremely light interaction between these two coils to allow an extremely tiny amount of signal for feeding back from the output to the input. I secured the "fixed regeneration" coil vertically by using a blob of clear glue from hot melt glue gun. As you can see, the pen casing is hollow, and enables you to slide an iron nail into it. If one introduces a metal such as iron, the interaction between the coils increases thereby increasing the feedback signal. This is a very simple way for beginners to experiment with regeneration.

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