This circuit is from an American documentation from 1975. The single junction transistors can be 2N2646 and the signal must be applied to the input of a good amplifier.
This amplifier was published in the July 1961 Radio Electronics magazine. It announced the release of...
This circuit was found in a 1967 Electronics World. SCRs are according the controller load,...
This sophisticated circuit using a liquid crystal display was found in Radio Electronics from the...