Described in the December 1969 Radio Electronics magazine, this circuit is intended to supply the previous circuit. The circuit is not isolated from the power grid.
In fact, this is the circuit also known as “vox”, that is, a relay triggered by sound. This...
This circuit was obtained from an English magazine from 1976. The signal from the circuit should be...
This receiver for listening on the phone was found in a Japanese magazine in 1967. The circuit uses...