This Vox or sound activated relay was found in an American documentation from 1975. Equivalent transistors can be used, and the SCR can be a TIC106. The relay is according to the supply voltage.
This good amplifier with output in complementary symmetry is from an old publication, and modern...
The integrated circuit used is a voltage reference from Motorola. This configuration was obtained in...
This circuit was obtained in a magazine Hands On-Electronics from June 1987. It is a circuit that...