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.
We found this circuit in a Popular Electronics of the 90s. The MOSFET can be of any type,...
In fact, the correct name would be a hearing aid amplifier. However, we use the name of the...
This circuit controls a relay causing it to open and close its contacts at a speed that depends on the...