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.
The time constant for this circuit found in a 1973 publication is given by R and C. The shot is...
Used with old projector films, this circuit found in Signalite documentation from the 1980s,...
This circuit generates damped sounds imitating a drum or other percussion instrument with...