This circuit was found in an old GE SCR manual. The SCR must be in accordance with the relay and transformer as well.
This circuit can also use other series operational amplifiers such as MC33172, MC33174, MC35171,...
Found in Popular Electronics from the 90s, this circuit mutes a scanner's speaker in the absence of a...
This circuit was found in General Electric documentation from 1965. The transistors are from that...