This circuit is suggested by General Electric in 1966 documentation. The Triac must match the engine. The resistors depend on the triac's sensitivity to firing.
Found in a 1990s William Sheets, this automatic gain control for audio amplifiers uses...
The power supply shown can supply voltages of approximately 0 V to 12 V with a maximum current of 4.5 A,...
The consumption of this circuit in the standby condition is only 1 uA. The circuit must be...