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.
This circuit can be implemented with other operational amplifiers. The formulas for calculating the...
This circuit is from a 1953 publication, consisting of an AM radio with 3 germanium transistors that,...
The sensor of this circuit is a common silicon diode and it directly drives a small cooler with a...