This circuit was obtained from a 1967 GE SCR manual. The SCRs must be rated for the wattage of the controlled heating element.
The circuit shown is from an old European publication. In it we have the way to activate a relay...
We found this circuit in a European publication from the 1990s. Transistors are still common types...
This circuit was found in an American documentation and can be added to common amplifiers of any...