We found this circuit in the July 1994 Radio Electronics magazine. The circuit uses a general-purpose transistor, and the power supply can be up to 12 V depending on the relay.
This adjustable source was found in a 1979 documentation, but all components are still common...
This temperature control was found in General Electric documentation from the 90's. The circuit uses...
This SCR circuit was found in an American 1980s documentation. The circuit is still current,...