This circuit was found in the July 1994 issue of Electronics Now magazine. The relay can be rated at up to 12 V and 100 mA. The transistor is a general purpose transistor.
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,...