This circuit from General Electric was found in a 1967 documentation. The SCR is of the time, as are the transistors, but equivalents can be used.
In this circuit, a load is fed only when the voltage reaches a certain value. Currents of up to a...
This circuit was found in an Argentine publication from the 1970s. The circuit can be assembled with...
This LC step with only one general-purpose PNP transistor, was found in an American documentation from the...