This circuit triggers by choosing the higher of two voltages. The circuit is from a 1964 Electronic Design. The transistors are of the time and can be replaced by current equivalents.
This control circuit or reversible contactor was found in a 1967 General Electric manual. The...
We found this circuit in a 1987 publication. Through a relay, it controls water valve solenoids at several...
The figure shows how to use a varicap in a conventional tuning circuit. The circuit may be an...