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 amplifier was found in a Japanese publication in 1972. Transistors are uncommon today, and...
The current of this source is 200 mA at the most, and the output depends on the zener that may...
Found in Mallory documentation from 1968 this circuit uses an integrated circuit from that time. The...