For a current of 5A and a supply of 6 V this circuit was found in documentation from the 70s. Transistors admit modern equivalents. Q1 is a PUT uncommon today.
The circuit in the figure is based on an LM101A; diodes can be replaced with equivalents. The...
This circuit, with magnetic sensor, uses an operational amplifier of the time. The circuit is from...
Found in a 90s Popular Electronics, this circuit checks if a remote-control transmitter is...