This circuit for incandescent lamps was found in a 70s documentation. The circuit uses an SCR according to the power of the controlled lamps. The delay is a few seconds, given by capacitor C1.
This circuit triggers the LED when the monitored battery voltage drops below 9 V for 12 V...
We found this circuit in a Radio Electronics from January 1967. The SCR is already the C106, which...
This power source with silicon diodes at a time when valves were still used was found in Radio...