This circuit was found in an 80's Poptronics. The circuit is a fast trigger whose signal can be taken from the Q2 collector. The supply can be done with voltages from 9 to 12 V.
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...