This two-transistor circuit was found in a 1966 US documentation. The power transistors are of the time. The system is intended for cars with contact breaker.
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...