This circuit was obtained in a 1967 Electronics World. The components are still common today, the SCRs can be replaced by equivalents and the unijunction transistors the 2N2646.
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...