This circuit multiplies the input voltage by 3 and can work with up to 12 V input. The current is a few mA. We found it in the Radio Electronics magazine of December 1992.
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...