This transistorized circuit appeared in a Radio Electronics magazine in March 1958. The frequency range depends on the tuned circuit, being within a few megahertz.
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...