The transistor can be a BC548 and the coil has the following characteristics for 1 MHz. L1 has 80 turns of wire 28 in a ferrite rod and L2 of 30 and 40 turns.
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...