The indicated circuit uses an unusual buffer from National Semiconductor. The frequency is given by resistors R1 and R2 as well as capacitors C1 and C2.
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...