The speed indication of this circuit is made on an analog instrument. The circuit is used to count pulses (rpm) and was found in April 1976 Radio Electronics magazine.
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...