This gas sensor circuit was found in July 1976 Radio Electronics magazine. The TGS sensor was a common type at the time. Note the power supply to the circuit.
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...