We found this circuit in the September 1971 Radio Electronics magazine. The SCR can be any of the 106 series and the buzzer can be replaced by a relay according to the supply voltage.
The regulation of high voltages through common semiconductor circuits, such as integrated circuits and...
The LM2904 is not very common today, but common comparators and operationals can be used in the...
This amplifier circuit was found in a Radio Electronics from April 1959. The circuit needs only 20 mV...