This circuit was found in the September 1971 Radio Electronics magazine. The buzzer can be replaced by a relay according to the supply voltage. R1 adjusts the sensitivity.
This is an amplifier circuit found in phonographs or portable record players from the 1970s. This...
This circuit is from the time when photos were revealed in darkrooms. We found it in a 1968...
The capacitance shown at the output of this circuit is given by the relationship between R1 and...