This 50 Hz rejector or notch filter was found in a 1975 documentation. Other frequencies can be obtained by changing components. The filter uses a Wien network and must use a symmetrical power supply.
We found this circuit in a 1973 documentation. The null adjustment trimpot is 10k. The circuit can be...
This circuit is from Radio Electronics from April 1977. The circuit is for analog lines using...
The indicator for this circuit is a mini buzzer with a 1.5 V oscillator. The circuit can also be...