This circuit was found in a 73 magazine for radio amateurs from the 90s. The circuit uses high voltage transistors and the relay is high voltage as well.
This 10 kHz filter is based on a 741 operational amplifier. The circuit is from Electronics Now...
This circuit can be used with common drills connected to the 110 V network. With change of R1 and...
Found in an Electronics World of 1966 this circuit is intended for use with a microphone as an...