Found in July 1975, Radio Electronics magazine this circuit can use any operating circuit, including the 741. The circuit must use a symmetrical power source.
This basic configuration can be found in a lot of articles on this site. In this case, the relay...
This circuit is from American documentation from the 1980s. The transistors are general purpose...
The circuit is simple, as it uses only one transistor and a relay that can be MC2RC1 or MC2RC2,...