This circuit was found in a Mallory documentation from 1968. The integrated circuit is of the time, unusual in our day. Input sensitivity is 20 mV for 2 W output.
This is the old name given to flip-flops or biestable multivibrators. In fact, this is a 1967...
One of the problems with common multimeters, especially analog ones, is that their low resistance scales...
This simple circuit uses small speakers for both listening and speaking (microphone). The feeding is...