Found in a 1980s documentation, this circuit uses transistors from that time. Modern equivalents can be used. The alarm is a piezoelectric buzzer with na included oscillator.
This circuit uses one of the first comercial transistor and is from a 1958’s magazine. Tone...
This circuit is intended to indicate the operation of transmitters with powers above 5 W. The...
Emitt This crystal-controlled oscillator can generate signals from 100 kHz to over 30MHz. The...