This sensitive circuit was found in an Electronics Hobbyists Handbook from the 1990s. The circuit can use common general-purpose transistors in place of the original ones.
This General Electric circuit is from the 80's. The PUTs used in this meter are not common...
Found in a 1964 Electronic Design, this circuit generates pulses based on an avalanche diode of...
This circuit, which consists of an audio oscillator, was found in a Radio Electronics magazine from...