This 1965 circuit uses a Philips 4068 tube to measure extremely small charges. The circuit has as indicator a micro ammeter and the transistors are of the time.
This 1985 circuit takes advantage of an old cassette recorder to answer and record phone calls,...
This circuit is from 1990 documentation. It can be implemented with BC548 transistors instead of...
We found this 50 kHz 25 MHz crystal tester in a 1978 QST magazine. The FET can be the BF245 and...