Found in an Electronics World of 1966, this circuit makes use of FETs of the time. Modern equivalents can be used. The high voltage supply suggests its use with tube amplifiers.
This circuit is from 1990 documentation. When we press D1 the lamp remains on for a time interval that...
Some old multimeters have a high resistance scale that has an internal circuit powered by a 22.5 V...
This circuit, from a 2001 documentation, appears elsewhere on this site. Its purpose is to obtain a...