This filter was found in an old publication from 1977. The circuit must use a simple two-voltage source and the components can be changed for operation at other frequencies.
This circuit was found in a NASA documentation from the 1980s. The components used are of the time...
This is a traditional version of electroscope with FET. We found it at Popular Electronics. The...
This circuit tests the grounding of a three-pin outlet. We found it in a Popular Electronics from the 80s....