This circuit can detect static charges or extremely low voltages. The circuit was found in ancient American documentation and makes use of a JFET. A BF245 which is a more modern transistor can be used.
This useful inductance bridge was found in a Radio Electronics from September 1963. The...
This circuit uses a 7-segment display to indicate the logic level of a test circuit. The power...
Powered by voltages from 6 to 12 V, this circuit from a Popular Electronics from the 90s,...