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 stage of low power audio amplification was very common in devices powered by the 60's and...
This different circuit was found in a Radio Electronics from August 1965. It works with a voltage of...
This circuit was found in a 1980s documentation from the manufacturer of the integrated. The...