This sensor circuit for currents of the order of nanoamperes was found in an American documentation from the 1980s. The components are from that time.
This circuit appears in several versions in publications of the time and can be modified by...
This configuration with FET and Unijunction can be found elsewhere on this site. The JFET admits...
We found this circuit in a Popular Electronics from the 90s. It operates at a frequency of 15 kHz....