This circuit appears in several versions in publications of the time and can be modified by changing the capacitors. This one is from Radio Electonics magazine from October 1992.
This sensor circuit for currents of the order of nanoamperes was found in an American...
This circuit was obtained from a 1964 magazine and has some interesting features such as the input...
Suggested by a 90’s Radio Electronics, this circuit automatically activates the recording switch of an...