This circuit was found in a 1965 Radio Shack documentation. The transistors are from that time. The circuit can be implemented with current transistors and lower voltage supply.
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...