Found in 1965 Delco Radio documentation, this circuit uses transistors from that era. Modern equivalents can be used. The characteristics of the inductor were not given.
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...