This circuit was found in a 1945 publication. The circuit was stated to be part of a walk talkie. Note that, as it is a portable assembly, it was powered by batteries. The jack was for microphone insertion.
This amplifier step with a transistor has an input impedance of 100k to 10 M. The transistor can be any...
This sensor circuit for currents of the order of nanoamperes was found in an American...
I found this circuit in a 1992 Electronics Experimenter Handbook. The circuit can be easily...