Found in a 1924 Gernsback publication this circuit uses 4 batteries for power and loop antenna. Listening is over a high-impedance type earphone or loudspeaker common at the time.
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...