This circuit responds to frequencies from 100 Hz to 3 MHz. We find it in a 90s Radio Electronics. Transistors are general purpose types.
This small earphone amplifier with germanium transistors was obtained in a Japanese publication from...
The sensor for this circuit is a phototransistor. We found it in the April 1971 issue of Radio...
Found in a 90s Popular Electronics, this circuit allows to select the operating ranges between...