Found in an American circuit manual from the 1970s, this circuit can use any general-purpose transistor. The operating frequency range is from 600 to 4000 Hz.
This circuit, from a 303 Circuits from the 90s, uses a telephone pickup coil as a sensor to...
This circuit was found in Delco documentation from 1965. The transistor is of the time, but any...
This circuit appears in several versions in publications of the time and can be modified by...