This circuit operates from 20 Hz to over 20 kHz and is easily tunable. We found it in a 70s documentation. The circuit can be implemented with modern operational amplifiers.
This version of the Pierce oscillator with the 2N3904 was found in the January 1994 issue of...
The traditional configuration of a non-inverting amplifier with the operational 741 shown in the...
This circuit is from a Radio Electronics from January 1958. The transistor is the CK722, and the...