This circuit was described in an article in the February 1993 Radio Electronics magazine. The frequency depends on the crystal and L1 is optional.
This configuration is from a 1964 US documentation valid for any FET. The range of power voltages...
The operational amplifier used in this circuit from a 1970s publication is no longer easily found...
This circuit was found in an old American documentation. It can operate with signals from 40 Hz to...