This circuit was suggested by Motorola in a 1969 publication. It makes use of components of the time, but both the FET and the bipolar may be general purpose current types.
We found this circuit in Intersil documentation from the 1980s. The circuit applies to other...
Using a dual 555 CMOS this very useful circuit on the bench was found in the July 1998 Electronics Now...
This beat frequency oscillator or BFO was found in an American 1980s documentation. The circuit is...