The circuit is from Ferranti's 1974 transistor manual. Transistors are general purpose types, and the output waveform is rectangular. Components can be changed to other frequencies.
With this circuit it is possible to vary the resistance by adjusting the mark/space reaction of...
We found this filter in documentation from the 1980s. The operational amplifier used is uncommon...
This circuit was obtained in a 90s Electronic Design. The circuit uses components from that time....