We found this precision circuit in a manual from the 80's. The operational amplifier is of a common type at the time, and equivalents can be tested. Transistors are general purpose types.
In this circuit found in the December 1972 Radio Electronics magazine. R can be from 1k to 22k,...
This circuit has a frequency range of 30 Hz to 100 kHz with an output signal of 1 Vrms. We found...
This circuit provides a signal that is twice the frequency of the input signal. The circuit was...