This circuit is placed between the instrument pickup and the amplifier input. The same version can be found from other sources in this section. This is from an English magazine from the 80s.
This circuit has the intensity of the signals controlled by the light that falls on the sensor....
The purpose of the diode in this oscillator circuit is to limit the amplitude of the output...
We found this ladder-shaped signal generator circuit in Radio Electronics magazine from August 1966....