The circuit shown here is a CCO. The frequency here depends on the current through the transistors. It can be controlled by a 1 M ohm potentiometer. The central frequency is given by the resistance of the transistor in a reference level and C1. The range of values for R1 is between 1 k ohm and 100 k ohm. For C1 the recommended band is between 100 pF and 100 nF. With the values shown in the diagram, the circuit will operate in the audio band.
Current-Controlled Oscillator (CCO)
