This circuit has the intensity of the signals controlled by the light that falls on the sensor. Note that it is not a frequency-controlled oscillator. Equivalent transistors can be used.
This circuit appeared in a noverber 1962s Practical Electronics. The magazine is no more, but the...
This circuit is from an American 80's documentation. The integrated circuit is from the time and...
Other series amplifiers such as the MC3301, MC3401 and LM2900 can be used on this circuit. We...