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.
In the figure we have the basic configuration of a regulator for 12 V x 1 A suggested by Motorola in...
This circuit for 1 kHz sinusoidal signals uses a common operational amplifier circuit and is...
This 800 Hz sinusoidal oscillator was found in a 1970s American documentation. The transistor...