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.
Found in General Electric and 1967 documentation, this circuit automatically turns off the...
This amplifier stage without an output transformer was found in Radio Electronics magazine from...
Found in an Electronics World of 1968 this circuit can use current SCRs and the diodes are...