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 incorporates a thermostat. The circuit is from Motorola's Linear Interface ICs from...
We found this circuit in a technical documentation from the 70s. The MC1555 is nothing more than...
This circuit was found in a 1967 RCA manual. The transistors are of the time. The adjustment is made to...