This circuit from Motorola is from 1968, appearing elsewhere on this site. The transistors admit equivalent and the relay is of the sensitive type for low voltage, according to the power supply.
The frequency of this oscillator depends on T, which for the audio band can be a common output...
This circuit can work with almost any JFET. The circuit is from an Electronics Now from April...
This voltage-controlled oscillator uses components that are still common in our market. The...