Found in a Linear Technology documentation from the 1990s, this circuit has the voltage adjusted by resistors R1 and R2 according to the formula given in the diagram.
This National Semiconductor circuit appears elsewhere on this site. The circuit must be powered by...
In this circuit the frequency is determined by the coil and the variable capacitor. Transistors like the...
This circuit is from old American documentation, but the transistor used is still very common...