RF or even switching transistors like the 2N2222 can be used in this circuit. The capacitors are ceramic and the frequency is determined by the crystal.
This circuit is from an old American documentation from the 70s. Transistor 2N3904 can be replaced by...
Based on an integrated LM3914 Bargraph circuit. this design causes voltage variations between 0...
This circuit is from 1995 documentation. The power depends on the transformer, which in this case...