This circuit was found in documentation from the 1970s. However, it can be implemented with modern transistors such as 2N2222 for Q1 and BF494 for Q2. The crystal depends on the desired frequency.
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...