This circuit is from an old Popular Electronics, but it can be easily implemented nowadays, even adapted to act as a shield. The circuit has the frequency given by C1 and adjusted in R1.
We found this circuit in a publication for radio amateurs in 1974. The bipolar transistors can be...
Found in a 1980s American documentation, this circuit has a current consumption of only 1 mA. The...
This adjustable power supply was found in Ferranti's transistor manual from 1974. Power...