This simple metronome, from 1985 documentation uses only transistors and has two settings. For voltages above 6 V, up to 12 V, replace the BC557 with a BD136.
In the figure below we have the main configurations of power supplies with the most used...
This circuit is a high voltage source for a gas LASER. We found it in a documentation from the...
This integrated amplifier was used in televisions from the 70s, with good sensitivity...