Found in an old publication about neon lamps this circuit works directly connected to the power grid, serving as an indicator for various situations. Ordinary neon lamps can be used.
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...