This circuit with a few watts of power was found in the April 1995 issue of Electronics Now magazine. The voltage obtained and the efficiency depend greatly on the transformer.
In the figure we have the way to implement a 5 to 45 V zener diode with 50 mA of maximum current...
This circuit is from a Radio Electronics magazine from December 1958. The indicator instrument is analog...
These integrated ones consist of class B amplifiers with gain fixed 24 internally for better...