This circuit with current up to 100 mA according to the transformer was found in the Radio Electronics magazine of October 1991. The regulation is done directly by the zeners.
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...