The circuit shown, with the printed circuit board, was found in an article in the June 1990 issue of Radio Electronics magazine. Integrated circuits must be equipped with heat sinks.
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...