We found this circuit in the Radio Electronics magazine of February 1993. The main integrated circuit is from that time and the power supply is made with voltages of 6 to 15 V.
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...