The time of this timer depends on C1. The circuit was found in the July 1994 Electronics Now magazine. The supply voltage depends on the relay and can go up to 12 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...