This circuit was found in a Popular Electronics from the 90's. Its purpose is to detect the ionization of the air. The meter can be replaced by the current scale of an ordinary multimeter.
The circuit shown is from an old European publication. In it we have the way to activate a relay...
We found this circuit in a European publication from the 1990s. Transistors are still common types...
This circuit was found in an American documentation and can be added to common amplifiers of any...