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.
This circuit had its assembly described in a Radio Electronics from March 1963. The circuit uses 2...
We found this configuration in a documentation for radio amateurs from 1974. The circuit can be...
We found this circuit in an English documentation from 1989. The integrated circuit used is not...