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.
Found in a 1960s documentation, this circuit uses a transistor to drive a relay as well as a set...
This approach alarm was found in Radio Electronics from July 1990. The circuit must be powered by a...
This 75 W power supply was found in American documentation from the 1980s. Transistors can be...