This grounding test circuit was found in an American 80's documentation. The circuit is for the 110 V power grid but can be changed to the 220 V power grid.
The component used in this regulator is not common today. The switching circuit is from an 80's...
This Hughes circuit is from 1968. Equivalent modern components can be used. The input impedance is...
This effects circuit can be used with microphones or guitars. The circuit is from an American...