This circuit is from a 1924 book by Gernsback. The receiver uses two tubes and listens to headphones. Power is supplied by battery with the indicated voltages.
This circuit generates a high negative voltage responsible to produce ions in a tip electrode. The circuit...
This photo-relay uses a Darlington stage to increase sensivity. Any photo-transistor can be used....
This circuit for alternating current loads has a built-in timer. SCR2 is according to the motor...