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 NEC commercial amplifier was manufactured in Japan in the 1960s. The circuit uses 4...
The operational 3403 is not currently common, but a similar configuration can be made with modern...
We found this circuit in an American documentation from 1969. The circuit works with the polarized...