Crystal triodes

This paper reviews the history of the development and the potentialities of crystal triodes. The properties of silicon and germanium diodes are described and explained with reference to a simplified picture of the mechanism of conduction in semi-conductors. In particular the importance of accurately controffing very small concentrations of impurities is stressed. The action of a germanium triode is outlined briefly, and various designs of germanium triode which have been produced are described. An equivalent network for the germanium triode is given, and the use of this equivalent in designing circuits containing the triode illustrated by a number of examples. It is shown that circuits developed for thermionic valves are generally not suitable for germanium triodes without modification, and also that the germanium triode lends itself to novel circuit developments which would not be feasible with thermionic valves. The limitations of the germanium triode compared with thermionic valves are considered, and it is concluded that with further development it will probably find many applications in which it performs better than the thermionic valves, but is never likely to compete in certain fields of application.