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In this tube the cathode is connected to the grid pin. The tube is marked US&SC (Union Switch and Signal Company). It was used in railway to help with the transfer of red, green or orange trackside signals to the train driver. Identification of hazardous situatons such as fog or smoke could be "forewarned", with the receiving unit being inside the drivers compartment of the locomotive.. The Idea of tubes to do this was first investigated as early as 1916 by General Electric and by 1924 there were many such installations. The GE PJ2 "train control" triode was the most widely used for many years.

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