Pliotron

Irving Langmuir, working for the General Electric Company of Schenectedy, had designed improved vacuum pumps and, about 1913, turned to development of the Audion type valve with a hard vacuum. He published his results in April, 1915. Two sizes were produced, one for transmitting, and, shown above, a receiving type.

The example above has wire spirals for both grid and anode and both ends of each are brought out through seals.

Early samples and documentation, detailing construction methods, were obtained in the U.S., just prior to the declaration of WW1, by a M. Paul Pichon, working for Telefunken in Germany. He attempted to return to Germany, but was arrested in Calais and the valves were passed to Colonel Ferié.. He used this information to develop the French TM valve.