This exhibit is an improved type T Pliotron for transmitter use. The pinch has the designation VT-12 written on it. The improvement over the original VT-12 looks to be the design of the anode supports. This design would marginally improve the anode dissipation but greatly improve the mechanical stability.
This design, for the US Signal Corps, is a low power oscillating triode used for telephone transmitters and was made by General Electric as a substitute for the Western Electric VT2. It was replaced by the VT-14.
The original box has no information present. The dimensions are 57 mm square and 127 mm tall.
The end of the box just carries the Type designation of VT-12.
Thanks to Joe Gruber for sending the images.
The balloon envelope is 35 mm in diameter and, excluding the UV base pins, is 101 mm tall.
References: J Gruber, 3002 & 1047. Type VT-12 was first introduced in 1918. See also1918 adverts.
