This exhibit from 1918 is a refined experimental Type G Pliotron. The markings are VT-1 & NX4. This design led to all of the Pliotrons that followed. It has a UV base cap with brass skirt. The locating pin is not visible in this image.
Western Electric made a VT-1 and General Electric made the VT-11.
From the Tyne Collection.
Thanks to Joe Gruber for sending the image.
The balloon envelope is mm in diameter and, excluding the UV base pins, is mm tall.
References: J Gruber & 1047. Type Pliotron was first introduced in 1915.
Updated October 20, 2019. shape:balloon construction:pinch type:triode age:pre.1920 base:uv pins:4 pin: