This exhibit from 1918 is a refined experimental Type G Pliotron. This design led to all of the Pliotrons that followed. The markings are VT-1 & NX4 on the pinch.
The General Electric book National in the World War mentions that the first VT-1 valves that they made for the US military all had NX4 on the pinch. (See the article above for more details.) This they quickly realised was incorrect and they renamed the valve VT-11. Joe Gruber states that this valve is one of only three known examples so marked.
This exhibit has a UV base cap with brass skirt. The locating pin is not visible in this image.
Western Electric made the 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 35 mm in diameter and, excluding the UV base pins, is 101 mm tall.
References: J Gruber & 1047. Type Pliotron was first introduced in 1915.
Updated February 08, 2021.