This exhibit from 1917 is a further refined experimental Type G Pliotron that led to the CG 886, VT-1 & VT-11. This has a UV base cap with brass skirt. Note the locating pin for the bayonet base.
The tungsten filament was formed into a helix.
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.