As with the A tube, the B class I tube was also made in the spherical version which is shown here. Moorhead was quite good at marking the early contract valves with a B etched on the glass, a B or 1mon the pinch or class 1 in ink on the base cap. Moorhead Laboratories often times followed those markings with patent and Warning notices. Serial numbers Were also added quite consistently.
Taken from Joe's article.
Thanks to Joe Gruber for sending the images.
The balloon envelope is mm in diameter and, excluding the UV base pins, is mm tall.
Reference: Joe Gruber. Type VT-B was first introduced in 1917.
Updated October 06, 2020. shape:balloon construction:pinch type:triode age:pre.1920 base:uv pins:4 pin:1.g1 pin:2.f pin:3.f pin:4.a