This exhibit is a VT Type B class I. It has a B on the glass, a 1 on the pinch and on the brass base cap.
Thanks to Joe Gruber for sending the images.
The balloon envelope is 44 mm in diameter and, excluding the UV base pins, is 104 mm tall.
Reference: Joe Gruber. Type VT-B was first introduced in 1917.
Updated October 04, 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