Earliest version of the US Army TB-1. Brass base cap, pins tipped with gold.
The original box. Sadly without operating details.
Thanks to Joe Gruber for sending the images.
The balloon envelope is 35 mm in diameter and, excluding the UV base pins, is 101 mm tall.
Reference: Joe Gruber. Type TB-1 was first introduced in 1918.
Updated March 07, 2020. shape:balloon construction:pinch type:triode age:1920.1930 base:uv pins:4 pin: