This exhibit is an Atlantic-Pacific Electron Relay. The design was short lived and used an anode similar to the tubular ER.
The original Atlantic-Pacific box. This is a new design of carton and at this time AP may have had a contract extension to use up their stock of boxes.
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.
Updated August 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