This exhibit is another 'Short and Shiny' anode Electron Relay from Atlantic and Pacific Co.
The brass base cap is unmarked. The glass has ER etched into it.
The original box for this Electron Relay. Dimensions are 50 mm square and 128 mm long.
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