Moorhead Labs made and started to advertise the external grid Electron Relay as a replacement for the internal grid ER in in 1916 in response to grid patent infringement threats from DeForest and rejections from national magazines he wanted to place adverts in because DeForest was threatening them with lawsuits as well. While the threats stopped, tube sales dropped because the external grid ER simply did not Work. The example above has a short, small loop single filament and a disk plate with Moorhead and patent pending stamped in and of course the brass grid on the outside of the glass bulb held on with a bolt and nut.
Taken from Joe's article.
Thanks to Joe Gruber for sending the images.
The thin glass tube envelope is mm in diameter and, excluding the base wires, is mm tall.
Reference: Joe Gruber. Type EXG was first introduced in 1916. See also 1916 adverts.
Updated February 08, 2021.