The Weagant tube was designed by Roy A Weagant for the Marconi Wireless Telegraph Company (USA) in late 1914 - early 1915 and several styles were made.
An external control was applied to the valve, in this case a lead covering and metal band. These valves were designed to circumvent the de Forest Audion patent.
This exhibit has the experimental valve mounted on a polished ebonite base. As development progressed the valve was fitted with caps at each end. The Weagent never went into commercial production.
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.
Updated July 16, 2021.