The Cunningham C-301 is equivalent to the UV201 made by General Electric and Westinghouse. The electrode mounting also follows the pattern of the earlier VT-14.
The envelope looks to have a small amount of phosphorus gettering. At the top of the anode can be seen the filament tension spring that ends in a J hook. The filament is a single inverted V loop.
The brass base cap with black printing. Like all of the UV-201 types the base cap is marked with the words, Licenced for amateur or experimental use only.
The envelope has the Cunningham C logo. Eventually the Cunningham company became an integral part of RCA, thus giving RCA access to the brand name alongside the RCA Radiotron brand.
The very rare box. The wording 'Trading as AudioTron Mfg Co of San Francisco, CA' was added by Cunningham in his first round of negotiations with RCA. After only a few boxes were produced RCA put a stop to using that wording as they did not want to be associated, at least on the box, with a patent infringer - which Cunningham was.
Thanks to Joe Gruber for sending the images.
The envelope is mm in diameter and, excluding the UV base pins, is mm tall.
Reference: Joe Gruber. Type C-301 was first introduced in 1920.