Pratt Radio Tubes
Pratt Radio Tube Company, Chicago?
Last seen: 28-Dec-1923
An unusual tube, Pratt appears to have 'invented' a new tube design. It's not clear whether his tube was ever produced, or whether he ever acquired a patent. It's possible he was snatched up in a buyout and disappeared. This tube looks a bit like the Cossors.
If you know of more info about this tube, drop me a note.