The tube you are referring to is the 5890.
http://lampes-et-tubes.info/vs/vs060.php?l=e
https://frank.pocnet.net/sheets/049/5/5890.pdf
It was intended for use as an HV shunt regulator in early theater projection TV sets, making it a forerunner of the 6BD4, 6BK4, 6EL4 etc. It is a pretty rare item, due to the limited application.
It consists of the gun structure of a 5TP4 CRT, aimed into an anode structure from a 2X2A. Has the standard 12-pin duodecal CRT base and a 3/8" anode cap.
I have a couple of them, and they do make a handy way to provide an HV load on a chassis without a CRT, or for testing a CRT tester.