See
http://i.imgur.com/TQaP0Qq.jpg
This tube seems to be fairly similar to the 16KP4 - no aluminization, almost the same specs. Looking at the gun assembly, it whole of it is tilted in the base by some amount. I thought that ion-trapping was done in only part of the gun assembly, not with the whole - but what the heck to I know.
Does it look right?