This tube looks like a IN-1 without the big brown base and a fine anode grid. This tube was either made for soldering into a board, but its more likely that this is a part of an IN-1. Maybe this part of the tube was manufactured and then assembled into a IN-1 by adding the base. It has no markings or anything else on the glass, but because of its shape it clearly can be identified as "IN-1". There is also a version with a normal grid.