This is another mystery valve the attached label says 2V4 but this may not be the type designation. Inspection of the valve shows that there are three wire grids and an inverted 'V' filament. From the word 'output' we may guess that it was used as the output stage in a radio receiver.
The screen grid of early pentode valves was often connected to a scre terminal on the side of the composition base.
Turned through 180 degrees the electrode structure is revealed. The side connection is to the screen grid. The suppressor grid is connected internally to the filament.
The balloon envelope is 41 mm in diameter, and excluding the B4 base pins is 92 mm tall.
Updated April 13, 2013.