This valve is an experimental VHF type from the late 1930s.
The anode is finned to radiate heat, at high frequencies the efficiency was very low, so a great deal of heat was generated. The anode and the grid are both taken to pairs of side pins on either side of the envelope. The grid is circular and surrounds the filament.
This is possibly an early 8012, later versions were exhausted from the top. Alternativly the valve could be an early version of the 1628.
The envelope is 25 mm in diameter and, excluding the base wires is 103 mm tall. Across the side pins is 60 mm tip to tip.
Reference: Observation. Type Experimental was first introduced in 1917.
Updated January 22, 2013.