This valve has no identification other than a paper label. The Type 2151 is a pentode.
The blackened anode has an oval cross section and there is a heat sink on the control grid supports. The control grid has been wound on copper rods and the third grid is of wire - a true pentode.
The pressed anode has been stitched together. The control grid heat sink is in the shape of a U.
A closer view of the top mica and grid supports.
The classic envelope is 44 mm in diameter, and excluding the UX6 base pins is 100 mm tall.
Reference: 1043. Type 2151 was first introduced in 1940. See also1940 adverts.