The only visible marking on the glass is the number 20026. This could be the Type designation but it can not be found in the literature we have. There is also a logo on the underside of the base.
The valve has a substantial 'feel' and was probably made for telephone repeater use.
The valve is an early bright emitter triode with a special four pin base and a metal base skirt. The glass envelope is spherical and the triode itself is a flat sandwich. The pins are larger than the B4 type. Two pin centres are 22 mm apart and the other two are 20 mm apart.
The two sides of the anode are bridged together at the top. The control grid is also made as two sections and held together at the top. The filamant is a single horizontal strand.
The filament is intact and held in folds of the supports
The grid has been stamped and folded from a single thin sheet.
The anode is made from thin sheet that hasbeen folded around the supports at the ends.
The base pins and in the centre of the base is a logo that we can not identify. The base pins are elaborately made and at this time most valves had simple split pins for the connections.
The balloon envelope is 40 mm in diameter, and excluding the base pins is 63 mm tall.