This rectifier is a high vacuum half wave power type. The identification is damaged and the first letter is not clear, the rest of the Type designation reads V0880. No details have yet been found.
The filament looks to be pure tungsten and is formed into a series of loops facing the domed anode. The cylinder around the filament is a shield and made of thin sheet.
The rectifier as an X-Ray image.
A more intense beam reveals the fine detail. Note how thin the wires are.
The balloon envelope is 90 mm in diameter, and excluding the ES base is 284 mm tall.
Updated July 22, 2014.