This NU29 is a high power half wave rectifier in a silica envelope. The rectifier is rated for a maximum PIV of 40 kV and a peak forward current of 5 Amps. Such high voltage valves were not gettered but pumped for longer to achieve a high vacuum. Gettering was not suitable for high voltage valves neither were coated filaments and this valve has a pure tungsten filament.
The valve is housed in a strong wooden box that measures 790 x 190 x 155 mm. During carriage the brass lugs in all corners would have been connected to springs and the whole assembly would have been encased in a wooden crate, although we do not have a crate for this exhibit.
This close-up of the top of the silica envelope shows the moulded lettering and within the envelope can be seen the basket weave of the nickel anode. The construction of silica envelope rectifiers closely matches the construction of the triode valves themselves.
This type of rectifier would have been used in association with radio transmitters in British Navy equipment.
Thanks to R J Sutherland for the valve data.
The silica tube envelope is 90 mm in diameter and, tip to tip is 700 mm tall.