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Few data available about this experimental silica triode. It was developed in 1941 to be used in a 240 MHz small-ship radar. Found some references to an experimental XN tube and to a NT88 admiralty code. Another reference to this tube is in the Paterson's diary in September 1942, about the poor quality of glass seals.
The double-wound basket-like anode made of molybdenum ribbons is very short, about 5 cm. Filamentary cathode is made by six hairpin-shaped segments of thick wire, likely thoriated-tungsten, all around an ideal cylinder of about 2 cm diameter. Each segment is welded on top to a short rod melted in a silica donut. Segments are series connected in two groups and the two groups are series connected at the outside pins. Grid and plate are connected each to a couple of top pins, shorted by short copper braids.
The development was abandoned in 1942, due to the mechanic weakness of the bulb and of the internal assembly and even to the unacceptable output variation from tube to tube because of the paramentric variations.
Some info available in the PRO File AVIA 7/715 which shows severe frequency limitations around 200 MHz. The output power, about 300 kW for a single tube, dropped abruptly around 200 MHz to less than 50 kW.
Further developments had been already abandoned when the code of the tube was assigned in the CV register.
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