The X481D is an experimental reflex klystron oscillator for X-Band radar receivers. As it is an experimental design no guarantee of full scale manufacture was given. The aim of the design was a fully rugged oscillator for hostile environments.
The frequency range was 8.5 to 9.6 GHz and the output power was 20 mW when operated at 250 Volts. Output was to a round flange and not the standard WG16 that is normally seen for X-Band.
The Type designation at the bottom and the resonator screw connection on the left.
The central vacuum tube is encased by three rings that are bolted together for strength.
The heater is the white lead and the heater/cathode connection is the black lead.
The outer rings are 30 mm in diameter, and including the base it is 60 mm tall.
References: Datasheet. Type X481D was first introduced in 1952.