This is a type 417A reflex klystron with a 'WL' prefix. The 'WL' prefix indicates the manufacturer. Small klystrons of this class were widely used as local oscillators in radar receivers. The 417A was used in the Radio Set AN/CPN-3.
The 417A was designed to operate at 2.65 to 3.33 GHz and generate 250 mW of RF. The cavity is integral to the design and the tuning is mechanical. The RF connectors can be seen to be co-axial.
They were normally tunable over a modest range and were adjusted to be exactly in tune with the (much more powerful) pulse transmitting valve (usually a cavity magnetron). The magnetron generated an RF output only briefly, when pulsed, but the klystron provided a continuous low-level RF signal which could be used to 'beat' (mix) with the faint echo signals in order to reveal small frequency differences of Doppler shifted echoes from moving aircraft.
The three cavity altering screws that set the maximum frequency art at the top. On the right is the mechanical tuning lever. Pushing it closer to the klystron body lowers the bottom resonator plate and thus increases the distance and lengthens the wavelength and hence lowers the frequency of operation.
The reflector connection at the top. The tuning lever has a scratch on the exposed metal showing where it was pushed by the tuning rod - probably threaded.
Top view. The twin output co-axial connectors on the left.
The IO base.
The wide metal tube envelope is 32 mm in diameter and, excluding the IO base pins, is 115 mm tall.