The 6442 is a triode for grounded-grid operation. As an oscillator in a suitable cavity it can produce useful output at up to 5 GHz. This particular exhibit was employed as a driver stage in an AN/ARC-52 UHF set. The final power amplifier would have been something like a 4X150A and the modulator would be a pair of 2E26's.
For microwave pulse operation, a 2 KW pulse is possible at 3.5 GHz or a wavelength of about 9 cm.
A clear view of the type designation code and the ceramic insulation. The cap at the top protects the pair of concentric heater connections. The metalwork is silver plated. Silver is the best conductor known and the skin effect forces the microwave currents to be in the surface layer of the metal.
The ceramic disc seal envelope is 10 mm in diameter, and overall base is 62 mm tall.
Reference: Datasheet. Type 6442 was first introduced in 1964.