The STC V245C/1K is a Heil Tube. Named after its German inventor, the Heil tube is a velocity modulated oscillator and the Heil tube was developed by STC during WWII. Unlike the klystron the electron beam in the Heil tube is focused by an external magnet. This refinement was originally added to keep the bunched electrons together as the electric charge would, of course, tend to repel the electrons one from another.
The operating range was 4.4 to 4.63 GHz with up to 200 mW of output.
The construction of the Heil Tube oscillator. The magnet is external.
The evacuation pip is on the side.
The central copper resonator.
Output is taken from the large disc that would be located within a co-axial housing.
The thin glass tube envelope is 19 mm in diameter, and excluding the B7G base pins is 61 mm tall.
Reference: Data-sheet. Type V245C/1K was first introduced in 1955.