The V240C/2K is a velocity modulated oscillator or Heil Tube designed for operation in the range of 3.95 to 4.05 GHz. The output is 350 mW and the V240C/2K is a direct equivalent of the CV2189 and this exhibit carries both Type designations.
The attached data-sheet includes a cross sectional diagram of the internal structure.
The heater and cathode is on the left and the electron beam passes across the width of the tube. The beam is velocity modulated within the central cavity (resonator) if placed between the poles of a magnet.
The external disc would be clamped to the outer face of the waveguide with the top pip as the output probe.
The thin glass tube envelope is 19 mm in diameter, and excluding the B7G base pins is 58 mm tall.
Reference: Datasheet. Type V240C/2K was first introduced in 1952.