The CV2487 is the commercial 4X250B and this example was made in the UK by STC. The 4CX250B is interchangeable with the 4X250B as the stated difference is the use of ceramic in the base of the 4CX250B to allow higher seal temperatures.
The base ring is connected at the base to pin one. This was for better performance at the higher frequencies where an RF cavity would house the valve.
The design is described as a radial beam power tetrode. Typically the cage grids are arranged so that the wires are optically aligned. SeeQV1-150A for details.
The valve would be operated in the special base and fitted with a ceramic chimney. Air would be forced from below through the chimney to cool the valve.
The white glass base. Here the connection between pin 1 and the g2 ring is internal.
The top of the valve carries the STC logo, Made in England and the 4X250B Type designation.
The thin metal tube envelope is 35 mm in diameter, and excluding the B8F base pins is 47 mm tall.