The QY4-250 is an all glass pulse power tetrode on a B5F base. The anode dissipation is given as 250 Watts. The maximum anode voltage was 4 kV. Mullard advertise the QY4-250 for use in high power audio applications probably in Class B for public address or transmitter modulators rather than hi-fi.
This Mullard valve carries the later logo and was made in France.
The CV data-sheet was issued by the Admiralty Surface Weapons Establishment. The CV5343 was probably used as a pulse modulator for a small radar magnetron. For a 100μS duration pulse the power delivered in the pulse is as high as 10 kW.
The cylindrical anode is held only at the top.
The B5F base with the pins set in a hard sintered glass disc.
The top cap.
The grid is a cylindrical cage of vertical wires.
The finned top cap connector. The screw looks to be a replacement as it it far too long.
The machined interior of the connector.
The wide glass tube envelope is 85 mm in diameter, and excluding the B5F base pins is 126 mm tall.
Reference: Datasheet. Type QY4-250 was first introduced in 1956.