The CV5081 ((commercially the 61SPT) is a screened pentode, but one with a high current rating. As a screened power RF pentode it may have been designed for use as a driver oscillator or for line output in CRT raster scanning.
The KB/K identifies this valve as being made to specification K1001 or K1006, the B denotes qualification by a UK authority and the K identifies the maker as ETEL, Electronic Tubes, High Wycombe. ETEL was a wholly owned subsidiary of Cossor.
The anode connects to the top cap and below the lower mica is a elliptical screen usually seen in the 807.
Above the lower mica can be seen the wires of all three grids.
The classic envelope is 50 mm in diameter, and excluding the IO base pins, is 122 mm tall.
