The CV850 is a low noise RF voltage amplifying pentode, designed to operate at VHF.
The KB/QDD identifies this valve as being made to specification K1001 or K1006, the B denotes qualification by a UK authority and the QDD identifies the maker as English Electric Valve Co., Stafford. The extra D is possibly for Mullard.
A true pentode, the open pitch suppressor grid helix with the closer wound screen grid within. The control grid wires are just visible either side of the support rods.
Side view: the heater can be seen to be coiled and then insulated.
The thin glass tube envelope is 18 mm in diameter and excluding the B7G base pins measures 36 mm tall.
References: Data-sheet & 1040. Type CV850 was first introduced in 1952. See also1952 adverts.
