The CV2171 is a noise generating diode for use up to 500 MHz. The filament is tungsten and the prototype was the VX3120. The commercial version is the A2087.
The KB/Z identifies this valve as being made to specification K1001 or K1006, the B denotes qualification by a UK authority and the Z identifies the maker as MO Valve Company, Hammersmith.
The box anode is mounted horizontally. The filament is a single V.
The bright filament is pure tungsten wire.
The thin glass tube envelope is 17 mm in diameter, and excluding the B7G base pins is 45 mm tall.
Reference: Data-sheet. Type CV2171 was first introduced in 1959. See also1959 adverts.