The CV2461 is a 1,200 Volt corona discharge shunt stabiliser for low current EHT power supplies. The commercial equivalent is the SC1/1200.
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.
Serial number 35.
Apart from the ceramic insulators there is not much to see.
The thin glass tube envelope is 18 mm in diameter and, excluding the B7G base pins, is 65 mm tall.
References: Data-sheet. Type CV2461 was first introduced in 1958. See also1958 adverts.