The CV4058 is a small RF power triode for HF and low VHF working. The commercial equivalent is the Type 6100 that is itself equivalent to the 6C4WA.
The KB/QDD identifies this valve as being made to specification K1001 or K1006, the B denotes qualification by a UK authority and the QD identifies the maker as both English Electric with the extra D not explained.
The rounded anode. The copper grid support is also visible.
Looking straight at the anode with the getter holder support in the foreground.
The thin glass tube envelope is 17 mm in diameter, and excluding the base pins is 47 mm tall.
References: Data-sheet & 1040 Type CV4058 was first introduced in 1956. See also1956 adverts.
