The CV139 miniature valve is a single triode with a commercial equivalent of the 6L34. Within the envelope can be seen a firm rod support structure.
The KB/D identifies this valve as being made to specification K1001 or K1006, the B denotes qualification by a UK authority and the D identifies the maker as Mullard Radio Valve Co., Mitcham.
The side view of the triode. Note the screening below the lower mica.
The flat face of the rectangular cathode and control grid wound on copper supports.
The thin glass tube envelope is 18 mm in diameter and, excluding the B7G base pins, is 46 mm tall.
