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 blue band inhibits gas release from the glass when bombarded by electrons.
The control grid has copper supports and a heat radiating fin at the top.
Side view.
The thin glass tube envelope is 18 mm in diameter and, excluding the B7G base pins, is 45 mm tall.
