The CV2104 is a battery sub-miniature diode pentode with flying leads. The commercial equivalent is the DAF70.
The data-sheet gives an output power of 20 mW.
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 thin thread of a filament can be seen on the left going behind the top of the diode anode.
The 4104 is visible in this image.
The valve is new and came enclosed in a paper tube.
G2 and G3 seen through the wall of the anode with the paper tube cover partly removed.
Another view.
The thin glass tube envelope is 10 mm in diameter and, excluding the B8D base wires, is 40 mm tall.
Reference: Data-sheet. Type CV2104 was first introduced in 1951. See also1951 adverts.
