The CV1758 is a miniature RF amplifier pentode with very low filament consumption. The direct equivalent is the 1L4 as the CV specification makes clear. CV1758 would be used for portable radio equipment.
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 bright screen obscures the inner details.
The lower of the pins in the centre foreground of this image is pin one and connects to the screen and f-. The pin above connects to to a flat plate inside the screen and this is the anode.
The thin glass tube envelope is 18 mm in diameter and, excluding the B7G base pins, is 47 mm tall.
