The CV5080 is based on the Mullard EF37A but the specification refers to use as an HF pentode with limited microphony and not as an audio pre amplifier valve.
The reverse is plain zinc paint.
Looking through the top of the glass reveals little: the cathode tub is cylindrical and the suppressor grid is close to the anode.
The wide glass tube envelope is 29 mm in diameter and, excluding the IO base pins, is 86 mm tall.
Reference: Data-sheet Type CV5080 was first introduced in 1963. See also1963 adverts.
