The CV1290 is an EHT rectifier based on the Cossor SU2150A. The old service code is NU33.
The Original Cossor design using a saddle anode was very reliable but not easy to mass produce. This design was for rapid assembly and considered to be inferior to the original.
The cylindrical anode connected to the screw top cap. For most valves the screw top cap was obsolete by the mid 1930's but this is labelled as a CV valve and thus must date to after 1941. Or have been re-labelled as the balloon envelope was also superseded by the shouldered or classic shape by the mid 1930's.
The oxide coated cathode cylinder is firmly held in the mica sheet that is mounted on two rods.
The balloon envelope is 50 mm in diameter and, excluding the B4 base pins, is 117 mm tall.