The CV378 is a full wave rectifier. The prototype was the R231 which is a 451U with a 5 Volt heater.
The KB/DA identifies this valve as being made to specification K1001 or K1006, the B denotes qualification by a UK authority and the DA identifies the maker as Mullard Radio Valve Co., Blackburn.
The twin rectifier sections. Each section has four wings around the cathode for maximum radiating area.
One anode seen face on and showing how it has been stitched together.
The classic envelope is 44 mm in diameter, and excluding the IO base pins is 127 mm tall.
