The CV378 is a full wave rectifier. The prototype was the R231 which is a 451U with a 5 Volt heater. Commercially the Mullard GZ33 is equivalent and has the same long envelope shape - suggesting that this is a Mullard valve.
Pins 3, 5 & 8 have been omitted.
One anode seen face on.
The twin section side by side.
The cathode tube of this indirectly heated rectifier is round and the insulated heater is folded in half so as to make four passes.
The classic envelope is 44 mm in diameter, and excluding the IO base pins is 127 mm tall.