The CV1823 (Commercially the 1N5GT) is a variable μ RF pentode for dry battery operation. The original design came from America but the CV specification would indicate specific requirements of the UK Government if they differed.
The CV1823 is used at both RF and IF in superhet receivers.
The /T identifies the maker as British Tungsram, Tottenham.
The bright oval anode.
The filament is a single vertical strand. The wire grids can be glimpsed through the notches in the anode wall. The top connection to the filament has a tension spring with the filament clamped in a small length of tube. The envelope printing includes the UK up arrow and the code NA.
The wide glass tube envelope is 29 mm in diameter, and excluding the IO base pins is 70 mm tall.
