The NR14 is a directly heated triode on an Inter Services type 1 base. The NR stands for Naval Receiving and as this designation predates the 1941 introduction of the CV or Common Valve specification for UK government valves the valve also dates from before this period.
The image shows the Copper external connection than takes the filament circuit to the top cap. The anode connection is a metal plate moulded into the base that is identified by the red spot and the letter A. Within the envelope at the top are the twin filament tension springs.
The coated filament passes through the zig-zag grid four times. The diagonal strip of metal is the anode.
The two horizontal elements are made of the insulating material Mica. The top mica is quite thick as it has to withstand the rotational force of the filament springs.
The wide glass tube envelope is 25 mm in diameter, and excluding the I/S1 base pins is 84 mm tall.