The NR45 is a pre CV UK Navy receiving valve. It is a variable-μ HF pentode based on the VMP4G. When used by the GPO it was known as a POVT119. With the advent of the CV register the name changed to CV1169 that was universal across Government departments.
The reverse carries the commercial VMP4G designation indicating complete equivalence.
Looking into the top of the glass reveals the top mica but little else.
The classic envelope is 44 mm in diameter and, excluding the B7 base pins, is 125 mm tall.