The NR61 is a vari-μ pentode specified by the Admiralty as pattern W265. In fact this is an M-OV design known commercially as the W42. With the advent of the CV system the NR61 became known as the CV1183.
The M-OV etched ellipse contains the W42 designation. This is the original marking and the NR61 has been overprinted for the Admiralty contract.
Not the greatest image of the three wire grids and the copper supports of the control grid.
The top of the envelope showing the wire from the control grid to the top cap. The cathode tube is round.
The classic envelope is 41 mm in diameter and, excluding the B7 base pins, is 103 mm tall.
