The NU1 is a half wave rectifier with flying leads. The bulb is spherical with tubes and pinches at each end. The maximum PIV is 14 kV and the anode dissipation is 150 Watts. The total emission is 240 mA.
The NU1 and NT1 (transmitting triode) were made by M-OV originally in 1917 to a theoretical design originated by the Admiralty Signal School. This exhibit is dated 1944 and illustrates the long lived nature of the transmitters.
The mounting of the rectifier is by means of a bronze strip assembly that connects to the end tubes with metal straps and buckles. The white insulation is asbestos tape. The flying leads have ceramic beads as initial high temperature insulation. Away from the bulb the insulation sleeve is woven cotton that has been varnished.
The NU1 takes second place to the CV1258 reference in this 1944 valve. The serial number is 8397C
The filament is tungsten wire, possibly thoriated, and held in folds of the supports. It forms a single V.
The top of the filament and heavy duty tensioning spring that is secured in the anode end pinch.
The balloon envelope is 120 mm in diameter, and excluding the base pins is 240 mm tall.