The NR73 was a very popular and useful double triode badged here as a Navy Receiving valve. It was later given the CV reference of CV1285 that also appears on the glass of this exhibit. A modified NR73 became the CV181 and commercially the ECC32.
Type NR73 and its commercial equivalent the 6N7G, is by no means a general-purpose double triode since it has a powerful heaters, a common cathode, and is designed to operate in push-pull Class B2 with zero grid bias. The anode to anode load is given as 8,000 Ω. As an audio power valve it is capable of 10 W output.
The twin triode sections seen end on. Both control grids have heat radiating fins attached to the top of the copper supports.
Face view showing the reduced diameter at the top of the cathode tube as it enters the top mica.
The classic envelope is 45 mm in diameter and, excluding the IO base pins, is 88 mm tall.
References: Data-sheet & 1043. Type NR73 was first introduced in 1937. See also1937 adverts.