Sensibly equivalent¶ to:
The NR15A is a British Navy triode receiving valve. Introduced in 1924 it was the first naval valve to have an oxide coated filament. This valve looks to have been made by the Azide process.
The photograph is essentially an M-OV type L410 manufactured during the mid to late 1930s. Although the Azide process was essentially obsolete by this time it was used occasionally, and British Navy specifications may have remained unchanged for years after the technology altered.
This example dates from 1936 by which time it was known as the 'Lord Louis' valve in honour of the improvements Lord Louis Mountbatten is reported to have suggested.
The balloon envelope is 40 mm in diameter and, excluding the B4 base pins, is 85 mm tall.
References: Datasheet, 1043 & private communication. Type NR15A was first introduced in 1924.
Absolute Maximum Operating Conditions¶
Updated April 04, 2015. shape:balloon construction:pinch type:triode age:1920.1930 base:b4 heater:4.0v pins:4 pin:1.a pin:2.g1 pin:3.f pin:4.f