Sensibly equivalent¶ to:
The NR57 is an audio output valve, in fact a type ML4 from M-OV made for military use in WWII. With a 4.0 Volt heater it was designed to be mains driven, so it is surprising to find the output power is so low. However, the data-sheet says that it was for use as a driver for a larger output valve.
The classic envelope is 42 mm in diameter and, excluding the B5 base pins, is 98 mm tall.
References: Data-sheet & 1043. Type NR57 was first introduced in 1929.
Absolute Maximum Operating Conditions¶
Updated December03, 2012. shape:classic construction:pinch type:triode age:1920.1930 base:b5 heater:4.0v pins:5 pin:1.a pin:2.g1 pin:3.h pin:4.h pin:5.k