The NR57 is an audio output valve, in fact a type ML4 from MOV made for military use in WW2. 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. The loudspeakers it was intended to drive in radio receiver applications would have had to have been sensitive.

The classic envelope is 42 mm in diameter and, excluding the B5 base pins, is 98 mm tall.

 
Pin Connections

B5	1	2	3	4	5
	a	g	h	h	k

 
Absolute Maximum Operating Conditions

Triode	Vh	Ah	Va	Vg	mAa	ra	gm	Pout
	4.0	1.0	200	-13.5	17	3,700	2.7	0.65W

This exhibit was last updated on 19 January 2003