The N31 is an audio output pentode for use with 300 mA heater chains and intended for single ended operation.

Internally the anode is a substantial box and contains a flat cathode tube and three grid supports. The first two wire grids are visible but not the third. The expectation is that it is a pentode as one would expect to see some sign of beam plates if fitted.

The size of the valve and the top cap connection together with the domestic Marconi label on this M-OV valve suggest that it was designed for line output stage service in early television receivers. See 20P1 as a line output valve.

The side view shows the Type designation but no additional internal detail.

The final picture shows the designation stamp in detail.

The classic envelope is 54 mm in diameter and, excluding the B7 base pins, is 128 mm tall.

 
Pin Connections

B7	1	2	3	4	5	6	7
	hct	-	g2	4	4	k	a

 
Absolute Maximum Operating Conditions

Pentode	Vh	Ah	Va	Vs	Vg	mAa	mAs	gm
	26	0.3	200	180	-4.4	40.0	10.6	10.0

Thanks to Frank Philipse for supplying the above datasheet

This exhibit was last updated on 02 February 2008 {find valves by name}