The N709 output pentode is the Marconi offering of the Mullard EL84.

The performance figures given here refer to class A operation. When used as a pair in push-pull with 43% distributed loading in the output transformer to feed the screen grid (g2) the output could reach 10W with 0.9% total distortion. The effect of distributed loading was to introduce negative feedback directly within the output stage.

The picture shows the grid radiators at the top and the ribs pressed into the anode for greater rigidity.

The side view of the anode seam.

A close-up of the radiating fins attached to the control grid support rods. At the centre can be seen the top of the rectangular cathode tube.

The thin glass tube envelope is 20 mm in diameter and, excluding the B9A base pins, is 68 mm tall.

 
Pin Connections

B9A	1	2	3	4	5	6	7	8	9
	ic	g1	k,g3	h	h	ic	a	ic	g2

 
Absolute Maximum Operating Conditions

Pentode	Vh	Ah	Va	Vs	Vg	mAa	mAs	gm	Pout	Pdiss
	6.3	0.76	250	250	-7.3	48	5.5	6.7	2.2	12W

Thanks to Frank Philipse for supplying the above datasheet

This exhibit was last updated on 04 July 2009