The EL84 output pentode was classically used in the Mullard 10W high quality audio amplifiers of the 1950s and 1960s.

The performance figures given here refer to class A operation.

When used as a pair in an ultra-linear push-pull configuration with 43% distributed loading the output could reach 10W with 0.9% total harmonic distortion.

With ultra-linear operation the screen grids were connected to taps in the in the output transformer primary winding. The valve operating conditions so produced were intermediate between a triode and a pentode. The operation of the distributed loading was to introduce negative feedback directly within the output stage.

By clicking the link from the exhibit name above, the full Mullard datasheet can be downloaded. Warning this is a very large PDF file.

The thin glass tube envelope is 20 mm in diameter and, excluding the B9A base pins, is 70 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

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This exhibit was last updated on 06 December 2008 {find valves by name}