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The EL84 output pentode was introduced by Mullard in 1954. To demonstrate its use and quality the Mullard applications lab produced an amplifier design. The now classic 5-10 high quality audio amplifier.

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 10 W 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.

See also UL84 & PL84 produced for designs using AC or DC mains without a mains transformer and a series heater chain. The PL84 was used for TV frame output service.

By clicking the link from the exhibit name above, the full Mullard data-sheet 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.

References: Data-sheet & ¹⁰⁴⁰. Type EL84 was first introduced in 1953. See also 1953 adverts.

Pin Connections

Absolute Maximum Operating Conditions^¶

Thanks to Frank Philipse for supplying the above PDF datasheet.