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The EL41 is an early all glass output pentode. Mullard describe the EL41 as an output pentode rated for 9 Watts anode dissipation, and intended primarily for use in AC mains operated equipment. They state that the EL41 should only be used with self-bias or semi-automatic bias.

Unlike the first B8A valves that had a metal base cover with locating spigot, this valve has a wider base to the envelope and a locating pip moulded into the glass. It indeed represents the transition point to the final all glass valve. The pins are still equi-spaced in the base and this soon gave way to the B9A and B7G styles that did not require a locating spigot or pip.

The anode plates stitched to offer a flange at the point of greatest heat generation. The control grid is wound on copper supports and has a small radiating fin at the top.

Looking along the grid axis, all three wire grids can be seen. Each of the control grid supports has the wide radiator fitted. These look to connect with the anode but are, of course, separate from it.

The thin glass tube envelope is 20 mm in diameter and, excluding the B8A base pins, is 67 mm tall.

References: Data-sheet & ¹⁰⁴⁰. Type EL41 was first introduced in 1947. See also 1947 adverts.

Pin Connections

Absolute Maximum Operating Conditions^¶

Thanks to Frank Philipse for supplying the above PDF datasheet.