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The EL42 is an audio output pentode designed for car radio use. The anode dissipation is 6 Watts and the HT requirement is modest. The Mullard data-sheet says: the limiting values, characteristics and audio performance of the EL42 and EL85 are identical. The diagram in the sheet is in the style of this exhibit.

The Pye Black Box amplifier used a pair of EL42's in the output stage to give a record player amplifier with 5 Watts output.

Valves on the B8A base originally had a metal locating spigot as well as a metal skirt with locating pip. These location aids were required as the pins were equi-spaced around the pin circle circumference. The style of this exhibit was the next development. The 22 mm diameter metal skirt with pressed locating pip was adequate without the spigot. The final version can be seen in EL42 where the skirt and locating pip are moulded into the glass envelope and the costs were thus further reduced.

A single ended Class A output stage could deliver 2.5 Watts. This was sufficient for most car radio receivers, but a pair in push-pull would generate a respectable 5.5 Watts for larger receivers and audio equipment.

The pressed pip. The control grid has fins attached to aid cooling.

The thin glass tube envelope is 20 mm in diameter, and excluding the B8A base pins is 53 mm tall.

References: Data-sheet, ³⁰⁰² & ¹⁰⁴⁰. Type EL42 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.