The EL42 is an audio output pentode. 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: Datasheet, ³⁰⁰² & ¹⁰⁴⁰. Type EL42 was first introduced^¶ in 1947.

 
Pin Connections

B8A	1	2	3	4	5	6	7	8
	h	a	ic	ic	g2	g1	k	h

 
Absolute Maximum Operating Conditions^¶

Pentode	Vh	Ah	Va	Vs	Vg	mAa	mAs	ra	gm	rk	rl	Pout	D
	6.3	0.2	225	225	-10.0	26.0	4.1	90,000	3.2	360	9,000	2.5	10%

Thanks to Frank Philipse for supplying the above PDF datasheet

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