The EL33 audio output valve is the little brother of the EL37 with which it shares pin connections. Mullard describe this valve as a high sensitivity output pentode for use in AC mains equipment. The EL33 could be used in push pull to deliver 8 Watts, but the normal use was in domestic radio receivers as a single ended stage.

The classic envelope is 42 mm in diameter and, excluding the IO base pins, is 104 mm tall.

References: Datasheet, ¹⁰⁴⁰ & ¹⁰⁴³. Type EL33 was first introduced^¶ in 1938.

 
Pin Connections

IO	1	2	3	4	5	6	7	8
	m	h	a	g2	g1	-	h	k

 
Absolute Maximum Operating Conditions^¶

Pentode	Vh	Ah	Va	Vs	Vg	mAa	mAs	ra	gm	Pout	D
	6.3	0.9	250	250	-6	36	4	50,000	9	4.5	10%

Thanks to Frank Philipse for supplying the above PDF datasheet