The 6BQ5 is another designation for the Mullard designed output pentode EL84.

The thin glass tube envelope is 72 mm long excluding the B9A base pins and the diameter is 20 mm.

References: Datasheet, ³⁰⁰² & ¹⁰⁴⁰. Type 6BQ5 was first introduced^¶ in 1953.

 
Pin Connections

B9A	1	2	3	4	5	6	7	8	9
	ic	g1	k,g3	h	h	ic	a	ic	g2

 
Absolute Maximum Operating Conditions^¶

Pentode	Vh	Ah	Va	Vs	Vg	mAa	mAs	gm	Pout	Pdiss
	6.3	0.76	250	250	-7.3	48	5.5	6.7	2.2	12W

Thanks to Frank Philipse for supplying the above PDF datasheet