The EF83 is a variable-mu AF voltage amplifying pentode.

The thin glass tube envelope is 20 mm in diameter and, excluding the B9A base pins, is 48 mm tall.

References: Datasheet, ³⁰⁰² & ¹⁰⁴⁰. Type EF83 was first introduced^¶ in 1956.

 
Pin Connections

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

 
Absolute Maximum Operating Conditions^¶

Pentode	Vh	Ah	Va	Vs	Vg	mAa	mAs	ra	gm
	6.3	0.2	250	50	-1.6	4.0	1.15	0.5M	1.6

Thanks to Frank Philipse for supplying the above PDF datasheet