The CV131 is a general purpose amplifying pentode. The commercial equivalent is the EF92 and the M8161 is a special quality version.

Seen in close-up the inner arrangement of the grids is visible where the anode shape allows.

The thin glass tube envelope is 18 mm in diameter, and excluding the B7G base pins, is 45 mm tall.

References: Datasheet & ¹⁰⁴⁰.

 
Pin Connections

B7G	1	2	3	4	5	6	7
	g1	k	h	h	a	g3	g2

 
Absolute Maximum Operating Conditions^¶

Pentode	Vh	Ah	Va	Vs	Vg	mAa	mAs	ra	gm
	6.3	0.2	250	150	-0.65	8	2	0.5M	2.5

Thanks to Frank Philipse for supplying the above PDF datasheet