The 9D6 miniature variable μ pentode was designed to operate at HF. This suggests radio frequency amplifiers as well as intermediate frequency amplifiers.

The thin glass tube envelope is 18 mm in diameter and excluding the B7G base pins, is 43 mm long.

References: Datasheet & ¹⁰⁴⁰. Type 9D6 was first introduced^¶ in 1947.

 
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