The DF97 was the last in the line of Mullard's low consumption dry battery amplifier pentodes.

At this time the Mullard production had moved offshore.

The thin glass tube envelope is 17 mm in diameter and, excluding the B7G base pins, is 46 mm tall.

References: Datasheet, ¹⁰⁴⁰ & ³⁰⁰². Type DF97 was first introduced^¶ in 1954.

 
Pin Connections

B7G	1	2	3	4	5	6	7
	f-,s	a	g2	g3	f-,s	g1	f+

 
Absolute Maximum Operating Conditions^¶

Pentode	Vh	Ah	Va	Vs	Vg	mAa	mAs	ra	gm
	1.4	0.025	85	62	0	1.7	0.7	0.45M	0.94

Thanks to Frank Philipse for supplying the above PDF datasheet