The 6A7E frequency changer is on a UX7 base, its sister valve the 6A8 is identical electrically but is on an International Octal base. We also have a 6A7 in the museum that is given as identical. The 6A7S appears to denote an external metalisation version.

The classic envelope is 37 mm in diameter and, excluding the UX7 base pins, is 98 mm tall.

References: Datasheet, ³⁰⁰² & ³⁰⁰². Type 6A7E was first introduced^¶ in 1936.

 
Pin Connections

UX7	1	2	3	4	5	6	7	tc
	h	a	g3,g5	g2	g1	k	h	g4

 
Absolute Maximum Operating Conditions^¶

Heptode	Vh	Ah	Va	Vs	Vg	mAa	mAs	ra	gm
	6.3	0.3	250	100	-3	3.5	2.7	0.36M	0.55

Thanks to Frank Philipse for supplying the above PDF datasheet