The 7S7 triode heptode was designed for frequency changer use in radio receivers. The 7S7 was also made for mobile use with 12 Volt vehicle batteries for the heater, in this case the valve was called the 14S7.

The Brimar identification is clear but the coating on the inside of the envelope partly obscures the details of the valve's construction. Close inspection under strong light reveals a single cathode and two valve sections mounted vertically.

The dome allows some view of the construction. The top section is the triode.

The wide glass tube envelope is 28 mm in diameter and, excluding the B8B base pins, is 57 mm tall.

References: Datasheet & ¹⁰⁴⁰. Type 7S7 was first introduced^¶ in 1948.

 
Pin Connections

B8B	1	2	3	4	5	6	7	8
	h	a	a(t)	g1(t),g3	g2,g4	g1	k	h

 
Absolute Maximum Operating Conditions^¶

Heptode	Vh	Ah	Va	Vs	Vg	mAa	mAs	ra	gm
	6.3	0.3	250	100	-2	1.8	3.0	1.25M	0.525

Triode	Va	mAa
	150	5.0

Thanks to Frank Philipse for supplying the above PDF datasheet

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