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Terry Collard had labeled the base to whick this valve was attached as a Philips 12A8, no markings exist on the valve itself.

The 12A8 is a heptode mixer known in America as a pentagrid converter. The local oscillator is formed between grids one and two. The screening grids are g3 and g5 and the signal is injected via the top-cap to g4.

The 12A8 as G and GT versions is the 12.6 Volt version of the 6A7 (UX7) or 6A8 (IO) and other characteristics are identical.

Unlike American metal valves, this is a glass envelope with a permanently fixed metal screening can.

The wide glass tube envelope is 32 mm in diameter, and excluding the IO base pins is 68 mm tall.

References: Data-sheet, ⁴⁰⁵⁹ & ¹⁰⁴⁰. Type 12A8 was first introduced in 1939. See also 1939 adverts.

Pin Connections

Absolute Maximum Operating Conditions^¶

Thanks to Frank Philipse for supplying the above PDF datasheet.