Sensibly equivalent¶ to:
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: Datasheet, 4059 & 1040. Type 12A8 was first introduced in 1939.
Absolute Maximum Operating Conditions¶
Updated November 23, 2016. shape:wide.glass.tube construction:pinch type:heptode age:1930.1940 base:io heater:12.6v pins:8 pin:1.s pin:2.h pin:3.a pin:4.g3.g5 pin:5.g1 pin:6.g2 pin:7.h pin:8.k pin:tc.g4