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The 6A7 is an American Pentagrid converter or heptode mixer. The 6A8 is the same valve electrically but on an IO base and the 12A8GT has a 12.6 Volt heater. The variants are: 6A7E and 6A7S.

The red band around the base reads 'Bell Telephone Manf. Co. No. 8318A'. The etching on the glass also reads ADZAM. The base shows the real maker to be RCA. As Adzam was a Belgium company (owned by Philips) this looks like a post war valve supplied to Adzam and sold locally by them.

The supports protruding through the top mica show the electrode spacing. The tie rod on the left joins the two screen grids together (g3 + g5). The signal grid (g4) has a lead taken to the top cap. The spacing on the notched rods show the winding pitch. The support for g2 is not notched and in many cases this grid as anode would just be two vertical rods.

The classic envelope is 38 mm in diameter and, excluding the UX7 base pins, is 98 mm tall.

References: Data-sheet, ¹⁰⁴³ & ³⁰⁰². Type 6A7 was first introduced in 1933. See also 1933 adverts.

Pin Connections

Absolute Maximum Operating Conditions^¶

Thanks to Frank Philipse for supplying the above PDF datasheet.