The 6A7 is an American Pentagrid converter or heptode mixer. The 6A8 is the same valve electrically but on an IO base. We also have the 6A7E in the museum.
The heater can be seen to be twisted as a double helix a form usually used to reduce hum in audio valves.
The National Union name and Made in USA on the base cap.
The screening grids g3 and g5 extend further than the others and are visible from the top.
Another view of the screening grids.
The top cap connects to g4. The top cap itself is of the top hat type but there is an adapter pushed onto it with a screw thread. This would then be a replacement valve for a set with screw-on top connections.
The classic envelope is 38 mm in diameter and, excluding the UX7 base pins, is 96 mm tall.
References: Data-sheet, 1040 & 1043. Type 6A7 was first introduced in 1933. See also1933 adverts.
