The 6A7 is an American designed 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 Brimar name on the base cap but the Type designation on the glass looks to be of American origin.
The tops of grids shows the construction with the signal from the top-cap going to a grid between the two joined screen grids.
A closer view of the top micas. Through the hole in the mica disc can be seen some of the circular wire grids.
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.
