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 red lettering reads Distributed by Mullard.
The top mica showing the round cathode and line of grid supports. G2 (oscillator anode) is a pair of plain rods. The signal input grid has the supports at 90° to the other grid supports. This g4 connects to the top cap.
Side view of the top section.
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.