The 6A7 is a heptode mixer, what is known in America as a Pentagrid converter. The UX7 base clearly identifies the design as American but here we have a British Tungsram made 6A7.
The 6A8 is the same valve electrically but on an IO base. We also have the 6A7E in the museum.
Looking above the top mica shows the screen grids g3 and g5 strapped together and the top cap connection (signal input) going to grid three. Grid two, the oscillator anode, is a plain rod placed in line with the other grid supports.
The outer grids are circular and the cathode tube is seamless. Clearly visible is the method of closing the anode after pressing, a double fold clamped together.
The classic envelope is 38 mm in diameter and, excluding the UX7 base pins, is 99 mm tall.
References: Data-sheet, 1040 & 1043. Type 6A7 was first introduced in 1933.