The 6A7E frequency changer is on a UX7 base, its sister valve the 6A8 is identical electrically but is on an International Octal base. We also have a 6A7 in the museum that is given as identical. The 6A7S appears to denote an external metalisation version.
The inner coating goes all the way round the valve.
The five grids supports above the top mica. Grid 4, connected to the top cap, has additional supports at right angles to the main grid axis.
The classic envelope is 38 mm in diameter and, excluding the UX7 base pins, is 100 mm tall.
References: Data-sheet, 3002 & 3002. Type 6A7E was first introduced in 1937. See also1937 adverts.