The E1750 is a dry battery heptode frequency changer. The top caps connect to grids g3 and g4. Grid 2, the oscillator anode, consists of two vertical rods.
The serial number of this experimental valve is 3 and the filament voltage is clear.
The top mica electrodes: the top cap connections to the grids are visible. Harder to see is that the filament is broken.
The wire grids. Note the grid 2 rod without wires.
The wide glass tube envelope is 29 mm in diameter, and excluding the IO base pins is 79 mm tall.
