The E1111 experimental valve from the M-OV labs is a tetrode. It is battery powered as is confirmed on the label. The interesting thing is the presence of rods at each end - beam plates reduced to four rods.
The filament is centre tapped and so the valve can be run from one or two dry calls on the filament. The serial number of this prototype is 70.
Both grids pass flat across the two filament strands and thus parallel to the anode. The strut in the middle of the anode connects to the filament tension spring and is the centre tap connection.
The top mica with filament strands and tension springs on the left.
The lower mica.
The wide glass tube envelope is 28 mm in diameter, and excluding the IO base pins is 74 mm tall.
Updated September 12, 2013.