The E1175 is an M-OV experimental code. The valve is also marked as a VT25.
The VT25 transmitting triode has a large square four pin base as can be seen from the picture. The anode box is quite large and blackened to radiate heat more effectively. This exhibit has a reduced depth L4 base as have VT25 and VT25. It is possible that the experimental type refers to this base variant.
Operating frequency would be in the HF range and the output power was of the order of 36 Watts.
The large box anode.
The box anode with the mica above fitting into the shoulder of the glass ebvelope.
The inner black box is the grid heat sink. Note the filament tension springs and the complicated support micas.
The other side of the glass has the VT25 and stores code 10E/7312.
Looking into the square anode the M shape of the oxide coated filaments can be seen as well as the grid winding.
The L4 base that came with the valve.
Another view of the base with the Anode and Grid pins marked.
The wide glass tube envelope is 57 mm in diameter and, excluding the L4 base pins, is 145 mm tall.