Marconi held a patent for cylindrical anodes and grids and we believe that the electrode shape used by Cossor was a way to get round the patent.
The pictures above and below show the electrode shape. The anode is a fan or parabolic shape in one elevation and straight sided in the other. The filament is not visible but is fan shaped to match the anode. The grid can be seen as a series of hoops attached to a support tray.
The fan shaped anode seen face-on.
The grid is formed from a series of wire loops.
A view of the box shows diagrams of the electrodes and gives details of the valve. The box dimensions are 60 mm square and 130 mm long, the construction is strong cardboard and the internal packing is horse-hair.
The wide glass tube envelope is 27 mm in diameter and, excluding the B4 base pins, is 80 mm tall.
References: 1003 & 1004 Type P1 was first introduced in 1922.