A new method of making accurate fine-wire grids for use in radio valves

New techniques are described for the manufacture of very accurate planar fine-wire grids for radio valves. A polygonal mandrel is used, at each corner of which is a rod, screw-cut to the pitch of the grid to be made. The grid wire is wound on to this mandrel so that each groove of the screw thread locates one turn of the wire. A grid frame is then brazed to each face of the winding in turn, by eddy-current heating in a reducing atmosphere. The method is especially suitable for grids made from wire of 10¿ diameter or less, and wound at 400 turns/in or more. It not only simplifies manufacture, but also produces grids more accurately than any other known method. These techniques can also be applied to the manufacture of double-sided grids by clamping two planar grids back-to-back. The method has been further extended to the automatic accurate alignment of grids of 500 turns/in, to an accuracy of about ±5¿.