X-rays in vacuum valve manufacture

X-ray examination of large water-cooled valves has eliminated hidden defects. Two views, at right-angles, are taken, and compared with corresponding drawings of the valve electrodes. The method has also been applied to multi-electrode glass valves; formerly, examination by dissection disturbed the errors of assembly, etc., sought for. Stereoscopic photographs are taken. Two equipments are described. That in Paris has a full-wave valve rectifier supplying 10 mA at 200 kV to an X-ray tube contained in a cabinet of 5-mm. lead. That in London employs a self-protected tube, supplied through flexible cables each supporting 90 kV, the mid-point being earthed. This tube has a grid; control p.d. is applied which limits the electron flow to the period of peak anode p.d., thus increasing the effective rating. Both installations use lead camera chambers.