This paper describes a new X-ray tube anti-cathode designed to improve the stability and rectifying efficiency of gas tubes of the clamped electrode variety. Methods of increasing the control of such tubes are discussed. Tests on a tube actually made to this design show that steady currents up to 15 milliamperes can be used; and the rectifying efficiency is fairly constant under working conditions, between 60 per cent. and 70 per cent. for the ratio D.C./A.C.