The Spray Shield Tube

A metal coating is applied to a vacuum tube covering the tube envelope and the shell of the base by successive operations of sand blasting and spraying metal from an oxyacetylene blow torch which produces a coating which is in intimate contact with the glass envelope. A negative potential is applied to the metal spray shield when the tube is operated which prevents cathode rays, which are not intercepted by the anode, from reaching the interior surface of the glass envelope. Secondary emission of electrons from the glass wall is avoided. Localized heating of the glass is prevented and the fluctuation component of anode current is suppressed. It is pointed out that a tube structure coöperating with the spray shield is more economical and the apparatus associated with the tube can be simplified in design.