GB1353872A - Cathode ray tubes - Google Patents

Abstract

1353872 Cathode-ray tubes; resistors THORN ELECTRICAL INDUSTRIES Ltd 5 July 1972 31514/72 Headings H1D and H1S A cathode-ray tube comprising inner and outer wall coatings over part of its envelope (e.g. the funnel of a display tube) forming a capacitor which may form part of the smoothing circuit of the power supply, is characterized in that the capacitor is connected to an electrode of the electron gun assembly by a resistor included in the assembly; the resistor limits current flow in case of flash-over, and thereby protects external components, e.g. solid state devices in supply and modulation circuits. In Fig. 2 the resistance 16 comprises a helical resistive coating 31 on the internal surface of a glass cylinder 32 and may be covered by a protective layer 33 of chromic oxide. Spring fingers connect the ends of the coating to a flange 40 on the final anode 15 and to a flanged member 36 which is connected by spring fingers 37 to the internal wall coating 25 and which also supports the getter 43. The flanged member 36 is secured to the flange 40 by glass rods 41 with lengths of stiff wires 42 embedded in them. The coating 25 is of graphite and extends over part of the funnel portion of the tube (not shown); the remainder of the interior of the funnel portion is coated with aluminium, which also covers the fluorescent screen. An anode button connected to the internal coating forms the sole H.T. connection for anode 15, and, apart from the area surrounding the button, the exterior of the funnel portion is coated with graphite which is connected to earth. The resistor 16 should have a resistance of at least 1000 ohms and may alternatively be an external coating over the glass cylinder.