Cathode ray tube having an improved indirectly heated cathode structure

A cathode ray tube having an evacuated envelope including a panel portion, a neck portion, a funnel portion for connecting said panel portion and said neck portion and a stem having a plurality of pins therethrough and being sealed to close said neck portion at one end thereof, a phosphor screen formed on an inner surface of said panel portion, an electron gun housed in said neck portion, said electron gun having an indirectly heated cathode structure and a plurality of electrodes disposed downstream of said indirectly heated cathode structure, spaced specified distances apart, arranged axially in a specified order, and fixed by insulating rods for projecting an electron beam toward said phosphor screen, and a deflection yoke mounted around a vicinity of a transitional region between said neck portion and said funnel portion for scanning the electron beam on said phosphor screen,

• said indirectly heated cathode structure comprising:
• a base metal having an electron emissive material coating on an outer top surface thereof;
• a metal sleeve having said base metal attached to a first end of said metal sleeve and having a second end opposite from said first end;
• a heater housed partly within said metal sleeve, said heater including a major heating portion having a spirally wound heating wire and leg portions connected to respective ends of said major heating portion and comprising heating wires wound spirally in a plurality of layers;
• an insulating film covering said major heating portion and a portion of each of said leg portions continuous with said major heating portion;
• and
• a black coating film covering a portion of said insulating film extending from said major heating portion toward each of said leg portions, a whole of said black coating film being housed within said metal sleeve.