Cathode ray tube having an improved heater

A cathode ray tube comprising:

• an evacuated envelope comprising 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 comprising an electron beam generating section including an indirectly heated cathode structure having a heater therein, a control electrode and an accelerating electrode, and a plurality of electrodes disposed downstream of said electron beam generating section for focusing and accelerating an electron beam emitted from said electron beam generating section toward said phosphor screen;
• and
• a deflection yoke mounted externally around said funnel portion for scanning said electron beam on said phosphor screen;
• said heater comprising a major heating portion having a spirally wound heating wire and two leg portions connected to opposite ends of said major heating portion,
• said two leg portions being welded to electrical conductors for applying voltages thereto at portions in the vicinity of open ends of said two leg portions, respectively,
• said heater being covered with an insulating film except for said portions for welding,
• said two leg portions comprising at least three layers of winding formed by spirally winding heating wires identical with said heating wire of said major heating portion,
• numbers of turns per unit length in each of said at least three layers of winding in said two leg portions being smaller than a number of turns per unit length of said heating wire of said major heating portion, and
• said numbers of turns per unit length in each of said at least three layers of winding in said two leg portions being within a plus or minus variation of not greater than 30% in said at least three layers.