Cathode ray tube having an improved indirectly heated cathode

A cathode ray tube comprising

• an evacuated envelope comprising a panel portion, a neck portion, a tunnel 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 comprising an indirectly heated cathode structure, a control electrode and an accelerating electrode, and a main lens for focusing an electron beam from said electron beam generating section onto 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 metal sleeve, a base metal having an electron emissive material coating on an outer top surface thereof and attached to one end of said metal sleeve, and a heater positioned within said metal sleeve,
• wherein said heater comprises a major heating portion having a spirally wound heating wire and leg portions disposed at ends of said major heating portion,
• each of said leg portions comprises a first multilayer winding portion having heating wires and a second multilayer winding portion disposed intermediate between said major heating portion and said first multilayer winding portion and having heating wires wound in a plurality of layers, said plurality of layers of said second multilayer winding portion being at least three layers, and said first multilayer winding portion being wound spirally in a plurality of layers greater in number than the at least three layers of said second multilayer winding portion,
• said major heating portion and at least a portion of said second multilayer winding portion are covered with an insulating coating, and
• said heater is welded to electrical conductors for applying a voltage thereto at said first multilayer winding portion.