A coil heater of an indirectly-heated type cathode electrode of a cathode ray tube

摘要

A cathode ray tube includes a phosphor screen (4) and an electron gun (9). The electron gun (9) includes an indirectly heated cathode structure (21) and plural grid electrodes in axially spaced relationship. The cathode structure includes a base metal (27) having an electron emissive material coating (26) and a heater (25) for heating the base metal (27). The heater (25) includes a major heating portion HM having a spirally wound heating wire and leg portions HL disposed at ends of the major heating portion HM, and each of the leg porstions HL includes a first multilayer winding portion having heating wires wound spirally in plural layers and a second multilayer winding portion disposed intermediate between the major heating portion HM and the first multilayer winding portion and having heating wires wound in plural layers. The major heating portion HM and at least a portion of the second multilayer winding portion are covered with an insulating coating, the heater is welded to electrical conductors for applying a voltage thereto at the first multilayer winding portion, and the number of layers in the second multilayer winding portion is at least three and the number of layers in the first multilayer winding portion is larger than that in the second multilayer winding portion. <IMAGE>