| 摘要 |
PURPOSE:To reduce the production cost, by composing a cathode, of a heater forming an alumina insulator layer over a heater core, metallic microwires wound over the heater, and an electron radiating substance spread over them. CONSTITUTION:A heater 3 consists of a heater core 1 of tungsten and an alumina insulator layer 2. Over the heater 3, tungsten wires are sound closely to form a cathode base 4 of metallic wires. In this case, the tungsten wires are wound closely from one end of the heater where the alumina insulator layer 2 is not applied, and the cathode base 4 and the heater 3 are connected electrically. Over the cathode base 4, an electron radiating substance 5 is spread and the both 4 and 5 form a cathode 6. The indirectly-heated cathode 6 does not use a tube-form substance as the cathode base like this. Therefore, a difficult work to penetrate a heater 3 in a small tube is not necessary. The production cost can be reduced consequently.
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