| 摘要 |
<p>PURPOSE:To avoid any secular change in an operating characteristic because of sticking of cathode material to an outer circumferential edge of an electron beam transmitting hole so effectively, by covering a shielder on an electron emission surface of the cathode, and limiting an emission part of electron beams out of the cathode, to only an electron beam transmitting hole part of a first grid. CONSTITUTION:This electron gun unit has an electrode group consisting of first to fifth grids inclusive of the first grid having an impregnated type cathode K and an end plate 4 where an electron beam transmitting hole h1 is installed in opposition to this impregnated cathode K. An electron emission surface 3 of the impregnated cathode K is covered with an electron emission shielder 10 for interrupting the electron emission, and a through hole 11a having a diameter phi0 in a part being opposed to the electron beam transmitting hole h1 of the first grid is installed therein whereby electron beams are made so as to be limitedly emitted out of a part of the electron emission surface 3. With this constitution, such a possibility that cathode material, for example, Ba to be evaporated out of the cathode is stuck and accumulated to a peripheral part of the electron beam transmitting hole h1 is effectively avoidable, and simultaneously the incurrence of decrease in an interspace d01 between the first grid and the cathode K is substantially avoidable, thus a secular change in cutoff voltage is remarkably reducible.</p> |
