GB1176964A - Television Pickup Tube Apparatus - Google Patents

Abstract

1,176,964. Image pick-up tubes. RCA CORP. 10 Aug., 1967 [20 Dec., 1966], No. 36870/67. Heading H1D. A vidicon is provided with two cathodes 44 and 46, Fig. 2, one cathode 44 producing a narrow (1 mil.) scanning beam and the other cathode 46 producing a broad (30 mils.) beam operative on the flyback of the scanning beam to discharge the target electrode. When the target is scanned from bottom to top, the scanning beam and cathode are arranged above the discharge beam and cathode, and both beams are arranged to be tangential to a magnetic flux line 52 or 62; this can be achieved by means of an auxiliary coil (40, Fig. 1, not shown) arranged outside the tube around the electron gun and connected in series with the focusing coil (32), the magnetic field of the auxiliary coil being adjusted by varying the current through it until the required tangential flux is provided. Each cathode comprises a cylinder arranged in a ceramic disc 54 and provided with an inclined end face covered with an emissive coating; and each cathode has its own lead-in connection 56 or 64. The control electrode 72 has individual apertures 76 and 78 for the respective beams, the aperture 78 being crossed by grid wires to preserve a uniform current density in the broad discharge beam, and a depending shield 82 prevents electron flow from one cathode to the other when the two are at different potentials. A second electrode 84 is similarly provided with grid wires across its aperture 92, and the electron gun is completed by a limiting aperture plate 96. If the scanning beam has a diameter of 1 mil. and the discharging beam a diameter of 30 mils., the discharging beam should preferably be disposed 50 mils. below the scanning beam on the target; if the magnification of the electron optics is one half, there should then be a spacing of 100 mils. between the apertures 100 and 102 in the plate 96.