| 摘要 |
472,860. Cathode-ray tubes. FARNSWORTH TELEVISION, Inc. June 23, 1936, No. 17419. Convention date, July 6, 1935. [Class 39 (i)] In producing optical images from television signals, a charge-storing grid 16 with a surface of insulating material is uniformly flooded with electrons and also bombarded and scanned by an electron beam from a gun 2 to build up charges on the insulating surface corresponding to picture signals and so to control the electron flow through the grid to form a picture on an adjacent luminescent screen 21. The flooding electrons are emitted by two indirectly heated cathodes 26 surrounded by spiral grid, lowvoltage anodes 34 and arranged on opposite sides of the beam from the gun 2. The cathodes 26 are spaced by a cross-bar 31 supported on the envelope 1 at 32. The grid 16 is a fine-mesh nickel screen smoked with fumes from burning magnesium to coat it with magnesium oxide and is spaced from the screen 21 by glass beads 24. The screen 21 is an incandescent screen of thin refractory sheet or knitted fabric of refractory wire of À00025 inch diameter. Electrons from the cathodes 26 have low velocities and build up a negative charge on the grid 16. High-velocity electrons from the gun 2 release secondary electrons from the grid 16 and form local positive charges allowing electrons from the gun 2 to pass to the screen. The beam from the gun 2 is focused by a coil 12, deflected by plates 7, 10 and modulated by picture signals on a grid 4 so that these positive charges correspond to the picture and leak away in slightly less than one scanning cycle, an intense flow of electrons from the cathodes 26 to the screen 21 resulting. The charges built up on the grid 16 depend on its bias, and negative charges corresponding to the picture may form on the back of the grid. The beam from the gun 2 may be unmodulated and the picture signals may be applied to the grid 16. |
