| 摘要 |
PURPOSE:To give a sufficiently high concentrating ability to apertures, and increase the transmittance of an electron beam by adjusting the heights of protruding parts provided around the apertures to 25% or above of the widths in the horizontal- or vertical-axis direction of the apertures. CONSTITUTION:The first mask 8 and the second mask 7 are provided with protruding parts 21 and protruding parts 23 which are positioned around apertures 20 and 22 respectively. When an anode voltage and a voltage lower than the anode voltage are applied to the masks 8 and 7 respectively, electric lines of force extending from the protruding parts 21 of the mask 8 to the protruding parts 23 of the mask 7 are produced to form a tetrode lens system. As a result, the components of the electric lines of force which are in a direction vertical to the traveling direction of a beam become relatively more intense than those realized in a general cylindrical lens system, and the focusing power of a color picture tube is increased. In addition, by maintaining the heights of the protruding parts 21 and 23 over 25% of the diameters of the apertures 20 and 22, the efficiency of the lens effect is improved, and the transmittance of the electron beam is increased. |
