Cathode ray, tube including an electron gun having specific relation of axial length of focus electrode and focus electrode-screen distance

A cathode ray tube comprising:

• a vacuum envelope comprising a panel portion, a neck portion, a funnel portion having a large-diameter end thereof connected to said panel portion and a small-diameter end thereof connected to said neck portion, and a stem having conductive pins embedded therein and closing off an open end of said neck portion on a side thereof opposite from said funnel portion;
• a phosphor screen formed on an inner surface of said panel portion;
• an electron gun housed within said neck portion;
• and
• a deflection yoke mounted externally of said vacuum envelope in a vicinity of a transition region between said neck portion and said funnel portion;
• wherein said electron gun comprises a cathode, a beam control electrode, an accelerating electrode, a first electrode, a focus electrode and an anode arranged in the order named with specified spacings therebetween,
• wherein said anode is formed of a large-diameter cylinder portion disposed on a phosphor screen side thereof and a small-diameter cylinder portion disposed on a cathode side thereof, said large-diameter cylinder portion and said small-diameter cylinder portion being connected together in a direction of an axis of said cathode ray tube,
• wherein said focus electrode is formed of a large-diameter cylinder portion disposed on a phosphor screen side thereof and having a diameter larger than a diameter of said small-diameter cylinder portion of said anode, and a small-diameter cylinder portion disposed on a cathode side thereof and having a diameter smaller than a diameter of said small-diameter cylinder portion of said anode, said large-diameter cylinder portion and said small-diameter cylinder portion of said focus electrode being connected together in the direction of the axis of said cathode ray tube, said large-diameter cylinder portion of said focus electrode being disposed concentrically with and within said large-diameter cylinder portion of said anode,
• wherein said anode and said first electrode are electrically connected together within said cathode ray tube, and
• wherein the following inequalities are satisfied:
• −LP+184.9≧LG4≧0.0004 LP3−0.1571 LP2+21.006 LP−922.41,
• where LG4 (mm) is an axial length of said focus electrode, and LP (mm) is a distance from a phosphor screen side end of said focus electrode to a center of said phosphor screen.