Shadow-mask having rectangular apertures

Claim 1

A shadow-mask type color cathode ray tube comprising: an evacuated envelope; a multi-color image screen including a plurality of interspersed groups of elemental fluorescent dots including blue; electron gun means including a plurality of electron guns for projecting a corresponding plurality of electron beam components towards said image screen, said electron gun corresponding to the blue fluorescent dots having an outside diameter smaller than those of the other electron guns, and said electron guns being arranged in an isosceles triangle having its apex corresponding to said electron gun for blue; and a shadow-mask having a plurality of substantially rectangular shaped apertures therein, said shadow-mask being disposed between said screen and said electron gun means for selectively directing said electron beam components onto said fluorescent dots; the distance Sx between a position at which each of said beam components is deflected and the axis of the electron gun unit as measured in the direction of scanning, and the distance q between the shadow-mask and the fluorescent surface being defined by q aL/3Sx Sx Sgx (L-q)/(Lsg-q) where a is the pitch of the beam passing apertures of said shadow-mask in the direction of scanning, L is the distance between the deflection position and the fluorescent surface, Sgx is the distance in the direction of scanning between the tip portion of the electron gun and the axis of the electron gun unit, and Lsg is the distance between the tip end of each electron gun and the fluorescent surface.