A Second Generation Color Tube Providing More Than Twice the Brightness and Improved Contrast

The parallax or shadow-mask type of tri-color tube was first described in the literature with a line-or grille-type color selection electrode1 but it first saw the light of commercial day in very much like its present form, using an apertured plate2 or mask for color selection. As thus introduced, the tube was distinctly wanting in brightness due principally to the poor electron-transmissivity of the aperture mask and efforts have been made ever since to improve its brightness capability. For the most part, emphasis has been placed on better tube fabricating techniques, which make possible the use of shadow mask structures having a higher electron transparency, and on new phosphor materials which yield brighter pictures in response to electron excitation. Even in its present commercial form, however, the shadow mask tube has not attained the desirable level of brightness, that is to say, sufficient for use in environments of high light ambients such as well lighted retail stores and similar display rooms, porches or rooms of residences that have large window areas and the like. When operated in such locations the shadow mask tube as it has been known heretofore suffers a serious loss in performance; specifically, the picture washes out both in respect of contrast and chroma.