Multi-digit fluorescent display tube with differently spaced planar control grid sections

A multi-digit fluorescent display tube comprising:

• a substrate;
• a plurality of multi-digit indicating patterns arranged in a row in spaced side-by-side relationship along the longitudinal width of said substrates, each of said indicating patterns comprising a plurality of segmented anodes on which phosphor layers are deposited;
• at least one electron emitting filament stretched along the longitudinal direction of said indicating patterns so as to be in parallel and opposite to each of said indicating patterns;
• a control grid comprised of a plurality of planar sections disposed between said filament and said indicating patterns, said planar sections of said control grid being positioned at different distances with respect to said filament;
• whereby the perveance of each of said indicating patterns is adjusted so as to illuminate each of said indicating patterns in uniform brightness when said fluorescent display tube is energized by heating said filament with a direct current power source;
• a light transparent evacuated sealed envelope in which the anodes, the filament and the control grid are disposed and through which the display may be viewed externally when the display tube is in operation.