Circuit for operating multiple position display tubes

Claim 1

A circuit for operating a display tube comprising a gasfilled envelope containing a plurality of groups of electrodes arrayed in spaced-apart relationship, each group including a plurality of glow cathodes spaced apart in a plane and an associated anode positioned for electric discharge therewith, the cathodes in each group being so arrayed that they can be energized in different combinations to represent different characters and each group having cathodes which correspond in location to the cathodes of said other groups, and an auxiliary electrode common to all of said groups of electrodes and shielding said groups of electrodes from each other, said circuit comprising: means for applying a first energizing potential to said anode electrodes from a source of operating potential, a common cathode conductor interconnecting the corresponding cathode electrodes of the different groups of cathodes, means for applying a second operating potential to each common cathode conductor, there being a current path from each anode through each cathode and the source of operating potential, and a circuit module coupled to all of said current paths and to the common auxiliary electrode for receiving the total current flowing in each group of cathodes as each is energized, said circuit module including means for conducting a current proportional to said total current and coupling it to said common auxiliary electrode.