Indicator tube
United States Patent 2991387

926,387. Glow-discharge lamps. BURROUGHS CORPORATION. Sept. 17, 1959 [Sept. 22, 1958], No. 31733/59. Drawings to Specification. Class 39 (1). A glow-discharge gas-filled indicator tube, comprises a filling of an ionizable gas and mercury, wherein the mercury reduces the energy of the ions and so sharply reduces the amount of spluttering from the cathode. In one form the device comprises a stack of cathodes of stainless steel, molybdenum, aluminium or " Nichrome " (Registered Trade Mark), shaped in the form of numerals mounted on two insulating supports. During assembly a small glass vial containing mercury and a heating filament is introduced into the device which is then evacuated, filled with a rare gas such as Ne or other ionizable gas at a pressure between 50-100 mms. of Hg, preferably 70 mms. of Hg, and the device is sealed. The tube is then partially aged, the filament is heated, thus shattering the glass vial, and liberating mercury vapour into the lamp; the aging of the tube is then completed. Alternatively, after sealing, the mercury may be liberated immediately and the tube is then aged completely. Any other method of introducing the mercury may be employed, i.e. a side tube may be used. The stack of cathodes are contained in a cup-shaped anode, which rests on a mica disc, and which has two diametrically disposed slots in its wall to enable leads to reach the cathodes, the anode thus also acting as a shield.

Mccanley, John H.
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313/546, 445/6, 445/16
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