Title: Method for cathode coating erosion suppression for a television tube

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Abstract: This disclosure depicts a novel method for use in the manufacture of a color television picture tube having a narrow neck wherein the neck has a front end joined with a flared portion of the tube and a rear end having an axially extending tubulator. The tube also has an electron gun having at least one cathode adjacent the rear end of the neck, said cathode having an electron emissive coating, a forward element adjacent the front end of the neck, and a plurality of electrodes interspaced between the cathode and the forward element. The electrodes and forward element each have at least one aperture wherein the apertures are coaxial. The apertures define a beam passageway for passing through the gun a stream of electrons emitted by the cathode during operation of the tube. The beam passageway unavoidably forms a gas conduit during evacuation of the tube. The method for suppressing erosion of the cathode coating during evacuation of the tube comprises: attaching a vacuum pump to the tube's exhaust tubulation and operating the pump in a first mode effective to evacuate the tube at a first rate during an initial pump-down phase when gas volume in the tube is highest. The pump is then operated in a second mode effective to evacuate the tube at a second higher rate during a subsequent pump-down phase when the gas volume is lower. As a result, the gas velocity through the tubulation is at all times at a low value effective to suppress erosion of the cathodes in the gun during evacuation.


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