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v‘Swift. 3; 1946. R... P. JOHNSON ErAL 2,407,082 GATHODE RAY DEVICE‘ Filed Jan. 27, .1943 v h a . n m | . t.TuR “PT-.samm, ,by RWW m e nol.4.: J06.0 ,5, Thei Attorney. Patented Sept. 3, 1946 2,407,082 UNITED STATES PATENT OFFICE “ RalphP. Johnson and WilliamR. Grams, Sche-~ nectady, N. Y.z assignors: to General Electric Company, a corporation ofv New York . Application January 27, 1943‘, Serial No. 473,706 4, Claims. (Cl. 250-164) 1 ~ I 2.. The present invention relates to cathode ray and associated. means for focusing and de?ect. devices of’ the. type. known as. dark‘ trace tubes: ing the electron beam are. well known to those (for skiatrons) wherein a dark pattern is. produced skilled; in. the art.v The chamber 5 is closed at. one endv by a relatively thick. screen-carrying; wall on a screen, of suitable material by the impinge ment. thereon of a. beam of electrons. It. is. the 1;- which may be flat,_ or: may have... a. moderate aim of our invention to improve; the optical eili ' convex curvature toincrease its resistance to cit-e ciency of. such devices. ternal air- pressure. The pattern on thescreen of. a dark tracetube. Before. the parts“ of- the device are assembled, may be viewed by light which falls. on the screen. the‘ interior surface of the tubular part. 6 of. the from an external source :andis diffusely re?ected. 10 envelope- is coated with a layer‘ 9} of graphite, or other‘ suitable conducting, medium. ‘ This layer‘ therefrom to the eye of the observer- The pat or: coating 9‘ may. be applied upon the interior tern on a dark trace screen also may be projected by optical means, including a mirror or lens ar surface; of the tubular part of the envelope be. ranged to form an enlarged image, the light. em fore the end closures are. applied. The method ployed for such projection being incident on the described in United StatesLetters Patent. 21,264,-‘ 358", issued. to Record, utilizing an: aque screen. from an external. source. In the past it ous suspension of: graphite admixed withya dis. has. been customary to provide on the interior persi'ng: agent, such. as, bentonite, is; suitable for surface of the. envelope of cathode ray tubes. an this purpose. The coating; preferably; is baked electrically conducting layer,’ for example, a graphite layer. Such layers alsov were light-ab in contact with the». sorbing.v ‘ In consequence. of our invention the e?ective ness; of darktrace cathode ray deviceshas been The cathode I4 of the electron. gun 8 is con nected. to. a. negative, terminal. of. a high voltage source 153 byagroundedconducton IS. The cath ode is provided with a. ?lamentary heater and improved by providing, on the interior or exterior ordinarily, is coatedexternally with. alkaline, earth surface of a. portion of. theenvelope a. matte oxideto promote; electron emissivity. white surface. A large. fraction of the impingElectrically in contact with the conducting: ing light penetrating through the screen. is. dif coating-llv and extending; to- the. sealed-in terminal fusely reflected. from this matte white surface and is returned. through the screen to the optical I illiiszaninternal. coating; l I of aluminum, or‘other system employed for. projecting the image,’ or 30 suitable re?ecting. metal. This coating consti tutesa the ‘so-called ?nal anode in the device. It is reaches the observer direct with accompanyingv advantages as will be explained. In a. preferred embodiment. of our invention a metallic. re?ect ing; foundation coating. ?rst is produced on. the interior glass: surfaceof the envelope; Upon this reflecting foundation. a layer of matte white. ma terial is deposited. I Fig. L of the accompanying drawing is a. side. view of a cathode ray device, shown partly broken away, and. embodying a preferred form of. our invention; Fig. 2 is a front view; Fig. 3 illustrates a. modi?cation; and Fig. 4 is a diagrammatic view of one form of an optical projection system ems bodying a dark trace cathode ray device. ‘ connected. through the sealed-in lead l0‘ and a. conductor l2 to, thepositive terminal of the high. voltagesource l3. Superimposed onthere?ect ing layer M is a layer of matte white material It; which. extends almost to the front wall. ‘I of the. envelope... In the fabrication. of‘ the device. before. the front wall. 1 is applied, aluminum or‘ other; re. flectingi metal chosen to form the layer IL, is vaporized in any suitable way, as by high fre quency induction heating or by passage of cur rent. through a wire of. refractory metal (not. shown) on which a. pellet of. the metal to be Theenvelope of the‘ cathode ray tube of Fig. 1, 45 vaporized has been placed. which may consist of glass or other transparent material, is elongated and includes an end cham her 5 which is of greater diameter than the ad A suitable gas-free, heat-resisting white. ma terial, for example magnesium oxide, next is de on the interior surface of the window 1. The also occur from a suspension of ?nely divided posited on the inner surface of the side wall of joining elongated tubular portion 6. Within the the cathode ray tube as the indicated layer l6, tubular portion 6 adjacent the opposite end 50 Fig. 1. In accordance with one method, metal lic magnesium may be burned in air and the (broken away in the drawing) is located a so resulting fumes or smoke conducted into contact called electron gun 8, whereby a beam of electrons with the surface to be coated. Deposition may is projected upon a screen which is deposited construction and operation of such electron guns 55 magnesium oxide in water. The suspension or 2,407,082 4 slip is suitably applied and the resulting adherent distant surface, diagrammatically indicated at layer is baked at about 400° C. in air. A getter material, for example barium or magnesium, may be introduced for the absorption of residual dele ten'ous gas in the tube. A spring-supported get ter metal, which can be vaporized by high fre 33 through a correcting lens 34 gripped on its periphery by a holder 35. If the cathode my device 30 is one which employs our invention, a large fraction of the light which proceeds through the screen of the device and strikes the wall of quency heating and deposited on the inner sur the envelope is returned in a forward direction, face of the neck, 6, is illustrated at IT. Small‘ masses of suitable screen material, for that is, through the screen into the concave mir ror and thence to the ?nal image, increasing its example potassium chloride, bromide, sodium 10 chloride 01' other suitable halide of an alkali brightness and visibility. We do not wish to limit ourselves to the par metal, are introduced in such Way that they are I ticular optical projection system shown in Fig. 4, deposited on the inner surface of the end wall ‘I. For example, masses of the screen material nor to the details of construction of the described cathode ray devices. We have described some may be held in the shallow metal ‘holders l8 15 of these details, which are not a part of the pres which are attached to a spring l9 engaging with ent invention, in order to make clear the nature wall protuberances 20 (Fig. 2). Heat is applied 7 of our invention and how it is to be performed. (as by high frequency induction) until the halide It will be evident to those skilled in the art that is vaporized. other details of construction of the cathode ray The face plate ‘I is fusion-sealed to the rim of 20 device can be chosen, and other forms of optical the main envelope 5 in any suitable way, for ex apparatus can be used for viewing the screen or ample by the combined effect of combustion heat ing and electrical high frequency heating, as de scribed in United States Letters Patent 2,306,054 for projecting the pattern appearing thereon, without departing from the spirit and scope of the present invention. issued to Guyer. The electron gun 8 is sealed 25 What we claim as new and desire to secure by into place and the envelope is exhausted and Letters Patent of the United States is: baked to free the walls and enclosed metal parts 1, A cathode ray devicelcomprising a tubular of deleterious gases, all by well-known technique. envelope, a dark trace screen therein, means for The screen material next is deposited on the glass producing a pattern on said screen and a matte foundation‘, for example by high frequency heat 30 white re?ector adjacent said screen in such posi ing of the cups [8 which contain the massive tion that said reflector will constitute a light material. It is sublimed and deposits as a thin diifusing background for a pattern on said said layer on the inner wall of the face plate 1. The screen. cathode is activated and the other well-known 2. An electron discharge device comprising an fabrication steps are taken as usual. The per elongated envelope, a dark trace screen located forated electrode or control grid 2| of the electron at one end of said device, cooperating electrodes gun is connected by the conductor 22 to a point in said device remote from said screen whereby of potential on the source ‘I3 which is negative electrons may be projected on said screen, and with respect to the cathode l4. The electrode a coating of white material on a side wall sur 23 also is connected to the source l3 by a con face of said envelope adjacent said screen, to ductor 24, as shown. . increase the visibility of a dark screen pattern In another form of our invention, as shown when illuminated by light projected thereon. in Fig. 3, the inner wall of the envelope 5 is left 3. A cathode ray device comprising an elon bare except for a narrow strip 25-of a suitable gated envelope having alcathode-ray-responsive conducting material, such as graphite, which con screen at one end thereof, means longitudinally nects the coating 9 to the sealed-in lead l0. After displaced in said envelope for projecting a beam fabrication of the device according to the method of electrons on said screen, means for de?ecting outlined above herein, a coat 26 of suitable white said beam in response to external impulses, a material, such as an enamel or paint, is applied coating of light-re?ecting material on the inner upon the exterior of the side wall of the envelope 50 surface of said envelope adjacent said screen, and 5. To-increase the diffuseness of reflection from a coating of light-diffusing material superim the wall of the vcathode ray tube, its inner sur posed on said re?ecting material. face may be roughened in any suitable fashion, 4. An electron discharge device comprising an such as by sandblasting, before the device is as elongated envelope, ascreen of alkali halide lo_ sembled. ' ~ The advantages of our invention in increasing the brightness and visibility of a pattern formed 55 cated at one end of said device, an electrode con on the screen by electron impact appear when our improved'devices are viewed directly or are em stituted of an electrically conductive coating on the inner surface of said envelopeadjacent said screen, cooperating electrodes in said device re mote from said screen whereby electrons may be ployed in' an optical projection system such as 60 projected on said screen, and a coating of mag the Schmidt projector shown in Fig. 4. As shown nesium oxide on said conductive coating on an here, the pattern on the screen of the cathode interior surface of said envelope adjacent said ray device 30 is illuminated by a projection lamp which is diagrammatically indicated at 3|. Light from the screen thus illuminated falls on the con 65 cave mirror 32 from which it. is projected on a screen. - ' RALPH P. JOHNSON. WILLIAM R. GRAMS.