US2567874A - Cathode-ray tube - Google Patents

Description

Sept. H, 1951 J. M. CAGE 2,567,874

CATHODE RAY TUBE Filed Aug. 28, 1948 4 Sheets-Sheet 1 /Z INVENTOR E (/UIH/V/M (3 765 (g MWWMJ ATTORNEYS Sept. 11, 1951 J. M. CAGE CATHODE. RAY TUBE 4 Sheets-Sheet 2 Filed Aug. 28, 1948 i E Q M 4 m1 MM m d ATTO R N 5Y5 Sept. H, 1951 J. M. CAGE 2,567,374

CATHODE RAY TUBE Filed Aug. 28, 1948 4 Sheets-Sheet 5 INVENTOR Jae/Mlthe;

ATTORNEYS pi. H, H9511 I J. M. CAGE 2,567,874

CATHODE RAY TUBE Filed Aug. 28, 1948 4 Sheets-Sheet 4 INVENTOR my. C'ne:

ATTORNEY 5 Sept. 11, 1951 CATHODE-RAY TUBE John M. Cage, Montclair, N. .l., assignor to Cage Projects, Ina, Union City,

of New Jersey N. J., a corporation Application August 28, 1948, Serial No. 465,585

This invention relates to image reproducing tubes and more particularly concerns a new and improved image reproducing tube for television and other similar applications. One object of the invention is a new and improved reproducing tube of the character set orth whereby increased brightness and definition and greatly improved stability and life are obtained.

Another object of the invention is an improved image reproducing tube particularly useful in the projection of televised and other images.

' Another object is a new and improved electron beam accelerating structure for reproducing tubes.

Another object is a new and improved method and means for shielding the electron beam of cathode ray tubes and to prevent the accumulation of free electrons on the tube walls.

Still another object is an improved cathode ray tube for the reproduction of images.

Another object is an improved shield or screen structure for cathode ray tubes.

Other objects of the invention will hereinafter appear.

For a better understanding of the invention reference is made to the following description and accompanying drawings forming a part of this application In the drawings- Fig. l is a somewhat diagrammatic view illustrating one embodiment of the invention;

Fig. 2 is a cross-sectional view of Fig. 1 taken along the lines i, 2 thereof Fig. 3 is another embodiment of the invention; h Fig. 4 is a cross-sectional view taken along the lines 6, d of Fig. 3;

Fig. 5 illustrates still another embodiment of the invention;

Fig. 6 is a cross-section of the embodiment shown in Fig. 5 along the lines 6,. 6 thereof;

Figs. 7 and 8 are cross-sectional views of still another embodiment of the invention;

Fig. 9 is a cross-section of a cathode ray tube embodying one form of the invention;

Figs. 10 and 11 illustrate still another form of the invention;

Figs. 12 and 13 illustrate still another form of the invention; and

Fig. 14 is a section along the line it, I l of Fig. 13.

In conventional image reproducing tubes the accumulation of free electrons on the tube walls is prevented by coating the inside of the glass hoot the portion of the tube where such shielding is desired. For example, in the conventional image reproducing tubes for television this coating in the form of colloidal graphite or carbon is applied to the cylindrical part of the tube at a point between the front end of the electron gun and the image reproducing screen.

The use of such a colloidal graphite or carbon solution as a coating for the conventional tubes is not entirely satisfactory. For instance, the higher the accelerating voltages used the greater the tendency of the carbon or graphite to contaminate the vacuum within the tube and materially impair the operation thereof. Moreover, the application of the shield directly to the glass tubing tends to limit the accelerating voltage which may be used due to the insulating problems, and the coating of the interior of the tube is a comparatively expensive operation. By means of my invention I avoid these and other objections to the disadvantages of the conventional tube structures.

In Fig. 1 I have shown somewhat diagrammatically a tube wherein contaminating coatings are dispensed with whileat the same time the beam can be adequately and completely shielded and the accumulation of free electrons prevented. This enables the use of very much higher voltages on image reproducing tubes and produces a tube that is more dependable and that will have a very much longer life. In the figure, it denotes the cylindrical section of the glass envelope, and I? a portion of the conical'section thereof. In the lefthand end of the cylindrical section lit the filament and cathode structure are denoted by the numeral It, the control grid or grids are denoted by the numeral Iti following the cathode and the next successive element is the second or high voltage electron beam accelerating anode iii. To shield the electron beam as it leaves the second anode it, I have provideda plurality of rod or wire-like members 2@ surrounding the beam and spaced from the cylindrical section it. These rod-like members it are substantially uniiormly spaced one from the other and are connected together at one end by means of a suitable metallic ring 22 which also acts as the mechanical support for the individual rods or wires it. This structure can be supported centrally within the tube it by any suitable means and may in turn also be arranged to support the second anode it. This may be advisable under certain conditions wherein it is desired to maintain both the shield and the second anode at the same high potential.

In cathode ray tubes embodying the magnetic deflection coils my new and improved" shield for the cathode ray beain is particularly effective since the coils usually surround the tube at a point after the second anode l8 and the magnetic fields must pass through the shield. With my shield I have been able to reduce both eddy and circulating currents to a minimum and by making the rod-like" members of a non-magnetic metallic material I have found that I can obtain excellent beam control characteristics of the tube with little or no undue load on the deflectin coil. As a matter of fact I have found that my new and improved shield has little or no effect on the power consumed by the surrounding magnetic deflection and focusing coils. while at the same time it effectively shields the cathode ray beam and prevents the collectionof free electrons during the operation of the tube and will not in any way contaminate the vacuum therein. If desired, the surface of the shield can be blackened and the tube coated on the outside thereof to reduce reflection of light onto .the image reproducing screen. 3

In Fig. *3 I have illustrated an embodiment of the invention wherein the shield or screen is formed integrally with the second anode element [8. In-this figure. .lfl denotes the cylindrical section of the tube and I2 denotes the conical section. At the left of the tube is again illustrated the cathode it having a filament l4 therein, a control grid or first anode l6 and a suitable in-: sulating'support 2| and-insulating. rods 26 for supporting the elements I4 and IS in proper alinement. The shield consists of a plurality of spaced metallic wires 28 preferably of a nonmagnetic material such as Monel or the like, although under certain conditions magnetic materials would be satisfactory. These wires are curved. inwardly toward the second anode l8 and are fastened thereto by welding or other suitable means. The righthand section of the wires 28 is curved outwardly as they pass the junction between the cylindrical and conical sections "of the tube envelope. so that the end portions of the wires will not interfere with the picture in any way. The second anode it together with the shielding wires 28 are supported in proper position within the tube by an inner cylinder 30 of insulating material having flanges 30' on each of its ends for fastening it in position within the tube It; Each of. the wires 28 is curved outwardly from the second anode [8 to meet the inner surface of the glass sleeve 30, whereupon it extends longitudinally along the surface 30 to the end thereof and is then curved outwardly as indicated at 28'. To rigidly support the wires in their spaced position, each wire 28 may be embedded-in the glass sleeve 30 substantially as shown at 32 in Fig. 4. Surrounding the cylindrical tube part III are coils 34 and 36 for focusing and deflecting the electron beam as it leaves the accelerating anode l8 through the orifice i8 therein.

The deflecting coil 6 generates two alternating magnetic fields so that the electron beam will scan the screen-in the tube in both horizontal and vertical directions. If a large body of metal or other conducting material of low resistance is placed in the center of the coil, large circulating and eddy currents will be induced therein. I have avoided the generation of these currents by shielding the beam with an electrically conductive shield having a plurality of spaced wiresconnected at only one end so that circulating current are completely eliminated and eddy-currents are reduced to an insignificant amount. Moreover, I have actually found that by using a plurality of spaced wiresin the manner illustrated a uniform electrostatic field is-produced about the beam to collect free electrons and there is no indication whatsoever in the resultant pic ture to indicate in any way that the shielding has been accomplished in this manner.

Although I have illustrated "in Figs.=- 1-4 wire or rod-like metallic members spaced about the beam and extending longitudinally thereof, each wire could 01' course be in the form of a helix, or the shield could comprise a screen formed by weaving individual strands of wire in such a manner as to prevent the generation of circulating currents that would place an undesirable load on the deflecting coils. In Figs. 7 and 8 I have shown a modification oi the structure illustrated able process and then removing the sliver from the surfaces 40 between the grooves 38. With the silver deposited inthe grooves 38, the second anode l8 having a plurality of short outwardly extending spring-like fingers 42 would then .be placed in the sleeve with each-finger resting in one of the grooves 3!! to contact the silver strips and connect them together.

An alternative arrangement is shown in Figs. 5 and 6 wherein I have illustrated the glass sleeve 30' fastened in the tube part It as previously described in connection with the sleeve. 30 in Fig.

I 3. In this adaptation the shield comprises an extremely thin layer 46 of platinum bright, palladium or other metallic coating having a resistance of preferably at least -200 ohmsper square inch. The material of which the surface 48 is formed should be of a non-evaporatable material when used under normal voltages and temperatures experienced in the operation of cathode ray tubes so that it will not contaminate the tube inany way. w

By embodying the insulating sleeve structure within the cylindrical tube part 'III as illustrated in this and other figures, I am able to apply. extremely high voltages-to the tube without the danger of puncturing the tube should a relatively low potential or grounded surface be brought into close proximity with the outer part of the tube envelope. This structure also effectively shields the tube beam and will not result in contamination of the tube with the application of high voltages thereto.

Moreover, with the structure I have been able to apply accelerating'potentials to the tube of the order of 50,000 to 75,000 volts and even higher without damaging the envelope 10, 12 in any way.

In the embodiment shown in Fig. 5 the second anode l8 can be supported by the glass sleeve 30' in any suitable manner as by a number; of springs 44 fastened to the anode and extending outwardly to bear against the metallized and non-evaporatable surface 46 of the inside of the sleeve 30. v

Fig. 6 is a cross-sectional view of the form of the invention of Fig. 5 and illustrates the spacing obtained between the outer surface of the tube envelope part III and the inner shielding layer 46. The gap between the concentric cyiin;

drical portions 35 and I is of course evacuated along with the evacuation of the tube as a whole and provides a high degree of insulation to prevent arc-over and irreparable damage to the tube.

Another important advantage of the structures heretofore described is realized particularly in humid weather. Normally a projection type ray tube, for instance. is completely enclosed in a cabinet and its temperature is therefore at a fairly low value with reference to the ambient temperature during times when the set is not operating. Under such conditions a thin film of moisture may condense on the outer surface of the tube and in the presence of dirt and dust which usually also settles on the tube a fairly good conductive layer to ground will be formed. If the potential on the shield, which is conventionally disposed on the inner wall of the tube part it. exceeds the normal dielectric strength of the glass, the tube wall will be punctured. This is a very definite limitation on the capacity of cathode ray tubes. With my invention, however, I can materially increase the potential to be applied to the shield without danger of breakdown and I can moreover avoid contamination of the tube by reason of the particular character of the shielding structure and, in addition, eliminate for all practical purposes circulating and eddy currents which produce an undue load on the deflection coil.

In Fig. 9 I have illustrated an alternate embodiment of the invention. This embodiment is somewhat similar to the embodiment shown in Fig. 3 in that a plurality of individual wires or rods it are fastened at one end to the second anode i8 and extend longitudinally of the tube. In this embodiment an internal tubular glass sleeve 50 is supported at the lefthand end at the base it! of the tube Ill, and is provided at its other end with a slightly flanged section 52 which curves outwardly to contact the inner surface of the cylindrical tube part It at the point where it begins to taper outwardly to form the conical or flared section it. In this embodiment the wires or rods terminate within the flanged section if and are flared outwardly so that the ends of the wires will not interfere with the electron beam at the edges of the picture to be formed on the screen of the tube. The wires 2t may be embedded in the glass tube 50 as previously set forth. or they may just rest against the inner surface thereof and be held in place by frictional contact. It would also be possible to use a structure such as shown, for instance, in Fig. '7 wherein the small grooves as may be used to retain the wires ft in properly spaced alinement about the inner surface thereof.

Still another method of forming my new and improved tube structure which I have found to be particularly satisfactory is illustrated in Figs. 10 and 11 wherein the cathode ray tube is formed of a cylindrical section we. as previously described, which terminates in a flared section if curving outwardly to form a bell-like part which is closed at its larger end to provide a surface for receiving and holding the fluorescent screen on which the picture is formed. In this embodiment a circular glass sleeve M1 is flared outwardly either side of a point substantially in line with the front or righthand end of the anode it. The wires as which are uniformly spaced about the electron beam and act to shield the electron beam, as previously described, are each fastened at their inner ends to the anode it and curved outwardly therefrom to form, in their position of rest, a cone with the base part being three or four times I end the diameter of the of the anode I8 is provided with a flange I! surrounding the anode and through which the several wires 56 are passed. The flange 58. however, tion of the tube 54 so that when the anode I8 is inserted from the lefthand end the flange 58 will contact the internal wall of the tube 54 to limit any further forward movement. Since the wires 56' are flared outwardly in their position of rest. they will, upon being compressed for insertion into the tube 54, expand to frictionally contact the inner wall of the front portion 54' of the glass tubular part 54 and tend in effect to pull the flange 58 forwardly to securely engage it with the internal wall of the sleeve 54. This structure provides a completely self-supporting structure for the second anode together with the shielding wires 56. The tube 54 may be held in position within the tube envelope part It! either by welding the sleeve 54 in position in the tube In, or by providing suitable flanges or projections on the inside of the tube part ill to limit the longitudinal movement of the inner sleeve or tube 5%.

This particular structure therefore provides a simple and efiective method for holding the second anode and shield in place and providing a relatively long leakage path inside the tube to prevent arc-over to the other controlled electrodes as well as to prevent breakdown through the tube walls due to the close proximity of a ground to the tube wall or the formation of a conductive path along the wall to a grounded point on the tube of the apparatus with which it may be associated.

With this new and improved gun structure and more particularly the new and improved.

shield and mounting therefor, a more dependable and stable tube is provided that is capable of producing a very much improved picture.

In each of the previous embodiments I have illustrated the shield as terminating at just inside the flange section I: of the tube and curved outwardly slightly so that it will not interfere with the normal excursions of the beam within the tube. This structure, however, particularly provides, in another aspect, other important advantages which result in further improvement in the cathode ray tube.

In conventional tubes to my knowledge the fluorescent screen is normally disposed on the closed end i2 of the flared section l2 of the tube and because of certain structural requirements'the front end of the tube i2 must necessarily be curved outwardly slightly. The formation of a picture on this curved surface produces some degree of distortion together with the fact that dirt, finger marks and other smudges on the outer part of the tube front i2 will tend to impair or obliterate the projected image to some nt. This is particularly noticeable in projection, since both the inner and outer surfaces of the front wall are substantially in focus.

' Moreover, since the screen is not flat it is sometimes necessaryto stop the lens down to some extent to increase the depth of focus so that all parts of the picture will be focused on the screen. Further distortion is also encountered because of the projection of a curved picture onto a flat screen. I

In Fig. 12 I have illustrated a structure in accordance with the invention whereby these disadvantages are overcome and at the same time I am able to completely shield the beam from the 6 glass tube 64. The front is slightly larger than the narrowest 8ec-,

second, anode part l8 to the screen upon which the picture is reproduced. The screen 60 is preferably made with an outer layer of quartz or other similar material 62. On the inner surface of the quartz or Pyrex layer is a layer of phos-v phor or phosphorescent material 68 which is then covered by a deposit 01' aluminum 65. Surrrounding the screen 60, which is preferably circular in shape, is a glass ring 66 having a plurality of openings extending therethrough at spaced intervals. A view of this ring 66 is shown in Fig. 14 having the radially spaced openings 61. In this embodiment I have shown a plurality of longi-, tudinally disposed wires 68 extending from the cylindrical section l0 oi the tube to the ring 66 with the front or screen ends oi thewires 68 being secured in the ring openings 6]. The wires 08 in this" particular embodiment constitute in eiiect extensions of the wires or rods 20 in Fig. 1 or the wires or rods 28 in Figs. 3, 9 and 10. The wires 88, therefore, are in effect connected to: gether'at the second anode while being insulated. at the screen part by the glass or quartz ring 66. The high voltage connection for energizing the second anode and the shield wires 68 is made through the connection and the lead "II to only one of the wires 68. The screen can be similarly polarized by a short connection .12 from the aluminum layer 65 of the screen to one of the wires 68. A substantially-rigid support can be provided for the screen 60 and the surrounde. ing glass ring 6-6 by providing a plurality of spaced brackets or springs ll extending outwardly from the ring 66 to contact the inner surface of the glass envelope 12. In the case of very 'highpotentials, the ring 66 itself can be increased in width so as to extend outwardly-and even directly contact and be weldedto the glass envelope 12.

Fig. 13 is another embodiment of the invention along the lines of that illustrated in 12.

In this embodiment, however, I have illustrated a structure wh reby I can get potential gradations between t e screen:60 and the second anode i8 as shown, for instance, in Fig. 3. In

this embodiment the wires 28 are illustrated as.

terminating just inside the flared section of the tube l2 and each of the wires is provided with an insulator 80 on its end. A second wire 82 extends from the other side of the insulator 20 Similarly, a series of jumpers 88 are provided between the wires 82 so that each of these wires can also be maintained at the same potential.

With this arrangement I apply the high voltage potential to the contact 10 extending through the wall l2 of the tube which in turn is connected to the wires 86 by a lead II. A high resistance 90 is connected between the lead II and one of the wires 82. A second resistance 92 is connected between one of the wires 82 and one of the wires 28. The side of the resistor 82 connected with one of the wires 28 is also connected with the terminal 94 extending through the glass and in turn connected to ground 96 through a resistor 88. In this way a voltage divider system is provided so that it tor instance 100,000 volts are applied at the contact 10 each or the wires 86 together with the screen will be at that potential. The resistors 90, "and 88 may then be proportioned, for example, so that the potential on the wires 82 will be, say,

75,000 volts and the potential applied to the wires 28 and the second anode lit-will be about 50,000 volts. The advantages of the employment of a high voltage on the screen to get added beam acceleration, and, therefore, increased brightness and definition of the image, will be realized while at the same time a materially lower voltage will actually be applied to thesecond anode so thata greater degree of safety and dependability will be realized when using thesevided. Since the front end of the tube is not-in focus when the picture is projected, dirt, smudges,

imperfections in the glass will not appear with objectionable clarity on the screen and no distortion will be encountered through the formation of a curved picture for projection on the screen.

I claim:

1. In a cathode ray tube a gun structure enclosed within the evacuated tube envelope com prising means for generating an electron beam,- means for controlling and focusing the beam and a second anode for accelerating the beam including a plurality of individual elongated conductive elements extending'from said anode in the direction of movement of the beam.

2. In a cathode ray tube, a gun structure enclosed within the evacuated tube envelope comprising means for generating an electron beam, means for controlling and focusing the beam and a second anode for accelerating the beam including a plurality 'of' wire-like elements extending from the anode in the'direction of movement of the beam, said elements being spaced about the beam and connected one to the other and to the second anode.

3. In a cathode ray tube according to claim 2 wherein said elementsare electrically connected together at the second anode and are spaced'substantially uniform y about the beam.

4. In an image reproducing tube, an anode for accelerating the, electron beam and a plurality of spaced elements each extending from the anode in the direction of movement of the beam, said elements surrounding and providing an electrostatic shield for'the beam.

5. In a cathode ray tube wherein the beam is magnetically deflected, means for shielding the electron beam between the accelerating anode and the screen comprising a plurality of spaced conductors surrounding the beam and connected together at a point removed from the point of deflection of the beam to form a unipotential shield.

6. In a cathode ray tube wherein the beam is magnetically deflected, means for shielding the electron beam between the accelerating anode and the screen comprising a plurality of spaced conductors surrounding the beam and connected together at a point removed from the point of deflection oi the beam, said conductors being in the form of thin rods connected together at the accelerating anode end thereof.

7. An image reproducing tube comprising a cathode for generating an electron beam, controlling means for said beam including an accelerating anode, a screen for intercepting said beam, and means for shielding said beam comprising a tubular insulator having flared end portions adapted to contactand be held in position between the anode and the screen by the reproducing tube wall, and a plurality of wires each fastened at one end to the anode and extending in spaced relation one to the other through the insulator and bearing firmly against the wall thereof, and means for connecting a high accelerating potential to the anode.

JOHN M. CAGE.

REFERENCES CITED UNITED STATES PATENTS Number Name Date Schwartz July 12, 1938 Schwartz June 13, 1939 Ruska Oct. '31, 1939 Shoenberg et al Nov. 7, 1939 Dillenburger Dec. 2, 1941 Epstein Mar. 3, 1942 Epstein -1 July 14, 1942 Gray Aug. 18, 1942

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