US2580250A

US2580250A - Cathode-ray type of electron discharge device

Info

Publication number: US2580250A
Application number: US176750A
Authority: US
Inventors: Henry M Smith
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1950-07-29
Filing date: 1950-07-29
Publication date: 1951-12-25
Anticipated expiration: 1968-12-25

Description

Dec. 25, 1951 s n- 2,580,250

CATHODE RAY TYPE OF ELECTRON DISCHARGE DEVICE Filed July 29, 1950 6 SOURCE OF DEFLECTON wlhwllwm Inventor:

Henry Hi8 Attor ey Patented Dec. 25, 1951 Fries OATHODE-RAY TYPE OF ELECTRON DISCHARGE DEVICE Henry M. Smith, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application July 29, 1950, Serial No. 176,750

This invention relates to electron discharge devices of the type in which electrons are caused to produce images on luminescent screens and, in particular, relates to cathode ray electron discharge devices of the kind used for purposes of projection of pictures in television receivers or for producing oscillograms.

It is known that in order to obtain a sufiiciently intense indication on the screen of a cathode ray electron discharge device it is necessary to impart high velocities to the electron beam which produces light on the screen. However, increasing the velocity of the electron beam by increasing the anode voltages which accelerate the beam gives rise to certain problems. If conventional beam'deflection circuits are employed, the electron discharge device has low deflection sensitivity; that is, since the electrons in the beam are moving faster, it takes a larger force to produce the same absolute deflection that would be produced with a lower velocity electron beam. In addition, a special design is required for the electron gun when high potentials are used on the various anodes. In a magnetic deflection cathode ray electron discharge device insulation of the second anode coating in the device from the deflection coil may present a serious problem when high potentials are used on the second anode.

Heretofore it has been proposed to interpose a shielding grid of the kind shown in U. S. Patent 1,810,018 between the luminescent screen of the cathode ray type of electron discharge device and the remainder of the electrode structure of the device. With this innovation it is possible to utilize a conventional deflection circuit in the electron gun portion of the device while at the same time achieve the advantages of a high velocity beam. It will be noted that with this arrangement the screen is operated at a much higher potential than the shielding grid. A cathode ray type of electron discharge device of the kind just described with a shielding grid has the disadvantage that the screen of the tube is subject to background illumination for reasons to be hereinafter described. It is to the solution of this problem of background illumination that the present invention is particularly addressed.

Accordingly, it is an object of my invention to provide means in cathode ray type of electron discharge apparatus whereby the advantages of a" high velocity beam may be combined with the advantages of high sensitivity deflection circuits without the serious limitations of devices combining these features.

9 Claims. (01. 315-1) It is another object of my invention to provide a cathode ray tube in which the advantages of high deflection sensitivity and high intensity illumination are present without the serious disadvantage of background illumination.

It is a further-object of my invention to provide improvements in cathode ray electron discharge apparatus.

The features of the invention desired to be protected are set forth in the appended claims. The invention itself, together with further objects and advantages thereof, may best be understood by reference to the following specification taken in connection with the accompanying drawing in which is shown a cathode ray type of electron discharge device, in section, connected in a manner to carry out the objects of my invention.

Briefly stated, the objects of the invention are achieved in one exemplary embodiment by providing a collector electrode or means behind the grid of the cathode ray type of electron discharge device and operated at a slightly higher potential than the shielding grid to collect the stray electrons which produce the background illumination of the luminescent screen.

Referring now to the single figure of the drawing, there is shown a cathode ray type of electron discharge device I having an hermetically sealed envelope 2. At one end of the envelope is located a cathode 3 supplying electrons for the device I. At the other end of the device I is located a lumi nescent screen 4 which is subject to the bombardment of the electrons from the cathode 3. In: termediate the cathode 3 and the screen 4 are located various electrodes entirely conventional in the art for the purpose of forming and focussing the electron beam. Coil 5a functions to deflect the beam in accordance with external signals. applied by a source 6. A shielding grid electrode l is located a short distance from the screen i'which is operated at a much higher potential than the grid 7 so that in efiect the cathode ray device to the left of the grid '1 operates substantially as a conventional low voltage cathode ray device. It will be appreciated that electrons from the cathode 3 will be easily deflected by the deflection means 6 because they are of low velocity, and upon passing through the grid 1 the electrons will be considerably accelerated and consequently will strike the screen 4 of the tube With high. energy thereby producing large amounts of light from the luminescent coating making up the screen 4. It is readily appreciated that by the provision of the grid 1 the advantages of a high deflection sensitivity device with a device that has high luminosity characteristics is achieved. 7

It will be noted that not all of the electrons will pass through the grid structure to the screen.

- Some of the electrons will impingeon the wire mesh iori'nin'gthe grid'l'with the-consequent liberation of secondary electrons. When the electrons reflected and liberated from the shieldin grid 1 pass in the vicinity of the open spaces of the shielding grid electrode 'L'the'y will be attracted through and strike the screen 4 thereby producing background illumination on the screen.- It will be appreciated that this -b'ackground illumination is of a shape corresponding to the shape of the grid. Background illumination may be eliminated by eliminating the electron cloud formed behind the grid. I have provided in one embodiment a collector electrode 8 for this purpose. The-collector electrode 8 -is-operated at a potential slightly higher than-the. potential of the grid "electrode '1. Preferably the second anode!) is operated at a potential slightly higher than collector eleotrodeB to insure substantially complete collectionof all stray electrons. It will :be readily appreciated that the-second -anode 9 may be utilized as a collector electrode as well. When the-second anode '9 is used as a'collector it would be necessary -to operate'the-seoond anode 9 ate. potential slightly higher than-the shielding grid electrode 1. A separate collector electrode may be thus eliminated. The collector electrode 8 and the second anode 9 may be connected together and operated at thesame potential slightly higher than the grid electrode '5.

Referring now to the particularities of construction of the cathode ray devices of my invention, there is shownin the drawing a conventional electron gun for the device comprising a cathode 3, an intensity-control electrode lfl, and a first anode electrode II. The deflection coil 5a, entirely conventional, iunctions to deflect the electron beam from the electron gun in-response to a deflection signal. It is understood of course that the electrongun-maybe focussed magnetically or electrostatically and likewise that the beam deflection maybe accomplished either-by electromagnetic or electrostatic means. "In the figure c0115 functions to'focus the electron beam. The second anode 9 comprises athinconduotive coating extending into the-neckofthe device I as shown. This conductive coating is usually-an aquadag coating, talthough o-f course other suit-. abl'e materials maybe employed. The grid of the device I is attached to a metalring I 2 suitably fastened to'one end of theglass cylinder I3.

The other end of the glass cylinder I3 is connected 'totlie 'body'of 'the glass envelope -2. The attachme'ntof the'irisulatin'g cylinder [3 to the body of theenvelo'pe 2 at alocatio'n rem'oved'from the screen 4 reduces the surfa'oe'voltage gradient between grid 1 and screen d thereby elimlnating the danger of' eleotrical'breakdown between these high voltage electrodes. On the'inside'surface of the glass cylinder l3, and fla"short"distan'ce behind the "grid 1 is located a conductivestrip'which'may be formed ofaqua'dag or any'dtner suitable mate-- rial. Conductorsl' l and icpermitthe'application of external potentials to the grid 1 and electrode 8 respectively.

The grid l is made'of'a fine mesh o'fwir'es, for instance, a tungsten ring strung with .001-or an inch tungsten wire wound 330 turns .per inch would be suitable. 'Inthe preceding example the grid then would comprise a series of .001 of an iparent glass base.

screen by the usual techniques. 'ran'gement has the known advantage of higher the grid 7.

"adapted to be-excited by-anelectronbea'm. The

screen 4 may be formed on a conducting trans- Also, a conductive aluminum film could be applied over the phosphor of the This latter arlight output because of light reflection from the aluminumfllm. The aluminum film also has the advantage that it helps to prevent any loose particles of phosphor from coming oil and getting on A conductive connection I6 is made through the glass envelope so that the screen may be externally energized by suitable potentials.

Referring -.-now to :the operation of I one of the above described embodiments ofmy inventiomthe cathode Sis connected'to oneend-of .a 'suitab'le source H of unidirectional potential. The screen It is connected to the highpotential end ofthe unidirectional source. Thesecond anod'e'9 is connected to atpotentialpoint intermediate the :potential applied between the cathode and the screen anode [-4. The collector electrode Bisconnected to a potentialpoint on the unidirectional source -l'.' which is-slightly higher than thesgrid "i but slightly less .positiveor the samelipo'tential as-the secondanode 9. Electrodes 10 and H are connected to suitablepotential points: on the-uniw directional source 1 i. .:If the beam current to be modulatedthecontrol grid 10 mustor'course be connected to-a modulating potential source. The defiectioncoils Saarec-onnectedtoa source of deflection signal =6. With the second anode operating at-a potential of about 10,000'=volts,"with the screen 4 operating at -apotential of about 45,000 volts, with the shieldinggridl operatingsat a potential-anywhere in the range of -300 volts lower than the second anode "9 and collectorelectrode 8, very satisfactoryoperationof "the device wasobtained. Background illumination was virtuallyeli-minated.

Advantages in the use of cathode ray tubes of the-type described above are that the conventional low voltage ele'ctronrgun and electro'static.ormag'- netic deflection system of low ipower 'can be-used. A further advantage is that no extra insulation in the neck of the c-athode ray devi'ceslisrequired for high -voltage operation. Furthermore, neither the beam focus nor deflection are afiected'lby the potential of thefluo-r'esc'ent screen; consequently, a high voltage-source of relatively 10W spo'w-er-"capabilities can be usedfor the application of potentials -to-=the luminescent screen.

-Whil=e I have shown and described particular embodiments 'of my invention, it will be obvious to those skilled in the art "that various changes and modifications may be made 'withoutdeparting -from my invention inits broadaspec'ts and therefore, airs in "the appended claims to "cover all suoh changes"and modificationsas fall'within the true scope of "my invention.

Wh'at I claim as *new' and desire *to secureby Le tors Patentin t h'e U'nite'd States is:

1. Cathode ray electron discharge "apparatus, comprising a cathode ra'y type -of -electron tlis charge de'v-ice craving a cathode, a luminescent szreen a'node, a second anode located between said cathode and said screen anod'e, an lectrode mounted between said second anode and said screen anode adjacent to said screen anode, means for maintaining said electrode at a slightly lower potential than said second anode and means for maintaining said screen anode at a considerably higher potential than said second anode.

2. The apparatus of claim 1 which said electrode comprises a fine mesh wire screen located substantially parallel to the face of the cathode ray electron discharge device.

3. The apparatus of claim 2 in which said second anode comprises a conductive ring located on the inside surface of the envelope of said electron discharge device.

4. Cathode ray electron discharge apparatus, comprising a cathode ray type of electron discharge device having a cathode, a luminescent screen anode, a second anode located between said cathode and said screen anode, said second anode comprising a conductive coating on the inside surface of the envelope of said cathode ray electron discharge device, an electrode mounted between said second anode and said screen anode and adjacent to said screen anode, a second electrode located between said first electrode and said second anode, means for maintaining said first electrode at a slightly lower potential than said second anode and said second electrode, and means for maintaining said second anode at a slightly higher potential with respect to said second electrode, and means for maintaining said screen anode at a considerably higher potential than said first electrode.

5. The apparatus of claim 4 in which said first and second electrodes are located on a cylindrical insulating member attached to the envelope of said electron discharge device at a location substantially removed from said screen anode, said first electrode comprising a wire mesh attached to the free end of said cylindrical member and located substantially parallel with respect to said screen anode, said second electrode comprising a conductive ring on the inside surface of said insulating member.

6. The apparatus of claim 5 in which means are provided for maintaining said second anode and said second electrode at substantially the same potential.

7. Cathode ray electron discharge apparatus, comprising a cathode ray electron discharge device having a cathode, a luminescent screen anode, a second anode located between said cathode and said screen anode, said second anode comprising a conductive coating on the inside surface of the envelope of said cathode ray electron discharge device, an electrode mounted between said second anode and said screen anode and adjacent to said screen anode on a cylindrical insulating member attached to the envelope of said electron discharge device at a location substantially removed from said screen anode, said electrode comprising a wire mesh attached to the free end of said cylindrical member and located substantially parallel with respect to said screen anode,

means for maintaining said first electrode at a slightly lower potential than said second anode, and means for maintaining said screen anode at a considerably higher potential than said first electrode.

8. Electron discharge apparatus comprising a cathode ray type of electron discharge device having an electron gun, a luminescent screen, electron beam deflecting means, a first electrode mounted near said screen, a second electrode mounted adjacent to said first electrode on the gun side of said first electrode, means for maintaining said second electrode at a slightly higher positive potential than said first electrode, means for maintaining said screen anode at a considerably higher potential than said first electrode, whereby high intensity illumination free of background illumination is produced on said screen while at the same time high deflection sensitivity is obtained.

9. Electron discharge apparatus comprising a cathode ray type of electron discharge device having an electron gun for developing a cathode ray beam, a luminescent screen adapted to be excited by said cathode ray beam, electron beam deflecting means in operative association with said cathode ray beam for deflecting said cathode ray beam, an electrode mounted near said screen, said electrode comprising a wire mesh located substantially parallel with respect to said screen, another electrode mounted adjacent to said first electrode on the gun side of said first electrode comprising a conductive coating on the inside surface of the envelope of said discharge device, energizing means for energizing said electron gun and said electrodes so that the deflection sensitivity of said cathode ray beam is high, energizing means for energizing said luminescent screen so that high intensity lumination is produced by the impingement of said electron beam on said screen, said second electrode adapted to be energized with a slightly higher positive potential than said first electrode while said screen is adapted to be energized by a substantially higher potential than said first electrode.

HENRY M. SMITH.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,810,018 Howes June 16, 1931 1,955,899 Zworykin Apr. 24, 1934 2,077,270 Schlesinger Apr. 13, 1937 2,239,769 Batchelor Apr. 29, 1941 2,289,906 Epstein July 14, 1942 2,315,367 Epstein Mar. 30, 1943 2,461,515 Bronwell Feb. 15, 1949 2,483,457 Feldt et a1 Oct. 4, 1949 2,518,200 Sziklai et a1 Aug. 8, 1950 2,543,477 Sziklai et al Feb. 27, 1951