US2227034A

US2227034A - Cathode ray tube

Info

Publication number: US2227034A
Application number: US218165A
Authority: US
Inventors: Schlesinger Kurt
Original assignee: LOEWE RADIO Inc
Current assignee: LOEWE RADIO Inc
Priority date: 1937-08-30
Filing date: 1938-07-08
Publication date: 1940-12-31
Anticipated expiration: 1957-12-31

Description

Dec. `31, 1940.

K.SCHLESNGER GATHODE RAY TUBE vFiled July 8, 1933 17 E79 11 Fig. 3

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Patented Dec. 31, 1940 UNITED STATES PATENT OFFICE l CATHODE RAY TUBE Kurt Schlesinger, Berlin, Germany, assignor, Vby

mesne assignments, to Loewe Radio, Inc., a corporation of New York Application July 8, 1938, Serial No. 218,165 In Germany August 30, 1937 4 Claims.

of thev cathode is produced between the'cathode` 10i-and the main reproducing lens. At this point of intersection a diaphragm for the purpose of obtaining particularly defined conditions is provided. As by the following electron-optic arrangement the aperture of this diaphragm is pro- 1151 jected upon the screen in somewhat reduced size its diameter must not surpass a small multiple of the image point, say-.B mm.

ri"he object of the invention is a special arrangement of the cathode and the adjacent electrodes 20 of a cathode ray tube and particularly of the said diaphragm to ensure that the intermediate image remains unaltered inits position in rela tion lto the main reproducing lens, when the rintensity of the cathode ray is controlled.

According to the invention, the opening in the diaphragm is preferably made to be .3.5mm. in diameter.

The invention may be more clearly understood by reference to the accompanying drawing. Figs. 30 1-3 showin a purely diagrammatic fashion and by way of example various kinds of electronop` tical systems to be used in a tube according to the invention. In the drawing longitudinal sections through the tubes are shown.`

35' Fig. 1 shows a tube having a cathode I, the

emissive surface of which has a concave shape, a

diameter of approximately 2 mm. and a radius of curvature of approximately l-1.5 mm., a control grid situated in front of the same, the open- 40; ing in which grid has a smaller diameter than the hollow cathode, and a first suctional anode 3, which follows on the grid and the diameter of the opening of which, in turn. is smaller than that of the grid. The point of `intersection oc- 4,5` curring in the path of the rays at thas a diameter amounting to approximately .3 mm. It is surrounded by the diaphragm 4. The diaphragm 4' is raised to the potential of the first anode 3. It is possible by adjusting the radius 50 of curvature of the cathode, or in the case of a given radius of curvature by adjusting the potential of the anode 3 and by simultaneous readjustment of the bias of the grid to remove any variation in size of the .image spot on the screen. In

55 the case of the stated diameters of the apertures (Cl. Z50-162) and the distances apart as shown in the drawing the critical potential of the suctional anode 3 was approximately 200 volts. The grid bias amounted to between 4.0 and l volts and the slope on an average to 3 mA. over 100 volts.

The point of intersection at 4 is reproduced sharply and Without loss on the screen by a main lens 6. A metallic tube 5 separates the lens zone from the preliminary optical system. The perforated plate l acts as main anode. A rst electron-optical system comprising a diaphragm 8 raised to low potential and a cylindrical electrode 9 has proved to be very useful for obtaining abright image spot devoid of halo effect. In the embodiment shown the tube cover 8 is connected in direct fashion with the suctional anode 3.

` The ring 9 is very important for holding back interfering secondary electrons which are always produced at the diaphragm 8. ing connected in direct fashion with the cathode I.

In the arrangement according to Fig. 2 the bias at the rst anode 3 is considerably` greater than in that according to Fig. 1. The cathode I is designed as a iiat cathode. Owing to the high potential at 3 it is accomplished that the system 2/3 does not exert any refractive effect, so that the direction of the single cathode rays remains un-affected by the grid potential. The possibility of makingthe cathode surface larger than the area of the aperture in 2 results in the considerable advantage that centering errors of the cathode member have not the least effect. Behind the first anode 3 there is located a lrst lens comprising a cylinder I2, which is connected for example with the cathode, and the diaphragm 8. The electrode 8 is connectedin direct fashion to the tubular member 5. If the lens cylinder I2 has approximately the same potential as the cathode I, a cross-over point is formed at 4. At this point there is included in the path of the rays the stated perforated diaphragm 4. As regards potential, this diaphragm is raised to the potential of the first anode 3. In order to avoid secondary emission the diaphragm may consist, at least on its surface, of a substance, such as graphite or hard carbon, which is incapable of performing secondary emission. With an effective cathode surface having a diameter of 1.5 mm. there is obtained with a spacing between and 4 amounting to 10 mm. a diameter of the intersection point of such kind that the same can .be enclosed practically without loss by a diaphragm having a diameter of .3-.5 mm.

The reproducing lens following thereon may It is shown as be' "-1," correspond to that set forth in Fig. 1. On occasion it has been found convenient, for the purpose of elminiating the halo of the image point caused by secondary emission at the diaphragm 4, to provide a special guard ring of approximately 5 mm. in diameter behind the diaphragm, this ring being connected with a very negative potential,l for example with the potential of the cathode. This ring exerts a returning action on the secondary rays deviating at a Very large angle from the axis of the beam, and leaves the main rays unaffected.

A further possible embodiment of the invention is illustrated in Fig. 3.` The cathode I is again a hollow cathode and forms'together with the control grid 2 and the anode 3 the control system. There follow a cylindrical ring 9 and a wide-aperture diaphragm 8. The cylinder Sreflects the stray electrons. The diaphragm 8 together with the tubular member 5, which is raised to a higher potential, build up, in themanner already indicated in the above, a rst electron lens. Themain lens of the tube is constituted A by the upper edge of the tubular member 5 and element 5a in conjunction with the anode diaphragm 1. v Y Y It has been found that it is possible to obtain on the screen a constant diameter of the image point, when. the radius of curvature of the emissive surface of the cathode is equal to approximately the distance of the centre of the cathode from the anode 3. Then all rays from the largesurface cathode converge to a point of intersection 4.

An arrangement o f this kind is described in the copending U. S. patent applicationiSer. No. 212,316, filed June 7, 1938.

The cross-over 4 produced by means of Aelements I, 2, 3, is again used as the object of the electron-optical reproduction on the screen and is, according to the present invention, enclosed by the diaphragm 4. The lens 5a/I reproduces this point of intersection on the screen 20.

Special means are provided for eliminating the loss of contrast due to a general illumination of the screen initially occurring upon` this reproduction. For this purpose there is provided the above mentioned first lens arranged in close proximity to the point of intersection. The equif potential surfaces indicated in broken lines re-` sult upon the reciprocal of the field of the tubular member 5.

Special means are provided for eliminating the loss of contrast due to a general illumination of.

' the screen initially occurring upon this V'reproduction. For this purpose there is provided the above mentioned first lens. The equi-potential surfaces indicated in broken lines result upon'the reciprocal of the eld of the tubular member 5, which is raised to approximately one-third of the anode potential, by reason of the intermediate diaphragm 8, which by means of apotentiometer 24 is adjusted to a lower potential than the tubular member. If the bias of the intermediate diaphragm 8 is suitably adjusted at I4, a refractive plane is built up between the point of intersection and 8.

The

diaphragm

8 and 3 can also be provided in fixed connection, and the bias of 5 adjusted alone, from the exterior, at a potentiometer 2l.- For this

purpose

5 and 5a are separated, as the potential at 5a has already been pre-determined by adjustment of the sharpness of the image point on the screen.

I claim :i

1. In a cathode ray tube comprising a target element, an indirectly heated large surface cathode, a first anode diaphragm, and a control electrode having the shape of a diaphragm and being arranged between said cathode and said first anode diaphragm: a cross-over forming electron optical system including said cathode, said control diaphragm, said rst anode diaphragm and a further diaphragm arranged adjacent to said rst anode diaphragm on its side facing said screen and closely surrounding said cross-over,

the spacing between said first anode diaphragm and said further diaphragm being approximately equal to the spacing between said rst anode diaphragm and said control diaphragm; an electron-optical lens system for producing an image of said cross-over on said target element; and means for deflecting said cathode ray to scan said target element.

2. In a cathode ray tube comprising a target element, an indirectly heated large surface cathode, a first anode diaphragm, and a control electrode having the shape of a diaphragm and being arranged between said cathode and said rst anode diaphragm: a cross-over forming electron optical system including said cathode, Said control diaphragm, vsaid rst anode diaphragm and a further'diaphragm arranged adjacent to said first anode diaphragm on its side facing said screen and closelyv surrounding said cross-over, the spacing between said first anode diaphragm and said further diaphragm being approximately equal to the spacing between said first anode diaphragm and said control diaphragm; an electronoptical lens system comprising a cylindrical electrode and a second anode diaphragm for producing an image of said cross-over on said target element, said cylindrical electrode and said second anode diaphragm being mounted in axial consecution adjacent to said further diaphragm on its side facing said target element, said cylindrical electrode being electrically insulated within the tube from said further diaphragm and from said second anode'diaphragm; and means for deflecting said cathode ray to scan said target element.

3. In a cathode ray tube comprising a target element, an indirectly heated large surface cathode, a first anode diaphragm, and a control electrode having the shape of a diaphragm and being arranged between said cathode and said rst anode diaphragm: a rst electron-optical system including said cathode, said control diaphragm and said rst anode and adapted to parallel the cathode ray after emergence from said cathode; a cross-over forming electron-optical system mounted adjacent to said first anode on its side facing said target element and including, in axial consecution, a cylindrical electrode, a second anode diaphragm, and a further diaphragm closely surrounding said cross-over, said cylin-` drical electrode being electrically insulated within the tube from said first anode diaphragm and from said second anode diaphragm; a further electron-optical system for producing an image of said cross-over on said target element; and means for deflecting said cathode ray to scan said target element.

4. In a cathode ray tube comprising a target element, an indirectly ,heated large surface cathode, a first anode diaphragm, and a control electrode having the shape of a diaphragm and being arranged between said cathode and said nrst anode diaphragm; a rst electron-optical system including said cathode, said control diaphragm and said first anode and adopted to parallel the cathode rayV after emergence from said cathode; a cross-over forming electron-optical system mounted adjacent to said first anode on its side facing said screen and including, in axial consecution, a cylindrical electrode, a second anode diaphragm, and a further diaphragm closely surrounding said cross-over, said cylindrical electrode being electrically insulated Within the tube from said first anode diaphragm and from said second anodediaphragm, said further diaphragm being connected to said first anode; a further electron-optical system for producing an image of said cross-over on said target element; and means for deflecting said cathode ray to scan said target element.

KURT SCI-ILESINGER.