US2137352A - Cathode ray tube - Google Patents

Description

Nov. 22, 1938. K. SCHLESINGER 2,137,352

CATZHODE RAY TUBE Filed Jan. 7, 1955 9n ven Far:

Patented Nov. 22, 193$ UNlTED srarss OATHODE RAY TUBE Kurt Schlesinger, Berlin, Germany, assignor to Radioaktiengesellschaft D.

Steglitz, Germany S. Loewe, Berlin- Application January '7, 1935, Serial No. 725

In Germany January 12, 1934.

22 Claims.

Braun tubes have already been described by the applicant in earlier applications, in which an emissive surface (i. e., the cathode, a diaphragm or a suitable intermediate surface) is reproduced sharply on the image screen by the use of an electron-optical system.

Further, means have already been described by the applicant for lighting a diaphragm of this nature with a bundle of electrons which is as parallel as possible.

The electron-optical systems employed in this connection consist fundamentally of an electrode linked up with a potential which is low by way of comparison, and an after-connected electrode having a high positive potential. Since the system employed for lighting the aperture of the diaphragm is also constructed on similar lines, it has been found that the electrode situated next to the cathode can possess merely a weak positive potential.

An increase in the potential of this first suctional electrode, by the suctional action of which there is determined in practice the maximum emission of the cathode, appeared impossible without either destruction of the electron-optical structure, making a sharp reproduction impossible, or employing extremely high potentials at -the last anode of the system.

In consequence it has not been possible in these tubes to obtain a cathode ray of great intensity, and accordingly image points of high luminosity.

The subject matter of the invention is an additional development of these arrangements, which avoids the disadvantages referred to and enables sharp image points of very high intensity of light to be produced by the use of the relatively low anode potentials usual heretofore (of the order of 1000-2000 volts).

According to the invention, the diaphragm to be reproduced-for example by connection with the high-potential anode-is raised to a potential as high as possible, and. the after-connected first electrode of the electron-optical system, which requires a positive potential that is low by Way 4'5 of comparison, is constructed in such fashion that the potential planes following the diaphragm remain substantially plano-parallel despite the great jump in potential between the diaphragm and the after-connected element.

50 This may be accomplished in accordance with the invention by the fact that the after-connected electrode is constructed in the form of a tube, the diameter of which is very large in, comparison with the aperture in the diaphragm.

55 If a special system is not. employed for lighting the diaphragm, the high potential thereof takes full effect as suctional potential. In this case, however, it is necessary to make the distance between the cathode and the diaphragm comparatively largefor example 10% of the length of 5 the tube following the diaphragm, i. e., with a length of tube amounting to 30 mm. approximately 3 mm., as otherwise in addition to the diaphragm there is also reproduced simultaneously the surface of the cathode itself, and in this 10 manner a large blurred image point formed having an edge.

If on the other hand a special system is employed for lighting the diaphragm, the element of this system connected in front of the diaphragm-as the latter is raised to a very high positive potential-*may always possess a comparatively high positive potential, which is completely adequate for the generation of an intense cathode ray. 20

In this case it is also possible to place the first element much nearer to the cathode-for example, to within /2 mm.

Certain forms of embodiment of the arrangement according to the invention are illustrated 25 by way of example in the drawing, in which Fig. 1 is an arrangement without preliminary concentration, whilst in Fig. 2 there is shown an arrangement with preliminary concentration, and in 30 Fig. 3 an arrangement with consideration to the deflecting plates, in which arrangement a potential distributing means may be arranged at the same time in the vacuum of the tube.

In the drawing: 35

I is the indirectly heated cathode having an oxide surface of exactly defined form, which is preferably let in and is heated by a filament 3. The aperture in the diaphragm d is lighted by the bundle of electrons proceeding from the oxide 40 surface. Behind the diaphragm l there is arranged the electron-optical system, which reproduces the aperture of the diaphragm on the image screen. The electron-optical system consists according to the invention of an electrostatic lens with large aperture, which is formed by two cylinders 6 and l, of which the front one possesses a higher positive potential than the cylinder '6. According to the invention, both cylinders are provided with a diameter which is very large in relation to the aperture in the diaphragm. In this manner it is accomplished that the electron-optical effect of the system remains substantially unaffected by the series-connected electrode of high potential (there is avoided the formation of a lens surface at the bounding plane between the electrode 3 and the cylinder 6) As already set forth, the distance between the cathode surface 2 and the diaphragm aperture requires to be comparatively large-for example, approximately 3 mm.

An additional form of embodiment of the arrangement according to the invention is illustrated in Fig. 2.

This relates to a tube for television purposes, which reveals in face 'of Fig. l the peculiarity that the strength of the emission current may be varied by means of a control grid 8 in front of the surface of the cathode. In order upon this operation to ensure that the form of the image point will be properly constant an auxiliary condenser lens comprising the two cylinder electrodes 9 and 4 has been found to be essential in tubes of this kind, in which connection the potential of the preliminary anode 9 requires. to. be less positive than the potential of the diaphragm 4, and in which, therefore, in the known arrangements, even a smaller suctional potential has been available in front of the cathode surface than in the tube according to Fig. 1. The orders of magnitude in practice are, for example:

7 Volts Main anode potential (7) 2000 Potential of the tube (6) 300 Potential of the preliminary anode (9) ap prox 50 There accordingly arises in the known arrangements with electrostatic acceleration lenses the diiiiculty of obtaining large current maxima from the cathodes, as the anode potentials available in front of the cathode are merely fractions of the total anode potential of the tube, and as they are of a fixed nature by reason of the electronoptical conditions of the focus and cannot be altered.

The basic idea of the invention consists in biasing the diaphragm 4, which represents the electron-optical object as regards the image point on the screen, to a particularly high positive potential, which is higher than the potential of the tube 6, i. e., the following lens element. This method is only capable of being performed if the potential planes linking up with the diaphragm l remain piano-parallel. There otherwise occurs, in addition to the unavoidable braking effect to which the electrons are subjected in the tube space 5 after leaving the diaphragm, an undesirable auxiliary refractive effect in the direction of concentration, which would result in an increase in the scale of reproduction, and accordingly in a thickening of the image point on the screen. According to the invention, therefore, the diameter of the tube 6 is made practically infinitely large as compared with the diameter of the aperture in the diaphragm or the medium cross-section of the ray in the vicinity of the diaphragm, and the diaphragm plate 4 is made flat. it may then be proved from a potentialtheoretical point of view, and also confirmed by experiment, that it is possible to introduce between the diaphragm i and the tube 6 differences in potential amounting to several times 100-1000 volts without the sharpness or the adjustment of the focus of the main electrostatic lens 6, 7 thus being changed. In accordance with the invention the diaphragm 4 in Figs. 1 and 2 may accordingly be connected, for example, as shown, with the main anode 1. Since with a constant scale of reproduction on the part of the condenser ens 2, 9, 4 the ratio of the potential between the stated electrodes also remains the same, the 150* tential at the anode 9, in accordance with the invention, may also be increased in proportion with the potential of 4. In the stated example, therefore, a suctional anode potential of approximately 300 volts is obtained. It has been measured in practice that with a maximum emission of, for example, 100 A., with the stated potentials and the connection of 4 and 6, an increase could be made up to a strength of emission current amounting to 550 A. after use of the separate biasing in accordance with the invention of the diaphragm 3 and the tube 6. The yield of current, i. e., the ratio between that measured at the screen 5 and the strength of emission current in the cathode line No, is equally good in both cases (over 80%) An additional important advantage of the stated bias between diaphragm 4 and tube 6 the equipotential observation shows that the usual secondary light at the screen 5, for example in the case of a tube according to Fig. l, disappears entirely even with small biases between 4 and 6. Tubes without a condenser according to Fig. 1 practically always reveal a strong general lighting of the luminous screen 5 also outside of the actual electronic image point. This lighting, as the applicant has found, is due primarily to marginal rays which are not to be avoided with the simple form of diaphragm lighting and owing to a spherical error in the main lens 6,] do not reach the point of reproduction (they are too greatly deflected). By reason of the bias according to the invention there is an appreciable concentrating effect in the space of the tube 6 in respect of marginal rays deviating to this extent, as in the tube the radial field densities, so far as the same are present at all, are directed at all points inwardly. t

In making use of this efiect, which is to be observed in practice, it has been found that the exact extent of the bias between 4 and 6 is not of utmost importance from the point of view of overcoming the halo effect. It is possible,- therefore, in accordance with the invention, by the provision of potential distributing resistances in the interior of the tube system, to produce a suitable bias, and at the same time to make do with merely one variable focal potential altogether outside of the tube.

Fig. 3 shows the diaphragm electrode 4 in conjunction with an outer terminal 4', which may be adjusted by hand in connection with a potential distributor. The two resistances l0 and l I are prow'ded withinthe tube, and amount for example to l and 2 megohms respectively, so that they do not represent an appreciable load on the anode battery. Whilst, therefore, the suction anode potential is adjusted at 4', regulation is performed simultaneously to the correct focal distance owing to the difference in potential 6-1, and there is obtained the desired positive bias of the diaphragm 4 in relation to the tube 5 according to the invention, and accordingly a sufficiently powerful emission of electrons from the cathode I-2. The oxide surface may possess in practice a diameter of approximately .5 mm., and the diaphragm aperture of 4 diameter of .3 mm.

Finally, it may be remarked that the tubular form of the main anode with relatively long tubular abutment (approximately 15 mm.) shownv throughout in the drawing represents merely a particular instance of other possible constructions of anode and lens. The same, however, ofiers the advantage of also possessing at the point where the cathode ray reveals its greatest diameter the largest aperture. It is possible, therefore, according to the invention, to furnish the tubular member with a relatively small outlet aperture, as the rays have been appreciably bundled together within the tubular anode. In this manner interference of the deflecting plates l2-l3, which are arranged behind the anode l, in the lens field will be avoided to a large extent, and good sharpness of the image point ensured up to the edge of the luminous image.

The arrangement according to Fig. 1 is particularly suitable for oscillographic purposes.

Also in the arrangement in which the diaphragm is lighted by the use of a special device having a bundle of electrons made parallel (as described in the above, the device is preferably so constructed that an intersection of the electronic rays is avoided in the place of the diaphragm) it may be desirable to arrange this device at a comparatively large distance (for example 2i-3 mm) from the surface of the cathode.

The arrangement or arrangements to the invention, with corresponding modification in the form of electrode (use of box or plate electrodes in place of the cylinder as described), may be used for amplifier tubes according to the transverse field principle.

I claim:

1. In a television arrangement a cathode ray tube comprising an electron beam producing system including a cathode, voltage supplying means associated with said system for causing said system to produce an electron beam, an image screen in said cathode ray tube; means for electronoptically reproducing a cross-sectional portion of said electron beam onto said image screen, said last mentioned means comprising electrodes 'mounted inside said cathode ray tube in the space between said cathode and said image screen to form an electron optical system, the first one of said electrodes taken from said cathode having the shape of a hollow cylinder of the diameter d, with its axis directed from said cathode to said image screen, and means for applying diiierent potentials to said electrodes, the potential applied to said first electrode taken from the cathode being in the order of 300 volts in relation to said cathode; a plate shaped electrode having an aperture of a diameter in the order of to V of d mounted in the space between said electronoptical system and said cathode in close vicinity of said first electrode of said electron-optical system; and means for applying to said plate shaped electrode a high positive potential in relation to said first electrode of said electron optical system.

2. In a television arrangement a cathode ray tube having a cathode, an anode, and an image screen, means for producing an electron beam in said cathode ray tube, said means comprising said cathode, said anode, and means for applying to said anode a high positive potential in relation to said cathode; means for electron-optically reproducing a cross-sectional portion of said electron beam onto said image screen, said last mentioned means comprising said anode and an electrode having the shape of a hollow cylinder of the diameter d, mounted in the space between said cathode and said anode with its axis directed from said cathode to said anode to form together with said anode an electron-optical system, and means for applying to said electrodes a potential considerably difierent from that applied to said anode; a plate shaped electrode having an aperture of a diameter in the order of to of d mounted in the space between said electronoptical system and said cathode in close vicinity of said first electrode of said electron-optical system; and means for directly connecting said plate shaped electrode with said anode.

3. In a television arrangement a cathode ray tube comprising an electron beam producing system including a cathode, voltage supplying means associated with said system for causing said system to produce an electron beam, an image screen in said cathode ray tube; means for electron-optically reproducing a cross-sectional portion of said electron beam onto said image screen, said last mentioned means comprising electrodes mounted inside said cathode ray tube in the space between said cathode and said image screen to form an electron-optical system, the first one of said electrodes taken from said cathode having the shape of a hollow cylinder of the diameter d, with its axis directed from said cathode to said image screen, the second one of said electrodes taken from the cathode having the shape of a hollow cylinder of the same mentioned diameter d and a length of the order of 2 to 3 centimetres, the axis of said second mentioned cylinder coinciding with that of said first mentioned cylinder, means for applying to said first mentioned cylinder a potential of the order of 300 volts in relation to said cathode, means for applying to said second mentioned cylinder a potential of the order of 1500 to 2000 volts in relation to said cathode; a plate shaped electrode having an aperture of a diameter in the order of A to of d mounted in the space between said electron-optical system and said cathode in close vicinity of said first electrode of said electron-optical system; and means for applying to said plate shaped electrode a high positive potential in relation to said first electrode of said electron optical system.

4. In a television arrangement a cathode ray tube comprising an electron beam producing system including a cathode, voltage supplying means associated with said system for causing said system to produce an electron beam, an image screen in said cathode ray tube; means for electron-optically reproducing a crosssectional portion of said electron beam onto said image screen, said last mentioned means comprising electrodes mounted inside said cathode ray tube in the space between said cathode and said image screen to form an electron optical system, the first one of said electrodes taken from said cathode having the shape of a hollow cylinder of the diameter d, with its axis directed from said cathode to said image screen, the second one of said electrodes taken from the cathode having the shape of a hollow cylinder of the same mentioned diameter d and a length of the order of 2 to 3 centimetres, the axis of said second men tioned cylinder coinciding with that of said first mentioned cylinder, a plate with an aperture of a diameter considerably smaller than 01 closing ofi said second mentioned cylinder on that side directed towards said image screen, means for applying to said first mentioned cylinder a potential of the order of 300 volts in relation to said cathode, means for applying to said second mentioned cylinder a potential of the order of 1500 to 2000 volts in relation to said cathode; a plate shaped electrode having an aperture of a diameter in the order of to & of d mounted in the space between said electron-optical system and said cathode in close vicinity of said first electrode of said electron-optical system; and means for applying to said plate shaped electrode a high positive potential in relation to said first electrode of said electron-optical system.

5. In a television arrangement a cathode ray tube comprising an electron beam producing system including a cathode, voltage supplying means associated with said system for causing said system to produce an electron beam, an image screen in said cathode ray tube; means for producing an electron optical reproduction of a cross-sectional portion of said electron beam on said screen; at least one pair of deflecting plates for causing said reproduction to scan at least a part of said image screen; said means for producing an electron-optical reproduction of said electron emissive surface comprising electrodes mounted inside said cathode ray tube in the space between said cathode and said image screen to form an electron optical system, the first one of said electrodes taken from said cathode having the shape of a hollow cylinder of the diameter d, with its axis directed from said cathode to said image screen, the second one of said electrodes taken from the cathode having the shape of a hollow cylinder of the same mentioned diameter d and a length of the order of 2 to 3 centimetres, the axis of said second mentioned cylinder coinciding with that of said first-mentioned cylinder, a plate with an aperture of a diameter smaller than the distance between the plates of said pair closingoff said second mentioned cylinder on that side directed towards said image screen, means for applying to said first mentioned cylinder a potential of the order of 300 volts in relation to said cathode, means for applying to said second mentioned cylinder a potential of the order of 1500 to 2000 volts in relation to said cathode; a plate shaped electrode having an aperture of a diameter in the order of to of (I mounted in the space between said electronoptical system and said cathode in close vicinity of said first electrode of said electron-optical system; and means for applying to said plate shaped electrode a high positive potential in relation to said first electrode of said electron-optical system.

6. In a television arrangement a cathode ray tube comprising an electron beam producing system including a cathode, voltage supplying means associated with said system for causing said system to produce an electron beam, an image screen in said cathode ray tube; means for electron-optically reproducing a cross-sectional portion of said electron beam onto said image screen,

said last mentioned means comprising electrodes mounted inside said cathode ray tube in the space between said cathode and said image screen to form an electron optical system, the first one of said electrodes taken from said cathode having the shape of a hollow cylinder of the diameter d, with its axis directed from said cathode to said image screen, and means for applying different potentials to said electrodes; a plate shaped electrode having an aperture, the diameter of which is in the order of to of d, mounted in the space between said electron-optical system and said cathode in close vicinity of said first electrode of said electron-optical system; and means for applying a high potential difference between said first electrode of said electronoptical system and said plate-shaped electrode.

7. In a television arrangement a cathode ray tube, comprising an electron beam producing system including a cathode, voltage supplying means associated with said system for causing said system to produce an electron beam, an image screen in said cathode ray tube; means for electronoptically reproducing a cross-sectional portion of said electron beam onto said image screen, said last mentioned means mounted inside said cathode ray tube in the space between said cathode and said image screen to form an electron optical system, the first one of said electrodes taken from said cathode having the shape of a hollow cylinder of the diameter d, with its axis directed from said cathode to said image screen, and means for applying different potentials to said electrodes; a plate shaped electrode having an aperture, the diameter of which is in the order of one-thirtieth to one-twentieth of d, mounted in the space between said electronoptical system and said cathode in close vicinity of said first electrode of said electron-optical system and in a distance of the order of 3 to 5 millimetres from the cathode to avoid a reproduction of the cathode surface onto said image screen.

8. In a television arrangement a cathode ray tube comprising an electron beam producing system including a cathode, voltage supplying means associated with said system for causing said syscomprising electrodes tem to produce an electron beam, an image screen in said cathode ray tube; means for electronoptically reproducing a cross-sectional portion of said electron beam onto said image screen, said last mentioned means comprising electrodes mounted inside said cathode ray tube in the space between said cathode and said image screen to form an electron optical system, the first one of said electrodes taken from said cathode having the shape of a hollow cylinder of the diameter d, with its axis directed from said cathode to said image screen, and means for applying different potentials to said electrodes; a plate shaped electrode having an aperture, the diameter of which is in the order of to /20 of d, mounted in the space between said electron-optical system and said cathode in close vicinity of said'first electrode of said electron-optical system; and means for applying to said plate-shaped electrode a high positive potential in relation to said first electrode of said electron-optical system.

9. In a television arrangement a cathode ray tube comprising an electron beam producing system including a cathode, voltage supplying means associated with said system for causing said system to produce an electron beam, an image screen in said cathode ray tube; means for producing in a part of the space enclosed by said tube between said cathode and said screen an electron lens field for reproducing a cross-sectional portion of said electron beam onto said image screen, a tubular electrode having a diameter 02 mounted between said cathode and said image screen with its axis directed from said cathode to said image screen, said tubular electrode extending, in the direction from said cathode to said image screen, at most up to the part of the space enclosed by said tube in which, as hereinbefore set forth, the electron lens field is formed, a plate-shaped electrode having an aperture, the diameter of which is in the order of to & of (I, mounted in the space between said tubular electrode and said cathode in close vicinity of said tubular electrode, and means for applying a high potential difierence between said tubular electrode and said plate-shaped electrode.

10. In a television arrangement a cathode ray tube having a cathode, an anode, and an image screen, means for producing an electron beam in said cathode ray tube, said means comprising said cathode, said anode, and means for applying to said-anodea high positive potential in relation to said cathode, means for electron-optically reproducing a cross-sectional portion of said electron beam onto said image screen, said last mentioned means comprising said anode and an electrode having the shape of a hollow cylinder of the diameter d, mounted in the space between said cathode and said anode with its axis directed from said cathode to said anode to form together with said anode an electron-optical system, and means for applying to said electrodes a potential consider ably different from that applied to said anode; a plate-shaped electrode having an aperture of a diameter in the order of ,6, to of d mounted in the space between said electron-optical system and said cathode in close vicinity of said first electrode of said electron-optical system; and means for applying to said plate-shaped electrode a potential which is considerably difierent from that applied to said first electrode of said electronoptical system.

11. In a television arrangement a cathode ray tube having a cathode, an anode, and an image scr en, means for producing an electron beam in said cathode ray tube, said means comprising said cathode, said anode, and means for applying to said anode a high positive potential in relation to said cathode; means for electron-optically reproducing a cross-sectional portion of said electron beam onto said image screen, said last i'mentioned means comprising said anode and. an electrode having the shape of a hollow cylinder of the diameter d, mounted in the space between said cathode and said anode with its axis directed from said cathode to said anode to form together with said anode an electron-optical system, and means for applying to said electrode a potential considerably lower than that applied to said anode; a plate-shaped electrode having an aperture of a diameter in the order of to of d mounted in the space between said electronopti-cal system and said cathode in close vicinity of said first electrode of said electron-optical system; and means for directly connecting said plate-shaped electrode with said anode.

12. In a television arrangement a cathode ray tube comprising an electron beam producing system including a cathode, voltage supplying means associated with said system for causing said system to produce an electron beam, an image screen in said cathode ray tube; means for electron-optically reproducing a cross-sectional portion of said electron beam onto said image screen, said last mentioned means comprising electrodes mounted inside said cathode ray tube in the space between said cathode and said image screen to form an electron-optical system, the first one of said electrodes taken from said cathode having the shape of a hollow cylinder of the diameter d, with its axis directed from said cathode to said image screen, and means for applying different potentials to said electrodes, the potential applied to said first electrode taken from the cathode being in the order of 300 volts positive in relation to said cathode; a plate shaped electrode having an aperture of a diameter in the order of /o to 1 of d mounted in the space between said electron-optical system and said cathode in close vicinity of said first electrode of said electron-optical system; and means for applying to said plate-shaped electrode a high positive potential in relation to said first electrode of said electron optical system.

13. In a television arrangement a cathode ray tube having'a cathode, an anode, and an image screen, means for producing an electron beam in said cathode ray tube, said means comprising said cathode, said anode, and means for supplying to said anode a high positive potential in relation to said cathode; means for electronoptically reproducing a cross-sectional portion of said electron beam onto said image screen, said last mentioned means comprising said anode and an electrode having the shape of a hollow cylinder of the diameter d, mounted in the space between said cathode and said anode with its axis directed from said cathode to said anode to form together with said anode an electron optical system and means for applying to said electrode a potential positive relatively to said cathode and considerably different from that applied to said anode; a plate-shaped electrode having an aperture of a diameter in the order of to & of d mounted in the space between said electronoptical system and said cathode in close vicinity of said first electrode of said electron-optical system; and means for directly connecting said plate-shaped electrode with said anode.

14. In a television arrangement a cathode ray tube comprising an electron beam producing system including a cathode, voltage supplying means associated with said system for causing said system to produce an electron beam, an image screen in said cathode ray tube; means for electron-optically reproducing a cross-sectional portion of said electron beam onto said image screen, said last mentioned means comprising electrodes mounted inside said cathode ray tube in the space between said cathodeand said image screen to form an electron-optical system, the first one of said electrodes taken from said cathode having the shape of a hollow cylinder of the diameter d, with its axis directed from said cathode to said image screen, the second one of said electrodes taken from the cathode having the shape of a hollow cylinder of the same mentioned diameter and a length of the order of 2 to 3 centimeters, the axis of said second mentioned cylinder coinciding with that first mentioned cylinder, means for applying to said first mentioned cylinder a potential of the order of 300 volts positive in relation to said cathode, means for applying to said second mentioned cylinder a potential of the order of 1500 to 2000 volts positive in relation to said cathode; a plateshaped electrode having an aperture of a diameter in the order of A to of d mounted in the space between said electron-optical system and said cathode in close vicinity of said first electrode of said electron-optical system; and means for applying to said plate-shaped electrode a high positive potential in relation to said first electrode of said electron-optical system.

15. In a television arrangement a cathode ray tube comprising an electron beam producing system including a cathode, voltage supplying means associated with said system for causing said system to produce an electron beam, an image screen in said cathode ray tube; means for electron-optically reproducing a cross-sectional portion of said electron beam onto said image screen, said last mentioned means comprising electrodes mounted inside said cathode ray tube in the space between said cathode and said image screen to form an electron-optical system, the first one of said electrodes taken from said cathode having the shape of a hollow cylinder of the diameter d, with its axis directed from said cathode to said image screen, the

second one of said electrodes taken from the cathode having the shape of a hollow cylinder of the same mentioned diameter d and a length of the order of 2 to 3 centimetres, the axis of said second mentioned cylinder coinciding with that of said first mentioned cylinder, a plate with .an aperture of a diameter considerably smaller than (2 closing off said second mentioned cylinder on that side directed towards said image screen, means for applying to said first mentioned cylinder a potential of the order of 300 volts positive in relation to said cathode, means for applying to said second mentioned cylinder a potential of the order of 1500 to 2000 volts positive in relation to said cathode; a plate-shaped electrode having an aperture of a diameter in the order of 1 to of d mounted in the space between said electronoptical system and said cathode in close vicinity of said first electrode of said electron-optical system; and means for applying to said plateshaped electrode a high positive potential in relation to said first electrode of said electronoptical system.

16. In a television arrangement a cathode ray tube comprising an electron-beam producing system including voltage supplying means associated with said system for causing said system to produce an electron beam, an image screen in said cathode ray tube; means for producing an electron-optical reproduction of a cross-sectional portion of said electron beam on said screen; at least one pair of deflecting plates for causing said reproduction to scan at least a part of said image screen; said means for producing an electron-optical reproduction of said electron emissive surface comprising electrodes mounted inside said cathode ray tube in the space between said cathode and said image screen to form an electron-optical system, the first one of said electrodes taken from said cathode having the shape of a hollow cylinder of the diameter d, with its axis directed from said cathode to said image screen, the second one of said electrodes taken from the cathode having the shape of a hollow cylinder of the same mentioned diameter d and a length of the order of 2 to 3 centimetres, the axis of said second mentioned cylinder coinciding with that of said first mentioned cylinder, a plate with an aperture of a diameter smaller than the distance between the plates of said pair closingofi" said second mentioned cylinder on that side directed towards said image screen, means for applying to said first mentioned cylinder a potential of the order of 300 volts positive in relation to said cathode, means for applying to said second mentioned cylinder a potential of the order of 1500 to 2000 volts positive in relation to said cathode; a plate-shaped electrode having an aperture of a diameter in the order of to of d mounted in the space between said electron-optical system and said cathode in close vicinity of said first electrode of said electronoptical system; and means for applying to said plate-shaped electrode a high positive potential in relation to said first electrode of said electronoptical system.

17. In a television arrangement a cathode ray tube comprising an electron beam producing system including a cathode, voltage supplying means associated with said system for causingsaid system to produce an electron beam, an image screen in said cathode ray tube; means-for electron-optically reproducing a cross-sectional portion of said electron beam onto said image screen, said last mentioned means comprising electrodes mounted inside said cathode ray tube in the space between said cathode and said image screen to form an electron-optical system, the first one of said electrodes taken from said cathode having the shape of a hollow cylinder of the diameter d, with its axis directed from said cathode to said image screen, and means for applying difierent potentials to said electrodes; a plateshaped electrode having an aperture, the diameter of which'is in the order of to $5 of d, mounted in the space between said electron-optical system and said cathode in close vicinity of said first electrode of said electron-optical system; means for maintaining said first electrode of said electron-optical system positive relatively to said cathode, and means for applying a high potential diflerence between said first electrode of said electron-optical system and said plate-shaped electrode.

18. In a television arrangement a cathode ray tube comprising an electron beam producing system including a cathode, voltage supplying means associated with said system for causing said system to produce an electron beam, an image screen in said cathode ray tube; means for electronoptically reproducing a cross-sectional portion of said electron beam onto said image screen, said last mentioned means comprising electrodes mounted inside said cathode ray tube tube in the space between said cathode and said image screen to form an electron-optical system, the first one of said electrodes taken from said cathode having the shape of a hollow cylinder of the diameter d, with its axis directed from said cathode to said image screen, and means for applying different potentials to said electrodes of which the potential applied to said first electrode of said electron-optical system is positive relatively to said cathode; a plate-shaped electrode having an aperture, the diameter of which is in the order of 1 to of d, mounted in the space between said electron-optical system and said cathode in close vicinity of said first electrode of said electron-optical system and at a distance of the order of 3 to 5 millimetres from the cathode to avoid a reproduction of the cathode surface onto said image screen.

19. In a television arrangement a cathode ray tube comprising an electron beam producing system including a cathode, voltage supplying means associated with said system for causing said system to produce an electron beam, an image screen in said cathode ray tube, means for electron-optically reproducing a cross-sectional portion of said electron beam onto said image screen, said last mentioned means comprising electrodes mounted inside said cathode ray tube in the space between said cathode and said image screen to form an electron-optical system, the first one of said electrodes taken from said cathode having the shape of a hollow cylinder of the diameter 07, with its axis directed from said cathode to said image screen, and means for applying difierent 20. In a television arrangement a cathode ray tube comprising an electron beam producing system including a cathode, voltage supplying means associated with said system for causing said system to produce an electron beam, an image screen in said cathode ray tube, means for producing in a part of the space enclosed by said tube between said cathode and said screen an electron lens field for reproducing a cross-sectional portion of said electron beam onto said image screen, a tubular electrode having a diameter d mounted between said cathode and said image screen with its axis directed from said cathode to said image screen, said tubular electrode extending, in the direction from said cathode to said image screen, at most up to the part of the space enclosed by said tube in which, as hereinbefore set forth, the electron-lens field is formed, a plate-shaped electrode having an aperture, the diameter of which is in the order of to of d, mounted in the space between said tubular electrode and said cathode in close vicinity of said tubular electrode, means for maintaining said tubular electrode positive relatively to said cathode, and means for applying a high potential difference between said tubular electrode and said plate-shaped electrode.

21. In a television arrangement a cathode ray tube having a cathode, an anode, and an image screen, means for producing an electron beam in said cathode ray tube, said means comprising said cathode, said anode, and means for applying to said anode a high positive potential in relation to said cathode, means for electron-optically reproducing a cross-sectional portion of said electron beam onto said image screen, said lastmentioned means comprising said anode and an electrode having the shape of a hollow cylinder of the diameter d, mounted in the space between said cathode and said anode with its axis directed from said cathode to said anode to form together with said anode an electron-optical system, and means for applying to said electrode a potential positive relatively to said cathode and considerably different from that applied to said anode; a plate-shaped electrode having an aperture of a diameter in the order of to 3 of d mounted in the space between said electron-optical system and said cathode in close vicinity of said hollow cylinder-shaped electrode; and means for applying to said plate-shaped electrode a potential which is considerably different from that applied to said hollow cylinder-shaped electrode.

22. In a television arrangement a cathode ray tube having a cathode, an anode, and an image screen, means for producing an electron beam in said cathode ray tube, said means comprising said cathode, said anode, and means for applying to said anode a high positive potential in relation to said cathode; means for electron-optically reproducing a cross-section portion of said electron beam onto said image screen; said last mentioned means comprising said anode and an electrode having the shape of a hollow cylinder of the diameter (I, mounted in the space between said cathode and said anode with its axis directed from said cathode to said anode to form together with said anode an electron-optical system, and means for applying to said electrode a potential positive relatively to said cathode and considerably lower than that applied to said anode; a plate-shaped electrode having an aperture of a diameter in the order of ,4, to $5 of d mounted in the space between said electron-optical system and said cathode in close vicinity of said hollow cylindershaped electrode; and means for directly connecting said plate-shaped electrode with said anode.

KURT SCHLESINGER.

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