US2126286A

US2126286A - Braun tube

Info

Publication number: US2126286A
Application number: US730111A
Authority: US
Inventors: Schlesinger Kurt
Original assignee: Loewe Opta GmbH
Current assignee: Loewe Opta GmbH
Priority date: 1933-06-10
Filing date: 1934-06-11
Publication date: 1938-08-09
Anticipated expiration: 1955-08-09
Also published as: GB442511A; CH208832A; BE403600A; GB442427A; FR774394A; NL45201C

Description

Aug. 9, 1938. K. SCHLESINGER 2,126,286

BRAUN TUBE Filed June 11, 1954 2 Sheets-Sheet 1 Ur: uenioc:

Aug. 9, 1938. K. SCHLESINGER 2,126,286

BRAUN TUBE Filed June 11, 1934 2 Sheets-Sheet 2 I w B Patented Aug. 9, 1938 PATENT OFFICE BRAUN TUBE Kurt Schlesinger, Berlin, Germany, assignor to Radioaktiengesellschaft D. S. Loewe, Berlin- Steglitz, Germany Application June 11, 1934, Serial No. 730,111 Germany June 10, 1933 16 Claims.

(Granted under the provisions of sec. 14, act of March 2, 1927; 357 0. G.

The object of the invention is a Braun tube, operated under high vacuum, with electrostatic concentration of the ray. I

According to the invention, the stream of elec- 5 trons is controlled in its intensity, preferably by space charge control, and by the use of suitable electrostatic fields or if desired also by the use of intermediate diaphragms, is preliminarily concentrated and projected on to a diaphragm. The aperture of this diaphragm, in accordance with the invention, is reproduced on the luminous screen of the Braun tube by means of an electron-optical system of constant focus.

Since the aperture in the diaphragm acts as surface of constant form and size but varying light intensity, it is possible in this fashion to produce image points, which are not dependent on their intensity as regards form and size, and in consequence also remain unaltered when a change-over takes place from lightest white to darkest black.

The diaphragm aperture to be reproduced on the luminous screen, the form of which aperture 25 determines the form of the image point, is conveniently made as small as possible (for example,

less than 1 mm.), and may be furnished with a rectangular, hexagonal or other suitable form. In order to avoid a thermal overloading of this diaphragm, the preliminary concentration device is constructed'in such fashion that the greatest preliminary concentration takes place when the intensity of the ray is at its maximum.

35 The diaphragm itself is preferably made of a good heat-conductive material with the highest possible fusing point, which material at the same time enables the diaphragm aperture to be furnished with a very exact form (clean-cut edges).

40 According to the invention, the diaphragm may conveniently consist of two parts, viz., a supporting ring composed of a suitable material, such as copper, and a diaphragm portion connected with this supporting ring and furnished with the aper- 5 ture, said portion consisting of a suitable material,

such as tungsten, tantalum or molybdenum.

As electron-optical system (electron lens) there are employed in accordance with the invention preferably systems which are constructed in such 50 fashion that the speed of the ray when passing through the same remains unaltered, or practically unaltered.

It is particularly convenient to employ systems which comprise fundamentally two positively 55 biassed electrodes, between which there is located a negatively biassed electrode of suitable form. The lens itself producing the optical efiect according to the invention then consists practically of the negative element and one of the said positive elements, the braking fleldextending 5 mainly between those two electrodes. The second positive electrode allows of adjusting the focus of the system without changing the speed which the electrons have before they enter the system. Therefore this -third electrode is practi- 1o cally of a great value but is not necessary as to the reproducing function of the system.

In this connection the positive electrodes may conveniently be constructed in the form of annular plates having aperture of the order of, for 16 example, approximately 5 mm., and if desired united by means of a metallic cylinder to form a sleeve, in'the interior of which there isprovlded the negatively biassed electrode.

The negative electrode, in accordance with the 20 invention, may be constructed, for example, in the form of a funnel-shaped electrode, the diameter of the smaller funnel preferably being approximately equal to the diameter of the openings of the positive electrode.

It is particularly convenient to make the negative electrode in the form of annular electrode with short set-on metallic cylinder. In this connection the diameter of the annular plate aperture will preferably be made almost as large as the diameter of the apertures in the positive electrode, for example of the order of approximately 5 mm. On the other hand the set-on metallic cylinder lsfurnished with a diameter of approximately twice the size.

It is also possible to employ as negative field generator an annular plate composed of insulating material, which is furnished on the one side with a spiral coating of a semi-conductive substance (for example, a highly ohmic spiral composed of graphite or colloidal carbon) the commencing point of the spiral situated adjacent the aperture being connected with a suitable positive potential and the end point thereof with a suitable negative potential, so that the potential decreases in proportion to the spacing from the centre point.

According to one feature of the invention the spacing of the negative electrode from the positive electrode directed towards the tube cathode is made as small as possible, so that a braking field of any appreciable kind is not formed between these two electrodes.

The two positive electrodes of the system are connected with each other, and may conveniently positive electrode on the cathode side, the electron-optical system acts in exactly the same mannor as an optical collecting lens.

Accordingly when using a system of this nature the size of the image point with given size of the aperture in the diaphragm is determined by the ratio between the distance of the diaphragm to be reproduced from the electron-optical system and the distance of the electron-optical system 4 from the image screen.

Since on the one hand it is impossible in practice to make the diaphragm aperture too small and on the other hand, for technical reasons, the image point may not exceed a certain size, which is dependent on the size of the image and the number of lines, the diaphragm, the opening of which is to be reproduced, is arranged, according to the invention, as far as possible from a practical point of view away from the electron-optical system.

A distance of approximately 6-8 cm., which with a length of bulb amounting to, say, 30 cm. cqrresponds with an approximately fourfold or fivefold enlargement, has been found to be fully sufilcient in practice.

According to the invention, the space between I the diaphragm and the electron-optical system with the positive electrodes of the electron-optical system.

If in contradistinction to the arrangement above described the negative electrode of the electron-optical system is disposed in such fashion that the smaller aperture thereof (small funnel aperture or cylinder holding plate) is directed towards the positive electrode on the image screen side, the electron-optical system corresponds fully in its properties with an optical dispersing lens.

According to another feature of the invention it is now quite readily possible by the use of dispersing lenses of this nature, or by the combination of electron-optical dispersing and collecting lenses, or also by the combination of collecting lenses of different focus (i. e., electronoptical systems, the negative electrodes of which are biassed to different extents whilst the positive electrodes possess the same potential) to conduct systems, which do not produce magnified images of the diaphragm aperture, but project the same on to the image screen in natural size or on a reduced scale.

Since the electron-optical collecting and dispersing lenses correspond fundamentally with the optical arrangements, it is possible to assemble difierent systems of this nature according to the principles well known in the optical art.

-The use of combined systems of this charac- 75 ter is of considerable importance according to the invention insofar as the same also allow of the production of the smallest image points with compact assembly of the system.

According to a further feature-of the invention it is possible to produce images with a small sur-: face, i. e., images of that nature, the diagonals of which do not difieii appreciably from the diameter of the neck of the tube in which the parts of the system are arranged. In this connection the diameter of the tube may conveniently be selected up to approximately 10-15 cm.

By reason of this dimensioning of the image it is possible to make the distance of the deflecting systems from the image screen comparatively small. f

Thus, the electron-optical system may be arranged in such fashion that its spacing from the image screen is considerably less than its distance from the diaphragm to be reproduced, so that the latter may be reproduced on the image screen even on a reduced scale.

The image produced in this fashion may then be reproduced on a desired scale of enlargement by suitable optical means. According to an additional form of embodiment of the invention the path of the ray within the neck 'of the tube may be multiplied by a single or multiple deviation of the ray.

In this manner it is also possible in direct fashion to produce television images of large size with small image points without necessity for increasing the length of the tube.

The deviation of the ray may preferably be caused by the use of magnetic fields.

The image point distribution may conveniently be performed by the use of pairs of deflecting plates having the deflecting plates disposed in titled relation to each other in the manner known per se. To avoid cross-current error the plates may be negatively biassed in relation to the ray,

Between the deflecting plates and the image screen there may be provided in accordance with the invention a preferably large-surface intercepting electrode, which is maintained at a potential that is positive in relation to the positive electrodes of the electron-optical system, and serves to intercept the return-flow electrons and to prevent the same from penetrating into the neck of the bulb containing the parts of the system.

On the inside of the wall of the tube there may be provided a metallic coating, which commences at approximately the level of the intercepting electrode and extends at least 8-12 cm. into the bulb of the tube.

In order to produce bright and at the same time comparatively small image points, it may be convenient to illuminate the diaphragm a'perture, which is to be reproduced, by means of a bundle of electrons directed as far as possible parallel, i. e., to pre-concentrate the ray preferably in such fashion that the electrons proceed-- ing from the cathode enter as far as practically possible parallel into the aperture in the diaphragm.

According to a further feature of the invention, there are provided between the cathode and the diaphragm to be reproduced concentrating means which may consist of two electron-optical systems, of which the one functions preferably as collecting lens and the other as dispersing lens.

-The electron-optical systems may each consist, in the manner set forth above, of one or two eleelement. The operation of the electron-optical system (i. e., the action as collecting or dispersing lens) is determined solely by the extent and nature of the bias of this intermediate element in relation to the outer elements. There may be said generally that completely similar electron-optical systems may be employed for the preliminary concentration of the ray andfor the reproduction of the anode aperture on the screen.

Some forms of embodiment of the tube according to the invention and also certain details are illustrated by way of example in the drawings in which a Fig. 1 shows the most elementary form of the total arrangement with a simple electron-optical system of the collecting lens type, whilst in Fig. 2 there is shown a form of embodiment of the anode, in

Figs. 3 and 4 two different types of electronoptical collecting lenses, and in Fig. 5 an electron-optical dispersing lens.

Fig. 6 shows a spiral semi-conductor electrode according to the invention, whilst Fig. 7 illustrates the combination of two of these electrodes to form a preliminary concentration system.

Fig. 8 shows a Braun tube according to the invention having pre-concentrating means of another type.

Fig. 9 shows an arrangement with single deviation of the ray, and

Fig. 10a detail of the arrangement illustrated in Fig 9, whilst in Fig. 11 there is'indicated an arrangement with double deviation of the ray.

The combination of a plurality of electronoptical collecting or collecting and dispersing systems accordingto the invention has not been particularly shown, as these difl'erent combinations may be readily obtained from the stated the preliminary concentration element, i the dia- Y phragm, which at the same time may be used as the anode, 5 the screening cylinder, i I the electron-optical system with the positive electrodes 6 and 8 and the electrode 7, which is furnished with a negative bias in relation thereto (for example, of approximately 200-500 volts), 9 and iii are the two pairs of deflecting plates, i2 is the intercepting electrode, l3 the metallic wall coating, and it the luminous screen.

All of the electrodes are preferably connected to form a system by the use of insulating holding means. The anode s, the cylinder 5 and the

plate electrodes

6 and 7 may be conductively connected with each other, and. if desired the

electrodes

6 and 1 supplemented to form a cylinder. The length of the cylinder 5 may be selected up to'approximately 15 cm. A dimensioning of this kind enables points to be produced or a size necessary for large-size television images with a simple electron-optical collecting system.

As shown in Fig. 2, the anode 4 may conveniently consist of a holding ring I5 of suitable material, such as copper, which carries the small plate i6 having the diaphragm aperture 41, this plate consisting, for example, of tantalum. In order to .avoid or reduce as far as possible the occurrence of secondary electrons, the part of the anode directed towards the cathode may conveniently be sooted. Further, the anode is preferably linked up with a potential as high as possible.

Fig. 3 shows an electron-opticaTcollecting lens system, in which the negative electrode is constructed in funnel-like form. According to the invention, the distance of the two funnel apertures from the positive electrodes is preferably made as small as possible, approximately 1 mm. or less.

In the system illustrated in Fig. 4 the negative electrode consists of the holding plate l9 and the set-on cylinder Hi, the diameter of which may conveniently amount to twice the diameter of the opening of the holding plate.

If, as shown in Fig. 5, the negative electrode is arranged in such fashion that the larger aperture thereof is directed towards the positive plate on the cathode side, the electron-optical system is able to act, as a dispersing lens.

In Fig. 6:

is an insulating plate with the aperture 22, on which there is provided the spiral 2i consisting of a semi-conductive material. The commencing point 24 of the spiral is connected with a positive potential (for example, the anode potential) and the end of the spiral 23 with a suitable negative potential.

Fig. '7 shows a system consisting of two electrodes 'of this nature, which system may be employed, for example, as preliminary concentration system.

The intermediate electrode in the electron-optical system according to the invention requires to be furnished with merely a weak negative bias, for example to the extent of 200-500 volts, in relation to the outer electrodes. Since this negative bias determines the focus of the system, the same should be selected in individual cases with consideration to the specific data of the tube.

The tube according to the invention may be operated with the relatively low anode potentials (for example, 1000-3000 volts) usual in the case of gas tubes. Thus, for example, it is possible to impart to the anode of the tube a potential of merely approximately 1000-1500 volts, and if desired to employ the wall coating as after-acceleration anode.

It is, however, also possible to impart to the metallic wall coating a potential which is negative as compared with the intercepting electrode provided according to the invention, and in this manner to effect after-concentration in the space of the bulb.

In Fig. 8:

i is the cathode with the

emissive surface

25, 2 the Wehnelt cylinder with the

control plate

26, 25 an electron-optical system acting as collecting lens, and 33 an electron-optical system acting as dispersing lens, whilst H is the electron-optical system which reproduces the diaphragm opening 21 on the image screen. The system 29 consists of the two (preferably earthed)

plates

28 and 3|, which are raised to anode potential, and the cylinder 30 which is arranged between the same and possesses a comparatively strong negative bias (for example 400 volts) in relation to the

plates

28 and 3|. 34 is the wall of the tube.

The potentials of the system I l, i. e. the potentials applied to the plates 6 .and 8 and the inner element 1 may correspond with the potentials of the system 29.

In contradis'tinction thereto the inner element The dispersing lens 33, in accordance with the invention, may preferably be constructed in such fashion-either by suitable dimensioning of the system elements and their spacing, or more preferably by correct adjustment of the potentialsthat its focal point coincides with the point of intersection of the rays of the condenser system- 28, which point in turn is disposed in or behind the diaphragm 6. The aperture of the dispersing lens and also its spacing from the diaphragm are preferably so chosen that the size of the diaphragm aperture is fully utilized.

In Figs. 9-11:

3% is the wall of the tube, i the cathode, 2 the Wehnelt cylinder with the drawn down

control plate

26, 3 and 3 are electrodes forming among them the preliminary concentration systems, 6, l and 8 electrodes forming among them the reproducing electron-optical system, 9 and iii the deflecting plates, 35 and 36 the magnet systems, 31 and 3B poleshoes arranged within the tube, and 62 is the cathode ray.

As shown by Fig. 9, the cathode ray emitted by l is controlled by the use of ,the plate 26 (the control potential is applied between the cathode i and the plate 26) preliminarily concentrated by the system comprising the anode 3, which may consist of a perforated plate with set-on cylinder or may also be constructed in mould-like form, and the high-tension anode 3, turned by the field generated by the magnet 35, and projected on to the image screen by the system comprising the elements 6, I and 8, the aperture in the diaphragm i which preferably is made as small as possible being reproduced on the image screen in natural size or on reduced scale.

In the arrangement according to Fig. 9 the preliminary concentration system comprises the preliminary anode 3 with the set-on cylinder, which may be furnished with a comparatively low positive potential (for example, 300-500 volts), and the anode t, which is connected with a lliigh positive potential (for example, 1500-2000 vo ts).

The electron-optical system consists of the two positively biassed plates 6 and 8, between which, in the manner described above, there is arranged the element 1, which is furnished with a negative bias in relation to the main plates and is constructed, for example, in the form of a cylinder' plate. The distances between i on the one hand and 8 and 8 on the other hand should be made as small as possible. In this manner it is ac? complished that the electronic ray does not vary its speed when passing through the system. The described electron system acts as an infinitely thin optical collecting lens.

The plates 6 and 8, if desired, may be united with the plate 4 and the element 1 with the element 3 to form a structural unit.

A possible form of arrangement and embodiment of the pole shoes 31 and 38 and of the magnet 35 is illustrated diagrammatically in Fig. 10.

In the arrangement shown in Fig. 11, the

araaase cathode ray M is first diverted by 180 by the field of the magnet 35-, and then by a further 180 by the field of the magnet 36, so that its final direction is parallel with its outlet directi on. Ac-' cording to the invention, it is also possible to, arrange thecathode and magnet fields'in such fashion that the final direction of the cathode ray coincides with the axis of the tube.

In the arrangement according to Fig. 11 ther is end loyed as preliminary concentration system a system comprising the preliminary anode 44, the main anode 3, and the element 3, which is arranged between the two and is weakly negative in relation to the preliminary anode.

The potentials of the preliminary concentration system should always be adjusted in such fashion that the electronic ray is preliminary sharply concentrated on the aperture in the diaphragm 4,

and the potentials of the electron-optical system should be so chosen that the same reproduces the diaphragm aperture sharply on the image screen.

It has been found to be necessary in the arrangement according to the invention also to avoid even the slightest action on the cathode ray on its path between the diaphragm and the electron-optical system. According, therefore, to the invention this complete .part of the path of the ray is screened ofi fully against both magnetic as well as electrostatic fields of interference by screening means arranged either within or on the outside of the tube. Such screening means in their simplest form consist of an iron or the like tube of /2-2 mm. wall thickness.

The invention is in no way limited to the forms of embodiment quoted merely by way of example. It is in fact quite possible to employ other suitable electrostatic preliminary concentratlon or collecting systems. The deviation of the cathode ray may also be performed in suitable manner as desired.

The tube according to the invention combines the advantages of the previously known gas tubes.

(low anode potential, wattless concentrationand control) with those of the known high vacuum tubes (great sharpness of the point and lack of secondary light caused by slow secondary electrons) without the disadvantages of these types of tubes.

If desired, the tube according to the invention may be operated with a filling of gas (preferabl as weak as possible).

I claim: Y

1. An electron-optical system for Braun tubes comprising one'plate-shaped element having an aperture and being adapted to be supplied with a high positive potential, and a second plateshaped element having an aperture and being furnished at least at its side facing the first said element with a metallic cylinder, the diameter of which is considerably greater than the diameter of said aperture, said second element being adapted to be supplied with a lower positive potential than said first element.

2. An electron-optical system for Braun tubes comprising one plate-shaped electrode having a 'diameter considerably above 10 millimetres, said plate-shaped electrode having an aperture, the diameter of which is in the order of five mm., said electrode being adapted to be supplied with a high positive potential, and a second plateshaped electrode having a diameter considerably above 10 millimetres, said second plate-shapedelectrode having an aperture, the diameter of nished at its side facing the first said electrode said electrode being adapted to be supplied with a high positive potential, and a second plate-shaped electrode having a diameter considerably above 10 millimetres, said second plate-shaped electrode having an aperture, the diameter of which is in the order of five mm. and being furnished at its side facing the first said electrode with a metallic cylinder surrounding said aperture, the diameter of said cylinder being in the order of ten mm., said second electrode being adapted to be supplied with a positive potential which is lower than the potential, which the first said electrode is to be supplied with, said second electrode being arranged at a small distance from the first said one, the edge of said cylinder being spaced from the first said electrode for about one mm.

4. An electron-optical system for Braun tubes comprising three electrodes arranged one after another, the first and the third of said electrodes consisting of a plate-shaped element having an aperture and being adapted to be supplied with a high positive voltage, the second electrode consisting of a plate-shaped element having an aperture and being furnished at its side facing said third electrode with a cylindrical abutment, the diameter of said abutment being about twice the diameter of said aperture, said second electrode being arranged in close proximity to said first electrode and near said third electrode. the distance between the plate-shaped element of the second electrode and the first said electrode on the one hand and the distance between the edge of said abutment and said third electrode on the other hand each amounting to approximately one mm., said second electrode being adapted to be supplied with a lower positive voltage, the arrangement being such that the braking field is mainly restricted to the space between said second and said third electrode.

5. A Braun tube for television purposes comprising an evacuated envelope, a cathode and an anode arranged in operative relationship thereto, said anode having an aperture of small diameter, a picture receiving screen, deflecting means for deflecting the cathode ray for producing a scanning of said screen, an electron-optical system for reproducing said anode aperture on said screen, said system being arranged between said anode and said deflecting plates, and means for parallelizing the cathode ray between said cathode and said aperture, said means including at least one electron-optical collecting lens system and at least one electron-optical dispersing lens system.

6. A Braun tube for television purposes comprising an evacuated envelope, a cathode and an anode arranged in operative relationship thereto, said anode consisting of a holding plate of good thermal conductive material and a small disc connected to said holding plate, said disc having a small aperture and consisting of a highly refractory material, means for concentrating the cathoderay on to said aperture, a picture receiving screen, deflecting means arranged between said anode and said screen and means for reproducing said aperture on said screen.

7. A Braun tube for television purposes comprising an evacuatedenvelope, a cathode and an anode arranged in operative relationship thereto, said anode aving an aperture, means for concentrating the cathode ray into said a-perture, a picture receiving screen, deflecting means for deflecting the cathode ray for scanning said screen, said deflecting means being arranged between said anode and said screen, an electron-optical system for reproducing said anode aperture on to said screen, said electron-optical system including one plate-shaped electrode being arranged between said anode and said deflecting means and having an opening the diameter of which is con-,

siderably greater than the diameter of said aperture, said electrode having at its side facing said screen a cylindrical abutment, the diameter of which is considerably greater than the diameter of said opening and the length of which is at least equal to its diameter, said electrode being adapted to be supplied with a positive potential, and a further plate-shaped electrode having an opening which is nearly equal to the opening of said first electrode, said further electrode being adapted to be supplied with a potential which is higher than that which the first said electrode is adapted to be supplied with, said further electrode being arranged between said first electrode and the screen, and a metallic tube having a diameter which is considerably greater than the diameter of said opening of said first electrode of said electronoptical system, said tube being arranged between said anode and said first electrode and being connected to one of these electrodes.

8. Braun tube for television purposes comprising an evacuated envelope, a cathode and an anode arranged in operative relationship thereto, said anode having an aperture, means for concentrating the cathode ray intosaid aperature,

a picture receiving screen, two pairs of deflecting plates, the plates of each pair being inclined against each other, said deflecting plates being arranged between said anode and said screen, an electron-optical system for reproducing said anode aperture on to said screen, said electron-optical system including one plate-shaped electrode arranged between said anode and said deflecting means and having an opening the diameter of which is considerably greater than the diameter of said aperture, said electrode having at its side facing said screen a cylindrical abutment the diameter of which is considerably greater than the diameter of said opening and the length of which is at least equal to its diameter, said electrode being adapted to be supplied with a positive potential, and a further plate-shaped electrode having an opening which is nearly equal to the opening of said first electrode, said further electrode being adapted to be supplied with a potential which is higher than that which the first said electrode is adapted to be supplied with, said further electrode being arranged between said first electrode and the screen, and a metallic tube having a diameter which is considerably greater than the diameter of said opening of said first electrode of said electron-optical system, said tube being arranged between said anode and said first electrode and being connected to one of these electrodes, an auxiliary electrode adapted to be supplied with a high positive potential, said auxiliary electrode being arranged between said deflecting plates and said picture receiving screen, and a metallic wall coating commencing near the first electrode of said electron-optical system and extending for at least eight cm. in the direction to the screen.

, 9. A Braun tube for television comprising an evacuated envelope, a cathode and an I anode arranged in operative relationship thereto,

said anode having an aperture, means for concentrating the cathode ray into said aperture, a

picture receiving screen, deflecting means tor deflecting the cathode ray for scanning said screen, said deflecting means being arranged between said anode and said screen, an electron-optical system for reproducing said anode aperture onto said screen, said electron-optical system including one plate-shaped electrode being arranged between said anode and said deflecting means, and having an opening the diameter of which is considerably greater than the diameter of said aperture, said electrode having at its side facing said screen a cylindrical abutment, the diameter of which is considerably greater than the diameter of said opening, said electrode being adapted to be supplied with a positive potential, and a iurther plate-shaped electrode having an opening which is nearly equal to the opening of said first electrode, said further electrode being adapted to be supplied with a. potential which is higher than that which the first said electrode is adapted to be supplied with, said further electrode being arranged between said first electrode and the screen, and a metallic tube having a diameter which is considerably greater than the diameter of said opening of said first electrode of said electron-optical system, said tube being arranged between said anode and said first electrode and being connected to one of these electrodes.

10. A Braun tube for television p p ses comprising an evacuated envelope, a cathode and an anode arranged in operative relationship thereto, saidanode having an aperture, means for concentrating the cathode ray into said aperture, a picture receiving screen, two pairs of deflecting plates, the plates of each pair being inclined against each other, said deflecting plates being arranged between said anode and said screen, an electron-optical system. for reproducing said anode aperture onto said screen, said electron-optical system including one plate-shaped electrode arranged between said anode and said deflecting means and having an opening the diameter of which is considerably greater than the diameter of said aperture, said electrode having at its side facing said screen a cylindrical abutment the diameter of which is considerably greater than the diameter of said opening, said electrode being adapted to be supplied with a positive potential, and a further plate-shaped electrode having an opening which is nearly equal to the opening of said first electrode, said further electrode being adapted to be supplied with a potential which is higher than that which the first said electrode is adapted to be supplied with, said further electrode being arranged between said first electrode and the screen, and a metallic tube having a diameter which is considerably greater than the diameter of said openingoi said first electrode of said electron-optical system, said tube being arranged between said anode and said first electrode and being connected to one of these electrodes, an auxiliary electrode adapted to be supplied with a high positive potential, said auxiliary electrode being arranged between said deflecting plates and said picture receiving screen, and a metallic wall coating commencing near the first electrode of said electron-optical system and extending for at least 8 centimetres in the'direction to the screen.

diameter, a picture receiving screen; deflecting means for deflecting the cathode ray tor producing ascanning of said screen, and means for reproducing said anode aperture on said screen, said means including at least one electron-optical collecting lens system and at least one electronoptical dispersing lens system, said collecting and dispersing lens systems being structurally united to form one single element.

12-. A Braun 'tube comprising means ior'proconcentrating system for concentrating the oathode-ray onto said diaphragm, an image screen, an electronoptical system for reproducing said diaphragm onto said image screen, and means for deviating the path of the cathode ray between said diaphragm and said electron-optical system to increase the path of the cathode ray between said diaphragm and said electron-optical system.

13. A Braun tube comprising means for pro-' ducing a cathode ray, a diaphragm, a preliminary concentrating system tor concentrating the oath-- ode ray onto said diaphragm, an image screen, an electronoptical system for reproducing said diaphragm onto said image screen, and magnetic field producers for, deviating the path of the cathode ray between said diaphragm and said electron-optical system to increase the path of said diaphragm and said electron-optical system.

15. An electron-optical system for Braun tubes comprising a plate-shaped electrode having an aperture, said electrode being adapted to be supplied with a high positive potential, and a second plate-shaped electrode having an aperture of substantially the same size as the first said aperture, said second plate-shaped electrode being furnished at its side facing the first said electrode with a metallic cylinder, surrounding said aperture in the second said electrode, the diameter of said cylinder being about twice the diameter of said apertures, the diameters of said plateshaped electrodes being substantially larger than the diameter of said cylinder, said second electrode being adapted to be supplied with a positive potential which is lower than the potential which the first said electrode is to be supplied with.

16. In a Braun tube more particularly for television purpcses in combination with a diaphragm having an aperture, with means including a cathode for producing a bundle of cathode ray to illuminate said aperture with cathode rays, with a picture receiving screen, and with means for electron-optically reproducing said aperture on said screen: a preliminarycathode ray concentrating system mounted between said cathode ducing a cathode ray, a diaphragm, a preliminary and said diaphragm for concentrating said bundle onto said aperture, and comprising at least one plate-shaped electrode and a cylindrical electrode mounted between said plate-shaped electrode and said diaphragm, said plate-shaped electrode beingadapted to be maintained positive in relation to said cathode; said cylindrical electrode being adapted to be maintained pofltive in relation to said cathode but negative in relation to said plate-shaped electrode.

KURT SCHLESINGER.