US1993565A - Braun tube - Google Patents

Description

March 5, 1935. H. G. MGLLER ET AL BRAUN TUBE 3 Sheets-Sheet 1 I venta/s March 5, 1935. 'H. G. MOLLER ET AL 1,993,565

' BRYVAUN TUBE Filed July 28, 1932 5 Sheets-Sheet 2 March 5, 1935'. v

HLG. MOLLER ET AL Filed July 28, 1952 a Sheets-:Shet 3 Patented Mar. 5, 1935 PATENT OFFICE BRAUN TUBE Hans Georg Milller, Bergedorf, near Hamburg, and Rolf Miiller, Zehlendorf, near Berlin, Germany, assignors to the firm of Fernseh Aktien- Gesellschaft, Zehlendorf, near Berlin, Germany Application July 28, 1932, Serial No. 625,484 In Germany July 31, 1931 4 Claims.

This invention relates to Braun tubes, such as employed for purposes of television, and more particularly to a method of controlling the intensity of the light.

5 When employing a Braun tube in television apparatusin'its capacity as an image-composing element the stream of electrons is deflected by means of electrical or magnetic fields in two directions which are vertical to each other in a manner corresponding with that in which the image is decomposed at the transmission end by the scanning device. Beyond this the intensity of the spot of light on the fluorescent screen (point of impact of the bundle of electrons) requires to possess at each particular moment the same intensity as that of the corresponding image point of the object scanned at the transmission end.

There are two possibilities of enabling the intensity of the spot of light to be varied, consisting in either varying the speed of the electrons whilst maintaining the latter constant in number, or in varying the number of electrons at a constant speed thereof. This variation is performed in accordance with the image frequency amplitudes transmitted.

The former method is extremely complicated to perform, as it is necessary, on account of the variation in the deflection at different speeds, to vary the deflection potentials in rhythm with the image frequency, which amounts to modulation of the deflection potentials with the image frequencies.

In performing the second method of control it is necessary to vary the number of electrons, which are united in the spot of light, in conformity with the image frequencies.

For this purpose various proposals have already been made which, however, are accompanied by the drawback that although therate of movement is maintained substantially constant the expanse of the spot of light cannot be sufiiciently confined or is not independent of the control-a disadvantage, which is hardly capable of leading to exact composition of the image.

It is the primary object of this invention to eliminate the drawbacks referred to, and-this is accomplished by the fact that in the Braun tube 'there is provided a relatively narrow diaphragm, through which a stream of electrons passes fluctuating in intensity, and that this shutter is reproduced electrically on the fluorescent screen, i. e., the electrons are united at one point of the screen. This reproduction may occur electro-magnetically by means of a spot-concentrating coil, 8r electro- 55 statically by an electrode arrangement, for example in cylindrical fornl. The control device governing the number of electrons may also operate electro-magnetically or electrostatically. In order to convey the largest possible number of the electrons emitted by the hot cathode through the 5 diaphragm, it is desirable to concentrate as far as possible right from the commencement the electrons proceeding from the filament. By variation of this concentration it is then possible for example, to vary the number of electrons leaving the 10 diaphragm.

The concentration device maybe, for example, a Wehnelt cylinder, the potential of which is varied in rhythm with the incoming image frequencies. 15 Other objects and advantages of the invention will become apparent as the description proceeds. The invention will now be described more fully with reference to the accompanying drawings, in which 1 20 Fig. 1 illustrates a possible embodiment of the invention in diagrammatical form,

Figs. 2 and 3 being modifications.

Referring now to the drawings, the hot cathode 1 is surrounded by the Wehnelt cylinder 2, and closely in front of the same there is provided the electrode 3, to which is applied a slight positive potential. The electrons emerging from the aperture 4 are concentrated by the cylinder 5, in which connection it may under certain circumstances, for the sake of improved concentration, be desirable to fill the tube with a gas. The field accelerating the electrons is created by the anode 6, which is linked up with a high potential. Correct composition of the image is obtained by means of the two pairs of deflecting plates '7 and 8. The electrostatical deflection may naturally also be replaced by an electro-magnetic one. The requisite current sources have not been shown in the drawings, as it is obvious that the cylinder 5 is preferably supplied with a potential which is negative in face of the electrode 3, and that the same potential ratio exists between the filament 1 and the Wehnelt cylinder 2. Under certain circumstances it might also be'practical to furnish the Wehnelt cylinder 2 with a potential which is positive as compared with the filament.

In order by this method to obtain a spot of small expanse on the fluorescent screen 9, the aperture 4 will require to be relatively small, and accordingly the number of electrons considerably f restricted. In this respect it is perhaps more convenient to employ the arrangement illustrated in Fig. 2, in which the same method of control is made use of, but in place of the electrostatical 2 1,998 concentration provision is made for an electromagnetic one with the assistance of a so-called spot-concentration coil 10.

In the method described in the above considerable difliculties are unfortunately encountered in the practical execution, as despite the use of the spot concentration coil it is not readily possible to produce a clearly defined bright spot of light on the fluorescent screen. By careful investigations it was found that this is due to the fact that exact concentration is dependent not only on the strength of the magnetic field and the speed of the electrons, but also on the distribution of their speed.

In accordance, therefore, with the invention,- and it is only in this manner that the method above referred to is rendered possiblethere is employed for each definite distribution of potential, and accordingly of the speed, a well defined electrode and spot-concentration coil arrangement. In the most elementary form, in which the field accelerating the electrons is disposed solely between the electrodes 3 and 6, the potential prevails between the anode 6 and the screen 9, and the spot-concentration coil is located in place of the anode 6, the distances between these electrodes must be selected in the ratio of 1:2.

If any other distribution of the potential is made use of, for example the fluorescent screen itself placed on full anode potential and merely a part potential applied to the anode 6, an arrangement which, as described later, possesses certain advantages, this spacing will require to differ accordingly. It is only as a result of this recognition that the method described may be utilized at all.

In the arrangement illustrated in Fig. 2 the glass bulb is relatively long. Since on account of the size of image to be obtained on the fluorescent screen there is a prescribed minimum distance between the screen and the deflecting plates (if this spacing were too small the deflection potentials would be excessively high, while moreover the laws of proportion as regards the deflection would no longer apply), the tubebecomes relatively long owing to the, necessary ratio of 1:2.

This arrangement would then have the additional advantage that the electrons traverse the deflection fields at a very low speed, so that very much smaller deflection potentials may be employed, which is above all of particular importance when the deflection potentials are generated at the transmission end, picked up at the receiving end and require to be amplified.

In this connection variation is desirable in the distribution of the potential (charging of the fluorescent screen with full anode potential). If, for example, the anode 6 is omitted entirely, the spot concentration coil should divide the distance between the electrode 3 and the fluorescent screen 9 in the ratio of 1:1.

The construction of the fluorescent screen as an electrode would normally be performed by applying the material to a metal plate. In this case, however, it is possible toobserve the television image merely through the lateral, usually conical portion of the Braun tube, which on account of. the reflection of the glass, distortions, and limitation of the visual angle is extremely unpleasant. In order now to permit of observation against the light in the normally usual manner, the fluorescent substance, in accordance with the invention, is applied to a metal screen, which is so thin that appreciable absorption of the light therein does not take place.

The metallic coating may naturally not be so thin that the same appreciably increases the resistance of the entire circuit. In the production of this metallic coating, which normally is applied to the inner glass wall in direct fashion, and on which there is then located the fluorescent mass, difficulties may possibly be encountered insofar as the fluorescent screen charges itself.

According, therefore, to the invention, the metallic coating is provided on the side of the fluorescent screen which is directed towards the deflecting plates, so that the metallic coating then acts in a manner of speaking as a Lenard window.

In the described method of concentration making use of a spot-concentration coil the cross-section of the bundle of electrons at the point of the anode 6, or at the point of location of the deflecting plates, will be relatively large.

This occasions wider spacing of the deflecting plates in order to avoid screening effect, and consequently a smaller deflection sensitivity. If now in addition to the electro-magnetic concentration there is also employed electrostatical concentration using a Wehnelt cylinder, the electrons will leave the shutter aperture 4 at a smaller angle in space, i. e., will be bunched together in more defined form right from the commencement, so. that the cross-section of the bundle of electrons will now also be smaller at the point of location of the deflecting plates, which in turn results in greater deflection sensitiveness.

As a modification of the arrangement illustrated in Fig. 1 the spacing between the hot cathode and the electrode 3 may also be made considerably larger. Upon variations in potential of the Wehnelt cylinder 2 the diameter of the cathode spot then fluctuates on the electrode 3. By means of the aperture 4 a certain section is shaded ofi dependent on the concentration of the bundle of electrons. It is naturally in this case also possible to employ as control element a socalled spot-concentration coil. Attention must naturally be paid to the fact that the self-induction thereof is not excessive, in order to avoid failure in the case of high control frequencies.

In the arrangement according to Fig. l the electrode 3 is situated as close as possible to the filament, and the Wehnelt cylinder 2 is approached as far as possible towards the electrode 3. There is then formed by the Wehnelt cylinder 2 and the electrode 3 a hollow space, in which is situated the filament, and which communicates by means of the narrow aperture 4.

If new the filament or the inner walls of the electrodes discharge gas, it may occur that the pressure compensation does not take place with sufiicient rapidity through the aperture 4, so that the filament then burns in a gas atmosphere and under these circumstances the length of life thereof may suffer accordingly. It is therefore desirable -to furnish the Wehnelt cylinder additionally with lateral openings, or also to make the same altogether of metal fabric.

In numerous cases, and more particularly if a gas filling is dispensed with, so-called wall charges disturb exact composition of the image and the control of the intensity. To avoid this the inner wall of the glass bulb may be furnished with a metallic coating, which is charged with a suitable constant potential, in order to render the wall charges ineflective.

For the sake of faultless operation of the tube the electrical field acting on the electrons should be of such disposal that the course of the potential is not varied independently of the deflection of the bundle of electrons. This requirement, however, is not fulfilled if the inner wall of the glass bulb is furnished with one single metallic coating.

According now to the invention, the metallic coatings are so produced that approximately the same potential prevails in a certain definite crosssection. A possible form of embodiment of.the inventive idea is illustrated in Fig 3, in which like reference characters have been employed to denote similar parts, with the exception that in addition there is provided a lead 11 electrically connected with the metal coating of the fluorescent screen.

This lead 11 is also connected with a metallic coating 12, which has been produced, for example, by chemical deposit, and possesses the serrated form indicated in the drawings. The intermediate spaces are engaged by the serrations of a metallic coating 13, which may be connected, for example, with the anode 6. The zi g-zag embodiment of the metal coating represents an extremely suitable form; naturally other arrangements are also possible, such as inter-engaging wire points. The same arrangement may also be used at other positions, for example between the cathode arrangement and the anode 6. It is naturally also possible to employ a number of rings spaced slightly apart, each ring being charged with a somewhat higher potential than the preceding one.

It will be understood that no restriction is made to the particular forms of embodiment shown, and that various modiflcationsare quite possible within the meaning of the above description and theannexed claims without departing from the spirit of the invention. The examples quoted are intended to represent possible embodiments of the basic idea of the invention, consisting in the fact that a number of electrons pass through a diaphragm in accordance with the oncoming image frequencies, and that this bundle of electrons is again united in electrostatical or electro-magnetc fashion on the fluorescent screen.

What we claim as new and desire to secure by Letters Patent is: 1

1. A Braun tube including a hotcathode, a fluorescentscreen, a diaphragm adjacent said cathode for allowing the passage of electrons in accordance with the incoming image'frequency amplitudes, and a transparent metallic coating on that side of the said screen which is directed towards said cathode.

2. A Braun tube including a hot cathode, a diaphragm adjacent said cathode for allowing the passage of electrons in accordance with the incoming image frequency amplitudes, an anode, a fluorescent screen adapted tohaving a potential different of that of the anode, and electrically separated metallic coatings applied in direct fashion to the side walls of the said tube between said anode and said screen for .avoiding variation in the potential of the field between anode and fluorescent screen traversed by the electrons. One of said coatings extending to said fluorescent screen and adapted to have applied thereto the same potential which is applied to said screen.

3. A Braun tube including a hot cathode, a diaphragm for allowing the passage a concentrated beam of electrons in accordance with the incoming image frequency amplitudes, an anode, a fluorescent screen adapted to having applied thereto a potential difierent from that which is applied to the anode, a transparent metallic coatingon said fluorescent screen, and metallic coatings applied in direct fashion to the side walls of the said tube between said anode and said screen, said coatings being electrically separated from each other one being connected to the anode and one being connected to thetransparent metallic coating on said fluorescent screen, the opposed edges of said side wall coatings having the shape of a serrated line.

4. A Braun tube, including ahot cathode, 9. diaphragm for allowing the passage a concentrated beam of electrons in accordance with the incoming image frequency amplitudes, an anode, a fluorescent screen adapted of having applied thereto a potential difierent from that which is applied to the anode, a transparent metallic coating on said fluorescent screen, and metallic coatings applied in direct fashion to the side walls of the said tube between said anode and said screen, said coatings being electrically separated from each other, one of said coatings being connected to the anode and the other one being connected to the transparent metallic coating on said fluorescent screen, said coatings including elongated sections confined by converging lines which terminate at their intersecting points, the elongated sections of each coating extending in longitudinal direction of the tube and extending into the intersp'aces between the adjacentelongated sections of the other coating.

' 2 HANS GEORG MbILER.

, ROLF Mdmnn. j

Images