US2129015A - Braun tube - Google Patents

Description

Sept. 6, 1938. s. LOEWE 2,129,015

BRAUN TUBE Filed March 14, 1935 2 sheets-sheet 1 Sept. 6, 1938. s. LOEWE BRAUN TUBE Filed March 14, 1933 2 Sheets-Sheet 2 hasgeesepca, 193s PATENT OFFICE BRAUN TUBE Siegmund Loewe, Berlin, Germany Application-March 14,

In Germany March 1933, Serial No. 660,642

13 om (ci. 25o-21.5)

This invention relates to Braun tubes, and to a method of producing the same.

According to the invention, the Braun tube is not produced in the hitherto customary fashion from one single bulb. but from a plurality of completely independent parts, which are connected together in vacuum-tight fashion by fusing, cementing, spraying or by a combination of these processes.

The body of the tube according to the invention is made of metal. The image window' consists of a planar sheet of glass, which is as thin as possible and, by means of cementing or the like, is connected in gastight fashion with the 15 body of the tube, on which there may be provided a specially constructed reception flange.

The system is mounted in its complete form on a base and centred, and the base is connected with the metallic body of the tube by fusing. cementing or the like. 'Ihe metallic body, however,

may also be furnished in such fashion with a ange that it is possible to fit the part supporting the system into this flange, so that the sys'` tem holder, which usually consists of glass, is protected by the metallic tube body against any mechanical strain from the exterior.

The outgassing of the metallic body of the tube is relatively difficult, and is performed in accordance with the invention as follows:

The metallic body is first heated to a temperature as high as possible, and then, upon cooling, is subjected to the action of that particular gas, say, helium, argon or the like, which is later employed as tube filling.

Upon the cooling of the metallic body, which supercially has been rendered entirely free of gas by the heating process, there is formed upon the surface a thin lm of absorbed hydrogen, rare gas or the like which, when the metallic body is introduced into air, prevents the adsorption of oxygen, nitrogen, etc. Owing to the fact that the metallic body during operations discharges slight amounts of the adsorbed lling gas, a deterioration in the working conditionssince the gas discharged is identical with the'` filling gas--is unable to take place.

To ensure, however, that any impurities in the tube are properly bound, there are provided within the tube, according to the invention, two special getter substances. The one getter substance may conveniently be employed for binding any deterimental traces of gas remaining in the tube after the evacuation, whilst the second getter substance is arranged in such fashion that the same may be applied by atomization 't0 'a completely outgassed part of the system, for example the anode. In this manner there is provided on this part of the system a coating of getter-substance completely free of gas, which coating, upon the operation of the tube when 5 the system is heated to a relatively high degree, evaporates and thus immediately binds any detrimental traces of gas which may occur in the operation. As well known, the rare gases employed for filling the tube are not bound by the 10 getter substance. In the same manner hydrogen is not attacked by magnesium, as the hydride formed as intermediate substance is again converted instantaneously into hydrogen and magnesium' at the temperatures which occur 15 in operation.

Since subsequent centring of the system is extremely diicult, there is `employed in accordance with the invention a system, which enables centring to be performed in simple and reliable 20 fashion.

According to the invention, there is employed a large-surface screening preliminary anode, which prevents any spreading eifect and is raised to a relatively low potential, and a screened 25 after-acceleration anode raised to a high potential. The screening anode is held in such fashion that its holding means completely screen off the high potential eld of the after-acceleration anode leads against the cathode. The holding 30 means for the screening anode and also the holding means for the delecting plates are made symmetrical. The upper pair of control plates is held by a separate ring. Between the ring and the one holding means there is provided a small 35 elastic insulating plate composed of a highly vacuum-prooi material readily capable of being outgassed, such, for example, as mica. An electrode each of the two pairs of control plates is raised to the same potential as the after-accel- 40 eration anode. In this manner there is safely prevented a variation in the speed of the ray during the passage through the pairs of control plates. The deflecting potentials are passed to the lower pair of plates through the medium of the one lateral holding means, which is insulated against the after-acceleration potential, and to the other pair of plates through the mediumof a special current lead, which is also insulated against the after-acceleration potential. The insulation, as already indicated, is ensured by the small thin plates composed of insulating material, for example mica.

The said small plates, however, are also required to exert an additional function. Upon the outgassing operation the complete holding system expands to a. by no means inconsiderable extent. In consequence elastic compensating members require to be provided, which take up this elastic expansion of the system, and after completion of the heating operation return forthwith into their original position. For this purpose there are employed the small mica plates described in the above, which are fitted at two or more points between the single holding members.

'I'he structurally distinct and extremely comprehensive embodiment of the complete system ensures an extremely simple and readily effected centring operation.

The use of a screening preliminary anode according to the invention reduces the danger of fiash-over between the cathode and the highpotential anode to a minimum. In the same manner the provision of this input anode greatly diminishes the ion bombardment to which, in the known tubes, the cathode is subjected to an extremely high degree. 'Ihis essential improvement in the electrical properties permits of the use of pointed cathodes, which are relatively sensitive to flash-over, and also more particularly the use of high-emission, metallic vapor cathodes, which heretofore could not be employed in Braun tubes by very reason of the so-called drumming eiect. It is true that it is also necessary when employing the arrangement according to the invention to use a filling of hydrogen, as when using rare gas the drumming effect would still be suiiiciently large to reduce the effectiveness of the metallic vapor cathode to a minimum in a very short space of time.

It is only when a hydrogen filling on the one hand and a screening anode on the other hand are employed simultaneously that it is Apossible to reduce the drumming effect to such extent that the requisite length of life of the high-emission cathode would appear to be ensured.

Further, the tube according to the invention is furnished with grid control. Conveniently the control grid may be constructed in the form of a small perforated shutter and arranged within the dark space of the cathode in the Wehnelt cylinder itself. When using a, pointed metallic vapor cathode according to the invention it is absolutely essential to vsuppress as far as possible every subsidiary emission which might proceed from the filament serving to heat the pointed cathode. In consequence there is provided within the Wehnelt cylinder, in accordance with the invention, a mica screen, which screens o the heating filament against the resulting metallic vapor. 'I'he highemission cathode is produced in the following manner: 'f

An ordinary, oxide-coated, pointed cathode is first completely assembled, whereupon there is placed over this cathode a mica screen, which screens olf the rear space of the Wehnelt cylinder, in which there is provided the filament. In front of the mica screen there are'furnished in the Wehnelt cylinder one or more light-metal substances or reaction pills, which serve for developing metallic vapor, and after the outgassing of the complete system and evacuation of the tube are caused to evaporate.

Naturally, it is also possible, in place of an oxide-coated point, to employ a point which is composed of tungsten coated as evenly as possible with tungsten oxides of defined composition. 'Ihe combined application of the oxide and emissive coating to the finally mounted cathode is extent beyond the also readily capable of being performed in practice.

In order to keep the hydrogen pressure in the tube constant, or to re-establish the same when hardening takes place, there may be provided in the tube a suitable hydrogen compound of correspondingly low dissociation pressure, for example a hydride or the like, or a piece of palladium metal or palladium sponge saturated with hydrogen, which discharges the hydrogen even upon slight heating. Y

Certain forms of embodiment of the tube according to the invention, or of details of the same, are illustrated by way of example in the drawings.

Fig. l shows a diagram of the tube according to the invention. In the same I is the metallic body of the tube having the flange II, into which there is tted in vacuum-tight fashion the planar, rectangular or round sheet of glass 2, which possesses on the rear face the luminous substance I8. For sealing purposes there is provided a cementing means I2. For mechanical attachment there may be employed a metal coating sprayed over the coating of sealing wax, cement or the like, or if necessary also a correspondingly fitted metal ring. 'I'he ange is preferably so dimensioned that it completely surrounds the piece of glass and projects to a slight edge of the same. 3 is the holder for the system, which holder is preferably composed of glass and may be connected with the metallic body I by fusing.

Naturally, the metallic body of the tube must be subjected to a corresponding preliminary treatment at the fusing in point, for example thinned down. In order to make the metallic body cornpletely vacuum-tight even in the case of the highest temperatures occurring in operation, the same is preferably coated on the Surface with a coherent gas-tight protective layer, which may consist for example of a ceramic substance,

rv,enamel glaze or the like, or also of organic substances, such as cellulose esters or ethers, organic polymerization products or hard vulcanized rubber, and may be applied in any desired manner known per se. 'Ihe coating may naturally be so arranged that it also covers the system holder (pinch) and the image sheet to a certain extent, and in a manner of speaking connects the same together. 'I'he system holder 3 carries the complete systemv structure, the Wehnelt cylinder 5, the cathode 4, the anode I1 and the two pairs of control plates 6 and 1. 8 and 9 are getter substances, and 20 and 2l screening means.`

'I'he getter substances and the screening means may conveniently be provided in direct fashion on the metallic body, and are either so constructed that it is possible to heat the same from the outside by eddy 'current heating to the ternperature necessary for atomization, or are furnished with a special heating coil. I9 is the metallic leak conductance for the luminous coating, which if necessary may be metaliized on the surface and employed as after-acceleration anode.

Fig. 2 shows a particular form of embodiment of the tube according to the invention, in which the system holder 3 is fitted in such fashion in a special flange I3 of the metallic tube body I that it is completely screened ofI by the tube body against mechanical influences.

For sealing purposes there is provided a layer of sealing wax or cement I5. For the mechanical attachment there is employed a ring Il, which is capable of being screwed in. Naturally, in

place of the ring it is also possible to employ a sprayed-on metallic coating. The sealing may also be effected in numerous different manners.

Figs. 3 and 4 show the attachment of the piece of glass 2 in the front flange of the metallic body.

In Figs. 5 and 6 there is illustrated the novel form of electrode system employed according to the invention.

Into the glass pinch 3, which carries at the centre the cathode with the Icontrol grid and also the Wehnelt cylinder, there are fused two relatively long holding wires and 3|, to which the pair of plates 6 are secured in direct fashion. 'I'he one holding wire carries at the same time the annular after-acceleration anode 21,' whilst toV the second wire there is applied the control current for the first pair of plates. 'Ihe second pair of control plates 1 are held in a special ring, which is held by the holding means 30 in direct fashion, and by the holding means 3| through the medium of the small plate 34, which consists of a highly refractory and elastic material readily capable of being outgassed, for example mica. The one plate of the pair is connected in immediate fashion with the ring 32, which is raised to the potential of the after-acceleration anode. The other plate, to which there is conducted the control current, is insulated against the holding ring with the assistance of a second, small insulating plate 35.

There are also fused into the glass pinch two holding wires and 36, which carry the screening anode |1, and are situated in the plane of the two outer holders. The holding portions 35, 36 and 30, 3|, in accordance with the invention, are constructed and arranged approximately symmetrically. By means of the holding members 35 and 33, which at the same time act as current leads for the screening anode I1, which is raised to a. relatively low potential, and accordingly pos- Sess the same low potential, the cathode and the cathode ray pencil are screened off against the high potential of the outer electrodes. Naturally in lieu of this the outer current leadsv 30 and 3| might also be furnished with a special screening means, e. g. insulated tubes 30' and 3|', which should preferably possess approximately the same potential as the cathode, generally speaking the potential of the member to be screened.

29 is'y the lead for the control current to the plate of the pair of 'control plates 1 which is insulated against theA holding ring.

As clearly discernible, more particularly from Fig. 6, the complete system viewed from the top constitutes a symmetrical figure, the sides of which are formed by the two pairs of plates, and the centre of which is constituted by the small aperture of the screening anode I1. The centring of the system may, therefore, be accomplished in extremely simple fashion by the use of a corresponding rectangular or square rod furnished with a point of suitable diameter.

In Fig. '7 there is shown separately the arrangement of the small, insulating plate 34. 3| is the holding wire, 34 a small, correspondingly shaped plate of insulating material, such for `example as mica or the like, and 32 the upper holding ring.

By the provision of this intermediate elastic element a faultless outgassing of the system, which necessitates the heating thereof to high temperatures, is rendered possible, as the mechanical expansion, which takes place upon the heating of the system, is taken up by the intermediate elastic elements, so that a permanent distortion of the single parts of the system is unable to occur.

If these intermediate elastic members, which take up the expansion pressure, were not provided, the considerable expansion of the parts of the system occurring upon the outgassing operation due to the heating might under certain circumstances lead to a complete rending apart of the rigidly mounted system.

As shown by Fig. 5, the screening anode I1 possesses a diameter of such size that merely an extremely narrow space remains between the same and the wall of the tube, so that spreading effects of any kind are unable to 'occur between the atteracceleration anode and the cathode. The screening anode is furnished at the sides with small recesses, through which there are passed the holding wires 30 and 3|.

Fig. 8 shows the pointed cathode 4, which according to the invention operates with a metallic emissive coating, and is indirectly heated by the filament 4' or in similar fashion. In the Wehnelt cylinder 5 there is arranged a screening means 38 in such a manner that merely the tip of the pointed cathode projects into the working space, whilst the filament is completely screened off auglainst this space. The screening means may consist of mica or a similar material which is insensitive to temperature and is easily to be outgassed. On the wall of` the Wehnelt cylinder there are provided the two small pieces of light metal o r light metal generating pills 39 and 40.

There is at first mounted a cathode, the emissive point of which is coated with a layer of tungsten oxide or alkaline earth oxide. After the heating and evacuation the light metal 39 and 40 is evaporated, so that a highly emissive coating oi' light metal is formed on the oxide point 4. 4| is the control grid, which is preferably constructed in the form of a perforated shutter, and is arranged in the dark space of the cathode.

It is readily possible, in place of the grid control according to the invention, to make use of any other desired light intensity control means of the kind known per se.

Naturally, it is possible to omit certain of the stated features or to replace them by others. Thus, for example, in place of the metallized luminous layer acting as second, after-acceleration anode, it is possible to employ a luminous layer completely void of metal, and to provide in the vicinity of the luminous surface a metallic ring of suitable potential insulated against the wall of the tube.

It is above all essential as regards the tube according to the invention that this tube is composed of different parts, which are produced independently of each other and consist of different kinds of materials, that a stable and selfcontaned electrode system is employed which may be centred in ready and reliable fashion, that a screening anode and anv after-acceleration ana ode are provided, and that the pairs of controll plates possess the same potential as the after-acceleration anode. A further essential feature resides in the use of the grid control and highly emissive pointed cathodes in conjunction with a hydrogen filling of low pressure.

The measures are also of particular importance which serve to produce a constant gas pressure, and ensure. stability of the electrode system, more particularly during the outgassing process.

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

1. A Braun tube comprising an enclosing envelope consisting of a metallic `tube furnished at the Whole of its outer surface with a thin, coherent,

vacuum-proof coating, a stem supporting a cathode, an anode and electrodes for controlling the intensity of the cathode ray, electrodes for concentrating the ray and electrodes for deilecting the connection between said flange and said glass plate.

2. A Braun tube comprising an enclosing envelope consisting of a metallic tube, the one end of which has a smaller diameter than the other end, said tube being furnished at the whole oi its outer side with a thin, coherent coating of a vacuumproof material, a stem connected to the smaller end of said tube in vacuum-prooi' fashion, a

' cathode, a concentrating cylinder, ascreening anode, a further anode adapted to be connected with a high voltage source, and two pairs of deilecting plates, means to attach all of said electrodes to said stem, said attaching means including means .for connecting all of said electrodes to their circuits, a ilange connected to the larger end of said tube, a planar plate of glass arranged in said flange, said glass plate being coated on its side facing the interior of said tube with a uorescent substance, a layer oi' vacuum-proof material coating the connection between said tube and said stem and a further layer of vacuum-proof material coating the connection between said ilange and said glass plate.

3. A Braun tube comprising an enclosing envelope consisting of a metallic tube, the one end of which has a smaller diameter than the other end, said tube being furnished at the whole of its outer side with a thin, coherent coating of a vacuumproof material, a stem connected to the smaller end of said tube in vacuum-prooi' fashion, a cathode, a concentrating cylinder, a screening anode, a further anode adapted to be 'connected with a high voltage source, and two pairs of deilecting plates, a container containing a vaporizable substance, means to attach all of said parts to said stem, said attaching means including means for connecting all of said electrodes to their circuits, a flange connected to the larger end of said tube, a planar plate of glass arranged in said flange, said glass plate being coated on its side facing the interior of said tube with a fluorescent substance, a layer of vacuum-proof material coating the connection between said tube and said stem and a further layer of vacuum-proof material coating the connection between said ilange and said glass plate.

4. A Braun tube comprising an enclosing envelope consisting of a metallic tube, the one end of which has a smaller diameter than the other end, said tube being furnished at the whole of its outer side with a thin, coherent coating of a vacuumprooi' material, a stem connected to the smaller end of said tube in vacuum-proof fashion, a cathode, a concentrating cylinder, a screening anode, a further anode adapted to` be connected with a high voltage source and two pairs of deecting plates, a container containing a Vaporizable substance, means to attach all of said parts to said stem, said attaching means including 'elastic members of vacuum-proof, insulating material and' means for connecting all of said electrodes to their circuits, a flange connected tothe larger end of said tube, aplanar plate of glass arranged in said flange, said glass plate being coated -on its side facing the interior o! said tube with a iiuorescent substance,`a layer ot vacuum-proof material coating the connection between said tube and said stem, and a further layer of vacuum-proof material coating the connection between said ange and said glass plate.

5. A Braun tube comprising an enclosing envelope consisting of a metallic tube, the one end of which has a smaller diameter than the other end, said tube being furnished at the whole of its outer sidewith a thin, coherent coating of a vacuumproof material, a stem connected to the smaller end oi' said tube in vacuum-proof fashion, a cathode, a concentratingcylinder, a screening anode, a further anode adapted to vbe connected with a high voltage source and two pairs oi' deilecting plates, a container containing a vaporizable substance, means to attach all of said parts to said stem, said attaching means including elastic members of vacuum-proof,I insulating material and means for connecting all of said electrodes to i theirl circuits, screening means for screening of! said connecting means against said electrodes, la

, ange connected to the larger end of said tube, a

planar plate of glass arranged in said flange, said glass plate being coated on its side facing the interior of said tube with a iluorescent substance, a layer of vacuum-proof material coating the connection between said tube and saidstem, and a further layer oi.' vacuum-proof material coating the connection between said flange and said glass plate.

6. A Braun tube comprising an enclosing envelope consisting of a metallic tube, the one end of which has a smaller diameter` than the other end, said tube being furnished at the whole of its outer side with a thin, coherent coating of a vacuumproof material, a gaseous atmosphere of hydrogen within said envelope, a stem connected to the smaller end of said tube in vacuum-proof fashion, a' cathode, a concentrating cylinder, a screening anode, a further anode adapted to be connected with a high voltage source, and two pairs of deilecting plates, a container containing a Vaporizable substance, means to attach all of said parts to said stem, said attaching means including elastic members of vacuum-proof, insulating material and means for connecting all of said electrodes to their circuits, screening means for screening oil.' said connecting means against said electrodes, a ilange connected'to the larger end of said tube, a planar plate of glass arranged in said flange, said glass plate being coated on its side facing the interior of said tube with a iluorescent substance, and layer of vacuum-proof material coating the connection between said tube and said stem, and a further layer of vacuum-proof material coating the connection between said flange and said glass plate, and a metal hydride to within said envelope to maintain the pressure of said hydrogen atmosphere constant.

7. A Braun tube comprising an enclosing enve-l lope consisting of a metallic tube, a stem sup# porting a cathode, an anode and electrodes for 4 controlling the intensity of the cathode ray, electrodes for concentrating the ray and electrodes for deiiecting the ray, said stem being connected 4to one end of said tube, said electrodes projecting into said tube, a container containing a vaporizable substance, said container being arranged near said stem and being adapted to be Y heated from the outside of the tube by eddy-curent heating, and a planar plate of glass furnished vith a fluorescent coating, said glass plate being :onnected to the other'end of said metallic tube.

8. A Braun tube comprising an enclosing enveope consisting of a metallic tube, a stem supportng a cathode, an anode, and electrodes for con- ;rolling the intensity of the ray, electrodes for :oncentrating the ray, and electrodes for deflectng the ray, said stem being connected to one end if said tube, said electrodes projecting into said ',ube, a coating of gas-free vaporizable substance Jeing applied to one of said electrodes, a con- ;ainer containing a vaporizable substance, said :ontainer being arranged near said stem and be- .ng' adapted to be heated from the outside of the tube by eddy-current heating, and a planar plate 3f glass furnished with a fluorescent coating, said glass plate being connected to the other end of said metallic tube.

9. A Braun tube comprising an enclosing envelope consisting of a metallic tube having one cyllndrical and one conical part, the diameter or said conical part at its side opposite said cylindrical part being considerably greater than the diameter of said cylindrical part, one flange being provided at each end of said metallic tube, a stem supportlng a cathode, an anode, electrodes for controlling the intensity ofthe cathode ray, electrodes for concentrating the ray, and electrodes for deflecting the ray, said stem being inserted into the ange provided at the cylindrical end of said tube and being completely encompassed by said flange, and a glass plate arranged in the second ange, said glass plate being provided at its side facing said electrodes with a fluorescent coating.

10. A Braun tube comprising an enclosing envelope, a stem atone end-oi' said envelope, a cathode, a concentrating electrode, a screening anode, a further anode, and two pairs of deiiecting plates, means to attach said cathode, said concentrating electrode, said screening anode, said further anode, and said deilecting plates to said stem, said attaching means including at least one elastic member of vacuum-proof material.

11. A Braun tube comprising an enclosing envelope, a stem at one end of said envelope, a cathode, a concentrating electrode, a screening anode, a further anode, and two pairs of deflecting plates, means to attach said cathode, said concentrating electrode, said screening anode, said further anode, and said deecting plates to said stem, said attaching means including at least one elastic member of vacuum-proof insulating material, said elastic member being at the same time adapted to insulate from each other two of the mentioned members attached as stated to said stern.

12. A Braun tube comprising an enclosing envelope, a stem at one end of said envelope, electrodes in said envelope for producing, concentrating, accelerating and deecting a cathode ray, said electrodes including two pairs of deflecting plates mounted one behind the other as viewed from said stem, holding means secured to said stem and to said plates for supporting said plates 'from said/stem, the holding means for one plate of that one of said pairs disposed nearer said stem being adapted for conducting at the same time control currents to the last mentioned plate.

13. A Braun tube comprising an enclosing envelope, a stem at one end of said envelope, a cathode, a concentrating electrode, a screening anode, a further anode adapted to be connected with a high voltage source, and two pairs of deilecting plates, means to attach said cathode, said concentrating electrode, said screening anode, said further anode and said delecting plates to said stem,

means for connecting said cathode, said concentrating electrode, said screening anode, said further anode and said deflecting plates to their circuits, and screening means for screening-off against at least part oi.' said connecting means at least part of the mentioned members connected as stated to their circuits, said screening means consisting of insulated tubes, each adaptedl to be mtalntained at the potential of the member to be screened.

SIEGMUND LOEWE.

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