US2131192A - High vacuum television tube - Google Patents

Description

P 1933- K. SCHLESINGER 2,131,192

HIGH VACUUM TELEVISION TUBE Filed May 4, 1935 2 Sheets-Sheet 1 Mia/M.

Sept. 27, 1938.

K. SCHLESINGER 2,131,192

HIGH VACUUM TELEVISION TUBE Filed May 4, 1955 2 Sheets-Sheet 2 Patented Sept. 27, 1938 UNITED STATES 2,131,192 r HIGH VACUUM TELEVISION TUBE Kurt Schlesinger, Berlin, Germany, assignor to Radioaktiengesellschaft D. S. Loewe, Berlin- Steglitz, Germany Application May 4, 1935, Serial No, 19,817 In Germany May a, 1934 Claims.

The present invention relates to a Braun tube for television purposes which is preferably operated in a highly evacuated condition, in which electro-static fields are employed throughout for 5 producing and deflecting the image point, and in which all of the electrodes by means of which the fields are produced aregarranged within the tube, so that the tube is at once in an operable condition without further external auxiliary devices, such as coils and the like.

The tube according to the invention, an embodiment of which is illustrated by way of example in Fig. 1, may, broadly speaking from the point of view of physics, be divided into three parts: first, the beam condensing device (condenser" in an optical sense) with control grid and perforated diaphragm, secondly the reproducing lens with tubular. member up to the anode, and thirdly two deflecting condensers.

The indirectly heated cathode consists of a small nickel hood I, which at its front end, the diameter of which is 2 mm., is ground completely fiat and is furnished with a small recess 2 of .1 mm. only in depth, which is filled up with a highly emissive substance, for example a mixture of earth alkaline oxides, such as are well known in the art. In selecting the size of the recess 2 the size of the picture and the number of scanning lines are to be taken into consideration; the exact calculation of the size of the em ssive layer will be set forth below. The glow hood 2 is heated by means of a preferably slotted spiral 3 arranged in the interior of the hood, which may be insulated from 2 by a small insulating tube (not shown) consisting for example of magnesia. The complete cathode is located exactly in axial position within a control cylinder 4 by the use of a cylindrical fitting, so that the emissive surface is exactly aligned with the tube axis. 40 The cylinder 4, in turn, is fitted by means of two stamped collars 5 and 6 onto certain elementsfor example glass rodsprovided for centering the whole of the tube system in itself, and carries at a small distance from its upper end a dia- 45 phragm 1 having a narrow aperture, which diaphragm is disposed in close neighbourhood of the glow head I, for example at a distance of within .5 mm. therefrom. The cylinder extends beyond the grid diaphragm I by a definite amount 8 (see below).

The cathode ray proceeding from 2 and controlled in its intensity by I is preliminarily concentrated by 8 and impinges on a narrow diaphragm aperture 9 of approximately the same size as the emissive surface 2. The diaphragm plate carrying the aperture 9 consists of a completely outgassed metal having a high fusing point, for example molybdenum, which preferably is welded on to a bronze supporting plate Hi to form the diaphragm proper. The supporting plate Ill possesses a considerably wider aperture, so that the same is not touched by the directly impinging cathode ray and a local heating of the bronze plate is prevented. In this way the danger of subsequent discharge of gas within the tube is eliminated.

The aperture in the perforated diaphragm 9 onto which the cathode ray is projected with varying intensity is reproduced by an electron optical system on the screen, viz, by the electrode system comprising electrodes ll, l2, l3 and It. The main purpose of tubular member I I (bronze) consists in screening the cathode ray traversing the interior thereof against external electrostatic fields. The length which this member is to be given may be readily calculated from the desired scale of enlargement of the reproduction with a given constructional length of the tube (see below). The tubular member H is linked up with a lower positive bias than the main anode l4 and preferably than the diaphragm it) also. The path of the cathode ray does not undergo any electronoptical refraction within the tubular member, since in accordance with the invention the diameter of the tubular member is selected to be large as compared with the diaphragm aperture 9. It is true that the applicant has been able to ascertain definitely that a wide tubular member of this kind which is biased negatively in relation to the rays is ineffective in practice only as regards rays in the vicinity of the axis, i. e., the main bundle of rays, whilst as regards such marginal ray as stray to an appreciable extent it effects an auxiliary concentration which is very helpful for a satisfactory operation of the tube. It is possible, for example, to completely suppress by a bias of this kind of the tubular member in relation to the diaphragm the known halation eifects, which otherwise will appear on the luminous screen.

By means of an intermediate diaphragm with large aperture l2 and a short tubular extension l3 in coniunction'with the double anode l4 situated in front of the tubular member the cathode ray refraction proper is produced. The peculiar form of the electrodes is the result of systematic investigations of electron-optical lenses. The problem which has been solved in this respect consisted in the first place in producing by electrical design and adjustment the effect of a spherically corrected lens having for the marginal rays the same focal distance as for the central rays. Secondly no refraction should be ex erted on the electrons after leaving the main anode l4, and thirdly it should be possible to provide deflecting plates behind the anode without the symmetry of rotation of the lens being lost. (Behind means: more remote from the cathode than.)

The lens l2, l3, I4 as shown satisfies these reby means of two plates i6, i! in the horizontal means 26, are fully suflicient. The one oi the two mediate diaphragm l2 quirements as soon as the correct difference in potential has been adjusted between I! and i4, it being maintained electron optical refraction, is performed by means of a potentiometer I 6 which is connected with the terminal l5, and is connected between theearth potential, which is simultaneously linked up with the diaphragm l0 and the anode I4, and the potential oi the cathode. The refractive iield is ited to the lens space (i. e., the space between the electrodes producing the lens) by virtue oi the screened construction of the lens electrodes both towards the front as well as towards the rear. The

apertures may preferably be made not larger than the largest cross-section of the electron bundle.

The spherical correction of the lens is obtained 1 only upon introduction of the rear intermediate diaphragm i2 into the tubular member. lithe width of this diaphragm i2 is made approximatelyj as large as'the tubular extension it, the potential levels have substantially the form of an inscribed spherical surface,and the lens acts as a spherically corrected one, which is not trueii the interis omitted. It may be added that the diaphragm l2 acts at the same time as a select on pupil by which those marginal rays are stoppedwhich divergetoo strongly.

The third requirement, viz, the? independency.

oi" the symmetry of the lens field from thefle1ds of the deflectingplates arranged behind the anode I4, is obtained by-increasing the axial length of the anode to a certain extent by a small tube i5.

plates arranged behind the anode ll into e lens In this manner the penetration of the ileljizpf the fleld is greatly reduced, and it is in fact produced by the use oi a circular diaphragm 9, is an undisturbed round point. g, v The deflection of the cathode rays takes place direction, and l8. IS in the vertical direction. The

deflection is unavoidably associated with simul,-,

taneous 1 disturbances in the sharpness oi the image point at the edge ofthe image it, as heretofore usual, the one plate being connected with the deflecting voltage generator, the other plate is earthed.

In accordance with the invention. it is possible to overcome this difliculty, which heretofore has prevented the construction of tubes operating with purely electrostatic means, by, operating the two plates in reverse phase with respect to each other. For this purpose there is provided a special relaxation oscillation apparatus, for example as shown, of the twin circuit including a twin tube 20. ent grid-anode systems 22, 23 and, 28 are arranged about a common cathode. Simple single grid systems with a reciprocalnoi approximately 2% incombination with a;mica disc screening systems, for example, the lower one, is connected directly with the is charged through the medium 01' the resistance 21, and discharged through the medium of a gas? filled grid-controlleddischarge device 29,01 that general type. a well known representative of which. is the tube called "'Ihyratron (registered trade-H mark). The anode 25 of the system here in question is connected with a working resistance 20 of approximately 100,000ohms, and with the one dcfleeting plate I1 01' the televisiontubethrough the medium of a coupling condenser 3| In order now to obtain for the other deflecting plate It an equal positive. in relation to II, This adjustment, which determines the degree. oi

accomplished that the stationary image point, whichis which consists, amplifier tube Two independ relaxation condenser 20, which potential of opposite phase the plate leakage resistance 32 (not exceeding 100,000 ohms) is connected; with the second control, grid 221-oi the upper r'systemof the twin. amplifier tube 20, the

relaxation potential being reduced by means of a 6 tapping 32', exactly to the extentto which the 3 same has been amplified in the lower half of the ,tube 24, 25 (amplification factorl/D). There is accordingly obtainedat the working resistance 33 of; thesecond; anode 22 the desired reverse relaxation potential havingthe same amplitude but reverse phase. This reverse potential is conducted to the second deflecting plate It of the television tube through the medium of a second coupling condenser; this deflecting plate being also earthed through a leakage resistance 34 larger than 32.

By meansof a similarrelaxation arrangement likewise comprising a countercadence amplifier the front pair of deflecting plates l8, i9 is also operated in reverse phase. It mustbe particu-., larly emphasized that without such. reverse phase circuit the problem does not appear capable of solution. The errorswhich then occur, 1. e., in the case oi the usual single phase operation are lack of sharpness atthe, edge by variation 01' the focal distance, and a trapezoidal shape of the picture. These errors inthe image are all avoided byfreverse phase operation of the two deflecting plates. It is true that the mutual approach of the pairs of plates, towards. each other and the anode should not be driven farther than to within two to three times the width oimouth (distance between, the rear edges, directed towards the cathode, of the plates of a pair of deflecting plates).

Improvements in "theoperation at the plates. may be obtained by giving them a suitable shape.

It is convenient to disposethem ina tilted position in relation to each other, asa certain gain in their specific sensitivity (deflection in mm. per volt) is thereby obtained. Beyond this the sensitivity of the deflection is, with the use of a reverse phase circuit, twice as great as with a. usual circuit, 1, e., the anode battery potential 35,,may be halt asgreat as usually, which is of particular advantagein the case of short-ray high-vacuum tubes in which the; deflecting plates require to be approached as near as possible towards the screen. It has been found that to avoid interfering displacement of the ray owing to wall charges a silver coating 36 should be provided, which may preferably be connected with earth,i. e., with the anode I 4 or diaphragm III.; The applicant has ascertained, however, that this'silvercoating requires to cover merely a part of the bulb, viz, it

requires to extend only iromthe anode it up to the front plates i8, i9, which already project into the interior'oi the bulb. Equally asimportant as this screening is an outermagnetic screening oi the tube by means 01 an iron shield 31, which needs only to consist of ,a sheet of approximately 1 mm. thickness having a good magnetical conductivity, which, however, must be closed in annu-, lar form (welded or drawn) ,and need merely extend from the hot cathode to the anode.

The shield is preferably, likewise connected with i earth. It isonly with the provision of this shield that it is possible to operate the tube in any desired position in relationg t o the magnetic earth field, so thatparticular potentiometers for adjusting the position of the centre oithe image are unnecessary.

. lack ofsensitivenessagainst field disturbances is favoured bythe extensive preliminary acceleration of the ray which iseilected accord- 7 ing to the invention by the high positive potential of the diaphragm 9.

The light intensity and function of the whole tube is essentially determined by the path of the rays between cathode and diaphragm. The rays should be suitably influenced in this particular region, 1. e., in such manner that as far as possible all electrons in the first place are passed through the narrow aperture, and secondly continue to move in such a narrow cone that no stopping-of electrons occurs later neither in the lens nor in the diaphragm and that all electrons reach the screen in one definite image point. The better the form of the bundle obtained, the more sensitive the deflection may be made, as a. bundle having a small cross section in the plate field practically is not subject to disturbances even in highly sensitivev plate systems, whilst a bundle having a large cross section in the region in question undergoes lateral distortions in such systems.

The applicant has found that the simple condensing lens I, 8, III as shown, which exactly corresponds in its operation with the main lens l2, l3, I4, is capable of fulfilling the stated requirements, but merely under the condition that the free length of the ray between cathode and diaphragm is not too small. The applicant has found that the spacing l/lll must amount to at least 10 mm. This spacing is calculated in practice by use of the simple diopter law on the basis of the required width of bundle. One may in fact obtain a survey on the conditions of ray propagation as influenced by the condensing lens by drawing the most unfavourable rays from edge of the cathode spot over the edge of the di phragm aperture. These rays must then undergo such a,

refraction in the condensing lenses as to pass through the image producing lens and through the space between the deflecting plates.

With a large spacing 'I/ III as stated above and the cylinder extension 8 necessary for spherically correcting the condensing lens, which extension fills out approximately one-half of the spacing. it is clear that the anode fleldattracting the electrons is rather weakened. If only for this reason alone the separate and sumciently strong positive bias of the diaphragm I0 is essential if it is desired to obtain bright images. In particular cases it may be necessary to provide a screening grid diaphragm 38 together with a particular intermediate cylinder 39, in order to be able to make the requirement for suitably guiding of the ray unobstructedly consistent with the requirement for sufiicient anodic strength of field as is necessary for producing cathode rays of great intensity.

In the following it will be set forth in what manner a tube according to the invention may be dimensioned in practice.

Diameter of aperture in diaphragm for 180- line picture size 17x20 mm .5

Form of aperture is reproduced sharply; therefore also square or hexagonal apertures may be used.

Current utilizationggg: m} giggfifigg Length of tubular member II approximately mm 100 Diameter of aperture of lens ll, l2 mm 7 Tubular member extension 13 mm 7 Diameter of tubular member mm 20 Spacing between edge of tubular member and anode mm 7 Diameter of anode tube I5 mm 7 Length of anode tube l5"; mm 7 Space between anode l5 and edge of rear deflecting plate mm 10 Width of mouth of rear deflecting plates system mm 6 and 15 Length of rear deflecting plates mm 35 Width of mouth of front deflecting plates system mm 6 and 20 Distance between rear plates system and front plates system mm 20 Spacing between anode I5 and luminous screen mm 250 Anode potential volts 2,000 Maximum power required watt 1 Heating 4 volts, A. C. or D. C amp .4 Potential of tubular member, volts variable,

approx 1,500

lation generator 35 volts 800 It is to be understood that the above data only refer to a particular form of embodiment of the tube according to the invention, to which the invention is in no way limited.

The individual parts of the system may be mounted on the base of the tube and centered in relation to each other preferably by the use of insulating supporting means, which may preferably consist of glass. The individual current leads are preferably all taken to a socket secured to the base of the tube. The current supply to the metallic coating 36 is preferably efiected so as to avoid special fusing-in points by means of springs fixed to the electrode system and conductively connected for example with the anode. These springs may at the same time serve for supporting or guiding the system within the neck of the tube. For this purpose they may be constructed for example in the form of comparatively strong, bent blade springs.

A practical and convenient technical form of embodiment of the tube according to the invention is illustrated by way of example in Fig. 2, like references being given to like parts in the two figures.

I claim:

1. A Braun tube more particularly for television purposes comprising means including a cathode disposed near one end of the tube for producing a cathode ray, an image screen disposed at the end of the tube opposite to that end near which said cathode is disposed, and an electron-optical lens system for projecting the cathode ray onto said image screen in the form of a sharply defined image point, said electron-optical lens system comprising a tubular member having its axis disposed in the direction from said cathode to said screen and having a diameter which is considerably larger than the diameter which the cathode ray possesses when travelling through said tubular member, an apertured disc shaped sion purposes comprising means including a cathode disposed .near one end of. the tube for producing a cathode ray, an image screen dis posed at the end of the-tube opposite to that end near which said cathode is disposed, and an electron-optical lens system fortmfflicting the cathode my: onto said image screen in the form of a sharply defined image point, said electronoptical lens system comprising a tubular member having its axis disposedin the direction from said cathode to said screen and having a diameter which is considerably largerthan the diameter which the cathode ray possesses when travelling through said tubular member, an anode mounted near said tubular member between said tubular member and said image screen, said anode comprising at its side facing said tubularmemher an apertured plate shaped portion disposed perpendicularly to the axis of said tubular member, said anode having a tube-like extension in the direction away from said tubular member. and an apertured d aphragm separating said tubular member into two parts and being mounted near that edgeof said tubularmember facing said anode, said anode being adapted to be supplied with a h gh positive potential in relation to said cathode. said tubularmemberbe ing adapted to be supplied with apotential positive in relationto said cathode butnegative in relation to said anode. l

3. A Braun tube more particularly for television purposescomprising means for producing a cathode ray, means to produce difierent electric fields for influencing the cathode ray in different axially consecutive zones of the tube; an image screen disposed at one end of the tube to be hit by the cathode ray after the cathoderay has passed through the mentionedaxially consecu tive zones, an electrode system located in a space of the Braun tube, both at the sides of which space facing said screen and facing away from said screen at least one of said fields is located, said electrode system comprising electrodes adapted to produce an electron-optically refractive field, and to at the same time screen. this refractive held against the fields at the side of said electrode system facing said screen as well as at the side of said electrode system facing away from said screen, said electrode system comprising a tubular member having its axis directed towards said screen and having a diameter which is considerably larger than the diameter which the cathode ray possesses when travelling through said tubular member, an apertured disc shaped anode mounted perpendicularly tothe axis of said tubular member near said tubular member between said tubular memberand said image screen, and an apertured diaphragm separating said tubular member into two parts ,and

being mounted near that edge of said tubular edge of saidtubular member.

ducing a cathode ray,

said anode being high positive potential in relation to said cathode, said tubular member being adapted to besupplied with a potential positiveiin relation to said cathode but negative in relation to said anode.:

4. A Braun tube more particularly fortelevision purposes comprising means including a cathode disposed near one end of the tube for proan image screen disposed atthe end of the tube opposite to that end near whichsaid cathode is disposed, and an electronoptical lens system for projecting the cathode ray onto said image screen in. theform of a sharply defined image point, said electronvoptical lens system comprising a tubular member having its axis disposed in the direction from said cathode to said screen and having a diameter which is, considerably larger thanthe diameter which the cathode ray possesses when travelling through said tubular member, an apertured disc-shaped, anode mounted perpendicularly to the axis of. said tubular member near saidtubular member between said tubular memberandsaid jmage screen, and an apertured diaphragm separating near that edge of said tubular member sion purposes comprising means including a oathode disposed near one end of J the tube for producing a cathode ray, an image screen disposed at the end of the tube opposite to' that end near which said cathode is disposed,and an electronoptical lens system for projecting'the cathode ray onto said image screen in the form of a sharply defined image, point, said electron-op this! lens system comprising; a tubular member having its axis disposed in the direction from said cathode to said screen and having a diameter which is considerably largerthan the diameter which the cathode ray possesseswhen traveling through said tubular member, anapertured disc shaped anode mounted perpendicularly to the axis of said tubular member near said tubular member between said tubular member andsaid image screen, and an apertured diaphragm separating said tubular member into two parts and beingzmounted near that edge of said tubular; member facing said anode, both said anode and said apertured diaphragm having apertures the cross-sectionsof which are substantially equal to the cross-sections which the cathode ray has in the respective planes of said apertures, the

distance of said apertured diaphragm. from the edge of said tubular member facing said anode being approximately equalto the diameter of the aperture in said apertured diaphragm, said anode being adapted to be supplied with a high positive potential in relation to said cathode, said tubularmember being adapted tobe supplied with a potential positive in relation to saidcathode but negativein relation to said anode.

KURT SCHLESINGER.

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