US2356418A - Braun tube - Google Patents

Description

BRAUN TUBE Filed Feb. 4, 1939 SOUQCE OF PULSA T/A/G D/REC; CURRENT I l I fm/enfop: Na x/imfian Mess/7e! Patented Aug. 22, 1944 NT or ies IBRAUN TUBE Maximilian Messner, Berlin, Germany; vested in the Alien Property Custodian Application February 4, 1939,. Serial No. 254,581

In Germany-February 7, 1938 Claims.

This invention relates to improvements in or concerning cathode ray or Braun tubes, and more particularly to the high vacuum type of such tubes for use in television systems.

It -.has been experienced in the pastthat the fluorescent screen of high vacuum. Braun tubes becomes damaged under ditions. Investigations in this respect have proven that the fluorescent screen suffers during the course or longer active use, even in cases that the tube is of the hard vacuum type, and that the damage occurson the fluorescent screen in theshape of a dark line or spot, whether the cathode ray is electromagnetically deflected along one or both coordinates of the coordinate system. It must be noted in this connection that the damages heretofore referred to are not identical with the well known injuries of the fluorescent screen due to the screen etching phenomenon. Further,

out in this field teaches research work carried that damages of the first mentioned kind result from the action of certain ions, the barium ions, for example, which practically remain uninfiuenced by the cathode ray deflecting means, provided that the Braun tube operates with electromagnetic deflection. It has beenfound that the above mentioned ions which have frequently been observed and also taken in account in connection with glow cathode tubes become influenced in Braun tubes solely in cases that electrostatic deflection of the cathode ray is employed, but remain almost immune to an electromagnetic deflection due to their very great mass as compared with that of the electrons. Anelectrostatic field imparts the same deflection to all particles of equal charge independent of their mass, since particles of greater mass move with a correspondingly reduced velocity, provided that they have previously been accelerated by the same potential, while on subjecting these'particles to an electromagnetic deflection under exactly the same operating conditions as heretofore mentioned, the relationship between the efiective defiections is: VE/m, where VE denotes the charge, and m the mass. This rule clearly shows that certain precautions must be taken in connection with electromagnetic cathode ray deflection in order to eliminate the above mentioned difliculties.

This is accomplished according to the main feature of my present invention by directing the a cathode ray in its state of rest toward the outer edge or idle area of the fluorescent screen, instead of leaving the cathode ray incident upon the active image area of said screen also during certain operating con- 'right angles to that current sources 3 and the absence of, incoming image and synchronizaf tion impulses.

is effected by means of an electrostaticdirect current field which removes deleterious. ions .irpm

the active image area.

The invention will be more readily'understood from the following description taken in conjunc tion with the accompanying drawing, of which Braun tube of stan d Fig. 1 schematically shows a ard type to which the invention is applied, and Fig. 2 shows a tube in which a modification of the invention.

away from its new to on account of schematically shown in spect to said initial or flection. This facility actual area of the image, so that the harmful ions are withdrawn from the image reproducing,

surface ofthe fluorescent screen. The corresponding deflection along the othercoordinate at heretofore considered may.

be carried out either by means of electrostaticor electromagnetic fields. The actual or useful deflection of the cathode beam takes place at the point B of the drawing along the coordinate oi the electrostatic initial or biasing deflection, for instance, by the agency of coils or windings I and 2 through which pulsating direct current from t flow but no alternating current flows. This may be realized according to a further feature of my invention by directly connecting the deflecting coils or windings in the anode circuit of a final tube following a time base generator. The direct current portion thus applied to the deflecting coils magnetically restores the initial or biasing electrostatic deflection to the range of active operation. Because of the fact that the characteristic of the above mentioned final tube hardly becomes utilized exactly to the current value nil, the residual current thus present involves an appreciable minimum deflection in the vicinity of the artificial position of rest of the cathode ray which position might be critical due to the presence of the harmful ions,

so that all possibilities for these ions to detrimentally affect the virtual area of the fluorescent screen are reliably eliminated.

It is also possible in accordance with still a there, is included- Y fed coils or windings which havexfor their object to convey back to the cen tral surface of the fluorescent screen the electrons onlyof the combined mixture of electrons and ionsginitially removed therefrom on account of' the biasing electrostatic deflection.

The pure. electron .beam thus incident upon the central or vactive area of. a Braun tube fluo- ;rescent screen may ,beutilized for a variety of purposes, e. g. for being so deflected as to produce image in accordance with any optional meth- ,-od or scheme without running the risk that the deleterious ionic effect might injure thescreen.

Of course, precautions must 'be taken thflt the range through which the electronic beam passes during the useful deflection doesnot become enlarged into the range of the cathoderay vit 'titl cially produced therefor by virtue of the eiectro.-

static initial or biasing deflection.

' It 'isan-essential advantageof thearrangernent today vabove described invention-that theewell lsnown standard'type' of cathoderay or Braunetubes-requires noprincipal alterations for its application." "The only additional means which are necessary'for carrying outmyinvention is a simpleelectrode structure such asa pair of deates for generating the necessary electrostatic direct current fleld.

Whatisclaimed is: 1. A cathode ray tube including an electron gun. emitting a cathode ray, a fluorescent screen having an active vand an idle area, electromag- -netic means for deflecting said cathode ray over the active :area .of said fluorescent screen, and electrostatic means for maintaining an electrostaticcathode-ray biassing fleld in the path of said cathode i'ay for deflecting ions onto the idle area said electrostatic means.

:2. A cathode ray tube including an electron gun emitting a cathode ray, afluorescentlscreen having .an active and idle area,and electromagnetic image deflection means including a coil for deflecting said cathode ray over the active area nation a cathode ray further feature of the invention to provide pargticular direct current of said fluorescent screen, electrostatic means for always deflectingions from impingement upon the 'activearea of said fluorescent screen, and means for passing a direct current component of current through said coil for directing only electrons to impinge upon said fluorescent screen.

3. A cathode ray tube according to claim 1, havingdirect current fed windings for restoring electrons emitted from said electron gun into the .1

active areaof said fluorescent screen.

4. in a discharge tube arrangement in combie tube comprising a luminescent screen and means includinga cathode an ,anode for producing a cathode ray and for focusing said cathode ray on' saidscreen, a deflecting system arranged. between said anode and said screen and comprising a pair of magnet coils.

for causing said ray to scan said screen, a pair ofv deflecting plates mounted betweensaid anode and said deflecting system. said pair of deflecting plates being so arranged that; in operation the lines of force of said deflecting plates extend substantially vertically to'the lines of force of "said. 7

coils, means for applying a potential difference *between; the plates ofsaid pair of such an amount thatsaid cathoderay after emergence frosnthe space between said plates is directed out of image fleld, and means forfeeding saidooils, with .a direct current of such cathode ray upon the centre of said screen.

5. A cathode ray tube including anele tlun gun emitting a cathode ray, a fluorescent screen hay and an idle area, electromagnetic.

ing an v.active means'for deflecting said cathode .ray overthe 7 active area of said fluorescent screen. and else trostatic means for maintaining .an'electrostatic cathode ray biasing fleld in the path of said oaths Node ray for deflecting ions away from the active .area of said fluore'scentscreensaid electromagnetic means including a coil for creating an electromagnetic fleld and means for passing a pulsating direct" current through said coil, the current component of which creates a biasing fleld equal and opposite in its eifect upon electrons to the effect upon electrons produced by said electrostatic means.

' 1 F MAXIMILIAN MEBSN-EB.

an intensity that said in its stationary position impinges

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