US2225099A - Cathode-ray tube - Google Patents

Description

1940- P. S.'CHR|STALDI 2,225,099

CATHODE-RAY TUBE Filed June 10, 1939 2 Shets-Sheet 1 INVENTOR 1940- P. s. CHRISTALDI 2,225,099

CATHODE-RAY TUBE Filed June 10, 1939 2 Sheets-Sheet 2 INVENTOR 1 2/? J? (Z2! 04/! BY ,Betel' S- Christaldii v; Allen -B.-Du Mont As aresult of -1ievelopment of the so called Braun tube for television' reception, it has-been I v r eral type disclosed in the patent -1 referred to.

As a result; the usesftowhich such'tubeseanbe definitely determined that certain valuesfwhether they be "of operatingpotentials or certain-electrodes, or of dimensions in' the tube structure itself, must be properly correlated inorder to obtain the desired operatingaction. For example, it is known that byincreasing the operating potential on an accelerating anode of a conventional cathode-ray tube, the intensityor brightness of the traceor picture is increased.

A point or potential range' is finally reached, however, whereat the sensitivity of deflection is reduced a prohibitive amount, so that it is notpractical tofurther increase the brightness of the picture'by this method alone. Another difilculty has been found to reside in the matter of main-,

taming the'scanning'electron ray at a good focus on the fluorescent screen. *That is, in making certain chwang'es or variations in some of F'the operating potentials or *in the structure of the tube itself to correct for or improve upon certain operating conditions, the result has been to impair, at the same time, the operating action in other ways, suchas'by causing some formof distortion of the pattern or by causing some degree 80- of defocusing of the-electronray-pn the fluores cent screen." Along with this development work,

the subject of electron opticshas beengiven considerable attention, in an attempt to formulate some working basis or formulae for use in :the"

85 most efficient design of cathode-ray tubes. for television reception. "In putting this theoretical information to practice, however, it has been found that there-are "still limitations in the way of'an occurringv decreasegin eflicincy ofv opera- 40 tion of the tube'in one important sense if certain changes are made-to'cause anincrease in eflic'iency of' operation of the tube .in another sense.-

-Many different types of cathode-ray tubes have been cons cted inywhich there is postdefle'ction accel ration of "the electron beam. In most of these various constructions, however, an elaboratesystem .of electrodes has been necessary which makes thesetubes impractical. so A simplified construction or system, employposed in proximity to the fluorescent screen, is

disclosed-in Patent No. 2,186,635 issued January 9, 1940, to Allen l3. Du Mont and Alfred J. Hinck. so This novel ,coiistruzition makes feasible cominvention; relates to improvementsfin; cathode-ray tubes of theflgeneral type ftn ore-- particularly adapted for-televisionreception ing a single electrode in the form of a ring disuction'pf cathode-ray tubes having peiiating characterlstics referred to. v heimportance of'electrode: posi v ids'i i s ap and nacinz 'orthe same, has bee overlooked in cathode-ray'tubes of the gen- I 5 acceleration wpreeacceleration potential; I have found that unless'c'ertain designs are. ap- 15- plied, defocussing of thefiiiorescent' spotv occurs, I

distorting fields are set up, andit maybe-impos "sible to utilize more than'thirty 'per lcent of'tlie e effective fluorescent screen area;

With the foregoing in mind, it "is one of these" objects of my inventi njtoprovlde an improved cdnstructionof cathode-ray tube of the chars, acter referred to in which the operating p'ote'n tials, and diinensionsin the tube structure itself,

are such thatla picture of the desiredbrightness on the fluorescent screen can be obtained'without' necessarily or unduly interfering with" the focus" or the sensitivity of deflection, Another object of my invention resides in the provision of an improved constructionof cathode-, 3Q

"ray' tubeof 'thereharacter referred to, which has, advent gesflover those'proposedvheretoi'ore in the 7 way (if-{3i brighter or moreintense picture on the fluorescent screen -forv similar operating 'condi- I tions, higher picture detail, and greater uni- .35

formity of'the pattern.

Another object of my invention resides in the provision of a simplified construction for, a cathode-ray tube in whichethere is post-deflection acceleration of 'the electron beam or ray, and 40 "(which overcomes the; disadvantages and the limitations of the various designs proposed'heretofore. H Other objects and advantages will hereinafter appear.

5 v For the purpose of illustrating my invention, an 1 j embodiment thereof 15 shown in the drawings, wherein R 1 v Figure 1 is an enlarged, fragmentary, sectional view taken from Fig; 4, showing-details ofthe gun construction; 1 p Figs. 2 and 3 are views similar'to Fig. 1, show.- ing modifications; =1 l Fig. 4 is af longitudinal, central sectional view of a cathode-ray tube constructed and operating in accordance with my invention;

Fig. 5 is a view similar to Fig. 1, showing a modification; and

Fig. 6 is an enlarged, sectional view, the Section being taken on the line 6-6 in Fig. 5.

The drawings show a cathode-ray tube having a gun construction similar to that described in the patent referred to. For convenience of comparison, the various parts have been designated by the same reference numerals as the corresponding and respective parts in this pending application.

with reference to Figs. 1 and 4, my improved.

cathode-ray tube comprises a tube l0 having a bulbous portion ii on the end wall of which is a fluorescent screen 3. In the neck portion l2 of the tube is the gun for developing the ray of electrons directed at and focused on the screen.

The gun is supported from the stem i5 which is sealed to the open end of the neck l2, and comprises a cathode IS, a modulating electrode in which the cathode I6 is disposed, a first accelerating electrode 22 supported from the stem by a lead wire 23, and a mica disc 24 supported from the stem by lead wires 25 and 28 which pass through the stem to the exterior of the tube.

The gun comprises further a focusing electrode 23 supported by glass beads from a second accelerating electrode 30 which in turn is supported from a mica disc 32. Deflecting plates 33 are supported by the wires shown from the mica disc 32. A second set of deflecting plates 36 is supported by the wires shown from the disc 32.

The first or preacceleratingeelectrode 22 above the modulating electrode 20 is operated at the same voltage as the second accelerating electrode 30. For this purp'ose, a connection 42 is made from the electrode 30 to the lead wire 23. By applying a high voltage to the electrode 22, a brighter spot is obtained, and there is less tendency to defocus during modulation.

In my improved construction, there is a relatively large distance A from the tip 41 of the gun to the adjacent edges 43 of the second set of deflecting plates 36. The relation exists approximately, where A is measured in inches, C is the diameter in inches of the fluorescent screen, and B is the distance in inches from the screen to the adjacent edges 43 of the flrst set of deflecting plates 33. Satisfactory results have been obtained by making A equal to .4 inch with C and B both 14 inches. In the constructions used heretofore, the distance A is much less. By making the distance A greater, and using the relation above expressed, defocusing of the spot during deflection is eliminated. The reason for this is that in my improved construction no appreciable bending or deflection of the beam or ray within the gun structure takes place. Heretofore it has been generally supposed that no motion or deflection of the ray occurs below the deflecting plates. Actually, this is not true, and the motion of the ray in the gun during deflection has been the cause of poor focusing in the prior constructions.

Important and novel characteristics of my improved tube reside in the provision of the ring electrodes 58 and 53, whichmay be in the form of silver coatings on the inside surface of the tube i0, and in the dimensions and relations hereinafter specified. By this nieans, it is possible with my improved tube to obtain a very intense trace 'or picture by using an extremely high final accelerating voltage, but without, at the sametime, reducing the deflection sensitivity by about 50%, when the final accelerating voltage is doubled, for example, as would be the case in the various television receiver tubes used heretofore. The reason for this is that in my improved tube the deflection sensitivity is not an inverse function of final accelerating voltage or potential, as is the case in tubes of the prior art.

In the case of my improved tube, a potential of say 10,000 volts can be applied to the top ring electrode 53, 5,000 volts to the electrode 30, and a 14-inch 9-inch tube tube Inches Inches Distance from edges 49 to screen 9 16:3 13% Mean diameter of electrode 59 (E) 3 4 4 Mean diameter of electrode 58 1334 9% Distance from edge 60to edges 49 (2).. 1 1 Diameter of screen 9 11% 8 Width of ring electrode 59 (Y) $4 In either case, Y may be made equal to Z.

In either case, with E from 2 to 4 inches, Z may be made from inch to 1 inches.

The following voltages, measured with respect to cathode, have been found to give satisfactory results for the 14 inch tube.

Volts Grid (16) Preaccelerator (22) +5.000 First anode (29) +1,500 Second anode (30) +5.000 Deflection plates +5,000:respective signal voltages Ring electrode 58 440,000 Ring electrode 59 +5,000

The ring electrode 58 may be about one-quarter of an inch or more in width, and may be disposed a distance of about onehalf of an inch from the screen 3 or even about mid-way between the screen and the edge 60 of electrode 53.

It is possible with my improved tube, embodying the structural features and using the relations and values given above, to employ an extremely high final accelerating voltage in order to get a very intense trace or picture, and still deflect the ray to cause the same to scan substantially the entire area of the screen3, since the deflection sensitivity is only reduced by approximately 18%, as against about reduction in the cathode-ray tubes 'of the prior art, should the final accelerating voltage be doubled.

It has been found that when the distance from the edges 43 to the edge is too great, electrostatic flelds are set up such that the useful area of screen 3 is reduced as a strong function of the ratio of potentials on electrodes 58 and 53. In addition to the reduction of possible, effective On the other hand, when the distance from 49 to is too small, the electrostatic lines of force that would normally termi'nateinfl to produce a spherical field within the intervening space, terminate instead on the deflection plates 33 and, to some extent, on the deflection plates 36. As a result, the accelerating fleld in that space is no longer spherical and produces a distortion of the fluorescent spot. Thus a normally round spot would become elliptical with its major axis parallel to the edges 49. e

Another important structural feature of my improvedtelevision receiver tube resides in the provision of a conducting shield for collecting stray electrons which otherwise'would form or/set up a halo on the screen 9 in the absence or presence of signal voltage. Such a'halo, whensignal is present, would reduce contrast. This shield also acts as a 'light shield to prevent the heatercathodefrominterfering with the picture. As shown-in Fig. 1, the shield may be-provided for by making the supporting mica disc 32 relatively thick to impart sufiicient rigidity, and of a large diameter so that its edge is in close proximity to the wall of the neck of the tube. On the cathode In this case, the shield has a third function,

which is that of shielding one set of plates from the other to reduce interaction or coupling between the two orthogonal systems, which interaction would be seen as pattern distortion and/or defocusing of the trace. The annular coating BI is electrically connected to the second anode 30, as in Fig. 1.

It would also be possible to place the electron shield 32 beyond the deflecting plates 33, or to associate it with the first or focusing anode. 29 as shown in Fig. 3. In the latter case, the shield would replace and in addition serve the function of the supporting mica disc 24 in Fig. 1. In the arrangement shown in Fig. 3, the shield would be connected to the flrst anode 2.9 or to the lead wire 42 connecting to the second anode 30.

For the purpose of making good contact between the second acceleration electrode 30 and thering electrode 59, a spring connection element 64 is used. One end of this element contacts the electrode-59, the other end .being fixed to the gun structure, but insulated therefrom by a glass head 65 and providedwith a coil spring .63. I

The element 64 is therefore spring-biased laterally outwardly with respect to the gun ,to hold its 3 quency heating current used in. processing'the reason, a glass insulating bead is inserted in the element 68, as shown. 7

In Fig. .5 a simplified construction is shown. 1

The elements 84a and 68a correspond to'and serve the same purposes as the elements 64 and 33, respectively, in Fig. 1. However, the elements 84a and 68a. are fastened to the holding straps I sibility of distortion of the pattern would be reduced.

ftube tends to burn these elements and the coat-1 I ing 59,.as a closed circuit isformed. For this It will be understood that various modifications within the conception of those skilled in the art, I

of my invention or the scope of the claims;

I claim as my invention: v 1 In a cathode-ray tube, a tube having a screen at the end wall thereof, a gun disposed in said tube for developing a ray of electrons directed at and focused on said screen, means for deflecting said ray to cause the same to scan said screen and comprising a first set of deflecting plates and a second set of deflecting pla'tesdisposed between said first set and the tip of said gun, an electrode extending along said tube and beyond the outermost edges of said first set of plates in the direction toward said screen a distance in the range substantially from one-half inch to one and one-half inches, and a secondelectrode disposed between said screen and said first-named electrode, said second electrode oper-' ating ata potential positive with respect to the potential of operation ofsaid first-named electrode, the mean diameter of said flrst named electrode being in the range substantially from two inches to four inches.

2. In a cathode-ray tube, a tube having a screen at the end wall thereof, a gun disposed in said tube for developing a ray of electronsdirected at and focused on said screen, means for deflecting said ray to cause the same to scan said screen and comprising a first setv of deflecting plates and a second set .of deflecting plates disposed between said first set and the tip of saidgun, an electrode extending along said tube and beyond the outermost edges of said first set of plates in the dlrectiontoward said'screen a distance of substantially one inch, and a second electrode disposed between said screen and said first-named electrode, said second electrode operating at a potential positive with respect to the potential of operation of said first-named electrode, the mean diameter of said first-named electrode being in the range substantially from two inches to four inches.

3. In a cathode-ray tube, a tube having a screen at the end wall thereof, a gun disposed in said tube for developing a ray of electrons directed at and focused on said screen, means'for deflecting said ray to cause the same to scan said screen and comprising a first set of' deflecting plates and a second set of deflecting plates disposed between said first set and the thief said gun, an electrode extending along said tube and beyond the outermost edges of said first set of plates in the direction toward said screen a distance in the range substantially-from one-half inch to one and one-half inches, and a second electrode disposed between said screen and said first-named electrode, said second electrode operating at a potential positive with respect to the potential of operation of said first-named electrode, the mean diameter of said second electrode being greater than the effective diameter of said screen by substantially two inches, the mean diameter of said first-named electrode being in the range substantially from two inches to four inches.

4. In a cathode-ray tube, a tube having a screen at the end wall thereof, a gun disposed in said tube for developing a ray of electrons directed at and focused on said screen, means for deflecting said my to cause the same to scan said screen and comprising a first set of deflecting plates and a second set of deflecting plates disposed between said first set and the tip of said gun, 'an electrode extending along said tube and beyond the outermost edges of said first set of plates in the direction toward said screen a distance in the range substantially from one-half inch to one and one-half inches, and asecond electrode disposed between said screen and said first-named electrode said second electrode operating at a potential positive with respect to the potential of operation of said first-named electrode, the distance from the tip of said gun to said screen being substantially seventeen inches, the diameter of said second electrode being substantially fourteen inches, the eflective diameter of said screen being substantially twelve inches, the mean diameter of said first-named electrode being in the range substantially from two 40 inches to four inches.

5. In a cathode-ray tube, a tube having a screen at the end wall thereof, a gun disposed in said tube for developing a ray of electrons directed at and focused on said screen, means for deflecting said ray to cause the same to scan said screen and comprising a first set of deflecting plates and a second set of deflecting plates disposed between said first set and the tip of said gun, an electrode extending along said tube and beyond the outermost edges of said first set of plates in the direction toward said screen a distance in the range substantially from one-half inch to one and one-half inches, and a second electrode disposed between said screen and said first-named electrode, said second electrode operating at a potential positive with respect to the potential of operation of said first-named electrode, the distance from the tip of said gun to said screen being substantially fourteen inches, the diameter of said second electrode being substantially ten inches, the efiective diameter of said screen being substantially eight inches, the mean diameter of said first-named electrode being in the range substantially from two inches to four inches.

6. In a cathode-ray tube, a tube having a screen at the end wall thereof, a gun having a cathode and disposed in said tube for developing a ray of electrons directed at and focused on said screen, means for deflecting said ray to cause the same to scan said screen and comprising a first set 01' deflecting plates and a second set of deflecting plates disposed between said first set and the tip of said gun, an electrode extending along said tube and beyond the outermost edges of said first set of plates in the direction toward said screen a distance in the range substantially from one-half inch to one and onehalf inches, and a second electrode disposed between said screen and said first-named electrode, said second electrode operating at a potential positive with respects to the potential of operation of said first-named electrode, the potential of said second electrode with respect to said cathode being substantially twice the potential of said first-named electrode with respect to said cathode, the mean diameter of said first-named electrode being in the range substantially from two inches to four inches.

7. In a cathode-ray tube, a tube having a screen at the end wall thereof, a gun having a first preacceierating anode and a secondaccelerating anode and disposed in said tube for developing a ray of electrons directed at and focused on said screen, means for deflecting said ray to cause the same to scan. said screen and comprising a first set of deflecting plates and a second set of deflecting plates disposed between said first set and said second anode, and a shield in the form of an electrically-conductive disc disposed between said second anode and said second set of plates with its edge in close proximity to the wall of said tube, said shield being electrical- 1y connected to one of said anodes.

8. In a. cathode-ray tube, a tube having a screen at the end wall thereof, a gun disposed in said tube for developing a ray of electrons directed at and focused on said screen, means for deflecting said ray to cause the same to scan said screen, an electrode extending along said tube and beyond said deflecting means in the direction toward .said screen, and a second electrode disposed between said screen and said first-named electrode, said second electrode operating at a potential positive with respect to the potential of operation of said first-named electrode, the diaineter of said tube at a. plane in proximity to said screen being substantially greater than the maximum effective diameter of said screen.

9. In a cathode-ray tube, a tube having a screen at the end wall thereof, a gun disposed in said tube for developing a ray of electrons directed at and focused on said screen, means for deflecting said ray to cause the same to scan said screen and comprising a first set of deflecting plates and a second set of deflecting plates disposed between said first set and the tip of said gun, an electrode extending along said tube and beyond the outermost edges of said first set of plates in the direction toward said screen a distance in the range substantially from one-half inch to one and one-half inches, and a second electrode disposed between said screen and said first-named electrode, said second electrode operating at a potential positivewith respect to the potential of operation of said first-named electrode, the diameter of said tube at a plane in proximity to said screen being substantially greater than the maximum effective diameter of said screen, the mean diameter of said firstnamed electrode being in the range substantially from two inches to four inches.

10. In a cathode-ray tube, a tube having a screen at the end wall thereof, a gun having a first preaccelerating anode and a second accelerating anode and disposed in said tube for developing a ray of electrons directed at and focused on said screen, means for deflecting said ray to cause the same to scan said screen and comprising a first set of deflecting plates and a second Ill set of deflecting plates disposed between said first set and said second anode, and a shield in the forr'n of an electrically-conductive disc associated with the gun structure and disposed with its edge in close proximity to the wall of said tube, said shield being electrically connected to said second anode.

11. In a cathode-ray tube, a tube having a screen at the end wall thereof, a gun disposed in said tube for developing a ray of electrons directed at and focused on said screen and comprising a first set of deflecting plates and a second set of deflecting plates disposed between said first set and the tip of said gun, an electrode extending along said tube and beyond the outermost edges of said first set of plates in the direction toward said screen, and a second electrode disposed between said screen and said firstnamed electrode, said second electrode operating at a potential positive with respect to the potential of operation of said first-named electrode, said tube being characterized by the fact that the ratio of the mean diamet r, expressed in inches, of said first-named elec rode to the distance, expressed in inches, from said edges of said first set of plates to that edge of said first named electrode nearer said screen is in the range substantially from two to four.

PETER S. CHRISTALDI.

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