US2081942A - Cathode ray tube - Google Patents

Description

Patented June .l, 1937 umrissv STATE CATHODE TUBE Harry B.. Lubcke, Los Angeles, Colli.

Application-June i6,

My invention relates to electron emitting de' vices, and particularly to such types of cathode ray tubes-as are adapted for television and oscillographic purposes. Among the salient objects l5 of the invention are; first, to simplify and im prove such devices, by providing a new type of cathode that is adapted to restrict the electronic emission to a single desired direction, and which inay be operateddirectly by alternating electrical energy; second, to provide-a new'type of grid that is adapted to greatly reduce the input capacitance of devices of this kind; third, .to provide a new type of anode that is adapted to focus an electronic stream in a new and improved manner, so as to make it unnecessary to use the now commonly employed interior plating of the glass envelope, vandy which does not require the presence of gas in the tube; fourth, to provide a j new and improved shape and arrangement of deilecting plates in cathode ray tubes; fth, to secure greater response of uorescentscreens to cathode rays than can be accomplished in hitherto @own ways; and, sixth, to supply a new and improved means4 for maintaining a constant focus of an electronic stream, regardless of changes in its intensity.

My objectshave been attained inthe manner illustrated in the accompanying drawing, in

i0 Figure i shows, diagrammatically, a cathode ray tube that embodies the elements of my invention, and indicates the manner inwhich this tube may he connected to standard thermionic and other electrical equipment, for securing the de- I i i5 sired results; and

Figure 2 shows an alternative arrangement of the elements of my invention that may Alie used in such a tube.

My improved cathode preferably takes the form of a deeply cupped conducting annulus. This has anouter cylindrical portion t; and 'an inner cylindrical portion 6 of smaller diameter, coaxial withthe outer portion axial-tubes are conductively connected, by means 4 and spaced there from. Onespair of the extremities ofthese cov 1933, Serial No. 676,078

iol. 25o-#215) of a, hollow truncated conical portion l. Thus one end of the cathode is given the shape ofa protruding truncated cone. The co-axial cylindrical portions necessarily are somewhat displaced with respect'to each other in a longitudinal direction, that vthe free -end of the outer portion, extends considerably beyond the free end of the inner portion. A.- preferred method oi constructing this cathode is to form it, as by means of proper dies, from a single integral piece of sheet nickel or other suitable metal. .Such a cathode may he supported in a glass envelope B of a cathode ray tube, by means of conductors in the glass in the usual manner. Conductor d is electrically connected to the free extremity of outer portion 5 of the cathode, and conductor it is connected to the free extremity of inner portion t. These conductors are utilized for carrying the heating current to the cathode, as from a battery i2 or other suitable source of energy.

llt will be appreciated that', inasmuch as Fis. l is diagrammatic only, the proportions ci the parts are shown ,somewhat exaggerated, ll'hev cathode, comprisingl elements E, 6, and 'l is, in fact, relatively small; and it may be heated elec- `hically, without diiiiculty. Inner cylinder t, V of smaller cross-sectional area, and because of its inner location, will reach the highest temperature; the outer cyliner 5 will act as a and their respective lengths are such 9 and tLsealed thermal shield, and effectively lecrease the rate i from the hotter inner cylinder. lt will be appreciatedfurther Vthat the cross sections of the tubular portions and t may be square or any other shape desired.

The described construction makes the cathode very emcient so far as consumption of heat en orgy is concerned, and it provides a very simple and.V convenient path for the heating current. The inner surface of inner cylinder e, is coated with suitable electron-emitting material, such as barium oxide.

in my improved cathode, the maximum rate of electron emission may he made to occur at the junction of cylinder t and cone i, by suitably proportioning the thicmess and size of the vari.

ous mrtions in ways that are well and the electrical resistive centerV of the cathode also may be located at this junction. when this is done, it is entirely feasible to employ a-source of alternating current in place of battery i2. l

The electronic emission from my cathode will take place as if from a unipotential surface; thus accomplishing in a unitary cathme, what'has hitherto remiired'the use of a unipotential cathof radiation of heat understood;

inner surface of cylinder 8) and the physical" form of the cathode, will restrict the emission of electrons in such a manner as to produce-a single 10 electronic stream, thus eliminating the necessity for using an electron-restricting electrode. In alternating current operation, my single cathode is capable of performing the function of the three electrodes that hitherto have been necessary for accomplishing the same result.

I'he intensity of the electronic stream is controlled in my improved tube, by varying the potential of a grid I3 in the usual manner, the potential of the grid commonly being negative with respect to the cathode. My preferred grid, however, takes the form of a hollow .truncated cone, with its apex toward the cathode; and it is relatively small. This grid is supported in tube 8 by means of a conductor Il, which passes through the wall of the glass envelope, and is sealed thereinto. This support wire preferably leads through the envelope separately, for convenience in keeping the capacitance to ground small.

'I'he conical grid shape. and the described arrangement, provides a minimum capacitance and a maximum control constant. It is well known that the closer that a grid is located to the cathode, the greater will be its controlling effect; and,

since a cathode ray tube is a voltage-operated device, it is desirable to keep the control coelcient high.` The point where the maximum control eil'ect upon the electronic stream is exerted, is the truncated apex of the grid. This is the part that approaches the cathode most closely, and the distance between these two elements' may be made very small. In a grid of circular cross-section, such as the usual wire employed Y for that purpose, the theoretical point of control is at the center of its cross-section: and it necessarily has to be located, for this reason, further away from the cathode than the controlling apex of my improved grid construction.

As a part of the anode of my device, I prefer to employ a conducting tube I8; having an integral circular shield I8 thereupon. near the longitudinal center, its vicinity. 'Ihe location of this shield, and the ,conical shape of the cathode extremity 1, make the grid to ground capacitance relatively small. The portion of the effective anode lIust described is maintained in its position in tube 8, and is operatively connected in circuit, by means of conductor I1 which passes the wall of the tube and is sealed thereinto.

In addition to anode elements I8 and I8, I employ a separate perforated disk anode element I8, supported in place and connected lin circuit by conductor I8. The gun anode element I8 is given the highest potential in the system, whereby it is able to greatly accelerate the electronic stream passing therethrough. Disk I8 has a centra] hole 2I, `o1 larger diameter than the bore of tube I8. its potential is made approximately haii' that of portion I8, and it is slightly spaced from the discharge end of this gun anode. The described arrangement makes it possible to further concentrate the electronic stream', by means oi the radial held of force, which is of negative polarity, exerted between the margins of hole 2I and portion I8. This force opposes any tendency for removing stray electrons in' acens-ia of individual electrons to depart .from the electronic stream because of their mutual repulsion. Thus, the usual dispersive eiect, tending to produce a relatively large spot on the tluorescent screen, may be wholly overcome; and a minimum 5 screen spot may be secured, by adjusting the potential of disk anode I8.

The concentration method just described is operative and effective under a high vacuum, and the cathode ray tube may be pumped to the high- 10 est evacuation obtainable, without incurring any of the undesirable features of high vacuum tubes that hitherto have, been experienced. Also the disadvantages of short life and the necessity for adjusting the pressure during manufacture, l5v

hithertoY accompanying the use of low vacuum tubes, may be eliminated.

Piate electrodes, for deflecting the electronic stream up and down, i. e., in the plane of the paper, are indicated at 22 and 2l. It 'is well known that theY closer such plates are to each other, the greater will be their deflecting eiect; but, on the other hand, ii they are too close, they will physically obstruct the electronic stream vat the extremes of its deflection, thus reducing the eilective working area of the fluorescent screen. It has been common practice hitherto, to employ parallel deilection plates that are rather widely spaced, so as not to interfere with the electronic stream at its maximum deflection. In my improved construction I employdiverging plates. 'these being much closer together at their initial edges than at their final edges. Thus, a strong defiective action is secured where the electronic stream enters the deecting field (at which point 3" it has no deflection) and the wide spacing at the final edges of the plates, prevents obstruction of the stream at its maximum deflection;

Defiecting plates 22 and 23 are adapted for deilecting the electronic stream up and down only, i. e., in the plane oi the paper, to the limits of the final spacing of these plates. 'Ihey areunable, however, to cause any deilection in a plane perpendicular vto that of the paper. Consequently they may'be made quite narrow, `being merely wide enough to prevent their edge effects from inuencing the electronic stream. Making these plates narrow will lower the capacitance between them, and this is verydesirable in oscillographic work. Plates 22l and 23 are supported in the 50 cathode ray tube 8, by means of conductors 2,4 and 28, leading to them respectively through, and sealed' into, the glass wall of tube 8.

Deflecting plates 28 and 21 are used for deecting the electronic stream in a horizontal 55 plane, i. e., perpendicular to the plane of the paper. 'Ihese also are diverging for reasons similar to those stated. The spacing between these plates at their initial edges. is no greater than the spacing between the initial edges of plates 22 and 23; and the spacing at their final edges is made such as not to interfere with the electronic stream at its' maximum horizontal deflection. Plates 28 and 21, instead of being made rectangular and` narrow, are trapezoidal in form as indicated, the divergence between the top and bottom edges being the same as the divergence between plates 22 and 2l, for obvious reasons. Plates 28 and 21 are maintained in position by means of conductors 28 and 28 leading to them respectively, these conductors passing through the walls oi tube 8, and being sealed thereinto.

For the purposes of television deilection, wherein comparatively low frequency detlecting fields are employed, and the detection plate capacitance 75 5. may be made nearly ity, wider. angle consequently is o! little importance, the nrst pair oi deecting platesmay be very slightly from disk anoderll and from the last pair oi' plates. The sensitivity of the two pairs of plates by virtue of their being far .removed from the iiuorescent screen. It is believed that the new shape and arrangement of deecting plates that has been disclosed, provides for greater sensitivof deilection of the electronic stream, and less capacitance in the deflecting ystem than it has'been possible to attain herei'ai! ore.

A iiuorescent screen is shown at 3l, the usual position. For the nuorescent I prefer to use the mineral willemite, to common practice; but I have discovered that material,

great advantages may be obtained by mixing the as many, or more,

i `mannerthat-the potential of the lgrid is moduiiuorescent material with a nely divided substance that is capable. of emitting what I will herein call secondary electro The metal thorium may Ghe used very satisfactorily for this purpose; Under the' bombardment of the electronic'stream the usual screen soon becomes negf ativelycharged. This naturally decreases the velocity of the electrons when they'are about to impinge upon the screen, trostatic repelling force.

by reason of the elec- 'Ihe intensity of iiuowill be decreased emitting substance is used in the screen, however, secondary electrons may be caused to leave the screen as the number of primary electrons in the electronic stream that impinges upon it. In this manner it is possible to keep the iiuorescent screen uncharged, or evenv to cause it to take on a positive charge. This will greatly increase the velocity of the primary electrons when they are about to impine upon the screen, and will cause the screen to give a much greater iiuorescent Obviously, the secondary electrons that are emitted from the screen will be shot oi! in all directions. lii'iey will tend to obstruct the in iront of the, screen, and to interfere with the incoming primary electronic stream (although not as seriously as though they were resident upon the screen itself, as usual) unless means are previded to get ridbf them. Therefore, I locate a conductive electrode 32 in front of the screen at a slight distance therefrom; and @ve it a high positive potential, for removing the stray electrons, secondary or otherwise, in its vicinity. This electrode should'appr'oximately conform to the shape of the eii'e'ctive area be of such dimensions as not to interiere with the primary electronic stream at its um deection. Electrode 32 may be supported hy its conductor tiled through the glass envelope oi the tube d and sealed therein In the use off cathode ray tubes that hitherto have'been mown to the art, the active spot on the uorescent screen changes in size with the intensity oi the electronic stream. and the intensity g spot, without noticeably affecting its intensity. if.

therefore, the potential supplied to the disk anode is. modulated bythe incoming signal, in the same lated, the screen spot constant size maybemaintainedata equal, and relatively great,

located in plication accordingv ci the screen, and

Suitable apparatus for mv l cttnoaersy tube, is shown diagrammatlcany in the lower part oi Fis. 1. An ampliner tube, for

- supplying the input signal coming in through concondenser 38, which is of negligible impdanceto the frequencies involved; and the'signal appears as potential variations at griddgyer resistor 39.

. Vacuum tubes M and 42, and theirA associated apparatus shown, constitutea resistance-capacitance coupled amplifier, used to increase the signai amplitude for impression *upon the less sensitive disk anode i8, over resistor I3. The amof this amplifying system, and the voltages of batteries I2, Il, and are adjusted to give a constant spot screen: or for anymodulated variationof spot size, within limits, that may be desired.

It will be appreciated that, if the signal amputude 'is great enough, electrodes I3 and i8A can be excited from resistor 31; condenser d6 being connected to the top of resistor 31: and condenser 3%, by a tap well toward the bottom thereof; so that a small portion of the signal will be impressed on grid I3. .amplifying tubes Il and d2, and their associated apparatus, are not required when this is done. Y

Certain other apparatus for modulating electronic streams, is known to thefart, in the use of which the screen spot becomes smaller as it becomes less in intensity. Subh apparatus can be used to maintain a constant size of screen spot if employed with a disk anode, such as is illustrated at i8, and if the excitation of this anode size upon the fluorescent is modulated out of phase with respect to the modulation of the grid, by including only one stage This can be accomplished of amplication hetween the grid and the disk anode, as by connectis placed between elements it and d! co-amal therewith.

Elements i3 and id are connected in el, and

are modulated from` a single signal source. The "shield anode di in this case, takes the place o gun anode i5 and ofshieid I8 of if l: and, m addition, functions with electrode da in the same way as gun anode ils-ie, for foe electronic stream. ma tive potential on the order of onethat oi the gun anode gt4-i6 of Pig. 1.Y Control electrode da thus will act upon slower moving electrons than in the case of the arrangent of Fig. i, and will have sumcient enact fili f if when excited by onlythe signal amplitudeV is impressed upon control electrode i2.

Control electrode d@ is maintained in its position in tube d by means of its conductor 52: and "shield anode di is maintained in position by means oi its-conductor W8.

the` electronic stream A l end of cathode cylinder i. The use of the anode,

however, makes this practically impossible; and

only the end of the cathode, that is nearest to the anode is eective for emitting electrons. orecver the left-hand end of cylinder l could heblocjkedoifthereappearedto beany pracshield anode di isheld at aY 4 tical reason for doing this. In case auch bl ing oi! should be done, the interior surface of the closure should 'be coated with an electron-emitting substance. for increasing the effective capacf ityof the cathode.

In Fig. l, I have conventionally indicated alternating current generators at; I4 and It, for

` called saw-tooth" wave form of energy are greatly to be preferred. When-the cathode ray tube is to be used for oscillographic purposes, the potentials tobe measured are connected to the respective pairsof deilecting plates 22--23 and 26--2l.

Having thus fully described and illustrated my invention in a manner that will be readily understood by those familiar with the art involved, I claim: A

l. A cathode ray tube comprising a cathode and an anode; the cathode being formed ofV two coaxial nested and spaced tubular shells of conducting material, the shells being conductively connected at one end of each; and substantially parallel for a portion of their lengths, said cathode structure being adapted for passing an electric current through the material thereof for directly heating the inner shell: and the inner surface of the'inner shell being-adapted for emitting electrons when so heated.

\ 2. A cathode ray tube comprising a cathode and an anode; the cathode being formed as a cupped annulus having a cylindrical inmost surface, and with electrical terminals at its inner andvouter rims respectively; said surface being adapted for direct heating by passing an electric current through the material of the annulus between said terminals, and for emitting electrons when so heated; 'and the electrical resistive center of the annuius,.with respect to said terminals. being at the inner-end of said surface.

3. A cathode ray-tube comprising a cathode and with electrical terminals at its inner and outer rims respectively; -the intermediate portion of the annulus being in the form of a protruding hollow truncated cone with its apex at the adiacent extremity of said surface; said surface being adapted for direct heating by passing an electric current through th material of the annulus between said terminals, and for emitting electrons when so heated: andthe electrical resistive center of the annulus, with respect to said terminals, being at said apex.

4. A cathode ray tube comprising; a cathode; an anode; a pair of narrow parallel-sided and diverging plate electrodes. adapted to deflect in one plane, an electronic stream issuing from the cathode. the plates being similarly disposed on opposite sides of the normal path of said stream; and a second`pair of trapezoidally shaped and diverging plate electrodes, adapted to deilect said stream in a diiferentplane, the last said plates being similarly disposed on opposite sides of the normal path ofsaid stream; the spacing between the plates of each of said pairs being least at the point. where said stream path enters their respective i'ields of influence, and only slightly greater than the cross-sectional dimension of said stream; and the angle of divergence between each of said pairs of plates corresponding to the maximum angular deflection of said stream, pro duced thereby.

5. A cathode ray' tube comprising; an anode:

I a cathode adaptedI to be held at a large negative potential with respect to the anode and for emitting an electronic stream; and a control grid adapted to be held at an average potential approximating that ofthe cathode, in the form of a hollow truncated cone, in the path of said stream and co-axial therewith; said control grid having its apex directed toward the cathode and, when energized, being adapted for controlling the intensity of said stream.

'minarv P.. man.

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