US3264510A

US3264510A - Degassing of cathode ray tubes

Info

Publication number: US3264510A
Application number: US304786A
Authority: US
Inventors: Leighton E Griffiths
Original assignee: Individual
Current assignee: Individual
Priority date: 1963-08-27
Filing date: 1963-08-27
Publication date: 1966-08-02
Anticipated expiration: 1983-08-02

Description

Aug. 2, 1966 1... E. GRIFFITHS DEGASSING OF CATHODE RAY TUBES 2 Sheets-Sheet 1 Filed Aug. 27, 1963 INVENTOR LE /EH70 E. G'fi/FF/THS ATTORNEY-5' Aug.'2, 1966 E. GRIFFITHS DEGASSING 0F CATHODE RAY TUBES 2 Sheets-Sheet 2 Filed Aug. 27, 1963 INVENTOR ATTORNEYS United States Patent 3,264,510 DEGASSING 63F CATHODE RAY TUBES Leighton E. Griffiths, Newark, NJ.

(18 Cedar St., Pompton Lakes, NJ.) Filed Aug. 27, 1963, er. No. 34,786

11 Ciaims. (Cl. 313176) This invention relates to cathode ray tubes and more particularly to such tubes used primarily as television picture tubes.

More particularly the invention deals with getters and diagnosing processes for use with picture tubes having laminar faces using plastic adhesives subject to damage at the usual temperatures at which such tubes are degassed.

It is ageneral object of the present invention to provide a novel combination of getters for use in connection with rebuilding picture tubes having laminar faces and novel processes for degassing such tubes at temperatures which do not damage the tube faces.

More particularly, it is an object of the invention to provide getters and procedures which permit the proper degassing and maintenance of sufliciently low gas pressures. during the shelf and use life of picture tubes even if they are rebuilt in envelopes having laminar faces subject to damage by temperatures much below those normally used during pumping and degassing.

An important object of the invention resides in the use of a plurality of getters in a rebuilt picture tube, all of which are mounted on the replacement gun assembly, and some of which are flashed shortly after the tube is sealed off and others which are of a character to actively adsorb gases at intermediate temperature ranges during the operation of the tube throughout its life.

Another important object of the invention is to provide for both initial and subsequent degassing of a picture tube, following necessary low temperature pump-down, by providing a plurality of different type getters distributed about the gun, some for degassing immediately subsequent to scaling off and others effective throughout the life of the gun.

One of the features of the cold degassing of a picture tube having a face laminated with the use of a plastic adhesive between the two glass laminae is the covering of the tube face with a heat reflective layer enabling inductive heating of the gun remotely positioned in the tube neck with damage to the face adhesive.

Another feature of the invention which serves to prolong the useful life of a rebuilt picture tube which has been degassed cold is the provision of a getter of zirconium positioned adjacent to the No. 1 grid of the gun which is electronically heated in parallel to the cathode heater. The arrangement being such that the total heater consumption of power is the same as that used by the original heater for the cathode whereby the rebuilt picture tube can be used as television sets having all of the tubes connected in a series and known as string sets, which avoids the use of a heater transformer. The new cathode is designed to be as effective as the original one although operation is on one-half the original wattage.

Other and further objects and features of the invention will be more apparent to those skilled in the art upon a consideration of the following specification and the accompanying drawings, wherein are disclosed embodiments of the invention with the understanding that such changes and modifications may be made therein as fall within the scope of the appended claims without departing from the spirit of the invention.

In said drawings:

FIGURE 1 is a small scale elevational view, partly in longitudinal section, of a cathode ray tube and illustrating a laminated screen face;

"ice

FIGURE 2 is an elevation, on an enlarged scale, of an electron gun for use in the neck of a cathode ray tube of the type shown in FIGURE 1 and illustrating several getters in place thereon;

FIGURE 3 is a longitudinal central section, on a still larger scale, of the No. 1 grid, cathode and heater assembly of FIGURE 2 illustrating two hot getters in place thereon;

FIGURE 4 is an elevation, partly broken away, of a No. 1 grid assembly like that of FIGURE 3 with an added external heated getter mounted thereon; and

FIGURE 5 is a view similar to FIGURE 4 but showing a different external heated getter.

Cathode ray tubes of the type known to most television viewers as picture tubes have a relatively long life if not damaged or abused but eventually the operation becomes poor due to the reduction in electron emission from the cathode and the picture becomes weak. It may cease altogether resulting from burnout of the cathode heater. Since the glass envelope of the tube is large and heavy it represents with its interior fluorescent screen the major cost item of the finished product and it is thus economically feasible to renew the tube by replacing the electron gun assembly in the neck to achieve a new cathode and heater.

Relatively large industries have grown up for the manufacture of new guns and for the rebuilding of worn-out picture tubes. Replacement components and practices had become relatively standardized and well known until the advent of the laminated tube face, produced by adding a second curved glass plate over the integral face of the tube using a sheet of suitable heat-softened plastic as the adhesive in the manner of manufacture of automobile safety glass. This permitted the elimination of the separate protective glass cover for the tube face with the attendant dust collecting and cleaning problems and, to some extent, prevented certain annoying reflections, but added to the rebuilders problems.

When tubes are built new, the problems of degassing them before and after sealing is simplified by their acceptance of heating temperatures of at least 400 degrees C. without damage, so that occluded gases in and on the glass and metal parts are fairly easily pumped out and/or sorbed (adsorbed and absorbed) by more or less standardized practices. However, the presence of the plastic laminant in the new safety front tubes limits the temperature to which the envelope can be safely heated to approximately degrees C. Early attempts to obviate this disadvantage required removal of the extra glass and the laminant. This, however, is costly and the same or another glass front had to be replaced after degassing. The process was found to be uneconomical leading to the development of the present cold degassing where the envelope temperature is kept below 80 degrees C. The new process will now be described along with descriptions of the several getters.

Referring first to FIGURE 1 of the drawings, 10 illustrate the envelope of a more or less conventional type of cathode ray tube, primarily as used for television viewing, and it is an integral unit having a glass neck 11, a flare or conical portion 12, extending forwardly from the front end of the neck, and a front closure or screen portion 13, the inner surface of which is coated as at 14 with -a suitable material which fluoresces when impinged by a cathode ray, from the electron gun in the neck as will be later disclosed. The material of the screen i a suitable chemical which has the property of emitting light when bombarded by electrons. This fluorescence, as it is called, provides for a continued emission of light for a short time after bombardment referred to as phosphorescence. The length of time that it lasts is referred to as persistence and may vary in accordance with the intended use for the cathode ray tube.

In any event, thecost of the glassware plus the formation of the phosphorescent screen represents a largeportion of the total cost of a cathode ray tube which is.used for television viewing, and the desirability of retaining the portions which do not deteriorate during use has led to what is known as rebuilding, i.e. replacing the cathode ray gun, which, of course, necessitates. re-purnpmg the vacuum and eliminating undesirable gases from the interior of the tube since these have a deteriorating effect on the action of the emitting material on the.

cathode and in general on the performance of the whole tube.

The degassing of rebuilt tubes has been complicated by a later development in the manufacture of the envelope. integral with the remainder of the envelope and in order to protect the face against mechanical damage and for safety purposes it was mounted behind a laminated Earlier tubes have merely a glass face at 13 safety glass which formed a portion of the cabinet in e which the tube was mounted, but this offered many problems, particularly the accumulation of dust on the face of :the tube and on the rear. of the safety glass,

necessitating removing the chassis on which the tube is. mounted for the purpose of cleaning these otherwise The accumulation of dust is relawhich'reinforces the whole laminated face-and securely attaches the two

glass parts

13 and 15 .to each other.

In the absence of the extrapane 15 and the plastic 16, degassing was accomplished more readily'by heating the whole glass envelope in an oven to a relatively high temperature of approximately 400 degrees C., which could be donewithout damaging it. However, the cost 1 of softening. the laminate, removing the pane 15 and a subsequently replacing it in order to permitdegassing after rebuilding, by the use of high temperature heata ing of the envelope is too costly,-and there is a demand for means for degassing tubes without removing the,

face laminant.

The cathode ray gun 18 illustrated in FIGURE 2 contains substantially all of the components necessary to complete the cathode ray tube, and is mounted within the neck 11 by welding the rear end of the neck to the rim of the glass disc 19 at the base of the gun. The r several leads and supports 20 fromthe various compo-4 nentsof the gun extend through presses 21 on the disc, which is tubulated at 22 whereby air and any gases are pumped out during evacuation of the tube, the tubulation issealed off after as much gas has been pumped out as possible- Thereafter approximate ones of the;

conductors 20 are attached to contact pins which are mounted in a base secured to the; end of the neck of the tube all =in a conventional manner.

As viewed .in FIGURE 2 thetwo outermost leads 20 are sufliciently heavy to act as supports for the whole of the gunand they are connected to straps 24 which are secured to and support the inverted cup-like first grid 25 the components of which are shown in greater detail 1 in the section of FIGURE 3.

These straps also extend outwardly and are fused into the glass support rods 27 to which are attached zstraps 28 carrying the second grid 29 and straps 30 supporting the anode 31. This latter is an elongated cylinder usually equipped with a top closure plate having a small perforation and a radiating rim 33 which here is shown supporting a pair of clamps 34, one carrying the plate orstrap 35 mounting the cylindrical getter ring 36 above the top of the anode and having a number of indentations eachtfilled witha getter paste 37 of barium or like material which are adapted to be flashed as by heating the metallic ring; 36 inductively at an appropriate time during or following the degassing of the tube. The indentations face radially outwardly to project the vgetter vapors=. agai r1st. the walls of the neck of the :cathode ,ray tube for properly absorbing vapors within and on the surface .of

the glass of the; neck, .and the parts ofthe Mounted ,above the; ring 36 by'mean ofwa second clamp mount ing wire 38' isthe annular getter channel 40, which'is U-shaped .in: cross-section: as seen at 41 and :contains a barium getter 42 in the bottom of this channel. I Thisv second getter is adapted to be flashed simultaneously with getters 37, but thering is so designed andconfigured that it'projects the vapors from theqbarium or other suitable material into the hate of the envelope and.

toward the surfaces-of the screen at the front thereof to absorb undesired vapors and gases in a more or less conventional manner.

FIGURE; 3 shows, insubstantial enlargement, the

component of the zfirst grid 25. It will be noted that this is an invertedstraight walledrmetal cup open at the bottom and closed at the ,top except for a small aperture ,44tythrough which the electronbeam is projected from .an emissive material; 45 i'mounted on the flat upper ;end ofv the cathode cylinder 46 ='CO11C6I1t1'10- with grid cylinder 25 and-positioned a carefully measured distance below the aperture 44 by being. supported in-a ceramic disc 47 'by .means of beads 48 and 49. respectively engaging the upper and lower surfaces of the disc. ,The disc is fitted tightly inthe cylinder 25 and supported. from beneath .by the ;right angled Iannulus 50 of metal welded t-o' the grid jcup wallsz. Thef upper surface, of the, cathode tube 'is properly spaced.

from the .topwall ofithe gridcup 25:by means of the cylindrical sleeve 52 which has'an annular foot 53 l1m 1t-. ing the insertion of the ceramic disc .47 and.w1th :ltS

upper end engaging the :-said' top :walllto which-it may be secured by weldingif desired.-

The above features are more or less-conventional-in certain makes of electron guns and the emissive material 45 on the. head of the cathode tube is appropriately heated by a double wound insulated wire-helix 55, supported ,within *the' cathode tube, and closely spaced from the walls thereof, by-means of the leads 56' therefrom. which are attached as seenjmFIGUREZ to a pair 2'32.

of the wires which pass throughEthedisc '19. They not only conduct: current-to the heater but port itiin position within the cathode. The heater wire isiappropriately covered withan insulatingceramic material preventing it:from short currenting against the metal cathode tube.

Because of the necessity for degassing a rebuilt cathode' ray tube, having the laminated .face described above, at temperaturesnothigher than about degreesC. forthe envelope, the getter actionmust be muchlmore efiective thanunder the old process where the envelope could be heated to asymuch as 400 degrees C; while themetal parts of the gun were inductively heatedsometimes to a low red temperature. The metal parts can also be heatedto this temperature in {the present construction sincethey are remote from the tube face.

The getter already'described at 37 andAZ are'eifectivev at the: time of degassing andpu-mp-out to eliminate free gases and air remnants which the. pumps have been unable to remove, but there still remain certain small quantities of the sorbed gaseson the surfaces, and sometimes belowthem, of the glass and metal, partsof-the tube assembly and since the getters already described are flashed but once they have no further action toward eliminating these gases which :may :be subsequently liberated slowly throughout the life of the tube.

For the purpose of removing these remnant gases the applicantproposes to add .what may be termed =hot getmechanically supters, i.e. those which are heated every time the tube is in use and thus serve throughout its life to continue to absorb any liberated gases and vapors including hydrocarbon vapors from the diffusion pumps. One such getter is shown at 60 surrounding the spacer cylinder 52. It is in the form of a foil or thin metal strip surrounding the spacer 52 and closely secured thereto by welding or the like so that it is heated whenever the heater 56 is energized, by conduction and radiation therefrom. Proferably this getter 60 is titanium metal which when heated to a temperature of about 200 degrees C., readily achieved in the construction shown, becomes an active getter and has a maxi-mum sorbing action for gases such as hydrogen, oxygen, nitrogen and the oxides of carbon. Since the reaction between the getter material and these gases is an irreversible one, any which are liberated, either during the shelf life of the tube before use, or subsequently in operation, or between operations are continuously removed every time the tube is turned on and hence the life of the tube and of the components which might be harmed by these gases is extended to at least equal that of the tubes which could be degassed at the high temperatures mentioned previously in the absence of the laminated front face.

As a further supplement to the titanium getter just described a second hot getter is illustrated at 61 in the form of a sheet of zirconium metal surrounding the end of the cathode tube 46, below the ceramic or porcelain disc 47, and it is also preferably attached by welding to improve the heat conductivity. This material, which will be heated to a temperature of about 800 degrees C. by the cathode heater 55 which it surrounds finds this an optimum temperature for maximum effectiveness and note that the zirconium also absorbs water vapor.

Zirconium strip 61 acts as a hot getter and sorbs gases that would otherwise increase the pressure within the tube enough so that the cathode might be attacked or poisoned during the time the tube is being scanned or the screen excited but by sorbing these gases the vacuum is kept low enough so that the cathode is neither attacked during shelf life nor at other times when the tube is not being used.

The four getters described above including the

barium getters

37 and 40, which are flashed after the tube is sealed, and the two hot getters 60 and 61 are usually adequate to give the tube a normal life of the order of about 3,000 hours of use but under some circumstances and as an added precaution against the liberation of undesired gases, which might attack and poison the emissive material of the cathode a filfth getter may be added in the manner illustrated in either FIGURE 4 or FIGURE 5.

Referring to FIGURE 4, the first grid is shown at 25 entirely in elevation and it will be understood that it is equipped with the conventional cathode and heater and with the titanium and zirconium hot getters just described above. In this figure there is illustrated a cylinder 65 of zirconium metal sup-ported by welded wires 66 from the first grid and parallel to its axis and closely adjacent thereto and within this is fitted a heater coil 67 which may be of the same nature as the cathode heater with ceramic insulation on the wire. The tube may be open top and bottom but is preferably closed at the top as shown. The heater has two leads 68 which are connected in parallel to the leads 56', from the cathode heater so that when the cathode heater is in operation the heater 67 will also be energized.

For use with tubes whose heaters are connected in parallel to the heaters of the smaller tubes in the cathode ray television set and all energized from a 6.3 volt transformer secondary, the consumption of additional current by the heater 67 is unimportant, as long as it is within the capacity of the transformer, but where television sets of the string type are used with all heaters in series on the usual house voltage of 110 it is highly important that the total current consumption by the heaters in the cathode ray tube is the same in a rebuilt tube as in a new one.

The normal current consumption for a 6.3 volt heater is 600 milliamperes but it has been found that by appropriate design of the cathode, the emitting material, and the cathode heater, 300 milliamperes provide a beam as effective as the normal 600 milliampere heater and this leaves 300 mililamperes which can be used for heater 67 for the fifth getter, thereby providing a cathode ray tube with a total current consumption of 600 milliamperes to properly fit in the series tube string without upsetting the current and potential available for each of the other tubes therein.

In FIGURE 5 the first grid 25" is arranged and equipped as is the one in FIGURE 4 but the type of getter supported thereby is somewhat different. In this case a ceramic rod 70 is molded about an axial support wire 71 which is bent at right angles and welded at 72 to the wall of the grid so that the rod is parallel thereto as shown, and about this rod is wound a relatively heavy open coil conductor 73 of zirconium wire which is connected in parallel to the conductors 23 leading to the cathode heater so that both are energized in parallel. The zirconium wire 73 can by appropriate design be arranged to assume the most effective temperature at which the metal thereof sorbs gases and vapors from the interior of the tube. It will be appreciated that in the embodiment of FIGURE 5 the zirconium metal is heated immediately on turning on the current and thus acts somewhat more promptly than a zirconium at 61 in FIGURE 3 which is only heated after some delay.

The following schedule is suggested as the procedure for evacuating a rebuilt cathode ray tube having a laminated face plate and fitted with a new electron gun equipped with getters according to the present invention:

Pump the tube for one and a half hours at a temperature of degrees C. for the envelope;

Bomb the gun at a low visible temperature for fifteen minutes (this means inductive heating of the metal in the gun by a coil energized by HP. alternating current);

Convert the cathode in the usual manner which includes energizing the heater at a higher than normal voltage. This conversion requires heating the cathode sufficiently to convert the barium carbonate on its upper end to barium oxide which occurs at approximately 850 degrees C, requiring a heater voltage of about 13. This same voltage being applied to the heater 67 or 73 for the zirconium getters shown in FIGURES 4 and S heats it to a temperature between 880 degrees C. and 1200 degrees C. which at the then existing vacuum of about 10- results in an excellent clean up of any gases in the zirconium. Later, when the heater voltage is reduced to normal, the zirconium reverts to its ability to absorb about 1500 times its volume of hydrogen (at S T P). Thus, every time the tube is turned on, the zirconium is heated to its best absorptive temperature;

After cathode conversion keep the heater at nine volts and bomb for another ten minutes;

Shut off the bomber and continue pumping for another ten minutes with the heater still on at nine volts;

Tip the tube off;

Remove the tube face up from the oven being careful not to touch the laminated face as the plastic is soft;

Allow the tube to cool in the amtosphere;

Flash the barium getters in the tube neck for approximately 25 seconds;

Then age the tube in the normal manner.

It is suggested that aluminum foil be fitted closely over the face of the tube before pump down is started and that windows should be placed in the dag on the neck of the tube so that the flashing of the barium getters may be watched and properly controlled.

The tube is now ready for use immediately or after a reasonable lapse of time and will have an effective life of as long as a new tube which has been degassed at much higher temperatures.

7 I claim: 1. .An electron gun assembly for replacement use, in I cathode ray tubes having an envelope temperature limitation-of about 80 degrees C. and including a first grid r cylinder having a substantially closed upper end, a

ceramicdisc mounted in said cylinder, a cathode tube secured in and extending throughsaid disc, a heater in said cathode tube, a metal sleeve spacing said disc and the active end of said tube from said closed upper end, a titanium getter strip surrounding and secured to said sleeve, a zirconium getter strip surrounding and secured to said cathode tube below said disc, a barium getter, mounted on and above said gun assembly and arranged to be. flashed toward the envelope face and side wall, a second barium getter adjacent to the first one and ar- 1 ranged to be flashed toward the envelope neck, a zirconiclosed flat upper end and an open bottom; a ceramic disc secured across said cylinder intermediate to its ends; a

cathode tube having a closed upper end and an open lower end-secured in and extending through said disc; a heater in said cathode tube; a metal sleeve surrounding and spaced from the upper portion of said tube and engaging the disc and said flat upper end of said grid cylinder to space the tube closed end therefrom; a getter strip surrounding and secured to said spacer and comprising.

a metal effective to absorb residual gases in the tube at a temperature of the order of ZOO'degrees C.; a second getter strip surrounding and secured to saidcathode tube below said disc and comprising a metal effective to absorb gases in the tube at'a temperature of the order of 800. degrees C.; getters mounted 'on and above the gun as sembly to'be flashed, after the tube is sealed, toward the envelope face, side wall and neck; a metal getter supported near and by and insulated from said grid cylinder and means to continuously heat said getter electrically in parallel to the cathode heater when the latter is energized.

3. An electron gun assembly for replacement use in a cathode ray tube having the screen face thereof laminated by the use of a plastic which limits envelope heating to about 80 degrees C. for degassing; saidgun including a first grid cylinder of metal having a substantially closed flat upper end and an open bottom; a ceramic disc secured across said cylinder intermediate to its ends; a cathode tube having a closed upper end and an open lower end secured in and extending through said disc; a heater in said cathode tube; a metal sleeve surrounding and spaced from the upper portion of said tube and en.- gaging the disc and said fiat upper end of said grid cylinder to space the tube closed end therefrom; a getter strip surrounding and secured .to said spacer and comprising a metal effective to absorb residual gases in the tube at a temperature of the order of 200 degrees C.; a second getter strip surrounding and secured to said cathode tube below said'disc and comprising a metal effective to absorb gases in the tube at a temperature of the order of 800 degrees C. and getters mounted on and above the gun assembly to be flashed, after the tube is sealed, toward the envelope face, side wall and neck.

4. An electron gun assembly for replacement use in a cathode ray tube having a screen face subject to a m-axi-. mum P atv e mit of about 80 degrees C. when de- 8: gassing; said gunw including in addition to conventional flash getters used after pumping, at'least two low temperature getters effective zthroughout thetv life of the tube whenever it is in use; a first grid incorporatedin said gun and including a metal cylinderhaving a closed upper end and an open lower one; a ceramic disc secured across said cylinder intermediate its-ends; a metal cathode tube hav-- ing aclosedupper end and an open lower endsecured in andextending throughthe center;of-said disc; ametal sleeve surroundingand spaced from the upper, portion of said cathode tube and engaging the disc and the upper end of said grid cylinderto space the tube closed end accurately from said upper end of said grid cylinder; a heater in said cathode tube; one of said low temperature getters surrounding and engaging theportion ofsaid cathodettube beneath said ceramic disc and the: second low temperature getter surrounding andengaging the said spacer sleeve. I

5. The electron gun assemblyjas defined in .Claim 4 in which said low temperature getter onthe cathode tube is; of a material most effective tosorb gases when operated at a temperature of the order of 800 degrees C. and the second lowtemperature .getterbeing of material most effective tosorb gases when operatedat a temperature of the order of 200 degrees C.

6. The electron gunassembly as defined in claim 4 in which the getter on the cathode is;a thinsheet of zirconium welded to said cathode tube and the. getter on the spacer sleeve .is. a thin sheet of titanium welded to said spacer sleeve.

7. The electron gun-assembly as defined in claim-4 in which a further getter issupported adjacent said first grid and comprised .of a metal having the gettering properties of zirconium and means connected in parallel to said cathode heater to heat said further getter during operation of the cathode ray tube.

8. Anelectrongun assemblyfifor replacement use in a cathode .ray tube having a screen face limited to a maximu-mtemperature of degree Cjwhen'degassing and.

including a first grid,.in the formof an inverted metal cup, a ceramic discsecured across said cup intermediate its length; a cathode cylinder; extending axially through said disc, a heater in said cylinder, a metal sleeve larger thantsaid 'cylin'der'and smaller than the cup spacing the disc fromthe closed upperend of the cup and a strip of gettermetal secured to the outer surfaceof-said sleeve and effective to sorb gases from the cathode ray tube interior at the temperature to which it is heated by the said cathode cylinder heater.

9. The electrongun assembly as defined in claim 8 in which said getter metal is titanium and the, temperature isof the order'of 200 degrees C.

10. :The electron gun assembly as claimed in claim 8 including a second getter outside .of said metal cup and means inparallel to said cathode heater to heatsaid sec- 0nd getter during tube use.

11. The :electron gun assemblyas defined in" claim 10 in which the cathode and getter heater means have a totalcurrentconsu-mption of the cathode heater alonein the original gun in the cathode ray tube.

References Cited by the Examiner UNITED STATES PATENTS i 2,273,637 2/1942, Glover 3l 3-,-176 X" 2,638,559 1 5/1953 Giacchetti "7313-X 2,875,361 2/1959. Stone 3l-3,--l78 X 2,919,380 12/1959 Barnett 3131l80 X 2,935,635 5/1960 Boothroyd etal 3l3-76 3,215,884 11/1965 Watson et al 313178 JAMES LAWRENCE, Primary Examiner;

R. SEGAL, Assistant Examiner.

Claims

8. AN ELECTRON GUN ASSEMBLY FOR REPLACEMENT USE IN A CATHODE RAY TUBE HAVING A SCREEN FACE LIMITED TO A MAXIMUM TEMPERATURE OF 80 DEGREE C. WHEN DEGRASSING AND INCLUDING A FIRST GRID, IN THE FORM OF AN INVERTED METAL CUP, A CERAMIC DISC SECURED ACROSS SAID CUP INTERMEDIATE ITS LENGTH, A CATHODE CYLINDER EXTENDING AXIALLY THROUGH SAID DISC, A HEATER IN SAID CYLINDER, A METAL SLEEVE LARGER THAN SAID CYLINDER AND SMALLER THAN THE CUP SPACING THE DISC FROM THE CLOSED UPPER END OF THE CUP AND A STRIP OF GETTER METAL SECURED TO THE OUTER SURFACE OF SAID SLEEVE AND EFFECTIVE TO SORB GASES FROM THE CATHODE RAY TUBE INTERIOR AT THE TEMPERATURE OF WHICH IT IS HEATED BY THE SAID CATHODE CYLINDER HEATER.