US2275864A

US2275864A - Cathode ray tube

Info

Publication number: US2275864A
Application number: US367385A
Authority: US
Inventors: Le Roy E Record
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1940-11-27
Filing date: 1940-11-27
Publication date: 1942-03-10
Anticipated expiration: 1959-03-10
Also published as: FR877309A

Description

March 10, 1942. LE ROY 5 RECORD 2,275,864

CATHODE RAY TUBE Filed Nov. 27, 1940 I Inventor. LeRoy ERec'ord,

by IV 64% His tt'orney.

Patented Mar. 10, 1942 2,275,864 CATHODE RAY TUBE Le Roy E. Record, Ballston Spa, N. Y., assignor to General Electric Company, a corporation of New York Application November 27, 1940, Serial No. 367,385

11 Claims.

The present invention relates to cathode ray tubes, such as picture reproducing tubes for use in television receiving apparatus.

It is an object of the invention to provide an improved cathode ray tube assembly and in particular, an improved gettering arrangement for the removal of gaseous impurities from the interior of such tubes.

An important feature of the invention consists in the use of a tube envelope which comprises a bulbous portion having a relatively large opening and a flanged shaft portion sealed into this opening by means of a fusion seal, In the fabrication of the tube a gettering assembly, larger than is usually employed in tubes of the type under consideration, is introduced into the bulbous portion of the envelope through the abovementioned opening prior to or concurrently with the closing of the opening by the incorporation of the shaft portion of the envelope. With this arrangement it proves possible to do a better job than has previously seemed feasible with respect to the removal (by the gettering means) of objectionable gases developed within the interior of the tube envelope. At the same time the deposition of vaporized gettering material in parts of the tube which are apt to be adversely affected by its presence is avoided.

The construction described above also leads to an improved procedure for providing the interior wall surfaces of the tube envelope with a continuous conductive coating, as is required for most satisfactory operation of the tube. In this connection the two envelope parts are preferably separately coated internally prior to their assembly, and the two coatings are electrically joined after the tube is assembled by means of metal vapor generated from the gettering means. This procedure eliminates certain difliculties encountered when it is attempted to form the conductive coating as a whole after the tube envelope has been completely assembled.

The features which I desire to protect herein are pointed out with particularity in the appended claims. The invention itself, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the drawing, in which Fig. 1 represents a cathode ray tube suitably embodying the invention; Fig. 2 represents an intermediate stage in the fabrication of a cathode ray tube according to the invention; Fig. 3 is an enlarged perspective view showing the details of the gettering means used in the device of Fig. 1; Fig. 4 represents a further stage in tube fabrication; Fig. 5 is an enlarged fragmentary detail view of one element of the gettering means shown in Fig. 2; Fig. 6 is a fragmentary sectional view useful in explaining the nature and effect of the gettering operation; Fig. 7 is an enlarged view showing the manner in which the anode terminal connection of the tube of Fig. 1 may be used as an evacuating duct during the exhaust operation; Fig. 8 shows an alternative type of getter with which the invention may be practiced, and Fig. 9 shows an alternative way of mounting the gettering means.

Referring particularly to Fig. 1 there is shown a completely assembled cathode ray tube of the type used in television for picture reproduction purposes. The envelope of this tube comprises an enlarged bulbous part II) of glass and an elongated glass shaft portion II connected therewith. The bulbous portion is provided with a flattened wall lOa which is assumed to be coated internally with a material adapted to luminesce upon the impingement of an electron beam. (This material may consist, for example, of a fluorescent powder of known type such as a composition of zinc sulfide and zinc cadmium sulfide.) The shaft portion I I, which contains electrode structure for producing an electron beam, terminates in an outwardly extending flange lla which is fusion sealed at its periphery to a tubular extension of the bulbous part of the envelope.

The electrode structure within the envelope shaft portion ll comprises a cathode M which is shown in dotted outline and an apertured control electrode l5, commonly called a grid. The cathode acts as the source of an electron stream which may be modulated (i. e. varied in intensity) by the action of the control electrode l5. To this end the control electrode is ordinarily biased to a negative potential and is connected to a source of signal voltage (not shown). The electrodes 14 and I5 are both mounted on a common stem press l1 and connect with bayonet terminals l8 which project from the extremity of the tube. A basing cap is which is cemented to the tube serves to support the terminals l8 in rigid fashion.

Both the bulbous and shaft portions of the envelope are provided internally with conductive coatings (respectively indicated at Zla and 2th) which in the normal operation of the tube are to be maintained at a common potential. These coatings should be constituted of a conductive substance such as a thin layer of metal or a layer of graphite deposited in a suitable manner. If graphite is used, one may employ, for example,

either a colloidal suspension of graphite in water or a mixture of graphite with bentonite as described in my copending application S. N. 321,030, filedmruary 27, 1940.

The shaft coating Zlb terminates at a point which is in close proximity to the extremity of the grid l5 and, when connected to a source of high potential, serves as an anode for accelerating and to some extent for focusing the electron stream delivered by the cathode. The beam of electrons thus formed may be additionally focused by magnetic means and may be caused to move transversely so as to scan the surface of the envelope window llla by the action of appropriate deflecting means. (Since the focusing and deflecting means form no part of my present invention. they are not shown in the drawing).

In fabricating a cathode ray tube in accordance with my present invention, the tube envelope is formed by the junction of two parts, of which one comprises a bulbous portion corresponding to the part Ill as the same is shown in Fig. 1, but having a tubular extension lOb of the character indicated in Fig. 2. The other part of the envelope is the flanged shaft portion I l (Figs. 1 and 2).

Prior to joining the parts It) and II, each part is preferably provided internally with a conductive coating (i. e. the coatings 2 la and 2 lb) Due to the ready accessibility of the interior surfaces of the respective parts, these coatings may be easily applied by a brushing technique or by temporarily introducing a liquid suspension of coating material into the part to be coated to cause deposition of the coating material on the appropriate surfaces.

As a further preliminary to the assembling operation a gettering assembly is mounted on the shaft flange Ila. This assembly, which may be of the nature illustrated in Fig. 3, comprises the combination of a gettering ring 24 and a flared or frustro-conical shield 26, preferably of metal (e. g. nickel), to which the gettering ring is at- These wires should preferably support the shield 26 in spaced relation with respect to the flange so that subsequent heating of the shield will have no tendency to crack the glass of which the flange is constituted.

Following the mounting of the gettering assembly the flanged portion of the envelope shaft is introduced into the tubular part l?) of the bulbous envelope portion as illustrated in Fig. 2. Thereafter, heat is applied to the outer surfaces of the part lllb so that it contracts into sealing contact with the periphery of the flange. The excess of glass depending below the flange is then dropped on and the seal is brought to the finished condition indicated in Fig. 4, The stem press I! bearing the electrodes l4 and I5 may then be sealed in place and the tube baked out and exhausted.

The procedure outlined in the foregoing necessarily leaves a gap 30 (Fig. 4) between the conductive coatings 2| a and 2lb which respectively line the interiors of the two parts of the envelope. This gap is objectionable in that it prevents the potential of the two coatings from being fixed by means of a single lead-in connection. This difficulty is overcome, however, by using gettering metal derived from the ring 24 as a means for bridging the gap 30.

The gettering ring, which is shown in enlarged section in Fig. 5, preferably comprises an annular metal tube consisting, for example, of nickel or copper. This tube may be filled with a chemically active, readily vaporizable metal 25 such as barium or magnesium which in its vapor state is capable of cleaning up objectionable gases apt to be present within the tube envelope in the final stages of the exhaust procedure. A thin portion 240. provided in the wall of the annular tube 24 permits the tube to be readily ruptured so as to facilitate the escape of the vaporizable material 25.

Heating of the gettering assembly may be readily accomplished by inductive means because of the loop form of the assembly; that is to say, a high frequency field produced in the vicinity of the gettering assembly can induce currents in the shield 26 and also in the gettering ring 24 sufficient to heat the same above the vaporizing temperature of the metal 25, thus causing the metal to be released. The form of the shield 26 causes the vaporized metal to be projected almost exclusively against the portion of the envelope wall corresponding to the uncoated gap 30 so that the metal as it condenses forms a conductive bridge between the coatings 2la and 2 lb as indicated at 3| in Fig. 6. The effect, therefore, is to make the two conductive coatings electrically continuous.

It is a special advantage of the arrangement specified that the confinement of the gettering material to the intermediate region of the tube envelope prevents any deposition of vaporized metal either on the fluorescent screen of the tube or in proximity to the electrodes l4 and I5. On the latter point in particular, this is in contradistinction to arrangements previously employed in which the gettering device has been positioned near the extreme end of the envelope shaft portion. Under these latter circumstances the length of the electrode-supporting stem must be made relatively long in order to prevent electrical leakage between the high and low voltage electrode elements as a result of the deposition on the stem of particles of the gettering substance. This requires either an objectionable increase in the overall length of the tube or a sacrifice of the so-called image-to-object ratio, this latter quantity being at least indirectly a function of the distance between the electron source and the bulb of the tube.

In addition to the foregoing, the arrangement of Fig. 1 permits a more adequate amount of gettering material to be used than is practicable when the source of such material is located in the tube shaft. In the first place, the relatively large dimensions of the space within which the gettering element is positioned and the fact that it is wholly remote from the electron beam path eliminate any need for limitation of its size for reasons of space economy. Moreover, the advantageous location of the gettering ring means that an increase in its size does not materially increase the danger of short-circuiting the electrode parts when the gettering metal is vaporized.

The final evacuation of a tube constructed in the manner specified in the foregoing may conveniently be carried out by an appropriate use of the high voltage contact terminal 33. This terminal, which in th finished tube affords a means of connecting the conductive coating within the tube envelope to an external source of high potential may be initially of the character shown in Fig. 7. As there illustrated, the terminal comprises a flanged eyelet which is constituted of a chrome-iron alloy orof some other alloy readily sealed to glass. The eyelet has an aperture 34 atone end and may be used for the evacuating function by fusing its extremity to a glass tubulation 35 which is connected to a vacuum pump (not shown). After the envelope has. i been evacuated to the desired extent, the tubulation 35 is pinched oil and fused down so that it completely fills the aperture 34, thus leaving the tube in sealed condition. A connection between the eyelet 33 and the internal conductive coating is provided simplyby forming the internal coating Zia in such fashion that it extends over the eyelet flange as indicated at 31.

It is not necessary'to form the active portion of the gettering means as a continuous ring as is suggested by Fig. 2. Alternatively, one may employ gettering capsules such as the capsules 39 and 40 illustrated in Fig. 8. These may be supported by means of a'conductive ring 4| or in any other manner which permits them to be heated in some convenient way. In use, they should be, associated with shielding means functioning in the manner of the shield 26 of Fig. 2 to confine the vaporized metal to the desired cation and to assure its deposition in a location where it will form a bridging connection between the conductive coatings 21a and 2). In some cases it is even practicable touse asingle gettering capsule provided means are associated with the capsule for directing the metal released from it in the proper path.

Fig. 9 represents, an alternative method of mounting the gettering assembly. In this case the mounting means comprises a plurality of wires bent in the manner exemplified by the wire 43. The extremity of this wire is provided with a hook-like portion 44 of which the tip is embedded in the joint between the glass flange Ila and the tubular envelopeepart lllb at the time the seal between these parts is formed.

Certain additional advantages are realized by modifying the order of procedure which has been described in the foregoing to make the formation ity of the interior of the shaft before it is" Joined to the bulb I0, it is possible to secure substantially perfect alignment of the electrodes by the use of internal jigs which are introducedinto the flanged end of theshaft. Theconductive coating 2lb maybe applied either before or after the elect'rode assembly is introduced.

. gettering material in the vicinity of What I claim as new and desire to secur by Letters Patent of the United States, is: I

1. A cathode ray tube having electrode structure for generating electrons, a terminally flanged insulating cylinder deflning an. elongated passage for the electrons, a bulbous envelope having an opening in which the cylinder flange is sealed by means of a fusionseal, and a gettering assembly within the bulbous portion of the envelope and arranged to assure the deposition of vaporized the fusion seal.

2. A cathode ray tube having electrode structure for generating electrons, a terminally flanged insulating cylinder defining an elongated passage for the electrons, a bulbous envelope having a tubular extension to which the cylin- 'said tubular extension and by the said flange.

3. -A cathode ray tube having electrode structure for gettering electrons, a terminally flanged insulating cylinder defining an elongated passage fortheFelectrons, a bulbous envelope having an opening in which the cylinder flange is sealed by means of a peripheral fusion seal, and a getterin'g assembly of annular configuration supported within the envelope in proximity tothe said flange, the said gettering assembly being so The production of the luminescent coating which is applied to the interior of the tube window Illa and the formation of the internal conductive coating Ma may obviously be accomplished with ease through the relatively large opening which exists in the bulb before the shaft portion I l is joined to it.

While I have described my invention by reference to particular embodiments thereof, it will.

be understood that numerous modifications may be made by those skilled in the art without departing from the invention. I, therefore, aim in theappended claims to cover'all such variations foregoing disclosure.

' from is deposited arranged that gettering material vaporized therein the region of the said fusion seal. l

4. A cathode ray tube having electrode structure for generating electrons, a terminally flanged insulating cylinderdefining an elongated passage for the electrons, a bulbous envelope having an opening in which the cylinder flange is sealed by means of a peripheral fusion seal, and a gettering assembly supported within the envelope in proximity 'to the said flange, the said gettering assembly 'comprising a gettering ring coaxial with the said cylinder and anannular shield for confining metal vaporized from said ring to the region. of the fusion seal. I 5. A cathode ray tube having electrode structure for generating electrons, an insulating cylinder defining an elongatedpassage for the electrons, a bulbousenvelope joined to the-extremity of the said cylinder by a fusion seal, separate conductivecoatings respectively applied to the interior surfaces of the said cylinder and envelope for fixing the potential thereof, there being a gap between the said coating at the region' of the seal between the cylinder and envelope, a layer of vaporizable metal conductively bridging the said gap, and means positioned in proximity,

to the said gap and serving during the fabrication of the tube as a source of the said vaporizable metal from which the said layer. of such metal may be deposited.

6. A cathode ray tube having electrode structure for generating electrons, an insulating cylinder defining an elongated passage for the electrons, a bulbous'envelope joined to the extremity of the said cylinder by a fusion seal, separate conductive coatings respectively applied to the interior surfaces of the said cylinder and en-- velope for fixing the potential thereof, therebeing a gap betweenthe said coatings in the re- 3 gion of the seal between the cylinder and envelope, a layer of chemically active vaporizable metal conductively bridging the said gap, means positioned in proximity to the said gap and serving during the fabrication of the tube as a source. of vaporization of the said vaporizable metal, and

means for confining deposition of metal vaporized from said source substantially to the region of the said gap."

trons and terminating in an outwardly extending flange, a bulbous envelope merging into a tubular part which is joined to the periphery of the 7. A cathode ray tube having etectrode struc- .ture for generating electrons, an insulating cylinder defining an elongated passage for the electrons, a bulbous envelope joined to the extremity of the said cylinder by a fusion seal, separate conductive coatings respectively applied to the interior surfaces of the said cylinder and envelope for fixing the potential thereof; there being an annular gap between the said coatings at thereigon of the seal between the cylinder and envelope, a layer of chemically active vaporizable metal bridging the said gap, and a gettering ring conforming approximately to the said gap and positioned in proximity thereto, said gettering ring servingduring the fabrication of the tube as a source from which the said layer of vaporizable material may be deposited, and shielding means associated with the said gettering ring for confining deposition of metal vaporized therefrom substantially to the region of the said gap.

8. A cathode ray tube having electrode structure for generating electrons, an insulating cylinder defining an elongated passage for the electrons and terminating in an outwardly extending fiange, a bulbous envelope merging into a tubular part which-is'joined to the periphery of the said flange by a fusion seal, separate conductive coatings respectively applied 'to the interior surfaces of the said cylinder and envelope/for fixing the aforementioned means for confining the deposition of metal vaporized from such means substantially to the region of the said gap.

10/ In a method of fabricating a discharge tube of the type which in finished form includes an assembly of two major glass envelope parts having a conductive sheath extending continuously over the interior surfaces of the said two parts,

the steps which comprise separately internally coating the respective envelope parts with con-' ductive material prior to uniting the parts, thereafter joining the parts by a fusion seal, and finally depositing metal by vaporization over the region of the said seal, thereby conductively to connect the respective coatings of the parts into a continuous sheath.

potential thereof, there being a gap between the said coatings at the region of the seal between the said flange and the said tubular part, a layer of vaporizable metal conductively bridging the said gap, and means positioned in proximity to the saidgap and serving during the fabrication of the tube as a source of vaporization of the said metal from which the-said layer thereof may be deposited.

9. A cathode ray tubehaving electrode. structure for generating electrons, an insulating cylinder defining an elongated passage for the elec- 11. In amethod of fabricating a discharge tube envelope of a type which in finished form in cludes the assembly of a bulbous portion and an elongated shaft portion provided internally with a conductive sheath extending continuously of the surfaces over both portions, the steps which I comprise separately internally coating the said two envelope portions with a conductive material prior to assembling the said portions;there-- after joining said portions by a fusion seal, and

finally vaporizing agettering metal over the re-' gion of the said seal, thereby conductively to connect the coatings of the respective envelope portions into a continuous sheath.

LE ROY a. RECORD.