US2758240A

US2758240A - Electron-discharge devices

Info

Publication number: US2758240A
Application number: US401127A
Authority: US
Inventors: Constantin S Szegho
Original assignee: Rauland Borg Corp
Current assignee: Rauland Borg Corp
Priority date: 1953-12-30
Filing date: 1953-12-30
Publication date: 1956-08-07
Anticipated expiration: 1973-08-07
Also published as: GB755819A

Description

Aug. 7, 1956 c. s. SZEGHO ELECTRON-DISCHARGE DEVICES Filed Dec 4 V/ Z// 2 1 w Grid 3 M vo ooooooow oooooooooooooooomu W////// ///////////////////U////U Q: OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOV CONSTANTIN A. SZEGHO PIC-5.1

IN V EN TOR.

HIS ATTORNEY.

United States Patent I O ELECTRON-DISCHARGE DEVICES Constantin S. Szegho, Chicago, Ill., assignor to The Rauland Corporation, a corporation of Illinois Application December 30, 1953, Serial No. 401,127

Claims. (Cl. 315-3) The invention relates to electron-discharge devices and more particularly to electron-discharge devices of the cathode-ray type suitable for use as image-reproducing devices in television receivers.

Conventional electron-discharge devices of the cathoderay type comprise a substantially evacuated envelope enclosing a luminescent screen and an electron gun for producing and accelerating an electron beam toward the screen. The screen is normally composed of a coating of discrete phosphor particles which emit light in response to electron bombardment, and is disposed upon the viewing surface of the envelope. deflecting systems are employed to concentrate the electron beam and to deflect it in the formation of a twodimensional scanning pattern or raster upon the screen. In the fabrication of such devices, a high degree of vacuum is produced through the use of a mechanical evacuation means; a dispersion pump is commonly used for this purpose. It is well known that the efiic'iency of operation and the emission life of the electron source varies with the degree of evacuation of the tube. Residual gas molecules may form positive and negative ions through bombardment by the electron beam in its passage toward the screen, and since the cathode or electron-emissive surface is normally at a negative potential with respect to the other electrodes, the positive ions are propelled toward it and reduce the emission life by bombarding and physically displacing particles of electron-emissive material.

In an eilort to meet this problem, a getter material is usually introduced into the tube to absorb the gas molecules remaining after mechanical evacuation. The getter material is normally distributed within the tube by flashing with an external source of energy such as radio-frequency electromagnetic radiation. In the flashing process the getter material is heated to a temperature at which it vaporizes and is thus deposited in a thin film upon a large area of the enclosing envelope. This technique of gettering is imperfect in many instances because the one flashing may dispose of gas molecules present at the time but it does effect the continuous absorption of additional gas molecules which often times are released in the normal course of operation of the tube. In accordance with another technique, the getter is continuously energized by electric current during normal operation of the tube. Although the use of such a continuous getter results in prolonging the life of an electron-discharge tube, the maximum attainable extension of tube life is not realized be cause the continuous energization of the getter causes it to deteriorate at a relatively rapid rate.

It is an object of the present invention, therefore, to provide a new and improved electron-discharge device which avoids one or more of the disadvantages of prior art structures.

It is a further object of the present invention to provide an electron-discharge device in which the emission life of the electron source is extended by more effective absorption of gas molecules through the action of a getter Suitable focussing and "ice material than has been achieved by conventional practices.

It is yet another object of the present invention to produce an electron-discharge device in which the tube life is extended by replenishing the electron-emissive source with emissive material released in the volatilization of the getter material.

In accordance with the invention, an electron-discharge device comprises a substantially evacuated envelope including an electron gun having a plurality of electrodes and including a thermionic cathode. An energizing circuit is coupled to the cathode to cause electron emission by heating the cathode. Additional energizing circuits are provided for applying predetermined operating potentials to the other tube electrodes. A thermally responsive switch is mounted within the envelope in a position exposed to heat originating at one of the electrodes. An electrical circuit is coupled in parallel with one of the energizing circuits and includes a conductive element of current-responsive getter material supported within the envelope and connected in series with the switch.

The features of the invention which are believed to be novel are set forth with particularity in the appended claims. The organization and manner of operation of the invention, together with further objects and advantages thereof, may best be understood by reference to the following description taken in conjunction with theaccompanying drawing in the several figures of which like reference numerals indicate like elements and in which:

Figure 1 is a fragmentary side elevation partly in cross section and partly cut away, of an electron discharge device constructed in accordance with the invention;

Figure 2 is a fragmentary view, similar to a portion of that of Figure l, of an alternative embodiment of the invention; and

Figure 3 is a top view, partly in cross-section of a portion of the illustrated embodiment of Figure 2.

The image-reproducing device of Figure 1 comprises a luminescent screen 10 affixed to the glass targetportion 11 of an evacuated cathode-ray tube envelope which also comprises a glass neck portion 12 enclosing an electron gun and an electrostatic focussing system. The electron gun comprises a plurality of electrodes including a cathode 13. A heater element 40, which may be of any conventional construction such as a helically'wound conductor, is disposed within cathode 13 and physically maintained in place by a spacing element 41 of suitable heat conducting but electrically insulating material such as aluminum oxide. Conductive leads 42 connect heater 40 to appropriate external pins 43 in the base of the tube to constitute an energizing circuit to which an external potential source (not shown) is applied for the purpose of heating cathode 13 to an emitting temperature.

The electron gun further includes a control electrode 14, and first and second tubular accelerating

electrodes

15 and 16, respectively. A diaphragm 17 having a central aperture 18 is disposed across the outlet end of second accelerating electrode 16, and aperture 18 is symmetrically centered with respect to the tube axis A-A which is perpendicular to the center of the fluorescent screen 10. Electrode 16 is laterally offset relative to electrode 15 to provide a steady transverse electrostaticdetlection field component in the region between these twoelectrodes, and the entire electron gun structure is tilted with respect to the tube axis AA by an angle p.

An electrostatic focussing system of the unipotential lens type is disposed between the electron gun and the screen. The focussing system comprises the outlet end of electrode 16, a lens electrode 19, and an additional electrode 20 which are all coaxially mounted with respect to the tube axis A-A. Electrodes 19 and 20 may be provided with corona rings 33 and 35'. A centrally apertured conductive disc 21 is disposed in the neck portion oi the envelope between the focussing system and target portion 11. A conductive coating 22 of colloidal graphite, such as aquadag or the like, extends from the direction of target portion 11 into the neck portion of the envelope, and conductive disc 21 is maintained at a common potential with conductive coating 22 by means of metal contact springs 23.

For convenience,

electrodes

14, 15, 16, 19 and 20 may be termed grids and may be designated by number starting with control electrode 14 as the first grid and progressing in the direction of beam travel to electrode 20 which is the fifth grid. All five grids are supported in predetermined mutually spaced relation by means of nected to grids 3 and by means of metal strips 27. 9

Operating potential for the conductive coating 22, and therefore for the third and fifth grids, may be supplied by means of a conventional contact button if the envelope is of the all glass type, or directly to the metal cone if the tube' is of the glass-metal variety. In other words the electrode leads, basing pins or high-voltage terminals provide energizing circuits for applying operating potentials to the electrode system of the tube.

An external permanent magnet 28, supported in a spring clamp 29 which fits snugly around the neck of the tube and is movable both axially and rotationally, is provided to develop a magnetic field within the tube to provide separation of the negative ions from the electron beam.

The tube is evacuated, sealed and based in accordance with well known procedures and suitable getters 31 are supported from the surface of conductive disc 21 facing fluorescent screen to absorb residual gases after evacuation.

The structure as thus far described is a well-known cathode-ray tube and the details of its electrode system as well as its operation in developing a beam of electrons,

v 4 The trough of element 44 is filled with a current responsivegetter material 45, which preferably consists of an alloy of barium; however, other commercial products such as alloys of magnesium or calcium, may be employed.

Suitable getter materials may be composed of any of the following mixtures of barium, aluminum and magnesium or other convenient percentages of these elements: Ba 25%, Mg Al'20%', Ba 37%, Mg. 37%, Al 26%; Ba 43%, Mg 20%, Al 37. Metallic barium would be preferable to an alloy except for its instant reaction to gaseous molecules or to gaseous vapors present in the air. The use of an alloy of barium has an advantage in that in this form barium is inert, but may be energized by flashing. Another getter material that may be used is a carbonate or oxide of barium which is reduced to barium by outgassing at a temperature lower than that of the flashing temperature. In the latter case a temperature of 800 to 1100 degrees centigrade reduces the barium compound to yield about 40% barium. By flashing at a higher temperature, usually inthe range of 1200 to 1300 degrees centigrade, the barium acts as a getter in the well known manner.

A normally-closed thermally responsive switch 46, preferably of the bimetallic type, is connected in series with element 44 and is positioned adjacent to electrode 14. Switch 46 may comprise any thermostatic structure known in the art which makes or breaks an electrical circuit in response to its attaining a predetermined temperature. Such switches are composed of two metals having different temperature coefiicients affixed to one another to distort away from and open a contact upon the application of heat. Frequently, a strip of nickel and a strip of copper are employed although other combinations of dissimilar metals are equally satisfactory. It has been found that sufiicient heat is generated by the cathode structure, which may attain an operating temperature in the vicinity of 800 degrees Centigrade, to actuate switch separating unwanted ions from the beam, and projecting the purified beam toward the luminescent screen are well understood. They are described in particular, for example, in U. S. Patent No. 2,658,160, issued November 3, 1953, in the name of Russel S. Peterman, and assigned to the same assignee as the present invention. The details of corona rings 33 and 35 and their function in the tube are described and claimed in a copending applicar tion of Constantin S. Szegho, Serial No. 229,013, filed May 31, 1951, now U. S. Patent 2,673,305, and assigned to the same assignee.

In order to extend the useful life of the tube,

recognizing that conventional gettering techniques utilizing pellets 31 may not adequately protect against the possibility of occluded gases, the present invention provides an improved gettering structure. More specifically,

an electrical circuit including a conductive element 44 conveniently wound in contact with the surface of electrode 14, it may be insulated therefrom by simple spacers of electrically non-conducting material, as for example, aluminum oxide or the like. Of course, in either case the support for element 44 may be grooved to strengthen the assembly mechanically. In addition, element 44 may be wound around and supported by glass supports 24.

46 and the positioning of the switch is not critical so long as during the operation of the tube the elements of the switch achieve the temperature at which the switch opens. A shield 48, which may be a small piece of sheet metal welded to electrode 14 and disposed between getter 45 and glass support 24, prevents volatilized getter material from being deposited upon the surface of the glass support and causing a short circuit between some of the gun electrodes.

In explaining the operation of the described getter circuit, it may be assumed that the tube is'incorporated into suitable apparatus; for example, it may serve as the image-reproducing device of a television receiver. To operate the tube in any such environment, energizing potentials are applied to its several electrodes. Concurrently with the application of such energizing potentials. current How is initiated through the getter circuit since it is connected in parallel with the filament of the cathode. The flow of current through element 44 generates sufficient heat in this element to vaporize getter material 45 which in the art is referred to as flashing the getter. The actuation of the getter causes any undesirable gas molecules present in the tube to be absorbed in the usual manner and the activation of the getter continues until such time as switch 46 of the getter circuit is opened. After a relatively short interval, the energizing potentials applied to the electrode systems of the tube raise the cathode structure in particular to an operating temperature which, as has been described, is sufficiently high to open switch 46. At this point, current no longer flows in the getter circuit.

When the electron-discharge device is turned off, electrode 14 returns to ambient temperature, resulting in the closure of the contacts of bimetallic switch 46. Upon reenergization of the electron-discharge device, however, another, cycle of the above-described operation is begun and the getter material vaporizes further to absorb any 5 residual gas molecules. Since during the normal operation of the tube occluded gas molecules are liberated from many areas, particularly from fluorescent screen 10, it is advantageous to re-energize the getter in this cyclic fashion to prolong the life of the tube.

It has been found that if the emissive coating of cathode 13 is composed of metallic barium and if the getter material is also composed of a preponderance of barium, an additional extension of the emissivc life of cathode 13 may result. Apparently, the barium coating upon the surface of cathode 13 is replenished in part by molecules of the barium getter material when itis volatilized. It would appear that because of random movement the mole cules of barium from the getter are deposited upon cathode 13 to replace the electron-emissive coating depleted by normal tube operation.

The full benefits of the invention are not realized if the getter material completely flashes upon the first application of current to element 44. Protection against ex hausting the getter at the first flashing may be attained by employing as conductive element 44 atube that is substantially continuous in cross section but is so thinin wall thickness as to be porous and hence partially pervious to barium vapor. With such a construction the getter material is not completely vaporized in any one cycle of operation; instead a substantial portion is retained within the tube from one flashing to the next. Alternatively, the enclosing tube may be impervious to vapors of the getter material except for a narrow section that may be slotted, perforated or otherwise rendered pervious to the getter vapor to permit vaporization of the getter in a controlled manner and to direct the vapor over a predetermined area of tube neck 12. Such a construction is represented in the embodiment of Figures 2 and 3, which is identical in function and structure to that of Figure 1 except that conductive element 44' entirely encloses the getter material and further, instead of being wound externally of electrode 14, in this embodiment it is disposed upwardly in the neck or" the cathode-ray tube. In this latter arrangement, getter material 45 may be deposited over a greater area of neck 12 resulting in a more efficient absorption of residual gas molecules. In this embodiment conductive element 44' enclosing the getter material is mechanically supported by

rigid spacers

50 and 51 inserted into supports 2 and extends into the neck portion 12 of the cathode-ray tube longitudinally alon these supports. Perforations 52. are disposed along the longitudinal surface of element 44 to permit controlled vaporization of the enclosed getter. Electrical terminations are connected to one filament lead of heater element 40 and to grid 2. The energizing current whi h heats element 44 to volatilize the getter material is produced by the potential difference between grid 2 which is usually maintained at B+ and the grounded side of the filament lead to heater element 40. Although this arrangement may be suitable for practical re-energization of the getter material in cyclic fashion, conductive element 44 may be advantageously wound spirally about the surface of grid 3 provided it is maintained therefrom by insulating spacers (not shown). The particular configuration of the getter support structure is shown for purposes of illustration only and should not be considered a limitation upon the subject invention.

In addition, although switch 46 may be conveniently operated by heat generated in the cathode structure, it may also be operated by heat generated in other portions of the tube. A simple proportioning of the thickness of one of the metallic strips comprising the bimetallic elements permits an adjustment of the radius of curvature formed by the distortion of the armature of the switch in response to heat. in the usual case the bias necessary to make positive electrical contact may be enhanced by a mechanical spring in the manner well known in the art. As an illustration of another of the possible operating positions of switch 46, Figure 2 shows it disposed in the 6 vicinity of diaphragm 17 of grid 3. This area of the tube is heated by electron bombardment upon the surface of diaphragm 17. Switch 46 maintained in position by

metal rods

55 and 56 mechanically and electrically connecting it to element 44 as illustrated in Figure 3, a top view taken along line 33 of Figure 2.

Therefore the present invention discloses a new and improved electron-discharge device which includes a builtin provision for extending life of the cathode by momentarily actuating a getter material automatically each time the device is placed in normal use. It is through a simple structural addition that the residual gas molecules remaining within the envelope and liberated in the course of normal operation are absorbed to prolong the useful tube life. In addition, an even greater extension of tube life may be realized by employing an appropriate getter material to replenish the electron-emissive material from time to time with molecules of volatilized getter which upon deposition also become electron-emissive. Further the cyclic operation of applicants invention prolongs the effective life of the getter beyond that usually found in the use of a continuous getter which is rapidly dissipated.

While particular embodiments of the invention have been shown and described, modifications may be made and it is intended in the appended claims to cover all such modifications as may fall Within the true spirit and scope of the invention.

I claim:

1. An electron-discharge device comprising: a substantially evacuated envelope; a plurality of electrodes including a thermionic cathode supported within said envelope; an energizing circuit for heating said cathode to cause electron emission therefrom; additional energizing circuits for applying predetermined operating potentials to said electrodes; a thermally responsive switch mounted within said envelope in a position exposed to heat originating at one of said electrodes; and an electrical circuit coupled in parallel with one of said energizing circuits and including a conductive element of current-responsive getter material supported Within said envelope and connected in series with said switch.

2. An electron-discharge device comprising: a substantially evacuated envelope; a plurality of electrodes including a thermionic cathode supported within said envelope; an energizing circuit for heating said cathode to cause electron emission therefrom; additional energizing circuits for applying predetermined operating potentials to said electrodes; a normally-closed thermally responsive switch mounted within said envelope in a position attaining at least a predetermined temperature in normal operation of said device and adapted to open upon attaining said predetermined temperature; and an electrical circuit coupled in parallel with one of said energizing circuits and including a conductive element of current responsive getter material supported within said envelope and connected in series with said switch.

3. An electron-discharge device comprising: a substantially evacuated envelope; a plurality of electrodes including a thermionic cathode supported within said envelope; an energizing circuit for heating said cathode to cause electron emission therefrom; a normally-closed thermally responsive switch mounted within said envelope in a position attaining at least a predetermined temperature in normal operation of said device and adapted to open upon attaining said predetermined temperature; and an electrical circuit coupled in parallel with said energizing circuit and including a conductive element of current-responsive getter material supported within said envelope and connected in series with said switch, whereby said getter material is momentarily activated each time normal operation of said electron-discharge device is initiated.

4. An electron-discharge device comprising: a substantially evacuated envelope; a plurality of electrodes including a thermionic cathode and a control grid supported within said envelope; an energizing circuit for heating said cathode to cause electron emission therefrom; additional energizing circuits for applying predetermined operating potentials to said electrodes; a thermally responsive switch mounted adjacent said control grid in a position exposed to heat emanating from said control grid; and an electrical circuit coupled in parallel with one of said energizing circuits and including a conductive element of current-responsive getter material supported within said envelope and connected in series with said switch.

5. An electron-discharge device comprising: a substantially evacuated envelope; a plurality of electrodes including a thermionic cathode and an accelerating anode supported within said envelope; a first energizing circuit for heating said cathode to cause electron emission therefrom; additional energizing circuits for applying predetermined operating potentials to said electrodes; a thermally responsive switch mounted Within said envelope in a position exposed to heat originating at one of said electrodes; and an electrical circuit coupled between said accelerating anode and said first energizing circuit and including a conductive element of current-responsive getter material supported within said envelope and connected in series with said switch.

6. An electron-discharge device comprising: a substantially evacuated envelope; a plurality of electrodes including a thermionic cathode supported within said envelope; an energizing circuit for heating said cathode to cause electron emission therefrom; additional energizing circuits for applying predetermined operating potentials to said electrodes; a thermally responsive switch mounted within said envelope in a position exposed to heat originating at one of said electrodes; an electrically conductive element of semitubular cross-section partially enclosing current-responsive getter material supported within said envelope; and an electrical circuit coupled in parallel with one of said energizing circuits and including said electrically conductive element and connected in series with said switch.

7. An electron-discharge device having a longitudinal dimensional greater than its transverse dimension and comprising: a substantially evacuated envelope; a plurality of electrodes including a thermionic cathode, all

maintained in fixed relationship within said envelope by 1 a plurality of supporting elements; an energizing circuit for heating said cathode to cause electron emission therefrom: additional energizing circuits for applying predetermined operating potentials to said electrodes; a thermally responsive switch mounted within said envelope in a position exposed to heat originating at one of said electrodes; an electrically conductive element of substantially circular cross-section mechanically maintained in a predetermined position by at least one of said supporting elements along said longitudinal dimension and partially enclosing current-responsive getter material supported within said envelope; and an electrical circuit coupled in parallel with one of said energizing circuits, including said electrically conductive element and connected in series with said switch.

8. An electron-discharge device comprising: a substantially evacuated envelope; a plurality of electrodes including a thermionic cathode supported within said envelope; an energizing circuit for heating said cathode to cause electron emission therefrom; additional energizing circuits for applying predetermined operating potentials to said electrodes; a thermally responsive switch mounted Within said envelope in a position exposed to heat originating at one of said electrodes; an electrically conductive element of semitubular cross-section wound spirally around one of said electrodes and partially enclosing current-responsive getter material supported within said envelope; and an electrical circuit coupled in parallel with one of said energizing circuits and including said electrically conductive element and connected in series with said switch.

9. An electron-discharge device comprising: a substantially evacuated envelope; a plurality of electrodes including a thermionic cathode and an accelerating anode supported within said envelope; an energizing circuit for heating said cathode to cause electron emission therefrom; additional energizing circuits for applying predetermined operating potentials to said electrodes; a thermally responsive switch mounted within said envelope in a position exposed to heat originating at said accelerating anode; and an electrical circuit coupled in parallel with one of said energizing circuits and including said electrically conductive element and connected in series with said switch device.

10. An electron-discharge device comprising: a substantially evacuated envelope; a plurality of electrodes including a thermionic cathode supported within said envelope and comprising an electron emissive element of barium; an energizing circuit for heating said cathode to cause electron emission therefrom; additional energizing circuits for applying predetermined operating potentials to said electrodes; a thermally responsive switch mounted within said envelope in a position exposed to heat originating at one of said electrodes; and an electrical circuit coupled in parallel with one of said energizing circuits and including a conductive element of current-responsive getter material comprising barium supported within said envelope and connected in series with said switch.

References Cited in the file of this patent UNITED STATES PATENTS 1,739,043 Ruben Dec. 10, 1929 1,787,300 Alexanderson Dec. 30, 1930 2,392,969 Bickley Jan. 15, 1946 2,575,835 Pohle Nov. 20, 1951 2,638,559 Giacchetti May 12, 1953 2,668,253 Taylor Feb. 2, 1954