US3354340A

US3354340A - Cap-shaped control electrode securing cathode by thin supporting members

Info

Publication number: US3354340A
Application number: US591367A
Authority: US
Inventors: Almer Friedrich Herman Raymund; Schrijnemakers Gerardus Marie; Kuiper Adrianus; Alphonsus Petrus Van Rooy
Original assignee: US Philips Corp
Current assignee: US Philips Corp; North American Philips Co Inc
Priority date: 1965-10-22
Filing date: 1966-10-14
Publication date: 1967-11-21
Anticipated expiration: 1984-11-21
Also published as: ES332473A1; DE1564462A1; AT261691B; BE688801A; GB1113748A; DE1564462C3; NL6513665A; CH458549A; FR1504694A; DE1564462B2

Description

Nov. 21, 1967 CAP-SHAPED Filed 0012. 14, 1966 F. H. R. ALMER ETAL 3,354,340 CONTROL ELECTRODE SECURING CATHODE BY THIN SUPPORTING MEMBERS 2 Sheets-Sheet 1 VZ// /Ellll r, //%-21 1967 F. H. R. ALMER ETAL 3,35

CAP-SHAPED CONTROL ELECTRODE SECURING CATHODE BY THIN SUPPORTING MEMBERS Filed 001;. 14, 1966 2 Sheets-Sheet 2 Flu FIG. 3

INVENTORS ALMER FRIEDRICH H- R.

GERARDUS SM. SCHR IJNEMAKERS ADRIANUS KUIPER ALPHONSUS P. VAN ROOY AGENT United States Patent @hfice 3,354,340 Patented Nov. 21, 1967 3 354 340 CAP-SHAPED CONTRUL ELECTRODE SECURING CATHODE BY THIN SUPPORTING MEMBERS Friedrich Hermann Raymund Aimer, Gerardus Servaas Marie Schrijnernakers, Adrianus Kuiper, and Alphonsus Petrus van Rooy, Emmasingel, Eindhoven, Netherlands, assiguors to North American Philips Company, Inc., New York, N.Y., a corporation of Delaware Filed Oct. 14, 1966, Ser. No. 591,367 Claims priority, application Netherlands, Gct. 22, 1965, 65-13,66S 14 Claims. (Cl. 313-82) ABSTRACT OF THE DISCLOSURE A quick heating narrow tolerance, easily manufactured electron source for a cathode-ray tube comprising a perforated, cap-shaped control electrode in which a cylindrical cathode having an emissive end surface is secured by a plurality of thin supporting members, a supporting cylinder, an annular insulating body, and an annular metal body which is secured to the cap-shaped control electrode.

This invention relates to an electron source for an electron gun, comprising a perforated, cap-shaped control electrode in which a cylindrical cathode having an emissive end surface is secured by means of a plurality of thin supporting members, a supporting cylinder, an insulating body in the form of a cylindrical ring, and an annular metal body which is secured to the control electrode. 7 Many constructions are already known in which a cathode is suppOrted in an insulating body by means of a plurality of thin supporting members in the form of narrow strips and a supporting cylinder, said insulating body being secured in a cap-shaped control electrode, possibly with the use of a supporting ring which can be moved within the control electrode for adjusting the correct distance between cathode and control electrode and is then secured to the control electrode. Frequent use is also made of parts expanding in opposite directions, resulting in the distance between cathode and control electrode being maintained constant independently of variations in the temperature of the cathode. However, these known constructions invariably have, in addition to cer tain advantages, in some respect one or more disadvantages.

A construction which is advantageous in every respect is obtained for such an electron gun comprising a perforated cap-shaped control electrode in which a cylindrical cathode having an emissive end surface is secured by means of a plurality of supporting members, a supporting cylinder, an insulating body in the form of a cylindrical ring, and an annular metal body which is secured to the control electrode if, according to the invention, the outer'cylindrical face of the insulating body is connected to the annular metal body and its inner cylindrical face is secured to the supporting cylinder by means of a substance fused thereon, the ends of the supporting cylinder projecting from the insulating body and the supporting members of the cathode being secured to the cathode support and to a flange provided on the end of the supporting cylinder adjacent the emissive surface of the cathode, while the annular metal body also being secured to a plurality of tongues recessed in the cylindrical wall of the control electrode.

The insulating body may advantageously comprise a body of prepressed glass which may be secured by fusion to both the supporting cylinder and the annular metal body. However, the connection to the metal ring is preferably obtained by pressure-welding. The same may be the case with an insulator made of crystallized glass or fusible ceramic material composed of, for example, a mixture of 50% by weight of A1 0 and 50% by weight of a mixture consisting of equal parts by weight of CaO and B203.

However, if the electron gun must be able to sustain a high degassing temperature, the insulating ring will have to be made of crystallized glass or ceramic material. The said construction affords the advantage that the cylindrical faces only of the ceramic insulator and hence not part of its upper and/ or lower surfaces must be metallized for soldering said faces to the supporting cylinder and the metal ring respectively. The end-faces of the insulating ring may be deprived of any metal deposited thereon by merely grinding it flat. A plurality of supporting rods for securing the heating body may be sealed or soldered in the insulating ring.

The invention will now be described with reference to the accompanying drawings, in which:

FIGURE 1 is a sectional view of one embodiment of an electron source according to the invention;

FIGURE 2 shows another embodiment of a cathode construction according to the invention;

FIGURE 3 shows another mode of connection of the insulator and the supporting cylinder, and

FIGURE 4 is a developed view of the material forming the control electrode.

In FIGURE 1, reference numeral 1 indicates the cathode Which is secured in a cap-like control electrode 2 by means of three thin supporting strips 3 welded to a flange 14 of a supporting cylinder 4. The supporting cylinder 4 is sealed in an insulating cylindrical ring 5, the cylindrical outer face of which is connected, by fusion or by so-called pressure-welding to an annular metal body 6, which, following the adjustment of the correct distance of cathode 1 relative to control electrode 2, is Welded to strips 7, recessed in a cylindrical side-wall 18 of control electrode 2. The said cathode-control electrode distance is preferably adjusted by adjusting the capacitance of cathode 1 relative to a first anode 21, as is known per se.

The shielding of the cathode relative to the first anode which is thus required is obtained by clamping the ring 6 on a welding electrode (not shown) which is formed as a hollow cylinder housing the insulated resilient member which may make contact with the lower end of supporting cylinder 4. The correct cathode to control electrode distance is adjusted by displacing the electron gun relative to the cathode 1. Subsequently the ring 6 is welded to the strips 7. Since the strips 7 are slightly resilient the distance between the cathode 1 and the control electrode 2 is prevented from being influenced during the welding operation.

The cathode 1 has a cap-like support, the emissive layer being present on the closed end surface. The support comprises a cathode cylinder 8 which serves as an envelope for a heating body 9. However, the cathode cylinder 8 does not serve as a structural element, since the supporting strips 3 of the cathode are Welded to the cathode support 4 itself. The cathode cylinder 8 may therefore be made of thin material so that the heat content may be small and a short heating-up time is obtained. This is especially true if the heating element is substantially concentrated adjacent the closed end of the cathode and hence near its emissive surface, in which event a very small wall thickness (even less than 25p) may be used since the heat conduction of the cylinder is then less important.

However, due to the small dimensions of the cathode a 1, it is in general impossible for the heating element to be arranged entirely within the cathode cap, although the construction of the heating element may be such that most of the heat is evolved close to the emissive layer.

Since the length of the cathode cylinder 8 has no function at all, in structural respect it may be varied so that different heating energies can be used. In fact, the cathode cylinder has the task not only to envelop the heating element, but also to reduce the heating-up time of the cathode, the cathode reaching its emission temperature when the heating element is concentrated in it, much sooner than the cylinder 8 which then receives its heat substantially through conduction from the cathode support 1. After the cathode is already emitting electrons the temperature of cylinder 8 increases so that the radiation towards the supporting cylinder 4 increases and hence the thermal losses increase and excessive heating of the cathode is avoided.

An even shorter heating-up time of the emissive layer may be obtained by reducing the length and hence the mass of the cathode support, as shown in FIGURE 2. However, the radiating surface thus becomes too small for preventing excessive heating of the cathode. This may be compensated for by blackening the outer surface of cathode cylinder 8 and possibly also of cathode support 1, so that eventually the same amount of energy is radiated. In this case, preferably the inner side of supporting cylinder 4 is also blackened.

In order to retard the thermal conduction from the cathode 1 to the cylinder 8, the cathode cylinder 8 within the supporting cap emerges into at least two, preferably three, narrow tongues the ends of which are secured by welding, at 20, inside the. cathode support 1 closely below the upper face thereof. Consequently, a larger part of the inner surface of cathode support 1 is radiated directly by the heating body 9, while the tongues of the cathode cylinder are also warmed up, resulting in the heat dissipation from the support 1 through the welding areas of said tongues to the part of cathode cylinder 8 projecting below the cathode being retarded. Thus, the emissive end surface of the cathode soon reaches the operating temperature.

The open end of the cathode support 1 is provided with a flange for obtaining greater rigidity. Furthermore, the supporting strips 3 of the cathode may be welded to the said cathode flange. It has been found that, if the angle made by the strips 3 with the surface of a flange 14 on supporting cylinder 4 is chosen suitably, also in connection with the coefficients of thermal expansion of the cathode support 1, the control electrode 2, the strips 3 and the supporting cylinder 4, not only the displacement of the emissive surface relative to the control electrode 2 can be maintained very small in a large range of different temperaturesfbut also the influence of the mechanical tolerances in the manufacture of these various parts exerted on the cathode-to-control electrode distance may, be reduced substantially to zero. The optimum angle will generally be comprised between and 60. The strips 3 must then be formed so that they can bend during the heating-up of the cathode and with strong variations in temperature, only near the points of bending adjacent the flanges to which they are secured. To this end, the strips are strengthened, between their points of bending by meansof impressed grooves or the like.

The strips 3 may alternatively have the form of thin rods depressed slightly at the points of bending in order to reduce the rigidity at these areas so thatbending during the expansion of the various component parts will occur in situ.

To reduce as far as possible the dissipation of heat from the cathode 1, through the supporting member 3 the latter are made of hard material, such as nickel-iron and nickel-iron-molybdenum compounds, so that they can be thin while having the required strength.

Since the cathode-to-control electrode distance in an electron source of the described composition remains substantially constant, the said distance may be made very small without the cathode being liable to contact the control electrode during the rapid and strong heating on de' gassing the electrodes in the cathode-ray tube.

The heat radiated by the cathode cylinder 8 is collected and reflected by the supporting cylinder 4 which reaches a comparatively high temperature. The cylinder 4 may consist of an alloy of a low coefficient of, expansion, such as fernico, which can be sealed in glass and is also a comparatively poor thermal conductor. Since the cylinder 4 contacts the insulating ring 5 only over a small part of its length, the dissipation of heat to the insulating material maybe small. If desired, the heat con duction may be reduced further by means of recesses in the annular inner surface of the insulator 5 so that it is not connected to the supporting cylinder 4 throughout its periphery, as shown in FIGURE 3. Due to the poor heat conduction of the material forming the cylinder 4, the end 15 thereof which projects from the insulator 5 assumes a high temperature owing to the heat radiation from the cathode 1, so that the supporting members 3 cause only a low thermal loss.

The supporting cylinder 4 also acts as a screen for metal vapour which might deposit from the cathode 1 and the cathode cylinder 8 onto the insulator 5. Furthermore, the supporting cylinder 4 ensures that during the final assembly, that is during all the remaining assembling operations on the electron gun after the ring 6 has been secured to the control electrode 2, the cathode cylinder 8 is not touched which would involve the risk that the adjustment of the cathode might be modified.

In the insulating ring 5 there are sealed or soldered two supporting rods 10 to which a fastening clasp 11 for the heating-wire ends of a heating element 9 is secured, the said fastening clasp being divided later by cutting away a portion 11. The clasp 11 substantially has the shape of an M the limbs of which become aligned with the supporting rods 10 so that the clasp 11 may be wholly enclosed in the above-described hollow welding electrode during the ca pacitive adjustment of the cathode-to-control electrode distance. After the electron source is mounted in an electron gun, the parts of the clasp 11 are welded through the tongues 12 to current-supply pins sealed in a base part. The tongues 12 may be bent over, if necessary, without the adjustment of the heating body in the cathode being influenced thereby. The supporting cylinder 4 is provided with a current supply conductor 13 for the cathode.

Since the insulating body 5 is connected to the supporting cylinder 4 by using a fused substance, the thermal contact obtained is reproducible so that little differences in the temperatures of different cathodes occur. This is also the case if the insulating part 5 is made of ceramic material since the connection to the metal cylinder 4 is then obtained :by soldering. Also, the dissipation of heat from the insulating body 5 through a pressure weld to the annular body 6 is satisfactorily reproducible.

The control electrode 2 may be manufactured in a very simple manner from a metal plate shaped into the form shown in FIGURE 4. When this plate is pushed through a cylindrical template, a cap-shaped electrode results having its cylindrical side-wall formed by parts 18 and the tongues 7.

The invention providesan electron source for an electron gun which may have a very small working distance between cathode and control electrode, which has a very stable operation independent of variations in temperature, which is mechanically rigid and resistant to shocks, which has a very low tendency to cause microphonic interference and which can be manufactured in a very simple manner and at low cost since mechanical tolerances exert only small influence on the adjustment.

What is claimed is:

1. An electron source for an electron gun, comprising a perforated, cap-shaped control electrode in which a cylindrical cathode having an emissive end surface is secured by means of a plurality of thin supporting members, a supporting cylinder, an insulating body in the form of a cylindrical ring, and an annular metal body which is secured to the control electrode, characterized in that the outer cylindrical face of the insulating body is connected to the annular metal body and its inner cylindrical face is secured to the supporting cylinder by means of a substance fused thereon, the ends of the supporting cylinder projecting from the insulating body and the supporting members of the cathode being secured to the cathode support and to a flange provided on the end of the supporting cylinder adjacent the emissive surface of the cathode, while the annular metal body being secured to a plurality of tongues recessed in the cylindrical Wall of the control electrode.

2. An electron source as claimed in claim 1, characterized in that the insulating body consists of glass and is fused at least with the supporting cylinder and connected to the annular metallic body.

3. An electron source as claimed in claim 1 characterized in that the insulating body consists of crystallized glass.

4. An electron source as claimed in claim 1, characterized in that the insulating body consists of fusible ceramic material and is fused at least with the supporting cylinder and connected to the annular metallic body.

5. An electron source as claimed in claim 4, characterized in that the insulating body is of ceramic material, its cylindrical side faces being metallized and connected by means of solder to the supporting cylinder.

6. An electron source as claimed in claim 1 characterized in that the inner annular surface of the insulating body is provided with recesses, so that the said surface is secured to he supporting cylinder only over part of the periphery thereof.

7. An electron source as claimed in claim 1 characterized in that a plurality of supporting rods for the ends of the heating wire are secured in the insulating body.

8. An electron source as claimed in claim 7, characterized in that the heating body is connected to the sup- 6 porting rods by means of an initially M-shaped clasp the limbs of which are aligned with the supporting rods, the clasp being divided into two parts by removal of its central piece.

9. An electron source as claimed in claim 1 characterized in that the two ends of the supporting cylinder project from the insulating body, the end of the supporting cylinder adjacent the emissive surface of the cathode being provided with a flange to which the ends of the supporting members of the cathode are welded.

10. An electron source as claimed in claim 1 characterized in that the supporting members of the cathode are secured to a flange on the open end of the cap-shaped cathode support itself.

11. An electron source as claimed in claim 1 characterized in that the cathode cylinder inside the cap-shaped cathode support merges into at least two tongues the ends of which are welded to the inner surface of the said sup port, the heating element being concentrated substantially near the closed end of the cathode.

12. An electron source as claimed in claim 1 characterized in that the wall thickness of the cathode cylinder is less than 25 1, the heating element being concentrated substantially near the closed end of the cathode.

13. An electron source as claimed in claim 1 characterized in that at least one of the outer surfaces of the cathode cylinder, of the cathode support and the inner surface of the supporting cylinder are blackened.

14. An electron source as claimed in claim 1 characterized in that the annular metallic :body is welded to tongues formed in the cylindrical side-wall of the cupshaped control electrode.

References Cited UNITED STATES PATENTS 2,833,952 5/1958 Hemphill et al. 313-82 X 3,155,865 11/1964 Ney 31382 X ROBERT SEGAL, Primary Examiner.

Claims

1. AN ELECTRON SOURCE FOR AN ELECTRON GUN, COMPRISING A PERFORATED, CAP-SHAPED CONTROL ELECTRODE IN WHICH A CYLINDRICAL CATHODE HAVING AN EMISSIVE END SURFACE IS SECURED BY MEANS OF A PLURALITY OF THIN SUPPORTING MEMBERS, A SUPPORTING CYLINDER, AN INSULATING BODY IN THE FROM OF A CYLINDRICAL RING, AND AN ANNULAR METAL BODY WHICH IS SECURED TO THE CONTROL ELECTRODE, CHARACTERIZED IN THAT THE OUTER CYLINDRICAL FACE OF THE INSULATING BODY IS CONNECTED TO THE ANNULAR METAL BODY AND ITS INNER CYLINDRICAL FACE IS SECURED TO THE SUPPORTING CYLINDER BY MEANS OF A SUBSTANCE FUSED THEREON, THE ENDS OF THE SUPPORTING MEMBERS ING FROM THE INSULATING BODY AND THE SUPPORTING CYLINDER OF THE CAHTODE BEING SECURED TO THE CATHODE SUPPORT AND TO A FLANGE PROVIDED ON THE END OF THE SUPPORTING CYLINDER ADJACENT THE EMISSIVE SURFACE OF THE CATHODE, WHILE THE ANNULAR METAL BODY BEING SECURED TO A PLURALITY OF TONGUES RECESSED IN THE CYLINDRICAL WALL OF THE CONTROL ELECTRODE.