EP0367652A1 - Electronic tube with a compact construction, and its manufacturing process - Google Patents

Abstract

The invention relates to electron tubes. <??>A tube such as a cathode-ray tube is composed of several parts, namely the stem, the neck, the cone, and the front-face glass. <??>In order to construct such a tube in a more compact manner whilst improving the manufacturing quality, a new construction for the neck is proposed: in the prior art, the neck is a glass tube to which is fused a glass stem through which the connecting terminals pass axially towards the various electrodes inside the tube; here, the neck is constructed in the form of an alternating stack of metal rings and ceramic rings. The metal rings (60, 80, 100, 110) serve as support and electrical connection for the internal electrodes (G1, G2, G3). The ceramic rings (30, 70, 90) serving the insulating of the metal rings. The seams between metal rings and ceramic rings ensure vacuum sealing. The base of the tube is a ceramic disc without perforations other than lateral ones for the passage of connections. The connections are taken principally around the neck on the metal rings. <IMAGE>

Description

The invention relates to electronic tubes.

To better understand the invention, we will describe more precisely its application to a cathode ray tube, that is to say a tube comprising on the one hand an electron gun producing an electron beam and on the other hand a screen luminescent reacting to the impact of the beam to produce a bright image.

A cathode ray tube is generally formed of a glass bulb in which the various organs (and in particular the various electrodes) have been placed allowing the tube to function; a high vacuum is then established in the bulb.

The glass bulb consists of four different main parts which are respectively:
- the lens or front face of the tube, constituting the luminescent screen on which the electron beam is directed;
- the cone, in which the electron beam moves; the wide part of the cone ends on the front face; the narrow part is connected to the neck of the bulb;
- the neck, which is a glass tube of small diameter compared to the dimensions of the front face; in the cone are placed mainly the electron gun with the beam focusing electrodes; coils of angular deflection of the beam are placed around the neck;
- the foot, which is in practice a terminal glass plate closing the neck on the side opposite the tube; this plate is crossed by connection terminals allowing the electrical connection between each of the electrodes inside the tube and the outside; the bushings are vacuum tight; the base generally has a stopper for vacuuming by pumping.

The foot, after assembly of the internal organs of the tube, is welded to the neck by a glass / glass weld, that is to say by fusion of the foot glass and the neck glass, using a torch .

In the prior art, the electrodes of the electron gun are supported by metal pins embedded in glass bars extending in the neck, at the periphery thereof, in a direction parallel to the axis of the neck. The metal pins are pressed into the glass bars by prior heating of these bars to a temperature which makes the glass pasty. These pins are also welded to the periphery of the electrodes which they must support.

The different potentials necessary for the operation of the electrodes are brought either by the connection terminals of the foot, or, for certain electrodes, by springs in contact indirectly (via a layer of graphite deposited on the inside wall of the neck and cone) with the front of the bulb.

Other springs are provided to ensure the centering of the barrel in the neck, its maintenance, and its resistance to vibrations.

On the left side of Figure 1, there is shown such a conventional arrangement of cathode ray tube; only the foot (bottom of the figure) and the neck have been shown; the cone and the front face are not shown; they would extend to the top of the figure.

The foot is designated by the reference 10, the neck by the reference 12, the weld between the foot and the neck by 14, connection terminals through the foot by 16, interior glass bars by 18, support pins electrodes by 20, electrodes by G1, G2, G3, G4, the pumping line by 22.

Note that the right part of Figure 1 does not represent the prior art but the invention.

Furthermore, elements external to the tube have not been shown, such as the electromagnetic coils used for the deflection of the electron beam; these coils surround the neck so as to act on the path of the electrons between the electron gun and the end of the neck.

An object of the invention is to produce less bulky electronic tubes in the width and / or length direction.

Another object is to produce tubes in which the energy consumption of the deflection coils is minimized.

Another object of the invention is to maximize the diameter of the electrostatic focusing electrodes in the space allocated inside the neck, in order to minimize spherical aberrations.

Another object is to improve the general robustness of the tube.

Yet another object is to minimize the risks of production of solid particles inside the tube during manufacture or during operation, these particles being able to deteriorate the quality of operation of the tube (the quality of the image for example).

Finally, an aim is to avoid any chemical pollution of certain sensitive organs, such as the screen of the tube or the cathode of the electron gun, by products such as water vapor or other elements resulting from the combustion in a torch used to weld or heat certain parts of the tube.

To achieve these goals, the invention provides an electronic tube comprising a neck, at least part of which consists of a stack of metal support rings and ceramic rings, the metal rings serving as a support and electrical connection to the various internal electrodes. of the tube, the ceramic rings used for electrical isolation and for the physical separation of the metal rings. The metal rings are brazed on the ceramic rings to ensure vacuum tightness and they have an internal part to the tube to serve as a support for an electrode (separate from the ring) and an external part for the electrical connection to the outside.

The electrodes are welded by metal-to-metal welding (electrical or laser welding, without pollution) on the metal rings which serve as their support and connection. This welding takes place after the ceramic-metal brazing, which is polluting; in this way, the cathode (in particular) is not affected by the soldering operations.

The base of the tube is preferably formed by a ceramic washer, and does not have holes in the axis of the tube to ensure the electrical connection with the electrodes of the tube. It only has lateral holes for passing cathode and cathode heating filament connections; the external connections with the other electrodes are taken directly at the periphery of the neck by contact with the metal rings.

Preferably, for holding and connecting an electrode in the form of a cylindrical ring, provision is made for one of the metal support rings to have on the one hand a cylindrical part coaxial with the axis of the neck, the inner surface of which is welded to the cylindrical outer surface of the electrode, and on the other hand a planar annular part extending in a plane perpendicular to the axis of the neck and concentric therewith, the planar annular part extending from the part cylindrical axial to the outside of the neck, and being brazed on a flat annular surface of a ceramic ring.

This arrangement makes it possible in particular to facilitate the adjustment of the position of the electrodes at the time of manufacture of the tube: according to requirements, it is possible to slide such and such an electrode in the direction of the axis of the tube to weld it in a place which may vary depending on the performance requested from the tube.

In an exemplary embodiment, the stack of rings is as follows: the base of the tube is a ceramic washer in the form of a bowl, the concavity of which faces the front of the tube, and the bottom of which constitutes the rear end of the tube; a first metal ring supporting a first grid of the tube and serving for its connection with the outside is brazed on the edges of the ceramic washer; another ceramic ring insulates the first metal ring from a second one which serves to support and connect a second grid (of acceleration) of the tube; another ceramic ring is used for insulation between the second metal ring and a third metal ring used to support and connect to the outside of a third grid (focusing) of the tube; finally, the third metal ring is welded by a glass-metal weld to the glass parts of the tube. Pumping is done by a pipe in a glass part of the tube (on the cone).

The entire neck, thus produced by superimposing metal rings and ceramic rings, is vacuum tight thanks to
- ceramic-metal solders between the rings;
- metal-to-metal welds between different metal parts when a ring is produced by assembling several metal parts;
- the glass-to-metal welds that remain, namely practically only at the junction between the last metal ring of the stack and the glass parts of the tube.

The manufacturing process includes the following operations: making a stack of ceramic rings brazed to metal rings interposed between these ceramic rings, then electrically or laser welding of electrodes on the rings of the stack.

Preferably, the process takes place according to the following operations:
- Producing a first assembly comprising at least one ceramic ring brazed to a metal ring;
- produce a second set comprising a stack of ceramic rings brazed to metal rings interposed between these ceramic rings,
- mount a cathode in the first set, and weld at least one grid by electrical or laser welding, on a metal ring of the second set,
- weld by an electric or laser weld a metal ring of the first set to a metal ring of the second set to secure in a vacuum-tight manner the two sets carrying the cathode and the grid respectively.

• - la figure 1 représente sur sa partie gauche un tube à rayons cathodiques de la technique antérieure et sur sa partie droite un tube selon l'invention;
• - la figure 2 représente en vue agrandie le détail de la construction du pied et du col du tube selon l'invention.

Other characteristics and advantages of the invention will appear on reading the detailed description which follows and which is given with reference to the appended drawings in which:

• - Figure 1 shows on its left side a cathode ray tube of the prior art and on its right side a tube according to the invention;
• - Figure 2 shows in enlarged view the detail of the construction of the foot and the neck of the tube according to the invention.

Figure 1 will not be described in more detail: it is a combined representation of both a cathode ray tube according to the prior art and a tube according to the invention; these two tubes are essentially circularly symmetrical around the vertical axis represented by a dashed line in the center of the figure, but the part to the left of the axis represents the tube of the prior art while the part to the right of the axis represents a tube according to the invention; with regard to the left part of the figure (prior art), it has already been described with its drawbacks; the right-hand side shows the construction according to the invention on the same scale, so that the advantages obtained can be measured from the point of view of the overall width and length; the improvement is considerable. We will return later to the various advantages resulting from this reduced size.

The references to the main elements which will now be described in detail with reference to FIG. 2 have been recalled on the right side of FIG. 1.

In Figure 2, we see the detail of the construction according to the invention, in a particular example of application which is a cathode ray tube having a cathode, three grids brought to different potentials in front of the electron gun, a fourth electrode constituted by a layer of graphite deposited inside the neck and the cone of the tube, and an anode constituted by a display screen on the front face of the tube.

As in Figure 1, only the base and the neck of the tube are shown but not the cone or the front face.

Figure 2 shows only the right half of the tube, but it should be understood that (similarly, moreover than in Figure 1) the tube is symmetrical about the axis represented by a dashed line.

The base of the tube is a solid ceramic washer 30, cup-shaped, the flat bottom of which constitutes the rear face of the tube and the concavity of which faces the front of the tube. The rear face or bottom 35 of the washer 30 is not pierced with passages for electrode connections with the outside; but the side edges 50 are pierced with passages 52 for the connection of the cathode and the cathode heating filament.

To facilitate understanding of the shape of this washer 30, it is shown in perspective cut in Figure 2 next to the corresponding sectional view.

In the main sectional view of FIG. 2, we see a cathode connection 42 which connects a cathode 44 to an external terminal 46. Similar connections, not visible in the section in FIG. 2 connect a heating filament to terminals external to the tube, through the lateral holes 52 of the edges of the washer 30.

The ceramic used for all the parts of the tube will in principle be sintered alumina.

In general, the metal rings which must be brazed on the ceramic are made of stainless steel, the thermal expansion characteristics of which are adapted to those ceramics; such stainless steels are well known and commonly used when parts combining metal and ceramic are required.

In all that follows, we will speak of the rear face for a face facing the side of the tube base, and of the front face for a face facing the side of the screen of the tube (i.e. looking in the direction of movement of the electron beam emitted by the electron gun).

A metal ring for supporting the control grid, generally designated by the reference 60, is brazed on the front face of the ceramic washer 30. This ring is intended to support a control grid G1, placed in the immediate vicinity of the cathode and to be brought to a potential different from that of the cathode.

For reasons related to the ease of manufacture, taking into account that the grid G1 must be kept very close to the cathode, the support ring 60 of the control grid G1 is made in three parts (in this example), and we will explain later how these parts are in fact assembled together at different times in the overall assembly of the electron gun.

The first part of the ring 60 is a ring 62 having an annular planar part brazed on the front face of the edges 50 of the ceramic washer 30, and a cylindrical part 63, surrounding the planar part on the side radially outside that -this. We will see that this part is a constituent of the cathode filament assembly, and that it is only late welded to the rest of the barrel.

The second part of the metal ring 60 is a ring 64 having on the one hand a cylindrical part surrounding the cylindrical part of the part 62 and welded thereto (when the barrel is finished), and on the other hand a flat part annular 66, extending radially inside the cylindrical part.

The third part is a metal spacer 68 welded to the rear of the planar annular part 66; the grid G1 is welded to this spacer 68.

The electrical connection of the grid G1 to the outside is made by the external surface of the part 64.

A ceramic ring 70, having two planar annular faces, is brazed by its rear face on the front face of the annular part 66 of the part 64.

The tightness of the passage of the control grid connection G1 to the outside is ensured by the brazing of the part 62 on the edges 50 of the ceramic washer 30, by the brazing of the part 64 on the ceramic 70, and by a sealed weld (preferably a continuous laser weld) between the parts 62 and 64 of the ring 60.

A second metal ring 80 serves as a support and electrical connection for an acceleration grid G2.

The grid G2 is a ring-shaped grid having an outer cylindrical wall 82 welded peripherally to a corresponding inner wall 84 of the ring 80.

The metal ring 80 preferably has a U-shaped section facing the outside of the tube, the bottom of the U constituting the inner wall welded to the grid G2, a side wall of the U being brazed on the front face of the annular ceramic 70; the other side wall of the U is brazed on a final annular ceramic ring 90.

The electrical connection of the grid G2 to the outside of the tube is taken on the ring 80, outside of the latter.

The tightness of the passage of this connection from the inside to the outside is ensured on one side by the solder with the ceramic ring 70 and on the other side by the solder with the ceramic ring 90.

The ceramic ring 90 is similar to the ring 70 and the ring 50; it has two flat annular faces, the rear face being brazed on the metal ring 80 and the front face being brazed onto a metal ring 100 for the support and electrical connection of a focusing grid G3.

The G3 grid is similar to the G2 grid and placed in front of it. It has the shape of a ring with a cylindrical wall 102 whose outer surface is welded to the corresponding inner surface of a cylindrical wall 104 which constitutes a part of the ring 100.

The ring 100 comprises, in addition to this cylindrical wall 104, a planar annular part 106 extending radially towards the outside of the tube. It is this annular part 106 which is brazed by its rear face to the front face of the last ceramic ring 90.

On the front face of the planar annular part 106 of the ring 100 is welded another metal ring 110, by a sealed weld, for example a continuous laser weld (made at the end of manufacture). The ring 110 comprises a planar annular part 112 welded on the front face of the ring 100, and a cylindrical wall 114. The end of the cylindrical wall 114 is welded, by a glass-metal weld, to a portion of casing 120 glass of the tube. This portion extends forward the alternating stack of ceramic and metal rings which constitutes the main body of the neck of the tube according to the invention.

The seal at the level of the passage of the focusing grid connection G3 is therefore constituted by the ceramic-metal solder between the ring 100 and the ceramic 90, by the sealed weld between the rings 100 and 110, and finally by the glass weld. -metal between the part 110 and the glass tube 120.

The part 110 is made of stainless steel chosen for its compatibility with a glass-to-metal weld; suitable stainless steels are well known and widely used in this field.

The neck of the electronic tube according to the invention therefore consists of the association between a portion of glass envelope and the stack of metal rings and ceramic rings which has just been described.

Note in Figure 2 that a graphite layer 122 has been shown on the inner wall of the tube 120, this layer constituting another part (G4) of the focusing electrode.

The pumping of the tube is done by a pipe not shown, located on the glass tube 120 in the cone not shown.

The tube is preferably produced as follows: the following elements of the alternating stack of metal rings and ceramic rings are assembled by welding and brazing: ring 100, ring 90, ring 80, ring 70, parts 64 and 68 of the ring 60.

The grid G2 is then welded to the ring 80 (and there, the distance between the grid G2 and the grid G1 can be adjusted as desired by sliding the grid along the cylindrical part 84 of the ring 80).

The grid G3 is then welded to the cylindrical wall of the ring 100, and here again the distance between the grids G2 and G3 can be adjusted by sliding the grid G3 to the desired height.

Finally, the grid G1 is welded to part 68.

The rear part of the tube is also prepared: brazing of the first part 62 of the metal ring 60 on the ceramic washer 30, passage of the connections and fixing in place of the assembly of the cathode 44 and the heating filament.

The parts 62 and 64 of the ring 60 are welded together by a peripheral laser weld, thus joining the two parts of the stack.

On the other hand, the front part of the tube is prepared: cone terminated at the front by a screen and terminated at the rear by the start of a glass neck 120 (a pumping pipe being formed in the cone), getter at inside the cone. The part 114 of the ring 110 is welded by a glass-to-metal weld on the rear end of the glass neck 120; then the screen is fixed to the front of the cone; finally, we weld together by a peripheral laser weld the metal ring 110 terminating at the rear the cone of glass and the metal ring 100 terminating at the front the complete assembly of the electron gun with all its electrodes.

Compared to the tubes of the prior art, it can be seen that all the glass bars and the metal pins inserted in these bars have been eliminated. The gain in diameter of the tube is significant; this is all the more true since the bars are generally thick enough so that they are not weakened by the pins.

As the energy required to supply the electromagnetic deflection coils (located around the neck of the tube) is greater the larger the diameter, we therefore gain not only in terms of size but simultaneously also in consumption of the tube.

The base of the tube no longer includes passages other than lateral for the connection terminals; it is only made up of a ceramic disc; so we save a lot on the overall dimensions, which is important in certain applications (example: head-up displays for helicopters).

The construction is robust, all the centering and holding springs which are no longer necessary have been eliminated; the vibration resistance of this assembly is very good, the elements all being integral with each other.

The whole of the electron gun (cathode and different electrodes), mounted on its protective envelope constituted by the stack of alternating rings of ceramic and metal, is assembled with the glass tube not by welding with a torch (glass on glass) as in the prior art, but by laser welding between the metal rings 100 and 110. As a result, no particles are created in the tube at the time of assembly, whereas in the past the welding the foot to the neck created glass particles in the tube.

The tube according to the invention also avoids the production in the tube of graphite particles due to the friction of springs, during assembly, on the graphite layer constituting the G4 electrode.

Finally, the risks of pollution of the cathode or of the screen which existed in the prior art during the welding operation of the foot on the neck are avoided, this pollution coming from water vapor and other products of combustion of the welding torch. In the tube according to the invention, the welding or brazing operations at high temperature are carried out without the presence of the cathode or the screen of the tube, and the final assembly, when the cathode and the screen are present, can be done at a temperature which is practically room temperature (laser welding).

Thanks to the invention, the following performances can be obtained by way of example:
- useful diameter 65 mm
- neck diameter 14 mm
- length 93 mm
- luminance of the trace 65,000 candelas / m2 for a spot diameter less than 0.2mm
- beam deflection energy 300 microjoules

Claims (10)

1. Electronic tube characterized in that it comprises a neck, at least part of which consists of a stack of metal support rings (60, 80, 100, 110) and ceramic rings (30, 70, 90), the metal rings serving as support and electrical connection to internal electrodes of the tube (G1, G2, G3) distinct from these rings, the ceramic rings serving for the electrical isolation and for the physical separation of the metal rings. 2. Electronic tube according to claim 1, characterized in that the metal rings are brazed on the ceramic rings to ensure vacuum tightness and they have an internal part to the tube to serve as support for an electrode and an external part to serve to the electrical connection to the outside. 3. Tube according to one of the preceding claims, characterized in that the electrodes are welded to the rings by an electric weld or a laser weld. 4. Electronic tube according to one of claims 1 to 3, characterized in that it comprises a base constituted by a ceramic washer (30) without axial holes for ensuring the electrical connection with the electrodes of the tube, the external connections being taken directly at the periphery of the neck by contact with the metal rings. 5. Electronic tube according to claim 4, characterized in that the ceramic washer (30) is cup-shaped, the concavity of which faces the front of the tube, the bottom (35) constituting the rear end of the tube, and the edges lateral (50) being provided with lateral holes (52) for the passage of connections (46). 6. Electronic tube according to one of claims 1 to 5, characterized in that, to ensure the maintenance and connection of an electrode in the form of a cylindrical ring, provision is made for one of the metal support rings (80, 100 ) has on the one hand a cylindrical part (84, 104) coaxial with the axis of the neck, the inner surface of which is welded to the cylindrical outer surface of the electrode, and on the other hand a planar annular part extending in a plane perpendicular to and concentric with the neck axis, the planar annular part extending from the axial cylindrical part to the outside of the neck, and being brazed on a planar annular surface of a ring ceramic (70, 90). 7. Electronic tube according to one of claims 1 to 6, characterized in that the stack of rings is as follows: the tube comprises a base constituted by a ceramic washer (30) in the form of a bowl; a first metal ring (60) supporting a first grid (G1) of the tube and serving for its connection with the outside is brazed on this disc; a ceramic ring (70) brazed on the first metal ring separates the latter from a second metal ring (80); the second metal ring is used to support and connect a second grid (G2) of the tube; another ceramic ring (90) isolates the second metal ring from a third (100) which serves to support and connect a third grid (G3) of the tube; finally, the third metal ring is welded by a glass-metal weld to the glass parts of the tube. 8. Tube according to one of the preceding claims, characterized in that certain metal rings (60) are consisting of an assembly of several parts (62, 64, 68) welded together. 9. A method of manufacturing an electronic tube, characterized in that it comprises the following operations:
make a stack of ceramic rings brazed to metal rings interposed between these ceramic rings, then electrically or laser weld electrodes on the rings of the stack. 10. The manufacturing method according to claim 9, characterized in that it comprises the following operations:
- Producing a first assembly comprising at least one ceramic ring brazed to a metal ring;
- produce a second set comprising a stack of ceramic rings brazed to metal rings interposed between these ceramic rings,
- mount a cathode in the first set, and weld at least one grid by electrical or laser welding, on a metal ring of the second set,
- weld by an electric or laser weld a metal ring of the first set to a metal ring of the second set to secure in a vacuum-tight manner the two sets carrying the cathode and the grid respectively.

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