US2854599A - Beam type electron tube - Google Patents

Description

Sept 30, 1958 v D. H. PREIST 2,854,599

BEAM TYPE ELECTRON TUBE Fil ed Sept. 50, 1955 Tuss was I CATHODE ILL 5.4-

INVENTOR. Donald H. Prue/'57 ATTORNE Y United States Patent BEAM rvrn ELECTRON TUBE Donald H. Preist, Mill Valley, Calif., assignor to Eitel- McCullough, Inc., San Bruno, Califl, a corporation of California Application September. 30, 1955, Serial No. 537,707

12 Claims. (Cl. 31381) This invention relates to electron tubes and more particularly to an improved tube construction which overcomes many of the limitations found in conventional tubes having grids. I

Tubes with grids interposed between a Cathode and anode have many disadvantages, including such serious things as grid heating and grid emission, which come about because the grids are immersed in the electron stream. Such gridded tubes also fail in many higher' Another object is to provide a focusing electrode as sociated with the cathode to form a structure for focusing the electrons into the desired radial beam formation.

Still another object is to provide an electrode structure between the focusing electrode and anode for con-.

trolling how of electrons in the beam without danger of intercepting the electrons.

The latter object is efiectively accomplished by a control electrode structure which cooperates with the focusing electrode to form an electrostatic field, preventing electrons from impinging on-the control electrode.

Further objects include the provision of adequate electrode support and shielding means, and an improved terminal arrangement on the tube envelope.

Accomplishment of the above objects provides an electron tube having many uses, such as a switch tube, control tube, amplifier or modulator. The improved tube is characterized by improved performance in such services and especially in high voltage applications.

The invention possesses other objects and features of advantage, some of which, with the foregoing, will be set forth in the following description of the invention. It is to be understood that the invention is not limited to the disclosed species, as variant embodiments thereof. are contemplated and may be adopted within the scope of the claims.

Referring to the drawings:

Figure 1 is a diagrammatic view disclosing the principal features of the invention as represented by a radial section through the electrodes and showing in dotted lines the shape of the electron beam.

Figure 2 is a vertical sectional view takenon the center line of a complete tube embodying the improvements of the invention.

Figure 3 is a horizontal sectional view taken on the line 33 in Figure 2; and

Figure 4 is a vertical sectional view of a portion of the tube envelope showing a modified arrangement incorporating an external apede.

2,854,599 Patented Sept. 30, 1958 See Referring in more detail to Figure 1, it will be seen that the principal features of the invention may be represented by a cathode disposed about the vertical tube axis, a focusing electrode positionedadjacent the, cathode, a control electrode positioned outwardly ofthe focusing electrode, and an anode positioned outwardly of the control electrode. For reference purposes, an intermediate plane is considered as passing through the tube axis between the ends of the tube at the location of the various electrodes.

The focusing electrode, which comprises a pair of vertically spaced annular plates adjacent the cathode, serves to direct or focus electrons from the cathode in a substantially fiat radial beam along the intermediate plane. The control electrode, which comprises'a second pair of vertically spaced annular plates, cooper'ates with the focusing electrode to form an electrostatic field which prevents electrons from impinging on the control electrode and results in a beam having a shape such as is represented in Figure 1 by the dotted lines which delineate the upper and lower surfaces of the beam. Since the electrons from the cathode arethus prevented from striking the control electrode, there will be no current to the control electrode and no harmful emission which would occur if electrons from the cathode were allowed to strike the control electrode. Thus the problems of grid heating and grid emission which limit the use of tubes having grids are avoided by this'invention.

Normally the focusing electrode is operated at zero voltage-with respect to the cathode, in other words, at cathode potential. Under these conditions the electrode presents a retarding field to the electrons and hence tends to withhold the flow of electrons at the region of the cathode. 1

Normally the anode is operated at positive voltage with respect to the cathode. However, as long as the control electrode is without positive voltage relative to the cathode, the shielding action of the control eleo trgde prevents electrons from flowing from the cathode (p the, anode. Thus, even with anode voltage applied} beam is cut off when the control electrode is at'c'atliode potential.

When positive voltage is applied to the control electrode with respect to the cathode, the accelerating field thereby produced causes electrons to flow from the cathode to the anode, the amount of current flowing depending upon the voltage on the control electrode.

The tube thus operates in a very simple manner from cut oif to full anode current, with sharp cut olfcharacteristics which make the tube particularly useful for high voltage switch service. Since the beam is radial, a

large amount of current can be handled in the beam.

As previously explained, the focusing electrode is normally operated at cathode potentiaL' Thus, it will be appreciated that no negative bias on the focusing electrode is required for operation of the tube. However, it should be understood that the focusing electrode canbe operated at a negative potential with r'espect to the cathode. As a matter of fact, operating the focusing'electrode at negative potential will reduce the current flow through the tube. This fact makes it possible to obtain additional modulation of the electron beam by varying the'potential on the focusing electrode.

Referring now to the complete tube shown in Figures 2 and 3, it will be seen that the tube comprises a cathode indicated generally at 5, a focusing electrode indicated at 6, a control electrode indicated at 7, and an anode indicated at 8;

The cathode 5 is preferably of the type comprising a heater and-an oxide-coated emitting surface. In the arrangement shown in the drawing, the cathode 5 comprises 3 a cylindrical emitting ring connected between upper and lower metal plates 11 and 12, respectively. The cathode is supported by means of a cylindrical metal skirt14, which is connected to the lower plate 12 and is advantageously extended out of the tube envelope to provide a terminal for the cathode. A heater for the cathode is provided in the form of a wire coil 15, which is separated from the cathode ring 10 by means of the insulating material 16. The upper end of wire is connected to the upper cathode plate 11, so that cathode skirt 14 serves as a terminal for the heater as well as the cathode. The lower end of wire 15 is passed downwardly through an insulating plug 18 in the lower cathode plate 12 to a met al heater pin 19. Pin 19 is concentrically positioned within the cathode skirt 14 and is separated therefrom by an annular plug seal 20 of insulating material. The metal parts of the cathode, as well as the various other metal parts hereinafter referred to, are preferably made of material having good electrical conductivity.

- The focusing electrode 6 comprises a pair of vertically spaced annular plates 22 and 23 madeof metal and positioned adjacent the opposite ends of the emitting ring 10. A tubular support portion 24 of metal extends downwardly from the lower annular plate 22 and is extended outwardly of the tube envelope to form a terminal for the focusing electrode. A dish-shaped cap portion 25 of metal extends upwardly over the upper annular plate 23. It will be seen that the tubular support portion 24 concentrically surrounds cathode skirt 14 and is separated therefrom by an annular plug seal 26 of insulating material. Means for connecting the annular plates 22 and 23 are provided in the form of one or more vertical ribs such as the metal pins 27 shown in Figure 3.

The control electrode 7 comprises a pair of vertically spaced annular plates 30 and 31 made of metal and positioned outwardly of the focusing electrode plates 22 and 23. A tubular support portion 32 of metal extends upwardly from the upper annular plate 31 to the top of the tube, where it is brazed to a terminal plug 33. Since the tube is designed for high voltage use, it is desirable to braze a corona ring 34 on plug 33 to prevent external arcing. A tubular skirt portion 35 of metal extends downwardly from the lower annular plate 30. Means for connecting the annular plates 30 and 31 are provided in the form of one or more vertical ribs such as the metal pins 36 shown in Figure 3.

The anode 8 comprises a pair of metal rings 38 and 39 brazed or otherwise connected together at theirouter ends and shaped to provide an anode having an annular V-shaped recess indicated at 40 -and opening toward the cathode. The reason for the recessed anode is to trap 'within the anode the electrons it emits as a result of bombardment by the electron stream, so that the electrons emitted by the anode will not travel to the highly positive controlelectrode 7. The anode rings 38 and 39 are supported by an annular metal disk 42, which is brazed or otherwise secured to the upper anode ring 39 and clamped between the metal sealing rings 43 and 44 which arewelded together at their outer ends and form the anode terminal. When the tube is used for high voltage operation, there is a possibility of internal arcing between the anode and the control electrode, particularly when the latter is oil during switch service. In order to lessen this possibility of arcing, the outer edges of flanges 30 and 31 and the inner edges of rings 38 and 39 are preferably rounded as shown in Figure 2.

The envelope for the tube comprises a lower dish 4 of insulating material, with the sealing ring .44 sealed in its lower rim. The upper portion of section 49 has a hole therein to permit passage of the terminal plug 33, and a sealing ring 50 is sealed in the rim of said hole and brazed or otherwise secured to plug 33.

By arranging the terminal ,for anode 8 about the circumference of the envelope and the control and focusing electrode terminals 33 and 24 at opposite ends of the envelope, a maximum amount of spacing and insulating 'path is provided between the terminals, which is desirable for high voltage operation.

It is desirable to shield the cathode from the control electrode and anode, except in the line of the radial beam, to prevent stray fields from disturbing the beam-forming field established by the focusing and control electrodes. This is one of the reasons for providing the long tubular portion 24 and the complete cap portion 25 on the annular plates 22 and 23 of the focusing electrode 6. Similarly, one of the reasons for providing the long tubular portions 32 and 35 on the annular plates 31 and 30 of the control electrode is to shield the anode from the cathode and focusing electrode. In addition, the tubular portions 24, 32, and 35 and the cap portion 25 serve to prevent bombardment of the envelope by stray electrons which could cause rupture of the insulating material, this being particularly troublesome in tubes working at high voltages. Another purpose for these portions, at least in the area adjacent their respective annular plates 22, 23, 30 and 31, is to cooperate with the annular plates in establishing the desired beam-forming field.

Figure 4 discloses a modified form of the invention in which the anode 8' projects outwardly of the tube envelope and may be more easily cooled. If it is desired to maintain the electrode sizes and spacing of Figure 2 in the external anode version of Figure 4, the diameters of envelope sections 47' and 49' can simply be made less than the diameters of sections 47 and 49 in Figure 2. In somewhat similar manner to that shown in Figure 2, the anode plates 38' and'39 in Figure 4 are connected to the envelope sections 47 and 49 by means of the sealing rings 43' and 44, respectively.

Having thus described the invention, what is claimed as new and desired to be secured by Letters Patent is:

1. An electron tube having an axis intersecting an intermediate plane, a cylindrical cathode about said axis, a focusing electrode adjacent the cathode and comprising a pair of annular plates focusing electrons from said cathode in a substantially flat radial beam along the intermediate plane, an anode encircling the cathode collecting electrons from the beam, and a control electrode interposed between the focusing electrode and anode and comprising a second pair of annular plates immediately adjacentthe plates of said focussing electrode controlling flow of electrons in the beam from the cathode to said anode.

2. An electron tube having an axis intersecting an intermediate plane, a cylindrical cathode about said axis, a focusing electrode adjacent the cathode and comprising a pair of annular plates focusing electrons from said cathode in a substantially flat radial beam along the intermediate plane, an anode encircling the cathode collecting electrons from the beam, and a control electrode interposed between the focusing electrode and anode and comprising a second pair of annular plates immediately adjacent the plates of said focussing electrode controlling flow of electrons in the beam from the cathode to said anode, the plates of said focusing and control electrodes being shaped and positioned to form an electrostatic field preventing electrons from impinging on said control electrode.

3. An electron tube having an axis intersecting an intermediate plane, a cylindrical cathode about said axis, a focusing electrode adjacent the cathode and comprising a pair of annular plates focusing electrons from said cathode in a substantially fiat radial beam along the intermediate plane, an anode encircling the cathode collecting electrons from the beam, a control electrode interposed between the focusing electrode and anode and comprising a second pair of annular plates controlling flow of electrons in the beam from the cathode to said anode, and means electrically connected to the focusing electrode shielding the cathode from other portions of the tube.

' 4. An electron tube having an axis intersecting an intermediate plane, a cylindrical cathode about said axis, a focusing electrode adjacent the cathode and comprising a pair of annular plates focusing electrons from said cathode in a substantially flat radial beam along the intermediate plane, an anode encircling the cathode collecting electrons from the beam, a control electrode interposed between the focusing electrode and anode and comprising a second pair of annular plates controlling flow of electrons in the beam from the cathode to said anode, and supporting means for the focusing electrode providing shields between the cathode and other portions of the tube.

5. An electron tube having an axis intersecting an intermediate plane, a cylindrical cathode about said axis, a focusing electrode adjacent the cathode and comprising a pair of annular plates focusing electrons from said cathode in a substantially flat radial beam along the intermediate plane, an anode encircling the cathode collecting electrons from the beam, a control electrode interposed between the focusing electrode and anode and comprising a second pair of annular plates controlling the flow of electrons in the beam from the cathode to said anode, means including insulating material forming an envelope disposed about the tube axis, an anode terminal circumferentially of the envelope, a control electrode terminal at one end of the envelope, and a focusing electrode terminal at the other end of the envelope.

6. An electron tube having an axis intersecting an intermediate plane, a cylindrical cathode about said axis, a focusing electrode adjacent the cathode and comprising a pair of annular plates focusing electrons from said cathode in a substantially fiat radial beam along the intermediate plane, an anode encircling the cathode collecting electrons from the beam, a control electrode interposed between the focusing electrode and anode and comprising a second pair of annular plates controlling the flow of electrons in the beam from the cathode to said anode, means including insulating material forming an envelope disposed about the tube axis, an anode terminal circumferentially of the envelope, a control electrode terminal at one end of the envelope, a focusing electrode terminal at the other end of the envelope, and a cathode terminal at the last mentioned end.

7. An electron tube having an axis intersecting an intermediate plane, a cylindrical cathode about said axis, a focusing electrode adjacent the cathode and comprising a pair of annular plates focusing electrons from said cathode in a substantially flat radial beam along the intermediate plane, an anode encircling the cathode collecting electrons from the beam, a control electrode interposed between the focusing electrode and anode and comprising a second pair of annular plates controlling the flow of electrons in the beam from the cathode to said anode, means including insulating material forming an envelope disposed about the tube axis, an anode terminal circurnferentially of the envelope, a control electrode terminal at one end of the envelope, a focusing electrode terminal at the other end of the envelope, and a cathode terminal at the last mentioned end, said terminals being coaxial.

8. An electron tube having an axis intersecting an intermediate plane, a cylindrical cathode about said axis, a focusing electrode adjacent the cathode and comprising a pair of annular plates focusing electrons from said cathode in a substantially flat radial beam along the intermediate plane, an anode encircling the cathode collecting electrons from the beam, said anode having an annular V-shaped recess opening toward said cathode, and a control electrode interposed between the focusing elect-rode and anode and comprising a eeond'aair of annular plates conti'dlling flow of electrons in the beam from the pathodeto said anode. i j i 7' 9. An electron tube having a vertical axis intersecting an intermediate plane, a c ylindrical c'athode"about said axis, a focusing electrode adjacent the cathode and comprising a pair of vertically spaced annular plates focusing electrons from said cathode in a substantially fiat radial beam along the intermediate plane, an anode encircling the cathode collecting electrons from the beam, a control electrode interposed between the focusing electrode and anode and comprising a second pair of vertically spaced annular plates controlling flow of electrons in the beam from the cathode to said anode, a tubular portion projecting downwardly from the lower of said second plates, and a tubular portion projecting upwardly from the upper of said second plates, said'tubular portions cooperating with said first and second mentioned plates to form an electrostatic field preventing electrons from impinging on said control electrode.

10. An electron tube comprising an envelope having an axis intersecting an intermediate plane, a cylindrical cathode in the envelope about said axis, a focusing electrode adjacent the cathode and comprising a pair of annular plates focusing electrons from said cathode in a substantially flat radial beam along the intermediate plane, an anode collecting electrons from the beam and supported circumferentially of the envelope, a control electrode interposed between the focusing electrode and anode and comprising a second pair of annular plates controlling flow of electrons in the beam from the cathode to said anode, terminals at opposite ends of the envelope, means supporting the focusing electrode on one of the terminals and providing a shield about the cathode, and means supporting the control electrode on the other terminal and providing another shield about the cathode.

11. An electron tube comprising an envelope having an axis intersecting an intermediate plane, a cylindrical cathode in the envelope about said axis, a focusing electrode adjacent the cathode and comprising a pair of annular plates focusing electrons from said cathode in a substantially flat radial beam along the intermediate plane, an anode collecting electrons from the beam and supported circumferentially of the envelope, a control electrode interposed between the focusing electrode and anode and comprising a second pair of annular plates controlling fiow of electrons in the beam from the cathode to said anode, terminals at opposite ends of the envelope, a tubular support shield from the lower plate of the focusing electrode and extending downwardly to one of the terminals, a cap shield on the upper plate of the focusing electrode covering the cathode, a tubular support shield on the upper plate of the control electrode extending upwardly to another of said terminals, and a skirt shield on the lower plate of the control electrode projecting downwardly toward the lower end of the envelope.

12. An electron tube comprising an envelope having an axis intersecting an intermediate plane, a cylindrical cathode in the envelope about said axis, a focusing electrode adjacent the cathode and comprising a pair of annular plates focusing electrons from said cathode in a substantially flat radial beam along the intermediate plane, .an anode collecting electrons from the beam and supported circumferentially of the envelope, a control electrode interposed between the focusing electrode and anode and comprising a second pair of annular plates controlling flow of electrons in the beam from the cathode to said anode, terminals at opposite ends of the envelope, a tubular support shield from the lower plate of the focusing electrode and extending downwardly to one of the terminals, a cap shield on the upper plate of the focusing electrode covering the cathode, a tubular support shield on the upper plate of the control electrode extending upwardly to another of said terminals, a skirt shield on the lower References Cited in the file of this patent UNITED STATES PATENTS Hollmann July 4, 1939 Hollmann Oct. 17, 1939 Johnson July 13, 1943 Fleming-Williams July 10, 1945 Hahn Nov. 27, 1945 Chat-ton Oct. 28, 1952 Coleman Feb. 1,, 1955

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