US2813215A - Electron beam tube - Google Patents

Description

Nov. 12, 1957 D. REICHERT ELECTRON BEAM TUBE Filed Sept, 15, 1954- R w w m f N m M m Wm 1 J a r I M n Z v M M T V fi wnwunillluliulllnwl .F m

United States Patent ELECTRON BEAM TUBE Robert D. Reicllert, Irvington, N. 1., assignor to Radio Corporation of America, a corporation of Delaware Application September 15, 1954, Serial No. 456,215

15 Claims. (Cl. 313-82) This invention relates to electron beam tubes and more particularly to electron beam tubes adapted to be operated at a relatively high anode potential. The invention provides an electron tube which has at one end thereof a cathode and a wound grid on an axis normal to a longitudinal tube axis. A tubular anode around the tube axis and spaced along the axis from the grid is sealed into the tube envelope at the other end of the tube. An electron tube employing the structure described is especially useful as a regulator triode in a high voltage system for a color television receiver. The anode structure of the tube described is generally of the type illustrated in copending application Serial No. 459,409,

filed September 30, 1954, of R. E. Byram and A. P. Sweet and assigned to the same assignee as the present application.

Tube applications are known wherein a relatively high voltage at a relatively low but constantly changing current is required. In such applications it is often necessary to maintain that relatively high voltage at a relatively constant potential. For example, the high voltage supply system for a kinescope in a color television receiver requires a relatively high current for a bright picture and a relatively low current for a dark picture. In such a kinescope the convergence of an electron beam is adversely aitected by voltage changes; the voltage changes make for poor color fidelity. As the high voltage supply system for such a receiver has an appreciable internal impedance, changes in load current cause changes in the output voltage. A means is thus required to hold constant the potential of the high voltage supply output.

A regulator tube of the type described may be used to provide what is termed waste regulation to stabilize the high voltage supply system for-a color kinescope. Asis known, the provision of a constant load for a voltage supply system stabilizes the voltage output of the system. A regulator tube is therefore connected across the high voltage supply output in parallel with the kinescope. The regulator tube is operated so that the sum of the current drawn by the kinescope and the regulator tube is essentially constant. For example, if the kinescope draws a current of one milliampere, which may represent the current load for a bright picture, the regulator draws no appreciable current. When the kinescope draws no appreciable current, i. e., current of the order of say about 50 microamperes, the regulator tube draws about one milliampere.

Previous regulator tubes, usually in the form of regulator triodes, proved relatively ineflicient. A. relatively massive supporting structure was required for a cathode and grid adapted to operate at relatively high voltages. Then, too, the cathode and grid construction used proved relatively expensive. A cathode and grid of the type used in conventional receiving tubes, such as a tubular cathode and a wound grid, could not heretofore be adapted to be used in theprevious regulator tube design. "The structure used in previous regulatortriodes, usually from the cathode, through thegrid shieldalso has a portion thereof. disposed between a planar cathode and grid with ceramic supports, required a relatively high heater current for normal v operation and limited the tubes to relatively. low amplificationfactors.

Accordingly, it is an object of the invention to provide an improved. electron tube adapted totbeused in relatively high voltage applications common to. color kinescopes.

It is a further object of the inventionto provide .an electron tube adapted to be operated at. a relatively h anode potential and havingimprovedlmeans :for producing an electron lens which. focuses .anelectronbeam. int a narrow stream directed into a tubular anode sealedlinto an end of a tube envelope.

It is a further object of the invention to provide an improved electron beam tube having athennionic cathode and a helical grid around the cathodeand on ,anaxis substantially normal to the longitudinal axis of the tube.

It is a further object of the invention to provide an improved electron tube havingahelical grid. and adapted to be operated at a relatively highanode potential and in which the kinetic energy of antelectron beam is dissipated in a relatively small anodearea causingthe region adjacent that area to operate.;at red heat, and having getter material around that-region.

It is a further object ofthe invention toprovide an improved electron tube adapted. to be used asa-regulator triode in a color television receiver and which employs a cathode adapted to be operated with a relatively low heater current.

It is a further object of theinvention to provide an improved elongated electronytube: having a helical grid on an axis substantially normal to the longitudinal axis of the tube and adapted-topbe operated at a relatively high anode potential and in which thelenergy of a beam of electrons impinging upon .;an anode is dissipated without overheating the tube envelope.

It is a further object pftheinve-ntion .to provide an improved regulator triode having a relatively high amplification factor.

According to oneembodiment of the invention anelongated electron beam tube isprovidedhaving beam forming means at one end of the tube and adjacentabase thereof, and an anode sealed throughtheother end. The beam forming means comprises a cathode, a wound .grid around the cathode, and an .electronulens at one side of the grid. The cathode, which maybe thermionically emissive, may be tubular in form. rThe-grid has an axis lying in a plane substantially normal tothe longitudinal axis of the tube. .The grid-mavhave a plurality of side rods around which is .wound a griduwinding. The electron lens may take the form of a cup which contains the cathode and grid and which operates to shield the cathode and grid from positive ion bombardment. The cup referred to has an aperture to provide communication between the grid and the anode. The cup or shield is adapted to be biased at substantially cathode potential so that the aperture focusesa stream of electrons and the aperture, to form an electron beam directed to the anode. The the grid and the tube base so as .to shield the portion of the tube adjacent the basefrOmemission from the cathode. An anode, whichis spaced along the longitudinal tube axis from the beam 'forming means, has a tubular portion around the tu be axis apd a ,target plate across said tubular portion. Thus-the target plate is positioned in the path of the electron beam; 'lfhetarget plateintercepts the electron beam that thef' beam dissipates substantiallyall of its energy ,at that plate, rai s g to a red heat. A getter. isdi sposed arolind j e ide of the anode in registry with-the target plate within the tube adjacent the base.

he a e anode for absorbing gases released within the tube during like numerals refer to like parts. The embodiment described is presented solely for illustrative purposes and not byway of limitation.

In the drawing:

Figure'l is a side elevation partly in section of an electron beam tube embodying the invention.

' Figure 2 is a sectional view taken along line 22 of Figure 1. I I v Referring now to the drawingin greater detail there is shown in Figure i an electron beam tube employing a tube structure according to the invention. The electron tube, includes an elongated, evacuated envelope 12.

Prongs 14 extend from a base 16 at one end of the en- Velope. Some of the internal tube elements may be connected tothese prongs.

, Beam forming means 18 are provided at the end of the The beam forming means inciudes a tubular thermionic cathode 2t! having an axis (shown in Figure 2 as line 22) lying in a plane substantially" normal to the longitudinal axis 24 of the tube.

' The cathode may have a coating of an electron emissive material and is provided with a heater 25. A wound grid 26 is disposed around the cathode. The grid may have two side rods 28 and a grid winding 30 around the side rods. An apertured shield cup 32 encloses the cathode and grid. The shield cup is adapted to be biased at substantially the same potential as the cathode so as to form an electron lens. An aperture 34 in the shield cup focuses a stream of electrons from the cathode through the grid and through the aperture to an anode 36 which is sealed to the end of the envelope remote from the base.

The anode 36 may include a conductive cylinder 38 around the longitudinal'tube axis 24 and spaced along the axis from the beam forming means 18. The cylinder 38 is fixed to an anode lead cap 39 which extends through an anode-envelope seal 40. The anode lead cap is provided with a number of apertures 42 at a portion thereof Within the evacuated envelope. The apertures serve to reduce the conduction of heat through the anode during a sealing operation in the manufacture of the tube. The conductive cylinder 38 is provided with a cup-shaped target plate 44 within the cylinder. The target may be of a material having a relatively high melting point such as tantalum. The distance between the target plate and the end of the conductive cylinder adjacent the beam forming means is about half the distance between the target plate and the end of the cylinder remote from the beam forming means. The target plate is thus positioned at a sufficient distance from the anode-envelope seal so that the target plate may be heated to incandescence without danger of failure of the anode-envelope seal. A getter 45 is positioned around the outside of the anode cylinder in registry with the target plate. The getter, which may be of zirconium, getters gases released Within the tube during normal tube operation. The portion of the cylinder between the target plate and the end of the cylinder adjacent the beam'forming means, shields the tube envelope from relatively high energy X-ray radiation produced by a bombardment of the electron beam on the target plate. The tube envelope'may be of lead glass; substantially all hard X-ray radiation is thus entrapped within the tube by the shielding effect of the anode cylinder and of the tube envelope. Whatever X-ray radiation reaches the outside of the tube envelope is therefore of substantially 'reduced energy.

positioning of the elements within the shield cup 32. The shield cup is provided With a shield portion 46 there- Within. The shield portion 46 is disposed between the tube base and the grid for substantially shielding a portion of the tube adjacent the base from emission from the cathode. The shield portion also serves to support spacer plates 48 which hold the cathode and grid in desired space relation. The spacer plates 43 support the cathode 20 and the grid 26 in a position substantially normal to the tube axis above referred to. The shield portion 46 is also supported within the shield can by the spacer plates.

The tube described is capable of typical operation with a potential of about 27,000 volts applied to the anode. As the tube structure is double ended, the anode connection is adequately spaced from other tube leads so that the tube may withstand relatively high voltages without brealo down. Since the tube is adapted to be operated at rela tively high voltages the shield cup 46 descfibedabove is adapted to shield the tube elements within thecu'pfrom bombardment by relatively high energy positive ions which would otherwise tend to destroy the electron emissive coating on the cathode and evolve water vapor from the spacer plates which support the tube elements within the shield cup. s 1

A regulator triode using the beam forming structure described Was operated witha heater current of 0.2' amperes at 6.3 volts. In contrast, a regular triode using a beam forming structure having a planar cathode and grid required a heater current of 0.6 amperes at 6.3 volts under the same operating conditions. V v

An electron tube triode employing the structure described has a relatively high triode transconductance. While previous regulator triodes exhibit amplification factors of the order of 1650, regulator triodes using a beam forming structure of the invention exhibit amplification factors of over 1800. Where tube operation is desired with anode potentials as high as say 50,000 volts regulator tubes using a structure according to the invention may be made with amplification factors of the order of 3000.

In a typical application, the regulator triode described may be used where it is desired to present a substantially constant load to a high voltage source. The regulator triode may be connected in a shunt voltage-regulator circuit to provide a regulated direct current output voltage. The anode of the triode is connected to the positive termi= nal of the output of the regulated voltage supply. The grid is supplied with a bias voltage through a voltage divider network between the positive and negative terminals of the output of the regulated voltage supply. The grid thus receives a bias voltage which is a proportional sample of the relatively high voltage applied to the output. The cathode is connected to a predetermined positive reference voltage with respect to the grid so as to al-' low the grid to see a positively biased cathode; i. e. the cathode sees a negatively biased grid. When a relatively high voltage is applied to the output terminal, and hence to the anode, the grid receives a predetermined portion of that relatively high voltage. The grid be comes more positively, or more properly, less negatively biased with respect to the cathode. This causes the tube to draw current. The current drawn by the tube, in turn, results in a load on the high voltage source resulting in a potential drop in the high voltage supply. Similarly, when the load on the regulated output is relatively high causing the output potential to drop, the regulator tube grid, which receives a predetermined proportion of the voltage across the output, is biased at a relatively low positive potential; hence the tube draws only a relatively small amount of current. Thus the tube stabilizes the load voltage.

It will be apparent from the foregoing description of a regulator triode using the invention that a novel and advantageous electron tube having a relatively highamplification factor anddrawing a'relativelylow heater current is provided which is adapted to be used in relatively high voltage applications and'in which the cathode and grid employed are of a type novel to this type of tube.

What is claimed is:

1. An elongated electron beam tube having at one end thereof a cathode and a. wound grid around said cathode, said cathode being positioned on an axis normal to the longitudinal axis of said tube, a tubular anode around said tube axis and spaced along said tube axis from said grid and having a target plate therewithin in a position to receive an electron beam from said cathode through said grid, and a getter around said anode at a portion thereof in registry with said target plate for gettering gases within said tube whereby electrons from said cathode travel toward said anode in a path along said tube axis.

2. An electron beamtube comprising an envelope containinga cathode and wound grid at one end of said tube for producing an electron beam along an axis of said tube, said grid being positioned around said cathode and on an axis normal to said tube axis, and a tubular anode disposed about said tube axis and spaced from said grid, said anode being sealed, adjacent to one end thereof, into said envelope at the other end of said tube, said anode having a target therein positioned to intercept said beam and dis posed closer to the end of said anode adjacent to said gridthan to said one end of said anode.

3. An electron beam tube comprising an envelope containing beam forming means for producing an electron beam along a tube axis and an anode adapted to receive said beam, said beam forming means including a tubular cathode having an axis lying in a plane substantially normal to said tube axis and a wound grid around said cathode, said grid having a plurality of side rods lying in planes substantially normal to said tube axis and having a grid winding. around said side rods, said anode including a hollow cylinder around said longtiudinal axis and spaced from said beam forming means and having a target within a central portion thereof and spaced from said envelope by a distance greater than the distance between said target and the end of said cylinder adjacent to said beam forming means, said beam forming means being adapted to focus said beam at said plate whereby substantially all of the energy of said beam is dissipated at said plate without overheating said envelope.

4. An electron beam tube having an envelope defining a longitudinal tube axis therethrough and containing beam forming means for producing a beam of electrons in a path along said axis, and an anode within said path and spaced along said axis from said beam forming means and adapted to receive said beam, said beam forming means including a thermionic cathode and a helical grid around saidcathode, said anode including a tubular portion thereof around said path and a target plate within said tubular portion and across said path and spaced from said envelope by a distance greater than the distance between said target plate and theend of said tubular portion adjacent to said; beam forming means, whereby substantially all of the energy of said beam is dissipated at said target plate.

5. An electron beam tube comprising an envelope defining a longitudinal tube. axis therethrough and containing a cathodeand a grid at one end of said envelope for producing a beamof electrons with a path along said axis, an anode supported by said envelope at the other end thereof, said cathode lying ina plane substantially normal to said axis, said grid disposed around said cathode and forming a helix around said cathode, said anode being disposed within said path and spaced along said axis from said grid and'adapted to receive said beam and including a conductive cylinder around said path anda target plate within a central portion of said cylinder and across said path whereby substantially all of theenergy of said beam is dissipated at said target plate without overheating said envelope, and a getter around said anode at a portion thereof in registry with said target plate within said anode so as to getter gas released within said envelope due to said beam during the normal life of said tube.

6. An electron beam tube having an envelope containing beam forming means for producing a cylindrical beam of electrons along a path and an elongated anode sealed adjacent to one end thereof to said envelope and spaced :along and within said path and adapted to receive said beam; said beam forming means including a thermionic cathode for producing a stream of electrons, a helical grid around said cathode for regulating the flow of said stream through said grid, and means for focusing said stream of electrons into a beam directed, at said anode, said anode including a tubular portion thereof around said path and a target plate within said tubular portion, said plate being spaced from said anode end by a distance equal to at least half of the length of said anode and disposed across the path of said beam of electrons so that substantially allof the energy of said beam is dissipated at said target plate, whereby said stream of electrons from said cathode is formed into a regulated beam of electrons which is. received by said anode without overheating said envelope.

7. An electron beam tube comprising an envelopedefining a longitudinal tube axis therethrough and containing a cathode .and a grid at one end of said envelope forproducing a beam of electrons with a path along said axis, an anode supported at the other end of said envelope thereby, and a shielding member around said cathode and said grid and between said grid and said anode and having an aperture therein between said grid and said anode, said member being adaptedto be biased at a negative potential with respect to said anode so as to shield said cathode and said grid from positive ion bombardment and to form a focused electron beam from said cathode through said grid and said aperture to said anode, said cathode lying in a plane substantially normal to said axis, said grid having a plurality of side rods around said cathode and a grid winding around said side rods, said anode being-disposed within said path and adapted to receive said beam and including a conductive cylinder around said path and a target plate within a central portion of said cylinder and. across said path and spaced from said other end of said envelope by .a distance greater than that represented by half the length of said cylinder whereby substantially all of the energy of said. beam is dissipated at said target plate without overheating said envelope.

8. An electron beam tube comprising an envelope defining a, longitudinal tube axis therethrough and containing beam forming means for producing an electron beam along said axis. and an elongated, hollow anode sealed adjacent to one end thereof to said envelope and spaced along said axis from said beam forming means and adapted toreceive said beam, said beam forrningm-eans including a cathode lying in a. plane substantially normal to said axis for producing a stream of electrons, a grid around said cathode for regulating the flow of said stream through said .grid, and an apertured shield between said grid and said 55 anode for forming a portion of said stream into a cylindrical beam, whereby said stream of electrons from said cathode is formed into a regulated electron beam directed at relatively small area of said anode, said anode having a target in the path of said beam and disposed within said anode and closer to theend of said anode adjacent to said beam forming means than to said one end thereof,

9. An electron beam tube comprising an envelope defin- I ing a longitudinal tube axis therethrough and containing beam forming means for producing an electron beam along said tube axis and an elongated anode sealed adjacent to one end thereof to said envelopeand spaced along said tube axis from said beam forming means and adapted to receive said beam, said beam forming means including a tubular cathode having an axis lying in a plane substantially normal to said tube axis for producing :a stream of electrons,.a grid around said cathode for regulating the flow of said stream through said grid, said grid h-avinga it plurality of side rods around said grid and a grid Winding around said side rods, and :a shield having one portion thereof positioned around said cathode and said grid and between said grid and said anode and having an aperture therein between said grid and said anode, said shield exposing said anode to said cathode through said grid while shielding said envelope from emission from said cathode and protecting said cathode and said grid from positive ion bombardment and being adapted to form a focused electron beam from said cathode through said grid and said aperture to said anode, said shield having another portion thereof between said base and said grid for substantially shielding a portion of the tube adjacent said base from emission from said cathode, said anode including a cylinder and a target within a central portion of said cylinder and in the path of said beam and spaced from said end of said anode a distance equal to about two-thirds of the length of said anode whereby said beam forming means directs a regulated beam at said target and substantially all of the energy of said beam is dissipated at said target without overheating said envelope.

10. An electron beam tube comprising an envelope defining a longitudinal tube axis therethrough and containing beam forming means for producing an electron beam having a path along said tube axis, and an anode spaced along said tube axis from said beam forming means and adapted to receive said beam, said beam forming means including a tubular cathode having an axis in a plane substantially normal to said tube axis, a grid around said cathode, and a shield including a portion thereof containing said cathode and said grid and having an aperture therein between said grid and said anode, said shield being adapted to protect said cathode and said grid from positive ion bombardment and to form a focused electron beam from said cathode through said grid and said aperture to said anode, said anode including a tubular portion thereof around said tube axis and a target within a central part of said portion, said target being disposed across said tubular portion and across said path of said beam, the distance between the end of said tubular portion adjacent said beam forming means and said target being about half the distance between the end of said tubular portion remote from said beam forming means and said target thereby spacing said target from said envelope for dissipating substantially all of the energy of said beam at said target without overheating said envelope.

11. An electron beam tube having a base at one end thereof and comprising an envelope containing at an end thereof adjacent said base a tubular thermionically emissive cathode and a wound grid around said cathode and supporting within the other end thereof a tubular anode defining therethrough a tube axis, said grid having a plurality of side rods and a grid winding around said side rods, said cathode and said grid having axes lying in planes substantially normal to said tube axis, a shield containing said cathode andsaid grid and including a portion thereof lying between said grid and said anode and having an aperture therein between said grid and said anode, said shield being adapted to protect said cathode and said grid from positive ion bombardment and to form a focused electron beam from said cathode through said grid and said aperture to said anode, said shield having a portion thereof between said base and said grid for substantially shielding a portion of the tube adjacent said base from emission from said cathode, a target plate within said anode and across a central portion thereof for intercepting said electron beam and thereby dissipating substantially all the energy of said beam at said plate without overheating said envelope and whereby the anode forms an X-ray shield for shielding said envelope from hard radiation produced by the bombardment of said plate by said beam, and a getter around said anode at a portion thereof in registry with said target plate within said anode for get- ;tering gases released within said envelope.

12'. An electron beam tube comprising an envelope defining a longitudinal tube axis therethrough and containing beam forming means for producing a beam of electrons in a path along said tube axis, an anode supported by said envelope at the other end thereof, said beam forming means including a tubular cathode having an axis lying in a plane substantially normal to said tube axis, a wound grid disposed around said cathode, and. an apertured shield between said grid and said anode for forming a beam of electrons from said cathode through said grid and said aperture to said anode, said. anode being disposed within said path and adapted to receive said beam and including a cylinder around said path and a target Within a central portion of said cylinder and positioned across said path of said beam whereby substantially all of the energy of said beam is dissipated at said target without overheating said envelope, and a getter around said cylinder at a portion thereof in registry with said target within said cylinder for gettering gasreleased within said envelope by said beam, said getter being of a material including zirconium whereby said getter produces continuous getter action during tube operation for the normal life of said tube.

13. An electron beam tube comprising an envelope containing beam forming means for producing an electron beam along a longitudinal axis and an elongated anode sealed adjacent to one end thereof to said envelope and adapted to receive said beam, said beam forming means including a tubular cathode having an axis lying in a plane substantially normal to said longitudinal axis and a wound grid around said cathode, said grid having a plurality of side rods lying in planes substantially normal to said longitudinal axis and having a grid winding around said side rods, said anode including a hollow conductive cylinder around said longitudinal axis and spaced from said beam forming means and having a beam receiving portion within said cylinder and spaced from said end of said anode by a distance equal to at least about half of the length of said cylinder thereby to thermally insulate said envelope from a heating of said portion by electron bombardment, said beam forming means being adapted to focus said beam on said anode portion whereby substantially all of the energy of said beam is dissipated within said cylinder and hard X-ray radiation produced within said cylinder by the bombardment of said anode by said beam is largely entrapped within said cylinder.

14. An electron beam tube comprising a base; beam forming means adjacent to said base and adapted to produce an electron beam along a tube axis, said beam forming means including a tubular cathode adjacent to said base and having an axis lying in a plane substantially normal to said tube axis, a wound grid around said cathode, and a cup-shaped member having a portion thereof on the side of said grid remote from said base; and an anode spaced along said tube axis from said member, said anode including a tubular element positioned along said axis and having an open end facing said member and a target plate within and across a portion of said element intermediate the ends thereof and disposed closer to said open end than to the other end of said element; said member having a circular passageway disposed around said tube axis and exposing said anode to said grid through said passageway thereby being adapted to focus electrons from said cathode through said grid and said passageway in a cylindrical beam along said tube axis and into said anode.

15. An electron beam tube comprising a base; beam forming means adjacent to said base and adapted to produce an electron beam along a tube axis, said beam forming means including a tubular cathode adjacent to said base and having an axis lying in a plane substantially normal to said tube axis, a wound grid around said cathode, and a cup-shaped member having a portion thereof on the side of said grid remote from said base;

and an anode spaced along said tube axis from said member; said member having a circular passageway disposed around said tube axis and exposing said anode to said grid through said passageway thereby being adapted References Cited in the file of this patent UNITED STATES PATENTS Schade Feb. 8, 1938 Hergenrother July 9, 1940 Bull Dec. 3, 1940 Winans Oct. 13, 1942 Litton Dec. 24, 1946 Grimm June 26, 1951 Hensel Aug. 7, 1956

Images