US3917973A - Electron tube duplex grid structure - Google Patents

Electron tube duplex grid structure Download PDF

Info

Publication number
US3917973A
US3917973A US487406A US48740674A US3917973A US 3917973 A US3917973 A US 3917973A US 487406 A US487406 A US 487406A US 48740674 A US48740674 A US 48740674A US 3917973 A US3917973 A US 3917973A
Authority
US
United States
Prior art keywords
grid
cathode
bars
wires
areas
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
US487406A
Other languages
English (en)
Inventor
Jules S Needle
William H Sain
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Varian Medical Systems Inc
Original Assignee
Varian Associates Inc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Varian Associates Inc filed Critical Varian Associates Inc
Priority to US487406A priority Critical patent/US3917973A/en
Priority to DE19752528562 priority patent/DE2528562A1/de
Priority to FR7520986A priority patent/FR2278154A1/fr
Priority to NL7508140A priority patent/NL7508140A/xx
Priority to GB2885675A priority patent/GB1464201A/en
Priority to CH898175A priority patent/CH587564A5/xx
Priority to JP50084021A priority patent/JPS5812971B2/ja
Application granted granted Critical
Publication of US3917973A publication Critical patent/US3917973A/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

Links

Images

Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J21/00—Vacuum tubes
    • H01J21/02—Tubes with a single discharge path
    • H01J21/06—Tubes with a single discharge path having electrostatic control means only
    • H01J21/065—Devices for short wave tubes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J1/00—Details of electrodes, of magnetic control means, of screens, or of the mounting or spacing thereof, common to two or more basic types of discharge tubes or lamps
    • H01J1/02—Main electrodes
    • H01J1/13—Solid thermionic cathodes
    • H01J1/20—Cathodes heated indirectly by an electric current; Cathodes heated by electron or ion bombardment
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J19/00—Details of vacuum tubes of the types covered by group H01J21/00
    • H01J19/28—Non-electron-emitting electrodes; Screens
    • H01J19/32—Anodes
    • H01J19/34—Anodes forming part of the envelope
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J2893/00—Discharge tubes and lamps
    • H01J2893/0001—Electrodes and electrode systems suitable for discharge tubes or lamps
    • H01J2893/0002—Construction arrangements of electrode systems
    • H01J2893/0003—Anodes forming part of vessel walls

Definitions

  • Attached to the side of the grid bars facing the cathode is an array of closely spaced fine wires which increase the electric field due to the grid at the emitting surface, and decrease the penetration of field due to the anode, thereby increasing the transconductance and amplification factor, decreasing the transit time of electrons, and improving the uniformity of emission current density.
  • FIG. 9a is a diagrammatic representation of FIG. 9a
  • FIG. IOCI PRIOR ART ELECTRON TUBE DUPLEX GRID STRUCTURE FIELD OF THE INVENTION The invention pertains to gridded electron tubes such as widely used to generate radio frequency power.
  • the control grid next to the cathode is driven to a voltage positive with respect to the cathode for at least a portion of the radio frequency cycle.
  • the grid can then collect electrons and become heated by their bombardment energy, causing impaired performance or possible failure by melting.
  • Various tube characteristics are dependent on the grid structure.
  • the amplification factor increases with the size of the grid wires and the ratio of their spacing from the cathode to their mutual spacing.
  • the amplification factor decreases and the increase in transconductance is very limited. If one scales down in geometric ratio the wire size. mutual spacing and cathode-grid spacing, the amplification factor remains relatively constant and the transconductance increases. Also, the electron transit time through the grid struc ture is reduced and the high frequency performance of the tube is thereby improved. However, a point is soon reached where the mechanical tolerances of construction and the lack of rigidity and thermal dissipation ability of the fine wires make the structure impractical.
  • the aforementioned Sain patent discloses a method of overcoming some of these problems.
  • the grid elements By making the grid elements as strips elongated perpendicular to the cathode instead of round wires, their heat dissipation and rigidity are increased, with no appreciable increase in intercepted current because the area exposed to the cathode is not increased. Furthermore. the amplification factor, determined by the percentage if electric field from the anode which penetrates through the grid to the cathode, increases. Left unsolved were the prob lems of transconductance vs. grid size. the divergence of the electron stream by the positive grid potential, and nonuniform emission.
  • An objective of the present invention is to provide a means for achieving the electrical benefits of a close spaced grid while maintaining the mechanical and thermal advantages of a coarse grid.
  • a further objective is to provide a higher amplification factor than is practical with prior-art grids.
  • a further objective is to provide uniform emission from the emitting areas.
  • a further objective is to provide improved focusing of electron streams between the primary grid elements.
  • the added interception by the secondary grid is countered by the ability to make the wires exceedingly fine and by the low positive grid voltage needed to draw current. Also, the improved electron optics reduces interception by the massive primary grid bars.
  • the amplification factor increases approximately as the product of the amplification factors of the two grids so that great isolation of input and output voltages is achieved.
  • FIG. I shows, partly in section through the tube axis, a cylindrical triode tube embodying the features of the invention.
  • FIG. 2 shows in perspective a portion of the grid structure of the tube in FIG. 1.
  • FIG. 3 shows in perspective an alternative grid structure according to the invention.
  • FIG. 4 is a partial section of FIG. I perpendicular to the tube axis.
  • FIG. 5 is an enlarged section of a portion of the cathode and grid region as indicated by line 55 in FIG. 4.
  • FIG. 6 is a view similar to FIG. 5 but showing an alternative structure of the cathode.
  • FIG. 7 shows a section of the cathode and grid region of a planar tube embodying the invention.
  • FIG. 8 shows a section of a tetrode tube embodying the invention.
  • FIG. 9a is an illustration of the electric field pattern in the grid region of a prior art tube.
  • FIG. 9b is the field pattern in a tube embodying the invention.
  • FIG. 10a is an illustration of the pattern of emission density from the cathode of a prior art tube.
  • FIG. 10b is the emission density pattern ofa tube embodying the invention.
  • FIG. 1 a practical embodiment of the invention in a cylindrical triode tube.
  • the tube has a vacuum tight envelope consisting of; a metallic cup 10, as of copper, a portion 11 of whose inner surface serves as the tube anode, a sealed-off exhaust tubulation 12, concentric insulators 13, 14, 15, 16, as of ceramic, isolating the electrical connections to the electrodes, and a series of thin metallic flanges 17, l8, 19, 20, 21, 22, hermetically sealed to the insulators and to anode ll and heater lead-in 23.
  • a cooling jacket 24 surrounds anode cup 10 and is bonded to cup 10, as by soldering, to provide thermal conductivity.
  • Final assembly of the tube is accomplished by sealing, as by welding, flange l9 bearing the anode subassembly to flange bearing the cathodegrid assembly.
  • a spiral radiant heater 25 is connected at one end to heater lead-in 23 and at the other to flange 22 by a lead 26 supported by a ceramic insulator 27.
  • a hollow cathode cylinder 28, as of nickel, is supported coaxially to heater 25 by a thin metallic heat dam 29, as of iron-nickel-cobalt alloy, mounted on flange 21.
  • the upper end of cathode 28 is closed by two spaced metallic discs 30 having a reflecting heat shield 3l between them.
  • Coaxially spaced outside cathode 28 is a cylindrical grid structure 32 comprising massive axially directed metallic bars 33, preferably of a refractory metal such as molybdenum, uniformly spaced about the circumference. At their top ends the bars are joined, as by spot welding, to a flanged disc 34. A ceramic plug 35 passes through the center ofdisc 34 and cathode end discs 30 to maintain axial alignment. The bottom ends of bars 33 are joined to a flange 36 mounted on envelope flange 20.
  • a cylindrical woven mesh of fine metallic wires 37 as of tungsten is bonded to bars 33, as by diffusion brazing with a plated gold film.
  • the mesh 37 is preferably arranged diagonally to bars 33 so that individual wires form ap proximate helices, allowing them to expand thermally without substantially deforming the structure.
  • FIG. 2 shows an inside view of a portion of the grid structure.
  • FIG. 3 is an alternative grid structure in which only one set of parallel helical wires 37' is used in place of the mesh 37.
  • the multiple helix 37 presents a desirable smooth surface on a small scale but is harder to fabricate than the mesh structure 37.
  • FIG. 4 shows in detail the electrode structure of the tube of FIG. 1, and FIG. 5 shows an enlarged portion of the cathode and grid structures which are the essence of the present invention.
  • the surface of cathode 28 facing grid structure 32 comprises axial strips 38 of emissive material, such as a mixed oxide of barium, strontium and calcium. Between emissive strips 38 and opposite grid bars 33 are strips 39 of non-emissive material, such as uncoated nickel. In the example shown. the emissive strips 38 are recessed below non-emissive strips 39 in a direction away from the grid 32.
  • the reparked structure provides improved focusing of the 4 electron beams 40 between bars 33 by the covergence of the electric field leaving the edges of emissive areas 38, corresponding to the converging electron trajecto ries 40.
  • Grid bars 33 are, in this example. elongated in cross section in the direction perpendicular to the cathode 28, whereby their rigidity and thermal capacity are greater than that of a round wire of the same width, but the intercepted current is not increased appreciably. Also, the elongated bars increase shielding of the cathode from the electric field of the anode l1 and thus increase the amplification factor of the tube.
  • FIG. 6 shows an alternative structure in which nonemissive strips 39' form a continuous smooth surface with emissive strips 38. This structure has more uniform emission density than that shown in FIG. 5 and may be easier to build.
  • P10. 7 shows an embodiment of the invention as a planar tube. It will be apparent to those skilled in the art that the invention concerns the detailed structure of the cathode-grid region and may be embodied in tubes having many different overall geometries, including planar and cylindrical.
  • FIG. 8 shows a tetrode incorporating the invention.
  • Screen grid wires 41 are aligned with grid bars 33, between grid structure 32 and anode 11.
  • the electron paths are focused between wires 41, so the screen grid collects very little current.
  • FIG. 9 shows the electric fleld lines in a small section of electrode structure.
  • FIG. 9a corresponds to prior-art tubes, such as described in Sain in U.S. Pat. No. 3,814,972 referenced above. It is seen that, as electrons approach the grid from the cathode side, they experience a diverging transverse component of field 45 which will tend to defocus the electron beam. Leaving the grid on the anode side they experience a focusing transverse component 42, but by then some electrons may have been drawn to the grid bars 33.
  • FIG. 9b illustrates the fields according to the present invention. Since the fine grid 37 forms a smooth, essentially equipotential surface, there is no divergent field and the electrons pass grid 37 flowing essentially perpendicular to it. Between grid bars 33 the field has only converging transverse field components 42'.
  • FIG. 10 illustrates the variation of emission density across the width of the emissive strips for a constant positive grid voltage.
  • the emission current density is determined by the electric field.
  • FIG. 10a shows the density variation in the prior art structure of FIG. 9a.
  • the field is highest near the edges 43 of the emissive strip 38, because the edges are closer to the grid bars 33.
  • the center 44 where the emissive surface is far ther from the bars 33, the field and hence current density are lower.
  • the non-uniform emission density is undesirable because the cathode must be run hot enough to supply the highest density, but the low density regions are not contributing fully to the useful current.
  • FIG. 9b With the structure according to the present invention as shown in FIG. 9b, the emission as illustrated in FIG.
  • a certain triode tube constructed according to its teachings has a cut-off amplification factor of 2000.
  • This factor is the ratio of the minimum negative grid voltage to the positive anode voltage which just stops emission current from the cathode. in a prior art triode similar in all respects except not having the fine mesh secondary grid array, the amplification factor was only 200.
  • the improvement provides a tube of increased utility as an on-off"switch which can be controlled by a low grid voltage.
  • the increased shielding of the cathodegrid space from the anode voltage eliminated harmful regenerative feedback which had produced distortion of the amplified signalv
  • An electron tube comprising: a cathode. an anode, and at least one grid electrode therebetween; the sur face of said cathode facing said grid composed of areas of electron-emissive material alternating with intervening areas of relatively non-emissive material; said grid electrode comprising, a set of conducting bars spaced from said cathode surface and aligned adjacent said non-emissive areas, an array of conducting wires of size and spacing less than said bars. said wires crossing the 6 spacing between adjacent bars and joined electrically and mechanically to the area of said bars facing said cathode surface.

Landscapes

  • Microwave Tubes (AREA)
  • Solid Thermionic Cathode (AREA)
US487406A 1974-07-10 1974-07-10 Electron tube duplex grid structure Expired - Lifetime US3917973A (en)

Priority Applications (7)

Application Number Priority Date Filing Date Title
US487406A US3917973A (en) 1974-07-10 1974-07-10 Electron tube duplex grid structure
DE19752528562 DE2528562A1 (de) 1974-07-10 1975-06-26 Elektronenroehre
FR7520986A FR2278154A1 (fr) 1974-07-10 1975-07-03 Tube electronique a grille
NL7508140A NL7508140A (nl) 1974-07-10 1975-07-08 Elektronenbuis met duplexrooster.
GB2885675A GB1464201A (en) 1974-07-10 1975-07-09 Electron tube grid structure
CH898175A CH587564A5 (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html) 1974-07-10 1975-07-09
JP50084021A JPS5812971B2 (ja) 1974-07-10 1975-07-10 フクシキコウシコウゾウデンシカン

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US487406A US3917973A (en) 1974-07-10 1974-07-10 Electron tube duplex grid structure

Publications (1)

Publication Number Publication Date
US3917973A true US3917973A (en) 1975-11-04

Family

ID=23935601

Family Applications (1)

Application Number Title Priority Date Filing Date
US487406A Expired - Lifetime US3917973A (en) 1974-07-10 1974-07-10 Electron tube duplex grid structure

Country Status (7)

Country Link
US (1) US3917973A (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html)
JP (1) JPS5812971B2 (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html)
CH (1) CH587564A5 (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html)
DE (1) DE2528562A1 (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html)
FR (1) FR2278154A1 (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html)
GB (1) GB1464201A (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html)
NL (1) NL7508140A (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2627898A1 (fr) * 1988-02-26 1989-09-01 Thomson Csf Tube electronique refroidi par circulation d'un fluide
US20080061690A1 (en) * 2004-01-08 2008-03-13 Hamamatsu Photonics K.K. Photomultiplier Tube

Families Citing this family (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5069419A (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html) * 1973-10-22 1975-06-10
WO1982000734A1 (en) * 1980-08-27 1982-03-04 Shapiro A Electron-beam tube
JPS633082Y2 (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html) * 1980-12-18 1988-01-26
JPS5930530U (ja) * 1982-05-14 1984-02-25 三菱電機株式会社 内燃機関のアイドル回転数制御装置

Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2844752A (en) * 1956-03-09 1958-07-22 Rca Corp Electron discharge device
US2932754A (en) * 1957-07-30 1960-04-12 Machlett Lab Inc Electron tubes
US3562576A (en) * 1967-03-15 1971-02-09 Patelhold Patentverwertung Three-element electron discharge tube
US3573535A (en) * 1968-11-12 1971-04-06 Gen Electric High-frequency electronic tube having novel grid mounting
US3725717A (en) * 1970-06-22 1973-04-03 A Leliovsky Grid-controlled microwave thermionic device
US3800378A (en) * 1972-06-07 1974-04-02 Rca Corp Method of making a directly-heated cathode
US3814972A (en) * 1971-07-12 1974-06-04 Varian Associates Triode electron tube with segmented cathode and vane grid

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2844752A (en) * 1956-03-09 1958-07-22 Rca Corp Electron discharge device
US2932754A (en) * 1957-07-30 1960-04-12 Machlett Lab Inc Electron tubes
US3562576A (en) * 1967-03-15 1971-02-09 Patelhold Patentverwertung Three-element electron discharge tube
US3573535A (en) * 1968-11-12 1971-04-06 Gen Electric High-frequency electronic tube having novel grid mounting
US3725717A (en) * 1970-06-22 1973-04-03 A Leliovsky Grid-controlled microwave thermionic device
US3814972A (en) * 1971-07-12 1974-06-04 Varian Associates Triode electron tube with segmented cathode and vane grid
US3800378A (en) * 1972-06-07 1974-04-02 Rca Corp Method of making a directly-heated cathode

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2627898A1 (fr) * 1988-02-26 1989-09-01 Thomson Csf Tube electronique refroidi par circulation d'un fluide
US20080061690A1 (en) * 2004-01-08 2008-03-13 Hamamatsu Photonics K.K. Photomultiplier Tube
EP1708243A4 (en) * 2004-01-08 2008-06-04 Hamamatsu Photonics Kk Photomultiplier tube
US7855510B2 (en) 2004-01-08 2010-12-21 Hamamatsu Photonics K.K. Photomultiplier tube

Also Published As

Publication number Publication date
FR2278154A1 (fr) 1976-02-06
NL7508140A (nl) 1976-01-13
JPS5812971B2 (ja) 1983-03-11
JPS5132172A (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html) 1976-03-18
CH587564A5 (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html) 1977-05-13
DE2528562A1 (de) 1976-01-29
GB1464201A (en) 1977-02-09

Similar Documents

Publication Publication Date Title
US3882339A (en) Gridded X-ray tube gun
US3967150A (en) Grid controlled electron source and method of making same
US3558967A (en) Linear beam tube with plural cathode beamlets providing a convergent electron stream
US3500110A (en) Noncurrent intercepting electron beam control element
US3154711A (en) Electron beam focusing by means of contact differences of potential
US3983446A (en) Gridded convergent flow electron gun for linear beam tubes
US2953706A (en) Electric discharge device
US2254095A (en) Electron beam discharge device
US3917973A (en) Electron tube duplex grid structure
US2914694A (en) Cathode assembly
US4227116A (en) Zero-bias gridded gun
US2727177A (en) Electrostatic lens system
US2967260A (en) Electron tube
US3334263A (en) High frequency electron discharge device having a grooved cathode and electrodes therefor
US2930933A (en) Voltage tunable magnetron
US3934168A (en) Grid support means for a planar tube
US4011481A (en) Modular electron discharge device
US2454031A (en) Electric discharge device of the magnetron type
US3706002A (en) Electron gun
US4321505A (en) Zero-bias gridded gun
US3392300A (en) Hollow-beam electron gun with a control electrode
US2806166A (en) Electron discharge device
US3389295A (en) Broadband discharge devices of the transmission line type
US3431420A (en) Crossfield photoelectron multiplier tube having channeled secondary emissive dynodes
US2790922A (en) Electron multiplier tube