US3449625A - Electron tube having improved low-impedance cathode connecting means - Google Patents

Electron tube having improved low-impedance cathode connecting means Download PDF

Info

Publication number
US3449625A
US3449625A US633512A US3449625DA US3449625A US 3449625 A US3449625 A US 3449625A US 633512 A US633512 A US 633512A US 3449625D A US3449625D A US 3449625DA US 3449625 A US3449625 A US 3449625A
Authority
US
United States
Prior art keywords
cathode
tube
impedance
connector
terminal
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
US633512A
Other languages
English (en)
Inventor
Pierre Gerlach
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.)
Compagnie Francaise Thomson Houston SA
Original Assignee
Compagnie Francaise Thomson Houston SA
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 Compagnie Francaise Thomson Houston SA filed Critical Compagnie Francaise Thomson Houston SA
Application granted granted Critical
Publication of US3449625A publication Critical patent/US3449625A/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
    • H01J1/15—Cathodes heated directly by an electric current
    • 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
    • H01J19/42—Mounting, supporting, spacing, or insulating of electrodes or of electrode assemblies
    • H01J19/50—Spacing members extending to 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
    • H01J2893/0005—Fixing of electrodes
    • H01J2893/0008—Supply leads; Electrode supports via rigid connection to vessel

Definitions

  • the central grid terminal conductor and the cathode conductor of greater diameter are intended to be connected to the external input circuit which is very often made up of a coaxial line tunable by means of a plunger.
  • a DC. voltage source is connected to the cathode terminal conductors for providing the cathode heating-current.
  • the said massive conductor rods are, in operation, traversed both by the DC. heating current and by the signal-frequency alternating currents. While such an arrangement has been widely used and accepted as satisfactory, it has been found to increase unnecessarily the ohmic component as well as the reactive component of the input impedance of the tube especially in the higher frequency ranges, of the order of a hundred to a thousand megacycles per second and over. The reasons are the following.
  • the signal currents are due to skin efiect, conveyed exclusively over shallower and shallower surface or skin layers of the conductor rods. Since the conductor rods are necessarily limited in number owing to structural considerations, and since the rods must be made from high melting refractory metals, e.g., molybdenum, which 3,449,625 Patented June 10, 1969 are relatively poor conductors and may not have too good a surface condition, the flow section area for the signal frequency currents becomes insufficiently large and the ohmic resistance therefore rises. For signal frequencies of the order of some hundred megacycles per second, this resistance may assume a very high value in the conventional tube constructions, with the disadvantageous results noted above. It is an object of this invention to provide a cathode connecting arrangement in which this difiiculty is entirely eliminated.
  • the conductive rods connecting the cathode to its respective coaxial plates have a great inductance.
  • said rods and cathode assembly constitutes within the tube envelope an extension of the coaxial line that makes up the input circuit outside the tube.
  • the radial spacing between the adjacent coaxial electrodes is made very small, so that the characteristic impedance therebetween is very low.
  • the radial spacing between the adjacent coaxial connector terminals between the conductors of the exterior coaxial line must be substantially greater, this being necessary to ensure safe insulation and also for accessibility. An impedance mismatch is therefore present as between the characteristic impedance value measured across the electrodes, and the characteristic impedance value measured across the connector terminals.
  • the mismatch is increased by the fact that between these two coaxial line sections is inserted another line section, i.e., the coaxial line made up of the conductive rods used as cathode supply conductors, said line having a characteristic impedance higher than that of the two other coaxial line sections chiefly for wide waveband amplifiers, this double discontinuity, of the characteristic impedance increases the difficulties for obtaining a constant ohmic loading of the input circuit by the electronic input resistance of the tube. It is an object of this invention to reduce the impedance mismatch present between the cathode and grid of a power tube, and their respective terminal connectors.
  • a tube having a direct-heated cathode and massive conductor means connecting each end of the cathode to a related connector terminal of the tube and providing a low-resistance path for direct current therethrough to heat the cathode, thin sheet or strip conductor means connecting one end of the cathode to one of said terminals in parallel with, but distinct from, a portion of said first path and providing in turn a low-impedance path for signal-frequency current therethrough.
  • the lowimpedance path defined by the sheet conductor means includes a tapered impedance matching section.
  • FIG. 1 is a simplified view, generally in axial cross section, of the cathode and grid assembly of a coaxialeleotrode tube constructed according to the invention.
  • FIG. 2 is a similar view of a modified embodiment.
  • the electron tube structure partly shown in FIG. 1 includes a cathode 1 in the form of a cylindrical tubular mesh of helical wires disposed in cross relation.
  • the tubular mesh is secured at its respective ends to a pair of supporting discs 8 and 9 which serve for the mechanical support of the cathode and for the electrical connection thereof in a current circuit as will be presently disclosed.
  • the tube further includes a grid structure generally designated 2, which is cylindrical and coaxially surrounds the cathode 1. It will be understood that the complete tube assembly further includes a cylindrical anode which coaxially surrounds the grid 2 and may constitute part of the envelope of the tube.
  • the anode and related elements are not here illustrated since they are irrelevent to the present invention and may be conventional.
  • the electrode supporting and connecting means illustrated comprise three coaxial terminal connector plates 3, 4, 5 arranged in the stepped relationship shown, being spaced axially with respect to one another by means of ceramic rings 6 and 7, and having downbent peripheral flanges that are spaced axially and radially from one another.
  • the lower terminal connector plates 3 and 4 are associated with the cathode and the upper, largeradius terminal connector plate 5 is associated with the grid.
  • the lowermost terminal connector plate 3 has a massive conductive metal rod 10 projecting from its center, the upper end of the rod being suitably secured to the central part of the upper cathode supporting disc 8.
  • Rod 10 extends through a central opening of the lower cathode supporting disc 9 so as to be electrically insulated from it.
  • the intermediate terminal connector disc 4 is likewise centrally apertured for the free passing through it of the connector post 10, and has a tubular connector member 11 upstanding from an intermediate region thereof.
  • a flanged plate 115 is fitted in and secured to the upper end part of member 11 and has a central opening through which the central post 10 freely extends.
  • Three further massive connector rods or posts 13, have their lower ends secured in equispaced relation to the transverse wall of flanged member 115, and have their upper ends secured to corrsponding points of the lower end cathode supporting disc 9.
  • the cathode and grid electrodes are rigidly supported in their coaxial assembled relationship.
  • the cathode terminal rings 3 and 4 are connected across a source of direct current for heating the cathode.
  • the heating power required may be quite large, higher than 1 kilowatt, usually with a relatively low voltage and a correspondingly high current of the order of several hundred amperes.
  • the heating current flows, e.g., from terminal ring 3 through central post 10, upper cathode supporting flange 8, tubular mesh 1, lower supporting disc 9, rods 13 and members 11511 to the other cathode terminal ring 4.
  • thermionic emissive properties such as thoriated tungsten
  • the cathode has further conductor means connected to it for carrying the UHF alternating signal currents that are normally present in the operation of such a tube.
  • the signal-frequency conductor means comprise an annular series of thin strips 14 having their upper ends connected to the lower cathode supporting disc 9, preferably by being soldered to the inner surface of a peripheral flange of said disc as shown.
  • the lower ends of the strips 14 are similarly connected around the upper end of the upstanding cathode connector sleeve 11.
  • the thin conductive strips 14 provide a low-impedance conductive path for signal frequency current from (or to) the cathode 1 to the terminal connector means 11-4, this path being in parallel with the DC. current path through the rods 13.
  • the cathode-heating direct current and the signal frequency current will each follow its own low-impedance path, ensuring minimum losses and maximum efliciency of tube performance especially for very high signal frequencies, as of the order of hundreds of megacycles per second.
  • the conductor strips 14 may be shaped to provide a gradual transition for the characteristic impedance of the tube from the value thereof as measured between the cathode 1 and grid 2, to the value thereof as measured between the terminal connectors of the respective electrodes.
  • the electrodes of a power tube must be very closely spaced for a number of reasons including the requirement to rise the transconductance and to minimize transition time.
  • the characteristic impedance between the closely spaced cathode 1 and grid 2 regarded as a coaxial line, is correspondingly low, being given by the equation.
  • Characteristic impedanco ⁇ /%z138 log where L represents inductance, C capacitance, and R and R the radii of the outer and inner coaxial electrodes, regarded as the conductors of a coaxial line. Because of the small radial spacing between the cathode and grid, this value is extremely small being of the order of only a few ohms. On the other hand, the spacing between the terminal connectors such as 4 and 5 of the cathode and grid must be considerably larger, in order to provide safe insulation against flashover, and also for reasons for accessibility. The characteristic impedance as measured at the level of said terminal connectors is, therefore, considera'bly larger than the value measured at the level of the electrodes themselves. According to the invention, as illustrated in FIG.
  • this impedance mismatch is minimized by bending the conductor strips 14 to the over-all frustoconical shape shown, whereby to provide a gradual transition between the large-radius portion adjacent the cathode support disc 9 and the smaller-radius portion adjacent the cylindrical connector member 11. Further, a conductive ring 15 is shown connected to the inner wall surface of the cylindrical grid connector member 12 opposite the cathode connector member 11, in order to reduce the effective radial spacing therebetween.
  • the general construction of the electrode assembly is similar to that shown in FIG. 1 and only the differences will be described.
  • the signal frequency conductor strips 14 in this case have their upper ends secured as by welding around an annular shoulder presented by the lower cathode supporting plate 9, which in this instance is of dished construction.
  • the strips 14 are more or less straight, or very slightly cambered, and their lower ends are secured, as with suitable solder, around an annular transition member or ring 16 secured around the circumference of the cylindrical cathode connector member 11.
  • the transition ring 16 has a downwardly tapered frusto-conical surface 17 at its lower end, which provides the desired progressive transition between the characteristic impedance values as measured at the electrode and as measured at the terminal connectors, as explained above.
  • the signal frequency conductor strips 14 of the invention may be made of any suitable temperature-resistant electrically conductive metal, such as tantalum, preferably having polished surfaces to reduce radiation heat losses.
  • the strips may be, e.g., 0.2 mm. thick, and they may have any suitable width, e.g., about 1 cm.
  • the number of strips used and their mutual spacing have any desired values, but are preferably such that the strips are almost juxtaposed around the circumference to define an almost continuous cylindrical surface.
  • the set of conductor strips 14 may conceivably be replaced by a continuous sleeve of thin metal sheet interconnecting the cathode end plate 9 and the cylindrical connector 11, although the construction herein described as comprising a number of separate strips is preferred for a number of reasons including convenience of assembly.
  • the bend imparted to strip 14 in the FIG. 1 construction, and the camber imparted to the strips 14 in the FIG. 2 construction, serves to permit free expansion and contraction of the strips in response to temperature variations. If desired, a swanneck or other sinuous configuration may be imparted to the strips 14 in a suitable region of their length in order to enhance this effect.
  • the grid connector member 12 had an inner diameter of 43 mm. at its lower, end and the cathode connector member 11 had an outer diameter of 32 mm.
  • the transition ring 16 had an outer diameter of 37 mm. and the axial length of the transition surface 17 was about 3 mm.
  • Said ring 16 was made of molybdenum, but various other high-melting metals, such as tungsten, tantalum and the like may be used.
  • thin sheet conductor means connecting one end of the cathode to one of said terminals as to shunt a portion of said first path and providing a low-impedance path for signal-frequency current therethrough in parallel with but distinct from said direct-current path.
  • a cathode in the form of a tubular wire mesh
  • a tubular grid electrode coaxially surrounding and closely spaced from said cathode; coaxially arranged connector terminal means connectable with external circuitry exteriorly of the tube and including two cathode connector terminals and a grid connector terminal;
  • thin sheet conductor means defining a generally tubular surface having its upper end connected to said lower supporting plate and its lower end connected to said other cathode connector terminal, whereby to shunt a portion of said first path and provide a low-impedance path for signal-frequency current in parallel with but distinct from said direct-current path.
  • said sheet conductor means includes a tapered section of diminishing diameter in the direction from said lower cathode supporting plate towards said other connector terminal.

Landscapes

  • Electron Tubes For Measurement (AREA)
  • Microwave Tubes (AREA)
  • Medicines That Contain Protein Lipid Enzymes And Other Medicines (AREA)
  • Electron Sources, Ion Sources (AREA)
US633512A 1966-05-27 1967-04-25 Electron tube having improved low-impedance cathode connecting means Expired - Lifetime US3449625A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
FR63239A FR1490592A (fr) 1966-05-27 1966-05-27 Perfectionnements aux tubes électroniques pour hyperfréquences, notamment aux moyens de connexion interne des électrodes coaxiales de ces tubes

Publications (1)

Publication Number Publication Date
US3449625A true US3449625A (en) 1969-06-10

Family

ID=8609606

Family Applications (1)

Application Number Title Priority Date Filing Date
US633512A Expired - Lifetime US3449625A (en) 1966-05-27 1967-04-25 Electron tube having improved low-impedance cathode connecting means

Country Status (5)

Country Link
US (1) US3449625A (fr)
CH (1) CH462328A (fr)
FR (1) FR1490592A (fr)
GB (1) GB1181574A (fr)
NL (1) NL6707380A (fr)

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2259402B (en) * 1991-09-06 1995-04-26 Burle Technologies Thermally graded filament assembly

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2490786A (en) * 1947-06-26 1949-12-13 Standard Telephones Cables Ltd Cathode for electron discharge devices
US2534548A (en) * 1948-12-30 1950-12-19 Bell Telephone Labor Inc High-power water-cooled electron discharge device
US2542639A (en) * 1948-11-23 1951-02-20 Gen Electric Electrode structure for electric discharge devices
US2683237A (en) * 1951-12-29 1954-07-06 Westinghouse Electric Corp Radio frequency tube with low internal impedance

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2490786A (en) * 1947-06-26 1949-12-13 Standard Telephones Cables Ltd Cathode for electron discharge devices
US2542639A (en) * 1948-11-23 1951-02-20 Gen Electric Electrode structure for electric discharge devices
US2534548A (en) * 1948-12-30 1950-12-19 Bell Telephone Labor Inc High-power water-cooled electron discharge device
US2683237A (en) * 1951-12-29 1954-07-06 Westinghouse Electric Corp Radio frequency tube with low internal impedance

Also Published As

Publication number Publication date
CH462328A (fr) 1968-09-15
DE1589613A1 (de) 1970-07-30
FR1490592A (fr) 1967-08-04
NL6707380A (fr) 1967-11-28
GB1181574A (en) 1970-02-18
DE1589613B2 (de) 1975-09-04

Similar Documents

Publication Publication Date Title
US2353743A (en) High-frequency electronic discharge device
US2585582A (en) Electron gun
US2075876A (en) Cathode organization
US3449625A (en) Electron tube having improved low-impedance cathode connecting means
US2204306A (en) Vacuum tube
US2288380A (en) High frequency radio tube
US2765421A (en) Electron discharge devices
US3979634A (en) Travelling-wave tube with an improved electron gun
US3327156A (en) Electron tube assembly
US2281041A (en) High frequency electron discharge tube
US2513920A (en) Fluid-cooled electric discharge device
USRE15278E (en) Electron-discharge apparatus
US2048023A (en) Dual purpose thermionic tube
US2081415A (en) Electron emitter
US2472942A (en) Electron tube
US2416566A (en) Cathode
US2554078A (en) Electron discharge device and locking means therefor
US2841736A (en) Electron tube and filamentary cathode
US1712402A (en) Vacuum electric tube
US2471424A (en) Electron discharge device
US2859371A (en) Electron discharge device structure
US2247779A (en) High frequency apparatus
US1909051A (en) Thermionic vacuum tube
US3450927A (en) Thermionic cathode with heat shield having a heating current by-pass
US1917991A (en) Vacuum tube filament structure