US2073885A - Electric discharge tube - Google Patents

Description

March 16, 1937. H. J. SPANNER ET AL ELECTRIC DISCHARGE TUBE Filed Oct. 4, 1929 INVENTORS 5 0/13 J-fiiammer Os'kflr ATTORNEYS Patented Mar. 16, 1931 9 UNITED "STA-TE ELECTRIC DISCHARGE TUBE Hans J. Spanner and Oscar Gadamer, Berlin, Germany, assignors, by mesne assignments, to said Hans J. Spanner Application October 4, 1929; Serial No. 391,421

In Germany July 1, 1929 10 Claim.

This invention relates to gaseous electrical discharge devices and more particularly to such devices in which an electrode is heated to glowing temperature by the action of the discharge.

As described in prior applications of the applicant, Spanner, alone and with others. there have been developed cathodes for electric discharge tubes which are capable of sustaining discharges at 220 volts either direct current or the alternating current, such dimensions of the tubes may be approximately a meter long by 2 centimeters in diameter.

In order to start such discharges various devices have been employed which require a plurality of leading-in wires in each stem, many of the devices requiring three or more wires in each stem.

Onev object of our present invention is to provide an improved and simplified construction wherein only one leading-in wire is required. The foregoing and other objects of the invention may best be understood from the following description of one embodiment thereof taken in connection with the accompanying drawing in which Fig. 1 is a plane view of a discharge tube showing the cathodes and supporting structure;

Fig. 2 is an enlarged perspective view of one of the cathodes and the supporting structure therefor; and

Fig. 3 is a greatly enlarged perspective view showing the construction in detail of one turn of the cathode helix.

Referring to the drawing more in detail the reference character ll indicates a gas discharge device with enlarged end portions l2 and IS in each of which there is sealed a stem I4 which serves the same function as the usual stem. A

single leading-in wire I5 is sealed-into each stem and carries a supporting frame iii. A closed loop "is secured to the supporting frame as at i8 and i9 and is supported thereby in such a manner that it lies disposed substantially perpendicular to the supporting frame. A cathode is indicated at 20 and is so disposed that it constitutes a portion of the electric path provided by the closed loop l'l. While the electrode shown at 20 is described as a cathode it is to be understood that in a tube adapted to be used on an alternating current circuit each electrode 20 acts alternately as a cathode and as an anode as the polarity-of the potentialdifierence across the tube terminalsis periodically reversed. Small pieces of magnesium 2| may be mounted on the loop l1 and secured thereto in any suitable manner as by bending'overand clinching. If desired provision may also be" made for additional quantities of getter-material such as magnesium by securing a small box 22 or similar receptacle to the frame It. This is preferably so disposed that the open side of the box is toward the glass of the container.

Provision may be made for setting up induced currents in the closed loop II. A coil 23 having its axis in the same general direction as axis of the loop l'l is positioned around the tube ii and is supplied with high frequency current by any suitable means not shown. The coil 23 is shown at one end only but it is to be understood that a similar coil may be provided at the other end.

In order to facilitate the starting of the discharge the outer wall of the glass tube may be provided with a conductive coating. This may. be in the form of a bronze varnish, one portion of such coating being shown at 24 which portion is connected with one of the leading-in wires ii. The other portion is indicated at 25 and is connected with the other leading-in wire I5. A space as indicated at 26 separatesthe two portions of the conductive coating and is preferably positioned near one of the cathodes 20. It is to be understood that the thickness of these coatings as shown on the drawing is greatly exaggerated. A second coating similar to the first one may be applied to the other side of the tube, the two portions 21 and 28 of the coating being separated by a space 29 near the opposite cathode 20. It is not essential that there shall be two coatings, one on each side of the tube, but such an arrangement is advantageous in case one of the conductive coatings fails to function to start the discharge. For red tubes a gold varnish is preferable and for blue tubes a silver varnish.

The cathode may have associated therewith specially activated materials such as barium or compounds thereof and preferably with the addition of amphoteric compounds and may be constructed in the form of a thorn crown cathode. Such a construction is shown in Fig. 3. A plurality of wires 30 are loosely twisted together and at certain points may be cut and pulled outwardly as indicated at 3! giving to the whole arrangement the appearance of a crown of thorns. The discharge takes place quite readily at the points and thereafter passes over to the other portions of the cathode. The interstices in the loosely arranged wires afford space for activated material such as barium and by the construction shown such material is well held in place mechanically.

In degassing the cathode the evacuated tube may be filled with a rare gas such as argon to a pressure of about 2 millimeters when the tube may be sealed off and the ultimate formation of thecathode undertaken together with the cleaning of the rare gases in the sealed-off condition. For this purpose the two leading-in wires l5 are connected through a ballast resistance to a 220- volt alternating current circuit. When the discharge current reaches a value of three to'ten amperes the cathodes and the loops start to glow and the magnesium gets so hot that it vaporires and through its getter eflect purifies the rare gases. gas with the addition of metallic vapor.

In discharge tubes designed for operation on alternating current circuits the cathodes at each end of the tube are of the same constructions when the tube is designed for operation on direct current circuits only, one end may be constructed as an anode of any suitable type and material such as carbon or sheet nickel and the anode may be provided if desired with getter material.

The above described discharge tube may be used for various purposes, especially for neon tubes operating directly from the supply lines, ultraviolet radiators, rectifiers, and also for oscillation and modulation tubes.

' It is to be understood that the above described embodiment of the invention is for the purpose of illustration only and various changes may be made therein without departing from the spirit and scope of the invention as defined in the subjoined claims.

We claim: I

l. A self-heating cathode for gaseous discharge devices which comprises a body of conductive material having fine points of its conductive material projecting therefrom to form isolated points at which an initial discharge may be concentrated whereby to heat said point and thereby to increase its electron emissivity, and activation material carried by said body near said points to render the body emissive when cold.

2. A gaseous discharge device of the type having a sealed tube, a gaseous filling therein adapted to carry the discharge, and thermionic cathodes at opposite ends of the tube which operate at incandescence, which is characterized by at least two conductive members substantially in contact with the wall of the tube adjacent the opposite cathodes, each adjacent one of the cathodes and connected to the opposite cathode whereby to bring its charge to a substantial part of the wall adjacent the first-named cathode.

3. A gaseous discharge device of the type having a sealed tube, a gaseous filling therein adapted to carry the discharge and thermionic cathodes at opposite ends of the tube which operate at incandescence, which is characterized by at least two conductive members substantially in contact with the wall of the tube symmetrically arranged about the circumference thereof.

4. A hot cathode arc discharge device which comprises a sealed tube; electrodes positioned at opposite ends of said tube at least one of which is a cathode comprising a conductive base having thin isolated projectionsthereon adapted to carry the initial discharge with concentration of the heating therefrom and massive activation .which is emissive when cold surrounding said projections whereby to be heated thereby to increase its emissivity; a single lead-in wire for each electrode; and a conductive strip near the path of the discharge adapted to prevent the blocking of said path by accumulation of excessive charges.

5. In a radiant discharge, an elongated tube permeable to radiation from the discharge, elec- The tube may also be fllled with inert portions to a glowing temperature and, with the decreased potential drop across the tube which results upon heating of the isolated portions of a the electrode, to provide a current loading sumcient to heat substantially the entire electrode to glowing temperature.

6. In a radiant gaseous discharge device an elongated tube permeable to radiation from the discharge, electrodes spaced apart therein, a filling adapted to provide a discharge conducting atmosphere between the electrodes, and an energizing circuit to start and maintain the discharge in said atmosphere, in which at least one of the electrodes comprises a plurality of wires longitudinally interlaced and having in the interstices between them a material which is electron emissive at room temperatures and having substantially isolated portions of the wires projecting from the body formed by the wires and associated with the electron emissive material, and said energizing circuit is adapted to provide an initial current loading which is suificient to heat said isolated portions to a glowing temperature and, with the decreased potential drop across the tube which results upon said heating of the isolated portions, to provide a current loading sufficient to heat substantially the entire electrode to glowing temperature.

'7. The method of activating an electrode in a gaseous discharge device, which comprises applying to the electrode an activating material, sealing the electrode into a discharge tube, pumping the tube, subjecting the electrode to heating by induced high frequency eddy currents, and thereafter heating the electrode to glowing temperature by a gaseous discharge from said electrode.

8. A uni-potential electrodev for an electric gaseous discharge device comprising a stranded wire of refractory metal, oppositeends of which are electrically connected together, and having strands thereof in' loosely engaged side-by-side relation, and an electron emitting activation material held by said wire and within the space between said strands.

9. A uni-potential electrode for an electric gaseous discharge device comprising a body of refractory wires, the wire at the surface of said body being relatively fine as compared with the mounted with respect to wire within the body under said surface wire, and an electron emitting activation material held by said wires and within the interstices therebetween.

10. An electric gaseous discharge device comprising a sealed envelope, a gaseous atmosphere therein, and a plurality of electrodes sealed within said envelope, at least one of said electrodes consisting of a body of a refractory metal in the form of wire, and having wire at the surface thereof loosely overlying wire within the body and an electron emitting activating material held by said wire and within the interstices between said inner and overlying portions. 1

HANS J. SPANNER. OSCAR GADAMER.

thickness of the body as a whole and being loosely

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