US1875002A - Discharge tube with glow cathode - Google Patents

Description

Aug. 30, 1932. HQLST 1,875,002

DISCHARGE TUBE WITH GLOW CATHODE Filed March 17, 1924 l'l'l'l l'l ifl l l @AZZM/W 5 L7; 747% Patented Aug. 30, 1932 UNITED STATES,

PATENT OFFICE GILLES HOLST, OF EINDHOVEN, NETHERLANDS, ASSIGNOR TO NAAMLOOZE VENNOOT- SCHAP PHILIPS GLOEILAMPENFABRIEKE'N, 0F EINDHOVEN, NETHERLANDS DISCHARGE TUBE-WITH GLOW CATHODE Applicationifiled March 17, 1924, Serial No. 699,906, and in the Netherlands March 29, 1923.

This invention relates to improvements in incandescent cathode-discharge tubes, and more particularly to the arrangement and the construction of the incandescent cathode as well asin the way of heating the same.

The invention has special advantages when applied to electric discharge tubes having threeelectrodes and used as receiving tubes for detectors in wireless telegraphy, wireless telephony and similar purposes.

In this kind of discharge tubes particularly when used byamateurs the disadvantage has made itself felt, in that a batteryof direct current is necessary for heating the oathode and the repeated recharging of said battery is troublesome and expensive. Heating the filament with alternating current has the disadvantage that in consequence of the changes of temperature of the incandescent cathode and the changes in intensity of the magnetic field produced around the latter additional sounds are observed in the telephone.

The invention has for its purpose to enable the use of alternating current whilst avoiding the aforesaid detrimental efiects.

It is known to heat the incandescent cathode of electric discharge tubes by conduction or radiation of heatwith the aid of heating units disposed Within the tube. It has also been suggested to provide incandescent cathodes, the surface of WhlCll'GOIlDLlIlS material which yields an emission of electrons that is sufiicient for the operation of the tube at a materially lower temperature than that of an incandescent tungsten filament.

, According to the invention the discharge tube comprises such a cathode and in addition one or more heating units which conduct an electric current and are to be heated by said current, said heating units being locally in direct contact with the cathode but for a considerable part clear of it, said cathode being heated essentially by the conduction of the heat developed in the heating units to the cathode across the place of contact.

This method has the advantage that the heating current does not flow through the cathode itself, and alternating current can be usedfor heating the heating units without the aforesaid disadvantages.

It is of course, obvious that it is not possible to heat the cathode by heat conduction to such a temperature as would be necessary for a sufiiciently intensive emission of electrons of tungsten. It is moreover unneces sary if the surface of the vcathode has applied thereto material which at a low temperature easily emits electrons. It is also obvious that the cathode may be constructed entirely of the said material. It is essential only that the surface of the cathode contains material having the aforesaid favorable property. Such'materials which at a comparatively low temperature emit electrons to a marked extent and neither fuse at this temperature nor obtain an inadmissably high tension of vapour are known. As an example the oxides of the alkaline earth metals, for example barium oxide may be mentioned.

It mustbe remarked that the heating of the cathode which according to the invention principally takes place by heat conduction is partly effected in another way, that is to say, by radiation of heat.

According to the invention a particularly simple construction is obtained if the heating units also supports the cathode.

Furthermore it is advantageous to make the cathode principally of a metal that conducts beat well, and the heating units are preferably constructed of material such for example as chrome iron, nickel-chromium, or similar material having a high resistance.

The choice of a material having a high specific resistance is advantageous because the heating wires if they also support the cathode, must for this reason have a relatively large diameter.

When applying the invention to a discharge tube in which the electrodes are arranged concentrically, the cathode may at each end he carried by a heating wire.

Furthermore it is advisable to supply the heating units and the incandescent cathode with separate leading-in wires, so that the incandescent current circuits are quite independent of the cathode grid circuit and the cathode anode circuit.

For heating the heating units, a transformer may be used, the primary winding of which is capable of being connected to a voltage of alternating current of the usual value for example to the lighting systeln of a town.

Obviously it is detrimental if the cathode leads current from one heating unit to the other. In order to prevent this, one may either heat the heating units in entirely separated circuits for example by using separate secondary coils or 'care may be taken that the cathode makes contact with those pointsof the heating units whichhave practically the same potential.

' cient. -More0ver all the points of the cathode I as the invention.

In the latter case the leadin wires for the heating unitsinay also be branched-within the lamp, so that less leading-in wires need be sealed in and one secondary Winding 1s sufiihavethe same potential,so that it is possible to maintain the advantages of the known equiment.

"Figure 2 is a. side view of the tube shown in Figure 1.

Figure 3 represents in perspectivethe stem of tube shown in Figure 1; said stem having fixed thereto the cathode.

Figure 4' shows a different construction of an electron emitting cathode with heating units.

The tube shown on the drawing comprises an exhausted vessel 1 of glass for example having vhermetically sealed thereto a glass stem 2, leading-in wires for the various parts of the discharge tube being. hermetically sealed in the clamped portion of the stem.

' VVithin' the envelope 1 are en'closed'an anode 3, a grid and anelectron emitting cathode 5. Theanode 8 consists of a cylindricall y bent plate. which maybe of some suitable electrode material such for example as, nickel, and 'is carried atthe two ends by supporting wires 6 and 7, the latter of which also serves as a leading-in wire.

-: The grid 4. consists of 'a helically' bent wire 7 for example of nickelg n olybdenum, tungsten, or other suitable material, and is carried at the two ends by supporting wires 8 and 9, the latterof whichalso serves as leading-in wire.

In the agrisof the electrodes 3 and 4, which front elevation of a discharge I The other electrodes are omitted in th s figure.

are arranged concentrically in relationto" each other is found the cathode 5 which is preferably of material that conducts heat Well, for example of copper and Wliiclris coated at its surface with materialthat easily emits electrons at a comparatively low' teni perature such for example as an alkaline earth metal oxide.

The cathode is carried at its end by two wireloops 11 and- 12 (see also Figure 3% which serve as heating wires and preferably consist, of material having a high resistance such for example as chrome-iron or nickelchromium. Theloop I1 is carried'at its ends by supporting wires 13 and 1 1, the lattero'f which serves as a leadingin wire, whereas the loop 12 is carried by supporting wires 15' and wires are inconductiveconnection by wires the wire'15fbeing used asia leadingi 'i Withinthe tube the ends of the heating 17 and18-s0 that for i'eeding the current-to V the said heating wires it is only-necessary that p two wires are sealed in-the clamped portion of the stem.

' The drawing shows that thecathode 5' makes contact with thosepoints of-the heat s ing wires'that practically have the same' potential' 'so that no current fiows" through thecathode '5. In addition the cathode 5 ispro vided with'a' separate leading-in wire 10,

which has the aforementioned advantages.

a A high vacuum maybe provided in known 1 manner within-thebulb land for. this pur pose'the. glass walland' the-surface of the electrodes may in knownmanner be deprived of the occluded gases; F or obtaining a three electrode tube of these-called soft typeg-a sorted to.

-By reference to Figure 1--the 'circuitarrangenient oi? the' discharge tube shown on the drawing will be briefiydescribed For heating the heatingwires 11' and 12 a transformer 20, 19 is provideditheprimary gaseous filling of'low pressure may; b re winding 20 of which may beconnected by means of a switch 21 to an alternating current circuit of the usual voltagerlorexample to.

the lightingsystem of a town; The transformer whi'ch need transmit only a very: low

power maybe of simple construction. In'the anode circuit are. interposed a battery 23 and a telephone 25," whereas the grid circuit are provided: airegulating con;

denser 26iand parallel thereto a regulating inductance 24, the latter of which: maybe used for intercepting variations ofvoltage;

i In a. construction shown in Figure 4; a

cathode-3O is carried by heating coils 31 and 82, a thin layer of insulating material33: be ing applied between thecathode and the wire 1. In an electron discharge tube, cathode unit including a thermallyiconductive.catlh.

ode member adapted to emit electrons when heated, a plurality of independent electric heaters each in thermally conductive relation to said member, a plurality of pairs of branch conductors, the branch conductors in each of said pairs being respectively connected at their adjacent ends to one of said heaters to supply current thereto, and two main conductors each connected respectively to the free end of one branch conductor in each of said pairs whereby currents alike in phase are delivered tosaid heaters simultaneously, and whereby said cathode member is established in relation to said heaters at equi-potential points in said heater and branch conductor circuits.

7 '2. In an electron discharge tube, an elongated thermally and electrically conductive cathode adapted to emit electrons when heated, a grid and an anode, a plurality of electric heaters thermally and conductively connected to said cathode, and conductors to supply currents to said heaters, said cathode being electrically connected to equipotential points of said heaters.

3. In an electron discharge tube, an electrically and thermally conductive cathode of substantial heat capacity adapted to emit electrons when heated, a grid and an anode, a conductor including branches to supply heating current, an electric heater in each of said branches, said cathode being connected in thermally and electrically conductive rela tion to said heaters at equipotential points on said branches.

4. A cathode comprising an electron-emitting member and a plurality of heating units, each of the heating units being adapted to conduct an electric current and to be heated by said current, the electron-emitting member contacting with each of the heating units at only one point, the electron-emitting member being supported by the heating units at those points at which the electron-emitting member is in contact with the heating units.

5. A cathode comprising an electron-emitting member and a plurality of heating units, each of the heating units being adapted to conduct an electric current and to be heated by said current, the electron-emitting member contacting with each of the heating units at only one point, the electron-emitting member being supported by the heating units.

6. A cathode comprising an electron-emitting member and a plurality of heating units,

each of the heating units being adapted to conduct an electric current and to be heated by said current, the electron-emitting member contacting with each of the heating units at only one point, the electron-emitting member contacting with those points of the heating units which have substantially the same potential. V

7 In an electron discharge tube an elongated thermally conductive cathode adapted to emit electrons when heated, a grid, an anode, and a plurality of electric heaters in thermally conductive relation to said cathode, said heaters being spaced apart and surrounding oppo'site ends of said cathode.

8. An electron discharge tube comprising an anode, a grid, and an elongated thermally conductive cathode capable when heated of emitting electrons from its middle portion, and a pair of electric heaters positioned adj acent the end portions only of said cathode and spaced apart sufficiently to permit an unobstructed emission of electrons from the outer surface of the middle portion of said cathode, each of said heaters comprising a wire loop outside of and in thermally conductive relation to the cathode end adjacent said loop.

In testimony whereof I aflix my signature, at the city of Eindhoven, this 25th February DR. GILLES HOLST.

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