US1929043A - Gas filled tube - Google Patents

Description

Oct. 3, 1933.

Filed Aug. 30, 1930 C. J. R. H. VON WEDEL GAS FILLED TUBE INVENTOR ATTORNEYS Patented Oct. 3, 1933 UNITED STATES PAT "I: V f m"j assignor to Electrons, Inc.,. a corporation Delaware OFFICE.

Arman; August so, 1930. SerialNo. 41:355.

' -10; (awe-ms This invention relates to gas fllled tubes of the type adapted to, carry relatively heavy currents,

such as rectifier-s, and has for its object means to prevent injury to suchtubes by a rush of plate 5 current at the time ofstarting thetubes.

The present construction of gas filled rectihers, except in-thecase of very small tubes, requires closing the filament'circuit and waiting for the filament to heat up before closing the platoon- 1n .cuit. The necessity for this delay is due to the fact that with tubes more than approximately 50 volts on the plate, the gas becomes ionized as soonastheplate direct current circuit closed. 7 These ions falling 15 through the full potential of the plate circuit ac- (wire a high velocity and bombard the filament causing a rapid. and sputtering of the latter. After the fllament'is heated up, however, it emits sumcient elxtrons to neutralize '30 most of the ions before they reach the filament,

and those which do fall on the filament have only a velocity corresponding to the potential drop across the are which is relatively low, being of the order. of 10 volts, and do not-cause rapid g disintegration of the fllament.

Also, when currents of low amperage are used 'the bombardment duringthe starting period of thetube is fairly well distributed over the entire cathode or filament and the disintegration may 0 be sufficiently slow to givethe tube a practical life. But with currents of theorder of ampere or more the bombardment is apt to concentrate on one spot, heating it up sothat it emits electrons with the result that the whole load is carried on one small hot spot or scintillation point, andthe cathode and its oxide coating grate rapidly at this point. The result is that the tube will only standa'verylimitednumber of cold starts, and each reduces the life considerably, so that such tubes. are not practical commercially. v v V The delay in waiting for the filament to attm'n the proper temperature is inconvenient, and is not always observed, so that many manufacturers will not risk putting out apparatus inwhich the proper performance depends upon the operator waiting the requisite period'of beforeclosing the plate current switch. The alternative isto'use an expensive time relay the cost of which is often prohibitive and is many times the cost of the tube itself. 7 I

In my invention I overcome the above objections by providing an electric shield or screen to prevent bombardment of the filament during the starting period, which screen does not interfere withthe normal operation of the tube after the filament has reached the proper operating temperature.

Fig. 1 of the drawing is a side view partly in section of'a tube constructed in accordance with my invention;

Fig. 2 is a section of the anode assembly taken along line 2 -2 of Fig. 1'; and b Fig. 335 a view of my screen looking downward as indicated by line 3-3 of Fig. 1.

Referring to Fig. 1 a gas-filled tube adapted for full wave rectification and having an anode assembly comprising carbon plates 1 and 1, metallic anode shield 2 and supporting stem 3 is shown. Conductors and 4' connect the respective plates in circuit with a transformer winding 9 which serves as the source of supply. A mid-point connectiomfas shown, from winding Qgoes to one side of the direct current line, the other side of the line returning to the mid-point of winding 10 of the filament supply transformer to complete the plate circuit, The shield 2 (a sectional view of which is shown by Fig. 2) is separated from the plates by, a dntance approximately equal to the mean free path of an electron in a tube of this so type and prevents short circuiting action between the anodes in a full wave rectifier. This shield is also connected to member 6 by conductor 8 to maintain a proper potential thereon. Any other desired anode arrangement, however, may be used. 35

The oxide coatedfilament or cathode elements 5 shown in Figs. 1 and 3 may also be of any detype altho I prefer to use the coil type-and energize the same from the secondary 10 of an alternating current Supply transformer. Surrounding the filaments is a cylindrical metallic shield memherfi which is maintained at approximatelycathode potential by connecting the filaments thereto at their upper ends as shown. At the upper endof member 6 is a metallic shield 7 in theionnof a wire mesh screen which is thus inserted between the filaments and plate. The electrostatic field and therefore the ionization of the gas exists largely between this shield and theplate, and the difierence in potential and voltage gradient between the screen and the filamerits will be very small.

During starting of the tube the shield acts as a cathode andreceives all the bombardment and disintegration whereas the filaments are only bombarded by a few stray ions falling through thescreen. Practically all of the field is between the screen and plate and but very little ionization occurs within the member 6. After the filament-is heated up, however, the ionization is such as nickel, which will not disintegrate as rapidly as the oxide coating of the filaments, and can also be made so that a considerable amountj of disintegration of the screen can take place' without interfering with; the =-operation oi the tube. proper temperature the electronsemitted by them ionize the gas between the. screen and the fila. ments, and the field exerted by the" screen is'"'almost completely neutralized by'theqions ontthe surface of the screen, and the tube'operates very much as if'the screen 'were not present, the "only difference being 'a'slightconstrictionlof the area of the arc discharge due to the space talr'en'up by'the screen and by the sheath of'ions'surrounding'each wire;-- In some cases-thismayincrease the arc drop in the tube a fraction of'af'voltfo'r The screen serves ano'theriirnpojrtant purpose, as follows: When the tube is operating andtlie' load is suddenlyincreased, a transient-condition of ionization is set up during whichltiine" th'earc drop is considerably highe'ntha-n-normal'. {This condition lasts for several eycle's before 'thefila' ments have" readjusted themselves'to thenew temperature and 5 emissive conditions necessary to restore thearc drop to it"s"normal-valuel fpurfing this {time the screen tends'tofmaintain a more normal arc drop in tlie neighborhood'of the filamentsand takes the bombardment due to the higher arc drop'fromsc'reen' to plate This shielding lengthens 'tlielife of the" tuba-subjected to intermittent and rapidly 'fluctuating loads. The 'fact that it screens the filaments from bombardmentreduces thetendency to sputterthe coating during startingand' transient conditions and thus reduces the "tende'n'ey pf'ar'c o'verinthe The side andbottoxnof the shield S'may'be made of nickel or'other suitable material, andthe 'con ne'ctiont ofthe lower end of-the filaments passed through an insulating tubell," the upper end of the'filaments being connected to' the nickel member. Lead-in-wir'es 12 connected in parallel to-"provide greater current carrying ca pacity are connected to the common terminal of filaments 5, while lead-in wires '13, also connected in multiple, serve to support themember 6' and provide'a connectionto complete the filament heating 'circuit. The tubemaybe connected to its external filament and plate circuits in various other ways; than I the "conventional manner Shown V N While the above construction"emb'odies'la preferred form of 'my mvemion,-1fi is to b'e'regar'ded as illustrative only since various-additional'u'ses and modifications thereof will readily suggest themselves to those skilled iri'the iart'yithout the exercise ofinventive skill and without departing from the spirit and scope of my invention: I claim:*

1; In combination ina gas fin d tubgsn anode,

a heatable emissive cathode, means comprising a shield enclosing said cathode an d having a' discharge opening of s'ufilcie r'it area'to offer substantially no resistanc eto the discharge cur After the filaments. havezreached. the

x nected within said tube.

rent, and conductive means dividing said opening into numerous small openings and adapted to prevent destructive bombardment of the oathode during periods of relatively low cathode emission. I

2. A low voltage are tube having cathode and plate electrodes, an electron emissive coating on said. cathode, a metallic shield interposed between said electrodes having a large opening for the main discharge path and a conductive mesh covering said opening, and means for maintaining said shield and mesh at approximately cathode potential, whereby said coating is protected from destructive ionic bombardment during periods --when,. the cathode emission is inadequate for the. discharge current. .3. A gas filled tube having a plate electrode and a filament with an emissive coating thereon,

a cylindrical metallic shield within the tube and surroundingthe filament, said shield being maintained atapproximately filament potential and having its end which is adjacent the said plate electrode covered with metallic mesh to prevent 'ionic'bombarfn'ent ofthe filament coating during starting of the tube and before'the filamen't'has reached the proper emitting temperature, but permitting normal operationof the tube when the proper emissive condition of the filament obtains, f V 4. A gaseousrectifier tube havinga plate electro'de amra plurality" of filaments with emissive coatings thereon, a cylindrical metallic shield Within the tubean'd' enclosing said filaments, one

end of" eachfilament being connected to the s'hield to maintain the same at approximately imam'em potential, and'a conductive mesh formingfthat part of 'said shield between the plate and filamentsf'to prevent ionic bombardment of the filament coatings before the filaments have reached proper emitting temperature but perriitting-normaloperation of the tube when the prope'nemissive conditionof the filament obtains.

""5. A cathode structure m a" gaseous "dis;

chargetube' comprising a heatable filament,- an

electron emissive 'coatingthereon, a metallic enclosure for said filament having a main'discharge bpening therein anda conductive mesh screen fo'v'ei said opening. r

r '6. A gaseous discharge tube comprising a plu? "rality (if-electron emissive filaments connected in parallel, a metallic enclosure for "said filaments, a plurality of anodes external to said enclosure, said enclosure having. an opening therein fora gaseous dischargefbetween said filaments and anodes, a substantially .non-emissive metallic screen covering said/opening, and a' metallic shieldseparating said anodes, said 'screemshield, enclosure and filaments, being conduetivelycon I 7, Agasfilleddischarge tube having a heat able emissive cathode, an anode, a metallic screen member interposed between said electrodes and adjacent the cathodegmeans cooperating',with saidmember for directing the main discharge current through the openings therein, and means for maintaining said member at approximately cathode potential, the said' member preventing destructiveionic bombardment of the cathode surface during periods when the cathode'isnot l

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