US2094760A - High-power rectifier - Google Patents

Description

Oct. 5 1937. 1., sfiENcER HIGH POWER RECTIFIER Filed March 6, 19256 4 Sheets-Sheet -1 lriAyiiarphL II H I! .IIIAII liqvninvaiir l WWW Oct. 5, 1937. P. I. SPENCER HIGH POWER RECTIFIER Filed Marph 6, 1936 4' Sheets$heet 2 Wow lllllllllu 4 Z J J Hunt m .M. n ll Oct. 5,1937. P. 1.. SPENCER 2,094;760

HIGH POWER RECTIFIER Filed March a, 1936 4Sheejbs-Sheet s Oct. 5, 1937. P. SPENCER 2,094,760

HIGH POWER RECTIFIER Filed Mar ch 6, 1936 4 Sheets-Sheet 4 Z I az 153.12. 8

I 7111611701 PERCY L. 51 5mm? Patented a. 5, 1931 UNITED STATES PATENT OFFICE 2.094.7 0 men-rowan RECTIFIER Percy L. Spencer, West Newton,'Mass., assignor v to Raytheon Manufacturing Company, Newton, Mass., a corporation of Delaware Application March c, 1936, Serial No. 67,411}

16 Claims. (c 250-275) This-invention relates to high-power rectiflers, and more particularly to such rectifiers in which the current is carried by an ionized gaseous dis- Another object of this invention is -to so con- I struct the rectifier that the possibility-of'material particles getting onto the anodes is substantially eliminated.

A further object of this invention is to reduce I the'inversecurrent drawn by the anodes to a minimum.

A still further object is to devise an arrangement whereby the control of pressure around .the anode may be effected substantially independent of ambient temperature around the device.

'I'heforegoing and other objects of my invention will be best understood from the following description of exemplifications thereof, reference being had to the accompanying drawings, wherein:

Fig. l is a side view of one embodiment of my invention, with the front glass wall partly broken Fig. 2 is a vertical section taken along the line 2 2 of Fig. land in addition has a diagrammatical showing of one circuit with which-the tube may be used; v

Fig. 3 is a cross-section taken along line 3- -19 of Fig. 2;

Fig. 4 is a cross-section taken along line ii-6 of Fig. 2; p

Fig. 5 is a perspective view of a portion of the cathode of the tube shown in Figs. 1 and 2;

Fig. 6 is a perspective view of a portion'of the conduit surrounding the cathode of Figs. 1-

and 2;

Fig. 7 is aside view of another embodiment of my invention showing a six-anode rectifier:

Fig. 8 is a vertical section ofthe tube shown in Fig. 7;

Figs.- 9 and 10 are perspective views of portions of the conduit and cylinder surrounding the cathode of Fig. 8;

11 is a perspective view on. portion of the cathode of Fig. 8; Y

' Fig. 1315 a cross-section taken. alongline Iii-i3 of Fig.8;and Fig. 14 is a diagrammatic view of a circuit in which the tube of Fig. 8 may be used. 3

various ways. I were so constructed that vapor or gas streams backs occur.

In rec tifiers, and particularly those which are intended to ,carry high currents and withstand high reverse voltages, difliculties have heretofore been encountered in that such devices had a tendency to .fiask back, that is, that current would flow through the device 'in the reverse direction substantially at the same voltage as it would flow in the conducting direction, and therefore the device nolonger acted as a rectifier. Flashbacks are particularly destructive, not only to the tube itself but also. to the apparatus with which the tube is connected. The

art has attempted to take'care of flashbacks primarily by the use of auxiliary protective devices associated with the rectifier. However, these devices are expensive and relatively unsatisfactory. The present invention-is one which-sub- Flashback "is a, haphazard occurrence which nevertheless is dependent upon a certain number of independent factors. One factor which affects the occurrence of flashbacks is the deposition of material particles on the anode. Such particles may consist of material liberated from the cathode itself.or from various other parts within the tube. In the case where vapor, such as mercury vapor, is used as the ionized medium. the particles mayinclude small droplets of I merbury. Such particles can get onto the anodes in For example, previous devices occurred which were often directed toward the anovzle, and in this way the stream which carried the particles would transfer these particles onto the anode. Even where definite streams of gas or vapor were absent, particles within the interior of the tube would be conveyed, by, the

action of the Brownian movement of the gas- I creases the frequency at which flashbacks occur while a decrease in .the magnitude of the inverse current decreases the frequency at which fiash-.

Where but a single anode is present, the ordinaryinverse current is due to the anode attracting, during the inactive part of the cycle, residual .positive ions which are created during the active part of the cycle but which persist for'a certain length of time after the anode has become negative. the anode has become contaminatedby a par- Of course if the surface of tlcle being depositedupon it and the anode is possibility of any particles getting onto the anode, but also by decreasing the vapor density adjacent the anode. The number of positive ions which exist adjacent the anode is dependent to a large degree upon the vapor density, and therefore a decrease in the vapor density adjacent the anode will decrease the amount of inverse current due to residual ionization.

While the problem offlashbacks has existed to a' considerable degree even with asingle anode, it has been most marked in the case where a plurality of anodes were attempted to be used in a single rectifier. Rectifier tubes having two or more anodes so as to rectify both halves of a1 ternating voltages applied to such a tube had the frequency of flashback occurrence greatly increased over thecase of a single anode rectifier. One factor affecting flashbacks which is greatly increased in the ordinary multiple anode tube is the inverse current which each anode carries. This increase is due to the fact that while one of the anodes is idle, some other anode in the tube is conducting current and producing ionization within the tube. The ions created by such an active anode are accessible to the other anodes in the tube, and thus the idle anode being at a negative potential attracts some of these ions and greatly increases the amount of inverse current which that idle anode draws. Other factors whichincrease the tendency for multiple anode tubes to flash back are those introduced by the increased tendency for material particles to be deposited'onto the anodes. The presence of a plurality of anodes energized in' various. phase relationships to each other produces rotating or moving magnetic and electrostatic fields which tend to produce vapor or gas swirls withfins 5, preferably of the same metal as that of i,

in the tube and which inturnincrease the tendency of any particles within the tubeto reach the anodes. I

The present invention decreases all of the above-noted effects tending. to reduce flashbacks to a minimum so that two and six anode tubes of high voltage and current capacityhave been constructed and operated for periods of many.

hundreds of hours without any flashbacks occurring. I In Figs'.-1 to 6, incfiisive, there is illustrated one-form of a plural anode rectifier incorporating the-above principles. The rectifier comprises a glass envelope l containing a cathode 2, and a plurality of anodes 3. The cathode, as shown most'clearly in Figs. 2 and 5, consists of a cylirider 4 of a refractory metal, such as, for example, tantalum carrying a plurality ofexternal radial the cylinder 4. The *lower end of the cylinder 4' is closed by a metal plug 6. The exterior of the cylinder4and the fins 5 may be coated with an electron-emissive coating, such as, for example, the oxides of the alkaline earth metals, although it is possible and often desirable-merely to oxidize these surfaces which become activated'by subsequently depositing an activating material,

. thereon, as will be described below. The exterior of the cylinder 4 and the fins "5 are heated to a temperature of thermionic emission by means of a heating filament 'I placed within the cylinder 4 and connected at its lower end to the plug 6-.

vaporizable material,

the cathode.

flexible lead III to a lead-in wire I I sealed through a glass stem l2, as shown in Fig. 2. In order to provide a connection to the cathode for carrying the load current and also for providing the other terminal for the heating filament, the upper end of the cylinder 4 is surrounded by a clamp 54 which is provided with extensions and 56 at the opposite sides thereof, as shown in Figs. 1 and 4. The outer end of extension 55 has connected. thereto a lead IS, the upper end of which is in turn connected to the lead-in wire l4 likewise sealed through the glass stem l2.

As pointed out in the co-pending applications of Marshall and Spencer, Serial No. 605,249, filed April 14, 1932, and Serial No. 729,101, filed June 5, 1934, it is desirable to have a relatively high density of gas or vapor adjacent the emitting surfaces of the cathode and also to provide means for continuously depositing on the emitting surfaces of the cathode a material which maintains the electron-emissive properties thereof. These features are claimed in said co-pending applications. I make use of these principles by surrounding the cathode 2 with a tubular conduit l5, the lower end of which dips into a pool I6 which preferably consists of an easily such as mercury, with which is mixed an activating material, such as an alkaline earth metal, preferably barium. The glass envelope I is provided with a lower well I! which contains the pool l6 and also the lower end of the conduit IS. The lower end of the conduit [5 is heat insulated, so as to maintain the portion of the pool l6 within the conduit at a higher temperature than the portion thereof external to the conduit. This is accomplished by surrounding the lower end of the conduit l5 by a cylinder l8 spaced ashort distance from the exterior walls of the conduit l5. The space'between the cylinder and the conduit I5 is closed at the lower end by a ring l9, and at the upper end by an annular cap 20. The heat liberated at the cathode by the heating filament I and also by the passage of the discharge will be radiated down onto the upper surface of the pool 16 within the conduit I5, and some heat will also travel the conduit l5 and past the emitting surfaces of This action maintains the emitting' surfaces'of the cathode as described and claimed in said co-pending applications. i

The anodes 3 cooperating with the cathode 2 are located outside of the conduit l5, and the discharge from the cathodeto each anode passes through an opening 22 provided in the walls of the conduit l5 adjacent each anode. Each anode is mounted on a lead-in conductor 23 which is sealed, througha stem 24. The portion of the lead -in conductor 23 between the stem 24 and the anode is protected by. a carbon sleeve 25 closely"surrounding the lead-in conductor 23. The lower end of the carbonsleeve 25 is preferably seated in a recess. 26 provided in the upper .end of each anode 3.

In order to decrease the inverse current to each anode to aminimu-m, each anode is entirely separated from'each of the other anodes in the tube,

\ that the positive ions created by the discharge passing to. one of the anodes are not available to increase the inverse current to any of the idle J anodes. Thus the anodes are surrounded by a box-like structure. This box-like structure includes the cylinder 28 surrounding the anodes,

and preferably is constructed of two semi-circu-" The space between the cylinder 28- lar plates. and the conduit I5 is closed at its lower end by an annular plate 29. The upper end of this space is likewise clcsedby an annular plate 30 Y which is'provided with a plurality of openings 3| 28, completely separating the two anodes. The

to allow the lead-in wires 23 carrying the carbon sleeves 25 to pass through. These openings 3| are in turn closed off from the'interlor of the tube by sleeves 32. each fastened at its lower end to the plate by means of a welding ring 2|,

. and clamped at its upper end around the stem 24 by meansiof a clamp 33. The anodes 3 are separated from each other within the box-like structure by means of partition plates 34 which extend from the top to the bottom of the cylinder partition plates 34 are preferably retainedinplace by being weldedat one end thereof between the ends of the semi -circular plates, constituting the cylinder 28, and-at the other end thereof be Qtween two semi-circular portions constituting the portion or the conduit l5 adjacent-thereto.

, Although the'anodes 3 are separated from each other within the cylinder 28 by means of the partitioning plates 34, yet a path for the passage of positive ions from one anode to another might exist through the openings 22 in the conduit Id. In order to avoid this possibility, the radial fins 15 of the cathode 2; in addition to serving as additional electron-emitting surfaces of the cathode, arejso' arranged as tointercept any such path betweenthe anodes. For this reason the radial finsi are arranged as shown most clearly in Fig. 3, wherein a fin [extends on each side of an opening 22 from. the cylinder 4 to the inner walls of the conduit I5. In addition, the cathode is operated-at a sufficient degree of electron emission so that the cathode-surfaces in the regionadjacent each opening 22' and surrounded by the two adjacent fins v5 emit a sufllcient number of electrons to carry the maximum current flowwhich can be drawn by that idle anode. The

inverse current drawn by the anodes.

the tube is made produce a beneficial eifect by the indentation of the walls of the conduit I! below each opening 22 forming a louvre 35. In this way an aspirator action is produced at each opening 22,-tending to evacuate the space adjacent each of the anodes 3. This aspirator-tends to remove any particles which may exist in the space adjacent the anodes, and therefore the movement of any such particles, instead of being in -a direction toward the anodes, is in a direction away from the anodes so that the possibility of such particles getting onto the anodes is greatly decreased. Furthermore, the anodes being completely enclosed, as shown, the aspirator 1 action will produce a decrease in the gas or vapor densityadjacent the anodes, and as pointed out above this in turnwill produce a decrease in the amount of residual ionization adjacent each anode, which in turn will reduce the amount of The evacnation by the vapor stream of the anode region can be so designed that the pressure conditions around the anodes are made substantiallyindewhich pressure condition is not subjected to any -"site sides of the extensions 55 and I8, and at complete enclosure of each 'anode in the manner indicated also decreases the amount of inverse! current due to residual ionization-adjacent each anode. The structure surrounding each anode provides a large amount of recombinings'uri'aces for the residual ions so that at the termination or the active part of the cycle, the residual ions will tend to recombine-largely on these recombination surfaces. and relatively few of these residual ions will be available to supply'inve'rse current to the anode.

The jet of vapor from the pool I, which as previously mentioned passes up past the surfaces sudden variations or disturbances which might present. This steady pressure or density state of the vapor or gas adjacent the anodes eliminates the possibility of any sudden swirls or eddies of vapor which wouldupset pressure conditions adjacent the anode, and might carry particles onto the anode. If such conditions are present. it has been found that the anodes tend to flash back. Having eliminated these conditions vided which surrounds the upper end'of the conduit l5 and extends from the plate 30 to a level considerably above the upper end of the conduit ii; The duct 38 is also preferablymade of two semi-circular plates, and is held in placc'by having these plates welded at their lower ends on oppotheir upper ends on opposite sides of the conductor I I3 The upper end of the duct 36 is open so that the vapor which passes up through. the conduit l5 and into the duct 38 is free to pass out into the space within the glass envelope I. The vapor thus passing outinto the envelope I condenses and runs back into the pool 16. The duct 38 prevents drops of vapor, which condense within the envelope I and drop down onto various parts of thestructure therein, fronr' splashing back into the conduit Ii. Therefore, the possibility of any condensed vapor drops passing'into the discharge space where they might. :-create pressure dissubstantially eliminated. In order further to eliminate the possibilities of any such droplets turbances which tend to produce a flashback is 6 falling directly into the duct 34. a shield cap 3'! is provided over the upper end of the duct It so as to prevent any droplets from falling directly into the duct". The cap 31 may be supported by being welded to one of the lead-inconductors l4. It is insulated from the other lead-in conductor ll byan insulator l0.

- The stems l2 and 24 are formed as part of a larger reentrant stem '3! in the upper end of the glass envelope I. In order to remove strain from the stems l2 and 24 and in order to,support the structure within the tube more rigidly, a clamp 40 is provided around'the stem 39. This clamp 40 moved from the stems l2 and 24. In order to prevent an excess amount of heat from .being radiated to the lower wall of the envelope 1, which in turn would tend to evaporate mercury from the external portion of the pool IS, an annular shield 42 is provided below the plate 29, and is supported by being welded to the outer wall of the conduit l5.

The lead-in wires H, l4 and 23 are preferably provided with external flexible leads 43, 44 and 45, respectively for the heating filament l, a transformer 46- having its secondary 41 connected to the two leads 43 and 44 is provided. In order to-supply the main current to be rectified, a load transformer 48 may be provided whose secondary 49 has its opposite ends connected to the two leads 45 which in turn are connected to the two anodes 3. Since the flexible lead 44 which is connected to the lead-in wire l4,is connected directly to the cathode, it is made to serve as one of the leads for the load current. A center tap50 is provided on the sec-1 ondary 49 which has a connection 5| extending to the lead 44. In the connection 5i may be connected a filter 52 to the output terminals of which a load 53 may be connected.

When the transformers 46 and 48 are energized, the heating filament I will raise the cathode to temperature of thermionic emission, a stream of vapor will be given ofi from the pool 16, and a discharge will fiow between the cathode 2 and the anodes 3, resulting in the fiow of a rectified current through the connection 5|. This current will be smoothedout by the filter 52, and a'substantially uniform direct current will flow through the load 53. As described above, the tube under such operation will be able to handle large currents and voltages without danger of flashback.

If it is desired to increase the size of the anodes, the-spacing between them, and the number of anodes involved over that shown in Figs. 1 to 6, inclusive, 2. structure such as that illustrated in Figs. 7 .to 14, inclusive, may be utilized. In these figures the tube shown comprises a glass envelope 51 containing a cathode 58 and a plurality of anodes 59. In the embodiment shown in these figur'es, six such .anodes are shown. The cathode. is very similar to that described above, and consists of a cylinder 68 having a heating filament 6| within it and carrying a plurality ofradial provided by a clamp H3 surrounding the upper end of the cylinder 68 and provided with extenslons 68 and 69. To the outer end of the extension 68 is connected a flexiblelead 18 which in turn is conne'ctedat its upper end to the lead-in con-- ductor II also sealed through the stem 66. i

In order to supply heating current 1 ductor 19 sealed through a stem 80.

As in the case of Fig. 2, the cathode 58 issurrounded with conduit 12 having a plurality of openings [3 through which the discharge passes from the cathode '58 to the respective anodes 58. The lower end of the conduit I2 dips down into a pool 14 contained in the lower well 15 of the envelope 51. The pool 14 likewise preferably consists of a mixture of barium and mercury. The end of the conduit 12 dipping into the pool I4 is insulated by a heat shield 16 of similar construction ,to thatshown in Fig. 2. In order to .control and regulate the amount of vapor given off from the pool 14, one or more heat baffies 11 are interposed between the cathode structure and the pool 14. These heat baffles extend into the conduit 12, and are provided with central openings 18 through which the vapor given off from the pool 14 may pass, and likewise through which heat from the cathode structure may be radiated down onto the pool inorder to produce the vaporization. By regulating the size of the opening 78, the amount of vapor given off from the pool 14 may likewise be regulated. By making the heat baffles continuous from the' openings 78 to the exterior of the conduit I2, the radiant heat intercepted by the heat baffles I1 is radially conducted along these heat baflies and radiated by the portion thereof external to the conduit 12. Likewise by intercepting the continuity of the walls of theconduit I2 by the interposition'." of the heat baflles 11, the amount of heat conducted directly down along the Walls of the conduit is reduced to a relatively small amount, and therefore the amount of vapor produced .is determined primarilyv by the size of the openings 18.

Each anode 59 is mounted upon a lead-in con- In order to produce a high-leakage path along the seal of the stem 88 in the; case where high voltages are being used, the stem 80 may be provided with an integral sleeve 8| surrounding the leadin conductor J9 and extending from the stem 88 to the end of the anode 59. Each anode is likewise provided with a shield 82, the outer end of which is clamped around. the stem 88 bymeans of a clamp 83, and is prevented from rototing on the stem 80 by means of a glass bead 84 projecting into a cooperating opening in the shield 82 and the clamp 83. The shield 82, which at one. end is of. the same diameter as the stem 80, may be provided with'a portion 85 of inprovided with a central opening through which the end of the anode can project. In this opening is welded a sleeve 88 over the outer end of which the member 85 fits snugly. Between each one of the side wall plates 81 is welded a partition wall 89 which extends from the side wall plates to a cylindrical member 98 surrounding the conduit 12 within the box-like structure 88. This cylindrical member 80' is provided so that the partition walls 89 may be readily welded thereto. The cylindrical member 90 is prefer ably placed as" close as possible to the outer wallsof the conduit 12, but may be spaced theretromat a definite distance by means of spacing a,oe4,vco 4 associated shield a: is inserted through the outer members In order "to provide a passage for .each, 01' the anode discharges, the cylindrical member 90 is provided with openings 92 each adjacent the corresponding opening I3 in the conduit 12. The top and the bottom of the box-like structure 88 are closed by means of a plurality of wedge-shaped plate sectors 93. In

order to prevent the accumulation or any condensed mercury on the top of the box-like structure, it isfurther provided with a smooth plate 00 covering the top wedge-shaped sector plates 9!. The plate 94 is provided .with a central opening .through which the upper end of the conduit 12 projects.

Inorder to complete the separation between the anodes, the radial fins 02 of the cathode 58 extend from the outer walls oi the cylinder 60 to the inner walls of the conduit 12. Each radial fin is located intermediate two openings 13 so bounded by two adjacent radial fins 82. As in the case of the previous modification, this arrangement prevents ionization irom any active anode from reaching an idle'anode so as to increase the inverse current thereto. By operate ing the cathode at the degree of emissivity suggested, the ionization does not extend below the lower end of the cathode 58 nor above the upper end thereof, and in this way substantially no ions can travel from one anode discharge to another.

As in'the case of the first embodiment described, the conduit 12 is provided below each of the openingslii with an indentation forming a louvre member 95. These louvre members produce the aspirating action which results in the various advantages as pointed out in connectlonwith said first modification. The structure is also provided with an upper; duct member 96 consisting of two semi-cylindrical plates welded together on opposite sides of the projections 68 and and on the opposite sides of the upper end of the flexible conductor 10. The upper end of the duct 96 is protected against condensed vapor.v droplets falling into 'it by the shielding invention within the art.

cap 91 which may, be supported by being welded together to the lead-in. conductor II. The cap may be insulated from thelead-in conductor '00 by means of an insulator 98. The shielding cap 91 may further be steadied by means of a.

stay wire welded to the cap 91 and the duct 98.

The stem 80 is formed as part of a reentrant portion I00 in the upper end oi! the envelope 51.

The reentrant portion I00 is provided with a clamp I 0| which in turn carries a plurality oi! supporting channels I02 welded at their upper ends thereto and at their lower ends to the boxlikestructure 06, whereby the weight of the internal structure ofthe tube is" supported mainly from the reentrant portion I00.- Each 01 the anode stems l0is formed in the outer end of ra- Each anode stem 00 carrying its anode I9 and endot anarm I03 until the member 0! slides over the outer end of sleeve. The stem '00 is then sealed in the outer end of the arm I03.-

The six-anode structure described above may be connected in any suitable circuit, one of which is shown for example in Fig. .14. -A heating transformer I04 has its secondary I05 connected to'the two conductors II and 60 so as to supply heating current tothe heating-filament 0|. In order to supply the main load current to be rectifled, a load transformer having a three-phase primary winding 100 and a six-phase secondary winding I0! is provided. The outer end of each 0! the secondary coils llll ot the secondary winding I0! is connected'to'one of the conductors l0, andthus to an-anode 59. The central point I09 0! the-secondary winding 101 is provided with a connection H0 extending to the cathode conductor II. filter III, to the output terminals of which is The connection may be provided with a connected 9. load II2. When the load andheating transformer are energized, heating current flowing in the heatvapor from the pool I4 up through the conduit I2, supplying an ionizable vapor within the tube .and also performing the various other functions de- [scribed above. The potential impressed between ing filament BI raises the cathode to temperature .25

.of thermionic emission, and produces a flow of This invention is not' limited. to particular details of construction, materials, or processes as described above as many equivalents will suggest themselves to those skilled in the art. For, ex-

ample, certain features of this invention, par-.

ticularly those associated with the complete seping active material thereon for its continued life.

Other modifications and equivalents will readily present themselves. It is accordingly desired that the appended claims be given a broad interpretati'on commensurate with the scope of the What is claimed is: v L-An electrical space discharge device com-- prising an envelope containing a cathode and an anode spaced apart to provide a discharge path between them, a body of vaporiz'able material adapted to supply a vapor filling to said envelope, surfaces within said envelope upon which said vapor condenses, means for conducting said vapor through said discharge path in 'a direction away vfrom said anode to said condensing surfaces, andv means separating and shielding said discharge path from allot said surfaces upon which said cles are prevented from entering said discharge path from said surfaces. v

2. An electrical space discharge device .comprising-amenvelope containing a cathode and an anodespaced apart to-provide a discharge path between them, an enclosure enclosing said anode,

the'wall 0! said enclosure-being perforated to vapor may. condense, whereby condensed parti- 45 ,plurality of anodes, each anode spaced from said cathode to provide a separate discharge path befilling in said envelope, means for producing a stream of said gas'filling past said opening, and means adjacent said opening to produce an aspirator action by said stream tending to evacuate said enclosure. I

3. An electrical space discharge devicecomprising an envelope containing a cathode and an anode spaced apart to provide 'a discharge path between them, a body of vaporizable material adapted to supply a vapor filling to said envelope, surfaces within said envelope upon which said vapor condenses, an enclosure enclosing said anode, the wall of said enclosure being perforated to provide an opening insaid enclosure wall, means for producing a stream of said vapor filling past said opening to said condensing surfaces, means adjacent said opening to produce an aspirator action by said stream tending to evacuate said enclosure, and means separating and shielding said discharge path from all of said surfaces upon which said vapor may condense, whereby condensed particles are prevented from entering said discharge path from said surfaces.

4. Anelectrical space discharge device comprising an envelope containing a cathode and a plurality of anodes, each anode spaced from said cathode to provide a separate discharge path between said cathode and anode, a gas filling in produce an aspirator action by said stream tendingto evacuate said enclosures.

5. An electrical space discharge device comprising an envelope containing a cathode and a tween said cathode and anode, a body of vaporizable material adapted to. supply a vapor filling to I velope upon which said vapor condenses, sepa- I said envelope, surfaces within said envelope upon which said vapor condenses, separating means substantially completely separating each of said discharge paths from each other whereby positive ions created by an active anode are not available to supply an inverse current toan idle anode, said separating means comprising an enclosure enclosing each of said anodes, a wall of each of said enclosures being perforated to pro- ,vide an opening in each of said enclosure walls,

means for producing a stream of said vapor filling past said openings to said condensing surfaces, and means separating and shielding said discharge paths from all of said surfaces upon which said vapor may condense, whereby condensed particles are prevented from entering said .discharge paths from said surfaces.

6. An electrical space discharge device comprising an envelope containing a cathode and a plurality of anodes, each anode spaced from said cathode to provide a separate discharge path between "said cathode and anode, a body of vaporizable material adapted to supply a vapor filling to said envelope, surfaces within said enrating means substantially completely separating each of said'discharge paths from each other provide an opening in said enclosure wall, a gas whereby positive ions created by an active anode are not available to supply an inverse current to an idle anode, said separating means comprising an enclosure enclosing each of said anodes,

a wall of each of said enclosures being perforated to provide an opening in each of said enclosure walls, means for producing ,a stream of said vapor filling past said openings to said condensing surfaces, means adjacent each of said openings to produce an aspirator action by said stream 10 tending to evacuate said enclosures, and means separating and shielding said discharge paths from all of said surfaces upon which said vapor may condense, whereby condensed particles are prevented from entering said discharge paths from said surfaces 7. An electrical space discharge device comprising an envelope containing a cathode and an anode spaced apart to provide a discharge path between them, a body of vaporizable material adapted to supply a vapor filling to said envelope,

a conduit for conducting vapor from said body of vaporizable material past said cathode, said cathode being located insaid conduit, the wall of said conduit being perforated to provide an opening for passing the discharge between said cathode and anode, said conduit extending beyond the active surfaces of said cathode, shielding means for the exhaust end of said conduit for preventing condensed particles of said vaporizable material from entering said conduit through said exhaust end, and means surrounding said anode for preventing condensed particles of said vaporizable material from reaching said anode.

8. An electrical space discharge device comprising an envelope containing a cathode and an anode spaced apart to provide a discharge path between them, a. body of vaporizable material adapted to supply a vapor filling to said envelope, a conduit for conducting vapor from said body of vaporizable material past said cathode,

said cathode being located in said conduit, the wall of said conduit being perforated to provide an opening for passing the discharge between said cathode and anode, said conduit extending beyond the active surfaces of said .cathode, the

exhaust end of said conduit being located at a sufiiciently high level in said envelope that condensed or splashed particles of said vaporizable material cannot enter said exhaust end, and

means surrounding said anode for preventing condensed particles of said vaporizable material from reaching said anode.

9. An electrical space discharge device comprising an envelope containing a cathode and an anode spaced apart to provide a discharge path between them, a gas filling in said, envelope, an enclosure enclosing said anode, a conduit for conducting a stream of said gas past said cathode, said cathode-being located in said conduit, the 50 wall of said conduit being perforated to provide an opening therein communicating with the interior of said enclosure for passing the discharge between said cathode and anode, the wall of said conduit below said opening being indented to provide a louvre for producing an aspirator action by said stream' tending to evacuate said enclosure. I

10. An electrical space discharge device comprising an envelope containing a cathode and a plurality-of anodes, each anode spaced from said cathode to provide a separate discharge path between said cathode and anode, a gas filling in said envelope, means for restricting the discharge from each anode to a different restricted part of said cathode, said, cathode supplying from each of said restricted parts thereof suificient thermionic emission to, supply the maximum discharge to the associated anode which the device is designed to carry, and separating means for substantially completely separating each of said discharge paths from each other, whereby positive ions created by an active anode are not available to supply an inverse current to an idle anode.

11. An electrical space discharge device comprising an envelope containing a cathode and a plurality of anodes, each anode spaced from said cathode to provide a separate discharge path between said cathode and anode, a gas filling in said envelope, means for restricting the discharge from each anode to a different restricted part of said cathode, said cathode supplying from each said surfaces.

' 14, An electrical space discharge device comof said restricted parts thereof sufiicient thermi- I onic emission to supply the maximum discharge to the associated anode which the device is designed to carry, and separatingmeans for separating each of said discharge paths from each other, comprising separate enclosure means enclosing each anode and communicating with the restricted part of said cathode associated with the respective anode.

12. An electrical space discharge device cbm, prising an envelope containing a cathode and an a anode spaced apart to provide a' discharge path between them, a body of vaporizable material adapted to supply a vapor filling tosaid envelope,

' surfaces within said envelope upon which said vapor'condenses, means for conducting said vapor through said discharge path tosaid= condensing surfaces, and means separating and shielding said discharge path from all of said sur- 'faces upon which said vapor may condense,-

whereby condensed particles are prevented from.

entering said discharge path from said s 4o.

13. An electrical space discharge device comprisingan envelope containing a cathode and a plurality of anodes, each anode spaced'from saidcathode to provide a separate discharge path between said cathode and'anode, abody' of vaporizable material adapted to supply a vapor filling aangaid shielding said discharge paths from 1' all of said surfacesv uponwhich said vapor mayv A condense, whereby condensed particles are prevented from entering said discharge paths from prising an envelope containing a cathode and an] anode spaced apart'to provide a-discharge path between them, a body of vaporizable material adapted to supply a vapor filling to said envelope,

a conduit for conducting vapor ,frorn'said body ofv vaporizable material past saidcathode, an opening in the wall of said conduit. for passing the discharge between said cathode .andanode, sur-' faces within said envelope upon which-said vapor condenses, and means separating and shielding said dischargepath from all of said surfaces upon which said vapor may condense, whereby con-- densed'particles are prevented from entering said discharge path from said surfaces.

4 15. An electrical space discharge device 'comprising an envelope containing a cathode and a plurality of anodes, each anode spaced from said cathode to provide. a separate dischargefpath between said cathode 'and'anode, a body of vaporizable materialadapted to supply a vapor filling to said envelope, a conduit for conducting vapor from said body of vaporizable'matrialpast said cathode, openings-in the wall of said conduit for I passing discharges between said eathodeandanodes, surfaces within saidenvelopeupon which said vapor condenses, and means separating and shielding said discharge paths from all of said :surfaces upon which said vapor 'may condense,

wherebycondensed particles are prevented from] entering said discharge paths from said surfaces.

16. Anelectrical space discharge device com prising an envelope containing acathode and an anode spaced apart to provide a discharge path to said envelope, surfaces within said envelope" upon which said vapor condenses, means for conducting said vapor through said discharge path to saidcondensing surfaces, and means sepaare prevented from entering said from said surfaces.

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