US2459593A - Feed-back system for electronic tubes comprising hollow body resonators - Google Patents

Description

Jan. 18, 1949. D. H. sLoAN 2,459,593

FEED-BACK SYSTEM FOR ELECTRONIC TUBES COMPRISING HOLLOW BODY RESONATORS Filed March 1v, 1944 43 .E BY

ATTORNEY Patented Jan. 18, 1949 FEED-BACK SYSTEM FOR ELECTRONIC TUBES COMPRISING HOLLOW BODY RESONATORS DavidH. Sloan, Pittsburgh, Pa., assignor to`WestinghousefElectric Corporation, East Pittsburgh, Pa., .a corporation of Pennsylvania 2 Claims. t 1

This invention relates `to a `feed-baci: :system for electronic tubes and has particular relation to `a `fee`d=back system `for `use with 'a tube of the resnatron type iorgenerating ultra high frequency power.

A 'tube of the resnatron `type generally com prises a pair of resonators adapted to lhave relectromagnetic oscillations of substantiallyxthe same frequency.` established therein. A .cathode is mounted within `the first resonator and an .anode is'mounted within the second resonator. The two `resonators are positioned'adjacentr'each other and have openings in `the adjacent walls thereof to permit a flow oi electronsufromV the cathode to the anode. One or more grids are located between the cathode andanode and preferably include a control grid formedby 'the .wall of Avthe irst `resonator about `the openings therein :and anaccelerating grid formed by the Wall of the second resonator about the Openings therein. Means are then provided to supply current through `the cathode to'heat it and to impressa direct-current potential difference betweenthe anode and cathode, the accelerating grid and cathode, and the control grid and cathode.

The resnatron `tube operates `as a tuned-plate, tuned-grid, class C oscillator with the rstiresonator in the controlrgrid-cathode circuit andithe second resonator in the anode or plate circuit. Each ofthe two resonators isrdesgnedto have a principal mode of oscillation in "which .the `vector of the electric field is substantially parallel to the electron path betweenthe cathode andfanode and the fields within the resonators :have a-delnite phase relationship. During operation the anodeand acceleratingogrid have a `relatively high, positive direct current voltage thereon frelative to the cathode tending to liberate electrons from the cathode but the control gridhas 'afnegative voltage such that a group of electrons "are liberated from the cathode only during the peak portion of each `half cycle of the iield in the iirst resonator in which that field `tends 'to Vaid in effecting `liberation of `electrons and movement thereof toward the anode. Thus sharp pulses of electrons are liberated at regular intervals from the cathode.

After liberation, `the electrons are `accelerated in their movement toward the anode by l'the high voltage on the accelerating grid. Thespa/c'ingbetween the *cathode `and anode with respect to the speed of the 'electrons provides #an electron transit time of one-half cycle. Thus, the zliberated electrons rst receive lenergy uirom #theroscil-L lating `field of the rst resonator aswelinsrom l the -.di1ec.t current voltage iields but .they .enter the field of .the :second :resonator while .it op poses their motion and the electronsreonsequentl;r giveupenergy-to the eldpf the second resonator' to iproduce fthe desired `oscillations therein.

A portion rof ithe @power thus :generated in .the second :resonator is `:fed-back to :the .rst `resonator .to maint-ain the ldesired oscillations rtherein. This ifeedback is accomplished through a concentric transmission gline having one .end coupled -to :the :second resonator by ra coupling loop 1.0i :the .usual construction and vthe other end coupled into :the-first :resonator by another similarcoupling. loop. The couplingrproduoesoscillationsin .the :first resonator rin which the controlggrid '.toocathode high frequency voltage is inphase with rthelanode toqaccelerating grid high frequency voltage. The .remaining fpower .is extraoted :fromdshe second resonator by still Kanother coupling loop connected to an outputrtransmission dine. l

The resnatrontube, rwhenproperly constructed, operates asdescribed. `rHowlever, `it has been hfound desirable eto improve -the :feed-back `coupling fsystem .and 4to increase the .powerfoutput :available from .a l.tube of ithis type. The energy -.delivered by thefrelectrons :to :the .eld -o'f .the .second resonatmnnay :be increased by increasing the voltages @impressed .on 1the various .elements which increases Ain =turn thespeed of lthe electrons .fentering .the `second resonator. With :the .increased speed,` however.the transit time of the electrons is `reduced. Whenstlietransit .timerof the elecf trans fis reduced, an increase lin `the `spacings between rthe 1 elements along the lelectron path `is rrequired which @in .turnirequires a `'higher 'voltage to maintain .therelectronspeedso kthat.et-:satisfactorytpower :increase byfthis Lrneans-is rimpractical.

.The feed-back -icoupling 1 system as "usedin lprior tubes :is arsourcefof ,power `.lossas :well as asource of considerable :manufacturing fdiiculty. It :is extremely difficult and .almost Limpossiblegrrom :a practical standpoint to avoid rstanding `wavesin the `:feed-back line. 'Iheserstanding `waves cause appreciable :power losses and introduce `thigh voltage Aproblerrvs. :In reddition, `glass rseals are usually employedxin A`theieed-b1arckiine to permit the maintenance of vthe necessary Vhigh `vacuum fwithinrthe tubc.- However, rthefhigh Moltagesresmtingpfromwthestandirrg waves :in :the 'feed-.back line, are 'very `rlestructive `of the tgl-ass and, with gesfinthe A.form of air in the line, rthe A.sealsare often Abrokensnoring operation of the ytube.

'To avoid the troubles encountered with Vthe glass seals, :a vacuum-.tight feed-.back` `line has Another object of my invention is to provide a new and improved resnatron tube .having an increased power output.

A further object of my invention is to pro- V vide a novel resnatron tube having a new and improved feed-back system.

Still another object of my invention is to provide a novel resnatron tube having a highly ef'- cient feed-back system which avoids the introduction of problems associated with maintaining a vacuum.

More specifically, it is an object of my invention to provide a new and improved resnatron tube having a novel feed-back system and an increased power output.

-Myinvention arises from the realization that the direct-current voltages employed with the resnatron tube can be increased to increase the electron voltage, and, therefore, the power output, with the same spacings between cathode, grids andanode if the phase of the .voltage component of the field within the first resonator be- 4tween the control grid and cathode is shifted to lag by an amount of the order of 90 degrees behind 'the voltage component of lthe eld of the second resonator between the anode and accelerating grid. If the Voltage within the rst resonator lags 90 degrees behind that in the second resonator instead of being in phase, the electron voltage may be increased by four times with the transit time of the electrons reduced to onequarter cycle.

In accordance with my invention, a 90 phase shift of the field voltage of the rst resonator relative'to -the' second can be obtained by connecting a small capacity between the anode and cathode and tuning the first resonator, Within which the cathode is mounted, to substantially the same frequency as the second resonator so thatl the'cathode to control grid impedance is neither inductive nor capacitive. This capacity may be conveniently obtained by positioning a conductive member adjacent to, but spaced from, the anode, and conductively connecting the memberto the cathode. Preferably, this arrangement comprises a molybdenum or tungsten wire attachedto the cathode and extending through the grids into the anode region with the end portion of the wire bent at right angles to form a conductive member adjacent to, but spaced from, the anode. In some eases, where not as much capacity is required, the wire need not be bent at the endneXt the anode but instead may merely extend toward the anode with the end of the wire spaced therefrom.

The coupling wire may be attached to any part of the cathode other than a point of zero voltage with respect to the' control grid, but is preferably connected at a region of maximum voltage. At

this region on the cathode, the anti-resonant impedance of the cathode-grid circuit is at its largest value, with the grid-cathode voltage at a maximum and the current at a minimum. Such an anti-resonant impedance acts as a resistance connected in series with the `capacitance existing between the wire and the anode. When the eld in the second resonator is in a direction that the 4 anode is positive, current ows from the anode through the capacitance, wire and resistance. The voltage established across the resistance by the current leads the high frequency anode-accelerating grid voltage by about degrees with the cathode. positive relative to the control grid. Consequently, the eld in the rst resonator reaches a maximum in a direction aiding movement of electrons from the cathode to the anode electrons leaving the cathode during the peak vportion of a half-cycle of the rst resonator eld in which that eld is in a direction aiding movementof the electrons, enter the second resonator when the eld thereof is in a direction opposing the electron motion and the electrons give up energy to the eld of the second resonator.

If the first resonator is tuned to a slightly different resonan-t frequency, the amount of phase shift is changed as may be necessary or desirable with different spacings and different direct-current voltages.

The novel features which I consider characteristic of my invention are set forth with more particularity in the accompanying claims. The invention itself, however, with respect to the construction and operation of an embodiment thereof, as well as further objects and advantages ofthe invention, may be best understood from the following description of a specific embodiment with reference to the drawing, in which:

. Figure 1 is a cross-sectional View of a resnatron tube embodying my invention;

Fig. 2 is an enlarged, partial view of a crosssection of the tube shown in Fig. 1, as taken along line II--II;

Fig. 3 is an enlarged, partial view of a crosssection of the tube of Fig. 1 as takenalong the axis;

Fig. 4 is an elevational view of one of the anode units; and v Fig. 5 is a top View of the anode unit shown in Fig. 4. l

As shown in Fig. 1, the main portion-of the resnatron tube is enclosed within a generally cylindrical; chamber comprising an upper, cir-l cular plate unit II, two coaxial, cylindrical, metallic members I3 and I5 of the same diameter spaced apartby a coaxial, glass cylinder I1 of the same ldiameter sealed therebetween, with the upper cylindrical member I3 secured to the upper plate unit Il and the lower cylindrical member I5 secured to an intermediate plate unit I9. Another cylindrical member 2I is secured to the bottom of the intermediate plate unit I9 and the lower end of member 2l is secured to a bottom plate 23. A cathode unit 25 extends through a central opening in the bottom plate 23, being secured therein by a cap member 21 and support 28. A cooling fluid, supply chamber body 3U is threadedly mounted in a central opening in the upperplate unit II. The entire chamber 'I is sealed and a vacuum is created and maintained therein by a Ivacuum pump connected to the interior of the chamber by a passage which does not appear in Fig. 1.

The cathode unit 25 includes a plurality of cathode filament wires 29 spaced from each other but arranged to form a generally cylindrical cagelike structure in the center and about the axis of, the. .chamber 1, and a plurality of concentric 8 tubular membersl as `s'lrrown iin Fig 3. Complete details-ofthe cathode unit 525` are disclosedinmy copending application, Serial No. 526,883, 'led March 17,11'944and now U."S.\ Patent No. 21,451,- 981,granted October 119, 19118.

The upper ends `oftlie lamentwires `29 `are soldered aboutthe` circumference rof a 'threaded nut '53| whichis mounted ontheupper fend of one ofthe 'tubular members 33 of `the cathode unit 25. Fromthefnutl, each filament `Wire Z9 extends lradially Ioutward a short 'distance and then downwardly, parallel to theaxis,` with 'the lower "endl of thelament wire extending'radially inward-towardthe axis and secured -to another tubular member 35-Within thecathodeunit. The twotbularmembers and '35jto `which:thefilament wires "29'are attached are spaced from each other Lby insulating `pellets 31. A"'I'he central tubularl member lit!! ofthe cathode unit *25extends upwardly beyond the filament wires 29 to a tuning vplate 45. jThe ltubularmember' 39 is `movable vertically to move the'tuning `'plate 45, by rotation ofthehand `wheel 43 jat the bottom of the resnatrontube. The tuning plate 45i`s 'connected to the tubular member "33 through a ilexible bellows 41. 1

VA cylindricalmember 49 of conductive material is also positioned coaxially within thechamber 1 andsurrounds the cathode unit 25. This member `49, hereinafter called the control grid member, is mounted on another horizontal plate supported from bottom `plate 23 by a plurality of insulators 52. An end plate 53, spaced from the tuning plate 45, extends lacross the upper end of the control grid member. The lower endof the control grid member 49 is spaced from the cathode unit 25 but is associated with still another tubular `member 55, mounted on the support `28 for the cathode unit 25, to form a choke `for highfrequency oscillations. With this structure, a flrstresonator is formed by the plate 53, the control grid member49, member 55, and the cathode unit 25, the `cathode lament wires 29'being positioned within this first resonator.` A cooling UicLsuch-as water, is supplied through an `inlet pipe 561and plate-5I to cool the controlgrid member 49, `in a manner fully disclosed in my aforesaid copending application, and passesvout outlet pipe 58. i i l i.

Openings 51 are provided inthe wall of the control :grid :member V49 opposite each ,of ,thexilamentv wires 29, as illustratedin Fig. `2 to `provide aJg'rid. Means are also provided to cool the control grid member 49 but they are not visible Ain thecross-sectionoflig. 1 but are illustrated in my aforementioned copending application.

A cylindrical unit `63, designated the accelerating grid unit,` comprises :a plurality of 'vertical pipes 65 of conductive material arranged to outline la cylinder concentric with, and surrounding, the control grid member '49. The pipes 65 are spaced `fromeach other,as `shown in `Fig..2, so thatfin the vregion of the `filament Wires 29, the spaces between adjacent lpipes are radiallyoppo site corresponding filamentwires 29and .openings 51 inthe control grid member, `.whereby thepipes 95 form a grid. Secured to and surrounding the pipes 155 above the region of the Afilament wires is a conductive `metal `cylinder 61. A similar cylinder 68 -surrounds the pipes E5 `below `the region of ythe filament wires. A cap6`9 `is secured across the top of the cylinder61 and has openings extend, the capi-having r-anfiliterual `passage-in ccmmimicationwith:the open endsrof all of pipes 65. l

The entire accelerating gridrunit 63 -ismounted on a horizontal 'plate 10 `which `is-supported lfrom l the bottomlplate 123 'by a plurality of iinsulators (not shown). A cooling Aiiuid, `such as `water, fis supplied throughian `inlet `-pipe (notshown) and an `internal passage *1I in plate 10 to one-half of pipes diii. "Thefluidflows up'these pipesto cap 69 and returns through the other half -o'f the pipes to "another internal passage 13 .in plate '1B connected lto an outlet pipe (nots'hown).

The bottomoi the cooling `fluid-chamber body 30 within thechamber 1 lhas a plate 89 'secured thereon ywhich isfspaced from the cap S9 'onthe acceleratingngrid `member 63. This plate -89 is circular and supports a cylindrical member i91 which in turn supports theanode structure. Another cylindrical member 93 foi slightly larger diameter `than the anode supporting member 9| is mounted onthe lower plate 10 and extends upward with its upper end surrounding the anode supporting member andcooperating'therewith to form a quarter 'wave "length, high frequency choke. These two members 9| and 93 `with the plate89, lowerplate finland the accelerating grid member "B3 with Yits cap 69 form a second resonator.

The anode ofthe resnatron tube comprises a plurality of anode units 15, as shown in Figs. l, 4 and'5`, arranged within the second .resonator in a circle around the accelerating grid. .Each of the anode units '15 comprises afconvoluted section of `a hollow pipe `11 of `highly conductive material, such as copper, through which a cooling uid, such as Water, is to be passed. The two ends "19 and 'di of the hollow` pipe extend upwardly -frorn the convolutions with one endlH connected to acoolinguid .chamber S2 in body 3l)` `supplied with cooling fluid from an inlet .pipe line 85and with the .other end Bl connected to another chamber `83in body 35i Afrom which duid isremovedthroughan .outlet line.81.

'Ifhe convolutions .of each .anode unitincludes apluralityof substantially parallel and coextensive vertical, pipe portions whichare slightly longerthan the slotsin `the acceleratingandcontroljgrids 1and, of coursaareparallel `to the verticallament wiresZS. When all .of the plurality ofanode .units arearranged adjacent each other inlacircle about the 4accelerating grid as shown in Fig.` 2, that `part `of thecomplete `anode. having the` largest .diameter is made .upof pairs .of adjacent, Verticalpipe portionsg in engagement .with eachother withleach .pair positioned radially opposite .a filament Wire 29 so that .the center line ofthe electronpathirom a iilamen't wire may be representedbydotted line 92. The otherconvolutions cooperate `with each ,pair 9i! .to outline a groove radially opposite each filament wire into which the corresponding electron path projects. Further details ofthe anode structure and the obi jects and` advantages thereof aredisclosedin my copending application, Serial No. 526,883, iiled March"17,'1944.

A `plurality of feed-back coupling wires 99 are attached atome end 'to the `cathode unit 25 in the 'rstresonator and extend radially through the grids`l59 and Shinto the second resonator. Preferably, fourof these coupling Awires are yemployed,"the number, of courseydependingupon the amount `of lfeed-back power required to operate the 'liirst resonator. `As shown 'in Figs. i2 and '3, eachoffthe-couplingwvires 99 issecured tothe end o atubularlmember lllfl threadedly engaged with the tubular member 33 supporting the upper end of the iilament wires 29 and extends radially through a set of openings in the grids for which the filament wire is omitted. The outer end prtion of each coupling wire is bent at right angles to form a conducting member adjacent and parallel to, but spaced from,.the anode. Thus the coupling wire 99, in effect, provides a capacitance connected between the anode and cathode.

As previously mentioned, the end portion of the coupling wire need not be bent in some cases. It is also to be noted that the omission of a filament wire for each coupling wire may be avoided by connecting the coupling wire to the base |00 of bellows 47 and extending it radially above the lament wires through slightly enlarged openings in the grids.

The two resonators are designed so that their electric field vectors are along radial lines. Consequently, alternate points` of minimum and maximum voltage appear along the length of the cathode unit 25. The -coupling wires 99 may be connected to the cathode unit at any point other than a zero voltage point. However, it is preferable to connect the coupling wires at a point of maximum voltage with respect to the control grid. This is the point of minimum current and the anti-resonant impedance of the cathode-grid circuit with the rst resonator tuned to the same resonant frequency as the second resonator acts as a resistance connected in series with the capacitance existing between the coupling wire and the anode. The voltage drop across the resistance is then shifted on the order of 90 degrees in phase relative to the high frequency voltage be tween the anode and accelerating grid. As previously explained, the voltage drop across the resistance is effective to maintain the oscillations in the cathode resonator with the eld of the rst resonator rising to a maximum inthe direction aiding movement of the electrons 90 degrees behind the field in the second resonator. If the coupling wires are connected at -some point other than that of maximum Voltage, the impedance of the cathode-grid circuit is smaller and a greater capacity would be required to feed back the same power. Tuning of the rst resonator to another frequency changes the effect of the impedance and produces a different phase shift. It is to be noted that the second resonator may also be tuned by raising or lowering plate 89 by screws 04 which may be used to bend the diaphragm 96.

The cathode unit 25 also includes another concentric tubular member IOI positioned between the members 33 and 35. The tubular member IOI is connected at its upper end to the member 33 but is spaced from the tubular member 35 and extends downwardly for a distance equal to the one-quarter wave length. Thus a low impedance is established between member 35 supporting the lower ends of the lament wires 29 and the member 33, supporting the upper ends of the filament wires and the coupling wires, at the point A. This, in eiect, provides a short Icircuit for high-frequency currents in the lament and coupling wires and prevents the escape of high-frequency power through the filament supply circuit which is connected to tubular members 33 and 35.

Direct-current voltages are impressed on the anode, cathode and grids of the resnatron tube as shown schematically in Fig. 1. A source of direct-current potential, such as a battery |03, has its positive terminal I05 connected to the body 30 and, therefore, to the anode. An intermediate tap |01 on the battery |03 is connected to the plate I0 supporting the accelerating grid member' 63 and thenegative terminal |09, is connected through a threaded plug III in housing yI I3 to the tubular member 33 which is connected tothe The tubular upper ends of the filament wires. member 35 supporting the lower ends of the lament wires is grounded through the threaded plug II5 in thesupport 28. Filament current issup-` plied from a source I I9 through a transformer IZI connected to plugs III and II5. The control grid member 49lis connected through the plate 5 I which supports it and a resistor II1 to the nega-y tive terminal |09 of the battery |03. Typical direct current voltageswhich have beenv used in operating a resnatron tube constructed according to Fig. 1 with a 90 degree phase displacement. in the elds, establish the anode at 10,000 volts.

and the accelerating grid at 7,000vo1tsf The conf` trol grid is originally at zero voltage but when the oscillations are initiated, current flows from the control grid to the cathode and the resulting potential developed across the resistor II'I causes the control grid to build up to a voltage of approximately minus 1,000 volts. With other 'iield' displacements diierent voltages should befuse'df. In operating the resnatron tube, the two resolf nators are first tuned to substantially the 'same frequency by means of handwheel 43. The direct,y current voltages are then applied tothe elements in the tube and oscillations are initiated, Y1building'V up gradually until the control grid reaches operati-, ing voltage. Then in a half-cycle when'the field,` within the rst resonator is in a direction to aid-- movement of the electrons, a group of .electrons are liberated from the cathode during the peakI portion only of the half-cycle and move towardv the anode, picking up energy from the high-fre#` speed. WithA this greatly increased speed, the

electrons enter the second resonator approxilmately one-quarter. of a cycle `after leaving the cathode and with the phase displacement of the order of degreesbetween the fields of therst and second resonators, the iield of the second resonator is, at that time, in a direction opposing the motion of the electrons. Consequently, ,the electronsgive up energy to the eld of the second reasonator producing the oscillations therein. Sufficient power is fed back from the second reso nator to the rst resonator throughv the coupling1 wires 99 to maintain the oscillations in. the rst resonator and the greater remaining power in the second resonator is extracted by a coupling loop and fed to an output line 91.

It is to be noted that the feed-back coupling wire provides an eiiicient feed-back system ref. quiring but a Very low current with low losses and avoids any vacuum problems. In addition, the coupling `wire provides a suitable phase-shifting circuit to displace the phase of the field of the rst resonator with respect to the field ofthe second resonator and thus enables higher .direct-, current voltages to be employed resulting in a greater output power from the tube.

Although I have shown and described a specific4 embodiment of my invention, I am aware that other suitable modifications may be made..1,

the specific embodiment disc1osed .A

I claim as my invention:

1. An electronic tube apparatus comprising a pair of hollow body resonators adapted to have electromagnetic eld oscillations established therein, an anode mounted within one of said resonators, a cathode ymounted Within the other of said resonators, said pair of resonators being adjacent each other with openings therein be tween said anode and cathode permitting a ow of electrons from said cathode to said anode, a control grid between said cathode and anode, circuit means connected to said anode and cathode for establishing a direct current potential field therebetween tending to liberate electrons from said cathode and move them toward the anode, additional circuit means connected to said grid and cathode for establishing a direct current potential iield permitting electrons to be liberated from the cathode during the peak portion only of a half-cycle oi the eld within said other` resonator in which it is of a polarity to add energy to the electrons, the strengths of said ields movingsaid liberated electrons toward said anode with a speed causingr them to pass through said one resonator to said anode while the eld therein opposes their motion and absorbs energy therefrom, and a feed-back coupling between said resonators for supplying energy from said one resonator to said other resonator to maintain the field therein at substantially the same frequency but displaced in phase relative to the eld of the second resonator, said coupling comprising a conductor connected at one end to said cathode and extending into said one resonator with the other end thereof adjacent to, but spaced from, said anode to form a capacity connected between said anode and cathode, and tuning means connected to one of said resonators for adjusting the resonant irequency thereof whereby the amount of said phase displacement may be adjusted.

2. An electronic tube apparatus comprising a pair of hollow body resonators adapted to have electro-magnetic eld oscillations established therein, an anode mounted within one of said resonators, a cathode mounted Within the other of said resonators, said pair of resonators being adjacent each other with openings therein be- 10 tween said anode and cathode permitting a flow of electrons from said cathode to said anode, control grid between said cathode and anode, cir-- cuit means connected to said anode and cathode for establishing a direct current potential field therebetween tending to liberate electrons from said cathode and move them toward the anode, additional circuit means connected to said grid and cathode for establishing a direct current potential eld permitting electrons to be liberated from the cathode during the peak portion only oi a halfcycle of the eld within said other reso nator in which it is of a polarity to add energy to the electrons, the strengths of said ieids mov ing said liberated electrons toward said anode with a speed causing them to pass through said one resonator to said anode while the field therein opposes their motion and absorbs energy there from, and a feed-back coupling between said resonators for supplying energy from said one resonator to said other resonator to maintain the field therein at substantially the saine frequency but displaced in phase relative to the field of the second resonator, said coupling comprising a conductor connected at one end to said cathode at a point of substantially maximum high frequency eld voltage and extending into said one resoa nator with the other end thereof adjacent to, but spaced from, said anode to form a capacity connected between said anode and cathode, and tuning means connected to one of said resonators for adjusting the resonant frequency thereof whereby the amount of said phase displacement may be adjusted.

DAVID ii. SLOAN.

REFERENCES CITED The following references are of record in the nie o1 this patent:

UNITED STATES PATENTS Number Name Date 2,088,722 Potter Aug. 3, 1937 2,157,952 Dallenbach May 9, 1939 2,287,845 Varian et al. June 30, 1942 2,389,271 Mouromtseff et al` Nov. 20, 1945

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