US2447796A

US2447796A - Grid structure for electron discharge tubes

Info

Publication number: US2447796A
Application number: US748811A
Authority: US
Inventors: William H Bussey
Original assignee: ROBERT L KAHN
Current assignee: ROBERT L KAHN
Priority date: 1947-05-17
Filing date: 1947-05-17
Publication date: 1948-08-24
Anticipated expiration: 1965-08-24

Description

Aug. 24, 1948. w. H. BUSSEY 2,447,796

GRID STRUCTURE FOR ELECTRON DISCHARGE TUBES Filed May 17, 1947 AMPLIFIED D. C POWER AMPL /F/E/? Patented Aug. 24, 1948 UNITED STATES PATENT OFFICE can) STRUCTURE roitififiriticritofi DISCHARGE TUBES William H. Bussey; Chicago, Jill, assignor to Robert L. Kahn, trustee Glcncoe, Ill.

ApplicationMay i7; 1947, serialwa #485811 minute direct' po'tentials, are' limited and seriously handicapped b'y'wl'iat might be terme'dthe" inherently noisy characteristics of a thermionic cathode such" a cathode, when consldered with" respect to minute direct potentials is far from being stable or equi pot'ential. characteristics involve drifts and the variation" of electron emission with res'pectto time; The potential and elect'ronic instability of a'therm ionic cathode, with reference to minute' direct potentials; has been the subject of' coiisiderable AS a result, vacuum research and discussion.- tubes of the prior: art and vacuum-tube-circuits of'theprior' art havebeenlifnited'a's regards sensitivity by poor constant potential resolution of' a thermionic cathode. -It is evidentthat thelowest direct potentals upon Which'avacuumtube may operate with an'y'de'gfee'of reliability" are limited bythe magnitude of emission fluctuations present in thermionic cathodes; If such emissionfiuctuations canbe effectivelyeliminated, it will follow that the lower limitofconstant potentials to'b'e amplified may be reducedto a lower order;

By virtue ofthe invention disclosed herein;

there is provided a vacuum: tube'an'd circuit there'-"- for capable Ofbper'ating' on substantially lowerconstant potentials than has hitherto beencori sideredpossible. A system embodying the pres ent invention" reduces the effective instability of a thermionic/cathode to a lower fordef thah is now possible. l

The invention iii-general; contemplates a vacuum'tube having one-physical cathode systrh aridtwincontrol and twin anode electrodes.- The twin control electrod-esand' twin anode electrodes are" electrically and geometrically twins asse'en from" With respect to the: cathode; tha diiferences between eacn'otthe twin controlele'c trodes and each of the twin anodeelectrodes'is" the cathode;

temofcontrol and anode electrodes; the single thermioniccathode "may" be r'esolvedinto twin groups of thermionic I cathode elemental areas Thus, the invention maybe Such noisy The two groups are completelyintermingledso that any'variation in emissior'i' from the single physical cathode" may? be considered as divided The cathode may either be an a'ctual thermionic-cathode con structed in a conventional manner ormay con sist of f a" conventional tiierinioriic cathode hav ing, in addition, a 'suitable iomrepelhng electrode forming a virtual cathode for supplyingelectronsf Thus; twin tubes are provided, and the-difierences" between "them are of a lowerorderthan hithrt'o equally between the two groups;

considered" possible In orderthat the invntion 'may be'fully undefstood; a description thereofwill new begiveh in connection with the drawings wherein Figure *1 is a sectional'elevaticn of one 'form of a vacuurii tube embodying? thepresent 'invention; Figure'2 is a sectional plan view taken along IineI Z OT Figure -1; Figure" 3 is" an elevation of the F single ioncontr'o'l'giid; Figure 4'is an elevation of'one ofthe'control eleetiodes; Fig ur' fi isadiagrarn mat-in view" ota"circuit-embodying the present inventiori 'and withWhich'a tube shoWn in Fig ur'e l maybe u sedl A tube embodying: the present invention" may have a'conventional-base with "contact pins. The tube proper" has evacuated-envelope I l 2 of glass; Envelope-l 2'has reen-trant portion13 terminating: in" pressl4" upon which the electrode" mount is supported.

The electrode mount'maybe conveniently de-= signed as 'a'complete unit in -a manner generally resembling vacuumtubes now onthe market;

Thus; two mica discs l5 and IG-may-be provided, these discs being:suitablyapertured to clear'the v'ariou's supportinarods and wires." The electrode mount has cathode- 20' of any suitable construction: Preferably; cathode 2U-is-ot the filamentary type and -may consistof-a wire ofnickel; plati numor the like having a-surface=coated with suitable compounds; generally a mixture of barium and strontium oxides-l- Suchcathodes-are of the-Wehnelt-type.-- However, the thorlatedtype oi cathode may. alsobe used; in which case 1 wire 20* may be of tungsten or other suitable metalhaving: a-suitable quantity of thorium therein-to provide for" electronemission. Filamerit -2 0 passes through apertures T in the mica" discs and -istensioned at thetop' by spring g-l.

Leads 2' amaze sealed-in-thepress-support the filament and provide- -a heating: circuit.--

Cathode 2 ll has "disposed a-round it grid 25 for: repelling-ions. Such-a grid may have-impressed;- thereon a suitable bias; preferably positivewith; respect to the cathode. The grid maybe omitted if desired. Grid 25 is constructed in the usual manner and may consist of a simple coil of wire 25 carried by supporting

posts

21 and 28 passing through the mica discs and anchored in press l4.

Posts

21 and 28 have clips spot-welded thereto on opposite sides of the mica disc for support purposes. Such retaining means are well known in the tube art. The grid may consist of nickel or molybdenum, and the two posts may also be made of the same material. Other metals, such as tantalum, may be used. The actual construction of the grid and its attachment to the posts are Well known in the art and may be accomplished in any one of a number of ways. The pitch of the wire coil, wire diameter and its proximity to cathode surface 20 are all matters well within the skill of those versed in the vacuum tube art. Post 28 is extended through press M for connection purposes.

The vacuum tube so far described is of conventional construction. In accordance with the invention, a pair of interleaved control electrodes 30 and 3| are provided. The interleavedelectrodes may assume any one of several constructions, one of which may resemble the structure shown in Figure 4 and consist of wire rings attached to

posts

32 and 33 for electrode 30 and to posts 34 and'35 for electrode 3|. As shown in Figure 2, the ring supporting parts of

posts

32 and 33 for one electrode are in a, plane perpendicularto the plane of the ring supporting parts of posts 34 and 35 for the other electrode.

Posts 32 to 35 inclusive have their ends passing through the mica discs and have suitable means for maintaining them in position. Leads 35 and 3'! are connected to the respective control electrodes and extend upwardly through the top of the tube.

As clearly indicated in Figure 1, rings of one control electrode 30 are interleaved with rings of other control electrode 3|. Thus, a transverse view, as shown by Figure 1..discloses alternate rings of control electrodes 30 and 3| along the height of the mount. The spacing between adjacent rings-of the two electrodes 30 and 3! is equal. Other electrode constructions as two helical coils forming a sort of double thread may be used. In general, the two electrodes should be as symmetrical as possible with respect to the electron stream. Thus, one ring of one electrode should be mid-way between the adjacent rings of the other electrode. It is preferred to have the electrodes extend well beyond the eifective ends of the emitting part of the cathode so that, at the ends of the electrode structure, the elec- 4 leaved. It is understood that all of the supporting posts for the control electrodes and anodes are suitably supported in the mica discs by clips on opposite sides of each disc or other means. Leads 44 and 43 for connection to a source of potential are connected to the respective anodes. As with the rings on the control electrodes, rings 40 and 41' are flattened for post clearance.

While not essential, it is believed that best results will be obtained by having rings 40 and 4| match in number and spacing corresponding of itsassociated anode.

rings 30 and 31. Thus, looking at the tube from "-the side as seen in Figure 1, one ring of a consame as the size of wire forming the control electron stream is practically nothing. The size of wire, spacing between adjacent rings, diameter of the rings and the like are all matters well within the skill of a tube designer and will depend upon desired tube characteristics. In order for one series of Wire rings to clear the supporting posts of the other series of rings, it is preferred to make the rings somewhat elliptical as shown. The actual manner in which the wire rings are carried'by' the supporting posts may be varied.

Extending beyond the two control electrodes are anodes 40 and 4|. The anodes are constructed in substantially the same manner as the control'electrodes with anode 40 consisting of a series of rings carried by posts 42 and 43. Anode 4| is carried by posts 44 and 45. The plane of the ring supporting portions of one set of posts ispreferably atright angles to the plane of the ring'supporting portions of the other sets of posts so that the two series of rings may be intertrode rings. The diameter of the anode rings will be determined by considerations of tube characteristics. As shown in the drawing, supporting posts 42 and 43 carry rings 40, and these ringsare preferably in line with rings 30 carried by

posts

32 and 33. By proper shaping of the rings to avoid one pair of posts, it will be evident that symmetry for grids and anodes may be maintained.

It is desirable to enclose the entire mount in a shield to prevent electrons from drifting to the interior of the glass envelope and building up a charge. To this end, shield 46 is provided, this shield preferably though not necessarily having top and bottom parts 41. The shield may be made of any suitable metal and the top and bottom are suitably apertured to clear the various wires and supporting posts. The shield may be supported by

wires

48 and 49 sealed in the press. wire 49 for example being extended for connection'to a suitable source of constant potential, such as ground.

It is possible to obtain this shielding action by other means. Thus, a conducting metal coating of silver, magnesium or any other desired metal may be obtained on the inside of the glass envelope in a manner well known in the vacuum tube art. It is understood, of course, that such a conducting metal coating will be kept clear of the press'and leads going through the glass except that one lead from the coating for connection to ground may be provided.

No attempt has been made to show dimensions and proportions of electrodes or electrode spacing. Such matters will vary with desired tube characteristics. In general, such matters are well within the skill of those working in the tube art.

Referring now to Figure 5, a circuit diagram of a differential amplifier in which the tube embodying the invention may be used is disclosed. The various tube electrodes are identified by the same numbers as used in the tube itself. Thus, cathode 20 has one terminal connected to junction 50 and its other terminal connected to point 5|. Between points 50 and 5| is resistor 52. *Ion control grid 25 is connected to point 54. Between point 54 and 5| is resistor 55. Between point 54 and terminal 56 is resistor 51. Between point 50 and terminal 59 is resistor 58.

Resistors

58, 52, 55 and 51 may all form part of a tapped voltage divider. Between

terminals

56 and 59, battery 60 or other source of constant potential is connected, the polarity being such that terminal 56 is positive. It will be noted thatshield 46 is connected to ground. In the event that a mirror surface on the inside of the glass envelope is used, then it will be understood that such mirror surface is also grounded. The

shield may-:beconnected: to? any: other; point: ol

However, such valiresarmmerely exemplary and t anyuvaluesf necessary. may be used. Resistance 63: has grounded: tapz6'4r connectedibyi lead 1 i5.'l-.-.to terminalifl; the-control ,gridssbeingthereby.negas tively biased;

Junction 61 is connected. bylead; 66%- to ztermi nal161. Betweenterminalsrfli'bandrifis are-cone nected. in: shunt; source off constant potential? here shown .as battery; 69.;. and; potentiometer 1'6"." sistor'lll. and the wiper:is= connected: byvleadto one :termie nal of source l21whose'spotentiah is:to:-be ampliefied: Source. 12 :hasiiitsiothenterminalfconnectedz. Switch: contact :14: cooperates: withzfixed iCOI'ltfiiCtSf-H'i: and l by lead. 13 to movable :switch contact PM;

16 connected .to points--62: and-E Ekrespectively.

The polarity of potential sources: 69-: and 12 is such .as.=to provide oppositionnsotwipen'l I may be; adjusted .forvnullgoperation. This willprovidd a highzdegreesof sensitivity althoughsourceflt: may: be connected; directly: acrossl points 6 l and 62 orracross points fiiltandiMaori-"acrosspoints62. and-64; bothbe reversedzif desired; Inany event-it willgenerally bedesirablerto haveianygpossible potential across source;.12;small inicomparison to thenormal negative: bias of; the control; grids:

With switch: contact 14 on 15- asshown; symmetrical operation is'lsecured': However, contact M may be moved to 1B; andthe system will oper ate. In the-event that orietermi-nal onsource 12 is grounded; then the' optional switch position on 16 will be necessary, Whichever-poleofsource- 12 is grounded. source-$9 willbe so poledias to oppose source 12.

For sensitivity, it;;is: .adv-isablextogprovide high order of insulationresistance-to-sround for "those elements connectedtojunctions .6 I and 62:

Anodes; 4'8 7 and? 4 lare; connected to junctions 8liand8l respectivelm; Junctions dllandal have connected across them load resistorfii. Resistor 35 haswiper fifi'cooperating therewith, which wiper is connected to terminal 55. Wiper 86 is adapted to be' -manually adjustedto provide a normal no-load balanced tube condition. Under such condition, no difference in potential between terminals SI and 62 should exist.

It should'b-e noted that the" output circuit of the amplifier resembles a bridge: Thus, resistor iifi formsjtwo adjacent bridgearmswith wipers? as abridge-point. Cathode toeanode spacesiform remaining: adjacent bridge arms.- Batteryr sous connected across one bridge diagonal from wiper 86 to cathode 20. Bridge output points 80 and ti are across the other bridge diagonal.

Terminals 80 and BI may be considered as the output terminals of the amplifier and may have connected across them an suitable load. Thus, for a direct reading system, any suitable meter may be connected. It is also possible to connect the output of this amplifier to an additional direct current amplifier which may, if desired, be similar to the amplifier system so far described. Such additional amplifier or a direct current power amplifier indicated by numeral 88 may feed any suitable load.

Thus, as an example, power amplifier 88 may Resis- Wiper: I i' cooperates with resistor. 1d,.

The: polarity "of :sourceszfiSIandJZ-may beiconnected torijunctionpoints 8fl and 8t tobeoperated-whereby; Such a: power amplifier may amplifier embodyingthe present invention will be presentif: the amplifier. is operated in the neighborhood: of itsbalance point, i. .e. with the control electrodes atrthe same instantaneous potential. to be amplified, it is possible to provide means for maintaining an opposing potential. to balance control electrodes 30 and 3|. Thus, leads 99 and 91 may feed servo motor 93-which is mechanically connected to move wiper H. The system may; beset;up insuch a manner that the polarity anddifference of potential between leads and 9| willserveyto. move wlper'll and restore controlelectrodes-30 and 3| to abalanced potential condition. Scale-94 shows the position of wiper H and may be calibrated to read the potential due to. source, 12. The calibration may be in terms oftemperatureor other physical condition.

One battery or other source of constantpotentialjmay be used forenergizing the vacuum tube. In-practice, such abattery will generall have a lowpotentialwhichmay be of the order of about six:volts; Itisunderstood, however, that separate filament heating and plate-supply batteries may beused. Other. means for obtaininggrid bias may also .betused,

In order to utilize the full sensitivity of the system; it-m-ay-beadvisable to operate the cathode at temperatures: far below that used in conventionaLvacuumtubes.-v The same applies to control electrodebias and anodepotential. By virtue oithe low= potentials used, the possibilities of erraticz behavior, due; toion; bombardment, sec-- ondaryE emission andionization will be greatly reduced. Fonthe .sakeof simplicity, a filamen taryscathodehas been disclosed. However, it is understood thatth-is cathode may be replaced by an indirectly heated cathode. Other changes for adapting-:thertube or. circuit to meet special conditions may be made as :desired.

It Will.;be--apparent'that a pair. of twin control electrodes are provided havingthe effective portions. thereof interleaved. When such interleavedportions are projected on the cathode surface aisymmetri cal pattern will be formed, this patterncons isting'of elements of the twocontrol electrodesialternating with each other. Simila'rly, the anode electrodes have the effective portionsl thereof interleaved so that a projection from the two electrodes on the cathode will also provide an alternating symmetrical pattern. The alignment of the control electrode and anode interleaving portions is such that the projection on the cathode of the interleaving portions of one control electrode will coincide with the projection on the cathode of the interleaving portion of one anode electrode. The same applies to the remaining control and anode electrodes.

While it is preferred to have the physical structure of the anode electrodes similar to the control electrodes, this is not essential. Thus, two con trol electrodes of similar construction may have interleaved portions as shown, Two anode elec- Thus, .in the event that a potential is.

trodes of difierent construction than the control electrodes but with the two anode electrodes having similar construction will have interleaved portions. In such case, alignment between elements of a control electrode and an anode electrode will not be possible. However, it will be possible to arrange the control electrodes and anode electrodes in such a manner that symmetry and correspondence will be obtained.

By virtue of the invention, a sort of push-pull action is obtained not only on the control electrodes but also with the anode electrodes. This push-pull action differs from a conventional pushpull amplifier in that the dissimilarity between one vacuum tube unit consisting of cathode, control electrode and anode, and the other vacuum tube unit consisting of the same cathode, remaining control electrode and remaining anode is reduced to a lower order than has hitherto been possible.

What is claimed is:

l. A vacuum tube comprising an evacuated envelope, a thermionic cathode, a pair of twin control electrodes, a pair of twin anode electrodes, the two twins of each pair having interleaved'portions whereby a pair of twins are spatially dis' placed from each other to provide electrically distinct structures with the interleaved portions of a pair of twins forrnin a symmetrical pattern of alternating twin electrode portions when projected on the cathode.

2. The structure according to claim 1 wherein the twin control electrodes are similar to the twin anode electrodes and wherein the control and anode electrodes are aligned, the patterns formed by projection of the interleaved portions of the anode electrodes coinciding with the pattern formed by the projection of the control electrodes on the cathode.

3. A vacuum tube for use in a difierential amplifier comprising a thermionic cathode, a pair of twin control electrodes surrounding said cathode, said control electrodes having substantial portions thereof interleaved with each other, said twin control electrodes being electrically distinct but symmetrically disposed with respect to each other, so that interleaved portions of said control electrodes when projected on the cathode form a symmetrical pattern of alternating twin electrode portions, a pair of twin anode electrodes surrounding said control electrodes and having substantial portions thereof interleaved, said anode electrodes being electrically distinct but symmetrically disposed with respect to each other, interleaved portions of the anode electrodes when projected on the cathode forming a symmetrical pattern of alternating twin electrode portions, said cathode, control electrodes and anode electrodes together forming two vacuum tube units having a common cathode and individual control and anode electrodes with the order of operating dissimilarity between said units being substantially lower than between units having individual cathodes.

4. The structure according to claim 3- wherein the-control electrodes and anode electrodes are similar to each other in construction and have their interleaved portions aligned so that the projected patterns on the cathode of the anode electrodes coincide with the projected pattern of the control electrodes on the cathode.

5. A vacuum tube for use in a differential amplifier comprising a thermionic cathode, an ion control grid disposed around said cathode, a pair of twin control electrodes surrounding said ion control electrode, said control electrodes having substantial portions therof interleaved with each other, said control electrodes being electrically distinct and symmetrically disposed with respect to each other, said interleaved portions when projected on the cathode forming a symmetrical pattern of alternating twin electrode portions, a pair of twin anode electrodes surrounding said control electrodes and having substantial portions thereof interleaved, said anode electrodes being electrically distinct and being symmetrically disposed with respect to each other, said interleaved portions when projected on the cathode forming a symmetrical pattern of alternate twin electrode portions, the anode and control electrode portions being aligned, the pattern for the control electrode overlaying the pattern for the anode electrodes, said structure forming two vacuum tube units having a common cathode and ion control electrode but individual control and anode electrodes with the two units having a substantially lower order of operating dissimilarity between them than possible with units having individual cathodes.

6. The structure of claim 5 wherein a shield around the anodes is provided.

7. The structure of claim 3 wherein each of the control grids comprises a pair of supporting posts and a series of rings carried thereby, the rings for one control grid clearing the supporting posts for the twin control electrode.

8. The structure according to claim 3 wherein each of the twin electrodes comprises a pair of supporting posts and a series of metal rings, the rings for one of the twins being interleaved with the rings of the other twin and clearing the posts of the other twin.

WILLIAM H. BUSSEY.

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

UNITED STATES PATENTS