US2533750A

US2533750A - High-gain amplifier tube

Info

Publication number: US2533750A
Application number: US591712A
Authority: US
Inventors: Adler Robert; John G Prentiss
Original assignee: Zenith Radio Corp
Current assignee: Zenith Electronics LLC
Priority date: 1944-05-27
Filing date: 1945-05-03
Publication date: 1950-12-12
Anticipated expiration: 1967-12-12

Description

Dec. 12, 1950 R. ADLER ETAL HIGH-GAIN AMPLIFIER TUBE 4 Sheets-Sheet 1 Filed May 3, 1945 a u u n n n n: pl

INVENTORSZ ROBERT A'DL'ER JOHN G, P RENTI'SS fifm g THEIR ATTORNEY Dec. 12,1950 ADLER ETAL I 2,533,750

HIGH-GAIN AMPLIFIER TUBE Filed May 3, 1945 4 Sheets-Sheet 2 FIG. 4

INVENTOR'S .2

R OBERT A'DLER JOHNG. PRENTISS THEIR A TT RNEY' Dec. 12, 1950 ADLER ETAL 2,533,750

HIGH-GAIN AMPLIFIER TUBE Filed May 3, 1945 4 Sheets-Sheet 5 F l G. 7

ubnnnnnnnnnn nnaaan Izunuu F l G. 9

8O 8! SEC ON D ANODE CURRENT E1 1 FIRsT ANODE CURRENT I! I D o l F I L J SECOND ANODE VOLTAGE PREFERRED OPERATING RANGE INVENTORS R0 8 E RT ADLER J 0 HM G- P R NTI 55 THEIR A T ToR NEY Dec. 12, 1950 R. ADLER ETAL HIGH-GAIN AMPLIFIER TUBE 4 Sheets-Sheet 4 Filed May 5, 1945 WIILFIJ LNHHHHO HCIONV GNOOBS INVENTO RS I ROBERT ADLER JoHNGP RENTIS s B YCX THEIR AT TORNEY Patented Dec. 12, 1950 HIGH-GAIN AMPLIFIER TUBE Robert Adler, Chicago, and John G. Prentiss,

Berwyn, 111., assignors to Zenith Radio Corporation, a corporation of Illinois Original application May 27, 1944, Serial No.

537,704, now Patent No. 2,426,681, dated September 2, 1947.

Divided and this application May 3, 1945, Serial No. 591,712

6 Claims.

This invention relates to amplifiers, and more particularly to electron discharge amplifier devices.

The present application is a division of our copending application, Serial Number 537,704, filed May 27, 1944, for High Gain Amplifier which matured into Patent No. 2,426,681 on September 2, 1947.

It is a fundamental object of this invention to provide an improved form of electron discharge amplifier device.

It has often been considered necessary to provide, in an electron discharge amplifier device arranged to produce high gain, a cathode capable of emitting large electron currents. It is, accordingly, a further object of this invention to provide such an improved form of electron discharge amplifier device and circuit in which a cathode capable of emitting only a small space current is provided. When such an electron discharge amplifier device is arranged in accordance with this invention to produce high gain with the cathode emitting only a small space current, simultaneous savings are effected both in the power required to heat the cathode and in the power dissipated in the other elements of the discharge, device.

It is a corollary object of this invention to provide such an improved form of electron discharge device in which only a small number of electrodes is utilized and in which the device is stable in operation and. rugged and capable of easy manufacture and assembly.

It is also an object of this invention to provide an improved form of electron discharge device in which, in a single discharge device, gains in the order of at least 100 are readily obtainable.

The features of this invention which we believe to be novel are set forth with particularity in the appended claims. The invention itself, both as to its organization and manner of operation, together with further objects and advantages thereof' may best be understood by reference to the following description taken in connection with the accompanying drawings in which:

Figure l is a sectional view in elevation of a preferred form of electron discharge device constructed in accordance with the invention;

- Figure 2 is a sectional view of the device illustrated in Figure 1, taken along the line 2-2 in Figure 1;

Figure 3 is a sectional view of an alternative form of the invention, taken as along the line 2'2 of Figure 1; a

Figure 4 is a sectional view in elevation of a 2 somewhat difierent form of electron discharge device constructed according to the invention;

Figure 5 is a sectional view of the device illustrated in Figure 4, taken along the line 55 of Figure 4;

Figure 6 is a sectional view of a modified form of electron discharge device similar to that illustrated in sectional elevation in Figure 4;

Figure 7 is still another alternative form of an electron discharge device constructed in accordance with the invention especiallyfor operation at low voltages;

Figure 8 is a sectional view of the device illustrated in Figure 7, taken along the line 8-8 of Figure '7;

Figure 9 is a graph illustrating certain characteristics of the invention;

Figure 10 is a sectional view in elevation of still another embodiment of the invention;

Figure 11 is a sectional view of the device shown in Figure 10, taken along the line llll of Figure 10; and

Figure 12 is a graph illustrating certain other characteristics of the invention.

In Figure 1 an evacuated glass vessel [0 contains a filamentary cathode II, a first control electrode l2, a first anode l3, a second control electrode 14 and a second anode IS.

The filamentary cathode II is fastened at its lower end to a support 16, mounted on a leadin wire I! which passes through the wall of the glass vessel 10, and is drawn tense through accurately dimensioned'holes in the mica spacers l8 and I9 by a spring 20, to one end of which is fastened the supporting tab 2| on which the other end of the filamentary cathode II is fastened. The other end of the spring 20 is fastened to the support post 22 which passes downwardly through the mica spacers I9 and I8 respectively, and to the lower end of which is joined the lead-in conductor 23 which passes through the glass walls of the vessel l0.

A circuit is formed for heating the filamentary cathode I I from the lead-in conductor I! through the support IS, the cathode I I, the supporting tab 2|, the spring 20, the supporting post 22, and the lead-in wire 23. r

The first control electrode structure is formed by winding a cylindrical conductor of suitable diameter around two supporting

posts

24 and 25 helically with the turns of the conductor spaced apart a suitable distance. Each turn of the cylindrical conductor is fastened to the supporting

posts

24 and 25, as by welding or by providing slots in the

posts

24 and 25 within which the cylindrical 3 conductor is wound, the material at each side of the slot being swaged over the cylindrical conductor. The assembled control electrode I2 is placed between the mica separators I8 and I9 with the

posts

24 and 25 extending through suitable holes in those separators and the filament II is thereafter passed through the holes in the separators I8 and I9 and tensed therein, the holes for the supporting

posts

24 and 25 and the holes for the filament II being suitably spaced so'that accurately determined distances are maintained between the filament I I and the control electrode I2.

The first anode I3 and the second control electrode [4 are similarly constructed by the winding of a cylindrical conductoraround two supporting posts, the diameter of the conductor and the spacing between adjacent turns on the supporting posts being in each case suitable to provide a desired result, as will be explained more fully her'einafter. In each case" the supporting'{ posts i of" thefirst "anode I 3 and control electrode i 2 are received within suitably positionedh'oles in the n'iica separators'ifi and'lll so that accurate spacing is maintained between'the control electrode -I 2', the first anode I3 and the 'se'cond control electrode-I4. It is notable .here that, with-thiscdhstiuction and arrangement of a discharge 'device "and withcircuits described in the above-hientionedparent case, it is not necessary-"to inaint'ain any particular alignment between the turns of the cylindrical conductor of 'thefirst control electrode I2, the first anode I3, and-'the 'second control electrode It. :In other words, the vertical alignment of the meshes of those th'ree" electrodes may be leftentirely to chance.

Outside-of thesecond control electrode M the anode i5 is arrangedcylindrically between-the "rriica spacer's :I 8 and I29 with ithezaxis o'f the cylinder coincident with athe :filarnent I I "The anode E5 is supported by and electrically connected .to

its supporting"p'ost 30', which 'is placed symmetrically with the supporting post 22, and the upper l endof' which supports agetter-assernbly 3I'. filhe-sloiwer end of'the supporting post 30 is ccnn'ected 'witha lead-in-conductor 32, whichextends through ithe 'glas'scwallof the lenvelope I andprevidesfor "external electrical connection to the anodeili; -Similar:lead-in conductors 34 =and-z33fextend through thelglassvwall of the envelope ah"! "andare connected respectively with supporting posts for thefirstanode I3 and the second ccntrol electrode vI l, therehyproviding external electrical connection respectively with those electrodes. A' fixed lead-.in'conductor-35 *passes through the glass wall of the envelope Ill between-the-lead-in conductor I'I andthelead-in conductor '23, and is connected with the suptportin'gpost 2 to .providean external electrical cconnection for the first control electrode I2.

In Fig. 2, the same numerals area-pplied to llike partsoi the discharge device. The central hole through the :mica'spacer l8 can be seen as a triangle with the'filarnent II! at one apex. The fiat; sided first control electrode l2 at its intermediate portions lies relatively-close .to the I Thess'econd .control electrode l ilalso ihas fiat sides substantially parallel with the fiat sides of 4 the first control electrode I2 and the first anode i3, and the flat sides of the second control electrode M lies substantially closer to the first anode it than to the parts of the second anode I5 which receive the electron stream from the-cathode I i. That is, the shadowing .efiect iofzithe supporting posts as and 25 is such that the space discharge from the cathode II passes substantially perpendicularly through the fiat sides of the control electrodes I2 and I4 and first anode I3 to impinge upon only a portion of the anode l5 facedby the fiat sides of the inner electrodes.

Purely "by .way of example, a typical set of dimensions for such an electron discharge device is given to illustrate a specific manner in which the invention may be utilized. The filament II is made of tungsten wire a little more than ft inch in length and of such diameter that 50 miliiamperes of current flowing through it produce a voltage drop across it of about of a volt, The helical wire with which 'the electrcdes 1:2}, tS- and I4 are formed-is lllll2soflan inch in diameter. The first control electrode 52 is wound on the supporting posts in and .25 with- 72 turns per inch,-and.is so wound that its fiat sidestare spaced apart by =0180f .an inch. Thatis, the

wcundavith lz turns per inch and its. flat sides' are spaced. apart '.200-Iof..an inch. The diameter of the cylindrical-anode ll-Brie .375 .of'an inch, and the overall lengthiof sall of the elements between the mica lspacerslIB-andaI 9 vis about T55 of-aninch.

Such dimensions provide that the distance between the second -c0ntro1 electrode ..I l and the first anode-l3 is-rnuchdess than :the distance between the second-control electrode 14 and efiective parts of -the-anode I5. This spacing between-*the electrodes and the close meshiof (the second control-electrode I4; which is wound with-72 zturns per .-inch-,- provide that :the second control electrode l4 has a relatively high static amplificationvfactor with respect to the anode I 5,

and that factor :may "be-made in the-orde-rcf .10

.or more. Such an electron discharge :device .made i accordance with the invention, the usual ,precautions being taken as to upurityof materials and-.ireedom fromcontamination within the envelope leiandawith care in evacuatingland gettering the device, may :be :us ed in circuits :as described'hereinafter to produce great amplification, as great as several hundred times, while remaining stable in operation. Atthe'sameti-me, the discharge deviceis simple in constructionand rugged and. is easy to manufacture.

a In general, the constructionof the secondcon- :trolelectrode I4 is critical, ithe constructionof the remainder of the discharge :device being quite similar to. that-of --a normalipentode. The'second controlkelectrode 14 may; in a preferred form of the invention, --be ;placed about twice as .farfrom the anode- I5 as from'the first anode L3 and may have openings therethrough of such area that, when the second controlelectrode is substantially at the potential of the cathode II, space current zpassing'through thatsecond'control electrode I4 is aifectedibythe electrode I4 inv such a way-that, when the potentials on the anodes I5 and-"13am substantially. equa1',-=I= .the, 1 ratio between current the minimum ratio between those currents which is obtained when the potential of the second anode I is increased indefinitely in a positive direction. v

This condition does not obtain in a normal pentode in which a third electrode is of relatively open mesh, the mesh being so wide that, with the third electrode connected to the cathode, the third electrode produces substantially no efiect upon discharge current flowing from the second electrode to the anode. In other words, in a normal pentode, increase of anode potential, as is very -well known, does not substantially increase anode current. Expressed in another way, it is frequently said that the internal anode resistance of a normal pentode is extremely high, approaching infinity.

The construction of the second control electrode according to the invention may be described in still another way. The spacing between the first and second anodes and the fineness 01 mesh are such that, when the second control electrode is operated at cathode potential, or more accurately at a potential near that potential at which electron current begins to flow into the second control electrode, and when there are substantially equal positive potentials on the anodes, current flowing in the second anode I5 is substantially less than the current which would flow infthe second anode [5 with substantially equal positive anode potentials but with a more positive potential on the second control electrode l4. That is, the current in the second anode should be at least one-fifth less than the current which flows in the second anode after the second control electrode potential is made substantially more positive, and it is preferred that the second anode current be in the order of half the current which flows in the second anode after the second control electrode potential is made more positive. It is another aspect of this peculiar construction of the second control electrode that it is capable of efiecting substantial changes in electron current distribution between the two anodes when its potential is changed in small increments, its average potential being near cathode potential. That is, the static amplification factor of the second control electrode is sufiiciently high that, when it is near cathode potential, it has a substantial influence on the distribution of space current between the first and second anodes.

-As a general rule, the structures at the first and "second control electrodes will be somewhat similar insofar as their mesh and the size of the conductor from which theyare wound is concerned.

It should be noted at this point that, while it is 'preferredto have the second control electrode I4 closer to the first anode I3 than to the second anode 15, the second control electrode l4 can be constructed to produce the requisite results without being so spaced. In this connection, it should be pointed out that the term closer must be differently interpreted when applied to different forms of control electrodes. Where the control electrode I4 is fiat sided as illustrated in Fig. 2, the term closer" should be given the natural meaning that the actual distance between the first anode l3 and the control electrode [4 is less than the actual distance from the control electrode It to the anode [5, always remembering, of course, that thesedistances should be measured along a line perpendicular to the filamentary cathode II and perpendicular to the flat sides of the electrodes I3 and ll. 7

Where the electrode I4 is made generally cylin drical, the term close must be given the meaning that the ratio of the diameter of the first anode l3 to the diameter of the second control electrode 14 is greater than the ratio of the diameter of the second control electrode H to the anode l5.

In Fig. 3, there is illustrated a cross section of a second anode l5 than to the first anode 13. While this is not' generally a preferred construction of the invention, it is possible to construct a device in this manner and achieve resultsfalling within the scope of the invention. Purely by way of example, certain dimensionsof the device illustrated in Fig. 3 are given to illustrate how the second control electrode 40 can be made so that it has a sufficiently large static amplification factor to achieve the desired result. The filament H, the over-all length between the mica spac ers I8 and I9 of the elements, and thesize and spacing of the supporting posts may all be like those shown and described in connection with Fig. 1. Also, the spacing between the fiat sides of the first control electrode 12 may be .018 of an inch and the spacing between the fiat sides of the first anode 13 may be .112 of an inch. How

ever, the spacing between the sides of the second control electrode 40 along a line perpendicu lar to the filament ll and perpendicular to the fiat sides of the first anode I3 is made .250 of an inch. and along that same line the diameter of the anode l 5 is made .320 of an inch.

Such an arrangement as illustrated in Fig. 3 has in the second control electrode 40 a smaller static amplification factor -than if the electrode 40 were closer to the first anode [3 than to the second anode l 5, but the second control electrode 40, having 72 turns per inch of cylindrical conductor .002 of an inch in diameter, is, when near cathode potential, capable of substantially influencing the current distribution between the anodes l3 and I5.

In Fig. 4, there is illustrated an electron discharge device which is especially constructed for operation at substantially lower electrode potentials than the device illustrated in Fig. 1. Many elements are similar to the elements illustrated in the device of Fig. l and are given like reference characters. The first control electrode 50, the first anode 5|, second control electrode 52, and the second anode 53 are all constructed with different dimensions from the corresponding eleo-- trodes of Fig. 1 for the purpose of providing lower potential operation. The first control electrode 50 is made of somewhat more open mesh so that a relatively low positive potential on the first anode 5| is efifective to draw a substantial electron current flow from the cathode ll through the first control electrode 50. Similarly, the second control electrode 52 is made with somewhat more opeirmesh so that the anode 53 can draw asub The second control electrode 40 is ace-ates *1? tween the control electrode 52"and the first anode By sway-u of teXa'mple toillustrate .one manner in which the device of Figa may the-constructed,

theiirst controlcelectrodeiu may,be :woundwith. 6=l turns per inchtof cylindricalconductor .002ofl aminch in diameter,. wound.helically around, the 1 supporting

posts

24 and 25. The first; anode/i" may bewound with the same size conductor, but" withl 50 -lturnsper inchpanduthe second control.v electrode 52amay be .wound with the-same size conductorbut with 64 turns per inch In-iFig." 5,.like- .parts are given the same -refer encanumerals and the shapes of the electrodes 50; .5I 52-and 53 may,be.seen somewhat more clearly. The

controlelectrodes

50 and 52 and the first anodefii are woundwith flat sides, like the cor-responding electrodes shown in Fig.2, and the anode53 is cylindrical. The spacing between-the opposite fiat sides of the first control electrode '50 is .018 of aninch, and the spacing between the oppositeafiat sides of the-first .ancdefil and the second control electrode 52 are respectively .086. of -an inch and 136 of an inch. The diameter of the anode 5 3 is'.250 of aninch.

With the second control electrode52 substantiallycloser. to the=firstlanode 5i than to the second anode 53,land with thefirst-an'odefil relatively-closer .to the first control electrode 56, the two control.electrodesubeingof more open mesh, the anodes .51 and 53 may be operated at lower potentialsfthan is the. case withithe device illustrated in Fig.1; For .example anode supply potential for the. device. of Figs; 4 and 5 may be in the. order-f and volts Even ,with such cannot: be made indefinitelylow; Contact potentials, whichare in. theorder of one volt, and which are duevtosurface conditions of the various electrodes, the surface conditions being frequently altered bycontamination with cathode coating materiahmay affect very undesirably the anode currents. -Such contact potentials vary markedly v'fronrone discharge device to another and 'Eurthermore they vary during use of the discharge ,cevicei- These contact potentials affect the-actual:potentialof every electrode in the dis-v charge tdevice andrparticularly affect the effective bias potential of the secondcontrolelectrode. If the staticlamplification factor of the second control electrode. is high, the supply potential for both anodes-must be :high compared t-O-'-th8 COll taCt; potential of the second control electrode multiplied by its static vamplification factor If the supply potential for the anodes is not-high. compared to the contact potential ofv the; second controlelectrodeltimes its static ampliflcation factor; the contact potential may affectlthe anodecurrent adversely, and might evencut off completely the current flowing in the 1 second anode. In any case, in the particular circuits-with which this discharge device is particularly adapted to be used,itis undesirable that the contactvpotential of the second control electrodes afifect the current in either anode to any large, extent.v [I I Bearing in mind the effect ofccontactpotential otsthesecond control-electrode, whereflthosecona fled second anode. Like:-reerence numerals area seconds control electrode 4 are-the samer beingrt s tact-potentialsare the order ofaona voltn tastthe-y usually. are) it isevident :thatvif itbedesired'i to operate-the anodes from supply potentialsli the order of-twenty ,volts, the static amplification a factor of the secondcontrol electrode should not-i exceed a factor in the order of 10.- Anode supplies: potentials lower thaniabout 15 volts cannot Safely be used, .unless--contact potential is reducedlcors respondingly lower .thanll :voltja In-lFig 6,,there isillustrated linacross sectional taken: perpendicular to I thecfilamentary rcathodek a discharge-device similan toflthat illustrated in Figs. .1' and-2, .particularlyy-im thatithe s econd l control electrode -is mounted -;c1oser. ..to "the l-f rst J anodethanlto the second anode but with a .modi J applied to similar parts.- Difieient mica-spacers u areprovided, of whichthe lowernne 60-is-il1us.---, I, trated, in order to support the filamentary -.cathode. I I and the-:first -control-l electrtxzletfl,- first -anode I3, and secondsanode:I4 oifscenten-withm respect-to the glass-envelope. I 0. An anode-.6 I l of relatively4small:.areacompared-to one of-.-t he-: flat sides of I the second icontrolaelectroda I 4, iss

supported on a supporting ,post 6 2 .-.-between-the :1: 'mica separators and -isplaced substantially.syml-t metrically gwithrespect to a plane passing throughfa the filament .i I perpendicularly to the flat -sidez- I of the-second controllelectrodetfl. f p I Byiway of illustration, ..the dimensions for-ca.

as .follows. The. spacingsbetweenthe .flat sides;- of the control electrode I2-are=the same,beings v .018 ofaninch, and similarlyithe-spacingsbetween the fiat sides of the .first anode -V;I 3 andfiof th respectively ,-.1l2 of-an'inch and -.200 ofe-anrinohtge The 3 distance- -from-the filamentary cathode. I to the small anode--.6I-is.-.18'7: of an-linchs; As the case with the deviceilliistr-ated m Fig.1; @the vi mesh \of-theelectrodes; I2,- I 3 andal 4 is-:respectiv ely 72 turns per inch, turns per inch,rand 72 turnsper 7 inch. 7 V v Bymaking. the area'of the-anode- 6 I small,and in wfact substantially smaller: than n-the' -effective area-of the second control-electrode1.4,:the inter nal: anode resistance of the anode BI is-made hig' andthe effect of-potential-changes on the 'secon control electrode I t :upon the flow of: current toa th first anode i3 is substantiallyfreduced-i Thi structure -of.an.electronrdischarge device is espe' cially' useful in' a specia31-:-circuit employingregen erations That is; in a circuitdnwhichpotentials1 changes appearing" on the firsttanode': Iii-(whens;

signal? potentials-are limpressedaon the first control. electrode 1 2 )1 are impressed upon the-seconds;

,of the-second control electrode I4 Supon current fiowingiothe-first anode.- l 3 isereducedcnso'tha controlaelectrode I 4-, the discharge-device acts notonlye-lika a cascadedpairottriode amplifier-a st but also acts regeneratively. The regenerativee effect, ofspotentialsaimpressed on-secend'control electrode; I 4 day-the first anode I 3, up on 'thespace a? current flowing Ito the-first anode I3 -'may=lbe:"so'- great, as to .causell self-induced.-=oscillation. By makingtheeareaiof. the-anode 5| small, ;theeffects.

9 trode I4, the change in current distribution between the anodes I3 and 6| caused by the resulting efiect of the second control electrode I4 is in aiding relation on the first anode I3 and is therefore regenerative. This is true because an increase in the total cathode current from the filament II, caused by a change in potential in the first control electrode I2, causes a reduction in the positive potential of the first anode I3 and, when such reduction in potential is impressed on the second control electrode I4, causes a still further reduction in the potential of the first anode I3 by reason of the still further increased current flowing into the anode I3 because of the change in current distribution between the anodes I3 and BI induced by the change in potential on control electrode I4. This change in current distribution between the anode I3 and BI is suflicient to cause the potential of anode -6I to rise instead of falling as it would if the potential of second control electrode I4 had not changed. Because the anode BI is small, the first anode I3 takes substantially all of the electron current from the cathode II over most of its area and the control electrode I4 is therefore not effective to change the anode current distribution between anodes I3 and 6| as much as if the anode 6I entirely surrounded the control electrode I4. Consequently, the regenerative effect of potential changes of second control electrode I4 upon the first anode I3 may be made sufficiently small that self-induced oscillations cannot be started. Stable operation is therefore possible.

In Figure '7 there is illustrated an alternative form of electron discharge device which is especially suitable for operation with low anode supply potential, and without any sacrifice in gain by increase in mesh size of control electrode as in the case of the device illustrated in Figures 4 and 5. In this figure many elements are similar to those illustrated in Figure 1 and are given like reference character. A space charge electrode 10 is provided adjacent to the filamentary cathode II, and is followed consecutively by a first control electrode I I, a first anode 12, a second control electrode I3, and a second anode I4. These electrodes are all held in proper spaced relation by suitable mica spacers I and IS. The space charge electrode I0 is provided with an external connection through a lead-inconductor 19 extending through the glass wall of the envelope Ill.

The space charge electrode i0 is constructed so that it may be operated at a small positive potential, with the result that a substantial cathode current is caused to flow through the first control electrode H to the first anode I2, even though the first anode I2 is operated with a Very small anode supply potential (for example, as low as fifteen volts), and even though the static amplification factor of the first control electrode II with respect to the first anode 12 is substantial. In such a device, as in the ones previously described, the static amplification factor of the second control electrode l3 may be made high with respect to the anode 14, even though the anode supply potential for the anode 14 is very low, for example, as low as fifteen volts.

As a specific example, to illustrate exactly how one device of the type illustrated in Fig. 7 may be constructed, the space charge electrode it may be wound with 64 turns per inch of cylindrical wire of two thousands inch diameter, the first control electrode ll with 80 turns per inch, the

first anode 12 with 50 turns per inch, and the second control electrode I3 with 72 turns per,

inch, all being wound with cylindrical wire of two thousandths of an inch diameter.

Fig. 8, being a sectional view along the line 8- S of Fig. 7, makes it evident that the first con trol electrode ll is closer to the cathode II and to the space charge electrode '50 than it is to the first anode l2, and similarly the second control electrode 53 is closer to the first anode "52 than it is to the second anode 74. As a specific example, the diameter of the electrode shown in Fig. 8, wound like those described specifically in connection with Fig. '7, such diameters being taken along a line perpendicular to the filamentary cathode l I and to the flat side of the second control electrode 13, may be respectively 0.018 inch, 0.0%? inch, 0.125 inch, 0.2 inch, and 0.375 inch.

Such an arrangement as shown in Figs. 7 and 8, in which a space charge electrode I0 is provided is especially useful in connection with apparatus such as a hearing aid in which it is highly desirable, not only that low potential be necessary for all of the electrodes, in order that very small wearable batteries may be utilizedtc supply the potentials, but also that the current and power drain required by the discharge device be extremely small, so that the small Wearable batteries may have a reasonably long life.

In Fig. 9 certain operating characteristics of all the discharge devices so far described are illustrated, anode currents being plotted as ordinates, against second anode voltages, as abscissae. The characteristics illustrated are present in these discharge devices, provided cathode temperatur'eis high enough that electron emission from the cathode is not temperature limited. When the second anode voltage is verylow, and with a fixed first anode potential high enough to cause a substantial first anode current to flow with a zero potential on the second anode, with a small negative bias potential with respect to the cathode on the first control electrode, and with the second control electrode maintained at cathode potential, or more accurately at that potential at which the second control electrode just begins to take electron current, all current flows to the first anode. Curve illustrates the variation in first anode current under those conditions as the second anode voltage is increased from zero volts with respect to the cathode to a high positive voltage, and curve BI illustrates the variation in the current flowing in the second anode as the second anode voltage is so changed.

Curve 8!] shows that the first anode current is of substantial amount when the second anode voltage is zero with respect to the cathode and remains substantially constant as the second anode voltage is increased to a substantial ositive voltage with respect to the cathode. At some substantial positive second anode voltage, for example, a voltage in the order of ten volts, the first anode current begins to decrease as the second anode voltage increases, and continues decreasing, finally approaching a limiting minimum current which does not decrease as the second anode voltage approaches infinity.

Curve 8| illustrates that the second anode current is zero when the second anode voltage is zero with respect to the cathode, and remains zero as thesecond anode voltage is increased in that second anode voltage at which the anode currents are equal and that second anode voltage at which the second anode current first appears that it is preferred to operate the discharge detenn s-stain -twt steamin pasts ts vice made according to this invention. With the second control electrode constructed in accord-"' ance with the invention, the anode currents and the anode voltages'within this preferred operat- "ing rangeare of normal and reasonable magnitude, and the dircharge device may be used with various circuits to produce extremely high gain" amplification. With the second control electrode so constructedaccording to the invention, the s'econdanode voltage is impractically high, and too high for practical operation of the discharge device, where the second anode current is near maximum and the first anode current near minimum. It is in that region that the normal pentode operates, and it is able to operate in that region with a smaller anode voltage by reason of a different construction of its third grid, cominonly called the suppressor. The suppressor "electrode in a normal 'pentode is made with an open mesh so that it does not substantiall affect 'vviththedevic'es "illustrated in Figures'l through 1 8, that is, the discharge device illustrated 'in Figure isconstructed so that the anode supply potential for the

anodes

92 and 94 may be in the order of 200 volts, and shouldbe in the order of at least 45 volts. The first control electrode 9-3, between the first anode 92 and thecathode 9!, and the second "control electrode 95between the first 'aLn'o'deBZ and the secondanode 9's,are-100th Inade to have'a relatively high static amplification factor. The second'c'ontrol electrode 195 -may;

forejxample, be'so constructed that its static'arnfplification factor is in the order-of or more, thereby necessitating that the supply "potential for the second anode 94 be large relative to the static amplification factor of the control electrode 95 multiplied by the contact potential, which is in the order of 1 volt.

Except lfor the construction of the five electrodes of the discharge deviceiin Figure "10 so that the anodes "operate at higher positive 130- ftentials, lands?) that thet'cohtlol' electrode 95 hasi a' higher static'amplification"factor, the genjeral-prin cipl'es of "the-construction and operao f this discharge device are much the same as those illustrated in Figures '1 through *8.

Purelyb'y way of example, specific dimensions ferjtl ieelectrodes'are given. Thedia'riieter of ith e cylindrical unipote'ntial indirectly heated :cathode 9 l is ODfl'T-inCh. The firstcontrolelectrode-'9? menses-cf was OEGOSiI'icE in diam ter,

9 2 is formed 0f" ii/ire whose diameter-"1's 0.003 inch won aspirany arounatwt supporting pests as and 99 'with aims per inch. Thesccnd colftrol eletrode fi is 'foimd of Wire Wlidsiii- 'anieteris 0.002 inch wound spirally around two

s porting posts

100 and 101 with 72 turns per inch. These'cond anode 94 is formed of sheet meta-l havin fiat wing portion -'on opposite sidestithe heated fcatho'de 9 I.

V In Figure 11 fa 'se'c tional View of the device shown inFigu're 1'0 taken along the line ll-= illustrate "more-de rl the general shape off-the various electrodes of the device in a plane p'e'rpendicular to the axis of the cathode '91. [The Wings 102 and H13 oi" the anode 94 lie parallel'to eachoth'e'r and are spaced ar'oartlkSOO inch. The wings I02 and IE3 lie in planes which are p rallel with the axis of the indirectly heated cathode 91. The second control electrode 95 hasflat side's which are generally parallel with the wings "Ill? and "13 of the anode 94, and the'fla't sides of the second control electrode 95 are spaced "apart by 0.270 inch; Similarly, the first anode 92"has flat opposite sides generally parallel'with the Wings H12 and 103 of the anode 94, 'and 'the "fiat opposite sides are spaced apart by "0.172

I inch. The distances by which these flat sides are spaced apart are all measured along "a line perpendicular to the axis of the cathode 9! and "to the planes I02 and I03 of the anodej'lll. Along that same line the opposite curved" sides "of the first "control "electrode 93 are spaced "apart by 05075 inch. It should be noted that "theo'ppos'ite "sides oithe first control'electrode 93 are 'notfl'attenedjbut are-rounded, so that the control electrode 93 is substantially equidistant froinfall emitting'parts of the cathode 9|. The shadowing effect "of the control electrode 'sup-

Sporting post

96 and 91 is eifectiv'e to-suppress "electron'emis'sion from "portions of the surface "(if the cathode 9| near a plane passing through thefsupp'ortinglpos'ts 9B and 91. v

'Th'eelectrodes 9| through 95 "are all supfported'in symmetrical'relation with each other between mica spacers lll l and I 05,which in turn are held iniprope'r relation to one "another and which' arejheld a art in fixed relation-by iposts I08 a"nd"l'09; A suitable getter assembly I l-'0 -is supported in any desired fashion in the upper portion of the envelope 90.

Individual external connections 'for the five electrodes 9| through are provided, each extending through the glass 'wall of the envelope 90. A lead-in conductor Ill provides an external'connection for "the unipotential cathode 9|. A lead-in conductor I [2 provides an external connection for the first control electrode 93. Lead-in connections H3, H4 and H5 respec-- tively, provide external connections for the first anode 92, second control electrode 95, and sec 'ond anode 94. Lead-inconductors ll6..provide external connections -through which suitable continuous or alternating current may be supplied to"a"re'sistance heater \vithi'n tlie unipotential cathode 9|,

In Figure 12 certain characteristics or a discharge device constructed inacc'o'rdanc'e with this invention are presen'ted'ih a somewhat differentlight than in Figure 9.]In Figure 12"the currents flowing in the second anodeareplotted as ordinates 'andthe potentials of th'e's'e'cond anode-amended abscissae: Curve I20 is similar in significance to curve 8| of Figure 9 being taken with a fixed positive potential on the first anode, with a small negative bias potential on the first control electrode, and with no bias potential on the second control electrode. That is, curve I is taken with the second control electrode connected to the cathode, or more accurately adjusted to that potential at which current just begins to fiow in it.

Curve l2| may be observed under similar conditions, but with the potential of the second control electrode made a little more negative than is the case with curve I20. The curves i1- lustrate that the second anode current is throughout the operating range, with. a substantial negative bias potential on the second control electrode, substantially less than with no bias potential on the second control electrode.

-By referring to points on the curves I20 and |2| on a perpendicular line, such as the line (22, it may be determined how much current change (delta I) can be expected in the second anode in response to a predetermined small voltage change of the second control electrode, the first and second anode voltages remaining constant. Of course, in actual use, application of a small negative bias potential to the second control electrode tends to decrease the second anode current with a corresponding increase in the second anode voltage, because the second anode must be connected to a source of supply potential through a load impedance. Consequently, when a load impedance is connected with the second anode, the actual change, or reduction, in said second anode current upon an increase in negative bias potential of the second control electrode is smaller than might otherwise be expected. Expressed another way, the static transconductance from the second control electrode to the second anode is always greater than the transconductance between those two electrodes measured with a. load impedance connected with the second anode.

As pointed out previously, the peculiar construction of the second control electrode makes it possible to have these control characteristics with the second control electrode in the region of cathode potential. The normal pentode with a suppressor electrode operates at second anode voltages above the operating range indicated in Figure 12, and a suppressor electrode has a negligible transconductance over a substantial range of voltage near the cathode voltage. As a matter of fact, the second anode current does not drop to zero until the second anode voltage has reached P zero voltage with respect to the cathode, unlike the characteristic of the prefered form of discharge device according to the invention in which the construction of the second control electrode keeps the second anode current at zero even while the second anode voltage is at substantial positive level.

While we have shown and described the particular embodiments of this invention, it will be obvious to those skilled in the art that changes and modifications may be made without departing fromthis invention in its broader aspects, and we, therefore, aim in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of this invention.

We claim:

1. An electron discharge device having a plurality of electrodes including a source of electrons, a first control electrode consisting of a mesh having openings of a first size, a first anode consisting of a mesh having openings of a secondsize, greater than said first size, a second control electrode consisting of a mesh having openings of'a third size less than said second size, and alsecond anode, said electrodes being mounted serially and consecutively adjacent each other along the electron stream between said source and said second anode, said second control electrodebeing closer to said first anode than to said second anode whereby said second anode is operative at a low positive potential with respect to said source.

2. An electron discharge device having a plurality of electrodes including a source of electrons, a first control electrode consisting of a mesh having openings of a first size, a first anode consisting of a mesh having openings of a second size greater than said first size, a second control electrode consisting of a mesh having openings of a third size less than said first size, and a second anode, said electrodes being mounted serially and consecutively adjacent each other along the electron stream between said source and said second anode, said second anode having an area lying in said electron stream which is small compared to that area of said second control electrode lying in said stream, whereby stable operation of said electron discharge device is assured.

3. An electron discharge device comprising a plurality of electrodes consecutively adjacent each other along an electron stream including: a source of electrons; a first control electrode of a mesh having openings of a first size; a first anode of a mesh having openings of a second size greater than said first size and positioned at a distance from said first control electrode greater than the distance from said first control electrode to said source of electrons; a second control electrode of a mesh having openings of a size substantially equal to said first size; and a second anode positioned at a distance from said second control electrode greater than the distance from said first anode to said second control electrode.

4. An electron discharge device comprising a plurality of electrodes consecutively adjacent each other along an electron stream including: a source of electrons; a first control electrode of a mesh formed by a wire wound helically at a first winding pitch and positioned at a first distance from said source of electrons: a first anode of a mesh formed by a wire wound helically at a second winding pitch greater than said first pitch and positioned at a second distance from said source of electrons substantially equal to six times said first distance; a second control electrode of a mesh formed by a wire Wound helically at a winding pitch substantially equal to said first pitch and positioned at a third distance from said source of electrons substantially equal to ten times said first distance; and a second anode positioned at a distance from said second control electrode substantially equal to two times the distance from said first anode to said second control electrode.

5. An electron discharge device comprising a plurality of electrodes consecutively adjacent each other along an electron stream including: a source of electrons; a first control electrode of a mesh formed by a wire wound helically at a pitch in the order of '72 turns per inch and positioned at a distance in the order of .009 of an inch from said source of electrons; a first anode of a mesh formed by a wire wound helically at a pitch in the order of turns per inch and positioned at a distance in the order of .056 of an inch from said ipit chin the order of '72tiirns per inch and pos'iti n'data distance in'the order of .100'of an inch f'roinsaidsoi'irce of electrons ;''and asecond anode *bositlioned at a distance in the order of .187 of an infh fromsaid "source of electrons.

6. electron'discha'r'ge device having a plu- '-'rality' of electrodes including a source of elec- "ti'onsafirs't control electrode'eonsisting of amesh having openings of a fi'rst'size, a first anode consisting of a mesh having openings of a "second sizegraterthan-said first size,'a second control electrode consisting of a mesh 'havingop'enings substantially equal to saidfir'st size, and a second anodasaid electrodes being mou'nt'ed'serially and consecutively adjacent "each other along the electron stream flowing between said source and said *second anode, 'said *secondcontrol electrodelying closer to said first anode than to said second anode; Whereby'said second anode is operative at a --low"=positive potential with respect to said source, said second anode havingan area lying in said electron-stream which is small compared to ifiliatarafdfafd 5e u said elegtrdn streak-1 ix/Hereby self-induced os l1- latibn or 'sai'd 'elctrondis'liafge device is iii-e- RD a JOHN G. 'PR TISS.

The following references areof record in'the file of this patent; V

UNITED S ATES-PATENTS 5511" Overbeck' 11113 3051946