US2569971A - Beam amplifier tube - Google Patents

Description

Get. 2, 1951 N, z. BALLANTYNE BEAM AMPLIFIER TUBE E Filed June 16, 1949 N. Z. BALLANTYNE IN VENTOR ATTORNEYS.

A.F. ZERO RESISTANCE MODIFIER area. -;lens action and the two work together.

electro-static or electromagnetic potential.

be greatly changeda 3 the electron velocity, and the geometrical arrangement of the elements.

To be more detailed, the electrons leaving the accelerating structure near the positive deflection plate are thrown into a curve by the positive potential present and are also accelerated by it. The electrons passing close to the negative deflection plate are repelled from it and attracted both by the positive deflectionplate and the lumpedattractionof the target anode and target plate. Since the curve of the" electrons near the positive plate is near the calculated curve of the positive plate and the curve of these electron paths is flatter than the curve of the -electrons near the negative plate, which lose their original linear velocity more readily inapproaching'the negative deflection plate, the two curyes will come together at the point of focus. A shift in potential at one deflection plate causes a shift in the electron curve near that point. Since the vari- -ous curves are approaching. one point with the electrons travelingiatrelatively the same velocity,

that pointwill have a- 'veryhigh electron density perwunit area. ;Since the electrons contain the same charge, as the density increases as the electrons approach the/point of focus the electrons will become mutually .repulsive but since their angular velocity is converging the two relative velocities will vectorrinto a resultant component which momentarily, will collimate the electron paths. If the angular velocity component of either of the converging: paths is changed, then the resulting vector component will alsov be changed. By this means the beam will be shifted not so much by. the activity of direct electro-- static action but, rather by: thechange of relative angular velocities of the individual electron paths. It istrue thatashiftin deflection, plate potential does change .the electro-static density but it is also true that if bothdeflection plate voltages were shiftedrin-the same direction at the same time so that electrio-static field strength remained constant the beam would still shift. r Thus, in effect alens is formed between cathode and the target plate and this lens is shifted in contour to control the electron bombardment Electro-static action is secondary to the .zInthejpriorrart deflection of the beam was accomplished completely by a change ineither The beam was either diverging or approaching collimation; It was not converging nor was it using vector relationships as a control factor.

Another object of the invention is to provide a tube in which m icrophonic troubles are, to a large extent, eliminated. ,In the prior art, a primary cause of microphonics has been the relatively fragile grid windings which may be changed in physical length by'an increase in temperature with a resultant lo's's'of rigidity and the possibility of setting up vibrations within the tube structure. It is evident with rigid plates and without grid windings of 'any'kind it is impossible to set -up'vibrations within the tube due to expansion of the elements of the tube structure.

Since all unit lengths are linear to the cathode the major expansion will be parallel to the cathode and, therefore, the rigidity of elements cannot Another object of the invention is toprovide a tube which does not decelerate theelectrons as they leave .the cathodewallr This actionis a source of ineflicient operation in theconventional tube but is eliminated in this inventionbecause;

4 of the constant acceleration applied to the electrons.

Another object of the invention is to provide an electron discharge device in which the electron density per unit area of the beam cross section remains constant or becomes greater. Thus, the problems resulting from a shifting density in the electron stream is eliminated because electron density remains nearly constant.

Anotherobject of the invention is to provide a tube which can be constructed of vertically aligned parts. Since these parts expand or contract along the axis of major length with the result that practically zero change can be observed in width, no appreciable change in control' constants will result from changes in temperature.

This results in constant control factors which are not found in grid type tubes. Another object of this invention is to provide a tube with the ability. to be used as a push-pull amplifier within the one envelope. This is accomplished by controlling the lens action by shifting both negative and positive plate potentials simultaneously but in opposite phases (output can be single end or push-pull) Another object of this invention is to provide a tube in which there is no phase shift between input and output. Since in the common tube the current through the tube increases with a decrease in negative grid potential resulting in a decrease in plate voltage and consequent reduction in attraction the shift in plate voltage causes a decrease in the actual control exercised by the grid. ,Also when the grid potential increases (becomes more negative) the plate current decreases with a resulting increase in plate voltage and an increase in plate attraction. This action of the plate voltage opposing the change caused by grid voltage reduces the over-all efiiciency of the common tube and results in numerous other problems. In this invention when a control voltage is applied to the negative deflection plate and that plate becomes less negative, the beam is shifted towards the target anode. The target plate therefore becomes more positive and is in phase with the control voltage. A similar relationship exists between the positive deflection plate and the target anode. It is obvious that output voltages in phase with, or out of phase with, the input signal may be taken at will from this tube byusing the proper arrangement.

A further object of the invention is the reduction of harmonic distortion. Because of the very narrow limits of the linear curve in the conventional tube and the necessity of biasing and driving the tube within those narrow limits without causing non-linear .distortion to appear, circuits must be carefully constructed and operated, An increase in signal'voltage slightly above the curve limits causes distortion to appear while a change in circuit components will also cause such distortion.

With an increase in the length of the linear part of the curve, the possibilities of biasing at the wrong point or over driving the tube are consequently decreased. Since only a small part of thecurve is not straight so that linear response would result over almost. the entire curve harmonic distortion is largely reduced.

Still another object of the invention is the reduction of frequency distortion. In the conventional circuit where a cathode resistor is used and by-passed by a capacitor, the capacitive reactancev will vary as the operating frequency shifts. Also the common resistive-capacitive coupling=-produe es changes in capacitive reactance while the operating frequency changes. 1 These-points are sources -of=-frequency idistortion due to the changingefiective A C.*-resistance.

In-this tube when a resistor is used-in the ca'thode circuit, the-voltage drop across th atwresistor remains constant. Also the-fact that directecoupling-can beutilized;- in some circuitsy eliminates "the need for the-couplingcapacitor and consequently eliminates this source 'of distortion' if so connected.

It is-well to note thatother seurces -of -f*requency-distortionare--present}*but thosesources -are not in the'province'of the tube. Insoiar'as r possible the-causes -of tub ecaused *frequency 'distortion are eliminated. A- further objectf the invent-ion isto previde a tube which is simple andinexpensive to rnanu- "facture. Without the necessity bf -winding the grids andby constructing com'plet'ely f-rom easily 1 stamped parts-this tube --is very inexpensive'" to manufacture despite the precision required in constructional-detail.

*Another object of the invention is'to provide a -d'eflec-tion type -tube of sufficiently small construetion tcr-be 'utilized wit-hin the space limitations -of "themore conventional tubes. --Since't-he over- "2111SiZ8'0f this tu-be can be less than many of the conventional types it -iol'loWs"-that-- thisobject has been realized.

These" and other" obj cots are attained-by the novel construction and arrangement' 'of parts hereinafter described and "illustrated by theac- "companying drawing-forming apart-hereof -and "in-which:

"Figure lis a'plan view-of a" beam amplifiertube embodying the invention.

Figf2 is a sectional" view taken '-on-'1ine"2-' 2 "of-Fi 1. i

"Fig. 3 is a diagrammaticviewillustrating'anexternal circuit used' in conjunction withthe'device. Referring to the drawing; the tube is shown to comprise anenvelop" l in whichfis positionedra cathode 2;'Which"emitselectrons from alter-its coated surface when properly heated. "The coated surface" 3 of oxide *may' completely cover the exterior Of'thecathode or only apart of it, 'and the cathode may-be round orofa*fiatconstruction, or itmay have'aninwardly curvedsurface. Whatever the'cathodeconstructiorrmaybe, *thesurface coating emits electronswhen heated. Theemitted electrons are'repelled bythe neutral -or negative charge applied "to'the'focusingstruc- --ture 4 comprising ac-ylinder. *The'cpeninger' gap -5, in the focusing structure provides means-for the electrons to pass through"thafocusingstructure towards accelerating structure 6; also comprisinga cylinder. The efiective width ofthis gap can be controlledbyvaryingdhe vbltagerto the focusing structure. Just-beyond 'thegap-the accelerating structure 6 causes the electrons emitted from the cathode wall nearthegap to accelerate through the gap-towards theacc'elerating structure; because of" the-"positive-"potential applied-to that structure. As the-electrons reach =-and-pass through this structure they ha-vehad a high linear velocity-appliedand the "various -electron paths are approaching-=collimation in "the vertical plane; considering'thatthe-cathodeis verticallyalined.

In this manner the beain-is setup. "Ihe'focusing structure allows the ele'ctrcns- -tomove only --through the gap causingtheiormation'of'a-beam .in-the-horizontalplane and theaccelerating-structure' causing the electrons' toapproach'- collimati'orr in thewertical xplanes withzr resultant iequal electrorr' den'sity along the vertical axis.

Electrons moving outward from theaaccelerating 'structure' in the region bf the positive d'eflection ==plate mare attracted toward 'that plate. flowever, since the electrons have. avh-igh linearxw l locity-= andthe plate bends away: -from itheiri dine of -movement they :cannot -bombard it. Thev attraction, however, causes: some: angular-velocity -to -be applied which causes the electron pathiito become a relatively flat curve.

Ele'ctrons moving-outward :frorn' the acceler'a ing: structure 6 -in': the region near thec'negative "ldeflection' plate 8 cannot: bombard that structure althoughiitis directly im their path because it is m'aint'ained at orb'elow cathode-potential. Since the electrons: cannot bennbard this structure they '--begin to losethe linear velocityaapplied. TThe potenti'als. to ithe -target plate 9: and-: the ztarget anocle l I] form: an attractive field which applies :.high angularacceleration-to the electrons. l hus theelectronsfollowtasharply curved path-between the acceleratingstructure andthe :point of 'focus. 'Since the electrons near thempos'itive'fdeflec- 1 Ition plate have a. relativelyfiat curve and-i the electrons hear the negative defiectiomplatevhave a 'sharp curve, and the two-'curvesare in' 'the same direction, it follows that the curvesw'iltconverge as shown inlthedrawing.

lnvarying degrees :theseia'tztors of convergence "effect all of the electron paths. With all the electrons approachingone point it' is obvious that 1 an extremely high electron density per unit-area w'ill.develop atthe point- 0f 'focus. The high 1 r electron density. apparently causes 'theelectron tocollimate due to the mutual repulsion athigh 'Ldensities. This causes-the-beam:to-become highly -concentratedand movinginparallel lines in' the horizontal plane.

The electrons approaching: the -point-offocus are trav eling at 'r'elatively "the same velocitypbut in different; directions. 11 Since the resultant-ofithe -several'con-verging paths will be avector-of all the paths, itfollows that if one path'is changed the' final path will alsobe changed.

Whether the electron beam strikes the --target anodeworthe target plate 9 depends upon the -path the electrons near the structure in control (either the-positive-01 negative deflection plate) are causedto" take. Increasing the negativepotential on the negative deflection plate causes-a sharper curveto develop in that'region causing the vector-resultant of the severalcurves to move steward bombardment of the target 'plate *9. "Similarly an increase in the positive potentialapplied-t0 the positive deflection platewill cause -=a-' sharper curve near that structure resulting in -the beam again moving toward bombardment 'of the :target plate 9. Converse voltage applied .:Would cause the beam-to-move toward the tar e =anocle.

Fromithe above description it will-be seen' that the electrostatic field-shift is only a--small part -of :the total control factor. For that reason this tube-is not to be construed as simply an electrostatic deflecting tube. The electro-staticshift'is secondary-to thelens Warp which occurs-when --defiection-of platepotential is applied andshif-te'd. The separator plate H is operated atalower 7 =potential than the target anodeinsofar-as static potential is concerned and will maintain somepo- -tential difierence even atmax-imum 'swingsinthe voltage applied to- -either the target-anode-er stargetplate. '-'Si-noe=itis operated at a'--lower po- *-tential 'ina field- -of-"much" higher potential the if total amount of beam current bombarding the separator plate is at no time very large. When -thepoint of focus is, placed upon the separator .plate the beam will divide oneither'side of the plate and be flowing equallyto the target anode and to the target plate.

- From the above description it will be seen that there has been provided a tube using a beam of constant intensity, that is, the current drawn from the cathode is a constant, which is not true in tubes hereofore provided. In addition, in my tube no effort is made to establish electron multiplica- :tion or control secondary emission, although such use is not to be disregarded. Furthermore, in my tube the formation of the beam remains constant, its electron density remains constant or increases, the velocity of electron movement, the electrostatic density, and all other operational factors remain constant except for the voltage required to either the positive or negative deflection plates. Control over the beam is exercised by changing the voltage to the deflection plates causing the warping of an electro-static lens. 1

It will be seen that there has been provided a beam amplifier tube using a beam of constantintensity and near constant density controlled by means of lens warp. The tube draws a current from the cathode which is constant at all times; and shifts in voltage on either the negative or positive deflection plates will produce control action so that either positive control, with the advantage of direct coupling, or negative control, with certain advantages in its favor may be used. If an equal load is placed on the target plate and target anode circuits and the tube is biased properly, power phase inversion from one point of control is realized. Unequal loads may also be used with compensating changes in bias points. In the tube the rise in plate current on either the target plate or target anode becomes linear to the applied signal voltage 50 that in comparison with ordinary tubes, there is no EG-Ip curve but, rather, a very near linear rise. This means that harmonic distortion is almost entirely eliminated and that fidelity of response is exceptionally good when the tube is not driven out of its control voltage range. The presence of electro-static fields which cause the electron beam to come to a point of focus, causethe amplification factor of thetube to be high in comparison s to other types of beam tubes.

Since the control action and the point of bombardment are very close together and since the amount of current present in the beam remainsa constant, the drop off in efficiency as the higher frequencies are applied to the tube will be very small. Relatively small inter-electrode capacity exists between the positive deflection plate and the target plate. Feedback between these two elements, when positive deflection control is used, will, therefore, be relatively low. When negative control is used. the fact that the target plate and negative deflection voltage will be in phase will tend to reduce the capacity existing between them.

The tube as presently constructed consists of a single stage amplifier. The foregoing description should in no way limit the application of the same principles to a tube of symmetrical construc tion of a push-pull type. v Y I The invention having been described, what is claimed is:

1. In an electron discharge device of the beam amplifying type, an envelop, a cathode mounted .in the envelop, an oxide coating on the cathode,

.said coating emitting electrons when the oath-.

ode is heated, a focusing structure comprising a cylinder surrounding the cathode, said focusing structure having an opening through which emitted electrons can pass, an accelerating structure beyond the focusing structure and having an ,opening for the passage of electrons, a positive deflection plate and a negative deflection plate beyond the accelerating structure and curved substantially in the same direction, said negative deflection plate having a curvature greater than the curvature of the positive plate, a target plate curved in the direction opposite to the curvature of the negative plate and arranged to receive elecstructure comprising a cylinder surrounding, the

cathode, said focusing structure having an opening through which emitted electrons can pass, an accelerating structure comprising a cylinder having parts thereof mounted beyond the focusing structure and with an opening aligned with the opening in the focusing structure, a positive deflection and a negative deflection plate spaced apart and disposed beyond the accelerating structure and mounted on either side of the gap in that structure with these two members curved substantially in the same direction, said negative deflection plate having an arc length greater than the arc length of the positive deflection plate, a target plate curved in the direction opposite to the curvature of the negative deflection plate and arranged to receive electrons from the beam 'as directed by the positive and/or negative deflection plates, a target anode arranged to receive such electrons from the beam that are not absorbed by the target plate, and a separator plate between the target anode and the target plate upon which the electrons are focused, said separator plate operated at a lower potential in respect to the cathode than the target plate and target anode.

3. In an electron discharge device comprising an electron emitting cathode, a separator plate, means for focusing the electrons into a beam throughout their path of travel from the cathode to the focus point near the edge of the separator plate, means for accelerating the electrons, a curved positive deflection plate curved in the arc of a circle, and a curved negative deflection plate curved in the arc of a circle, so disposed as to give the beam a substantially curved path, a target anode, a target plate promoting focusing action, and a separator plate which is operated at a potential less positive in respect to the cathode than the target plate and target anode.

4. The structure set forth in claim 1 further characterized by the positive deflecting plate and the negative deflecting plate being curved in the arcs of circles in the same direction.

5. The structure as set forth in claim 1 further characterized by the target plate being curved in the arc of a circle and in a direction opposite to the curvature of the positive deflecting plate, and one end of the separator plate being positioned between and in spaced relation with the target plate and the'target anode.

6. In an electron discharge device, a cathode from which electrons are emitted when the cathode is heated, means for focusing the electrons, means for accelerating the electrons, a positive 2,569,971 9 10 deflection plate and a negative deflection plate di- UNITED STATES PATENTS recting the electron beam in a substantially linear path, a target anode, a target plate to assist in a Name Date focusing the electron beam on the target anode, Thompson 1942 and a separator plate operated at a potential 5 RE GN PA ENTS lower than the target plate and target anode. Number Country Date NORMAN BAILANTYNE- 232,225 Switzerland Aug. 1, 1944 REFERENCES CITED The following references are of record in the 10 file of this patent:

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