US3506870A - High power magnetically beamed vacuum tube with low hum - Google Patents

Description

A ril 14, 1970 B. M. SINGER ETAL 3,506,870

HIGH POWER MAGNETICALLY BEAMED VACUUM TUBE WITH LOW HUM Filed March 27, 1968 3 Sheets-Sheet 1 INVENTORS 24 BARRY M. SINGER CARL Z JOHNSON Apr l 14, 97 'B. M. SINGER ETAL 3,505,370

I HIGH POWER MAGNETICALLY BEAMED VACUUMiTUBE: WITH LOW HUM Filed March 27, 1968 5 Sheets-Sheet 2 F/G. Z

BARRY M. SINGER CA 7.' JOHNSON A ril 14, 1970 s. M. SINGER ETAL 3,505,370

HIGH POWER MAGNETIGALLY BEAMED VACUUM TUBE WITH LOW HUM Filed March 27. 1968 3 Sheets-Sheet s s F- H2 T [H N f "arm 2 1 (Wm My 1) 1 yyyw F/G. l0

INVENTORS BARRY M. SINGER 6 L 7. JOHNSON United States Patent O 3,506,870 HIGH POWER MAGNETICALLY BEAMED VACUUM TUBE WITH LOW HUM Barry M. Singer, New York, N.Y., and Carl T. Johnson, Chamblee, Ga., assignors to The Machiett Laboratories, Incorporated, Springdale, Conn., a corporation of Delaware Filed Mar. 27, 1968, Ser. No. 716,515 Int. Cl. H01j 1/50, 3/20, 3/32, 23/10, 29/76 US. Cl. 313154 9 Claims ABSTRACT OF THE DISCLOSURE An electron tube comprising an anode having an open ended cavity therein, an array of parallel filament wires disposed longitudinally within the anode cavity, each of the filament wires having a cross section which predetermines the maximum intensity of a magnetic field established around the wire by a peak value of alternating filament current, and an external magnet having opposing pole faces disposed one on either side of the anode in respective planes parallel to that of the filament array and a magnetic field therebetween which has an ntensity equal to or greater than the maximum intensity of the respective magnetic fields around the respective filament wires.

BACKGROUND OF THE INVENTION This invention is related generally to electron discharge devices and is concerned more particularly with reducing hum in the output of electron tubes which have a cathode heated by an alternating current.

In conventional triode power tubes, for example, electrons are thermionically emitted from a filamentary cathode and flow toward a highly positive anode under the influence of a signal voltage applied to an inter vening control grid. In order to supply the heavy electron emission required for power tube applications, a high value of current fiows through the respective filament Wires of the cathode thereby heating them to incandescence and producing a copious flow of electrons toward the anode. Because an alternating llament current introduces noise in the output of the tube, a direct current is generally preferred :for heating the filament wires to incandescence. However, the direct current is usually provided by an auxiliary power supply which rectifies the more readily available alternating current and filters out any ripple which may cause noise in the output of the tube. Therefore, for reasons of convenience and economy, it would be highly desirable to use alternating current for heating the filament wires if the noise factor does not seriously limit the performance of the power tube.

When using an alternating filament current, the noise component, which is superimposed on the amplified signal output of the tube, is characterized by a hum frequency which is tfice the fundamental frequency of the heating current. For example, if sixty cycle alternating current is used for heating the filament wires, the hum frequency in the output current of the tube is one hundred and twenty cycles. The condition results from the very nature of alternating current which reverses direction periodically and rises to a peak value twice during each cycle, once during each direction of current flow. Current flowing in the respective filament wires establishes a concentric magnetic field around each filament wire which can be measured by a magnetic flux density (B and represented by a magnetic field intensity vector (Hf). The magnetic flux density is greatest at the surface of the wire and falls off inversely with increasing distance from the axis of the wire. Because the magnetic flux 3,506,870 Patented Apr. 14, 1970 density is proportional to the instantaneous value of the current, it reaches a maximum value when the alternating filament current rises to a peak value in either direction of current flow. The magnetic field intensity vector (H is proportional in magnitude to the magnetic fiux density (B and is drawn parallel to the magnetic fiux lines. The clockwise or counterclockwise direction of the magnetic field intensity vector is determined by the direction of current flow and changes from one direction to the other when the alternating filament current reverses the direction of flow in the respective filament wires. The magnetic field intensity vector represents the magnetic force that will be exerted on a charged particle, such as an electron, which is moving transversely through the mag netic field in a direction perpendicular to the magnetic fiux lines. If the charged particle has a component of velocity parallel with the magnetic field, the motion of the particle in that direction will be unatfeced. If the charged particle has a component of velocity perpendicular to the magnetic field, it will be acted upon by a resultant force in a direction perpendicular to that component of velocity and to the magnetic intensity vector of the magnetic field.

Since the magnetic field intensity vector is concentric with the axis of a respective filament wire that is carrying current, small increments of the intensity vector can be considered as being perpendicular to radial lines drawn from the axis of the wire to the respective increments. Electrons emitted from the respective filament wires move radially through the respective coaxial magnetic fields and are acted upon by the respective magnetic forces of these fields. Since the electrons have respective velocity components that are perpendicular to the respective surrounding flux lines, the electrons will be deflected in longitudinal planes that pass through the respective filament wires. Thus, the electrons will not travel a direct path to the anode but will deviate from this path in a direction that is ultimately determined by the direction of current flow in the respective filament wires. As the instantaneous value of the filament current rises to a peak value, the respective coaxial magnetic fields increase in intensity, producing greater deviations of the electrons from a direct path to the anode, until a maximum deviation path is travelled by electrons going toward the anode. This deflection of electrons from a direct path to a path of maximum deviation causes the electron stream to sweep across a portion of the anode surface. The effect of this excursion is a change in the electron flow to the anode. More electrons arrive at the anode surface per unit of time when travelling a direct path to the anode than when the electrons are travelling the longer path of maximum deviation. Between these two extremes is a path of mean or average length which the electron stream sweeps through twice, once in moving toward the path of maximum deviation and once in returning to the direct path. The over-all effect in the unidirectional anode current is one cycle of hum frequency for one-half cycle of filament current. When the filament current reverses direction, the respective magnetic intensity vectors around each filament wire reverse direction also. As the filament current rises to a peak value in the reverse direction, the magnetic flux density increases in value correspondingly. The magnitude of the magnetic intensity vector will increase accordingly and the electron stream will be deflected progressively in the opposite direction of the same longitudinal plane. The electron stream will sweep across a portion of the anode surface equal to the first excursion and will have the same effect on the unidirectional anode current. Thus, two cycles of hum frequency will be produced in the output of the tube for one cycle of filament current. This hum frequency which is superimposed on the amplified signal current of the tube constitutes a significant source of noise in the tube. In order to minimize the hum in the anode current which results from the use of an alternating heater current, It is necessary to reduce the effects of the respective coaxial magnetic fields established around each of the filament wires by the alternating current flowing through the respective filament wires.

SUMMARY OF THE INVENTION Since the magnetic flux density is greatest at the surface of a wire carrying a current and reaches a maximum value when an alternating current flowing in the wire rises to a peak value, a cross-sectional dimension can be chosen for the wire which will determine the maximum value of magnetic field intensity around the wire for the peak value of alternating current. Therefore, an electron tube embodying this invention has a filament array comprising parallel wires, each having a cross section which predetermines the maximum magnetic force exerted by the respective coaxial magnetic fields on electrons emitted from the respective filament wires during peak flow of alternating current through the respective filament wires. A magnet is located external of the tube envelope and has opposing pole faces, one disposed on either side of the anode in respective planes that are parallel to the plane of the filament array. The magnetic field between the pole faces of the external magnet passes through the anode cavity in planes perpendicular to the respective wires of the filament array. The magnetic field of the external magnet interacts with the emitted electrons to reduce the effects of the respective coaxial magnetic fields around the respective filament wires and thereby minimizes the resultant hum in the output of the tube.

BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of this invention, reference is made to the drawing wherein:

FIG. 1 is a fragmentary axial view, partially in section of a tube embodying the invention;

FIG. 2 is a fragmentary cross-sectional view taken along line 2-2 of FIG. 1 looking in the direction of the arrows;

FIG. 3 is an enlarged, axial, diagrammatic representation showing the force exerted on an emitted electron when the filament current is flowing in one direction;

FIG. 4 is an enlarged, axial, diagrammatic representa tion of the change in electron path to the anode as a result of the force shown in FIG. 3;

FIG. 5 is an enlarged, axial, diagrammatic representation showing the force exerted on an emitted electron 'when the filament current is flowing in the opposite direction;

FIG. 6 is an enlarged, axial, diagrammatic representation of the change in electron path to the anode as a result of the force shown in FIG. 5;

FIG. 7 is a diagrammatic representative of an oscilloscope screen showing the magnitude of the hum current in the output of a tube with no external magnet;

FIG. 8 is an axial, diagrammatic representation of the paths taken by emitted electrons under the influence of the electrostatic field and the coaxial and external magnetic fields for filament current flow in one direction;

FIG. 9 is an axial, diagrammatic representation similar to that of FIG. 8 except for filament current how in the opposite direction;

FIG. 10 is a diagrammatic representation of an oscilloscope screen showing the reduction in hum current in the output of the tube.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawing wherein like characters of reference designate like parts throughout the several views, an electron tube embodying this invention is shown in FIGS. 1 and 2 with the grid partially removed in FIG. 1 for purposes of clarity. The tube comprises a gastight envelope closed at one end by an oval-shaped anode cup 21 which has extended flat sides 22 and 23. Anode 21 is made of a highly conductive metal, such as copper, for example, and encloses an oval-shaped anode cavity, designated generally as 24. The open end of anode 21 terminates in an outwardly extending flange 25 which has a circular perimeter and which functions as the anode terminal of the tube.

A metallic sleeve 26, preferably Kovar, is hermetically attached throughout one end to anode 21, adjacent the inner periphery of the open end. The other end of sleeve 26 is peripherally sealed to one end of dielectric cylinder 27, preferably ceramic, which is similarly sealed at the opposite end to one end of a metallic sleeve 28, preferably Kovar. The other end of sleeve 28 is circumferentially attached to one side of a metallic ring 29, preferably copper, which serves as the grid terminal of the tube. Terminal ring 29 extends radially inward and is hermetically attached on the opposite side, adjacent the inner periphery thereof, to one end of a metallic sleeve 30, preferably Kovar. The other end of sleeve 30 is peripherally sealed to one side of dielectric ring 31, preferably ceramic, which is similarly sealed on the opposite side to one end of a metallic sleeve 32, preferably Kovar. The other end of sleeve 32 is hermetically attached to a metallic ring 33, preferably copper, which functions as one of the cathode terminals of the tube. Cathode terminal ring 33 extends radially inward and is hermetically attached, adjacent the inner periphery thereof, to one end of metallic sleeve .34, preferably Kovar. The other end of sleeve 34 is peripherally sealed to one side of dielectric ring 35, preferably ceramic, which is similarly sealed on the opposite side to one end of metallic sleeve 36, preferably Kovar. The other end of sleeve 36 is peripherally attached to one side of a metallic ring 37, preferably copper, which serves as the other cathode terminal of the tube. Cathode terminal ring 37 extends radially inward and is hermetically attached, adjacent the inner periphery thereof, to one end of an exhaust tubulation 38, preferably copper, which is pinched off to form a vacuum-tight seal after processing of the tube is completed.

Within the gas-tight envelope just described, a coaxial support cylinder (not shown), preferably copper, connects cathode terminal 37 to oblong support desk 41, and a concentric support cylinder (not shown) preferably copper, connects cathode terminal 33 to oblong support deck 42. The two support cylinders are insulatingly spaced from each other and from the surrounding gas-tight envelope. For purposes of rigidity and alignment, support decks 41 and 42 are insulatingly attached to each other by conventional means, such as dielectric bushings and washers for example (not shown). Another support cylinder 43, preferably copper, is attached at one end to grid terminal ring 29 and extends longitudinally and coaxially with the aforementioned cathode support cylinders, insulatingly spaced therefrom and from the surrounding gas-tight envelope. The opposite end of support cylinder 43 terminates in two parallel shoulders 44, one on each side of the oblong support decks 41 and 42 and in spaced relationship therewith. Parallel connecting rods 45 are attached at one end to support decks 41 and 42 by conventional means, such as brazing for example, and eX- tend longitudinally in a plane centrally located between grid support shoulders 44. The connecting rods 45 attached to support deck 41 pass insulatingly through aligned holes in support deck 42 and terminate in the same transverse plane as the connecting rods 45 attached to support deck 41. The ends of parallel, U- shaped filament wires 46 are attached to the distal ends of connecting rods 45 by conventional means, such as welding for example. Each U-shaped filament wire 46 has one end attached to a conecting rod 45 that extends from support deck 41 and the other end attached to a connecting rod 45 that extends from support deck 42. The

resulting linear array of parallel filament wires 46 hangs longitudinally in a central axial plane of the anode cavity 24. Respective plates 47 and 48 are attached to the respective shoulders 44 of the grid support cylinder 43 by conventional means, such as machine screws for example (not shown). Plates 47 and 48 have straight sides adjacent the linear array of filament connecting rods 45 and in spaced relationship therewith. Respective ends of grid rods 49 are attached to the respective straight sides of plates 47 and 48 at regularly spaced intervals which coincide with longitudinal planes centrally located between adjacent filament wires 46.

As shown more clearly in FIG. 2, the grid electrode comprises two frames of parallel rods, one attached to each shoulder 44 by means of plates 47 and 48, respectively. The grid rods 49 extend longitudinally in planes parallel with and closely adjacent to the linear array of filament wires 46. The opposite ends of grid rods 49 are attached to opposing flat sides of an oblong plate (not shown) which is longitudinally spaced from the closed ends of the U-shaped filament wires 46 and which maintains the grid rods in the desired spaced relationship one to another and with the linear array of filament wires. A C-shaped, permanent magnet '50 is located external of the tube envelope and encloses one side of anode 21. The extended flat sides 51 and 52, which are the pole pieces of magnet 50, are disposed in respective planes which are parallel to the flat sides 22 and 23 of anode 21, the parallel frames of grid rods '49 and the linear array of filament wires 46. Thus, the magnetic lines of flux between the pole pieces 51 and 52 lie in planes perpendicular to the planes of the anode, grid and filament array. Therefore, the magnetic lines of force between pole pieces 51 and 52 are parallel to the intended direction of electron flow. A source of alternating current, surch as generator 53 for example, is connected across cathode terminals 33 and 37 as by conductors 54 and 56 and clamps 55 and '57 respectively.

In order to understand more fully the problem solved by this invention, reference is made to FIGS. 3-7. In FIG. 3 an enlarged filament wire 46 is shown wherein an instantaneous value of alternating current is flowing in the direction indicated by the arrow I For this direction of current flow, a concentric magnetic field, indicated by the circular vector H is established along the length of the filament wire 46. At this instant of time, an electron 61 is emitted from the filament wire 46 and travels a radial path, shown by arrow v through the coaxial magnetic field. An increment of vector H is perpendicular to the radial path v as shown by the arrow H and, therefore, a force is exerted on electron 61 which tends to move it in the direction indicated by arrow F As shown in FIG. 4, when the alternating current begins to flow in the direction shown by the arrow I the instantaneous value of the current in that direction is zero, and the intensity of the coaxial magnetic field H is a minimum value. Consequently, electrons emitted from the filament wire 46 during this interval of time are drawn directly toward the anode, as indicated by the arrow v as a result of the strong electrostatic force between filament wire 46 and the highly positive anode 21. When the instantaneous value of the alternating current reaches a mean or average value, the intensity of the coaxial magnetic field is increased and a force is exerted on the emitted electrons which deflects them in the direction indicated by arrow P in FIG. 3. At the same time, the electrostatic force exerted by the highly positive anode draws the electrons away from the filament wire 46, and the intensity of the magnetic field H falls otf inversely with increasing distance from the axis of the filament wire 46. As a result of being deflected in the direction of the force P while travelling toward the anode 21, the electrons emitted during this interval of time do not travel a direct path to the anode but travel a longer path shown by the arrow v The longer length of path v keeps the electrons in the space between the anode 21 and the filament wire 46 for a longer period of time. Therefore, the space charge in the interelectrode region builds up and electrons subsequently emitted from filament Wire 46 meet an increased electrostatic retarding force in the gap between the anode and the filament. Consequently, fewer electrons travel toward the anode and the anode current decreases correspondingly. When the instantaneous value of the alternating current reaches a peak value in the direcgion indicated by the arrow I the intensity of the magnetic field H surrounding flament Wire 46 reaches its maximum value and the electrons emitted during this interval of time are deflected a greater distance in the direction of the arrow P in FIG. 3. The electrons then travel a longer path, indicated by arrow v in FIG. 4, and are in the space between the anode 21 and filament Wire 46 for a longer interval of time. Therefore, the anode current decreases to a minimum value as a result of the larger space charge built up in the interelectrode space during the longer interval of time. The instantaneous value of the alternating current then decreases to the mean or average value and the emitted electrons again travel the path indicated by arrow v As a result, the space charge in the gap between the anode 21 and filament wire 46 is reduced and a greater number of emitted electrons travel toward the anode 21. Consequently, the anode-current increases to the value obtained when the electrons were previously traveling along path v The instantaneous value of the alternating current I then decreases to zero and the magnetic field surrounding fila- ,ment wire 46 reaches a minimum value. The emitted electrons are then drawn directly to the surface of anode {21 and the interelectrode space charge decreases accord- "ingly. Consequently, a greater number of electrons travel to the anode 21 and the anode current increases. Thus, one cycle of hum frequency current has been superimposed on the amplified output current of the tube.

In FIG. 5, the enlarged filament wire 46 is shown wherein the alternating current, after decreasing to zero value, has reversed direction and is now flowing in the direction indicated by the arrow I For this direction of current flow, a concentric magnetic field, indicated by the circular vector H is established along the length of the filament wire 46. At this instant of time, an electron 62 is emitted from the filament wire 46 and travels a radial path, shown by arrow v through the coaxial magnetic field. An increment of vector H is perpendicular to the radial path v as shown by the arrow H and, therefore, a force is exerted on electron 62 which tends to move it in the direction indicated by arrow F As shown in FIG. 6, when the alternating current, flowing in the direction indicated by arrow I rises to a peak value and decreases to zero, the emitted electrons travel the various path lengths indicated by the arrows v v v v and v The values of the filament current I during these corresponding intervals of time are equal to those of filament current I during equivalent intervals of time. Consequently, the intensity of the coaxial magnetic field, H reaches values equal in magnitude to those of the coaxial magnetic field H during equal intervals of time. However, the magnetic force of coaxial magnetic field H is exerted in the opposite direction to that of coaxial magnetic field H and the resultant force P tends to move the electron 62 in a direction diametrically opposite to that of resultant force F As a result, the electrons emitted from filament wire 46 during this half-cycle of filament current are deviated along paths such as v and v which are equal in length to those of v and v and equidistant from the direct path v Although the electrons impinge on a different surface area of the anode 21 during this half-cycle, the effect on the unidirectional anode current is the same as during the previous halfcycle. When the filament current 1, is rising to a peak value, the electrons are similarly retarded by a buildup of space charge in the inter-electrode gap and the anode current decreases to a value equal to that of the previous half-cycle at a corresponding instant of time. When the filament current 1, is decreasing toward a zero value, the space charge decreases in the interelectrode gap and the anode current returns to the value it had before the start of the second half-cycle of filament current. Thus, two cycles of noise frequency are superimposed on the amplified output of the tube for one cycle of filament current. FIG. 7 shows the screen of an oscilloscope which is connected across the output of the tube and has a filter network for removing the amplified output signal current. The remaining hum current is shown as hava frequency which is double that of the alternating filament current. The maximum peaks occur when the emitted electrons are travelling the direct path v to the anode. The minimum values occur when the emitted electrons are travelling along paths of maximum deviation, that is v or v to the anode. The base line values occur when the emitted electrons are travelling along mean or average paths, that is v or v to the anode. The noise frequency, as shown, limits the applications of the tube because it is superimposed on the output current and will pass on to associated circuitry.

In order to understand more fully how this invention solves the problem of minimizing hum current in the output of the tube, reference is made to FIGS. 8 and 9. In FIG. 8, respective electrons 61 are emitted from filament wire 46 and are deflected by the coaxial magnet field Hfl in the directions shown by the respective arrows v The velocity of each electron can be resolved into two components. One component of velocity, indicated by arrow v is parallel to the magnetic flux lines between the pole pieces 51 and 52, as indicated by the magnetic field intensity vector H. As a result, this component of velocity is unaffected by the magnetic field of the external magnet and the respective electrons 60 continue to move toward the anode 21 in the respective directions indicated by the respective arrows v The other component of velocity, indicated by arrow V is perpendicular to the magnetic flux lines between the external pole pieces 51 and 52. Consequently, there is a resultant force exerted on the electrons 60 which causes them to travel in circular paths while moving toward anode 21 under the influence of the parallel component of velocity v Thus, the electrons 61 travel in helical paths toward the anode, spiralling around the direct path, indicated by arrow v which they would have taken if unaffected by the coaxial magnetic field H In FIG. 9, respective electrons 62 are emitted from filament wire 46 and are deflected by the coaxial magnetic field H in the direction shown by the respective arrows v The respective velocities of these electrons 62 can also be resolved into respective components. One component of the velocity, indicated by arrow v is parallel to the magnetic lines of flux between the pole pieces 51 and 52 of the external magnet 50. The other component of velocity, indicated by the arrows v is perpendicular to the magnetic lines of flux of the external magnet and, consequently, to the magnetic field intensity vector H. Therefore, a resultant force is exerted on electrons 62 which causes them to travel in circular paths while moving toward the anode under the influence of the respective parallel components of velocity v As a result of the simultaneous linear and circular motion, the respective electrons 62 travel in helical paths toward the anode 21, spiralling around the direct paths, indicated by the arrows v which they would have taken if unaffected by the coaxial magnetic field H Although the pole piece 52 was arbitrarily chosen as the North Pole and pole piece 51 as the South Pole, the result would be the same if the position of the magnetic poles were reversed. The direction of circular motion would be reversed, but the electrons would still travel in helical paths toward the anode 21. In FIG. 10, the oscilloscope screen shows the result of the external magnetic force exerted on the electrons. The hum current shown in FIG. 7 has been reduced to a slight ripple which will not seriously affect the applications of the tube in amplifying signal voltages applied to the grid of the tube.

The deviation of the emitted electrons and the resultant magnitude of the hum current are directly proportronal to the flux density of the coaxial magnetic fields (H and (H and inversely proportional to the flux density of the external magnetic field (H). Consequently, 1f the flux density of the external magnetic field is increased, the deviation of the electrons and the magnitude of the hum current will decrease. Therefore, the lntensity of the external magnetic field H should be equal to or greater than the maximum intensity of the coaxial magnetic fields H and H The maximum intensity of the respective coaxial magnetic fields is directly proportional to the peak value of the alternating current flowing in the filament wire 46, in either direction, and is inversely proportional to the radius of the Wire. Therefore, for a known value of peak current flowing in the filament 46, a cross-sectional dimension can be chosen for the filament wire which predetermines the value of maximum flux density surrounding the filament wire during peak current flow.

The respective filament wires 46 shown in FIG. 1 have respective cross sections which predetermines the maximum value of magnetic flux density surrounding the respective filament wires during peak flow of the filament heater current. During operation of the illustrative tube embodying the invention, as shown in FIG. 1, an alternating current supply 53 is connected to the cathode terminal rings 33 and 37. Alternating current flows through one cathode terminal ring and connecting support structure, through the respective U-shaped filament wires 46, and returns to the alternating current supply through the other cathode terminal and connecting support structure. The alternating current heats filament wires 46 to incandescence and thereby causes electrons to be emitted from the filaments 46. When the alternating current is flowing through the filament Wires 46, respective coaxial magnetic fields are established along the lengths of the respective filament wires 46. The maximum intensity of the respective coaxial magntic fields can be determined from the peak value of alternating current flowing through the respective filament wires and the radii of the respective filament wires. The intensity of the magnetic field between the pole pieces 51 and 52 of the external magnet 50 is equal to or greater than the maximum intensity of the respective coaxal magnetic fields around the respective filament wires 46. When the respective coaxial magnetic fields tend to deflect emitted electrons from travelling direct paths to the anode 21, the magnetic field of the external magnet 50 spirals the electrons along a direct path to the anode 21. As a result, the effects of the respective coaxial magnetic fields are counteracted and the hum frequency in the output of the tube is minimized.

Thus, there has been disclosed herein an electron tube having novel means of hum control comprising an array of parallel filament wires 46, each having a cross section which predetermines the maximum intensity of a respective coaxial field established during peak flow of an alternating filament current. The filament array in the illustrated embodiment is longitudinally disposed in a central axial plane of the anode and a magnet is located external of the anode and has opposing pole pieces one disposed on either side of the anode. In accordance with this invention, the intensity of the magnetic field between the pole pieces of the external magnet is equal to or greater than the maximum intensity of the respective coaxial fields of the respective filament wires. Although. the illustrative tube is a triode, it should be obvious that this invention may be applied to many other types of electron tubes, which may have any selected electrode configuration. It should also be obvious that this invention may be applied to tubes having cylindrical or annular cathodes as well as those having linear configurations, as shown herein. These and other modifications may be made by those skilled in the art Without departing from the spirit of this invention as expressed in the claims appended hereto.

What is claimed is:

1. An electron discharge device comprising:

a gas-tight envelope having portions of first and second terminals insulatingly sealed therein;

a filamentary electrode disposed longitudinally within said enevelope and having a predtermined cross section and respective end portions connected respectively to said first and second terminals;

means external to said envelope and connected to said first and second terminals for producing an alternating current in said filamentary electrode and establishing a first magnetic field around the filamentary electrode which has a maximum magnetic intensity determined by said cross section of the filamentary electrode; and

magnetic means external to said envelope and having opposing pole pieces disposed in respective planes parallel to the filamentary electrode, one on either side of the tube envelope for establishing a second magnetic field between the pole pieces having a magnetic intensity equal to or greater than the maximum intensity of the first magnetic field.

2. An electron tube comprising:

an elongated gas-tight envelope;

first and second terminals having portions thereof insulatingly sealed within said envelope;

an array of filament wires disposed longitudinally within the envelope and spaced therefrom, each of the filament wires having respective cross sections of a predetermined dimension and end portions connected respectively to said respective first and second terminals;

an alternating current source connected to said first and second terminals whereby respective coaxial magnetic fields are established around the respective filament wires, each of which fields has a respective maximum magnetic intensity determined by the cross section of the respective filament wire; and

a magnet external to the envelope having opposing pole pieces disposed one on either side of the envelope in respective planes parallel to said array of filament wires and a magnetic field between the pole pieces which has a magnetic intensity equal to or greater than said maximum magnetic intensities of said respective coaxial magnetic fields.

3. An electron tube comprising:

an elongated gas-tight envelope having an anode as a part thereof, said anode having an open-ened cavity therein;

first tnd second terminals having portions thereof insulatingly sealed within said envelope;

an array of parallel filament wires disposed longitudinally within the anode cavity and spaced from the anode, each filament Wire having a respective cross section of predetermined dimension and having respective end portions connected to said respective first and second terminals;

an alternating current source external to said envelope and connected to said first and second terminals whereby an alternating current is caused to flow through the respective filament wires and establish respective coaxial magnetic fields therearound which have respective maximum intensities determined by the peak values of alternating current flow and the respective cross sections of the respective filament Wires;

and magnetic means external to the envelope having opposing pole pieces disposed one on either side of the anode cavity in respective planes parallel to said array of filament wires for establishing a magnetic field between the pole pieces which has a magnetic intensity equal to or greater than the maximum magnetic intensities of the respective coaxial fields around the respective filament wires.

4. An electron tube as set forth in claim 3 wherein said array of parallel filament wires is linear in configuration and disposed in a central axial plane of the anode cavity.

5. An electron tube as set forth in claim 4 wherein said anode cavity is planar.

'6. An electron tube as set forth in claim 4 wherein said filament wires are U-shaped and have respective end connected to said respective first and second terminals through respective supporting structurtes.

7. An electron tube comprising:

an elongated gas-tight envelope having an anode as a part thereof, said anode having an open-ended cavity therein;

first and second terminals having portions thereof insulatingly sealed within said envelope;

an array of parallel filament wires disposed longitudinally within the anode cavity and spaced from the anode, each filament wire having a respective cross section of predetermined dimension and having end portions connected to said respective first and second terminals;

an alternating current source external to said envelope and connected to said first and second terminals whereby an alternating current is caused to flow through the respective filament wires and establish coaxial magnetic fields therearound which have respective maximum magnetic intensities determined by the peak values of alternating current flow and the respective cross section of the respective filament wires; and

magnetic means external to the envelope having opposing pole pieces disposed one on either side of the anode cavity parallel to said array of filament wires for establishing a megnetic field between the pole pieces which has a magnetic intensity equal to or greater than the maximum magnetic intensities of the respective coaxial fields around the respective filament wires.

8. An electron tube as set forth in claim 7 wherein said array of parall filament wires is annular in configuration and disposed in a central axial plane of the anode cavity.

9. An electron tube as set forth in claim 8 whrein said filament wires are U-shaped and have respective ends connected to said respective first and second terminals through respective supporting structures.

References Cited UNITED STATES PATENTS 3,365,601 1/1968 Doolittle 313-21 JOHN W. HUCKERT, Primary Examiner B. ESTRIN, Assistant Examiner U.S. Cl. X.R.

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