US2533767A - Device comprising a discharge tube sensitive to space charge variations - Google Patents

Description

Dec. 12, 1950 F. COETERIER DEVICE COMPRISING A DISCHARGE TUBE SENSITIVE TO SPACE CHARGE VARIATIONS Filed April 22, 1946 1 LJ L..l

FIG. 4

INVENTOR. FREDERl K COETER I ER ATTORNEY Patented Dec. 12, 1950 DEVICE COMPBISIN G -A DISCHARGE TUBE SENSITIVE TO SPACE CHARGE VARIATIONS "Frederik Coeterier, Eindhoven, Netherlands, assignor, by mesne assignments, to Hartford National Bank and Trust Company, Hartford,

-Conn., as trustee Application April 22, 1946,, Serial No. 663,818 In the Netherlands February 5, 1942 Section 1, Public Law 690, August -8, 1946 Patent expires February 5, 1962 4 Claims. I

This invention relates to a device comprising a discharge tube sensitive to space charge variations whose cathode is heated directly by alternating current.

In such devices the electro-magnetic alternating .field which occurs ,round the filaments of the discharge tube often causes interference. This field is manifest by an undesired variation of the anode current with a frequency having double the value of that of the heating current.

This effect will be explained hereinafter by reference to .Figs. 1 and 2 of the accompanying drawing. ,Fig. 1 shows the inside of a discharge tube but the control grid and any further electrodes that may be present in the tube are not shown in order to obtain a sur-veyable figure.

Fig. 2 is asectional view of the discharge tube shown in Fig. 1.

Fig. 3 is a schematic internal view of an electron discharge tube omitting the control or other grids and illustrating one embodiment of the invention.

Fig. 4 is a sectional view of an electron discharge tube embodying the elements of Fig. 3 .and showing .in section, means to impose a fixed magnetic field on the elements of the tube, in accordance with the invention.

The discharge tu'bes'hown in Figs. 1 and v2 comprises a .filament I which by an alternating cur- .rent I supplied from a source of voltage 2 is raised to high incandescence .so that the filament I will emit electrons, and an anode 3 which is partly cut away and whose active part comprises two surfaces parallel to the plane of the filament I. The anode 3 has supplied to it from a source of direct voltage 4 a voltage which is positive with respect to the filament I so that a fiow of electrons I will pass from the cathode to the anode.

The direction of movement of the electrons emitted by the filament I under the influence of the electric field provided by the source of voltage 4 is indicated by arrows 12 which are perpendicular to the active part of the anode.

In the discharge tube described, in the proximity of the cathode a magnetic alternating field is set up, due to the alternating current I which passes through the filament l and whose lines of forces may approximately be drawn in a plane normal to the filament as circles H enclosing the filament. By this magnetic alternating field the electrons emerging from the cathode under the influence of the electric field between the anode and the cathode have exerted on them a force netic fieldis designated by arrows I-I.

which is normal to the. direction of the lines of force H of the magnetic field and to "the direction of movement 2; of the electrons. The direction of the force exerted on the electrons is therefore approximately parallel to the cathode. In Fig. 1 the said force is indicated by the arrows designated K.

In a discharge tube comprising a cathode heated directly by alternating current the electrons emitted by the cathode which move to the anode under the influence of the electric field will therefore obtain a velocity component in a direction parallel to the cathode under the influence of the magnetic alternating field, the value and direction of said component depending on the instantaneous amplitude and phase of the cathode supply current. In consequence, the electrons will move to the anode along curved paths with the result that the electrons stay longer in the proximity of the cathode, or in other words the space charge adjacent the oathode is increased.

Since the magnetic field due to the current I is an alternating field the space charge adjacent the filament will vary periodically with double the frequency of the alternating current I, because twice per cycle of this current the increase of the space charge is zero and twice it reaches its maximum value. v

According to the invention, the undesired hum component of the output current which is due to the supply of the cathode with alternating current is neutralized by placing the discharge tube in a constant or at any rate substantially constant magnetic field, whose lines of force are substantially parallel to the direction of movement of the active electrons.

The intensity of the magnet field provided is preferably such that it is at least several times "higher than that of the magnetic alternating field provided by the cathode alternating current at the area of the cathode. In the discharge tube shown in Fig. 3 the direction of the lines of force of the constant mag- These lines of force, which are parallel to the desired direction of movement of the electrons, are consequently normal to the active parts of the anode which are parallel to the plane of the cathode filament.

That the desired effect is obtained bythe provision of the said constant magnetic field follows from the well-known concentrating effect which a constant magnetic field produces on a flow of electrons in the direction of the lines of force,

any deflection of the direction of movement of the anode electrons from the direction of the lines of force thereby being counteracted. In a device according to the invention the electrons will therefore in spite of the presence of the magnetic alternating field adjacent the cathode move along substantially straight paths from the cathode to the active parts of the anode with the result that the fluctuations in the space charge adjacent the filament and the consequent undesired anode current variations are suppressed or at least weakened.

Fig. 4 shows a cathode I and an anode 3 positioned in a discharge tube 5. A magnet 6 imposes a fixed magnetic field of constant strength on the tube and elements in such a direction that the magnetic lines of force are substantially normal to the vertical, active surfaces of the anode 3, which active surfaces are parallel to the plane of the cathode filament l, in the tube 5. The tube 5 is supported on an insulating base 'Lwhich is provided with contact prongs 8. The cathode leads 9 and the anode lead l pass through the glass'base of the tube and the insulating base I, and are secured to the contact prongs 8.

I claim:

1. A device comprising an electron discharge tube having 2, directly heated electron emissive planar cathode portion and an anode portion,

means connected to said cathode to apply a heating alternating current to said cathode portion, ,means connected to said cathode and said anode to apply an electron accelerating voltage between said cathode portion and said anode, and means 2. A device comprising an electron discharge.

tube having a directly heated electron emissive planar cathode portion and an anode portion, means connected to said cathode to apply a heating alternating current to saidcathode portion, said current producing at said cathode portion an alternating magnetic field, means connected to said cathode and said anode to apply an electron accelerating voltage between said cathode portion and said anode, and means external to said tube to produce a magnetic field of fixed direction relative to the cathode portion and anode and having lines of force substantially perpendicular to said planar cathode portion and enclosing the electron path between said cathode portion and said anode to restrict the electrons from the cathode portion to said anode to paths substantially perpendicular to the plane of said cathode portion, said magnetic field of fixed direction having an intensity at least several times as great as the intensity of the said alternating magnetic field in the neighborhoodof said cathode portion.

3. A device comprising an electron discharge tube having a directly heated electron emissive filamentary planar cathode portion and having a planar anode portion with an operative surface substantially parallel to said cathode portion, means connected to said cathode to apply a heating alternating current to said cathode portion, said current producing at said cathode portion an alternating magnetic field normally tending to deflect electrons from the cathode portion in a direction at an angle to a line perpendicular to the plane of the cathode portion, means connected to said cathode and said anode to apply an electron accelerating voltage between said cathode portion and said anode portion, and means external to said tube to produce a magnetic field of fixed direction relative to the cathode and anode portions and having lines of force substantially perpendicular to said planar cathode portion and enclosing the electron paths between said cathode and anode portions to restrict the electrons from the cathode portion to the anode portion to paths substantially perpendicular to the plane of said cathode portion, said magnetic field of fixed direction having an intensity at least several times as great as the intensity of the said alternating magnetic field in the neighborhood of said cathode portion.

4. A device comprising an electron discharge a tube having a directly heated electron emissive filamentary planar cathode and an anode with two substantially parallel planar surfaces enclosing and parallel to said cathode, means connected to said cathode to apply a heating alternating current to said cathode, said current producing at said cathodean alternating magnetic field normally tending to deflect electrons from the cathode in a direction at an angle to a line perpendicular to the plane of the cathode, means connected to said cathode and said anode to apply an electron acceleratingvoltage between the cathode and anode, and means external to said tube to produce a magnetic field of fixed direction relative to the cathode and having lines of force substantially perpendicular to the plane of the cathode and enclosing the electron paths between the cathode and anode to restrict the electrons from the cathode to the anode to paths substantially perpendicular to the plane of the cathode, said magnetic field of fixed direction having an intensity at least several times as great as the intensity of the said alternating magnetic field in the neighborhood of said cathode.

FREDERIK COETERIER.

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

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