US1658478A - Electron tube - Google Patents

Description

Feb. 7, 1928. I 1,658,478

W. DAU MANN ELECTRON TUBE Filed June 1924 Patented Feb. 1192c.

UNITED STATES PATENT oF icE.

WILHELM nAUMANN,-oE HAMB RG, GERMANY, AssreNoE T 0. n. F. Mt'rLLEn,

EoNreENEonnENEABarx, 0E HAMBURG, GERMANY, A CORPORATION 0E GER- MANY. I

Application filed June 9, 1924, Serial Nb.

My present invention relates to electron tubes of. the type employing a filamentary electrode'in conjunctionwith a co-operating electrode having a relatively large surface. The object of this invention is to improve the construction of tubes of this. type, particularly such as "are intended for operation at high voltages, at which there is considerable danger of injury and even rupture of the '1 filament. g

According to my invention, the filamentary electrode is given the form of a loop or how situated partly or entirely within the co-operating electrode which has a concave surface directed toward the filamentary electrode, and apeculiar relation, explained in detail hereinafter, is established between the saidv two electrodes, to protect the filament against injury, and to prevent accidental contact of the two electrodes.

The invention will now be explained in detail with reference to. the accompanying drawings, in which Figs. 1 and 2 are two sections, taken axially of the tube, but at right angles to each other, showing a typical form of my invention, together with dotted lines indicating certain important relations which constitute the basis of my improved arrangement; Figs. 3 and 4 are axial sections, taken at right angles to each other, illustratinga second form of myin'vention; Fig.5 is an axial section of a third embodiment, which is also illustrated in partial plan view in Fig. 6 and in a detail perspective view in Fig. 7 Figs. 8 and 9 are respectively an elevation and a plan, with parts in sec- .tion, of another form of my invention, in which the large surfaced electrode is cylindr'ical; and. Figs. 10 and '11 are respectively an axial and a transverse section of a form of construction of the same general type as that shown in Figs. 8 and 9.

, Referring particularly to Figs. 1 and 2, I will describe this example of my invention as follows:

()ne of the electrodes, which constitutes the anode in the use of the device, is formed as a dished body 1 of spherical curvature,

ment to be perfectly flexible, that the farthes t points the filament could reach, within ELEo'rnoN TUBE.

718,755, and in Germany June 11, 1923.

while the other electrode, which in use will be the cathode, consists of an arched or looped filament 2, of any suitable conducting material, the ends of said filament being secured to conducting supports3, as indicated at 4. The large-surfaced electrode or anode 1 is made of sheet-metal or other suitable material. It will be understood that the two electrodes with the supports 3- are generally locatedwithin an evacuated bulb of any usual or approved construction; this remark will apply to all the forms of my invention illustrated in the drawings; for the sake of clearness, the bulb and the manner of connecting the electrodes with it have been only indicated in a general'way in Fig. 1, and any person skilled in this art will be able to provide a suitable way of arranging the saidparts within such a bulb. It will be noted that the major portion of the filament how 2 lies within the dished anode 1, the concave surface of which is directed toward said filament. It will also be understood that, generally, the filament is adapted for connection with a battery or other source of electricity located exteriorly of the electron tube, so that by the passage of a current from such external source, the filament may be heated to the temperature best adapted for the particular effect to be produced in each individual. case. Now, in the operation of the electron tube, when the filament is subjected to forces tending to deform it, there are two main. requirements: First, Whatever deformation or distortion the filament may undergo, it must never come in contact with the opposing electrode. Second, the main resultant of the forces actingon the filament should be such as to tend 'to give it an axial position substantially as shown, in other words, the tendency of such forces should be to pull the filament toward theaxis (the central vertical line -in Figs. 1 and 2) rather than to deflect it laterally from said axis. Now referring to Fig. 1 it will be obvious, assuming the filathe plane of Fig. 1, will lie on an ellipse such as the filament will describe if the fixed points 4 are used as the foci of the ellipse. This ellipse is indicated by the dotted line E, and it will be obvious that the major radius a of this ellipse will be equal to onehalf of the length Z of the filament, while its minor radius 1) will be equal to where the distance between the two fixed filament ends 4 is designated as 2 If such an ellipse is then" rotated about the axis connecting the two points 4, 4, the ellipsoid thus described will be the locus containingall the farthest points which the filament secured at 1, 4. can reach, assuming (as stated above) such filament to be perfectly flexible, substantially like a string. Now, the condition that the filament shall not be able to touch the electrode 1 is evidently fulfilled by arranging said electrode entirely outside of the ellipsoid above defined. In the projection Fig. 2 the'outline of said ellipsoid would appear as a circular line E. If the anode 1 were of an ellipsoidal shape parallel to the ellipsoid mentioned above, it would exert a uniform. action or attraction at all points on the filament, and there would be no tendency to give the latter a definite position. In order that there may be a tendency to give the filamentary electrode an axial position, the concave surface of the anode 1 is made to approach the surface of the said ellipsoid more closely at the axial portion than at other points or portions, or in other words, the radius of curvature of said anode surface will be greater than that of the said ellipsoid; this will be clear, particularly from Fig. 1. In practice, with an anode of the general dished form shown in Figs. 1 to 5,

- I have found that satisfactory results are obtained if the dimension [1, which I may term the height of the filament are or bow (said dimension being but slightly smaller than the minor radius 7) otthe aforesaid ellipsoid) is made smaller than the distance of any point of the straight line or base 4- 1 from the nearestpoint of the concave surface of the anode I. The curve G in Fig. 1 represents the limit case in which the distance from any point of the said base line H to the nearest point of the curve G is constant, being equal to the dimension h.

The anode and the filamentary cathode are in axial alignment, their axis coinciding with the longitudinal axis of the vacuum tube or electron tube.

The construction illustrated by Figs. 3

and t differs from the one shown in Figs.

1 and 2 simply by having the anode 5 bellshaped, with a curled flange, the filamentary cathode 6 having its loop or bow within the anode, and the relations as to filament length and position of the anode relatively thereto, being governed by the same rules as explained above in connection with Figs. 1 and 2. Y

lVhen the electron tube is intended for heavy duty, and particularly for. currents of great strength, incandescent filaments of considerable length are required. Instead of employing a single filament of great length, it is advisable in such cases, for practical (reasons, to employ a plurality of cathode loops or bows, the size of the anode surface being increased correspondingly. In certain prior constructions, a fiat or plane anodehas been used; this, however, would present material difiiculties in the case of a plurality of cathode loops facing such a plane anode, since the loops facing the marginal portion of the anode would lie in the region of strongly unsymmetrical fields and would thus be deflected or bent quite considerably. Furthermore, the cathode rays issuing from these marginal loops would not strike the anode portions lying next to them, but would deviate and reach points not constructed to receive the impact of such rays. Stray rays of this character are liable to injure the tube by perforating the glass bulb, especially during the evacuating pperation. Again, in the special case of using the electron tube for the generation of X-rays, rays straying from the intended path will evidently reduce the efiiciency or power of the tube, by diminishing the numof rays that become effective or avail a e.

From the above consideration, the advantage of giving the anode a shape such that it will enclose or surround the cathode loop or loops at least partly, will be apparent. The special construction adopted by me also neutralizes any forces tending to twist the individual loops; this result is another advantage of the particular proportioning of certain dimensions as explained above in connection with Figs. 1 and 2.

Several forms of my invention in which a plurality of filament loops are employed in conjunction with a curved anode surrounding them partly or entirely, are shown in Figs. 5 to 11.

In the construction illustrated by Figs. 5, 6, and 7, the anode 7 (Fig. 5), shown of spherical curvature, encloses or surrounds the loop portions of the three wires or filaments 8, 9, and 10, which are connected in series as will be understood best from Fig. 7. One end of the filament 8 is secured at 11 to the conducting support 13, while to the other secured to successive portions of said rod, forv conducting support 14 is secured, at 12, one end of the filament 10; the other ends of thesefilame'nts 8, 10, are secured to the ends of c the third or middle filament 9. The three filaments are disposed in planes which are substantially radial with respect to the spherically-curved anode 7. The relation of each of the three filaments to said anode is determined according to the same rules or proportions as those explained above in connection with the construction shown in Figs. 1 and 2. a

When a very great filament lengthis required, a construction such as shown in'Figs. 8 and 9 maybe used with advantagen In this case the anode has the shape of a cylinder 15 extending continuously around the space within which the filamentsare located.

For instance, a rod 16 consisting of arefractory insulating material, (quartz being suitable), is arranged axially within said cylinder 15 and constitutes a carrier for a series of spirally-disposed filament loops l7 there be any unsymmetrical action of theforces tending to bend the loops lengthwise of the cylinder, these can never lead to any dangerous distortion of the plane of the loop, for the reason that for each of.the loops theconditions explained above are observed,

. the .heightlof each loop being smaller than the distance of any point of its base from theinner surface of the cylindrical anode 15;

' also, the special relation of the anode surface to the ellipsoid described by each of the filament loop's if it were swung about its at tached ends, would hold in this case in-the same manner as I have explained above in connection with Figs. 1- and 2. These remarks will also apply to the further form of my invention illustrated by F igs.- 10 and 11. Here the individual filament loops 21 are arranged in two sets, in an axial plane, the cylinder anode 22 being, of the same type as the anode 15 of- Figs..8 and 9, and a rod or carrier 23, extendin axially .within the anode, the bases of the laments being parallel to the anode 'axls. The sev-' eral loops 21 are secured to collars 24 surrounding the central carrier ,rod 23, and form two sets or series arranged on opposlte v sides of the carrier, At the upper or inner,

end of the carrier, the farther ends of the last filaments or loops of the two sets are connected with each other asshown in Fig. 10; the other end of one set is connected with the lead 25, and that of the other set with a lead 26, while the several loops of the same set are connected in series. 7

Electron tubes of the type set forth herein may be used for the production of-X-rays,

or for anyother purpose for which tubes of this character are adapted. It will be understood that when cylindrical anodes are em-- ployed, as in Figs. 8 to 11, such anodes would be open at least at one end, the upper end being shown openin Figs. 8 and 10.

Various modifications may be made without departing from the nature of my invention as set forth in the appended claims.

I claim:

1. An electron tube including an anode having a concave surface and a filamentary cathode having 'a loop located within the anode, the ends of said filament being fixed, and the concave anode surface lying entirely outside of a rotation ellipsoid whose axis of rotation coincides with a line connecting the points at which the ends of the filament are fixed, and the axial section of said rotation ellipsoid exhibiting an ellipse Whose major radius is equal toone-half of the length of the filament, and whose minor radius'is equal to where Z designates the length of the filament, and 2 the distance between said fixed points. 2. An electron tube including an open anode having a concave surface and a filamentary cathode having a loop located within the' anode, the ends of said filament being fixed, and the height of the filamentpoint of the straight line connecting said fixed ends, from the nearest pointof the concavesurface of said anode.

3. An electron tube including an anode loop being smaller than the distance of any having a cylindrical concave surface, a carrier disposed axially with respect to said anode, and a plurality of filamentary looped cathode elementssupported by said carrier and located at difiierent points of its length,

each of said looped elements being of a height smaller than the distance of any point of the straight'line connecting the ends of such element, from the nearest point of .the concave surface of said anode.

4. An electron tube including an anode, having a cylindrical concave surface, a carrier disposed axially with respect to said anode, and a plurality of filamentary cathode elements each having fixed ends supported by said carrier, the several. elements being located at difi'erent points of the carriers length, and the concave anode surface lying entirely outside of the ellipsoidal surfaces which the filamentary elements would 5 describe it swung about their fixed ends.

5. An electron tube including an open anode having a concave surface and a filamentary cathode having a loop located Withspecification.

WILHELM DAUMANN.

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