US1966242A - Filament for thermionic tubes - Google Patents

Description

Y m, 1934. R. GURTLER FILAMENT FOR THERMIONIC TUBES Filed July 21, 1930 HZTII; V H 0# 4 Y a o m m/ooLP fiL/P/L ER INVENTOR 5Y7 ATTORNEY Patented July 10, 1934 UNITED STATES PATENT OFFICE 1,966,242 FILAMENT FOR THERMIONIC TUBES tion of Germany Application July '21, 1930, Serial No. 469,562 In Germany September 1'7, 1929 3 Claims; (Cl. 250-275) The direct electric heating or incandescing of cathodes or filaments in thermionic tubes in the majority of cases is so advantageous that a numberof undesirable effects occasioned by the current flowing through the filament are tolerated, though naturally attempts are made to obviate or lessen these effects as far as feasible.

It is especially the magnetron eifect which deserves attention. About the filament a magnetic field is set up by the current flowing therethrough, and this magnetic field causes a curving or bending of the trajectories of the electrons. Thus, in the presence of heavy heating currents some of the electrons are pulled back to the filament.

. This phenomenon, as will be noted,results in a modulation of the plate current in case an A. C.- is employed for heating, since the magnetic field periodically disappears and attains its (positive or negative) crest value twice during each cycle. The invention will be more clearly understood with the aid of the accompanying drawing, in which a Fig. 1 shows a schematic longitudinal section through a tube employing a V-shaped filament.

Fig. 2 represents a similar schematic showing of a tube in which the filament comprises two linear portions.

Fig. 3 shows the distribution of voltage along the V-shaped filament of Fig. 1.

Fig. 4 is a similar view showing the distribution of potential along the two linear portions of the filament of Fig. 2.

Fig. 5 is a longitudinal schematic showing of a filament comprising four linear sections.

Fig. 6 is a horizontal schematic showing of a filament comprising four linear sections but arranged differently from the filament of Fig. 5.

Fig. 7 is a longitudinal schematic showing of a filament adapted to be heated by three phase current.

Fig. 8 shows a similar arrangement whereby the filament comprises six heating wires.

Fig. 9 is a schematic cross-section of the filament shown in Fig. 8.

Fig. 10 is a schematic arrangement similar to Fig. 9 but showing the filament wires arranged in a different order.

A marked diminution of the magnetron effect is insured by choosing a bifilar arrangement, such as a V shape, for the filament, as shown in Fig. 1. AA is the plate; GG is the grid; HlH2 is the filament; and M is the middle thereof.

For D. C. heating, for example, the positive lead is united at Hz and the negative lead at H1, while H1 is used as the cathode point. Then the heating current Ih flows in opposite directions in both halves of the filament, so that the aggregate magnetic field .is far feebler than in the case of a linear arrangement of the filament.

In the case of A. C. heating, the heating po tential Eh is applied at H1 and H2, while point M usually located outside the tube and equipotential thereto is chosen as the cathode point. Also in this scheme the sense of the heating current in both halves is opposite at each instant, with the result that the aggregate field is small.

According to my invention, the filament is divided. For instance, two linear portions may be chosen, BC and KL, as shown in Fig. 2. The supply leads to B and K, on the one hand, and those to C and L, on the other hand, are united in the holder. or press of the tube. The full heating potential is applied to each linear filament, but due to the scheme of connection, the heating currents in both filaments have the opposite sense, with the result again of a marked reduction of the magnetic field.

An arrangement comprising two parallel linear filaments connected opposite and parallel, how= ever, offers additional advantages over the V- arrangement known to the prior art. Filaments stretched out parallel to one another, if necessary, can be placed at greater proximity than the two halves of the l-shaped filament, so that the magnetron effect can be still further diminished. In View of this action, for an arrangement as here disclosed, the heating potential applied at each filament portion B, C, K and L, generally speaking, will have to be only half as great.

For A. C. heating the cathode point will come to be placed in the middle M or M", respectively, of the filaments. In fact, it is no longer located at one end of the tube as in Fig. 1. The fall of heating potential will then be only half as great as in Fig. 1. As a result, all of the effects ascribable to the fall of the heating potential will be diminished.

But an improvement will be obtainable also in cases where D. C. is used for filament heating. Fig. 3 shows the potential of the constituent filament elements in relation to the cathode point from the tube axis H1 H2M for the V-shaped heating wire of Fig. 1. The same thing is illustrated for an arrangement as shown in Fig. 2. It will be noted that in this instance the fall of heating or filament potential Eh is of smaller influence; in other words, that the characteristic will be steeper and its curvature more marked, so that the tube will be more suited for plate rectification. This improvement will be particularly noticeable for the type of tube equipped with a plurality of grids, inasmuch as in this the slope depends essentially upon the filament potential.

The same consideration and inferences hold true similarly of A. C. heating. Figs. 3 and 4, for instance, may be representative of the potential distribution at the instant of maximum heating potential when the zero line is the dash-line perpendicular.

If the tubes of Figs. 1 and 2 are equivalent, then both are supplied with the same heating energy; but the tube of Fig. 2 is operated at half the heating potential and twice the heating current. In the tube holder or press, the heating current is divided between the two parallel filament parts as pointed out above.

The basic principle of subdivision may be directly applied also to other filaments than V-shaped. For instance, a V-shaped filament can be divided into two V-shaped or four linear Wires.

Generally and basically speaking, any desired number of parallel wires may be disposed inside one tube or bulb, though it is advisable from a practical viewpoint to use an even total inasmuch as in that case the magnetic field will be largely neutralized by pairs of current flowing in opposition to each other.

Figs. 5 and 6 show diagrammatically two different dispositions of four wires. All ends marked H1 are united with one heating-current lead, while the ends marked H2 are associated with the other lead.

In the case of S-phase current heating of a tube, instead of an arrangement as. shown in Fig. 7 (with the filaments for the sake of simplicity being shown all in one plane since only the electrical connection and not the geometric position in space is to be considered), a system of six heating wires in accordance with the idea underlying this invention may be employed (Fig. 8) and these most advantageously should be so arranged that they form the generatrices of a circular cylinder. A section at right angles to the axis is shown in Fig. 9, the wires designated as having the same sense of current being united at one end to form a star, say, at 111/, while the oth-' er three wires are united at the other end m".

Another useful connection of the six filaments is shown in Fig. 10. In this scheme the magnetic field of two contiguous filaments is considerably diminished, and the resultant field of the entire arrangement becomes still further diminished, because for the different phase currents there holds always the geometric relation:

iu+iv+iw=0.

The star point or neutral of the three phases constitutes the cathode point outside the tube. Fundamentally speaking, it is also possible to resort to triangle connection of the filaments.

I claim:

1. A cathode for an electron discharge device comprising a plurality of parallelly arranged filament sections, alternate sections being electrically connected together at one end, the remaining sections being electrically connected together at the opposite end, and a connection from each of the free ends of the filament sections adapted to be connected to a different phase of a poly-phase current source.

2. A cathode for an electron discharge device comprising a plurality of parallelly arranged filament sections, alternate sections being electrically connected together at one end, the remaining sections being electrically connected together at the opposite end, and a connection from the free ends of each pair of adjacent filament sections adapted to be connected to a different phase of a three-phase current source.

3. A cathode for an electric discharge device comprising three pair of electrode emitting filament sections arranged in a circle and parallel to one another, alternate sections being electrically connected togetherat their upper ends, the remaining alternate sections being electrically connected together at their lower ends, and a connection from the free ends of each pair of adjacent filament sections adapted to be connected to a different phase of a three-phase current source.

RUDOLF GURTLER.

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