US2144505A - High power tube structure - Google Patents

Description

Jan. 17, 1939. v v I. E. MOU M FF Ef AL 2,144,505

HIGH POWER TUBE STRUCTURE Filed Feb 20, '1936 WITNESSES:

. INVENTORS. 1 Maura f y Hen/a 1V fl ozan 0444547:

. ATTORN I UNITED STATE to apply the increased values of power and voltage to the tubes. It has been. found that tube strucftorily at these increased ratings.

water jacket.

Patented Jan. 17, 1939 auras N. Kozanowski, Collingswood, N. J., assignors to Westinghouse Electric & 'Manufacturing Company, East Pittsburgh, Pa., a corporation 1 of Pennsylvania Application February 20, 1936, Serial No. 64,858

6 Claims.

1 Our invention relates to electron discharge devices and especially to high power vacuum tube devices.

It is an object of our invention to provide a vacuum tube that will operate satisfactorily with high voltage and power inputs necessary for cer- -tain modern day installations.

In response to the demand for increased power from high power tubes, it has been the practiceto make sturdier the elements of these tubes and ture that operated satisfactorily at lower power and voltage ratings failed to perform satisfac- First, at cer- 'tain spots local boiling would occur inside the We have made a careful analysis of this phenomenon and have discovered the boil- "ing is caused by non-uniform distribution of electronic flow along the active portion of the tube I particularlyin the vicinityof cut-off bias point.

""This" reduces the permissible plate dissipation for j the tube;

In addition, at high operating plate and grid voltages; particularly in modulated class'C operation. flash-avers may occur within the tube. 'The main cause of this phenomenon is a concentrated "cold'discharge between the tube electrodes due to the existence ofsharp points, contamination and 13 absorbed gas molecules.

'The modifications will be apparent from the following description andthe drawing, in which: Figure 1 is a cross section through a preferred arrangement of the'vacuurn tube with, certain parts in elevation,

, Fig. 2 is a cross section at right angles to the view in Fig. 1 withcertain parts in elevation, and

Fig. 3 is a cross section on lines III-III of Fig. 2. I v a In the drawing, we have illustrated the high vacuum type of tube with the exterior anode l0 sealed to the glass insulating portion l l, as is well knownin 45 "ll'supports the familiar reentrant stem I2 havthe art. The glass insulating portion ing the cathode leads I3, 14' sealed therethrough. The-grid lead l5 likewise is sealed through a portion of the glass insulation II and is connected to' the grid structure comprised of sturdy support ing rods l6 extending longitudinally of the tube ient; manner.

and supported fromthe press l2 in any conven- The. control portion of the grid is constituted preferably bythe slender wires l1 wrapped helically around the grid supporting rods [6 throughout a large portion of the tube length.

aWealso prefer to have rod l8 preferably of tungfilament strands.

tween the various portions of the filament and ingly, we have '42 on the inner customary to use two V-shaped filaments with the resulting continuous variation in the filament to grid distance which is closest at the ends of the structure and greatest at the mid-point of the This variationin distance bethe grid and anode structure produces the abovementioned non-uniform electronic flow :along the filament resulting in very undesirable nonuniform heat dissipation in theanode. Accordgive a uniform distribution of electric current throughout the tube. Our preferred form of filament support is illustrated in the drawing. The two cathode leads I3 and M preferably continue through the seal as the sturdy upright rods I9 and 26 on either side of the rod l8. At the point 2|, these rods are bent outward to form ends 2?. spaced a predetermined distanceapart. At the inner end of the rod l8 are'attached the hooks 23 and 24 for the free end of the cathode. "These hooks are preferably broad metallic structures preferablyattached to an insulating quartz tube endof the filament support rod !8. A'U-shaped member 25 with an extension 26 from one of thearms'of the U is attached to the rod 18 at a portion adjacent the bend 2| in the rods l9 and 20,as illustrated'in the upper portion -of Fig. 2. This 'U-shaped member is preferably of tungsten or molybdenum. The distance between the arms 2! and 28"of the U is the same as that between the ends'22 of the rods l9 and 29. The result is that the arms 21 and 28 of the U-shaped member 25 and the ends of the rods l9 and 20 are spaced equi-distant apart So that they form the corners of the square. Likewise, ati the other end of the tube the hooks 23 and 24 have a breadth that is substantially. equal to the distance from one hook to the other, and, accord- 'ingly, the .outer edges of the hooksform the corners of a square similar in size and dimen-- ,,sions to that formed by the arms 2'! and 28 and a the cathode leads I9 and 20. A filament, preferably of tungsten, is attached to,the outer end 22 of the conductor 19 and a portion 3% extends longitudinally of the tube to'the hook 23where .it is threaded therethrough and the portion 3 l is tion 32 extends longitudinally of the tube through of the press devised the cathode structure to the hook 24 and a. portion not disclosed in the drawing extends back to the upper end of the cathode lead 20. The cathode circuit, accordingly, comprises the lead IS, the filament portion 30, 3!, the U-shaped member 25, the filament portion 32 and the return portion 33 (see Fig. 3) of the filament to the cathode lead 20.

If it is desired to increase the effective length of the filament without increasing the outside dimensions of the tube, this filament can be waved,

as shown in the drawing, to provide a greater emissive area. This structure permits the use of heavier filament wire resulting in longer filament life. This waving may take anydesired formation even to that of semi-circles as it -is shown in the drawing. It is preferred that the general axis of the wavy filaments be parallel to each other and be symmetrically, arranged around the axis of, their support.

Because of this parallel arrangement of the filament wires and their equal spacing from the grid and anode, there will not be the tendency for concentration of the electron stream at various portions of the tube.

We also preferto have the filaments arranged in symmetrical relation to the grid structure and especially as disclosed in Fig. 3. The grid structure comprises the sturdy sup-port portions IS with the more slender control portions ll. We desire to locate the filament strands 30 through 33 so that they are in planes substantially bisecting the spaces between thelongitudinal wires I6. In this particular arrangement, the electron stream will have a chance to flow from the filament portion to the anode intersected by the slender control portion I! of the grid and the electrons will not be apt to be absorbed by the large supporting structure [-6.

We have likewise discovered that where high voltage is placed on the grid and anode in. using these tubes as class B audio operation or as a modulated class C amplifier that sudden discharges are likely to occur at'certain spots of the anode, which interrupt the continuous operation of the tube. We have conducted tests on tubes and have found that such flash-overs may occur with a cathode not heated by the heating current and were able to record an instantaneous current as high as 800 amperesr We have discovered that these anode point discharges are prompted by sharp points and edges in tube structure, especially in the supporting means for the upper portion of the filament and free end of the 'gri'd'structure. We believe that this discharge is caused loythe high rate of potential gradient in the neighborhood of the sharp point or edge. Assuming, for instance, that there is an instantaneous difierence of say 40,000 volts between the grid and anode or cathode and anode which is not uncommon in water-cooled tubes, and that there is a quarter of an inch between the two, then there would be a potential gradientof the order of 160,000 volts per inch between the two members. The potential gradient would be non-uniform between the two structures if sharp edges or points exist and, at these sharp edges or points, the potential gradient would be many times greater than the value just mentioned. This edge or point, accordingly, would be apt to cause a local discharge between the tube elements and interruptthe smooth operation of the tube.

We have, accordingly, enclosed the outer supporting structure of the filament and grid with metallic shields 3'5 and 36. Thecathode shield '35 metallic grid supports.

may be supported by spot welding or riveting or any other convenient manner at 31 to the inner end of the. supporting rod 18 or the hook supporting structure 38 thereon. This cathode shield may take any convenient form, but we prefer to have it of a cylindrical form closed at one end with the cylindrical sides or skirtextending over and enclosing the sharp edges of-the hook supports 23 and 24. The grid shield 36 likewise is preferably of a cylindrical form with a closed curved end which may-instead be fiat if desired, enclosing the free end of the grid structure and the sharpedges of the coil I! and the supporting rods I 6. The edges of the shields 35 and 36 are rounded off so that they do not likewise present any tect the seal 4|.

The structure disclosed in the drawing is to be considered as illustrative of a preferred embodiment of our invention. Various modifications in the elements and their arrangement can obviously be made, and, accordingly, we do not intend our invention to be limited except as is necessitated by the prior art.

We claim as our invention:

1. An electrical discharge device comprising a.

cathode, anode and grid, said grid having a free end, a supporting hook for said cathode, and metallic shielding means intermediate the free endof said grid and the supporting hook of said cathode.

2. An electrical discharge device comprising an anode, cathode and grid, said cathode and grid supported at one endof said device and having other free ends extending into said anode and metallic shielding means interposed between the other free end of said grid and both the cathode and said anode.

'3. Supporting means for a filament cathode comprising a supporting mass, broad hooks attached to opposite sides of said mass, the breadth of said hooks being substantially equal to the distance between adjacent hooks and a shield attached to said mass overlapping said hooksJ 4. An electrical discharge device comprising a cathode of a plurality of filaments, a plurality of hooks supporting one of the ends of said cathode, the breadth of said Zhooks being substantially equivalent to the distance between adjacent'hooks, a grid structure surrounding said cathode and an anode surrounding said grid. structure, said grid structure comprising sturdy metallic supports and slender control wires, the general axes of said filaments being in planes substantially bisecting the space between said sturdy '5. An electrical discharge device comprising a cathode of a plurality of parallel filaments equidistant about a common axis, a'pluralityof hooks supporting one of the ends of said cathode, the

equivalent to the distance between adjacent hooks, a

breadth of said hooks being substantially grid structure surrounding said cathode and an anode surrounding said grid structure, said grid structure comprising sturdy metallic supports and slender control wires, the general axes of said filaments lying in planes substantially bisecting the space between said sturdy metallic grid supports and a metallic shield enclosing said hooks. I

6. An electrical discharge device comprising a cathode of a plurality of parallel filaments equidistant about a common axis, a plurality of hooks supporting one of the ends of said cathode, the breadth of said hooks being substantially equivalent to the distance between adjacent hooks, a grid structure surrounding said cathode and an anode surroundingsaid grid structure, said grid structure compising sturdy metallic supports and slender control wires, the general axes of said filaments in planes substantially bisecting the space between said sturdy metallic grid supports, a metallic shield enclosing said hooks and another metallic shield enclosing the adjacent end of said grid structure.

ILIA E. MOUROMTSEFF.

HENRY N. KOZANOWSKI.

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