US1859522A - Electron tube - Google Patents

Description

May 24, 1932. B. F. MIESSNER 1,859,522

ELECTRON TUBE Filed March 12. 1950 2 Sheets-Sheet 1 auvewsoz BE/VJA M/N E M/Z'JS/Vf/E y 1932- B. F. MIESSNER 1,859,522

ELECTRON TUBE Filed March 12. 1930 2 Sheets-Sheet 2 Patented May 24, 1932 warren STATES PATENT OFFICE BENJAMIN F. MIESSNER, SHORT HILLS, NEW JERSEY, ASSIGNOR TO. MIESSNER INVENTIONS INQ, OF SHORT HILLS, NEW JERSEY, A CORPORATION NEW JERSEY ELECTRON TUBE Application filed. March '12, 1930. Serial No. 435,046.

peratures, voltages or currents within the heater element when the same is energized by alternating current.

I have discovered that in this type of tube, having an indirectly heated cathode, one of the chief sources of hum in the output of the tube is due to the magnetic field of the heater current. Other features contributing to hum are the leakage of heater current through the insulating material into the cathode, and

' voltage eifects across segments of the heater element itself, as well as voltage eifects between the heater element and the cathode thimble. Tubes of present-day manufacture utilize a straight or helically coiled wire extending through the cathode thimble with or without an intervening insulator to prevent contact with the cathode thimble, or a hairpin type heater with straight parallel legs extending through a cylindrical insulator having two holes longitudinally throughout and parallel to its axis.

The heater wire in this latter type is round and the separation between the two sides or legs of the hair-pin is about A, the diameter 4 of the cylindrical insulator, which fits snugly into the cathode thimble.

The separation of the heater legs in such a type of cathode produces a considerable magnetic field, incompletely neutralized, which -15 reaches out into the electron stream near the cathode surface and there causes a change of direction in the flow of the electrons to the plate periodically with the rise and fall of the magnetic field following the alternation 53 of the heating current flow. This change in the magnetic field at the surface of the cathode is the primary element varying the length of travel of an electron from its source or origin to the plate or anode of the tube. This variation in length of path over which the electrons travel causes hum in the current flowing in the output circuit of such a tube.

An analysis of this structureshows that the distance from one of the legsto the cathode surface is about equal to the separation between the heater legs so that near'the plane bisecting the two legs of the hair-pin'there is considerable .unn'eutralizedfield on the cathode surface. In a surface portion on the cathode substantially parallel to this pla'ne there is substantial, neutralization between the magnetic fields produced by the individ- V fundamentalfeatures to be described hereinafter for minimizing the fluctuations in the magnetic field at the surface of the cathode.

The first is the feature of maintaining the centers of the legs of the heater element as close together as possible, thereby producing more nearly perfect neutralization between the magnetic fields thereof, the second is the location of the emissive surface along points on the cathode thimble wherein the most com plete neutralization of the magnetic fields from the two legs of the heater element is obtained, and the third is to so construct the anode that none of the electrons which, by chance, have, been subjected to a stronger magnetic field of the heater reach the anode, and therefore play no part in the space current of the tube. r

Referring to the drawings, in which like reference characters have been used throughout insofar as possible, a

Fig. l diagrammaticallyillustrates a complete electron tube of my improved form.

Fig. 2 shows the tube of Fig. 1 partly in section to disclose the relationship of the cathode connection and the connections to the heater element in relationship to the grid and plate leads. V

Fig. 3 diagrammatically illustrates a cross section of the tube of Fig. 1 on the line 3-3.

Fig. 4 is a cross section of acathode of my improved form;

Fig. 4A graphically illustrates the hum output of an electron tube with change of position of electron emissive material upon the surface of a cathodeof the type shown in Fig. 4; V

Fig. 5 is a cross section of a modified form of my invention; 7

Fig. 5A graphically illustrates the hum output of an electron tube with change of position of electron emissive material upon the surface of a cathode of the type of'Fig. 5;

Fig. 6 is a modification of thetype of cathode shown in Fig. 5

I Fig; 6A graphically illustrates the hum output'of anelectron .tube with change of position of electronemissive material upon iihe surface of a cathode of the type shown in ig. 6. V

Referring to Figs. 1 and 2, 1 designates a base having five prongs designated 2 to 6 respectively, such as employed in the standard base of heater type tubes of present-day manufacture. This base carries a glass envelope 7' preferably evacuated and within which there is a stem 8. Upon this stem 8 there'is rigidlymounted an anode 9 either cylindrical or oblong in cross-section surrounding a grid'10 and a cathode 11. Thegrid '10-is'of the usual cylindrical or oblong form, as shown.n The anode however has cut-away portions'as shown at 91 and 92.

The cathode is preferably one of the types disclosed and claimed inmy copending application hereinbefore referred to and is pro- Vided' with two heater connections 12 and 12 securely mounted Within the stem 8 and in continuation of lead-in wires 13and 13 which in'turn'are connected tothe socket pins 3 and 4 respectively. Thecathode thimble is provided with a connection 14' sealed through the stem 8 and in continuation of a lead-in wire 15 whichin turn is connected to prong 5.

' In these figures it"w*ill be noted that the,

cathode lead-in .15 is disposed between the lead-ins12 and 12 to the'heater element on one side and the lead-in 10 to the grid on the other side. This feature is to eliminate insofar as possible any induction in thealead-in wire to the grid of the tube. This is accom plished since the cathode lead-in is usually grounded and acts as a shield between these elements.

The cathode thimble itself may either be cylindrical, nearly elliptical or rectangular as shown in Figs. 4, 5 and 6, details of the description ofwhich follow hereinafter.

In such, a cathode structure the heater element is so arranged within the cathode thimble that the bend of the hair-pin does not protrude from the upper end of the cathode thimble, and I have found that a safe distance below the end of the cathode thimble for the bend of the hair-pin is approximately .06

inch, as an example of one of the tubes I have constructed in accordance with the features of my invention. The heater wires themselves at the bottom of the thimble should be as short as possible and connected to rugged supporting members of large heat Carrying capacity so that substantially no emission occurs from the heater element terminal protruding from the cathode thimble as shown in detail in Fig. 1.

In Fig. 4 I have shown a cross section of one form of my improved heater element in which numeral 16 refers to a cylindrical insulating element of isolantite fused quartz, magnesium oxide, or like insulating materials having adequate insulating properties i at the required high temperature, and having two cylindrical holes 17 and 18 through which the legs 19 and20 of'the heaterelement are passed. The insulating member 16 is of a type commonly used in slow heater cathode types of tubes available on the market at the present day, and in which the holes 17 and 18 are spaced at a distance of approximately 0.02 inches. Surrounding the insulating member 16, I have provided a cathode thimble 21 of nickelgapproximately 0.001 inches thick and about 0.05 inch diam-, eter. I

In examining the electrical constants of a cathode of this structure, I have determined that the fluctuating components presentin the plate circuit of a tube having a cathode of such a structure is due to effects of the magnetic field upon small portions of electron emissive material distributedabout the sur face of the cathode thimble 21.

In Fig. 4A, I have graphically developed as curves 22 and 23 in polar coordinates the hum in equivalent volts developed in the plate circuit of a tube having a'cathode of this character as a small amount of electron emissive material is progressively moved around the cathode. An analysis of curves 22 and 23 clearly illustrates that near the plane YY of r the cathode the electron emissive material lies in a region of substantially no fluctuating magnetic field. However, it will also be noticed that as the electron emissive material is moved away from the axis YY to other parts of the cathode surface, it enters regions of increasing magnetic flux with maxima being reached when the electron emissive material lies near a plane bisecting both legs 19 and 20 of the hair-pin heater. differing distances between the emissive material and the two heater legs 19 and 20. Therefore as one simple form of my invention I propose to coat the cathode thimble 21 shown in Fig. 4 only with strips of electron emissive material as indicated at 24 and 25; It will be noted herein that I have located the electron emissive material at those portions of the cathode wherein the bum curves This is due to the 22'and 23 of Fig. 4A do not depart appreciably from the zero polar ordinate of hum.

In Fig. 5 I have shown a cathode built up of a central thin sheet of insulating material 26 of mica or like heat resisting material, an insulator at high temperatures, upon opposite sides of which are placed flat ribbons 27 and 28 of tungsten or molybdenum wire about 0.001 inches thick and 0.020 inches wide, forming the legs of the heater element. Upon the outer sides of theheater legs 27 and 28 I have provided insulating strips of mica 29 and 30, or like insulating material. Upon the outside of these insulating strips 29 and 30, there is placed an oblong cathode thimble 31 sufficiently thick to maintain the insulating elements 26, 29 and 30 and the heater ribbons 27 and 28 in a fixed rigid condition at all temperatures. An investigation of the hum developed within the plate circuit of a vacuum tube employing a cathode of this character is shown inFig. 5A, wherein the curves 32 and 33 illustrate the hum as the electron emissive material is moved around over the surface of the cathode thin1- ble 31. Likewise in this structure it will be seen that near the plane YY there is substantially no fluctuating magnetic field due to alternating current energization of the heater element. In this structuretherefore, I employ the electron emissive material at the narrow ends of the oblong shape as shown at 34 and 35, thus placing the material as far remote from any magnetic influence as possible.

The graphs in this figure and those of Figs. 6Aare upon a scale enlarged by many times the scale of that of Fig. 4A in order to render the effect visible on a drawing of this size. In the actual structures built .the maximum magnetic field developed by the structure of Figs. 5 and 6 was substantially one fiftieth of that of the structure of Fig. 4.

Referring to Fig. 5A it will be noted that should any emissive .material be spilled or creep over the surface of the cathode 31 during the manufacture or use of the tube, there will be no appreciable hum developed in the output circuit of the tube due to the more complete neutralization of the magnetic fields of the two legs 27 and 28 of the ribbonshaped heater. This neutralization is ac complished because the centers of the elements 27 and 28 are extremely close together, and when the distance between the centers of these elements is compared to the distance therefrom of any electron emissive material, one might state that the electron emissive material in each of the Figures 4: and 5 is equidistant from the legs of the heater element.

In Fig. 6 I have shown a modified form of the structure shown in Fig. 5, in which the insulating elements 29 and 30 of Fig. 5 have been replaced by grooved isolantite or like material members 39 and 40, the groovesof which closely surround the legs 27 and 28 of the ribbon-like heater element. Around this entire structure, there is'placed a rectangular cathode-'thimble ll.

In Fig. 6A, I'have shown the effect of elecineffective in attracting electrons or not receptive to electrons, and partly of electronrec'eptive portions. An embodiment of this principle is illustrated in Figs. 1 to 3, and the detailsof construction ofthis anode will be best understood from Fig. 3. The portions 9a and 9b consist of'metal sheet and represent the electron-receptive portions, while 9l and- 92 indicate cut-away segments of the anode cylinder corresponding to neutral portions thereof.

I As will be further noted I show in the assembling of- Fig. 3 the partly cut-away anode cooperating with one of my partially coated cathodes as described in my co-pending application Ser. No.' l31,121. This cathode is appreciably electron-emissive only in the coated portions 24:, 25, whereas the uncoated segments 11 of the cathode cylinder are substantially non-electron-emissive. The operation of this assembling may, therefore, be: described as follows. The two legs 12 and 12' of the heater element, when energized with alternating current, are surrounded by a fluctuating electro-magnetic field of their own, which field is substantially neutralized in zones adjacent the plane passing symmetrically between the two heater legs. This field spreads out radially through the cathode thimble and reaches out to the anode surface and it may be said'to be composed of four sector-shaped solenoids two of which are bise'cted by said plane and two of which are bisected by a. plane passing through the centers of both heater legs. According to what has beensaid before the average magnetic flux density in the first two sectors is much lower than the average flux density in the last'two sectors.

In order to reduce hum in the output circuit of the tube, as caused. by electro-magnetic disturbances from the currentin the heater element, to a minimum I, therefore, place the electron- emissive portions 24, 25 of the cathode and also the electron-receptive portions 9a, 9b of the anode in the flux solenoids of relatively low average magnetic flux density;

Though I prefer an' arrangementof this kind, it will be understood that I can get a similar, but less complete effect,'if I combine an all-around coated cathode having surface portions .of'higher and lower magnetic disturbances with an" apertured anode of this invention. In this case I so orient the cathode that its surface portions of lower disturbance or more completely neutralized electro-magnetic field lie within flux solenoids subtending electron-receptive portions of the anode. If so oriented, electrons emitted from portions of highermagnetic field disturbances will, for the most part, fallback on the cathode es, pecially when checked by a gridelectrode of negative charge, since the neutral portions of the anode which do not exert any attraction at all on electrons lie in the same flux solenoid and the effective portions of the anode are too far removed to have a considerable influence OII 'thGSB more highly disturbed elelctrons! Cathode constructions especially suitable for thiszki'nd of cooperation with an apertured anode have-been described in my co-pending application Ser. No. 432,286, filed on March'l, 1930. i 1 Y The cathode shown in theassemblin of Fig-.13'is of the typeillustrated in-Fig; dfiiut, evidently, I can use in such an assembling with the same results" any of thecathodes shown-in Figs. 5'and 6. In'order to obtain like or-similar effects-asto hum suppression it will in all such assemblings onlybe necessary to-soorient the apertured anodeiwith-respect to the partially coated cathode that the cut-away areas of the anode and the non-electron emissive surface portions of the cathode lie substantially parallel to theplane passing symmetrically between thelegsof the heater element, or, in other words, thoseanode and cathode areas must be llliQWV-ISG'dlSPOSQd rela trve to said plane; 7

As an example of atube of this construci s tiion Iemployed a cathode heater-of the type illustrated in F ig; '5 oriented with respect to the anode in themanner described with reference to Fig. 3,-the-anode-being cylindrical ofa diameter of about .250 inches, having openings 91 and 92 therein of-.-about degrees each and the'grid 10 of a-diameter 01 .175 inches with the result that I produced aatube having the general amplifying characteristics of a 227 type of tube as commere but ratherrby the scope of .Tthe appended claims. I 1

Having thus described myinvention, what Iclaimisz' '1 1. In an electron tube, the'-c ombination .of a cathode thimble, a hair-pin heater element within" said thimble being insulated therefrom and extending substantially co-a'xially therewith, an anode surrounding said thim ble and spaced therefrom, said anode being cut away in an area substantially parallelto a plane passing symmetrically-between the legs of said heater element, and anel ectron emise sive coating upon said cathode thimble at points of substantially equal magnetic field strengthof each of the legs'of said heater ele-' ment.

r 2. Inan electron tube, the combination'of a cathode thimble, a-hair-pinheater element within said thimble being insulated therefrom. and extending substantially co-axially therewith, an anode surroundingsaidthimble and spaced therefrom, said anode beinglcut away in an area substantially parallel to a plane passing symmetrically between the legs of said heater element, and an electron 'emi's sive substance uponthe exterior of saidthimble, said thimblesurface being freeaoflelectron emissive material in an'are'a likewise dis-f posed relative tosaid plane as said cut-away area. v

3. In an electron tube, the combinationofa cathode thimble, an inverted. V-shaped heater element formed of a flat. ribbon, the legs'of which are closely disposed to each other with in said thimble and insulatedtherefrom, an

anode surrounding said thimble. and spaced apart-therefrom,.said anode being cut away in an area substantially parallel to a; plane passing symmetrically between :the :legsof said heater element, and an electron emissive material upon the surface of said-thimble,

said thimble surfacebeing v substantially free from electron em'issive material'in an .area

likewise disposed relative to :said' plane: as

saidcut-away area.

4:; In an electron discharge device includ"- ing a cathode having'an' electron-emissive thimble heated by a separate electric heater element which element extends interiorly of said thimble and substantially coaxially therewith'and is linked with an electro-mag,- netic field ofits own composed ofa plurality of. well-defined magnetic flux solenoids of lower and higher average flux density spreading radially through said thimble, the combinationtherewith of an anode having electronreceptive and neutral portions, said electronreceptive portions being'situated in saidflux solenoids of lower density andsaid neutral portions being situated in said flux solenoids of higher density. V

e 5. In an electron discharge device including. a cathode having a substantiallygnonelectron emissive thimble heated by a sepa rate electric heater element which element extends interiorly of said thimble substantially co-axially therewith and is linked with an electro-magnetic field of its own composed of a plurality of well-defined magnetic flux solenoids of lower and higher average flux density spreading radially through said thimble, the combination therewith of an electron-emissive substance substantially on surface portions only of said thimble lying in said solenoids of lower density, and of an anode having electron-receptive and neutral portions, said electron-receptive portions being situated substantially in said flux solenoids of lower density, said neutral portions being situated substantially in said flux solenoids of higher density.

6. In an electron discharge device including a cathode having an electron-emissive substantially cylindrical thimble heated by a separate electric heater element of inverted U-shape the two legs of which heater element extend interiorly of said thimble in close proximity to each other substantially coaxially therewith and are linked with a resultant electro-magnetic field of their own composed of two diametrically opposed flux solenoids each of a sector-shaped cross-section symmetrically disposed relative to a plane passing symmetrically between said two heater legs and both solenoids of relatively low value of average flux density and of two diametrically opposed flux solenoids each of a sector-shaped cross-section symmetrically disposed relative to aplane passing through both centers of said heater legs and both solenoids of relatively high value of average flux density, the combination therewith of an anode having electron-receptive and cut-away segments, said lower-density flux sectors subtending said electron-receptive segments, and said higher-density flux sectors subtending said cut-away segments.

7. In an electron discharge device including a cathode having a substantially cylindrical thimble with electron-emissive and subnoids of relatively high value of average flux density, the combination therewith of an anode having electron-receptive and cutaway segments, said lower-density flux sec-- tors substantially subtending said electron-' emissive segmental portions of the cathode f thimble and said electron-receptive segments of said anode, and said higher-density flux sectors substantially subtending said nonstantially non-electron emissive segmental surface portions thereon heated by aseparate electric heater element of inverted U- shape the two legs of which heater element extend interiorly of said thimble in close proximity to each other substantially coaxially therewith and are linked with a resultant electro-magnet field of their own composed of two diametrically opposed flux solenoids each of a sector-shaped cross-section symmetrically disposed relative to a plane passing symmetrically between said two heater legs and both solenoids of relatively low value of average flux density and of two diametrically opposed flux vsolenoids each of a sector-shaped cross-section symmetrically disposed relative to a plane passing through both centers of said heater legs and both sole-

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