US1909051A

US1909051A - Thermionic vacuum tube

Info

Publication number: US1909051A
Application number: US611263A
Authority: US
Inventors: Hubert M Freeman; Wallace G Wade
Original assignee: Westinghouse Electric and Manufacturing Co
Current assignee: CBS Corp
Priority date: 1923-01-08
Filing date: 1923-01-08
Publication date: 1933-05-16
Anticipated expiration: 1950-05-16
Also published as: FR575004A; US1917963A; NL15733C; US1877838A; US2000695A; US2018257A; GB209415A

Description

May 16, 1933.

Fig. l.

H. M. FREEMAN ET AL THERMIONIC VACUUM TUBE- Filed Jan. 8, 1923 WITNESSES:

@,M /ffmffeff 2 sheets-sheet 1 Wallace G.

INVENTORS Wade 87 Hulcsr M. Freeman.

' ATTRNEY My 16, 1933. H. M. FREEMAN n A1. 1,9Q9051 THERMIONIC VACUUM TUBE wlTNEsSEs': lNvENToRs Wallace G. Wade. 87

Huberi- M. Freeman.

BY W 'ATTORNEY Patented May-16,1933

i UNITED STATES PATENT or-Fl'cE HUBERT M. FREEMAN, F EAST PITTSBURGH, AND WALLACE G. WADE, OF PITTSBURGH,

PENNSYLVANIA,- ASSIGNORS TO WESTINGHOUSE ELECTRIC AND- MANUFACTUR- ING COMPANY',y A CORPORATION 0F PENNSYLVANIA A THEBIIONIC VACUUM TUBE Application led January 8, 1923. Serial No. 611,263.

Our invention relates to space-current devices and more especially to the cathode structure of such devices.

The principal object of our invention is to provide a device of the character described which may be employed for detecting, amplit fying or rectifying alternating currents and which embodies a cathode structure adapted methods of manufacture and which shall embody parts capable of manufacture in existing automatic machinery with minimum expenditures of time and of money.

Heretofore', it has noty been practical to employ alternating currents for the excitation of the cathode or filament of a receiving or amplifying tube for the reason that such currents introduce variations in the plate current of the tube. Such variations are thought to be due to the following causes:

1. The variations in the intensity of the magnetic field established by the alternating currents traversing the filament, thereby resulting in a variable deflection of the electron stream emanating from the filament;

2. The variations in the` electric field around the filament which are caused -by the reversals in the potential-distribution along the filament;

3. The variations in the emissivity which are caused by the alternate heating and cooling of the filament.

We have'found that the desirable results outlined hereinabove may be obtainedby applying a cathode construction having an operating cathode surface which has no fall of potential along its surface, that is, a so-l called equipotential surface. Such cathode surface may be rendered thermionically activein a number of different Ways, as byl sub- ]ect1ng the same to heat or to an .electron bombardment. In one form of embodiment of ourlnvention, we provide a cathode construction comprising a central heater element and a co-operating equipotential cathode surface which is positioned immediately adjacent to the heater element. The thermal energy of the heater element may be transferred to the cathode surface. either by conduction or by radiation.

With these and other objects and applicatlons in yiew, our invention further consists in the combinations and details of construction and in the circuit arrangements hereinl after more fully set forth and claimed and illustrated in the accompanying drawings, wherein:

Figure 1 is a front elevational view of an evacuated electric device embodying our invention in a preferred form, a portion of the containing Walls of the envelope being broken away and the grid and plate elements being shown in longitudinal section,

Fig. 2 is a side elevational View of the construction of Fig. 1..

Fig. 3 is an enlarged detailed longitudinal sectional view of the cathode construction of Figs. 1 and 2.

Fig. 4 is a View, similar to Fig. 3, showing a modification in the form of the Amember constituting the equipotential cathode surface and also showing a modification in the means for insulatingly supporting and separating the branch portions of the heater element.

Fig. 5 is a View, similarto Fig. 4, showing an alternative construction for the equipotential cathode surface,

Fig. 6 is a view similar to Fig. 5, but showing the member forming the operating lcathode surface insulatingly carried by the heater element,

Figs. 7 and 8 are enlarged front and side Adetail elevational views of a further modified form of cathode construction embodying our invention,

Fig.I4 9 is a side elevational d etail view illustrating our invention applied to a.vac num-tube construction emp oymg a palr of controlling elements,

Figs. 10 and 11 are enlarged side elevational and top plan views of a cathode construction wherein the equipotential cathode surface is energized by thermal radiation rather than by thermal conduction, as in the preceding figures,

Fig. 12 is a diagran'imatic view of circuits and apparatus embodying one form of our invention and illustrating a circuit arrangement wherein the equipotential cathode element is connected to the heater clement within the inclosing envelope,

Fig. 13 is a View similar to Fig. 12 but showing a circuit arrangement wherein an additional lead for the equipotential cathode element is brought out from the tube permitting the usual vacuum-tube circuits to be electrically independent of the supply circuits for the heater element, and

Fig. 14 is a diagrammatic view of circuits and apparatus employing the vacuum-tube construction shown in F ig. 9."

In a preferred form of embodiment of our invention, as shown in Figs. 1, 2 and 3, we provide an elongated envelope 1 having a reentrant portion 2 terminating in a supporting press 3. A cathode construction 4 comprises a mass of refractory material 5 in the form of a slender solid cylinder provided with a pair of adjacently positioned perforations 6 and 7 which extend between the ends of the cylinder 5. The perforations 6 and 7 are of such dimensions as to receive a filamentary heating element 8 which is threaded up through one perforation and down through the other, providing a filament of inverted U-shaped having parallelly extendk ing

portions

9 and 11 and a top portion 12.

The distance between the

parallel portions

9 and 11 of the filament 8 is so small that the magnetic field established by currents traversing one portion or section substantially neutralizes the magnetic field established by currents traversing the other section, thereby avoiding one of the causes for variations in the plate current of vacuum tubes when employing alternating currents for the energization of the. cathode element. The filament 8 may be energized by connecting the same to

filament supply conductors

13 and 14 which are supported in the press 3 and are provided with

external extensions

15 and 16, respectively. 1

The cylindrical member 5 is preferably made of some insulating refractory material which, when heated to the temperature of the heater element 8, is free from chemical action therewith. In the course of much experimental work, we have found that Zircon possesses such desirable characteristics.

A member 17, which forms the equipotential cathode surface, is shown in the form of a tube having its inner surface closely embracing the tubular insulating member 5. The outer surface of the member 17 may be Coated with oxides of barium, strontium or other substance which is rendered 'thermionically active when subjected to heat.

The cathode construction 4 may be supported at its upper end by means of a carrier rod 18 extending from the press 3, as hereafter described. In practice, it has been found desirable to provide a spring connection between the cathode construction 4v and the supporting carrier rod 18 in order to provide for the expansion and contraction of the heating element 8. The desired result is obtained by welding a strip 19 to the upper end of the cathode construction, preferably to the tubular member 17, and connecting the strip 19 and the carrier rod 18 by means of a spring member 21. The equipotential cathode member 17 may be electrically connected externally of the tube 1 by Connecting the same to one of the supply conductors, for

example, conductor 13, by means of a conductor 22.

The cathode construction 4 may be surrounded by plate and

grid elements

23 and 24 of conventional design. As a matter of illustration, the grid 24 is shown in the form of a helical member with its axis coinciding with the longitudinal axis of the heater element 8. The grid 24 is supported in position by means of a carrier rod 25 extending from the press 3 and welded to the several helices thereol to provide additional stili"- ness to the grid construction.

The plate 23 is a tubular member symmetrically positioned with respect to the previlously mentioned elements and supported by

carrier rods

26 and 27 which are mounted in the press 3. One of the carrier rods, say 27, may be extended through the press 3 to form an external. circuit terminal 28.

The envelope 1 may be provided with a base 29, which comprises a solid circular insulating member 30 and a collar 31, opposite ends of the latter rigidly embracing the reentrant tube port-ion 2 of the evacuated electric device and the insulating member 30, in any approved manner. The outer end of the insulatingy block 30 may be provided .with a raised portion or base 32 and a plurality of hollowfterminal pins 33, 34, 35 and 36. The several external connections are disposed in the hollow portions of the terminal pins such that pins 33 and 34 are connected to the terminals of the heater element and pins 35 and 36 are connected to the terminals of the plate and

grid elements

23 and 24, respectively. The pin element 33 also serves as a terminal connection for the equipotential vcathode struction 37 which differs from that previ- I ously described in the following important respects. The

adjacent sections

9 and 11 of the heater element 8 are insulatingly supported and spaced by means of separate

tubular members

38 and 39, respectively. The

tubular members

38 and 39 may be made of any refractory material having properties similar to those described for the tubular su porting member 5 shown in Fig. 3. T e cathode construction herein shown has an equipontential electron-emitting element in the form of acylindricalcasing 41 having a cap portion 42 which is electricallyconnected to the bent portion 12 of the heater filament 8. The structure may besupported b means of a carrier rod 43 which is welde to the cap portion 42. The carrier rod 43 may be extended through the press 3 to serve also as an external terminal connection for the equipotential cathode member 41.

In Fig. 5 is shown a cathode construction which is differentiated from that of Fig. 4 in the form of the member constituting the equipotential cathode surface.. In this construction, the cathode surface is formed by spirally Winding an oxide-coated platinum strip 44 around the outer portions of the

tubular spacing members

38 and 39.

The construction 45 shown in Fi 6 is distinguishable over the preceding cat ode constructions in that the oxide-coated platinum strip 44 forming the equipotential cathode surface is wound directly around the

sections

9 and 11 of the heater element 8, the oxide coating on the platinum stri `44 serving to insulate the stri 44 from t e heating element 8. If additlonal insulation is necessary, the heating element 8 itself may be covered by some insulating oxide, such, for example, as magnesium oxide. The structure ma be supported by means of a carrier rod 46 w ich is welded to the bent portion 12 of the heater element and to the strip 44. The carrier rod 46 may also serve as a lead for the equipotential cathode member 44.

VIn Figs. 7 and 8, a cathode construction is shown which differs from the foregoin constructions in the following respects. heater element 47, which may Lbe in the form of a flatribbon of tungsten or other suitable material, is doubled to form a vpair of adjacently positioned

sections

48 and 49, as in the preceding figures. The

adjacent sections

48 and 49 are separated by a thin mica strip 51.

Equipotential cathode members

52 and 53, in the form of oxide-coated strips of nickel, are positioned immediately adjacent to the filamentsections 48 and 49, respectively, and are insulatingly spaced therefrom by

mica strips

54 and 55. The Astructure is bound tightly together at the opposite ends thereof by

collar members

56 and 57 and may be supported from the top'by means of a carrier rod 58 `having bail extensions 59 and tial cathode surface thereof is energized by means of thermal conduction, the insulating means separating the heater element and the equipotential cathode member serving as the geilt conducting means between the two mem'- ers.

Figs. 10 andll are greatly enlarged views of a construction 64 wherein an equipotential cathode member 65 is heated by thermal radi- ,ation rather than by thermal conduction.

The construction there shown comprises a heater element 66 in the form of adjacently positioned parallelly extending

filamentary sections

67 and 68, the sections being adjacently positioned to reduce the distorting effects of the varying magnetic fields estab lished by the filament exciting currents as. previously described. Adjacent ends ofthe filament sections are welded to a supporting member 69 of nickel or other suitablecon-4 ducting material. The equipotential cathode member 65 is shown in the form of a cylindrical casing inclosing the parallelly extending sections of the heater element 66 and is rigidly vsecuredlto the supporting block 69. The construction may be supported by means of a carrier rod 71 having one end rigidly secured to the supporting block 69. f

Fig. 12 is a diagrammatic View of the vacuum-tube construction shown in Figs. 1, 2 and 3 together with circuit connections whereby the tube may function as an amplifier of alternating currents. The grid 24 and the equipotential cathode 17 are connected by conductors 72 and 73, respectively, to a source of incoming signals (not shown). A platefilament circuit 74, which extends from the plate l23 to the equipotential cathode element 17 ,includes a detecting device 75 and a source 76 of direct-current energy. A source yof al- Aternating-current` energy (not shown) is operatively connected to the heater element 8 through a transformer 77. It is noted that, in this arrangement, the equipotential cathode member 17 is connected to the heater element 8 within the evacuated portions of the tube 1, thereby requiring only -four terminal pins in the base 2 Thesystem shown in Fig. 13 is distinguishable over that of Fig. 12 in the provision of separate connections for the equipotential member 17 and for the heater element 8, i

thereby making the energizing circuits for the heater element 8 electrically independent of the usual vacuum-tube grid, filament and plate circuits. Such arrangement, however, necessitates the provision of an additional plug element in the base 29 of the tube as indicated at in Fig. 13.

The system shown in Fig. 14 illustrates one application of the vacuum-tube construction (SQ shown in Fig. 9. The additional grid element 63 is connected to the equipotential cathode member 17 by means of a conductor 78 including a source `79 of direct-current energy tending to malte the grid 63 positive with respect to the equipotential surface. When such condition obtains, the grid 63 serves as an electrostatic screen tending to further decrease the tendency of the alter- -nating exciting currents to vary the tube characteristics. lVhen the grid 63 is made positive, as shown in the drawing, it forms, in effect, an artificial cathode, all as will be readily understood by those skilled in the art.

In practice, we have obtained remarkably high voltage amplification with vacuum tubes employing an indirectly heated cathode surface, as described in the foregoing portlons of the specification. The low-resistance type of vacuum tube heretofore employed has a plate impedance of from 15000 to 25000 ohms, with amplification factors ranging from 5 to 7, whereas the operating characteristics of a Vacuum-tube device embodying our invention are such that a tube may be designed having a plate impedance of 10000 ohms and a'ivolt` age amplification factor of 10. Thus, 1t 1s seen that the figure of merit, which is the ratio of the amplification factor squared to the plate resistance, is, in a vacuum-tube construction embodying our invention, approximately four times greater than that of the ordinary tubes heretofore employed.

IVhile we have shown a number of embodiments of our invention, for the purpose of describing the same and illustrating their principles of operation, it is apparent that various changes and modifications may be made in the nature and the mode of operation and in the details of construction Without departing from the spirit of our invention. IVe desire, therefore, that only such limitations shall be imposed thereon as are indicated by the appended claims or demanded by the prior art.

IVe claim as our invention:

1. Incombination, an equipotential cath- Aede structure comprising an equipotential surface, a substantially non-inductive electrical heater for rendering said surface thermionically active and an alternating current supply circuit operatively associated with said electrical heater for energizing the same.

2. In a cathode structure, a refractory member and a filament comprising branch portions disposed in said member, said branch portions being adjacent one another and the magnetic fields established by currents traversing the branch portions balancing one another.

3. In combination, a cathode structure comprising an equipotential cathode member, meansfor rendering said cathode member themionically active and means for resiliently supporting said member and said first-mentioned means.

4. In a vacuum-tube device, a iilamentary heater, a cathode surrounding the same and heated therefrom, a refractory body electrically insulating said heater from said cathode and a source of alternating current supplying said heater, said heater being so constructed that the magnetic field is substintially nil at all points outside said catho e.

5. In a vacuum-tube device, a refractory body, a heat-ing conductor colnprising two adjacent portions and a cathode surrounding Said two adjacent portions of said heating conductor and electrically insulated therefrom by said refractory body, the distance between said adjacent portions being small relative to the dimensions of said cathode, the magnetic field outside said cathode, due to current in said heating conductor, being substantially nil.

6. An equipotential cathode comprising a core of refractory materiaha surface of material adapted to emit electrons freely when heated supported by said core, and a heatingelement within said core comprising .outgoing and return conductors separated by the minimum distance that mechanical strength will permit.

7. In a system comprising a device adapted to transform electrical energy into sound, a source of electromotive force therefor, an electron tube having an anode and a .thermionically-emissive cathodeenergized from an alternating-current source through a heatlng element having conductors closely adjacent each other the magnetic field of said l? conductors being substantially neutralized between said anode and cathode and poducing no noticeable sound from said device.

8. In combination with an anode, a control electrode, a cathode adapted to emit electro,ns when heated, a separate heater therefor and a source of uctuating current connected to said heater, and a common junction between said cathode and said heater.

9. In a vacuum-tube device, an alternating current filamentary heater comprising branch portions adjacent one another, a cathode surrounding the same and heated therefrom, and a refractory body electrically insulating said heater from said cathode, the magnetic field from said heaterbeing substmtialy nil at all points outside said catho e.

10. In combination, a vacuum-tight envelope containing an anode and an equipotential cathode structure comprising an equipoand a source of constant'voltage interconnecting said cathode and said anode.

11. In a vacuum-tube device, an anode, a heater, a cathode surrounding the same and heated therefrom, a refractory body electrically insulating said heater from said cathode, a source of alternating current supplying said heater, said heater being so constructed that the magnetic eld therefrom is substantially nil at all points outside said cathode, and a source of constant voltage interconnecting said cathode and said anode.

12. In combination with an anode, a control electrode, a cathode adapted to emit electrons when heated, a separate heater therefor and a source of iuctuating current connected to said heater, a common junction between said cathode and said heater, and a source of constant voltage interconnecting said cathode and said anode.

13. In a vacuum-tube device, a heater, a cathode surrounding the same and heated therefrom, a refractory body electrically insulating said heater from said cathode and a source of alternating current supplying said heater, said heater being fs'o constructed that the magnetic field therefrom is substantialy nil at all points outside said cathode.

14. In combination with an anode, a control electrode, a cathode adapted to emit electrons when heated, a separate heater therefor, a source of fluctuating current connected to said heater, and a connection substantially devoid of reactance between said cathode and said heater.

15. In combination with an anode, acontrol electrode, a cathode adapted to emit electrons when heated,` a separate heater therefor, a source of fluctuating current connected to said heater, and a connection substantially devoid of impedance between said cathode and said heater;

16. In combination, an evacuated container, a cathode adapted to emit electrons freely when heated, an electric heater for said cathode so formed that substantially no magnetic field is vproduced thereby in the space adjacent the surface of said cathode, and means for electrically insulating the major portion of said heater from said cathode.

17. A cathode for a space current device, comprising a conducting memberhaving a plurality of. sections capable of being heated by an electric current, said sections being spaced from one another by a refractory material and so disposed with respect to each other that the magnetic fields, produced by the current flowing Athrough said members,

are caused to neutralize each other to prevent magnetic deviation of space current fiow.

18. In combination, a cathode comprising a tubular member and a conducting member extending through said tubular member,l a source of alternating current connected to said conducting member, said members being so constructed and arranged that the magnetic fields produced by the currents Howing in the members will substantially neutralize each other.

19. In a three-electrode vacuum-tube, a cathode for emitting a flow of electrons therefrom to the plate, and heated by a source of alternating current, the cathode having a low -voltage drop and a relatively large crosssectional area and having a heater which is doubled upon itself so that its opposite leg portions react upon each other to reduce the electromagnetic effect of the heating current to such a value that the voltage temperature `and electromagnetic effects on the said fiow of electrons to the plate of the cyclic changes in the heating current are neutralized.

20. The combination with a space' discharge vessel'comprising an anode, a control electrode, a cathode and. cathode heating means, a source of alternating current connected to said heating means, means for supplying anode potential to said anode, and means for preventing heating current in said heating means from causing variation in the average voltage between the cathode and the anodeduring a half-cycle of` alternatingcurrent. y

21. In a vacuum-tube device, an anode, a grid, a source of periodic heating current of audible frequency and a conductor within the tube heated thereby, said conductor having closely adjacent parallel portions connected in series, said conductor being so connected that the resultant field from said portions is insufficient to affect the space current substantially.

22. The combination with aspace discharge vessel comprising an anode, a control electrode, a cathode and cathode heating means in close proximity thereto, means supplying alternating current connected to said heating means, means for supplying anode potential to said anode, and means for preventing heating current in said heating means from causing variation in the average voltage between the cathode and the anode during a half-cycle of alternating-current.

23. An electron tube having an electron emitting cathode capable of being heated by alternating current sealed therein and comprising an inner heating element in an outer metallic sheath, coated with alkaline earth oxides, separated from the heating element by refractory insulating material, said core `having its opposite end portions disposed in closely spaced relation whereby to neutralize the inductive effect of the alternating heating current.

In testimom7 whereof, We have hereunto subscribed our names this 30th day of December, 1922.

HUBERT M. FREEMAN. WALLACE G. WADE.