US2018257A

US2018257A - Thermionic vacuum tube

Info

Publication number: US2018257A
Application number: US628696A
Authority: US
Inventors: Max W Reges; Wallace G Wade
Original assignee: Westinghouse Electric and Manufacturing Co
Current assignee: CBS Corp
Priority date: 1923-01-08
Filing date: 1932-08-13
Publication date: 1935-10-22
Anticipated expiration: 1952-10-22
Also published as: GB209415A; NL15733C; US1877838A; US1917963A; US1909051A; FR575004A; US2000695A

Description

Oct. 22, 1935. H. M. FREEMAN Er AL 2,018,257

THERMIONIC VACUUM TUBE Original Filed Jan. 8, 1923 2 Smets-Sheet l WITN ESSES Oct. 242, 1935. H. M. FREEMAN Er AL THERMIONI C VCUUM TUBE 2 Sheets-Sheet 2 Original Filed Jan. 8,'1923 INVENTORS eeman,eceased MFI FIR@ Hubert By Max ges Administrator E n WaZZaBce G. Wade.

Patented Cet. 2.2, 1935 UNITED STATES THERMIONIC VACUUM TUBE Hubert M. Freeman,

deceased, late of East Pittsburgh, Pa., by Max W. Reges, administrator,

Bloomfield, N. J.. delphia, Pa.:

and Wallace G. Wade, Philasaid Freeman and Wade assignors to Westinghouse Electric and Manufacturing Company, a corporation of Pennsylvania Original application January 8, 1923, Serial No.

611,263, now Patent No. Divided and this appli Serial No. 628,696

This application is a division of application Serial No. 611,263, led January 8, 1923, Patent No. 1,909,051, May 16, 1933.

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, amplifying or rectifying alternating currents and which embodies a cathode structure adapted for excitation from a source of low-voltage, commercial-frequency a1ternating--currents without the introduction of the alternating-current noises heretofore observed in the operation of such devices.

Another object of our invention is to provide a vacuum-tube structure having highly desirable operating characteristics, wherein a high voltage amplification factor may be obtained while simultaneously securing a comparatively low plate impedance.

A further object of our invention is to provide a vacuum-tube device of the class described embodying a construction which shall be adapted for quantity production 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 not been practical to employ alternating currents for the excitation of the cathode or lament 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.

l. 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 tleldaround 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 iilament.

We have found that the desirable results outlined hereinabove may be obtained by applying a cathode construction having an operating cathode surface which has no fall of potential along its surface, that is, a so-called equipotential surface". Such cathode surface may be rendered thermionically active in a number of different ways, as by subjecting the same to heat or to an electron bombardment. In one form of embodi- 1,909,051, May 16, 1933.

cation August 13, 1932,

13 Claims. (Cl. Z50-27) ment of our invention, we provide a cathode construction comprising a central heater element and a cooperating 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 applications in view, our invention further consists in the combinations and details of circuit arrangements hereinafter more fully set forth and claimed and illustrated in the accompanying drawings, wherein;

Figure l 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 member 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, similar to Fig. 4, showing an alternative construction for the equipotential cathode surface,

construction and in the 10 Fig. 6 is a view similar to Fig. 5, but showing the member forming the operating cathode "1 surface insulatingly carried by the heater element,

Figs. 7 and 8 are enlarged front and side detail elevational views of a furthermodied form of cathode construction embodying our invention.

Fig. 9 is a side elevational detail view illustrating our invention applied to a vacuum-tube construction employing a pair 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 ilgures.-

Fig. 12 is a diagrammatic 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 element 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 vacuumtube circuits to be electrically independent of the supply circuits for the heater element, and

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

In a preferred form of embodiment of our invention, as shown in Figs, 1, 2 and 3, we provide an elongated envelope I having a re-entrant portion 2 terminating in a supporting press 3. A cathode construction 4 comprises a mass of rei'ractory material 8 in the form of a slender solid cylinder provided with a pair of adjacently positioned

perforations

8 and 1 which extend between the ends of the cylinder 5. The

perforations

8 and 1 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-shape having parallelly extending portions 8 and Il and a top portion I2.

The distance between the parallel portions 8 and I l 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 energizaltion of the cathode element. 'I'he filament 8 may be energized by connecting the same to filament supply conductors I3 and I4 which are supported in the press 3 and are provided with external extensions I8 and I8, respectively.

The cylindrical member 5l 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 I1. which forms the equipotential cathode surface, is shown in the form of a tube having its inner surface closely embracing the tubular insulating member 8. The outer surface of the member I1 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 I8 extending from the press 3, as hereafter described. In practice, it has been found desirable to provide a spring connection between the cathode construction 4 and the supporting carrier rod I8 in order to provide for the expansion and contraction oi' the heating element 8. 'I'he desired result is obtained by welding a strip I8 to the upper end of the cathode construction, preferably to the tubular member I1, and connecting the strip I8 and the carrier rod I 8 by means of a spring member 2|. The equipotential cathode member I1 may be electrically connected externally of the tube I by connecting the same to one of the supply conductors, for example, conductor I3, by means of a conductor 22.

The cathode construction 4 may be surrounded by plate and

grid elements

23 and 24 of conventional design. lAs 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 thereof to provide additional stiffness to the grid construction.

The plate 23 is a tubular member symmetrically 4 positioned with respect to the previously men- 5 tioned elements and supported by

carrier rods

28 and 21 which are mounted in the press 3; One of the carrier rods, say 21, may be extended `through the press 3 to form an external circuit terminal 28. l0

The envelope I may be provided with a base 28, which comprises a solid circular insulating member 38 and a collar 3i, opposite ends of the latter rigidly embracing the re-entrant tube portion 2 of the evacuated electric device and the 15 insulating member 38, in any approved manner. 'Ihe outer end of the insulating block 30 may be provided with a raised portion or base 32 and a plurality of hollow terminal pins 33, 34, 35 and 38. The several external connections are dis- 20 posed 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 38 are connected to the terminals of the plate and grid elements 23`and 24, respectively. The pin 25 element 33 also serves as a terminal connection for the equipotential cathode member I1.

In Fig. 4 is shown an enlarged detail longitudinal sectional view of a cathode construction 31 which differs from that previously described in 30 the following important respects. The adjacent sections 3 and II of the heater element 8 are insulating supported and spaced by means of separate

tubular members

38 and 39, respectively. The

tubular members

38 and 38 may be made of 35 any refractory material having properties similar to those described for the tubular supporting member 8 shown in Fig. 3. The cathode construction herein shown has an equipotential electron-emitting element in the form of a cylindrical 4o casing 4I having a cap portion 42 which is electrically connected to the bent portion I2 of the heater filament 3. 'Ihe structure may be supported by means of a carrier rod 43 which is welded to the cap portion 42. 'I'he carrier rod 43 45v may be extended through the press 3 to serve also as an external terminal connection for the equipotential cathode member 4I.

In Fig. 5 is shown a cathode construction which is differentiated from that of Fig. 4 in the form of 50 the member constituting the equipotential cathode surface. In this construction, the cathode surface isy formed by spirally winding an oxidecoated platinum strip 44 around the outer portions of the

tubular spacing members

38 and 38. 55

The construction 45 shown in Fig. 6 is distinguishable over the preceding cathode constructions in that the oxide-coated platinum strip 44 forming the equipotential vcathode surface is wound directly around the sections 8 and I I of the 60 I heater element 8, the oxide coating on the platinum strip 44 serving to insulate the strip 44 from the heating element 8. If additional insulation is necessary, the heating element 8 itself may be covered by some insulating oxide, such, for ex- 65 ample, as magnesium oxide. 'I'he structure may be supported by means of a carrier rod 48 which is welded to the bent portion I2 of the heater element and to the strip 44. The carrier rod 48 may also serve as a lead for the equipotential cathode 70 member 44.

In Figs. 'I and 8, a cathode construction is shown which differs from the foregoing constructions in the following respects. A heater element 41. which may be in the lform of a fiat ribbon of 75 tungsten or other suitable material, is doubled to form apair of adjacently positioned

sections

48 and 49, as in the preceding figures. 'I'he

adjacent sections

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

Equipotential cathode members

52 and 53, in the form of oxide-coated strips ofv nickel, are positioned immediately adjacent to the

filament sections

48 and 49, respectively, and are insulatingly spaced therefrom by mica strips 54 and `65. 'I'he structure is bound tightly together at the opposite ends thereof by collar members 56 and 51 and may be supported from the top by mea-ns of a carrier rod 58 having bail extensions 59 and 6I secured to the collar 56. The carrier rod 58 may be extended through the press to serve as an external terminal connection for the

cathode members

52 and 53.

Fig. 9 is a greatly enlarged view of a vacuumtube construction 62 which is differentiated over that of Figs. 1 and 2 in the provision of an additional controlling element 63, all as described more fully hereinafter.

The foregoing cathode constructions are all characterized by the fact that the equipotential 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 heat conducting means between the two members.

Figs. 10 and 11 are greatly enlarged views of a construction S4 wherein an equipotential cathode member 65 is heated by thermal radiation rather than by thermal conduction. The construction there shown comprises a heater element 66 in the form of adjacently positioned parallelly extending lamentary sections 61 and 68, the sections being adjacently positioned to reduce the distorting effects of the varying magnetic fields established by the filament exciting currents as previously described. Adjacent ends of the filament sections are welded to a supporting member 69 of nickel or other suitable conducting 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 Asecured to the supporting block 59. The construction may be supported by means of a carrier rod 1I having one end rigidly secured to the supporting block G9.

Fig. 12 is a diagrammatic view of the vacuumtube 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 I1 are connected by

conductors

12 and 13, respectively, to a source of incoming signals (not shown). A plate-filament circuit 14, which extends frorn the plate 23 to the equipotential cathode element I1, includes a detecting device and a source 1E of direct-current energy. A source of alternating-current energy (not shown) is operatively connected to the heater element 8 through a transformer 11. It is noted that, in this arrangement, theequipotential cathode member I1 is connected to the heater element 8 within the evacuated portions of the tube I, thereby requiring only four terminal pins in the base 29.

The system shown in Fig. 13 is distinguishable over that of Fig. 12 in the provision of separate connections for the equipotential member I1 and for the heater element 8, 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 80 in Fig. 13.

The system shown in Fig. 14 illustrates one application of the vacuum-tube construction 62 shown in Fig. 9 'I'he additional grid element 63 '-is connected to the equipotential cathode member I1 by means of a conductor 18 including a source 19 of direct-current energy tendingto make 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 alternating exciting currents to vary the tube characteristics. When the grid 63 is made positive, as shown in the drawings, it forms, in effect, anartificial 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 portions of the specication. The low-resistance type of vacuum tube heretofore employed has a plate impedance of from 15,000 to 25,000 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 10,000 ohms and a voltage amplification factor of 10. Thus, it is seen that the figure of merit,

which is the ratio of the amplification factor squared to the plate resistance, is, in a vacuumtube construction embodying our invention, approximately four times greater than that of the ordinary tubes heretofore employed.

While 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. We desire, therefore, that only such limitations shall be imposed thereon as are indicated by the appended claims or demanded by the prior art.

We claim as our invention:

1. A thermionic tube having therein an anode and a cathode structure and having external anode and cathode-terminals and terminal provisions for a cathode-energizing circuit, said cathode-structure comprising resistance wire connected between said terminal provisions, each portion of such resistance wire being adjacent to but out of contact with another portion of such resistance wire, which exhibits at every instant an opposite electric polarity from the first-named portion, whenever said terminal provisions are connected in circuit with a source of alternating electric current, whereby external field effect of the cathode-heating current is neutralized.

2. A thermionic tube having therein a plate, a grid, and a cathode, said cathode comprising terminals and a filamentary structure connected between said terminals and comprising adjacent non-contiguous portions which exhibit opposite electric polarity when said terminals are connected in circuit with the ordinary alternating current lighting system.

3. A cathode structure comprising a plurality of parallel non-contiguous filaments each having terminals and supporting members connected thereto adapted to conduct energy to the said filaments, adjacent terminals of the said laments being connected to supporting members o! opposite polarity.

4. A cathode assembly comprising a cylindrical casing, electron emitting material on said casing, a conductive member across one end of said cylindrical casing and connected thereto and a plurality of filaments attached to said conductive member.

5. A cathode assembly comprising a cylindrical casing, electron emitting material on said casing, a conductive member across one end of said cylindrical casing, heating means connected to said conductive member and a combined supporting means and cathode lead connected to said conductive member.

6. An indirectly heated equipotential cathode assembly comprising a hollow cylindrical casing, electron emitting material on the outer surface of said casing. a conductive member across one end of said cylindrical casing, a pair of iilaments supported on said conductive member and extending parallel through said cylindrical casing and a combined supporting means and cathode lead connected to said conductive member.

7. Any electrical discharge device comprising a uni-potential cathode having an alternatingcurrent heater, an anode, a control electrode, and an electrostatic screening means positioned between the surface of said cathode and said anode. f

connecting said cathode and said anode, and an electrostatic screening means interposed between the surface of said cathode and said anode.

l0. An electrical discharge device comprising a cathode having a surface of conducting material with a thermionically emissive coating at least partially enclosing an electrical heater for rendering said surface thermionically emissive, an electrode external to said cathode surface and spaced therefrom, and an electrostatic screen between said cathode surface and said electrode.

11. An electrical discharge device comprising a cathode having a surface of conducting material with a thermionicaliy emissive coating at least partially enclosing an electrical heater for l5 rendering said surface thermionically emissive, an electrode external to said cathode surface and spaced therefrom, a control electrode and an electrostatic screen between said cathode and the mst-mentioned electrode.

12. An electrical discharge device comprising a cathode heated by alternating current, an anode,

a source of substantially constant voltage supply connected between said cathode and said anode, and electrostatic screening means positioned between the surface of said cathode and said anode and connected to said cathode through a current path which does not'include said source.

13. An electrical discharge device comprising a cathode heated by alternating current, an anode, a control electrode, leads for connecting said cathode and said control electrode to a source of varying voltage, a path for output currents responsive to said varying voltage connected between said cathode and said anode, and 35 electrostatic screening means positioned between the surface of said cathode and said anode and connected to said cathode through a current path which does not include said rst mentioned path.

MAX F. REGES. Administrator of lthe Estate of Hubert M. Freeman, Deceased.

WALLACE G. WADE.