US2541026A

US2541026A - Harmonic coaxial-line tube

Info

Publication number: US2541026A
Application number: US491469A
Authority: US
Inventors: Clarence A Boddie
Original assignee: Individual
Current assignee: Individual
Priority date: 1943-06-19
Filing date: 1943-06-19
Publication date: 1951-02-13
Anticipated expiration: 1968-02-13

Description

Feb. 13, 1951 c BODDIE 2,541,026

I HARMONIC COAXIAL-LINE TUBE Filed June 19, 1945 2 Sheets-Sheet 1 STANDING POTENTIAL WAVE ANDING POTENTIAL WAVE 3: 3d I l A 5 26 t i if F INVENTOR. CLARENCE A. BODDIE A'I'TDRNEY Feb. 13, 1951 c, BODDIE I 2,541,026

HARMONIC COAXIAL-LINE TUB E Filed June 19, 1943 2 Sheets-Sheet 2 I INVENTOR. CLARENCE A. BoDDIE ATTORNEY Patented Feb. 13, 1951 UNITED STATES- PATENT OFFICE 2,541,026 V HARMONIG Q' AXIAL-LINE' TUBE Clarence A. Boddie, Belmar, Application June 19,1943, Serial No. 491,469 26 Claims; (01. 250-475)- (Granted under the act of March 3, 1;8'83,'as

1: l The invention described herein may he manufactured and used by or for the Government for governmental purposes; without payment to me of' any royalty thereom This invention relates to electron emission tubes, particularly transmitter tubes working: at very high frequency;

The primary object of the present invention to genera'l-l'y improvevacuum tubes".

Such a tube may be made accordance with my copending applicationserial Number 491,374,

filed June is; 1943;: and now U. s. Patent No. 2,472,088, in two anodes disposed end toend are connected by an anode pipe forming. a

part of the tube: envelope and surround: grids connected by a grid. pipe,v said anode and grid pipes forming: a tuned coaxial line approximately a half-wavelongt Further objects of the present invention are; to'im'prove saiditube for use at extremely high frequencies and with multiplied electrode area for greatly augmented-power outare four cathodes cooperating with adjacent portions of the grid and anode pipes, the latter then having a standing wave: thereon which is harmonically related" to the anode=pipe.

To accomplish the foregoing general objects and other more specific objects-which will hereinaiter appear; my invention residesinthe very high frequency tubeandoscillator elements, and

theifi relation one to another as hereinafter are more particularly describedin the specification.

and sought to be defined in the claims. The I specification is accompanied by a drawing in which Figure 1 is a schematic diagram explanatory of one form of tube embodyingfeatures of my inr nt q Figure 2 is a similar diagrammatic showing; of

a modified tube havinga greater number of electrodes;

Figure 3 is a diagrammatic showing of an 0s-- oillator utilizing theitube ofEigure 1";

Figure 4 is; a longitudinalv section through a modification having anode and grid. pipe extensions; and

Figure 5 is asection through one end oi the tube drawutoenlarsedscalet amended April 30, 1928; 370 O. G. 757) .Referring to thedrawing, and more particularly to. Figure lathe tube'there: illustrated coin prises four cathodes 12,- I4 Hi, and I8, si'fa c'ed" approximately a: half-wave apart on a common 1 axis The cathodes are surrounded by grids 2'0,

which in turn are surrounded by an anode pip 22'.- This maybe thoughtof as four anodes sur 1 rounding grids 20' and connected by pipes, butin practice the connecting pipes may be a co'nti'nu' ation of the anodes, so that the resulting strut-- ture is simply asing le continuous pipe, which preferably forms a; major part or the evacuated envelope of the tube. The grids 20 may be con:- nected by pipes: 24' thus forming another tubular structure disposed coaxiallywithin the anode pipe 22. The grid assembly may; for convenienc'eg be: called a grid pipe havingaperturedportionsr said grid pipe is supported by lead-ins 26 Which pass insulatedly throughrthe envelope ofthe tube.

; In the present case, glass walls 28 are used to.

close the ends of the anode pipe 22 and the grid. lead-ins 26 pass through the said glass walls: 'I-hecathodes l2 and I4 are supported by a leadin- 30,. and areenergized through lead-

ins

32 and 34. Cathode F4 is connected to cathode l2 meansofspaced' eonduetorsw. The tube is sym'- metrical, and cathodes I6 and l8= are connectedtogether and are supported and energized through three leadsins arranged in the same manner as just described, but passing through the opposite:- glass end wall of the tube; It is not essential; that the: insulation or'the lead-ins beaprovided by glass end walls, nor that the lead-ins pass; through the: ends of the tube but I consider this;

, a-convenient construction.

The grid pipe assembly and: the anode pipe. 22 together form a tuned: coaxial line which is harmonically resonant to" the frequency at whichthe tube' is to. be operated; This Willbe clear from inspection of the potential curve E and the cur-. rent curve I shown in F-igure 1. Reference totlie curves will show that the" cathodes 12, M IB, and. l8= are electrically ahalf-swave length apart, thus making the tube-one and one-half wave-lengths long. It may be pointed out-that the electrode assemblies including theend cathodes I2 andware; preferably only about half as long as the elsetrode assemblies including the inner cathodes H and Hi. The reasonlior this is that theelectrodesl4 and I6 are disposed on both sides of the poten tial maxima 38 and 4 whereas the potential; maxima' 42 and 44 are located. at the outer ends of theelectrodes [-2 and 18;. Assuming-a sine wavc shape, anelectrode: 39 in length will experience a drop in potential of only 14 percent. Inthe:

case of the electrodes I4 and I6, this drop in potential will take place with electrodes 60 in length, there being only 30 electrode length on either side of the potential maximum. If the potential drop is limited to 14 percent in all of the electrodes, the end electrodes I2 and I8 should be only 30 in length, while the center electrodes I4 and I6 may be 60 in length.

It will be understood that while a tube having four electrodes is shown in Figure 1, the invention is not limited to that number. Figure 2 illustrates a generally similar tube using six electrode assemblies. Here again, the end electrodes are preferably only half the length of the intermediate electrodes. Three cathodes are energized through one end of the tube, while the other three are energized through the opposite end of the tube. The coaxial line provided by the grid and anode pipes will, in this case, be two and one-half waves in length.

The tube itself is nearly a complete oscillator, but it is preferable to provide the same with associated, external circuits, a typical example of which is illustrated in Figure 3. In Figure 3, the tube itself corresponds to that shown in Figure 1. In addition I provide external cathode-toground circuits and an external grid-to-grid circuit. In all cases, the external circuits are preferably adjustable to tune the same. In the specific case here illustrated, the grid-to-grid circuit includes an auxiliary grid pipe 40 and adjustable shorting bars 42 for connecting the same to the grid leads 26. In eifect, tuning trombones are provided. Tuning of the grid-to-grid circuit helps take care of some of the chargin current required for the grid-to-cathode capacitance of the tube. From another viewpoint, it may be said that inasmuch as grid leads of substantial length are required for structural reasons alone, it is advantageous to make these leads part of a tuned circuit, thereby increasing the fiiciency of operation.

The external grid circuit also provides a convenient way to supply grid bias potential to the grids. Grid bias potential is supplied through a lead 44, preferably connected to a midpoint or a potential node on the auxiliary pipe 40. In the present case, the grid bias potential is developed across a resistor 46, and this is preferably shunted by means of a distributed or lumped capacitance indicated at 48.

The cathodes are preferably maintained at ground potential with respect to radio frequency. This is most conveniently done by connecting the cathodes to ground by means of circuits which are electrically one or more halfwaves in length. In the present case, I provide an auxiliary cathode pipe 50 connected to the cathodes by means of adjustable shorting bars 52. These are clamped about the auxiliary pipe 50 at their lower ends, and about metal bushings 54 at their upper ends. The center support leads 30 of the tube are fixed conductively in the bushings 54. The heater leads 32 and 34 preferably pass insulatedly through bushing 54, thereby providing additional radio frequency coupling between the shorting bar 52 and the cathodes. The auxiliary cathode pipe 50 is grounded, as indicated by the ground connection 56, which in the present case is located at the midpoint of the pipe. Shorting bars 52 are adjusted to provide the desired resonant length of circuit to ground.

The cathodes are heated by direct current or low frequency alternating current power. This is indicated in the present case by an alternating current power line 60, coupled through transformers 82 to the cathode leads 32 and 34. Radio frequency chokes 64 may be inserted in the heater supply leads. Anode potential may be fed to the anodes through a lead 65 connected at the midpoint, or at a potential node on anode pipe 22. A radio frequency choke 08 is preferably inserted in lead 66.

Power may be taken from the oscillator by appropriate connection to the anode pipe 22, or to either of the auxiliary pipes 40 and 50. In the present case, however, transmission line connection I0 is tapped on the anode pipe 22 at points symmetrically disposed on opposite sides of the direct current anode connection 66. The spacing of the tapping points on the anode pipe may be used to match the impedance of the transmission line.

The grid and'anode pipes may, if desired, be extended by pipe extensions approximately a half-wave long. Such extensions have the advantage that the end electrodes then may be made of the same length as the intermediate electrodes. This is illustrated in Figure 4, in which it will be seen that the tube has four electrode assemblies, much as in Figure l, but all of the electrode assemblies are identical in dimension. The anode pipe I0 is prolonged by anode pipe extensions I2. The grid pipe I4 is prolonged by grid pipe extensions 10. The extensions are electrically a half-wave in length, thus making it possible to locate the potential maxima I8 at the center of the electrodes 80. It is for this reason that the electrodes may be as long as the intermediate electrodes 82.

The anode pipe extensions 12 are connected to the anode pipe H! by flanges or steps 84. The grid pipe extensions 16 are connected to and supported by the grid lead-ins. Two such lead-ins are here shown at each end of the tube, but in practice a greater number, say four, may be employed if it is desired to strengthen the support of the grid pipe inside the tube, and the support of the grid pipe extension outside the tube.

The construction of the tube itself is shown in greater detail in Figure 5, referring to which it will be seen that the anode pipe I0 is flared outwardly at 90, and there provided with a feathered edge which is sealed to the glass wall 92. The seal is preferably protected by a'metalshield 94.

The grid wires 96 and 9B are welded to a connecting pipe I00. Grid wires 96 are also welded to a support ring I02, while grid wires 98 are welded to the next connecting pipe I04. The end ring I02 is supported by metal struts I06, which in turn are carried by lead-ins I08. These pass through and are sealed to glass stems H0.

The

cathodes

80 and 82 are made of a pair of oppositely wound filaments. The center or supporting lead-in II2 passes centrally through the filaments, and its inner end is secured to the mid-- point II4 of filament 82. The spaced ends of filament 82 are secured to spaced connecting wires H8, which are held in proper relation to lead-in II2 by insulation spacers II8. The inner ends of filaments 80 are connected to the connecting wires I I6, while their outer ends are connected to the lead-ins I20 and I22. All three lead-ins II2, I20, and I22 pass through reentrant glass stems I24. While these have been shown in a single plane for clarity, it will be understood that, if desired, they may be located apart on a circle, thus facilitating the glass-blowing job by increasing the spacing between the stems.

In all cases it will be understood that the curves used to'illustrate. the potential and current on the anode pipe may also be referred to as illustrating the potential and current on the grid pipe, except that the standing wave on the grid pipe swings in opposite phase to that on the anode pipe. The curve representing the current. is 90 out of phase from the voltage. The grids and active anodes are therefore at. current. nodes, and at potential loops or maxima. The cathodes are at ground potential.

It is believed that the construction and operation, as well as the advantages, of my improved vacuum tube, will be apparent from the foregoing detailed description thereof. Because the standing wave on the anode and grid pipes, or coaxial line, is harmonically related to the length of the line, very high frequenciescan be obtained. The use of a substantial number of electrode assemblies makes possible substantial power output, even at very high frequencies.

It will be understood that although I have shown a grid pipe with grid sections at intervals therealong, it is also possible to use a continuous grid pipe, that is, one formed of wires throughout itslength, or one apertured throughout its length. Only those portions surrounding the cathodes will function as grids, and I therefore prefer, in the interests of structural strength, and conductivity, to employ solid pipe sections between the grid sections. If the cathodes are of the indirectly heated oxide-coated type, instead of the filament type here shown, a continuous. cathode pipe may be employed, the surface of which may be oxide coated at intervals. The oxide-coated portions will act as the actual cathodes. While I have shown the anodes as portions of continuous anode pipe, the anodes may be separate structural members made, for example, of one metal, and connected by short connecting pipes somewhat different in dimension or made of different metal.

It will therefore be apparent that while I have shown and described my invention in several pre.. ferred forms, many changes and modifications may be made in the structures disclosed without departing from the spirit of the invention, as sought to be defined in the following claims. In the claims the reference to a grid pipe apertured at intervals is intended to include the use of wire grid sections between solid pipe sections, as well as. the use of a continuously apertured or a continuous wire structure devoid of solid pipe sections.

I claim:

1. A very high frequency tube comprising an envelope, at least three cathodes. mounted end to end and having their mid-points spaced approximately a half-wave length apart on a common axis w th an inactive interval between adjacent ends, grids around said cathodes, anodes around said grids, anode pipe connecting the anodes, grid pipe connecting the grids, grid lead insulatedly passing through the envelope of the tube, and cathode leads insulatedly passing through the envelope of the tube, sad inactive interval being equal to a substantial fraction of the operating wave length. I

2. A very high frequency tube comprising an evacuated envelope, at least three cathodes mounted end to end and having their mid-points spaced approximately a half-wave length apart on a common axis with an inactive interval between adjacent ends equal to substantialfrad.

tion of the distance between said mid-points,

grids around said cathodes, anodes around said grids, anode pipe connecting anodes and forming a continuation of said anodes, said anodes and anode pipe forming a major portion of the evacuated envelope of the tube, grid pipe between the grids, a grid lead insulatedly passing through the envelope of the tube, and cathode leads insulated-v ly passing through the envelope of the tube, said grid and anode pipes forming an open end standing wave coaxial line resonant to a frequency for which the distance between said mid-points is approximately a half wave length.

3. A very high frequency oscillator tube com:- prising an envelope, at least three cathodes mounted. end to end and having their mid-points 1 spaced approximately a half-wave length apart on a common axis with an inactive interval be,- tween adjacent ends equal to substantial fraction of the distance between said mid-points,

grids around said cathodes, anodes around said.

grids, anode pipe connecting said anodes, said anodes and anode pipe forming a major portion 1 of the. envelope of the tube, glass end walls com--. pleting the envelope of the tube, grid pipe be.

spaced approximately a half-wave length apart' on acomrnon axis with an inactive interval between adjacent ends equal to a substantial fraction of the distance between said mid-points, grids around said cathodes, anodes around said grids, anode pipe connecting and forming a con tinuation of said anodes, said anodes and anode pipe forming a major portion of the evacuated envelope of the tube, glass walls at the ends of said anode and anode pipe assembly for completing the envelope of the tube, grid pipe between the grids, grid leads passing through said glass" ends, and cathode leads extending longitudinally within the tube between said cathodes and passing through the aforeraid glass walls, said grid and anode pipes forming an open end standing wave coaxial line resonant to a harmonic frequency for which the distance between said midpoin-ts is approximately a half wave-length.

5. A very high frequency tube comprising an envelope, four cathodes mounted end to end and having their mid-points spaced approximately a halfavavc length apart on a common axis with a substantial interval between adjacent ends, grids around said cathodes, anodes around said grids,

. anode pipe connecting said anodes, grid pipe between the grids, a grid lead insulatedly passing through the envelope of the tube, and cathode leads insulatedly passing through the envelope of the tube, said grid and anode pipes forming an open end standing wave coaxial line resonant to a harmonic of the fundamental frequency for which the distance between said mid-points is approximately a half wave-length.

6. A very high frequencytube comprising an evacuated envelope, four cathodes mounted end to end and having their inidpoints spaced approximately a half-wave length apart on a common axis with a substantial interval between adjacent ends, grids around said cathodes, anodes around said grids, anode pipe connecting and forming a continuation of said anodes, said anodes and anode pipe forming a major portion of the evacuated envelope of the tube, glass walls at the ends of said anode pipe completing the envelope of the tube, grid pipe between the grids, grid leads passing through said glass ends, cathode leads extending longitudinally within the tube between two of said cathodes and passing through the adjacent one of the glass walls, and cathode leads extending longitudinally within the tube between the other two cathodes and passing through the other glass wall, said grid and anode pipes forming an open end standing wave coaxial line resonant to a harmonic of the fundamental frequency for which the distance between said mid-points is approximately a half wave-length.

7. A very high frequency oscillator tube comprising a metal anode pipe more than a wavelength long, said pipe forming a major portion of the envelope of the tube, a grid pipe inside the anode pipe apertured at approximately half-wave length intervals, and cathodes approximately a half-wave length apart within said grid pipe at the aforesaid apertured portions thereof, intervals between the cathodes equal to a substantial part of said half wave-length, said anode and grid pipes forming a standing wave line for which the said half wave-length is a harmonic of the fundamental frequency.

8. A very high frequency oscillator tube comprising a metal anode pipe more than a wavelength long, a grid pipe inside the anode pipe apertured at at least three places at approximately half-wave length intervals, and at least three cathodes approximately a half-wave apart within said grid pipe at the aforesaid apertured portions thereof, intervals between the cathodes equal to a substantial part of said half-wave length, said anode and grid pipes forming a standing wave line for which the said half-wave length is a harmonic of the fundamental frequency.

9. A very high frequency oscillator tube comprising a metal anode pipe more than a wavelength long, glass walls closing the ends of said pipe, a grid pipe inside the anode pipe apertured at approximately half-wave length int-rvals, leads passing through the glass walls for supporting the grid pipe, cathodes approximately a halfwave length apart within said grid pipe at the aforesaid apertured portions thereof, intervals between the cathodes equal to a substantial part of said half-wave length and cathode leads extending longitudinally within the tube from some of the cathodes through one of the glass walls, and leads from the remaining cathodes through the other of said glass Walls, said anode and grid pipes forming a standing wave line for which the said half wave-length is a harmonic of the fundamental frequency.

10. A very high frequency oscillator tube comprising a metal anode pipe more than a wavelength long, glass walls closing the ends of said pipe, a grid pipe inside the anode pipe apertured at at least three places approximately at halfwave length intervals, leads passing through the glass walls for supporting the grid pipe, at least three cathodes approximately a half-wave length apart within said grid pipe at the aforesaid apertured portions thereof, intervals between the cathodes equal to a substantial part of said halfwave length, cathode leads extending longitudinally within the tube from some of the cathodes through one of the glass walls, and leads from the remaining cathodes through the other of said glass walls, said anode and grid pipes forming a standing wave coaxial line resonant to a harmonic of the line fundamental frequency for which the cathode spacing is approximately a half-wave length.

11. A very high frequency oscillator tube comprising a metal anode pipe of substantial length, a grid pipe inside the anode pipe and apertured at half-wave length intervals, cathodes within said grid pipe at the aforesaid apertured portions thereof, intervals between the cathodes equal to a substantial part of said half-wave length, said anode and grid pipes forming a standing Wave line, said cathodes and grids being located substantially at standing wave potential loops for which the said half-wave length spacing is a harmonic of the fundamental frequency.

12. A very high frequency oscillator tube comprising a metal anode pipe of substantial length, said pipe forming a major portion of the envelope of the tube, glass walls closing the ends of said pipe, a grid pipe inside the anode pipe and apertured at half-wave length intervals, leads passing through the glass walls for supporting the grid pipe, cathodes within said grid pipe at the aforesaid apertured portions thereof, intervals between the cathodes equal to a substantial part of said half-wave length, cathode leads from some of the cathodes through one of the glass walls, and leads from the remaining of said cathodes through the other of said glass walls, said anode and grid pipes forming a standing wave line, said cathodes and grids being located substantially at standing wave potential loops the said half-wave length spacing of which is a harmonic of the fundamental line frequency.

13. A very high frequency oscillator comprising a tube as defined in claim 1, and having cathode and grid leads connected to the end cathodes and end grids respectively, and tuned external cathode and grid circuits, said external cathode circuit comprising an auxiliary cathode pipe having an intermediate point grounded, and shorting bars adjustably bridged between the aforesaid cathode leads and the auxiliary cathode pipe, said external grid circuit comprising an auxiliary grid pipe, and shorting bars adjustably bridged between the aforesaid grid leads and the auxiliary grid pipe, and grid bias potential means connected from ground to an intermediate point on said auxiliary grid pipe.

14. A very high frequency oscillator comprising a tube as defined in claim 5, and having cathode and grid leads connected to the end cathodes and end grids respectively, and tuned external cathode and grid circuits, said external cathode circuit comprising an auxiliary cathode conductor grounded at an intermediate point, and shorting bars adjustably bridged between the aforesaid cathode leads and the end portions of said auxiliary cathode conductor, said external grid circuit comprising an auxiliary grid conductor and shorting bars adjustably bridged between the aforesaid grid leads and the end portions of said auxiliary grid conductor, and a grid bias resistor connected from ground to an intermediate point on said auxiliary grid conductor.

15. A very high frequency oscillator comprising a tube as defined in claim 9, and tuned expipe, said ternal cathode-to-cathode and grid t'o-grid circuits, said external cathode circuit comprising an auxiliary cathode conductor grounded at an intermediate point, and shorting bars adjustably bridged b'etweehthe aforesaid cathode leads and and end grids respectively, and tuned external cathode-to-cathode and grid-to'-grid circuits, said external cathode circuit comprising an auxiliary cathode pipe having an intermediate point grounded, and shorting bars adjustably bridged between the aforesaid end cathode leads and the endportions of said auxiliary cathode grid-to-grid circuit comprising an auxiliary grid pipe, and shorting bars adjustably bridged between the aforesaid grid leads and the end portions of said auxiliary grid pipe, and grid bias potential means connected from-ground to an intermediate pointon said auxiliary grid pipe.

17. A very high frequency oscillator comprising first and second parallel closely spaced conductors, n grids spaced approximately a half-wave length apart on first conductor where a is any whole number greater than two, areas on second conductor adjacent said grids constituting anodes,

' cathodes positioned longitudinally near said grids and on opposite sides thereof from the anodes, enclosure means for maintaining the cathode anode electron paths evacuated and air tight,

supporting means for the first conductor comprising third and fourth conductors passing through said enclosure connected to and supporting opposite ends respectively of the first conductor, supporting means for said cathodes passing through the enclosure, leads between said cathodes for supplying heating current and supported by said cathode supporting means, a cathode-tocathode current path external to the enclosure including tuning means therein, a grid-to-grid circuit external to the enclosure connected between outer ends of third and fourth conductors including tuning means therein, and a source of high potential direct current coupled between the cathodes and said second conductor.

18. A very high frequency oscillator comprising first and second parallel closely spaced conductors, n grids spaced approximately a half-wave length apart on first conductor where n is any whole number greater than two, areas on second conductor adjacent said grids constituting anodes, cathodes positioned longitudinally near said grids and on opposite sides thereof from the anodes, enclosure means for maintaining the cathode anode electron paths evacuated and air tight, supporting means for first conductor comprising third and fourth conductors passing through said enclosure connected to and supporting opposite ends respectively of the first conductor, supporting means for said cathodes passing through the enclosure, leads between said cathodes for supplying heating current and supported by said cathode supporting means, a cathode-to-cathode current path external to the enclosure including tuning means therein. a grid-to-grid circuit external I 10 to the enclosure connected between outer ends or third and fourth conductors and including a reactor therein for supplying the charging current required by said first conductor supporting means and a source of high potential direct current coupled between the cathode circuit and said second conductor.

19. A very high frequency oscillator comprisfi'rst and second parallel closely spaced conductors, n grids spaced approin'inately a halfwave length apart on first conductor where is any whole number greater than two, areas on I second conductor adjacent said grids constituting anodes, cathodes positioned longitudinally hear said grids and on opposite sides thereof from the anodes, enclosure means for maintaining the cathode anode electron paths evacuated and air tight, supporting means for first conductor cornprising third and fourth conductors passing through said enclosure connected to and supporting opposite ends respectively of the first echducto'r, supporting means for said cathodes passing through the enclosure, leads between said cathodes for supplying heating current and su ported by said cathode supporting means, a cathode -to cathode current path external to the enclosure including tuning means therein, a gi*i&=0 grid circuit external to the enclosure connected between outer ends of third and fourth conductors including tuning means there in for supplying' charging current to said first conductor supporting means and for varying the frequency of the oscillator.

20, A very high frequency oscillator comprising first and second parallelclosely spaced conductors, n grids spaced approximately a half wave length apart on first conductor where n is any whole number greater than two, areas on second conductor adjacent said grids constituting anodes, cathodes positioned longitudinally near said grids and on opposite sides thereof from the anodes, enclosure means for maintaining the cathode anode electron paths evacuated and air tight, supporting means for first conductor comprising third and fourth conductors passing through said enclosure connected to and supporting opposite ends respectively of first conductor, supporting means for said cathodes passing through the enclosure and extending within and parallel to first conductor, leads between the cathodes for supplying heating current, a cathode-to-cathode current path external to the enclosure including tuning means therein, pairs of variable length conductors external to the enclosure for tuning the oscillator connected respectively to first and second conductors and constituting extensions thereof, an external grid-to-grid current path, and a source of high potential direct current coupled between the cathode circuit and the anodes.

21. A very high frequency oscillator as defined in claim 3 and further including anode pipe and grid pipe extensions of the coaxial line beyond the body of the tube and terminating in an open end at a point approximately a half wave length beyond the mid-points of the end cathodes whereby the standing wave potential maximum occurs substantially at said cathode mid-points and extends symmetrically on either side thereof substantially doubling the effective length and power of the end sections of the tube.

22. A very high frequency oscillator tube as defined in claim 3 and means for substantially doubling the effective length and power of the end sections of the tube, said means including anode pipe and grid pipe extensions of thefco- 1 1 axial line beyond the body of the tube and terminating in an open end at a point approximately a half wave length beyond the mid-points of the end cathodes whereby the standing wave potential maximum occurs at said cathode mid- I. points and extends symmetrically on either side of said mid-points. 7 23. A very high frequency tube as defined in A claim 6 and means for substantially doubling the efiective length and power of the end sections of the tube, said means including anode pipe and grid pipe extensions of the coaxial line beyond the body of the tube and terminating in an open end at a point approximately a half wave length beyond the mid-points of said end sections whereby the standing wave potential maximum occurs 4 at said mid-points and extends symmetrically on either side of said mid-points.

24. A very high frequency tube asdefined in claim 9 and means for substantially doubling the effective length and power of the end sections of the tube, said means including anode pipe and grid pipe extensions of the coaxial line beyond the body of the tube and terminating in an open end at a point approximately a half wave length beyond the mid-points of said end sections whereby the standing wave potential 1 maximum occurs at said mid-points and extends symmetrically on either side of said mid-points.

25. A very high frequency oscillator tube as defined in claim 12 and means for substantially doubling the effective length and power of the end sections of the tube, said means including anode pipe and grid pipe extensions of the coaxial line beyond the body of the tube and ter minating in an open end at a point approximately a half wave length beyond the mid-points of said end sections whereby the standing wave potential maximum occurs at said mid-points and extends symmetrically on either side of said midpoints.

26. A very high frequency oscillator tube of the coaxial line standing wave type comprising, at least three coaxial sections each having active and inactive portions, said sections being coupled REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,978,021 Hollmann Oct. 23, 1934 1,979,668 Boddie Nov. 6, 1934 2,074,253 Dallenbach Mar. 16, 1937 2,108,900 Peterson Feb. 22, 1933 2,122,538 Potter July 5, 1938 2,250,698 Berline July 29, 1941 2,333,295 Chevigny Nov. 2, 1943 2,394,908 Gavin Feb. 12, 1946 2,402,600 Chevigny et al June 25, 1946