US2504894A

US2504894A - Electronic tube apparatus

Info

Publication number: US2504894A
Application number: US625910A
Authority: US
Inventors: David H Sloan
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1945-10-31
Filing date: 1945-10-31
Publication date: 1950-04-18
Anticipated expiration: 1967-04-18
Also published as: BE472428A; FR947275A; GB632210A

Description

April 8, 1950 D. H. SLOAN 2,504,894

ELECTRONIC TUBE APPARATUS Filed Oct. 31, 1945 3 Sheets-Sheet l WITNESSES: INVENTOR D7577 BY April 1950 DLH. SLOAN 2,504,894

ELECTRONIC TUBE APPARATUS F1163 Oct. 31, 1945 3 Sheets-Sheet 2 WITNESSES:

INVENTOR April 18, 1950 D. H. SLOAN 2,504,894

ELECTRONIC TUBE APPARATUS Filed Oct. 31, 1945 3 Sheets-Sheet 3 57 J19 7-7 E| I? 6 a5 fl :n /2

WITNESSES: INVENTOR 7 W. M flaw/db. 5/0427.

Patented Apr. 18, 1950 UNITED STATES PATENT OFFICE ELECTRONIC TUBE APPARATUS Application October 31, 1945, Serial No. 625,910

18 Claims.

Thi invention relates to electronic tube apparatus and has particular relation to high frequency apparatus involving a magnetron tube.

In a magnetron tube constructed in accordance with the teachings of the prior art, the anode may be mounted within an anode chamber, such as a copper cylinder which serves both as a resonant cavity and as a vacuum envelope. Operation of the magnetron requires a substan tially uniform magnetic field within the copper cylinder and substantially parallel to the axis thereof. To obtain such a field, two arrangements are in common use. In one arrangement, an air core solenoid winding surrounds the copper cylinder without important iron structures in the field. The other arrangement includes an iron yoke with magnet coils wound thereon, the yoke being arranged to have pole pieces between which the copper cylinder is positioned.

To introduce the output of the prior magnetron into a hollow wave guide, a coaxial line coupling section is provided with the center conductor thereof extending into and forming a loop within the copper cylinder at one end and extending into and forming a loop within the wave guide at the other end.

The apparatus described may be operated satisfactorily, being usually employed in producing high frequency oscillations. However, the magnetic circuit arrangement is rather clumsy and interferes with the arrangement of other parts of the apparatus nearby. Moreover, the coaxial coupling section requires various tuning and matching elements and is always a source of trouble. In addition, the coaxial coupling section tends to decrease the band width of the apparatus.

It is, accordingly, an object of my invention to provide a new and improved magnetron apparatus.

Another object of my invention is to provide a new and improved magnetic circuit for use with an electronic tube, such as a magnetron.

A further object of my invention is to provide a new and improved arrangement for coupling a magnetron to a load device.

Still another object of my invention is to provide a new arrangement for coupling the output of a high frequency generator into a wave guide.

More specifically, it is an object of my invention to provide a novel magnetron tube apparatus with an improved magnetic circuit arrangement and a more efiioient and less troublesome coupling of the magnetron tube to the load.

winding surrounds the anode chamber of a magnetron tube. The winding has an external shell of magnetic material cooperating with pole pieces of magnetic material built into the magnetron tube to effect a substantially complete enclosure of magnetic material about the winding and anode chamber, with the pole pieces ar ranged to establish a substantially uniform field within the chamber. With such an arrangement, a short high frequency lead of the resonant circuit of the magnetron is brought out of the anode chamber into the field free space just outside the enclosure of magnetic material to be coupled directly into the load equipment, such as a wave guide or a cavity resinator, as by an output coupling loop formed in said lead. Further improvement in the coupling may be provided by means of vanes or dome-like structures mounted on the output coupling loop to contribute capacitive coupling in proper phase to add to the magnetic coupling provided by the loop.

The novel features, which I consider cha teristic of my invention, are set forth with greater particularity in the accompanying claims. The invention itself, however, together with additional advantages and objects thereof may be better understood from the following description of specific embodiments when read in connection with the accompanying drawings in which:

Figure 1 is a cross-sectional view of apparatus including a magnetron tube of the split-anode type arranged to supply energy to a wave guide.

Fig. 2 is a partial end view of the apparatus taken along line 11-11 of Fig. 1.

Fig. 3 is a partial sectional view taken along theline III-III of Fig. 1.

Fig. 4 is a cross-sectional view taken along the line IVIV of Fig. l, the view of Fig. 1 having been taken along the line I-I of Fig. 2, and

Figs. 5 and 6 are partial sectional views illustrating alternate coupling arrangements.

A magnetron of the split-anode type is shown in the drawings and comprises a generally cylindrical anode chamber ll comprising a pair of end plates l3 and i5 and a connecting cylindrical wall it therebetween. A ring-like magnetic coil Iii surrounds the cylindrical wall I! of the anode chamber it. An external shell of magnetic material, such as iron or steel, is provided about the coil l9 and includes a pair of flat ring-like plates 2! l on each end and another ring member 23 about the circumference of the coil 19. The coil In accordance with my invention, a solenoid and shell are conveniently held together by means the anode chamber I'l. mounted on the cathode 25,- as shown in Fig. 4,

3 of supporting plates 22 at each end connected by bolts 24.

The two end plates i3 and I5 of the anode chamber H are also of magnetic material and cooperate with the external shell about the coil 19 to provide a substantially complete enclosure of magnetic material about the coil l9 and chamber ll. Consequently,-the end plates l3 and I5 serve as pole pieces and a magnetic field is established within the anode chamber between the two end plates which is substantially uniform and substantially parallel to the axis of the anode chamber.

Inasmuch as the end plates 13 and I5 of the anode chamber, which serve as pole pieces, are

of magnetic material, it is extremely" desirable from the standpoint of manufacturing of the tube to employ the same material for the cylindrical wall l1. However, it is necessary to avoid harmful distortion as a result of shunting the magnetic field within the anode chamber between the two end plates l3 and i5. I have found that :m'agnetic'material may be used forthe cylindrical wall I! interconnecting the two end plates if the wall is of such dimensions that it is saturated by the magnetic flux flowing 'therethrough.

-With such an arrangementthe usual magnetomotive'force remains effective across the region between the end'plates l3 and i5 and harmful distortion of the field'is avoided.

A generally cylindrical cathode '25 of the secondary'emitter type is mounted-coaxially within A small filament '21 is to provide electrons for initiating oscillations within the tube. The cathode 25 is supported on a long hollow stem 29 which extends through an opening 3! in the upper end plate I5 of the anode chamber H, being secured to the end plate l5 by a tubular member 33'but insulated therefrom "stem 29 and which are to be cooled by the passage of cooling fluid through pipes 43.

Aspreviously indicated, the magnetron is of the split-anode type. The anode includes a pair of

anode members

45 and 41 of highly conductive material, such as copper, arranged to form a generally cylindrical structure surrounding the cathode 25 as shown in Fig. 3, the inner surface of each

anode member

45 and 41 approximating a semi-cylinder. Each ofthe

anode members

45 and 41 is supported by a corresponding con-- ductive post Hand" 5!", respectively, mounted on theupper end plate l5'of the anode chamber H. The posts 49 and 5-! provide inductance for the "resonant circuit of the magnetron and they are positioned substantially parallel to the axis of the anode: structure.

Apair of frequency leads in the form of

tubes

53 and 55,'preferably of copper, extend from the

anode members

45 and 41, respectively, through openings 51 and 59 in the lower end plate l3 of the anode chamber ll. Below the lower end plate l3; each of the

tubes

53 and 55 forms a loop and is-securedto'the'center of the end plate l3. The ends of'the tubes- 53 and 55' forming the 'loops, open into opposite ends of a passageil provided within the lower end plate l3. The posts 49 and 5! on which the

anode members

45 and 41 are mounted, are hollow and a passage 63 connecting therewith is also provided through each of the

anode members

45 and 41 to the interior of the

tubes

53 and 55, respectively. Suitable cooling fluid, such as water, may then be circulated from supply lines 65 connected to posts '49 and 5! through the posts, the anode members 45 and M, the

tubes

53 and 55 and the end plate 13.

For purposes of convenience in manufacture, the anodemembers may be made of two parts with the cooling fluid passage extending therebetween 'as illustrated. In some cases, it may also be desirable to have a supporting post and at least part of the corresponding anode member ported in an internally threaded rotatable sleeve 15. mounted on end plate l5. Rotation of the sleeve 15 causes the screw E3 to be moved up or down resultingin an up or down movement of the tuning ring 6'! parallel to the axis of the anode structure. A plurality of spring-biased guide pins 16, shown in Fig. 3, are mounted radially on said tuning ring 6! with their outer ends ar- .ranged to engage the cylindrical wall ll of the anode chamber H to guide the tuning ring during movement thereof. A guide post ll mounted .on..the.upper end plate It serves to guide the movement of the supporting ring H, and a pair of bellows 79 about the pipes 69 and secured to the upper end plate !5 permits such movement without loss of the vacuum within the chamber as discussed hereinafter. The movement of the tuning ring is preferably arranged so that in its extreme upper position, the ring is positioned about the posts 49 and 5i and in its extreme lower position, it surrounds the

anode members

45 and 41.

The outer surfaces of the

anode members

45 and 41 are preferably substantially uniform in a direction parallel to the axis of the structure. With the posts 49 and 5| substantially parallel to the axis, the posts are preferably so positioned and theouter surfaces of the anode members have such a configuration, that a considerable portion, about two-thirds in the embodiment illustrated, of the surface of each post forms, in

effect, an extension of the outer surface of the corresponding anode member. The opening in the tuningring 6'! then preferably has the same general configuration as the combined outer surfaces of the anode members, as shown in Fig. 3,

1 and is arranged so that when the ring surrounds the anode members, which circuit in many cases is included as part of the magnetron itself. In 'theillustrate'd arrangement, the resonant circult is included within the tube and comprises the supporting posts 49 and 5!, the

anode members

45 and 41 and

tubes

53 and 55. In this resonant circuit the inductance provided by posts 49 and 5| and the capacitance between the anode members are of primary importance.

Now when the tuning ring 61 is in its extreme upper position, as illustrated in Fig. 1, it is closely adjacent to and partially surrounds each of the inductive posts 49 and 5|. Consequently, the tuning ring 61 tends to obstruct an electromagnetic field about each of the posts and so causes the inductance of the posts to be at a minimum. At the same time, the tuning ring Bl is a maximum distance from the

anode members

45 and 41 so the capacitance at the anodes is at a minimum. As a result, the resonant circuit is tuned to resonance at a relatively high frequency.

On the other hand, when the tuning ring 61 is in its extreme downward position, the anode capacity is greatly increased while the inductance of the posts is also increased. As a result, the resonant circuit is tuned to resonance at a relatively low frequency. Any desired tuning between these two limits may be obtained by adjustment of the tuning ring 61 between these two positions. This tuning arrangement is described in my copending application, Serial No. 625,909, filed October 31, 1945.

As previously indicated, the upper end plate l5 of the anode chamber is arranged to permit a vacuum within the chamber. However, the

tubes

53 and 55 extend through openings 5'! and 59 in the lower end plate I3 so that the anode chamber is not vacuum tight. For this reason, a dome 8! of material transparent to electromagnetic waves, prefer'ably glass, is mounted across the lower end plate l3 with its base sealed to a ring 83 of a suitable alloy having substantially the same coefiicient of expansion as the dome material, which ring is secured to the edge of end plate l3 through concentric rings 95 and 81. The dome 8| surrounds the output coupling loops formed by

tubes

53 and 55 and completes a vacuum tight space including the interiors of the dome and the anode chamber, though of course, electromagnetic waves may pass through the dome. This space is to be evacuated by means of a vacuum pump, not shown, which is associated therewith.

The magnet coil i9 is arranged to be cooled by air under pressure through supply lines 68, the air passing through passages 19 provided throughout the coil and out a plurality of openings T2 in ring 85. The openings 12 are arranged about the circumference of the seal at the base of the glass dome BI and serve to cool the seal.

The tuning ring 67 is adapted to be cooled by cooling fluid supplied through the supporting pipes 69 and circulated through a passage 90 in the tuning ring.

Because of the enclosure of magnetic material about the coil l9 and the anode chamber II, a

wave guide or other device constituting the load,

may be positioned closely adjacent to the anode chamber and directly coupled with the resonant circuit. A hollow wave guide89 which constitutes the load in the illustrated arrangement is provided in the form of a rectangular pipe of conductive material and has anend secured to the supporting plate 22 for the coil E9. The glass dome SI and the coupling loops of

tubes

53 and 55 within the dome, project into the guide 89. This provides a magnetic coupling between the magnetron and the guide which is free from intermediate lines or branch circuits. By such coupling the frequency band over which the coupling is correct is greatly increased and a complex adjustment is not required for proper loading.

The coupling loops of

tubes

53 and 55 are shown as connected to the lower end plate l3 in the center thereof. However, this center connection may be eliminated if desired and the two tubes connected directly together. The center connection is belived to be preferable however to provide a convenient path for the circulation of cooling fluid and a desirable structural support. In addition, the grounding of the coupling loops at approximately the center between the connection thereof to the two anode members tends to suppress the undesirable symmetric mode of oscillation of the magnetron, that is, the mode in which both anode members are positive at the same time.

A sheet metal shield is connected across the outer ends of the coupling loops to reduce the inductance provided by these loops in the resonant circuit. The upper edges of this shield have portions 93 thereof adjacent the openings 51 and 59 in the lower end plate l3 through which the

tubes

53 and 55 extend. These edge portions 93 are positioned crosswise of openings 5'! and 59 to aid in preventing electrons from the interior of the anode chamber from escaping into the dome 8!. The ring 8'! is preferably copper plated steel and extends just inside the alloy ring 83 to which the base of the glass dome BI is sealed to prevent overheating of the seal by eddy currents in the alloy ring.

The output loops of

tubes

53 and 55 are part of the main resonant circuit of the magnetron and couple the magnetron to the magnetic field within the guide 89 which may have the familiar rectangular cross-section. If it is desired to increase the coupling to the rectangular guide 89, two vanes 95 and 91 may be attached to the loops as in Fig. 5. These vanes 95 and 9'! extend parallel to the wider walls 99 of the guide with one vane relatively close to each wall 59. The vanes then contribute a capacitive coupling to the electric field in the guide 89 in proper phase to add to the magnetic coupling provided by the coupling loops of

tubes

53 and 55. This increased coupling is obtained without increasing the self-inductance of the output loops and so enables the magnetron to operate at higher frequencies. This arrangement provides a more uniform coupling over the wave length spectrum of the magnetron because the magnetic coupling is tighter at lower frequencies and the capacitive coupling is tighter at higher frequencies.

Another arrangement for increasing the direct coupling to the wave guide is shown in Fig. 6. Here a metal dome-like structure Nil is attached to the output loops. The sides of the dome structure provide a capacitive coupling with the walls of the guide 89 with the improvements as described in connection with the capacitive coupling of Fig. 5. In addition, the dome structure effectively short circuits the space within it so that the inductance of the output loops is further reduced. This provides an additional improvement in uniformity of coupling over a wider range.

Although I have shown and described a preferred embodiment of my invention, I am aware that many modifications thereof may be made and that it may be applied to other electronic tubes without departing from the spirit of the invention. I, therefore, do not intend to limit my invention to the specific embodiment and application described herein.

I claim as my invention: 1. Electronic tube apparatus for supplying high frequency oscillations to a load comprising a vacuum tight envelope including a, chamber, a magnet coil immediately surrounding said chamber and having an external shell of magnetic material, said chamber including a pair of end plates of magnetic material cooperating with said shell to provide a substantially complete enclosure of magnetic material about said coil and chamber, whereby a field may be established within said chamber between said plates, and a resonant circuit partially within said chamber and including an output coupling loop extending through one of said end plates for direct magnetic coupling to said load.

2. Electronic tube apparatus for supplying high frequency oscillations to a hollow, conductive load member comprising a vacuum-tight envelope iorming a chamber, a magnet coil immediately surrounding said chamber and having an external shell of magnetic material, said chamber including a pair of end plates of magnetic material connected with said shell to provide a substantially complete enclosure of magnetic material about said coil and chamber, whereby a field may be produced within said chamber between said plates, and a resonant circuit partially within said chamber and including an output coupling loop extending through one of said end plates, said envelope also including a dome of material transparent to electromagnetic waves sealed across said one end plate and surrounding said output loop, said dome being adapted to project into said hollow load member whereby said loop provides direct magnetic coupling between said circuit and load member.

3. Electronic tube apparatus for supplying high frequency electromagnetic oscillations to a hollow, conductive load member comprising a vacuum tight envelope forming a cylinder-like chamber, a magnet coil coaxial with and immediately surrounding said chamber and having an external shell of magnetic material, said chamber including a pair of end plates of magnetic material connected with said shell to provide a substantially complete enclosure of magnetic material about the coil and chamber whereby a substantially uniform magnetic field may be established within said chamber between said end plates, and

a resonant circuit partially within said chamber and including an output coupling loop extending through one of said end plates, said envelope also including a dome of material transparent to electromagnetic waves sealed across said one end plate, said dome being adapted to project into said load member whereby said loop provides a direct magnetic coupling between said circuit and load member.

4. Electronic tube apparatus for supplying high frequency electromagnetic oscillations to a hollow, conductive load member comprising a vacuum tight envelope forming a cylinder-like chamber, a magnet coil coaxial with and immediately surrounding said chamber and having an external shell of magnetic material, said chamber including a pair of end plates of magnetic material connected with said shell to provide a substantially complete enclosure of magnetic material about the coil and chamber, said chamber also including a generally cylindrical wall of magnetic material interconnecting said end plates and saturable by the magnetic fiux therethrough while said coil is energized, whereby a substantially uniform magnetic field maybe established within said chamber between said end plates, and a resonant circuit partially within said chamber and including an output coupling loop extending through one of said end plates, said envelope also including a dome of material transparent to electromagnetic waves sealed across said one end plate, said dome being adapted to project into said load member whereby said loop provides a direct magnetic coupling between said circuit and load member.

5. Electronic tube apparatus for supplying high frequency electromagnetic oscillations to a hollow, conductive load member, comprising a vacuum-tight envelope including a chamber, a mag net coil immediately surrounding said chamber and having an external shell of magnetic material, said chamber including a pair of end plates of magnetic material cooperating with said shell to provide a substantially complete enclosure of magnetic material about said coil and chamber, whereby a field may be established within said chamber between said plates, a resonant circuit partially within said chamber and including an output coupling loop extending through one of said end plates and adapted to project into said load member to provide an inductive coupling of the resonant circuit to the magnetic field within said load member, and a pair of conductive vanes attached to said loop substantially perpendicular to the plane of the loop and arranged to provide a capacitive coupling to the electric field within said load member in additive phase with the inductive coupling of said loop.

6. Electronic tube apparatus for supplying high frequency electromagnetic oscillations to a hollow, conductive load member, comprising a vacuum-tight envelope including a chamber, a magnet coil immediately surrounding said chamber and having an external shell of magnetic material, said chamber including a pair of end plates of magnetic material cooperating with said shell to provide a, substantially complete enclosure of magnetic material about said coil and chamber, whereby a field may be established within said chamber between said plates, a resonant circuit partially within said chamber and including an output coupling loop extending through one of said end plates and adapted to project into said load member to provide an inductive coupling of the resonant circuit to the magnetic field within said load member, and a conductive dome-like structure attached to and surrounding said loop to provide a capacitive coupling to the electric field within said load member in additive phase with the inductive coupling of said loop.

7. Electronic tube apparatus for supplying high frequency electromagnetic oscillations to a hollow, conductive load member, comprising a vacuum-tight envelope including a chamber, a magnet coil immediately surrounding said chamber and having an external shell of magnetic material, said chamber including a pair of end plates of magnetic material cooperating with said shell to provide a substantially complete enclosure of magnetic material about said coil and chamber, whereby a field may be established within said chamber between said plates, a resonant circuit partially within said chamber and including an output coupling loop extending through one of said end plates, said envelope also including a dome of material transparent to electro-magnetic waves sealed across said one end plate and surrounding said loop and adapted to project into said load member whereby the loop provides an inductance coupling of the resonant circuit to the magnetic field within said load member, and a pair of conductive vanes attached to said loop within said dome substantially perpendicular to the plane of the loop and arranged to provide a capacitive coupling to the electric field Within said load member in additive phase with the inductive coupling of said loop.

8. Electronic tube apparatus for supplying high frequency electromagnetic oscillations to a hollow, conductive load member, comprising a vacuum-tight envelope including a chamber, a magnet coil immediately surrounding said chamber and having an external shell of magnetic material, said chamber including a pair of end plates of magnetic material cooperating with said shell to provide a substantially complete enclosure of magnetic material about said coil and chamber, whereby a field may be established within said chamber between said plates, a resonant circuit partially within said chamber and including an output coupling loop extending through one of said end plates, said envelope also including a dome of material transparent to electromagnetic waves sealed across said one end plate and surrounding said loop and adapted to project into said load member whereby the loop provides an inductive coupling of the resonant circuit to the magnetic field within said load member, and a conductive dome-like structure attached to and surrounding said loop within said dome to provide a capacitive coupling to the electric field within said load member in additive phase with the inductive coupling of said loop.

9. In combination, a hollow, conductive load member, a vacuum-tight envelope forming a chamber, a magnet coil immediately surrounding said chamber and having an external shell of magnetic material, said chamber including a pair 4 of end plates of magnetic material connected with said shell to provide a substantially complete enclosure of magnetic material about said coil and chamber, whereby a field may be produced within said chamber between said plates, and a resonant circuit partially within said chamber and including an output coupling loop extending through one of said end plates, said envelope also including a dome of material transparent to electromagnetic waves sealed across said one end plate and surrounding said output loop, said dome projecting into said hollow load member whereby said loop provides direct magnetic coupling between said circuit and load member,

10. In combination, a hollow, conductive load member. a vacuum-tight envelope forming a cylinder-like chamber, a magnet coil coaxial with and immediately surrounding said chamber and having an external shell of magnetic material, said chamber including a pair of end plates of magnetic material connected with said shell to provide a substantially complete enclosure of magnetic material about the coil and chamber whereby a substantially uniform magnet c field may be established within said chamber between said end plates, and a resonant circuit partially within said chamber and including an output coupling loop extending through one of said end plates, said enevelope also including a dome of material transparent to electromagnetic waves sealed across said one end plate, said dome projecting into said load member whereby said loop provides a direct magnetic coupling between said circuit and load member.

5 having an external shell of magnetic material,

said chamber including a pair of end plates of magnetic material connected with said shell to provide a substantially complete enclosure of magnetic material about the coil and chamber,

said chamber also including a generally cylindrical wall of magnetic material interconnecting said end plates and saturable by the magnetic flux therethrough while said coil is energized, whereby a substantialy uniform magnetic field may be establishing within said chamber between said end plates, and a resonant circuit partially within said chamber and including an output coupling loop extending through one of said end plates, said envelope also including a dome of material transparent to electromagnetic waves sealed across said one end plate, said dome projecting into said load member whereby said loop provides a direct magnetic coupling between said circuit and load member.

12. Electronic tube apparatus for supplying high frequency oscillations to a hollow, conductive load member comprising a vacuum-tight envelope having therein a chamber, a magnet coil immediately surrounding said chamber and having an external shell of magnetic material, said chamber including a pair of end plates of magnetic material connected with said shell to provide a substantially complete enclosure of magnetic material about said coil and chamber,

whereby a field may be produced within said chamber between said plates, and a resonant circuit partially within said chamber and including an output coupling loop extending through one of said end plates, said loop consisting of at least two sections both terminating substantially at the center of said last-named end plate and each consisting of a sub-loop extending from a region in said last-named end plate, displaced from said center, to said center, said envelope also in- 5 eluding a dome of material transparent to electromagnetic waves sealed across said one end plate and surrounding said output 100p, said dome being adapted to project into said hollow load member whereby said loop provides direct 5 magnetic coupling between said circuit and lead member.

13. Electronic tube apparatus for supplying high frequency oscillations to a hollow, conductive load member comprising a vacuum-tight envelope having therein a chamber, a magnet coil vide a substantially complete enclosure of magnetic material about said coil and chamber, whereby a field may be produced within said chamber between said plates, and a resonant circuit partially within said chamber and including an output coupling loop extending through one of said end plates, said loop consisting of at least two sub-loops, said envelope also including a dome of material transparent to electromagnetic waves sealed across said one end plate and surrounding said output loop, said dome being adapted to project into said hollow load member whereby said loop provides direct magnetic coupling between said circuit and load member.

14. Electronic tube apparatus for supplying high frequency oscillations to a hollow, conductive load member comprising a vacuum-tight envelope having therein a chamber, a magnet coil immediately surrounding said chamber and having an external shell of magnetic material, said chamber including a pair of end plates of magnetic material connected with saidshell to provide a substantially complete enclosure ofma netic material about said coil and chamber, whereby a field may be produced within said chamber between said plates, and a resonant circuit partially within said chamber and including an output coupling loop extending through one of said end plates, said loopconsisting' of at least two sub loops connected together at a region in said last-named end plate, said envelope also including a dome of material transparent to electromagnetic waves sealed across said one end plate and surrounding said output loop, said dome being adapted to project into said hollow load member whereby said loop provides direct magnetic coupling between said circuit and load member.

15. Electronic tube apparatus for supplying high frequency oscillations to a hollow, conductive load member comprising a vacuum-tight ens velope having therein a chamber, a magnet coil immediately surrounding said chamber and having an external shell of magnetic material, said chamber including a pair of end plates of magnetic material connected with said shell to provide a substantially complete enclosure of magnetic material about said coil and chamber, whereby a field may be produced within said chamber between said plates, and a resonant circuit partially within said chamber and including an output coupling loop extending through one of said end plates, and means connected'to said loop to reduce the influence of the inductance of said loops on said resonant circuit; said envelope also including a dome of material transparent to electromagnetic waves sealed across said one end plate and surrounding said output loop, said dome being adapted to project into said hollow load member wherebysaid loop provides direct magnetic coupling between said circuit and load member.

16. Electronic tube apparatus for supplying high frequency oscillations to azhollow, conductive load member comprising a vacuum-tight envelope having therein a chamber, a" magnet coil immediately surrounding said chamber and having an external shell of magnetic material, said chamber including a pair of end plates of magnetic material connected with said shell to provide a substantially complete enclosure of magnetic material about said coil and chamber, whereby a field may be produced within said chamber between said plates, and a resonant circuit partially within said chamber and including an output coupling loop extending through one of said end plates, and a metal shield connected across the outer ends of said'loop to reduce the influence of the inductance of said loops on said resonant circuit, said envelope also including a dome of material transparent to electromagnetic waves sealed across said one end plate and surrounding said output loop, said dome being adapted to project'into said hollow 12 load member whereby said loop provides direct magnetic coupling between said circuit and load member.

17. Electronic tube apparatus for supplying high frequency oscillations to a hollow, conductiveloadmember comprising a vacuum-tight envelope having therein a chamber, a magnet coil immediately surrounding said chamber and having' an external shell of magnetic material, said chamber including a pair of end plates of magnetic material connected with said shell to provide a substantially complete enclosure of magnetic material about saidcoil and chamber, whereby a field may be produced within said chamber between said plates, and a resonant circuit partially within said chamber and including an output coupling. loop extending through one of said end plates, said resonant circuitine eluding an anode member and the terminals of said loop being connected to said anode mem-- bers, saidenvelope also including a dome of ma-. terial transparent to electromagnetic waves sealed. across said one end plate and surrounding: said: output loop, said dome being adapted to'project into'said hollow load'member whereby said loop provides direct magneticv coupling between said'lcircuit and load member;

18. In combination, a vacuum-tight envelope forminga chamber, a magnet coil immediately surrounding, said: chamber and having an external shellof magnetic material, said chamber including a pair of end plates of magnetic material connected with saidshell to provide a substantially complete enclosure of magnetic material about said coil and chamber, whereby a field may be produced-within said chamber between said plates, and a resonant circuit partially within said-chamber and including an output coupling loop extending through one of said end plates, said envelope also including a dome of material transparent to electromagnetic waves sealed'across said one endplate and surrounding: said-output-loop, saiddome being adapted to-project into a hollow load member whereby said loopprovides direct-magnetic coupling-between said circuit and load member.

DAVID H. SLOAN.

REFERENCES CITED The following references. are of record in the file of this patent:.

UNITED STATES PATENTS Number Name Date 841,386 De Forest Jan. 15, 1907' 2,103,303 Steenbeck Dec. 28, 1937 2,305,884 Litton Q. Dec. 22, 1942 2,352,657" Potts July 4, 1944 2,391,016 Ginzton et a1 Dec.'l8', 1945 2,406,277 Bondley Aug.'20, 1946 2,414,085 Hartman Jan. 14, 1947 2,424,886 l-lan'scll July 29, 1947- 2,43l,94l Kihn Dec. 2, 1947 2,433,074 Tuller Dec. 23, 1947 FOREIGN PATENTS Number Country Date 443,077 Great Britain Feb. 20, 1936