US2957997A

US2957997A - High frequency electric discharge device

Info

Publication number: US2957997A
Application number: US275522A
Authority: US
Inventors: Robert E Manfredi
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1952-03-08
Filing date: 1952-03-08
Publication date: 1960-10-25
Anticipated expiration: 1977-10-25

Description

m, 9 20w wV//// 5 .Q t M MNA-MM 5. 4/ 5 ,n V H- am 9, 9 mw .D nl //f////////HH/ lll e b mr o M R 1 M Vl n l l R. E. MANFREDI Filed March 8, 1952 HIGH FREQUENCY ELECTRIC DISCHARGE DEVICE oct. 25, 1960 His Attorney.

general requires a larger structure.

HIGH FREQUENCY ELECTRIC DISCHARGE DEVICE Robert E.,Manfredi, Schenectady, NX., assignor to General Electric Company, a corporation of New York Filed Mar. 8, 1952, Ser. No. 275,522

9 Claims. (Cl. 313286) My invention relates. to improved electric discharge devices `particularly suited for high frequency applications.

,fIn recent years, there has been extensive development .'of high frequency communication equipment with the result that there has been a continual demand for electric discharge devices capable of delivering higher and higher power outputs at higher and higher frequencies. Successful operation at higher frequencies requires in general that the lead inductance be low, that the interelectrode capacity below, and that the spacing between the electrodes be small. Atthe same time, the higher power requirements require large emission currents which to some extent .makes itnecessary to operate at higher temperatures or to provide larger electrodes. It is readily apparent that kthe requirements for high power and high frequency foperation are somewhat inconsistent one with the other in that the requirements for high frequency in general require a more compact structure, while higher power in Also, attempts to make more and more compact structures have increased the problems involved in the actual assembly of the various components of electric discharge devices.

According to an important aspect of my invention, I

provide an improved electric discharge device which is ,operable at high frequencies, with a high power output vandwhich is readily assembled by production methods.

anY improved envelope and terminal construction for a j highfrequency electric discharge device.

" Itis a further object of my invention to provide for lthe accuratehspacing of the electrodes of the device and 'to providerlow inductance from the various electrode ""terminals to the electrodes themselves. Y Y' It is a'still further object of my invention to provide an improved method of assembling and spacing a plurality -of electrodes of anelectric discharge device.

' vIt is another object of my invention to provide a new and improved cathode assembly, particularly suited for `high,V power, high frequency discharge devices.

Further objects and advantages of my invention will kbecome apparent as the following description proceeds, reference being had to the accompanying drawing, in

which Fig. 1 is an elevational view in section of electric Y discharge device embodying my invention; Fig. 2 is an enlarged elevational view, partially broken away, showing the cathode employed in the device of Fig. 1; Fig. 3 is an enlarged side elevational view of a cathode supporting part shown in Fig. l; and Fig. 4 is a top plan view of the control grid shown in Fig. 1.

Referring now to the drawing, I have shown my inventionembodied in an electric discharge device particularly 1United States Patent() f It is ,an important object of my invention to provide ICC seen that the envelope includes a generally cylindrical anode structure designated by the numeral 1, an annular anode terminal 2, an anode to screen grid insulator in the form of a ceramic cylinder 3, and a screen grid terminal 4. This much of the envelope forms the anode subassembly 5, one of the major subassemblies of the device, and is completed separately from the lower subassembly Vdesignated generally by the numeral 6. The novel features of the anode are more fully described and claimed in my U.S. Patent No. 2,731,244 issued January 17, 1956, on my application Serial No. 275,523, led concurrently herewith and assigned to the assignee of this application.

The lower subassembly includes a control grid support 7 of cylindrical form. The grid supporting cylinder is formed of good conducting material such as copper and as illustrated is of relatively heavy construction. A screen grid support and terminal member 8 is bonded to the upper end of cylindrical insulator 9, which is in turn joined to the lower outside surface of the grid support 7 by means of a grid terminal ring 10.

In a similar manner, the cathode and heater terminals are supported in mutually insulated relation from the upper end and inner surface of the grid support 7. As illustrated, the control grid-cathode insulator 11 is bonded to a metal ring 12 which is brazed at its upper end to Vthe upper and inner surface of the grid supporting cylinder 7. The lower end of the insulator 11 is joined to a cylindrical heater and cathode terminal member 13 provided at its lower end with a circular flange 14 to which is sealed the cylindrical insulator 15 which insulates the cathode from the heater terminal 17. The terminal 17 is joined to the lower end of a central supporting rod 18 which is in turn sealed to the ceramic cylinder 15 by means of a metal ring (19.

Before describing in detail the elements which make up the envelope of the electric discharge device and the manner in which they are assembled in accordance with the present invention, the electrode elements and their supports Within the discharge device will be described. The cathode is in the form of a hollow cylinder 20 substantially closed at its upper end and supported at its lower end from an annular collar 21 of refractory metal such as molybdenum. The collar is of smaller diameter at its lower extremity and is received within a relatively thin cathode supporting sleeve 22 which is brazed to the upper end of a generally cylindrical cathode support 23. The lower end of the member 23 is received within and brazed to the cathode terminal 13.

As shown more clearly in Fig. 2, the cathode cylinder 20 is provided at its lower end with slots 24 to facilitate assembly over the header 21. The cathode is also provided with circumferentially extending slots 25 and 26 near the lower and upper ends of the sleeve to minimize heat loss from the active cathode area to the support at the lower end and to the end cap at the upper end.

The heater for the cathode is in the form` of a double helix 27 of tungsten or other suitable wire. The ends of the heater wire are received within longitudinally extending grooves 28 formed in the upper enlarged portion of the collar and secured thereto asby welding (Fig. 3). A `Suitable overwinding of wire 29 received in a circumferential groove 30 may also be employed -if desired. It will be noted that the cathode sleeve 20 is joined to the large upper portion of the collar 21 so that the cathode and the ends of the heater are electrically joined to the collar 21 and by way of sleeves 22 and 23 to the cathode terminal 13. The upper end of the double helix is supported from a central heater support rod 31 which is received within and brazed to the larger heater support rod 18. The heater rod is maintained -in-a central position .byr'means of a `suitable annular ceramic lmember 32received within'the cylindrical member 23 and held in 3 position by van eyelet 33 brazed to the heater support rod 18.

The control grid is in the form of a generally hollow cylindrical structure made up of a plurality of longitudinally extending conductors 34 which are secured to a cylindrical collar 35 at .the lower vend Vand which are bound together by an overwind of wire 36 `at the upper end thereof. The ends 34 of the individual grid :wires labove the overwind are shorter than the radius of the grid and are bent inwardly in a radial direction in overlapped relationship and resistance Welded together. The grid collar 35 is supported from the upper end of a grid supporting cone 37 having an outwardly extending flange 38 at the .lower end thereof resting on an inwardly -directed circular ilange 39 formed integrally with the grid supporting cyl-inder 7. The grid is secured in position by means of suitable holding screws 40 extending through anges 38 and 39 and an overlying washer 41.

The screen grid is of generally similar construction including the same number of longitudinally extending wires 42 bonded to a `screen grid collar 43 at the lower end thereof and secured together by a wire overw-ind 44 4at the upper end. The screen grid is not closed at all at its upper end as was the case with the control grid, thus allowing maximum heat radiation from the top of the control grid. A screen grid supporting cone 45 is secured to the collar 43 of the screen grid and provided at its lower end with an outwardly extending flange 46 which rests upon an inwardly directed ange 47 on an annular screen grid support 48 bonded to the inner surface of the cylindrical screen grid terminal member 8.

In order to provide for easy rotational adjustment of the screen grid relative to the control grid for the purpose of aligning the screen grid wires 42 with the control grid wires 34, the screen grid cone 45 is secured to the flange 47 by means of a collar 49 recessed on its lower and inner surface to receive the outwardly extending flange 46 of the screen grid cone. The collar is secured by suitable screws 49 to the screen grid supporting flange 47, and, as will be readily apparent, permits the easy rotational adjustment of the screen grid cone 45.

It will also be noted that the supporting

cones

37 and 45 for the control grid and screen grid extend in closely spaced relation over an extended area and in this way provide very close coupling between these two grids with respect to high frequency voltages. In this Way, both grids may be maintained readily at the same high frequency potential.

The general organization and construction of the various components of an electric discharge device embodying my invention have been described. A more detailed description of some of the component elements and the manner in which they are assembled will serve to further emphasize certain of the features and advantages of my invention. It should be pointed out at this time that all of the bonds between the ceramic members and the metal members are accomplished in a Single brazing operation along with the making of the joints between the various metal elements of the envelope Iby use of a suitable brazing material such as a silver solder. The brazing to the ceramic is made possible by the prior metalizing of the ceramic in the region to be bonded. While many methods have been suggested in the prior art for metalizing ceramic members for this purpose, a particularly effective method involves the application of a powdered mixture of manganese and molybdenum to the regions to be bonded and heating the ceramic members thus coated in a hydrogen atmosphere. This coating may be built up by one or more plating steps, if desired, prior to the brazing operation. This method of metalizing and bonding to ceramics is described in detail and claimed in copending Nolte application, Serial No. 238,871, liled July 27, 1951, and assigned to the assignee of this application.

As previously pointed out, the lower portion of the envelope is assembled as a separate subassembly 6. This portion of the envelope includes screen grid terminal member 8, ceramic cylinder 9, sealing ring 10, grid support 7, sealing ring 12, ceramic cylinder 11, sealing ring 13, ceramic cylinder 15, sealing ring 19, and heater support 18. In addition to these envelope and terminal members, this subassembly includes the cathode supports 22, 23, the spacer 32 and eyelet 33; also, the heater rod 31 which is brazed as a preliminary step to the heater rod 18.

The parts enumerated above are assembled in a suitable brazing fixture in an inverted position with respect to that illustrated in the drawing. The fixture is provided with suitably spaced supporting surfaces for engaging the following surfaces of the subassembly: the surface 50 of the screen grid terminal, the supporting liange 47 of the screen support 48, supporting flange 39 of the grid support 7, the upper end of the cathode supporting cylinder 22, and the end of the heater supporting rod 31. It will be noted that when these surfaces are supported in an inverted position from that shown in the drawing, al1 of the remaining parts of the subassembly are self-supporting. To that end, the sealing rings including a portion of the screen grid terminal are indented at what is the upper edge of the ceramic, as shown in the drawing. These indentations are shown as providing

shoulders

51, 52 and 53, for example. The other sealing rings 10, 13 and 19 are inherently supported due to the decreasing dimensions of these members in the direction of the heater rod 18. It will be appreciated that the various brazed joints are made by positioning suitable solder rings or washers adjacent the joints as the subassembly is positioned on the iixture prior to the brazing operation.

It will be noted from an inspection of the drawing and the description that has preceded that the ceramic members are entirely free of any substantial stress due to the contact pressure that may be applied to the various terminals of the device. The anode contact is made with the outer flange 54 spaced from the anode-screen grid insulator 3. In a similar manner, the screen grid contact is made to the outer flange 55 of screen grid terminal 4. The remaining contacts are made against portions of the envelope which are supported by rigid metal members; the control grid contact being made to the sealing member 10 on the outer surface of the grid support 7, cathode contact being made to the ring 13 supported by the cathode support 23, and the heater terminal being made to a solid contact 17 at the end of the heater support rod 18.

It will be apparent from la consideration of the foregoing description that the invention provides, by virtue of the shape of the various members employed and the use of ceramic members which do not soften during the sealing process, a structure in which the relative positions are readily maintained and in which the lead-in inductance to the various electrodes is kept at a minimum. It will be noted that by connecting the cathode supports to the upper and inner surfaces of the grid supports, while the control grid-screen grid insulator is connected to the lower and outer surface of the control grid support, a much shorter structure is obtained. The final joint of the envelope structure is made at the lower edge of the two screen grid terminal members 4 and 8 and is designated by the numeral 56. After assembly, the tube is exhausted through a suitable exhaust tubulation 57 which is shown as protected by the surrounding cap 58.

While I have described a particular embodiment of my invention, it will be apparent to those skilled in the art that changes and modifications may be made Without departing from my invention in its broader aspects, and I aim `therefore in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

said support, a circular'flange of larger diameter and an intermediate portion connecting said ilanges, a hollow cylindricalceramic insulator received within said flange of larger diameter at one end and engaging said intermediate portion anda1.secoi1d sealing ring .having a circular flange encircling and bonded to lan outer surface of the said ceramic insulator at the opposite end thereof, said second ring having an inwardly projecting shoulder extending inwardly over and engaging the end of said insulator to position said ring relative to said insulator.

2. An envelope structure for an electric discharge device comprising a pair of metal sealing rings each including relatively smaller and larger concentric and axially displaced cylindrical anges joined by a frusto-conical section, an annular' ceramic insulator, the smaller ilange of one of said rings encircling one end of said insulator and the larger flange of the other of said rings encircling the other end of said insulator, said last-mentioned iianges being bonded to said insulator, a pair of hollow cylindrical conductive electrode supports, one of said supports comprising a wall section of said envelope and having an inner diameter larger than the outer diameter of said insulator and the other of said supports having an outer diameter smaller than the inner diameter of said insulator, the larger llange of said one of said rings and the smaller flange of said other of said rings being bonded respectively to an inner surface of said rst electrode support and to an outer surface of said second electrode support, and a third sealing ring having relatively smaller and larger concentric and axially displaced cylindrical flanges joined by a frusto-conical section, said smaller ilange of said third sealing ring being positioned about and bonded to the outer surface of said rst electrode support.

3. In combination, a hollow cylindrical electrode support, a metal sealing ring having a pair of relatively smaller and larger concentric and axially displaced cylindrical flanges, the larger of said flanges being bonded to a surface of said electrode support, an annular ceramic insulator, said smaller flange encircling said insulator at one end thereof and being bonded thereto, a second metal sealing ring including a pair of relatively smaller and larger concentric and axially displaced vcylindrical lianges joined by an intermediate cylindrical portion, the larger flange of said second ring encircling the other end of said ceramic insulator and being bonded thereto, a second hollow cylindrical electrode support, said intermediate portion of said second ring encircling said second electrode support and being bonded thereto, a third electrode support, said smaller flange of said second ring encircling said third electrode support and being bonded thereto.

4. In combination, a hollow cylindrical electrode support, a metal sealing ring constructed of relatively thinner material than said electrode support and having a pair of relatively smaller and larger concentric and axially displaced cylindrical llanges extending in opposite directions from an intermediate portion olf said ring, said ring being disposed in said electrode support and having said larger llange bonded to the inner surface of said support, an annular ceramic insulator havin-g an outer diameter substantially equal to the inner diameter of the smaller of said flanges, said smaller flange encircling said insulator at one end thereof, and inwardly projecting annular rib at the junction of said intermediate portion and the smaller of said llanges for positioning said ceramic insulator with respect to said sealing ring.

5. A cathode and heater assembly comprising a generally cylindrical support including a pair of longi- ,"tudinally extending recesses on oppositesides of said support,v arheater element having end portions received ,respectively in said recesses, a hollow cylindrical cathode surrounding said heater, said cathode having a plurality of circumferentially extending recesses adjacent opposite ends thereof for minimizing the transfer of heat to the closed end thereof and to said. support. f

6. A athod'e'rheater assembly comprising a generally cylindrical support, a pair of longitudinally extending leesses; onrs'aidwsupportLa heater` element having end portions received respectively in said recesses, a hollow cylindrical cathode member open at one end, said support being received Within the open end of said cathode and bonded thereto with said cathode surrounding said heater, said cathode having a plurality of circumferentially extending recesses adjacent said open end to minimize the transfer of heat to said support.

7. An electric discharge device envelope comprising a rigid cylindrical metal electrode support member constituting a Wall section of said envelope extending reentrantly in one end of said envelope, a pair lof metal sealing rings of a relatively thinner construction than said support member and each including relatively smaller and larger concentric and axially displaced cylindrical ilanges connected by a substantially frustoaconical portion, the smaller ange of one ring having the same diameter as the larger ange of the other ring, an annular ceramic insulator, the smaller ilange of one of said rings encircling one end of said insulator and the larger flange of the other of said rings encircling the other end of said insulator, said last mentioned ilanges being bonded to an outer surface of said insulator, and said seal-ing rings and insulators being reentrantly positioned in said support member with the largest of said flanges bonded to the inner surface of said support member adjacent the inner end thereof.

8. An electric discharge device comprising an envelope, electrodes in the envelope including an anode, grid and cathode, a first ceramic section included in the wall of said envelope, a tubular metal grid terminal having a flange encircling and bonded to the lower end of said rst ceramic section, a cathode stem comprising a metal stem member coaxial with the grid terminal, a metal supporting sleeve having la smaller outer diameter than the inner diameter of said iirst ceramic section and extending in said first ceramic section and said grid terminal, said sleeve having an edge registering with and being bonded to the lower edge of said grid terminal, a second ceramic section interposed between said stem member and said supporting sleeve, said second ceramic section having an inner diameter larger than the outer diameter of said stem member, metallic bonds uniting said second ceramic section to said stemmember and to said sleeve outwardly of the inner end of said sleeve whereby said inner end thereof is wholly disposed internally of said envelope, land said internally disposed end of said sleeve having a flange supporting said grid electrode.

9. An electric discharge device comprising an envelope, electrodes in said envelope including an anode, a pair of grids and a cathode, a rst cenamic section included in the wall of said envelope, a pair of axially displaced tubular metal grid terminals on said envelope, said irst ceramic section having the opposite ends thereof positioned in land bonded to the opposed ends of said grid terminals, a pair of coaxially spaced grid supports in said envelope, one of said supports being bonded to the internal surface of one of said grid terminals, the other of said supports comprising a metal sleeve of smaller diameter than said first terminal and constituting a wall section of said envelope extending in one end of said envelope, said sleeve having an edge registering with v7 the lower edge of the other of 4said grid terminals, a cathode stem comprising va metal Vstern member coaxial with the grid terminal, a second cenamic section having an outer diameter less vthan the inner diameter of Asaid support sleeve and an inner diameter larger than the outer diameter of said stem member, and sealing rings joining the inner end -of saidsecond ceramic section to the inner surface of said support sleeve andthe outer surface of said stem member.

References Cited in the file of this patent UNITED STATES PATENTS 2,445,237 Stone July 13, 1948 '8 2,517,334 Murdock Aug. 1, 1950 2,580,988 `Anderson Jan. 1, 1952 2,644,907 Drieschman et al. uly 7, 1953 '.5 FOREIGN PATENTS 773,488 France Sept. 3, 1934 OTHER REFERENCES Electronic Engineering, August 1941, pages 343, 344, '10 and 376.