US2569847A

US2569847A - High-frequency tetrode with built-in capacitor

Info

Publication number: US2569847A
Application number: US86231A
Authority: US
Inventors: William W Eitel; Jack A Mccullough
Original assignee: Eitel Mccullough Inc
Current assignee: Varian Medical Systems Inc
Priority date: 1949-04-08
Filing date: 1949-04-08
Publication date: 1951-10-02
Anticipated expiration: 1968-10-02

Description

Oct. 2, 1951 W W, E|TE| ETAL 2,569,847

HIGH-FREQUENCY TETRODE WITH BUILT-1N CAPACITOR Fired April s, 1949 s sheets-sheet 2 JNVENTORS` WML/,4M IM E/TEL By c/Ac/f A MECU az/GH ATTR/VEY Oct. 2, 1951 Filed April a, 1949 W. W. EITEL ETAL HIGH-FREQUENCY TETRODE WITH BUILT-IN CAPACITOR `3 Sheets-Sheet 5 Screen-Jro-ca+hode 6N ypass capaca''or.

4 8 Anode"\\` @0009@ 2 `/Cai'h'rnde Confrol grid /Screen grid Inpur resona'or Screen grid i'erminal Conrrol grid +erminal Tuning plunger ATTORNEY Patented Oct. 2, 1951 HIGH-FREQUENCY TETRODE WITH BUILT-IN CAPACITOR William W. Eitel, Woodside, and Jack; Ar. Mc- Cullough, Millbrac, Calif., assignors to-Eitel- McCullough, Inc., San Bruno, Calif. a corporation off California ApplicationApril 8, 1949, S'erialNo. 86,231

fa screen gridsuch asatetrcde, on:A account of the higher power gain, and other advantages of thetetrode.V The waytetrodes `have been made `in the., past i. however, involving; unsuitable electrode terminal arrangements ande requiring meansin the external circuit for bypassingradio frequency currents from-,screen grid tot cathode, it has notbeenpossiblefto` utilize'icav-ity circuitry to the `best advantage with1the tet-rode typetube.

TheV broad object' of our invention is t0 provide an electron` tube and circuit which` provides `the advantages of a" screengrid tube andalsothe advantages ot a simple cavity circuit;

Another object is, to. provide` a` tetrode having an internal bypass capacitor between the screen grid and cathode, incombination with azcoaxial terminal arrangement for the electrodes( Where- 4by the tube,v andassociated circuitry'functionin simpliiied manner.

Still another object istoprovide ar unique;l in- 4 ternal electrode structure embodying the-fbypass capacitor.

The invention possesses other'objeetsfandafeatures of advantage, some of which; with the foregoing, will be set forth in thafollow-ing"` description of our invention; Itis-,tol` be understood that we do= not limit` ourselvestc thisdisclosure ofspeciesl of, our invention, as we may adopt variant embodiments i thereof` within` the scopeof .the claims.

Referring to the drawings:

i 4 Figure 1 is'avertical sectionalviewroa tetrode embodying ourwinvention; 'and` Figure 2fr shows` a modiiied` tubeconstruction;

Figure 3` is a` diagrammaticsectional viexv of v a4 radio-frequency generator embodying our invention.

. Interms of. broad inclusion, our-improved electron tube comprises a cathode,` control grid, screengrid and anode, and a bypass capacitor 9 Claims. (Cl. S15- 58) wit'nirr` the tubeV envelope and,V connectedtoY the screen grid and cathode. The preferred con:- struction comprises coaxial electrodes with=the control grid terminating adjacent the upper end of the cathode, the bypass capacitor. being located above the electrodes' andiastened toheat isolatingysupports projectingyfrom the` upper ends of thescreen-grid and cathode.` In our improved tube the-control gridrterrninall1 is at the tube Vend opposite theanode, andv the,` screen grid terminal is interposed in.. the envelope-Wall between the control grid,terminaland the anode, these grid terminals being coaxial with each: other: and with the. anode.. A. radio-frequency generator embodyingV our invention,V and. incorporatingr a tube ofthe characterdescribedicomprises ae plurality of coaxial conductors externallyvv of thetube and connected tothe control gridandscreen,grid and anode; the conductors connected-to1the=con `trol grid and screen griddeiining-Aanzinput cavity resonator, and the` conductors: connected to: the screen grid and anode defining;anoutput-,cayity resonator.

In greater detail and referring-'to` Figure- 1 of the drawings, our improved` tetrode comprises,

coaxial electrodes-including a cathode 2, control grid 34 screengrid d and, anodef. Gathodel; is preferably. of the cylindrical indirectly heated type havinga thermionically active surface: such as the conventional oxide coa-ting, andis preferably heated by radiation from an internal heater coil 'L Grids 3 and Aarepreferably-'of vertical' bar construction, the. control grid ,3i being openu at the upper end andi terminating adjacent theupper endcf ,cathodef2.. Anode 6. is preferably of' the externalianodetypeand has a cylindrical recess 8 intoiwhichthe other electrodes project.

Metal anode 6 islocated adjacent the upper end 'of the envelope and, carries the coolerA 5 and also an exhaust tubulation., Ill which=is pinched off `after, evacuation ofthe envelope.

AA tubular stern member, I5;- coaxial with the electrodes. islocated atthe lower endfof the` en"- velope. This stem member comprises the ter"h mnal for the control; grid: 3g the latter being. supported A cna. sleeve .9i projecting from thextubular member 8. Leads. l0 and, H=- for 'the heater coil are, brought` out through the stem member,

being. sealed4 through, a. glass disk l2 carried` by a. U-shaped-.sealing ring llbrazed4 at I4.to,the lower` end of'` tubular member l5.

The tube envelope is made up-in two sections joined. at.a pair ofY interitting metal rings,- I6 and Il., The upper envelope-sectionWhichrsup ports theanodc comprises a. cylindricalglass. Wall section I8 sealed at the lower end to a flange I9 on ring I6 and at the upper end to a sealing ring 2| brazed to anode 6. This sealing ring 2| preferably has an upturned lip 2D providing a cylindrical contact surface which forms the anode terminal. The lower envelope section or header comprises a glass disk 22 sealed between stem member I and the inner flange 23 of the U- shaped ring I1. VVFinal closure of the envelope is made by brazing rings I6 and I1 ,together at 24.

United rings I6 and I1 comprise the screen grid terminal ring of our tube, this terminal being coaxial with the control grid terminal I 5, and interposed in the envelope wall between the anode terminal and the control grid terminal. The

Vscreen grid 4 is supported on its terminal by a cone 26 resting on a flange 21 secured to the inner surface of ring I1. Y

An important feature of our invention is that a bypass capacitor 28 is provided within the tube envelope for bypassing radio-frequency current from the Vscreen grid 4 to cathode 2. In our improved tube the cathode is effectively removed from the external R. F. circuits, and no terminal for R. F. connection to the cathode is shown in the tube structure of Figure 1, in fact, the entire cathode is supported from the screen grid.

In an ordinary tetrode having terminals for the cathode, anode, control grid and screen grid, a common type of amplifier, for example, involves an input circuit connected to the control grid and cathode terminals and an output circuit connected to the anode and cathode terminals, the screen grid being connected back to the cathode through an external bypass condenser. This and other similar arrangements is reasonably satisfactory for lower frequency applications involving circuitry with lumped constants, but is most awk- Ward to handle at high frequencies using coaxial lines or cavities as resonant circuits. The electrode lterminals inherently come out in the wrong relationship for the external circuits andthe need forthe external bypass complicates the circuit problem very badly.

Our improved tetrode is adaptable for use with cavity resonators in a very simple way as shown diagrammatically in Figure 3. The

coaxial conductors

3I, 32 and 33 are connected to the control grid terminal, screen grid terminal and anode terminal, respectively, so that the input resonator formed by the conductors 3I and 32 is connected between the control grid and screen grid, and so that the output resonator is connected between the screen grid and anode. Since the screen grid .Y is bypassed to the cathode within the tube there is no external bypass condenser and the cathode is not required to be connected directly to the external R. F. circuits. All that is required is a D. C. return connection for the cathode which may be a simple strap connection 34 between the cathode and vone of the heater leads I0 as illustrated in Figures 1 and 3. Suitable D. C. connections as indicated, and suitable input and output couplings (not shown), are provided as will be understood by those skilled in the art.

Referring to Figure l, the bypass capacitor 28 in our improved tube is mounted above the electrodes within the upper region of the anode. Since ythe control grid 3 is open ended and terminates at the upper'end of the cathode this intermediate grid does not interfere with connecting the capacitor 28 across the upper ends of the screen grid and cathode. A capacitor comprising concentric

cylindrical metal plates

36 and 31 is Shown for purposes of convenient illustration, it

being understood that these condenser plates may be of any other suitable shape and arrangement such as flat disks extending across the tops of the electrodes. The condenser plates are preferably spaced by a solid dielectric material 38 which also functions to bond the plates together into a single unitary structure.

The amount of capacitance desired, which will depend upon the electrical characteristics of a particular tube, will determine such things as plate size, spacing, number of plates, etc., as will be readily appreciated. An advantage of using the solid dielectric 38 between the condenser plates is that close spacings can be achieved which permits building up a relatively large capacitance in a small physical structure. Any suitable high temp-erature dielectric, such as one of the refractory metal oxides, capable of withstanding the operating temperatures involved in the tube envelope may be used. This refractory oxide' insulating material may bev applied as a coating and'sandwiched between the plates, and then the condenser structure red in a vacuum furnace for sintering or bonding the parts together.

In order to thermally isolate the capacitor 28 as much as possible from the tube electrodes, and to prevent heat from being conducted away from the cathode, the condenser plates are preferably connected to the cathode 2 and screen grid 4 by supporting sleeves 39 and 4I of thin sheet material, preferably of a metal Vor alloy having poor heat conductivity. Holes 48 in the sheet further serve to lower heat conductivity.

By the above arrangement the bypass capacitor 28 is closely coupled electrically to the cathode -and screen grid, and the capacitor structure also functions as a support for the cathode. In other words, the cathode as well as the capacitor derives support from the screen grid 4.

If desired, the cathode 2 may be provided with a separate R. F. terminal externally of the envelope, which may be desired in some circuit applications. structure in which the cathode is connected at the lower end by a sleeve 42 to a tubular cathode terminal 43 extending through the control grid terminal l5. In this case the latter terminal is preferably shortened and enlarged to take a sealing ring 44 brazed in place at 46, the cathode terminal 43 being sealed to ring 44 by a glass bead 41. One of the heater leads I0 is preferably connected directly to the cathode terminal 43 and the center lead I I is formed as an extension of a prong-like center terminal 48 projecting through the tubular cathode terminal 43. Prong 48 is sealed to the lower end of a sleeve 49 by a glass bead 5I which sleeve'projects downwardly into terminal 43 and is secured thereto at the braze 44.

The modified tube structure is therefore similar to that first described except that it provides an external R. F. terminal 43 for the cathode. The sleeve-like connection 42 to cathode 2 also provides a mount for the lower end of the cathode cylinder, so that the cathode is effectively supported at both ends, namely, at the top by the screen grid 4 Via the capacitor 28 and at the bottom by the cathode terminal 43. Likewise the screen grid gets support at the top from the cathode by this arrangement since the result is a mutually supporting structure. This mutual support for the electrodes is desirable in some cases, particularly where tubes are subjected to vibra- -tion in service. Also the support at both ends of the electrodes makes it easier to obtain and Figure 2 shows'such a modied tube maintain close and accurate interelectrode spacings.

While we have described our tube particularly in conjunction with cavity type circuits, it is understood that the improved tube iinds important uses in applications involving other and more conventional circuitry.

We claim:

1. An electron tube comprising coaxial electrodes including a cathode and control grid and screen grid, said control grid having an open end terminating adjacent the upper end of the cathode, and a bypass capacitor of fixed capacitance located above said electrodes and connected to the upper ends of the screen grid and cathode, said capacitor structure being bridged between the screen grid and cathode above the terminal end of said control grid.

2. An electron tube comprising coaxial electrodes including a cathode and control grid and -screen grid, said control grid having an open end terminating adjacent the upper end of the cathode, a bypass capacitor of fixed capacitance located above said electrodes, and supports having loW thermal conductivity connecting the capacitor to the upper ends of the screen grid and cathode, said capacitor structure being bridged between the screen grid and cathode above the terminal end of said control grid.

3. An electron tube comprising coaxial electrodes including a cylindrical cathode and control grid and screen grid, said control grid having an open end terminating adjacent the upper end of the cathode, a bypass capacitor located above said electrodes, and supporting sleeves projecting from the cathode and screen grid and connected to said capacitor.

4. An electron tube comprising an envelope having a recessed anode at the upper end, a cathode projecting into the anode, a control grid and screen grid surrounding the cathode, said control grid having an upper end terminating adjacent the upper end of the cathode, and a bypass capacitor located in the upper region of the anode and connected to the screen grid and cathode.

5. An electron tube comprising an envelope having a pair of coaxial terminal members, a cathode and control grid and screen grid in the envelope, the control grid being connected to one of said terminal members and the screen grid being connected to the other terminal member, and a bypass capacitor in the envelope connected to the screen grid and said cathode.

6. An electron tube comprising an envelope having a recessed anode at the upper end and a tubular stem member at the lower end, a terminal ring coaxial with the stem member nterposed in the envelope wall between said stem member and anode, a cathode projecting into the anode, a control grid surrounding the cathode and connected to the stem member, a screen grid surrounding the control grid and connected to the terminal ring, said control grid having an open end terminating adjacent the upper end of the cathode, and a bypass capacitor located in the upper region of the anode and connected to the screen grid and cathode.

7. An electron tube comprising an envelope having a recessed anode at the upper end and a tubular stem member at the lower end, a terminal ring coaxial with the stem member interposed in the envelope Wall between said stem member and anode, a cathode projecting into the anode, a control grid surrounding the cathode and connected to the stem member, a screen grid surrounding the control grid and connected to the terminal ring, a conductor for the cathode extending through the stem member, .said control grid having an open end terminating adjacent the upper end of the cathode, and a bypass capacitor located in the upper region of the anode and connected to the screen grid and cathode.

8. An electron tube comprising an envelope having a recessed anode at the upper end and a tubular stem member at the lower end, a terminal ring coaxial with the stem member interposed in the envelope wall between said stem member and anode, a cathode projecting into the anode, a control grid surrounding the cathode and connected to the stem member, a screen grid surrounding the control grid and connected to the terminal ring, a heater in the cathode, conductors for the cathode and heater extending through the stem member, said control grid having an open end terminating adjacent the upper end of the cathode, and a bypass capacitor located in the upper region of the anode and connected to the screen grid and cathode.

9. An electron tube comprising an envelope having a recessed anode at the upper end and a pair of coaxial tubular stern members at the lower end, a terminal ring coaxial with the stem members interposed in the envelope wall between the outer stem member and anode, a cathode projecting into the anode and connected to the inner stem member, a control grid surrounding the cathode and connected to the outer stem member, a screen grid surrounding the control grid and connected to the terminal ring, said control grid having an open end terminating adjacent the lupper end of the cathode, and a bypass capacitor located in the upper region of the anode and connected to the screen grid and cathode.

WILLIAM W. EITEL. JACK A. McCULLlOUGH.

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

UNITED STATES PATENTS Number Name Date 2,256,293 Salzberg Sept. 16, 1941 2,342,897 Goldstine Feb. 29, 1944 2,396,167 Ferris Mar. 5, 1946 2,446,379 McArthur Aug. 3, 1948 2,453,148 McCall et al Nov. 9, 1948 2,455,851 Beggs Dec. 7, 1948 2,489,873 Thorson Nov. 29, 1949