US2468417A

US2468417A - Cascade amplifying circuit using gaseous discharge tubes

Info

Publication number: US2468417A
Application number: US703778A
Authority: US
Inventors: Paul W Stutsman
Original assignee: Raytheon Manufacturing Co
Current assignee: Raytheon Co
Priority date: 1945-05-03
Filing date: 1946-10-17
Publication date: 1949-04-26
Anticipated expiration: 1966-04-26

Description

Aprll 26, 1949. w, STUTSMAN 2,468,417

CASCADE AMPLIFYING CIRCUIT USING GASEOUS DISCHARGE TUBES Original Filed May 3, 1945 3 Sheets-Sheet l nlll April 26, 1949.

Original Filed May 3, 1945 P. W. STUTSMAN CASCADE AMPLIFYING CIRCUIT USING GASEOUS DISCHARGE TUBES 3 Sneets-Sheet 2 P 1949- P. w. STUTSMAN 2,468,417

CASCADE AMPLIFYING CIRCUIT USING GASEOUS DISCHARGE TUBES Original Filed May 5, 1945 3 Sheets-Sheet 3 SIGNAL J ,na F'l,

Patented Apr. 26, 1949 CASCADE AMPLIFYIN G CIRCUIT USING GASEOUS DISCHARGE TUBES Paul W. Stutsman, Needham, Mass., assignor to Raytheon Manufacturing Company, Newton, Mass., a corporation of Delaware Original application May 3, 1945, Serial No. 591,778. Divided and this application October 17, 1946, Serial No. 703,778

This is a division of my copending application, Serial No. 591,778, filed May 3, 1945, now Patent No. 2,443,205, issued June 15, 1948.

This invention relates to an electrical system utilizing a grid-controlled gaseous discharge tube and to a novel tube utilized in said system and to a circuit for said tube.

One of the objects of the present invention is to provide an improved system and tube of the type described.

Another object of the present invention is to provide a circuit for the improved tube of the type referred to.

A further object of the present invention is to provide a tube of the general type referred to in which the gain, that is to say the ratio of output to input, is greatly increased.

These and such other aims and objects of the present invention as may hereinafter appear will be best understood from the following description of an exemplification thereof, reference being had to the accompanying drawings, wherein:

Fig. 1 is a broken away perspective view of a tube incorporating an illustrative embodiment of the present invention;

Fig. 2 is a sectiona1 view of th mount assembly illustrated in Fig. 1, taken on line 22 of Fig. 4;

Fig. 3 is a View similar to Fig. 2 taken on line 3-3 of Fig. 4;

Fig. 4 is an exploded perspective view of the mount assembly of Fig. 1;

Fig. 5 is a schematic diagram of an illustrative circuit including a tube of the type illustrated in Fig. 1; and

Fig. 6 is a schematic diagram of an illustrative circuit including two tubes of the type illustrated in Fig. 1 in cascade.

The tube incorporating the illustrative embodiment of the invention shown in Figs. 1 to 4 comprises an elongated envelope 2 provided with a reentrant stem 4 at the base thereof, the inturned end of said stem being closed by a press 6 which carries the mount assembly '8. A con ductor H] (see Fig. '1) is sealed through a glass bead l2, hermetically secured in the top Wall of said envelope 2, and is soldered to :a metal contact cap l4 cemented exteriorly to the top of the envelope 2 at I6. The other end of said conductor III is connected to the middle of a con- 1 Claim. (Cl. 179-171) ductor l8 having its ends welded to diametrically opposed points upon the inner surface of a hollow cylindrical cathode 20 of the glow discharge type, which it supports. Said conductor l0 serves as a lead-in for the cathode 20, which is preferably open at both ends, it having been found that the cathode operates more efiiciently if the opening through it is unobstructed. As clearly appears from the drawing, the area of the cylindrical walls of the cathode, which are substantially parallel to the side walls of said envelope, is relatively large. The cathode is formed of sheet metal, preferably nickel, thenicke1 sheet being preferably stamped out and then bent into cylindrical form.

It has been found that the presence of thorium oxide, or other suitable non-gasifying radioactive substance, aids in producing the constant low starting voltage which is characteristic of the present tube. This action is believed to be due to the radioactivity of these substances. Particles of the thorium oxide or other radioactive substance may be stamped into or otherwise imbedded in the surface of the cathode, but it is not necessary that said substance be on the cathode.

The cathode will preferably be oxidized to form thereon a coating of nickel oxide and is then coated with an alkaline earth metal or an alkali metal, hereinafter referred to as alkaline metals. I preferably use pure barium, which may be obtained by flashing a getter of the type known as batalum getter, within the tube.

Said getter (see Fig. 3) is shown at 22 and is conveniently connected at one end to the free end of an auxiliary electrode 24, serving as a stabilizing electrode, and at its other end to a conductor 26, extending through an electrically conductive eyelet 28, one of four which serve to hold the elements of the mount assembly together, said conductor being connected to a lead-in 34 (see Figs. 1 and 2) sealed through the press 6. Said stabilizing electrode 24 extends through a second eyelet of the aforesaid four eyelets 28, and is connected to a lead-in 30 sealed through said press 6.'

Referring more particularly to Fig. L'the top of said mount assembly 8 bears against a shoul der 36 formed} in the side walls of the envelope 2, said shoulder thus imparting rigidity to the internal structure of the tube and cutting 01f any paths around the outside of said mount assembly, whereby the electron discharge is compelled to take place through openings provided in said mount assembly. Insulating sleeves 38 and 49 (see Fig. 2) fused in said press 6 support said mount assembly.

In accordance with the present invention said mount assembly 8 comprises a plurality of circular insulating washers 42, preferably of mica, each provided with a relatively large central opening 44 (see Fig. 4) for the passage of the electron discharge, in addition to four smaller openings 46 for the reception of the before men: tioned four eyelets 28, and two suitable openings 48 for the reception of the upper portion of the previously mentioned insulating sleeves d8 and 40.

A flat disc-like anode 50 (see Fig. 2) is sandwiched between the two lowe insulating Washers, thus completely blocking the central openings M of said washers, but not the other openings in said washers. A suppressor or ion coilector grid 52 of flat wire mesh rests upon the top washer of the two insulating washers between whichv the anode B is, sandwiched, and above said suppressor grid are superposed in the order named, a screen grid 54, a control grid 56, and a cathannde grid 58, each of said grids being separated from the one above and the one below it by one of said insulating washers 42. Referring to F 5 it will be noted that in accordance with the present invention the screen grid 54 is connected back to the control grid 55 through a suitable resistance. This increases thesignal input impedance and enables, the device to operat with a l po r i n said ids com tely cover the ral aces cs 44 in said asher The upp r en of the aforementioned eyelets Z8. grip the insu: latilie Washe re ti upon t e cathanode grid 58, and the iower ends of said eyelets grip the. bot: tom washer of said mQl nt assembly so that the parts of the latter ar securely clamped together.

Two or more additional insulating washers, pro

vided, onl with central openings for the passage of the electronedischarge, may be mounted loosely above the washer which rests upon the cathanode grid at, and are held with their central openings in alignment with those of the other washers by the stabilizing electrode 24 and conductor which pass through perforations in said additional washers. The stabilizing electrode 2-4- is rnqunted adjacent the cathode in the ionization Space and serves to maintain. an ionizing discharge to the cathode and thus to maintain ionization in the cathode=cathanode space. This prevents the occurrence of objectionable relaxation oscillations in the cathanode circuit: by brin ing the ignition potential of the cathanode close to, the cathode drop. The suppressor or ion,v collector grid 52 has a negative potential, so that. it, tends to attract positive ions in their passage and prevent them from showering the control grid 56.. The suppressor grid 52- consists of parallel wire strands, twentywire strands to the, square inch, the wire being preferably of tungsten and .0007 inch-in diameter. The screen grid 54 will preferably be made of wire of a diameter of .005 inch and a mesh of x- 30 (900) openings to the square inch. This grid in pick-. ing up positive ions tends to, be driven positive inproportion to the number of ions. which in turn is erq q tio a o he number o ectr n fiow risisten to. amplify, th p ate swing n thus increas the amplification of the tube. The control grid which controls the electron flow from the cathode to the anode responsive to the input signal and the cathanode grid which draws an electronic discharge from the cathode and directs it toward the anode are preferably woven from wire of less than .005 inch and preferably .003 inch in diameter and have a mesh of 60 x 60 (3600) openings per square inch. It is also preferable that the openings of these two lastnamed grids coincide.

The anode 50 is connected to a rigid conductor 60 sealed in the press 6 and connected to a leadein 52 (see. Figs. 2 and 3). The suppressor grid 52 is connected to the cathanode E58 by a ribbon conductor I22. The screen grid 54 is connected to a conductor 64 by a ribbon 66, said conductor being sealed in said press 6 and con nected to a lead-in 68 also sealed in said press. The control grid {iii (see Fig. 2) is connected to a. rigid conductor 12 by a ribbon it, said conductor being-sealed in said press 6 and connected to a lead-in 16 also sealed in said press. The cathanode 58 is connected by a ribbon It to a conductor sealed in said press and connected to a lead-in {32 also sealed in the latter.

After the tube has been exhausted, a current is passed through the getter 22 from the leadins 3t and it (see Fig. 1), and heats the getter to a point at which barium is liberated to clean up residual gases and also to, deposit on the surface of the cathode 30 for the purpose described above. Thereupon an inert ionizable gaseous atmosphere is introduced, said gaseous atmosphere preferably consisting of a rare gas, such as argon or krypton, but preferably Xenon at a suitable pressure. The pressure is critical. I have found that a critical pressure region of about 300 to 1500 microns exists within which the tube will operate satisfactorily for the purposes herein indicated.

If the pressure is lower than 300 microns, the cathode drop tends to increase, and ii the pressureis above 1 500 microns, the mean free path of the electrons is too short to keep control of them in the embodiment described.

R f r g to Fig. and he circuit therein delineated, the cathode 20 is connected by condoctors 84, 86-, and 88 to the negative terminal 90 of a source of direct current which is grounded at 92, while the anQde 50; is connected to the positive terminal 94 of said source by a conductor 95 through a load resistance 93 of 10 megohms. The stabilizing electrodezdfor maintaining an ionizing. discharge to said cathode is adjacent said cathode and connected to said positive terminal 94 through resistance ltd of 30 megohmsby conductors 1-2, we, anddfi. The ioraminous cathanode 58 is mounted adjacent said ionizing space and. is connected by condllctcrs 103, N1 and 96 through a series resistance I06 of 10 megohms withsaid positive ter minal 94., whereby saidcathanode in drawing a scha om h ca hode .9.. servesas a virtual cathode with respecttottheanode 553 as more fully. explained in Patentv No. 1,962,159, issuedJune 12, 19.43,, to James-D. Le Van. The ont ol rid 5.671s ocate W n the ontrol Section upon the, opposite side of. said, cathanode from said; ioni ing. pac and; connected h e eh onduc ers ttt Wt. cen enser are nd. c nducto .6. to. i nal: nput termin Ila. It isalso. connectedtc the cathanode 55 through; conductorsxllla" and H0; resistance H2 of 20 megohms, and conductor I03. The cathanode 58 is connected back to the cathode 20 through conductor I03, condenser I30, and

conductors III, 86, and 84.

Said condenser I30 may have a value of 0.002

V tionable oscillations that'might otherwise occur in this circuit due to the presence of said condenser I30. The screen grid 54 is connected through resistance I20 and conductors I28 and I 08 to the control grid 56 which as already pointed out above increases the input impedance of the control grid. Condenser I26 functions as a grid coupling condenser, and may have a value of 0.002 microfarad. The suppressor grid 52 is adjacent the anode and connected back to the cathanode 58 by the conductor I22 as described above.

Two tubes constituted as herein described in accordance with my invention and connected in,

cascade will materially increase the gain. Fig. 6 shows schematically two tubes A and A in accordance with the present invention in cascade, and an illustrative circuit therefor. Referring to said Fig. 6, the cathode 20 of tube A is connected to the negative terminal I32 of .a source of direct current by a conductor I34, the cathode .20 of tube A being connected to said terminal by said conductor I34, conductor I36, and conductor I31. The anode 50 of tube A is connected to the positive terminal I38 of said source by conductors I40, I42, I44, I46, and I48 through a load resistance I50 of 10 megohms, and to the output terminal 224 by conductor I40, resistance I50, conductor I42, and a resistance 226 of 10 megohms. The anode 50 of tube A is connected by conductors I52 and I54 with terminal 2I6 of the output device 2I1; thence through said output device to the other terminal 224 of said output device; and thence through the resistance 226 and conductors I42, I44, I46, and I48 to said positive terminal I38.

The stabilizing electrode 24 of tube A, for maintaining a discharge to the cathode of said tube, is connected to the positive terminal I38 of said source of direct current by conductors I10, I12, I45, and I48 through a resistance I14 of 30 megohms, and the stabilizing grid 24 of tube A, for maintaining a discharge to the cathode of tube A, is connected to said positive terminal I38 of said source by conductors I16, I18, I46, and I 48 through a resistance I15 of 30 megohms.

The cathanode 58 of tube A, which draws a discharge from the cathode of said tube, is connected to said positive terminal I38 of said source of direct current through conductors I62, I12, I45 and I48, through a resistance I68 of 10 me ohms; and the cathanode 58' of tube A is con nected to said terminal I38 through a resistance I80 of 10 megohms, similar to the aforesaid resistance I68, and conductors I82, I84, I46, and I48.

The control grid 56 of tube A is connected to the cathanode 58 of said tube by conductors I86, I58, and I50 through a resistance I66. Said control grid is also connected to the signal input terminal 208 through conductors I86, 2) and condenser 2I2. The cathanode is connected back to the cathode by conductor 224, condenser 230,

and conductors 226, I 36, and I34. The condenser 230, inserted between the conductors 224 and 6: 226,. is-a bypass condenser .to bypass an variable voltages'b'etween the cathode and the cathanode. Similarly the control grid 56' of tube A" is connected by conductors I88, I90,'and I92 through .a resistance I 94 similar to the resistance 'l'fifiof tube A, to the cathanode 58 of said tube A; Said control grid 56 is supplied with the amplified output of tubeA by conductor 222 connected to theanod e lead I40 and thence through condenser 2I8 and conductor I88 to said control grid; The cathanode 58. is connected back to the cathode 20. by conductor 23 .6, condenser 24ll,'and conductors 236 and I31. The condenser 240 is a cathanode bypass condenser having the same function as the aforesaid condenser 230 and of the same capacity as the latter.

The screen grid 54 of tube A is connected to the control grid 56 of said tube through a resistance I 64 of 10 megohms and the conductors I56 and I86, and similarly the screen grid 54 of tube A is connected to the control grid 56' of said tube A through resistance I96 of 10 megohms andconductors 200 and I88.

The suppressor grid 52 of tube A is connected back to the cathanode 58 by conductor I 22, and the suppressor grid 52 of tube A is connected back to the cathanode 58 by conductor I22. The above connections of suppressor grids markedly lower the signal input power required to operate the system.

All of the above-mentioned resistances have been selected of predetermined values to give the optimum results in tubes as herein constituted in accordance with the present invention.

The signal input is indicated at 208 and is led in directly to the control grid 58 of tube A by conductors 2I0 and I through a coupling con denser 2I2, which may be of the order of 0.002 microfarad, to arrest any direct current, while allowing alternating current to pass. After being amplified in tube A, voltage is led from said tube A through conductors I40, 222, and I88 directly to the control grid 55 of tube A, and said voltage is thus still further amplified by said tube A. A coupling condenser 2I8 between conductors 22 and I88 exercises the same function as the aforesaid condenser 2I2 of tube A and may be of 0.002 microfarad. I

After being thus twice amplified, first in tube A and then in tube A, a portion of the output is reconducted from tube A back to tube A through conductors I52, I54, condenser 2I4, and conductor 2I5 to the screen grid 54 of tube A. Thus the signal is still further amplified and led back to tube A through th connections previously described. The coupling condenser 2I4 functions similarly to the coupling condenser 2I8, and may be about .000005 microfarad.

It will thus be seen that the output is regeneratively amplified, which accounts in part for the remarkable gain obtained with the system of my invention. Two tubes in cascade as above described will produce a voltage gain of 20 at 1000 cycles and one of 50 at 100 cycles and at volts.

I am aware that the present invention can be embodied in other specific forms without departing from the spirit or essential attributes thereof, and I therefore desire the present description to be considered in all respects as illustrative and not restrictive, reference being had to the appended claim rather than to the aforesaid description to indicate the scope of the invention.

What is claimed is:

The combination of two electrical-discharge meager:

7- tubes, each centaimngwan inem; ionizablex gas undersuitable pressure, a, glow-discharge caathede, an auxiliary electrede *for maintainingen ionizmg discharge to said cathude, aforammous cathanode adjacent the: space in. which said ionizing discharge occurs, a. control grid on theopposite side of said cathanode from "said ionizing dis.- charge space, a. screen'grid ad-jaeent said central grid; a suppressor grid adjacent said screen grid :amli connected to said: cathanede, an anode mijacentsaifi vsuppressor. grid, said screenagrid and said camarnode beingcunnectedback'wsaidmn- 8 m1 grid; and a drcmt connecting the anode of one tubev tn the control and screen grids and we cathanode of the second tube,ysaid circuit "con training a coupling condenser, a screen grid resistance and'a cathan'ode resistance, and the anone "of said: secondtube: heing' conneetaed by a feed. back condenser to the. screen and cord-.1101 lide; and the cathanede bi said first, tube.

PAUL W. STUTSMAN.

No references cited.