US1881910A - Thermionic tube - Google Patents

Description

Get. 11, 1932. H. w. PARKER 1,881,910

THERMIONIQYTUBE Filed Aug. 22, 1951 l 3 7 .I i 2/ I i Z5 1 I I 1 I 22 i I i I 24 I /5 I .ii" 51x,

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INVENTOR Hem M' Parker ATTORNEY atented Oct. H, 532

r W. PARKER, F TORONTO, ONTARIO, CANADA, ASSIGNOR TO ROGERS RADIO TUBES, LIMITED, OETORONTO, CANADA, A CORPORATION OF ONTARIO THERMIONIC TUBE Application filed August 22, 1931. Serial No. 558,675.

My invention pertains to electron discharge devices of the type known as thermionic tubes and relates specifically to thermionic tubes employing the negative resistance or dynatron efiect for'their operation.

The dynatron'or negative resistance effect in thermionic tubes iswell known, but has hitherto not been of much commercialimportance, owing to the fact that a dynatrontype of tube as heretofore constructed when used as an amplifier employed in more than one stage of amplification requires quite elaborate band pass filters to correct the tendency of very sharp side band cut-oil which is inherent in such tubes and further, as it has hitherto been thought impossible to provide the necessary copious secondary emission of electrons which is essential to achieve a sufficiently steep characteristic; of the anode cur rentfor satisfactory operation.

, An object of my invention comprises providing a thermionic tube whereby the dynatron effect may be commercially utilized in radio frequency amplification.

A further object comprises providing a thermionic tube utilizing negative resistance phenomena and-achieving high values of radio frequency amplification;

A still further object comprises providing a thermionic tube having a high value source of secondary emission within the tube for achieving 'efi'ectivelv the dynatron efi'ect.

' A stillfurther object of my invention; comprises providing a thermionic tube with an electrode having a surface adapted to have a high secondary to primary electron emission ratio to provide a steep characteristic of the anode current.

I accomplish all of the above desirable features and eliminate the above mentioned undesirable features by providing a tube in 9 atomic number may be vaporized from the which one of the electrodes, preferably a screening grid in close proximity with the anode, carries attached thereto small portions of a metal of low atomic number and large atomic volume, and providing means attached to the screening electrode whereby during the course' of manufacture of the tube the beads or portions of metal, of low screening grid and distilled upon the anode to provide a mirror-like uncontaminated surface capable of high secondary electronemission for cooperation with two additional properly spaced and related screening electrodes. d. I

My experiments with a tube so constructed have proven that a negative anode resistance may beobtained which is lower in value than has hitherto been deemed possible in such a Eube when used as a radio frequency amplier. l

Ihave obtained experimentally through the use of a tube constructed according to my invention stable radio frequency amplification per stage of an order higher than has hitherto been deemed possible by those familiar with the art.

' In the drawing accompanying and forming I a part of this specification and in which like reference numerals designate corresponding parts throughout:

Fig. 1 illustrates a the top of my improved tube.

Fig. 2 illustrates a partially sectioned view of the assembly of the electrodes in the stem of my improved tube, with the enclosing envelope omitted for purposes of clarity.

broken plan view of Referring now particularly to the figures,

my tube comprises the usual stenrand press 1 supporting the anode 8 by means of the standards 13 and 17, one of which,17-, serves as a terminal therefor. The anode is preferably constructed of nickel or other metal having a relatively high melting point.

A screen electrode 10 is provided closely adjacent to the inner surface of the anode 8 and there is attached to the standards of i i Surrounding the cathode and in relatively close proximity thereto, there is provided the usual control grid 4 to which is attached the terminal 5. Between the control grid 4 and the inner anode screen 10, there is provided a further screen electrode 11. Surrounding the anode 8, on the outside thereof, there is provided an additional screen electrode 7. The screen 11 is connected to screen ,10 by strap25 and also connected to screen 7 by strap 9. The screens 7, lO and 11 are. supported in the press by the supports 12 and 18 respectively, one of which, 12, serves as a terminal therefor. I

The cathode heater terminals are connected to supports 14 and 15 which also serve as terminals therefor, while a. terminal 16 is provided for the active cathode element. All of the electrodes of the tube are maintained in their relative positionsby means of insulating disks 2 and 3 of refractory material.

Screen electrode 11 serves to provide an accelerating potential for the electrons'emitted.

from the cathode and which are controlled by the control grid 4. Screen electrode 10, which is preferably maintained in quite close proximity to the inner surface of the anode 8, serves a double purpose. It provides a positive potential gradient close to the inner surface of the anode 8 for the purpose of collecting slow moving electrons emitted from the anode by providing such a steep positive po- I tential gradient that the negative potential space charge caused by the slow moving secondary electrons does not function to prevent these slow moving electrons from mov ing in the direction of the potential applied by the screen. Ifthis screen electrode 10 is removed to a considerable distance from the anode, a negative potential gradient-would be produced at the immediate surface of the anode by the large number of slow moving secondary electrons emitted from the anode by bombardment of the fast moving primary electrons arriving directly from the cathode through the mesh of the screen. This negative space charge of secondary electrons close to the anode I will refer to hereinafter as the secondary space charge, and the close proximity of screen electrode 10 to anode 8 is desirable to overcome this secondary space charge in order to obtain the maximum dynatron efiect.

Further, screen electrode 10 serves to provide a high value of amplification constant for the tube'as described in my application Ser. No..505,045, filed December Screen electrode 7 serves to minimize the direct capacity between the anode and control grid l'andsuch reduction of capacity is desirable when the tube is to function as a high gain voltage radio frequency amplifier.

Experimentally I have been able to, by

co-pending voltage amplification of several hundred per stage in commercial operation without the necessity of employing any filtering organization to compensate for sharp side-band cutoffs.

It is necessary to commercially realize the above noted results to provide a copious emission of secondary electrons in order that a maximum secondary emission may be obtained to provide the necessary steep characteristic to effectively achieve the wellknown negative resistance or dynatron effect.

In my co-pending application Serial No, 549,-821, filed July 10, 1931, I have illustrated and described the method and means whereby the grid wires and supports may be very highly heated during the tube exhaustion process and I have found that by utilizing this method I am able to vaporize from the grid standards metals of large atomic volume and low atomic number, such as aluminum, boron, and beryllium, or alloys of one or more of these-elements and to distill s'uch vaporized metals upon the inner surface of the anode to produce a clean mirror-like metallic surface which is capable of very high secondary electron emission.

By such distillation during the process of out-gassing an uncontaminated surface is obtained in a very short period of time and at a much lower cost than is the case where the entire anode is composed of a metal having high secondary emission properties. In carrying out my invention, I construct the grid supports carrying the beads or small portions of the metal desired to be vaporized,

of nickel or molybdenum, both metals having a higher melting pointthanthe metal which is vaporized therefrom As pointed out in my co-pending application last referred to, I am able to obtain the necessary high temperature by providing on the extremities of the standards or supports of screen grid 10 a wire 100 19 the plane of which is substantially at right angles to the plane of the grid supports which by induction from the radio frequency induction coil used in the process of evacuating the tube picks up suflicient radio frequency energy to heat the grid supports and the grid wires to a higher temperature than that of the a The high ratio of secondary tube electron emission depends not only on the nature of the metal as stated in my co-pending application Serial No. 542,494, filed June .6, 1931, but also on the nature of the surface. Consequently, a high ratio of secondary to pri-' mary electron emission may be attained either from a metal of low atomic. number and large atomic volume, or from a mirror like uncontaminated surface. Obviously, if the mirror-like uncontaminated surface is formed of a metal of low atomic number and large atomic volume,'a maximum high ratio of secondary to primary electron emission is obtained, although quite an eflicient ratio of secondary to primary emission may be high ratio of secondary to primary electronemission and by providing in close proximity to the innerand outer surfaces of the sion ratio, screening electrodes closely adjacent to both faces of said anode, and an additional screening electrode located between one of said electrodes closely adjacent to said anode and said control grid.

HENRY W. PARKER.

anode, screening electrodes-,that I am able to achieve low values of negative resistance and a high value of controllability with extremely high amplification and'tha't I have in this manner produced a commercially effective thermionic tube utilizing dynatron or negative resistance effect and suitable for use commercially as a high gain radio fre I quency amplifier. v

While I have chosen to describe only one specific embodiment of my invention, it is to be taken merely as illustrative, as,obviously various details and the form may be changed without altering the spirit or .nar-

rowing the vscope of my invention.

Having thus completely described my invention, what I claim'as new and desire to secure by Letters Patent of the United States 1. An electron discharge device comprising an envelope housing a cathode, a control grid, an anode, a screening electrode closely adjacent to said anode, means for distilling from said screening electrode and depositing by distillation on the surface of said anode, a metal of low atomic number and large atomic volume, and-an additional screening electrode located between said first men tioned screening electrode and said control 2.-- An electron discharge device compris-i ing an envelope housing a cathode, a control grid closely adjacent said cathode, an

anode composed of a metal of relatively high melting point and bearing on the surface thereof a coatingpf a metal having a high secondary to primary electron emis-

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