US2052712A - Electron discharge tube - Google Patents

Description

p 1936- G. JOBST ELECTRON DISCHARGE TUBE Filed April 21, 1935 619/0 VOL 77165 INVENTOR GOA/7H5? ATTORNEY Patented Sept. 1, 1936 ELEcTRoN -mscnancr: TUBE Gnnther .lJobst, Berlin, GermanyL-assignor to. V Telefunken .Gcsellschaft fiir .Drahtlose Tele- .graphie m. .h. .H., Berlin, Gern any, a corpora- "tion 015 Germany a .ApplicationiApvil 21, 1933, smaiinammn r JnQemianycFebmrmH, 1932 it he'present invention relates, linlgeneralato a thermionicrfievice .more particularly to -a thermionic tube containing aacathcde -of high emissivitygahlate orzanode anxl two ormore aux- 15 iliary electrodes. t i 1 The primary object oflthepresent invention is ;to provide a negativezr-esistance in a tube on'ly by the action of space charge and without any feedback iby external :coupling means and with- 10 out autilizing secondary emission. othero'bjects and features will .zbe.iapparent as the specificaetionis perused in connection with :the accom- .panying drawing, in whichyEig. 1 shows a characteristiccurve of a'grid of atube' made accordl ingztoirtherinvention Fig, 2 isa schematic circuit diagram of :a tube according to my invention connected J-tto generate oscillations; and Fig; --3 is a schematic circuit rdiagram of a tube according to my invention used as :a modulation oscillator; 20 The present invention :proceeds'irom the fact, .that. inn :tube containing a directly -or indirectly heated cathode of high emissivity, a plate or'aniode zand'one onmcre auxiliary electrodes situated :beimeen vrthe icathcde and ithe :anode, the -plate -25 rcurrentmay-idecrease in :spite of increasing the total'emission current. This result is attained -by-suitably zpmporttioning -the number and 'velocity tofstemitted electrons, both-depending -upon the voltages applied'to the -electrodes,- Assum- 3, :inglthe tube to comprise two -grid electrodes; both kept. :on .positive potentials-with respect to the cathode, the first :grid; in et-immediately *surrounding the cathode, -controls the number =of electrons or the density of the emission current, whereas the second-grii whifli is connected 'to a higher ipos'iti-ve potential, accelerates "the electrons and determines their velocity. Withrespect to this' ieature, the first grid is called 'hereinafter :density grid,=whereas the second grid is reierre'd to as acceleration grid. "If the-volt- V -ag'e .o'f the second grid is raised after having adquieted-the plate current on "a falling portion of its :characteristic, the current *drawn "by the 'sec- -ond grid-will increase at first, as a -space charge is built up 'between theplate and thesecond grid. l he space charge-forms a cloud org-negative particles and repels additional "electrons back to the' accelerationgrid; By further raising the voltage of the L second grid :the electrons reach a velocity suificient to break through the "space charge *and theplate current increases, whereas the second=grid draws lesselectronsyprovided-the total-emission currentremains substantially 'constant: 3

in order-to-obtain this resultitdsneces'sarythat :11; on s, (Cli250- -36) the actions of the "density grid and the accel- Jeration igri the independent from'eac'h other. sByaraising thezwoltage Ez-Of the secondgrid no augmentation of :the total emission current 'ShOIiId IOCOHI, the velocity only of the electrons #5 massisng through thesecond grid is to Ice-enhanced. Therefore :the influence of the -second" grid' (aciceleration :grid through the first-grid "(density :gridi :on the electrons 'laetween the iiir-s't grid and the -.'cathode11l'xas to be as:sma;ll possible (this rin'fluence-isii-n German known asDurchgrifi-) .This they be obta'ined by inserting an additional gridzielectrode between acceleration grid and density-grid. i a If fiche performance :o'fa tube of the 'kind -de- 15 :scribed above might be =compared with the acflzion of atubexo'f the well known space charge :gridatype. @roviding the total emission-current lto iremainmonstant or because of saturation efifect,=1xiiseo;f the voltage-fapplied to the space '20 change grid under certain conditions also' may icause decrease of the current drawn by the said space charge gr id. The use of tubesof the-space -c'harge" grid type in =orcler to obtain a -negative -characteristic'eon the *space'charge grid-is- 'unfavourable in various respects: iilaments of high em'issiv-ity, i. e. ior' iexample oxide coated cathode'aexl'iibit no stronglymarked saturation point. Sniallfiuct/iidtions of the filament voltagewm cons'ideralblytrifect the emission current. Besides; adjusting the emission current has "to be effected by varying filament current-'and' '-usual filament res'istances will not allow a regulation as exactand-fine as required. On the-other hand the control of current-density *by means of the voltage variation 'on additional grid renders quite exact adjustment, which -isfnot afiectedfby fluctuations or the filament current supply. If ,a --cathcde is "provided, the emissivity or which is =sui'licieht twemit more electrons than required, 3 thedensitylgrid will firaw'a-part only of the available=electrons. "In case nfincreasing the filament currenit no higher emission current "is allowed to pass through the density grid and in the case of lessfilament current the. "emissivity or the cathode -wil1-stillfbe .suflicierit to supply the required "emission current."' Furthermore the density grid lessens the space char'gebetweenac- {'celera'tion grid and cathode and allows greater electronemission. "a [f1 Figure 1 shows a characteristic curveofja itube "according to the present invention. .The plate voltage and the density ,gri'dtvoltage are kept kconstant throughout after .having' been adjusted "to a suitable positive value. The acceleration grid voltage E2 is gradually increased from zero and the current J2 flowing to the said grid is noted and plotted on the vertical axis. Along the portion a of the curve the current J2 increases in the ordinary way. After the point b has been reached, electrons will break through the space charge 'lbetweenj plate and'acceleration grid and the current J2 therefore decreases"('portion' c)',

This goes on until the point d is reached.fWe thus see that increasing the grid voltage E2 may cause a decrease in the grid Clirifllt Jg a.nd a;-

negative resistance in the grid circuit.

By virtue of its negativres'istance the' dlevice is capable of being used as gjenerat'orof 'alternating currents or continuous waves. 'f The'negative resistance may be made use of in a receiving set the potential of the acceleration grid isin creased up to a value correspondingto the point .b, the current, .When oscillations-are 'received,wi1l

be asymmetric and-the device -;may be 'used'as detector aswellas an amplifier, 1 r' Figure 2 shows, a complete arrangement; for generation ofoscillations. :The tubel contains apathode 2, density grid 3, acceleration grid'24 and'.;the 81101182011 plate. ,5 ,The :batteries B3, B4 and Bs are intended to: give the grids and. the plate positive Potentials; :The filament battery ,isomitted for the sake ;:of simplicity. .All the voltages of course preferably-- are: adjustable. IA negative resistance efiectis; obtained :in. the circuit of the second grid 4. The grid. oscillatory circuit comprises aninductance Landacapacity C which determinethe irequency-set upin the device. The battery B4- is,bridged,,by a fixed condenser C1 to ofier a;path1of .low impedance .for the generated current. The adjustment of the voltages B4 'andvBs may, be; chosenso that eithertheplate ,5 orthe accelerationigrid 4, gets 7 the highestpositive potential thetube. ,In

h e ren ementr ho n, I have ou d h owfv lt ses to. oduce s t s ac o operation;

volts voltage 9: plate 5,;10 volts; 1 Y

1n; order to. increase ,thespace charge between theplate and the acceleration gridgancadditional grid ma be inserted betweemthe said electrodes and s s reb yflb k t oa esa or a rosotential with respect to the filamenh; In the lat- Figure 3 illustrates a comple te arrangement for generating modulated oscillations The tube comprises as in Fig. 2a cathode), density" grid 3, acceleration. grid 4and plate A grid. electrode .6 is provided to make the activities of the grids 3 and 4 independent.irorneachother, whereas an additional "grid is designed, to' intensify the 1565 space chargeinirront orfthef anode 5. Theoscillations areset up in thecircuitL, C connected to the acceleration grid 4.. The modulation volt- "ages are suppliedtoth'e auxiliary electrode 1 by the transformerfT. The modulated waves are "radiated by the antenna A, which may becoupled to the oscillatory circuit in any usual 'manner.

In theicircuit arrangement shown I have: found and said tuned circuit.

plate 5:40 volts and voltage of grid 1 :5 volts 7 negative.

I As the general arrangement is rather'similar to that of a so-called grid dynatron, the following distinctions are referred to: the performance of a dynatron is based on secondaryemission.

gtiongi if there isa. negative biased grid between the 'plate-an'dthe positive charged grid, because the secondary electrons are prevented fromflowing to'the' positive grid.

thereto since many changes suggest themselves Having now -described my invention,! what I claimasnew and desireto secure by Letters Pat iAlthough variousmodifications of the present invention -'have been described, it is not limited potentialtorsaid acceleration ,gridvhigherfl than that of said density grid, an anode .icircuit substantially, free from inductive reactance including means for, applying a positive potential to said anode and a tuned circuit' connected to said acceleration grid and cathode whereby said tuned circuitoscillatesat the: desired frequency in the absence of, anytfeedback meansexternal to a said 4 1 tube between said anode circuit and saidtund ir uit c 2,. The combination defined in thev preceding claim in which the positive. potential applied to ,said anode is;less thanithat of'said acceleration rid. 1,,

3,, Anoscillationgenerator.comprising'an electronic tube having a cathode,;an anode,ian;accel .eration grid located between said cathode and anode, a density grid located between said cathode and=acceleration ,gridzthB potential of-said density grid alone regulating theamountof electrons passing therethrough, and a third .grid located between said anode and acceleration .gridFmeans .for applying a positive gpotentialto saiddensity grid, means for applying a 'positivezpptential to said anode and acceleration grid higher, than that of said -density =grid,,,=mc ans forapp y ns a pbtential. to said" third gridless than ;said anode potentialso asgto increasegthe space charge betw th anode and. said. a ce er tion d. n a coil and condenser forminga tuned circuitconnected betweensaid accelerationgrid and cathode whereby said-tuned-circuitoscillates atthe desired frequency in the absenc e, of any feedback external to said tubefbetweensaid anodecircuit I 4. A device of the class described comprising an electron tube having a cathode, "an" anode, .an

acceleration grid located between said cathode and anode, a density grid located between said cathode and acceleration ,grid and athird, grid me w e s id sue e an ae e r t d. means for applying a positive potential to -said e e lari r dl m ans; 9 ap ly n ah sh n fs tive potential to said acceleration grid, an anode circuit including means for applying a positive potential thereto less than that of said acceleration grid, a coil and a condenser forming a tuned circuit connected to said acceleration grid and cathode whereby said tuned circuit oscillates at the desired frequency in the absence of any feedback external to said tube between said anode circuit and said tuned circuit and a connection including a source of direct current potential between said cathode and said third grid.

5. An oscillation generator comprising a space discharge tube having a cathode, an anode, an acceleration grid located between said cathode and anode, a density control grid located between said cathode and acceleration grid, means for applying a positive potential to said density control-grid, the potential gradient adjacent said cathode being a function of the potential of said density grid only, and a third grid located between said anode and acceleration grid, means for applying a positive potential to said anode and acceleration grid higher than that of said density control grid, a circuit connecting said third grid and cathode and including an impedance and means for applying a potential to said grid which is negative with reference to said cathode, and an oscillation circuit connected between said acceleration grid and cathode.

6. The combination defined in the preceding claim in which an additional grid is located between said density and acceleration grids and means for applying a positive potential to said additional grid.

GUNTHER J OBST.

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