US1909411A - Equalized amplifying tube - Google Patents

Description

May 16, 1933.

E. H. KURTH 1,909,411

EQUALIZED AMPLIFYING TUBE Filed NOV. 13, 1928 OUTPUT In z/eniar Edward 2/. Zurzk.

.s'rATEs. PATENT OFFICE cuit, and also, as

Patented May 16, 1933 OF'PASADENA, cAIJIFoRNIA, ASSIGNTOR, ny'nmncr AND imsnn Ass'IGn ENTs; TO WESTERN ELECTRIC COMPANY, INCORPORATED, OF NEW XORK',

. Y, 'a'congonn'rronor nnw YORK.

he output-and pu e nt h r y.

unil teral.in. pe t 9 .Aai well k o In the coupling existing between the elements of the neutralized; or in, other words, which is truly Y ordinary; tube, and,particularly between the plateand grid, cause the amplifier to be inherently unstableand likely to break lnto undesirable .oscillation, this effect increasingl with the eificiency of the oscillation cir- 4 ,the circuit .is adjusted to higher frequencies. Y 1

"A number- ,01 systems have been devised and practiced to .prevent or. neutralize such oscillations, among the best and most common F of which may .be mentioned the system, (exemplifiedin the well known neutrodye err-'- cuit) which involves the feedingback of a small quantity of energy external of the tube, thisene rgy being suitable in amount and internal plate to grid feed-back of the three element tube. This energy .is ordinarily conducted between selected points of suitable phase relationship intheoutput and input circuits through a small. condenser, the capacity of which is adjustable to control the quantity of energy passed. An amplifying system embodying this principle, however, is not equally well neutralized for all frequencies because of an inherent lack of symmetry in the circuit and to the unavoidable presence of inductance and stray capacity in the feed-back condenser ,connection, which produce "unbala'nfc ed electro-magnetic and electro-static couplingeifects and a consequent tendency to ward oscillation. In other words, the neutralizing feed-back current does not pass overa circu t electrically identical under all conditions with that passing the original feedbaclr'current within the tube. These two mem airfrnmyme 'runn i npplication fi le d November-13,1928. am ne-319,151.

relates -to.thermionic.amplifying,tubes,and is particularlyconcerned the capacitive feed-back paths maypossibly be anade,el ectrically equivalent for, the amplificatiomof; one frequency, but forv the-amplification offa band of frequencies only. 'a-compromiswmayabe made in this adjustment. It is a well: known fact to t o se familar with the analytical theory. of these circuits, as-it known anyone whoyhas attempted to a'djustathem operation, that they cannot operate perfeetly over a wide bandof frequenciessuch, for instance, as is commonly used in broadcast work. H The primary object ofthe present invention may-now? be stated to be the provision of an amplifier tube and system which is-inherently equalized andunilateral for all frequencies and conditions. -j With this-preliminary discussion-of the; problem in mind,'I shall'proceed toa detaileddescrlption of my invention, fromwhich its various advantages and features of improvement will become apparent. For this purpose I refer to the accompanying drawing, in which:

Fig. 1 is a diagrammatic view showing the elements of the amplifier tube in elevation;

Fig. 2 is a diagrammatic plan view of the elements of the tube; and

Fig. 3 is a suitable electrical amplifier circuit for the tube.

It will be understood that the specific form and arrangement of the elements of the amplifier tube now to be described are but illustrative of the invention by way of show-- ing one typical means in which it may be carried out in practice; but that this specificarrangement is not controlling on the broad invention, which'may be embodied in any physical form or arrangement having the hereinafter specified electrical constants.

Referring now to the drawing, Figs. land 2 illustrate diagrammatically the elements of the amplifier tube, which will be understood to be mounted within a suitable evacuated enclosure, shown at V in Fig. 2. These .ele-

are identical in size and form, and are sym.- metricallylowted With respect to the other elements loffthe tube. The two Yinterlocked 15 grid's'Gland G2p'r'ovide a common compartment 12 in the center of which the filament F is mounted, the filament being. accurately located so that equal and opposite changes in the potentials of the two' gridsiwill result."

2 in equal and opposite changes in plate potentials. The two" plates Pland P2 are mounted-in the two outer compartments 13' and 145- respectively, in such a manner that thefour plate-to-gridstructure capacities C1,

255 G2," C3 and C4, indicated in FigiQfare all equal to' one another.-= Each of these several capacities may beconsideredas embracing the total capacitive couplingeffect existingbetween a-plate and one of.the grid structures .01: t-alienas a WllOlG, including not'o'n-ly the ad jacent'surface 10-orl 1-1, asthe case may be, but also the end portions and the remote porti'onon the; opposite'sideof the filament.

Of course, the capacity existing between the plate and the adjacent surfaces of the grid structure hasafar greater 'effect than does the capacity existing-between theplate and the remote portions" of the grid structure, which may be entirelynegligible-for practical purposes.

- ltwvill be noted that theoretically the exact equality of capacities will not be achieved by a perfectly 'centrallocation of each plate in its respective compartment, the best position in the arrangement ofpFigs. 1 and 2 being found with-each plate a little nearer to the'inner than to the outer adjacent grid surface. This eccentricity in plate location results from-a slight additional capacity due to the curved ends 15 of the outer grid surfaces. If, however, the edges-of the plate are not too close to the curved'ends -15 of the grid structure, compared with the space ing of the 1 plate and gri'd'surfacesthemselves, this eccentricity may'be'so small asto be negligible for all practical purposes, and the central location 'of-th'e plate maybe used."

It will be apparent that the outer or equalizing portions 11 of the-grids need notbe.

pervious. to electrons, and therefore need nothave-the samecharacteristic grid structure as the plate controlling portions 10; but

may take any form' convenient for manufacture so long as the equality ofcapacitiesis maintained.- And further, the end portions .c,age, in fact, is only a suggested form for manufacture, and may. bevaried in formand.

arrangement atwill so longasthe specified" electro-static relations are maintained;

In order to minimize capacitive and" inductive-relations between the leads from the elements of the tube, I prefer to bring leads 20=and21 fromhtheiwo. grid structures out of one end of the enclosure, and to bring the plate leads '22 and="23-=and'-the-filamentleads 24a'nd25out of the other end.' As-mmatter: of fact, the capacitive relation existing tween-the plateau-dgrid leads" from the' tube when these leads-arebroughtxout iir relatively close relationmay be utili'zed'fifia variational physicalembodiment of the invention. In this case-the grid leads-themselves serveas the equalizing grid" portions,- and new balanced-with respect to the plate I loads as to givethe desired capacitive rel'a tions for complete'equalizati'om The actual-design of the element'szin an specificcasewill depend upon the, charac teristicsdesired in the tubeforits particu lar appl cation, and as the principlesforsuch design are wellunderstood inthe art, no description thereof will be herein-1 re= quired- A circuit suitable for the applicationof this device in-the amplification of radio fre= quency energy is shown in Fig; 3; The two grids G1 and G2 are connectedto the oppoa site ends of the input impedance, which may" comprise a continuous inductive winding'30,- no paralleled by a variable tuning condenser*31,. and grounded at its center pointthr'oughia: filament return lead 32 having'aresistance 33 and a G-battery supply 34'; The" two'- plates P1 and P2. are connected to the opposlte ends of an output Winding 35, grounded at 111966111261 through a filament return lead 36 to the-B battery supply. The filamentF" lS grounded through its heating power; source,as will be understood.

The resistance 33,- which may be, say, of a few hundred ohms, is provided for the purpose of sup'ressing oscillations which may develop'in the circuits formed by the halfsections of the input inductance 30 andsthe 125 shunted grid-to-filament capacities of the, tube. These oscillations are of a frequency independent of the setting of tl1etuning'con-. denser, and do not cause squeals or whistlesr due to heterodyning with the input energy; 136' but are nevertheless objectionable by reason of loading the tube and decreasing its efficiency as an amplifier. Inclusion of the resistance 33, however, effectively suppresses these oscillations, while not lessening the efficiency of the circuit for the amplification of energy having a frequency for which the input circuit is tuned. This fact is obvious from the consideration that the potential difference developed upon the grids across the input impedance is independent of the value of this resistance; and the two components of the current which may be thought of as flowing through the resistance are equal and opposite and thus cancel one another.

This circuiting arrangement will be recognized to embody the general principles of the conventional push-pull type of amplifier, the general operation of which is understood and will require no detailed description here. The novel characteristics of the system will become apparent from the following considerations. As in the genuine push-pull circuit, the two plates, being at the opposite ends of their circuit impedance, are always 180 out of phase, or in other words the pontential of one plate reaches its maximum value as the potential of the other plate reaches its minimum value, and vice versa. It may now be seen that due to the peculiar grid structure, by which each grid is provided with a portion adjacent and in equal electrostatic relation to each of the plates, each grid is always under the balanced electrical influence of the two equally and oppositely charged plates, and can there fore receive energy from or be affected by neither. The consequence of this arrangement and its unique advantage is that no 1 current can flow to either grid as a result of any variation in the potential of the plate, or following a change in the frequency of this variation. Moreover, the arrangement is such that the entire system is perfectly symmetrical, and is therefore truly equalized and unilateral for any possible conditions that may be imposed.

It will be understood that the herein detailed embodiment is to be considered merely as illustrative of and not restrictive on the broader claims appended hereto, for various changes in design and arrangement may be made without departing from the spirit of the invention or from the scope of the said claims.

I claim:

1. A thermionic device comprising, a pair of spaced anode plates, a thermionic source located therebetween, a pair of interlocked grid structures, each surrounding the thermionic source and one of the plates, and the plates to grid capacities all being substantially equal to one another.

2. A thermionic device comprising, a pair of spaced anode plates, a thermionic source located therebetween, a pair of'int'e'rlocked each providing .a plate-controlling portion adjacent the inner face of the other plate,

and the plate to grid capacity, between each plate and each ofthe grid structures'asa whole being equal to one, another.

3. A thermionic vaccum tube device comprising, a pair of spaced anodes, a thermionic source located therebetween, and a pair of grid structures comprising interfitting spirals each surrounding the thermionic source and one of the anodes, the anode to grid capacities between the anodes and each of the spiral grid structures being substantially equal to one another.

4. A thermionic device comprising an electrode structure including a cathode, two anodes, and two grids, said grids having overlapping portions forming a central enclosure surrounding said cathode and portions forming outer enclosures, each outer enclosure surrounding one of said anodes.

5. A thermionic device comprising an electrode structure including a cathode, a pair of spaced anodes, and two grids, each of said grids comprising one portion having lateral wires extending completely between said cathode and each of said anodes and another portion having lateral wires extending exteriorly of an anode over an area greater than the surface of the anode.

6. A thermionic device comprising an electrode structure including a cathode, a pair of spaced anodes, and a pair of interfitting grids having grid laterals forming inner partitions between both of said anodes and said cathode and having other grid laterals forming outer partitions beyond the surfaces of said anode.

7. A thermionic device comprising an electrode structure including a cathode, a pair of spaced anodes, and a pair of interfitting grids having grid laterals formin inner partitions between both of said ano es and said cathode and having other grid laterals forming outer partitions beyond the surfaces of said anodes, said outer partitions, anodes and inner partitions being in equal electrostatic relation whereby each grid is under the balanced influence of said anodes.

8. A thermionic device comprising an electrode structure including a cathode, two anodes, and a pair of oval-shaped wire grids arranged to form two outer enclosures of equal area and a common central enclosure of lesser area, said cathode being located in said central enclosure, each of said outer enclosures containing one of said anodes.

9. A thermionic device comprising an electrode structure including a cathode, a pair of spaced anodes, and a pair of oval-shaped I wiresgrids: arranged to form two outer-"encl'osuresandas common centralenclosure said cathodebeing-:bcatedin said central enclorsuregzfleach outer enclosure?containingione of saidzanodegfliagrid laterals of said central 7 enelbsure'bei'ng a multiple of the grid lat-- -er;als=.of':said: outer: enclosures; 1

1 1m Witness that I claim the-foregoing I havet hereunfioisubscribed my name this 29th 10 day ofAugust,1928. 5 g Y Y Y ED WARD-HKURTH==

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