US1924469A - Push-pull amplifier - Google Patents

Description

Aug. 29, 1933- STRECKER 1,924,469

PUSH-PULL AMPLIFIER Filed Jan. 2, 1952 INVENTOR FEUX STRECKER BY Qmu/ ATTORNEY Patented Aug. 29, 1933 v 1 j I i e UNITED; STATES PATENT: OFFICE;

PUSH-PULL AMrniF En Felix StreckerfBerlm, Germany, assignor to Siemens & Halske, Aktiengesellschaft, Siemensstadt, near -Berlin, .Germany, a corpora-V .tion of Germany Application January 2, 1932, Serial N6.;5s4,4o6,

and in Germany October 22, 1930 i V 1 Claim. (c1.- 179-171 The object of the invention is a push-pull ment, whereas the output transiormer Ua at its amplifier circuitscheme which, asregards sym primary end is united through condensers Q with metry of output currents, compared with the the terminal points of the resistances and thus I arrangements known in the earlier art, is. adapted withthe plateslA; In this manner the potential. I r 5 to secure particularly high accuracy. I of theelectr Calmidpoint of the primary winding The arrangement here disclosed insures such oftheltransformerlis fixed, theaccuracy'ofsymi great, symmetry that instead of'ithe customary netrylis governed by the accuracy of the agreeoutput transformeror instead of a potential ment of thetwo resistances 'r. When push-pull divider comprising inductance coils, there is pro transformers are used, symmetry is governed by 10 vided an arrangement of ohmic resistances to the accuracy of agreement of the'propertiesof which the output transformer is associated cathe two. separatewindings ,(inductances, leak pacitively. ages, self-capacitance, etc) and thesame is The arrangement here disclosed offers partherefore substantially less close. Y ticularly great advantages in connection with the, Furthermore the secondary endfof the input '15 idea well known in the prior art of shunting "thetransformer Uejis connected with aresist'ance By .70 7

input transformer bymeans of two series conby way of 'a condenjser Q," the two, grids G1,

I nected similar ohmic resistances, the filaments and G2, being connected to the two terminals of being associatedjwith the midpoint of this series said resistance Ry. cathodes Kland K2 are arrangement, whereas the secondary end of the united with a point inside the resistance Rg,

20 input transformer is capacitively connected with and thisway also 1 symmetry ofthe inputis inthe resistance, by virtue of such symmetric dissured' t0 ,,an,extensive extentif i position both at'the input and the output ends Under the assumptionfthat both tubes as well of the amplifier the danger oi the arising vof as the balance of circuit elements'are perfectlyback-feeds is extensively precluded, contradistinct similar, a circuit scheme of this kind would be '25 from what is trueto a mark ed degree where syn 1 m e r m r s nd, free from. pur 8 1 In the drawing two embodiments ofithe basic thetvvo branch circuits betweenjk and the t 5 deserves special importance in this combination.

V59 gram.

metric conditions are 'securedonly at the input back-feds- W YC l fa defectsiand end. Quite apart from thereduction of ,the en at n a dduc d. owing to the fact chances of back-feedslbeing set up, an arranget t. P r y. the tu eney r bs ut y ment of the kind here disclosed ofier's advantages k V V 0 also in other respects. ,I n'the. presence 'offin- Accqlding q vfi t i h mil s .8 equality of the amplifier curves both as regards ay be obviated by suitable adjustment or fixing amplitude and phase, the two tubes, fail com- ,Qf he te mlnal foontacts upon the input res'isf l operate in an accurate manner also as amplifiance Rgand Onthe output resistance r.'.= 2r.,,A' I fiers, most particularly, at the, ,hppr ,frequen'cy circuit Scheme in wh c hE SQ .featureshavebeen j 35 limit. In other words, the amplifier is then adapta ep da po ated is illustrated in Fig.2; ed only for the lowerfrequency ranges. The I the fi st place attentionlshall be drawn to use of resistances secures a convenient equaliz'a the, advantages; obtained by 'Inakin'g,,,,-the termi-v tion also in this regard, while this is quite diflicult. rial 7:: or the plate potential vsourceBA shiftable. V where coils are employed, upon the resistance r'., Theplate'currents, in

idea of the inventionfareillustrated by way of m t 1 and 2 lt i drops b f t ti l 750 examp these scbe isc m e is that the residual plate potentials are dependent the idea of rendering the input end symmetric. upon thepositiofi" t e Contact oft'erminal indeed, the fundamental, idea of'this invention present some .dissymmetry or another which, if 1, i the contact is f were set to the --exact midpoint of the resistance would result in dissymmet'ric out put currents, then, by suitable selection of the Fig. lisabasic principle embodiment ofsuch an arrangement, while in Fig. 2 several particularly advantageous embodiments or construction- 9.1 features are shown ina detailed key dia- AS indicated i Fig L the plates A1 nd A venient adjustment of the slidable contact 70 of the two tubes R1 and R2 are inter-connected it is possible o eliminate t said e t. se in by way of two similar ohmic resistances r. The that the outputaltfi Curmnt i a u ction plate potential source BA.iS associated to a tap of the .plate potential. Arrangement could also 55 is disposed at the midpointjof this series arrangebe made in such a way that potentials of differ: 0

-Now, -if"the circuit elements; especiallyv the tubes," 6

plate potential relation, in other words, by conent value for the two tubes are taken from the plate potential source.

Another mode of insuring regulation consists in balancing out such discrepancies as may obtain in 'theinternal resistances of the two tubes by supplementary resistances T1 and T2. In this case the resistance shunting the plates comprises three parts, to the middle one of which the primary of the output transformer Ua is united by way'of the two condensers C andwhich has a constant value. The two outer sections T1 and r2, on the contrary, may beiset to anydesired value in fact, they serve for equalizing such discrepancies as may exist in'the' internal resistances .of-the tubes, 7

A similar idea could be usedwith referenceto the input end. vIn the example illustrated in the Figure, two resistances'having different taps are used, in fact, the contacts or connections for the grids G1 .andG2, those forthe filaments K1 andKZ and finally'also those for the secondary winding of the. input transformer Ue are adjustable ad libitum. This embodiment further shows that the grid biasing potential for, both tubes is separately regulable. This disposition makes it possible to neutralize, particularly irregularities in the valueof 1: a of the twotubes,

' (cross-grid actions of the plates) ,and the effects thereof. If in the presence of aperfectly symmetric setting of the ohmic input resistances both.

tubes are fed with the same, alternating current potential, then the inequality of 1: 1, has this effect that the ensuing 'electromotive forcesin M theplate circuits areunequal. This discrepancy,

however, could also be obviated by that the potentials supplied to the grids are altered in this sensethat thedifierences thus caused will compensate the differences in the values jof 1:

, The provision of different grid potentials (bias),

effect compensation from case to; case especially when this necessity arises owing to the substitution of a tube or tubes.

It will be obvious, that somesuchschemes of securing symmetry could 'be adopted also only for the input end, whilethis maybe dispensed with at the output end, this condition being. particularly present where no ohmic resistances 'are usedatthe' outpu't end. 5 The" samething,

of course, mightarisealso for the output'end. Another source of trouble resides in'capacitive dissymmetries. In order that these may be ob:

viated as far as feasible it is necessary that the circuit elements comprised, in the two paralleled amplifier branches should be made symmetric not only in electrical but also in spatial (geometric) respect, that is to say, to dispose them symmetrically not only in reference toeach other, but also in reference to the neighboring conductors. However, inasmuch as this is practically feasible onlyto a certain extent, inevitable ca-' pacitive dissymmetriescan be rendered harmless by capacitive equalization, as shown, for instance,

in Fig. 2 by the aid of condensers C". The chance of. insuring such capacitive equalization is a special advantage of the arrangement of this invention. For-when a push-pull amplifier involves inherent irregularities of an electrical nature, in other words, when due to dissimilarities in the resonancecurves the push-pull transformer and because of dissimilarities of the tubes the amplifier curves are different both as to amount and phase, such a capacity neutralization or compensation is not practicable.

If it were feasibleto secure the conditions here inbe'fore describedin an absolute sense, then a perfectly non-regenerative push-pull amplifier scheme would be obtained. Although, as will be understood'the conditions stipulated canbe fulfilled only to an approximate sense, it will be easily understood that a neutralization of ohmic resistances can be securedwith a far higher degree of accuracy or closeness than an equalization of transformers or inductance'coils, and'that as a result the quality of the amplifier here disclosed is far higher than that of arrangements known in the prior art.' 7 a V 7 What is claimed is: 1 a V In an amplification system, in'combination, two electron tubes each having cathode, grid and plate electrodes, a source of power connected to said'cathode electrodes, a pair of aperiodic input resistors, an. aperiodic output resistor, said input resistors being provided with a multiplicity of variable tap connections, two additional output resistors, a source of plate potential, a plurality of condensers, a balanced network including certain of said'tap connections wherein said cathode electrodes are connected together and to said in- .put resistors, said cathode electrodes being connected through said source of plate potentialto a variable. central tap on said output resistor, said grid electrodes being connected to certain of said taps on said inputresistors on opposite sidesof saidcatho de taps, each'ofjsaid plate electrodes being connected through one of said additional output resistors to said output resistor, said two plates being connected to opposite sides of said output resistor through variable taps, input connections'including a transformer for said amplifying system connected to certain of said variable input taps on said input' resistors through two of "said condensers, output connections including a transformer for said amplifying system connected fto said output resistor onopposite' sides of said central tap, thereof through two other of said condensers, whereby the energy supplied to said input connections'is amplified and delivered to said output connections substantially without distortion.

f FELIX STRECKER;

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