US1878741A - Push-pull amplifier - Google Patents

Description

Sept. 20, 1932. H, A. WHEELER PUSH-PULL AMPLIFIER 2 Sheets-Sheet l 1 Filed Aug. 17. 1929 INVENTOR //./I. Wheeler ATTORNEYS Sept. 20, 1932. H. A. WHEELER 3,878,741

PUSH-PULL AMPLIFI ER Filed Aug. 17, 1929 2 Sheets-Sheet 2 INVENTOR A. 4. W/lee/er Patented Sept. 20, 1932 UNITED STATES PATENT OFFICE.

HAROLD A. WHEELER, OF GREAT NECK, NEW YORK, ASSIGNOR 10 HAZELTINE CORPO- RATION, A CORPORATION OF DELAWARE PUSH-PULL Application filed August 17, 1929, Serial No.

This invention relates to improvements in amplifiers of the low frequency type adapted principally for amplifying currents in the audio frequency range. More particularly,

5 the invention is directed to improvements in thermionic amplifiers operating in so-called push-pull circuits.

An object of the invention is to provide an amplifier of the type mentioned which will furnish substantially distortionless amplificaof the type specified wherein the signaling current delivered to the output circuit is caused to flow in series thru the plate circuits of the tubes oppositely connected thereto, such arrangement permitting the most eflicient delivery of distortionless power to the output circuit.

A further object is to provide a meter in the amplifier circuit which gives a continuous indication of the signal intensity.

A further object is to provide an amplifier of the type specified having a relatively low output impedance, as a consequence of utilizing no biasing potential on the grids of the tubes and further as a result thereof requiring a correspondingly lower anode supply voltage than would otherwise be required where such biasing potential is used.

As a general proposition, one of the essential requisites to the distortionless amplification of the signaling currents by means of thermionic amplifiers consists in applying to the grids of the thermionic tubes a sufiiciently large initial or permanent negative biasing potential to maintain them at all times negative relative to the corresponding cathodes or filaments. For, if the incoming signal AMPLIFIER 386,543, and in Great Britain July 8, 1930.

wave has a sufficiently great peak value to carry the grid positive during a portion of each cycle, space current will flow in the grid circuit during such portion thereby causing an increased voltage drop in the input circuit associated with the tube with resultant decrease in voltage impressed between the grid and filament thereof as compared to that of the corresponding negative portion of the signaling wave. As a consequence of this, the amplified signaling wave will contain a flattened portion during each interval that the grid is positive, which effect, of course,

is distortion.

It is possible by means of a well designed thermionic amplifier utilizing a sufficiently large permanent negative biasing potential on the grid, to obtain substantially distortionless amplification, but such a result is attained only by sacrificingcertain other .desirable features. In the first place, the use of the negative biasing potential on the grid of a tube increases the plate circuit impedance thereof by a corresponding amount since the presence of the negative potential on the grid impedes the flow of electrons from the filament to the plate, thus requiring a higher plate circuit voltage for a given plate current. The increased plate voltage required, together with the added grid bias voltage, involves an added expense to the amplifier construction.

In order to partially overcome the above enumerated disadvantages accompanying the use of a permanent negative biasing potential on the grids of the tubes, the so called push-pull amplifier circuit was de- VlOPEd. The push-pull amplifier, as frequently constructed, comprises in essence an input transformer having the secondary winding thereof connected between the respective grids of'a pair of similar thermionic tubes, an output transformer having the primary winding thereof connected respective ly between the anodes of said tubes, and having the cathodes connected in common to the midpoint of the input transformer secondary winding and also thru a direct plate current supply source to the midpoint of the output transformer primary winding.

' such a push-pull amplifier, there will at each instant of time be a signal voltage impressed in a positive sense between grid and filament of one tube and an equal signal voltage impressed in the negative sense between grid and filament of the other tube, and since the voltages thus impressed produce additive effects in the output transformer secondary, it is thus insured that each positive half cycle of amplified signaling current will be identical in wave form with the corresponding negative half cycle. This, however, does not necessarily mean that the amplified wave will be distortionless; it merely means that the even harmonics of the fundamental frequency will be eliminated. The odd harmonics may still be present in sufficient magnitude to cause appreciable distortion.

In addition to the distortion effects noted with the push-pull amplifier as commonly constructed, any grid current in flowing thru the input transformer secondary winding will cause a considerable voltage drop therein which will'reduce the net signaling voltage applied between the grid and filament of the tubes and in this Way limit the amplification obtainable.

It is proposed in the present invention to improve the push-pull amplifier as common-- ly constructed in such manner as to substantially eliminate the above noted objectionable efiects which result from operating the same without applying an initial or permanent negative biasing potential to the grids of the vacuum tubes. The improvement is accomplished by serially interposing a high impedance element transversable by uni-directional current such as a choke coil but preferably a resistance in the lead connecting the midpoint of the input transformer secondary winding to the cathodes of the tubes.

The objects to beaccomplishedby such a modification are to prevent the flow of large currents in the grid circuits of the tubes and also to prevent the applied signaling wave from impressing an appreciable positive potential upon the grids since these two factors when present to any considerable extent are the cause of the above noted objectionable effects.

Since with the above modification, current flowing in the grid of either tube must traverse the high impedance element in returning to the cathode such impedance operates automatically to limit the magnitude of the current flow. By utilizing animpedance element of sufliciently large magnitude, the grid current can be limited to such a degree as to produce negligible distortional or amplification limiting effects due to the flow of grid current in the input transformer. Thus the grid current flowing in the input transformer secondary winding during signal reception can be so limited that 's'ubstantialy no load will be placed on the transformer to limit the signal voltage applied to the grid of the negatively biased tube, or to introduce distortional effects into the system.

By making the above mentioned high impedance element of large magnitude relative to the operating filament-to-grid resistances of the tubes, substantialy all of the voltage drop due to the flow of grid current will be across the high impedance element and very little across the tube'input. This means that each tube will be substantially inactive while the grid thereof is maintained positive by the impressed signaling wave, but will strongly repeat the signal While the grid is maintained negative thereby, since in the latter case the grid is maintained negative thereby, since in the latter case the grid to filament impedance amounts to practically an open circuit across which the full signaling voltage is necessarily impressed. Due to the opposite manner in which the tube input circuits are connected across their respective portions of the input transformer secondary winding, the grid of one tube will be charged positively by the aptially the entire signal wave repeated at each 1 instant to the output circuit, with the positively charged tube contributing Very little. This mode of operation is in marked contrast 'to that of the push-pull circuit amplifier as commonly constructed in which case it is the positively charged tube which is principally [active in repeating the signal.

A further important advantageresulting from the interposition of the high impedance element in the lead connecting the cathodes in common to the midpoint of the input transformer secondary winding is that such an arrangement automatically operates to impress at each instant across the tube having its grid l negative, substantially all of the voltage 1nduced in both portions of the transformer secondary winding. In other words, the operation is just as though the entire secondary winding were at each instant connected across the input of the tube the grid of which is maintained negative by the signaling current. Due to this fact the incoming signaling wave is impressed to the greatest extent across the tube which isactive in repeating the signal thereby offering a maximum degree of amplification.

The manner in which the above efl'ect is brought about is as follows. The flow of. grid current due to the voltage induced in the portion of the transformer connected to the tube having its grid positive, causes a Voltage drop in the high impedance element which makes the terminal thereof connected to the midpoint of the transformer secondary, negative with respect to the terminal connected to the cathodes. This negative potential is applied through the transformer winding to the negative grid of the opposite tube and thus adds to the negative voltage applied thereto due to the induced signaling voltage in the portion of the secondary winding connected to the tube having its grid negative. And since as was stated, practically the entire voltage drop due to the voltage induced in the transformer secondary connected to the tube having its grid positive is across the high impedance element, it follows that the total voltage applied to the tube having its grid negative amounts to substantially the voltage induced in the entire secondary Winding.

Due to the fact that with the proposed arrangement of the push-pull amplifier as disclosed herein only one tube at a time is active in delivering energy to the output circuit, it has been found that the ordinary means for connecting the tubes to such output circuit, namely, through an output transformer having the primary winding tapped at the midpoint and connected directly through a space current supply source to the filaments, does not permit the maximum delivery of power to the output circuit. Since only one tube at a time is active, the output transformer in such case acts as a threewinding transformer having a single primary connected to the plate resistance of-the active tube and a pair of windings connectedrespectively to the plate resistance of the inactive tube and to the output circuit. The dynamic plate resistances of both tubes are thus connected effectively in parallel with the output circuit so that the plate resistance of the inactive tube acts as a dissipative shunt across the output circuit.

It is well known that in the operation of thermionic tubes the maximum output consistent with good operation is obtained when the load impedance is substantially greater than the generator impedance. In the present instance, since the active tube is the generator, while the inactive tube and the output circuit connected in parallel constitute the eifective load impedance, it will be seen that with the commonly used push-pull arrangement, the load impedance is always less than that of the generator In contrast with the above arrangement, wherein the output circuit and the plate re sistances of the tubes are effectively in parallel, it is possible to so arrange the elements that the amplified signal current flows in series through the active and inactive plate resistances and through the output circuit. With such an arrangement, it is evident that the load impedance will always be greater than the generator impedance; so that the above ideal condition can be realized wherein substantially the entire output from the active tube is delivered to the output circuit. For a given amount of power delivered to the output circuit, the proposed series arrangement introduces considerably less distortion due to the non-linear plate current characteristic of the tubes than does the parallel arrangement, since in the former case considerably less signaling current flows in the plate circuit of the active tube.

The series arrangement for the output circuit is obtained by interposing a high impedance element traversable by unidirectional current in the lead connecting the midpoint of the output transformer primary winding through the space supply source to the cathodes of the tubes in common. resistance element may be used for this purpose, but preferably a choke coil should be used since ithas a considerably smaller effect on the total resistance of the space. supply i active and inactive tubes and through the output circuit.

The series type of output circuit is'inferior to the usual output transformer arrangement when applied to the push-pull amplifier as commonly constructed and utilizing a high initial negative-grid bias for the tubes. The reason is that for such an amplifier both tubes are about equally active at each instant in delivering current to the output circuit, and the less active tube is the one with the higher instantaneous plate resistance.

Referring now to the drawings- Fig. 1 shows in circuit diagram form a push-pull amplifier having its input circuit arranged in accordance with the present invention but with the output circuit inaccordance with the ordinary type of amplifier.

Fig. 2 shows in' circuitv diagram form a push-pull amplifier having both the input and output circuits arranged in accordance ith the present invention, wherein the novel results are obtained by the use of high resistance elements.

Fig. 3 shows a modification of Fig. 2 wherein choke coils instead of resistances are used for obtaining the novel results.

' Fig. 4 shows a two-stage amplifier in accordance with the present inventionutilizing both resistance and inductive elements to obtain the operative features of the present invention.

Fig. 5 shows an amplifier in accordance with the present invention. wherein a special type of loud speaker unit is connected directly in theanode circuit of the tubes with resultant advantages as pointed out below.

The expression divided input section and divided output section as used in the specification and claims denotes the push-pull connection of the amplifier tubes in which the cathodes of the push-pull connected tubes are joined together and connected respectively to an'intermediate point of the input circuit and output circuit, while the grids are connected to respective opposite outer terminals of the input circuit and the anodes are connected to opposite outer terminals of the output circui Referring to Fig. 1 the amplifier comprises vacuum tubes V and V each having grid G, plate or anode P, and filament or cathode F. The grids of tubes V and V are connected respectively to the upper and lower terminals of the secondary winding S of transformer T the primary P of which is connected between a pair of input terminals I. An auto-transformer T is connected between the cathodes of the respective tubes, the transformer terminals being connected in addition to a pair of output terminals O. The cathodes in common are connected by means of lead 1 thru a milliammeter M, for indicating the energy level of the impressed signal and through a high resistance R to the midpoint of the input transformer secondary S cathodes are connected by means of lead 2 through a space supply source B to the midpoint of the output transformer T The auto-transformer T may be replaced by a two winding transformer similarto T hav ing the primary windings connected to the output sections of the tubes and the secondary winding connected between the output terminals O. The cathodes F are heated by any suitable means", not shown.

In the operation of the amplifier assumethat at a given instant a signaling wave impressed upon the input terminals I is such as to make the lower terminal of the secondary winding S negative relative to the upper terminal thereof. The voltage thus induced in the secondary winding S will carry the grid of tube V negative and that of V positive. The positive potential on the grid of tube V will cause a current to flow in the space path from the filament F to grid G of the tube, through the upper portion of the value as compared to the impressed signaling wave, and will thus prevent the placing of an appreciable load uponthe transformer which otherwise would reduce the terminal ,volte'age of the secondary winding 5;; Further- In addition, the

more, the resistance R being of relatively large magnitude compared to the filament to .grid resistance of the tube, practically all of the voltage drop due to the fiow of grid current in the circuit traced will be across the resistance element R and very little will be impressed in a positive sense between filament and grid of the tube V with the resultant ad vantages pointed out above.

At the same time that the action described above is taking place in the grid circuit of tube V the voltage induced in the lower portion of the secondary Winding S is impressed in a negative sense between grid and filament of tube V Since the grid-to-filament impedance of the tube amounts to practically an open circuit, the full terminal voltage of the lower portion of the secondary winging S is impressed directly between grid and filament of tube V since for this tube there is no flow of grid current through the resistance element R to reduce the net voltage applied to the tube.

In addition to the negative potential applied to the grid of tube V due to the voltage induced in the lower portion of the transformer winding S an additional negative potential will be applied thereto due to the voltage drop across the resistance element R caused by the current flowing in the grid circuit of tube V This grid current flowing in the circuit traced above flows through the resistance element R in such a direction as to render terminal 3 thereof connected to the winding S negative relative to terminal 4 thereof connected to the cathodes. Since terminal 4 is connected to the cathode of tube V as well as that of tube V the potential drop across resistance R is immediately applied through the lower' portion of transformer winding S between the grid and filament of tube V and thus increases the negative potential applied to the grid of that tube by. the amount of the potential drop in the resistance element R Further since, as was explained above, practically the entire potential drop due to the voltage impressed in 'theupper portion of winding S is across the resistance element R the total .per terminal of winding S negative relative to the lower terminal, the conditions described above will be reversed, and the grid of tube V will be carried negative and that of tube V positive. Current will thus flow from the space path from filament to grid of tube V and in series through the lower portion of the winding S the resistance R;

1 by the tube having its grid positive will add and the meter M back to the filament. The voltage drop across the resistance element R due to this current flow will apply a negative potential to the grid of tube V which grid will be carried still further negative by the voltage induced in the upper portion of the winding S A large negative potential will thus be impressed upon the grid of tube V while a relatively small positive potential will be impressed upon the grid of tube V As a'result of the mode of operation described above, the tube having its grid nega tive at a given instant will strongly repeat the signal to the output circuit, while the tube having its grid positive will have very little effect thereon. Due, however, to the manner of combining the amplified signaling current in the output transformer T the signalin waves simultaneously repeated by both tu es will produce additive effects in the output circuit so that the signal weakly repeated its effect therein to that of the negative tube having its grid negative.

With the arrangement of Fig. 1, the plate resistances of tubes V and V are connected effectively in parallel with an output circuit connected across terminal 0, which results in a relatively large portion of the signaling energy delivered by the active tube being dissipgated in the plate resistance of the inactive tu e.

Referring now to Fig. 2, if a high impedance element such as the resistance R be interposed inlead 2 connecting the midpoint of the primary-winding P of the output transformer T with the filaments Fof the tube, the operation of the output circuit will be essentially changed in that the amplified signaling current will flow in series through the plate resistances of both the active and inactive tubes.

While no signals are being received, a steady direct current flows through the resistance R which is the sum of the space currents supplied to the plate circuits of tubes V and V If now a signaling voltage is impressed upon the input terminals 1 in such manner as to carry the grid of tube V negative, there will be a corresponding decrease inthe plate current of this tube. As a result the current flowing through the resistance R will decrease slightly, thus increasing the available potential between terminal 4 and the midpoint of winding P which added potential being immediately impressed across the plate circuit of tube V will increase the plate current thereof by substantially the same amount that the plate current of tube V is decreased. Since, therefore, the plate current of tube V simultaneously increases by substantially the same amount that that of.

tube V decreases, substantially all of the amplified signaling current in effect flows in series through the plate resistances of tubes V and V and both portions of the primary winding P the resistance element R being so great that practically no change in current takes place therein. Since the impedance of the primary winding P is determinedby the impedance of the output circuit connected to terminals 0, it will thus be seen that the repeated signal in effect flows in series through the resistances of the active and inactive tubes and through the output circuit.

Fig. 3 shows an arrangement whereby high impedance choke coils L and L replace the resistance elements R and R respectively, of Fig. 2. The use of the choke coil L permits the use of a smaller battery B to supply agiven space current to the tubes than is the case with the arrangement of Fig. 2. The circuit of Fig. 3 operates on the signaling wave in the same manner as that of Fig." 2.

Fig. 4 shows the method of arranging a two-stage amplifier in accordance with the present invention. The output sections of tubes V and V comprising the first amplifier stage, are connected by means of transformer T to the input sections of tubes V and V comprising the second amplifier stage. The output sections of'tubes V and V4 in turn are connected through transformer T to the output terminals 0.

In order to provide the series arrangement for the output circuit of the first amplifier stage, the resistance R is serially interposed in lead 2. The resistance R is serially interposed in lead 1 associated with the input circuit to the second amplifier stage, while the choke coil L is connected in lead 2 of the output circuit thereof in order to cause the amplifier to operate in accordance with the present invention.

The amplifier shown in Fig. 5 is similar to that shown in Fig. 1, with the exception that the anode circuits of tubes V and V contain the voice frequency actuatingcoils 5 and 6 respectively of aspecial type of loud speaker, known as a Farrand inductor dynamic speaker. This speaker, which is especially adapted for use with the type-of amplifier disclosed herein, comprises the cone shaped acoustical diaphragm 7 a permanent horse shoe magnet 8 having aflixed to the respective poles thereof oppositely positioned U shaped pole pieces 9 v and 10. The pole pieces 9 and 10 are so dimensioned and positioned as to leave equal air gaps between the opposed legs thereof, in'which space an armature 11 is suspended in such manner as to be free to vibrate in a perpendicular direction. A rod 12 connects the lower end of armature 11 to the central point of the cone 7, whereby the cone is vibrated in accordance with vertical movements of the armature.

The coil 5 is placed about the upper leg coil 6 directly in the plate circuit of tube V in such manner that the flux set up by the direct space current in each case aids the flux of the permanent magnet 8, threading the air gaps between the pole pieces.

The armature 11 has a length about equal to the distance between the centers of the legs of the pole piece, and is so positioned symmetrically within the air gap as to be pulled equally in opposite vertical directions by the steady flux threading the two air gaps re 'ing a high degree of substantially distortionspectively between the pole pieces.

If now a signal wave beimpressed upon the input terminals of the amplifier, the action of the amplifier is such that the current in signal coil 5 decreases when the grid of tube V is negative, and at the same time the current in signal coil 6 remains constant at the normal direct current value, or increases very little because the grid of tube V is positive. Likewise, when the grid of the tube V is positive the current in signal coil 5 is practically at the normal direct current value and the current in signal coil 6 is decreased. From the foregoing, it is seen that the signal coils are alternately operative and furthermore the coil which is inoperative exerts no in-.-

fluence upon the coil which is operative. This gives the result that the inactive tube of low plate resistance is not effectively a shunt across the output of the active tube, as would be true if a single output transformer were utilized.

The principal advantage of connecting the loud speaker directly in the output circuit is that all frequencies operate on the speaker unit to equal advantage, whereas, if the speaker were connected directly to the terminals of an output transformer, as for example, to terminals 0 of Fig. 2, the lower frequencies would in general be discriminated against. Another advantage of the arrangement of Fig. 5 lies in the elimination of the outputtransformer T which of course, represents an economy in amplifier construction. The greatest distortionless power out put is secured when coils 5 and 6 are practically without mutual magnetic coupling and when the effective impedance of each coil is approximately three times the output impedance of the vacuum tubes individually connected thereto.

With the series arrangement for the output circuit as disclosed in Figs. 2, 3 and 4, it has been found that best results are obtained when the apparent load impedance connected between the anodes of the tubes equals approximately four times the effective cathode to plate impedance of each tube.

I claim:

LA low-frequency amplifier for provid- 'ing a high degree of substantially distortionless amplification in the absence of a no ative biasing potential in the control circuits of said amplifier, comprising dlnded lnput and ing each tube substantially inactive while its grid is made positive by electric waves in said input section, whereby said waves are repeated by the tube having its grid negatively charged by said waves.

2. A low-frequency amplifier for providless amplification in the absence of a negative biasing potential in the control circuits of said amplifier, comprising divided input and output sections having connected in opposition therebetween, a pair of vacuum tubes each including -cathode and grid electrodes, and means interposed between said cathodes and said input section adapted to cause electric waves in said input section to be applied in substantial entirety upon the tube negatively charged thereby, whereby such tube alone repeats the signal.

3. In an electric wave repeating apparatus for providing a high degree of substantially distortionless amplification in the absence of biasing pptentials in the control circuits of said apparatus, divided input and output sections having connected in opposition therebetween a pair of vacuum tubes each including cathode and grid electrodes, and a high resistance free from reactance interposed between said cathodes and said input section for substantially preventing the flow of space current in the grid circuits of said tubes, whereby signal Wavespresent in said input sections are impressed in substantial entirety upon the tube whose grid momentarily receives a negative potential therefrom so that said latter tube alone repeats the signal.

4. A low-frequency amplifier for providing a high degree of substantially distortionless amplification in the absence of a biasing potential in the control circuits of said amplifier, comprising the combination of two repeating elements having a cathode, an anode and an input electrode, the cathodes of bothv and a high resistance interposedbetween said cathodes and said secondary winding adapted of itself to substantially prevent the flow of current in the control circuits of said repeating elements, whereby signal waves present in said repeating coil are impressed in substantial entirety upon the element whose input electrode momentarily receives a negative potential therefrom, so that said latter clement alone re ats the signal.

5. A push-pull amplifier for providing a high degree of substantially distortionless amplification in the absence of biasing potential in the grid circuits of said amplifier, comprising divided input and divided output circuits having connected in opposition therebetween, a pair of vacuum tubes eachincluding cathode, anode and grid electrodes, a high impedance interposed between said cathodes and said input circuit for substantially preventing the flow of current in the grid circuits of said tubes, whereby signal waves present in said input circuit are impressed in substantial entirety upon the tube whose grid momentarily receives a negative potential therefrom so that said latter tube alone repeats the signal, and a resistance free from reactance interposed between said cathodes and said output circuit for causing electric waves repeated in said output circuit to flow in series through the anode circuits of both said tubes and said output circuit.

6. A low-frequency amplifier for providing a high degree of substantially distortionless amplification in the absence of negative bias ing potential in the control circuits of said amplifier, comprising divided input and divided output circuits having connected in oppositi on therebetween, a pair of vacuumtubes each including cathode, anode and grid electrodes, a high resistance interposed between said cathodes and said input circuit adapted ofitselfto substantially prevent the flow of current in the grid circuits of said tubes, whereby signal waves present in said input circuit are impressed in substantial entirety upon the tube whose grid momentarily receives a negative potential therefrom so that said latter tube alone repeats the signal, and an inductive reactance interposed between said cathodes and said output circuit for causing electric waves repeated in said output circuit to flow in series through the anode circuits of both said tubes and said output circuit.

7. A low-frequency amplifier for providing a high degree of substantially distortionless amplification in the absence. of negative biasing potential in the input circuits of said amplifier, comprising the combination of two repeating elements each having a cathode, an anode and an input electrode, said cathodes being connected together, an input repeating coil and an output repeating coil, the secondary winding of said input repeating coil being divided and the divisions thereof connected to said input electrodes respectively, and the primary winding of said output repeating coil being divided and the divisions being connected to said repeating elements respectively, a high resistance free from reactance interposed between said cathodes and an intermediate point of said input repeating coil for substantially preventing the flow of current in the control circuits of said repeating elements, whereby signal waves present in said input coil are impressed in substantial entirety upon the. repeating element whose input electrode momentarily receives a negative potential therefrom so that said latter element alone is effective to repeat the signal, and an inductive reactance interposed between said cathodesand an intermediate point of said output repeating coil for causing electric waves repeated in said output circuit to flow in series through the output resistances of both said repeating elements.

8, An electric wave repeating apparatus comprisin in combination a pair of electron discharge 6 evices each including anode, cathode and. grid, an input transformer having a winding connected between said grids respectively, a connection from an intermediate point of said winding to said cathodes in common through impedance means adapted to cause a signaling wave impressed upon said input transformer to be repeated at each instant in substantial entirety by the said device which receives a negative potential therefrom.

9. An electric wave repeating apparatus comprising a pair of electron discharge devices each having anode, cathode and grid, an input transformer having a secondary winding connected between said grids respectively. a connection from an intermediate point of said, winding connected to said cathodes in common through impedance means of large magnitude relative to the lowest grid-tocathode resistances of said devices during operation for causing an impressed signaling wave to be repeated at each instance in substantial entirety by the said device which receives a negative potential therefrom.

10. An electric wave repeating apparatus comprising in combination a pair of electron discharge devices each having anode, cathode and grid, an input transformer having a winding connected between said grids respectively, a connection from an intermediate point of said winding to said cathodes in common, through impedance means adapted to cause a signaling wave impressed upon said transformer to be repeated at each instant in substantial entirety by the said device which receives a negative potential therefrom, an output transformer having a winding connected between said anodes respectively, and a connection from an intermediate point of said winding to said cathodesin common through impedance means traversable by direct current, adapted to cause the repeated signaling wave to flow in series through the anode circuits of both said devices.

11. An electric wave repeating apparatus comprising in combination a pair of electron discharge devices each including anode, cathode and grid, an input transformer having a secondary winding connected between said grids respectively, a connection from an intermediate point of said secondary winding to said cathodes in common through a re sistance of large magnitude relative to the lowest grid-to-cathode resistances of said devices during operation whereby a signaling wave impressed upon said input transformer is repeated at each instant in substantial entirety by the said device which receives anegative potential therefrom, an output transformer having a primary winding connected between said anodes respectively, a connection from an intermediate point of said primary winding to said cathodes in common through a space current supply source and an inductance of suflicient magnitude to cause the repeated signaling wave to flow in series through the anode circuits of both said devices and said primary winding.

12. The combination with a thermionic amplifier comprising a pair of vacuum tubes each having anode, cathode and grid, and a divided input circuit connected at an intermediate point to said cathodes in common through a high impedance and at opposite outer termina1s to said grids respectively, whereby signal waves present in said input circuit are impressed in substantial entirety upon the tube whose grid momentarily receives a nega tive potential therefrom so that said latter tube alone repeats the signal, of a loud peaker unit including means for producing a permanent magnetic flux adapted to maintain in dynamic equilibrium an armature afiiXed to an acoustical unit, a pair of signal current coils for actuating said armature situated re spectively at opposite ends thereof, and means so connecting said coils in the anode circuits of said tubes respectively that signal waves received at the input of said amplifier tubes affect said coils alternately and produce distortionless resultant eifects upon said armature.

In testimony whereof I affix my signature.

HAROLD A. WHEELER.

DESCLAEME 1,878,741.Har0ld A. Wheeler, Great Neck, N.Y. PUSH-PULL AMPLIFIER. Patent dated September 20, 1932. Disclaimer filed October 20, 1933, by the patentee, assignee, Hazelt'ine Corporation, consenting. Therefore enters this disclaimer to claims 1, 2, 3, 4, 8, and 9 of said Letters Patent, which are in the following words, to wit:

1. A low-frequency amplifier for providing a high degree of substantially distortionless amplification in the absence of a negative biasing potential in the control circuits of said amplifier, comprising divided input and divided output sections having connected in opposition therebetween a pair of vacuum tubes each including cathode and grid electrodes, and means interposed between said cathodes. and said input section for rendering each tube substantially inactive while its grid is made positive by electric waves in said input section, whereby said Waves are repeated by the tube having its grid negatively charged byjsaid waves. r

2. A low-frequency amplifier for providing a high degree of substantially .distortionless amplification in the absence of a negative biasing potential in the control circuits of said amplifier, comprising divided input and output sections having connected in opposition therebetween, a pair of vacuum tubes each includingcathode. and grid electrodes, and means interposed between said cathodes and said Input section adapted to cause electric waves in said input section to be applied in substantial entirety upon the tube negatively charged thereby, whereby such tubealone repeats the signal.

3. In an electric wave repeating apparatus for providing a high degree of substantially distortionless amplification in the absence of biasing potentials in the control circuits of said apparatus, divided input and output sections having connected in opposition therebetween a pair of vacuum tubes each including cathode and grid electrodes, and a high resistance free from reactance interposed between said cathodes and said input section for substantially preventing the flow of space current in the grid circuits of said tubes, whereby signal waves present in said input sections are impressed in substantial entirety upon the tube Whose grid momentarily recelves a negative potential therefrom so that said latter tube alone repeats the signal.

4. A low-frequency amplifier for providing a high degree of substantially distortionless amplification in the absence of a biasing potential'in the control circuits v of said amplifier, comprising the combination of two repeating elements having a cathode, an anode and an input electrode, the cathodes of both said elements being connected together, an input repeating coil the secondar'ywinding of which is connected at an intermediate point to said cathodes, and at its opposite terminals to said mput electrodes respectively, and a high resistance interposed between said cathodes and said secondary winding adapted of itself to substantially prevent the flow of current in the control circuits of said repeating elements, whereby signal Waves present 1n said repeating coil are impressed in substantial entirety upon theelement whose input electrode momentarily receives a negative potential therefrom, so that said latter element alone repeats the signal.

8. An electric wave repeating apparatus comprising in combination a pair of" electron discharge devices each including anode, cathode and grid, an input transformer having a winding connected between said grids respectively, a connection from an intermediate point of said winding to said cathodes in common thr ough impedance means adapted to cause a signaling wave impressed upon said mput transformer to be repeated at each instant in substantial entirety by the send devlce WlllCll receives a negative potential therefrom.

9. An electric wave repeating apparatus comprising a pair of electron discharge devices each having anode, cathode and grid, an input transformer having a secondary winding connected between said grids respectively, a connection from an intermedlate point of said winding connected to saidcathodes in common through impedance means oi large magnitude relative. to the lowest grid-to-cathode resistances of said devices during operation for causing an impressed signaling wave to be repeated at each mstance in substantial entirety by the said device whlch receives a negatlve potentlal therefrom. J

[Oficial Gazette November 1;, 1988.1

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