US2043587A - Distortionless transmission system - Google Patents

Description

June 1936 V w. MACALPINE 2,043,587

DISTORTIONLESS TRANSMISSION SYSTEM Filed Jan. 2, 1932 F -|i' llll} 55/ (59 5 INVENTOR 7 WViIIiIELI LS V Magipine ATTORNEY Patented June 9, 1936 UNITED STATES PATENT OFFICE DISTORTIONLESS TRANSMISSIoN SYSTEM Application January 2, 1932, Serial No. 584,357

6 Claims.

This invention relates to electrical amplifying systems and particularly to such systems having no intrinsic or extraneous distortion.

An object of the invention is to amplify efficiently, electrical signals.

Another object of the invention is to amplif electrical signal with fidelity.

A further object of the invention isto prevent the introduction of distortion during amplification with an electrical amplifier by neutralizing the distortion components during or after amplification.

It is well known in the art of amplification with amplifying systems employing thermionic vacuum tubes, or other amplifying devices of a like nature, that intrinsic distortion in the form of harmonics is introduced in the amplified signal by the non-linear characteristics of the amplifying device. There are also other sources of undesirable currents which are introduced in the amplified signal such as those from the power supplies for the different electrodes of the amplifying device. For instance, in a thermionic vacuum tube where the cathode heating source is alternating current, the fundamental or harmonics thereof may be found in the amplified output currents. Also B battery eliminatorsintroduce hum into signals being amplified whenever the filters for the eliminators are unbalanced or otherwise imperfect. Through indirectly heated cathodes, improved B eliminators and filters therefor, and by the use of push pull systems, a large amount of these undesirable components, such as the even harmonics, has been eliminated, although these methods fail to prevent tube noises caused by sputtering electrodes and odd harmonic components from being present in the output circuit.

The present invention contemplates a system in'which all undesirable current components of any form introduced during amplification are suppressed. This system not only eliminates the even harmonics, but other harmonic components which have a deleterious effect upon the amplified signals. a

The invention, in brief, operates on the principle of neutralizing the unwanted components either within the amplifying tube itself or in an auxiliary circuit. When a single tube'is used. a portion of the amplified signal output is returned to the input side of the amplifying device together with the distortion componentsin the proper phase relationship to prevent their creation within the tube. In another modification employing a small auxiliary amplifying device,

the distorting or noise portion of the output of the main amplifier is separated and amplified to the proper value to neutralize or balance out that present in the main output circuit when impressed thereon in reverse phase. In operation the system has produced exceptional results by correcting a very badly distorted output signal and which has been tested visually for a more accurate adjustment.

The invention will be more fully understood by 10 referring to the following description read in conjunction with the accompanying drawing in which:

Fig. 1 is a schematic of a single tube amplifying circuit in which the neutralization occurs within 15 the tube itself.

Fig. 2 is a schematic drawing of an amplifier circuit employing an auxiliary amplifier for corother means of obtaining the distortion components from the output of the amplifier proper.

Referring specificallyto Fig. 1, an amplifying device 5 is shown as a thermionic vacuum tube having an anode 6, cathode 1 and control electrode 8. An incoming line I U is coupled to the input circuit of the vacuum tube 5 by a coupling transformer II. The input circuit includes a biasing battery I2, the secondary of transformer H, and a feed back winding l3, which is one winding of three winding transformer I 4 The output circuit of tube 5 includes the anode 6, potential source l6 and primary winding 11 of transformer 14. An outgoing line l8 connectsto the secondary of transformer [4. The successful operation of this circuit depends upon the proper proportioning of the windings in the respective transformers, that is, winding l3 should have a smaller number of turns than winding H, dependent upon the amplification factor of the tube 5. The ratio of turns of windings l3 and I1 will vary inversely as the amplification factor.

In this particular circuit, neutralization is obtained by the induction from the winding I! to the winding I3 of both the fundamental and thedistortion components, the fundamental neutralizing about one half the voltage created across the secondary of transformer I I. In this manner the distortion components impressed upon the tube 5 are 180 out of phase with those being created by the tube 5 and neutralization is therefore obtained.

Referring now to Fig. 2 a circuit is shown in which the control is more flexible and in which all distortion components may be eliminated completely without loss of amplification in the main amplifier. An amplifier tube 20 has the usual electrodes and the usual grid biasing potential, cathode heating supply and anode polarizing source. An input line 22 is connected through the three winding transformer 23 to the input circuit of the tube 20, while the output circuit of the tube is connected to a primary 25 of another three winding transformer 26. An outgoing line is connected to the terminals 21 and consequently to the secondary of the transformer 26. Another vacuum tube similar to tube 20 but which may be of much smaller capacity has an input circuit including the third winding 3| .of transformer 26 and the third winding 32 of transformer 23, both of which are shunted by potentiometer resistances 33 and 34, respectively.

The windings 3| and 32 are connected in a series relationship so that the voltages therefrom are subtractive. Therefore, as the fundamental signal exists in both windings of the input circuit, but 180 out of phase, the proper adjustment of the potentiometers 33 and 34 will eliminate this signal so that the only voltage variations impressed upon the tube 30 are those added to the signal in the amplifying device 20. The adjustment of these potentiometers for neutralizing the fundamental signal is such that the voltage of the fundamental signal coming from potentiometer 33 is equal to the voltage of the signal coming from potentiometer 34. After amplification in the tube 30 these distortion components are impressed upon the output circuit 21 through an output transformer 36, in phase opposition to those already induced therein from winding 25, and therefore eliminate each other in this circuit. By adjusting the potentiometers 33 and 34, a proper neutralization amplitude may be obtained both in the input of the tube 30 for the signal and in the output circuit 21 for the distortion components. The adjustment of these potentiometers for neutralizing the distortion components is accomplished by moving both potentiometers simultaneously and in such amounts as to maintain neutralization of the fundamental signal, but which movement varies the input of the distortion components to the grid of tube 30, It is to be understood that the connections for. the various transformer windings are such as to produce phase opposition for the various portions of the amplified signal.

Referring to Fig. 3 in which a circuit similar to that shown in Fig. 2 is illustrated, there is a variation in the connections of the incoming and outgoing lines and in the output circuitof the main amplifier. In this schematic, a main amplifier tube 40 is connected to an incoming line 4|, through an input transformer 42. A correcting tube 44 is also connected to the incoming line 4| through an input transformer 45. The output of tube 40 is connected to an outgoing line 41 through an output transformer 48, the primary of which is shunted by a potentiometer resistance 49. Similarly, the distorting tube 44 is connected to outgoing line 41 through an output transformer 50. The potentiometer 49 operated in conjunction with a potentiometer 52 across the secondary of transformer controls the feed back from the output circuit of tube 40 to the input of tube 44. In this particular arrangement it is to be noted that a common anode potential source 54 serves for both tubes, and a blocking condenser 55 of large value prevents a short circuit of this battery and serves as a very low impedance to the feed back currents. A condenser 56 is shown shunting the secondary of transformer 45 to prevent high frequency singing but with the proper proportioning of the constants of the circuit it is usually not required. A high resistance 58 together with a biasing potential 59 serve to maintain the control electrode 44 at the proper operating point. It is to be noted in this circuit that instead of a transformer coupling between the output of the signal amplifying tube and the input of the correcting tube as shown in Fig. 2, that a direct connection is made but one which subtracts the voltage in the potentiometer 49 from the potential obtained across the used portion of the potentiometer 52. These two adjustments permit neutralization of the true signal passing through the amplifier 40 and permit only the distortion components to be impressed on the tube 44 for amplification therein. After amplification these components are impressed on the outgoing line 41 through the output transformer 50, thereby neutralizing those in the main amplifying circuit. This circuit has operated over a considerable band of frequencies with satisfactory visual and audible results. Transformers 42 and 45 may be combined into a single transformer with one primary and two secondaries, as illustrated by transformer 23 in Fig. 2, and transformers 48 and 59 may be combined into a single transformer with two primaries and q one secondary as illustrated by transformer 26 in Fig. 2.

In the above circuits, individual batteries have been shown for the respective electrodes of the amplifying tubes, but it is to be understood that these circuitsmay be connected to the usual B and A battery eliminators or the tube cathodes may be indirectly heated, the principles of the invention being applicable to the modern tubes and circuits therefor.

The invention is not limited to the three electrodetubes shown in the figures. It is particularly desirable for use with pentode tubes. If the two tubes 40 and 44 are of equal size, the

power output will beabout double that of one' tube, with the additional feature of eliminating distortion.

What is claimed is:

1. In an electrical amplifying system, a thermionic device adapted to amplify electrical signals, a cathode, an anode and a control electrode for said device, an input circuit for said device connected between said cathode and control electrode, an output circuit for said device connected between said cathode and anode, a second thermionic device having similar input and output circuits, said input circuit being associated with the input of said first thermionic device and said output circuit being associated with the output circuit of said first thermionic device, means for connecting the output circuit of said first thermionic device with the input circuit of said second thermionic device, and means included in said connecting means for varying the amplitude and phase of the currents in said connecting means.

2. In an electrical amplifying system, a thermionic device adapted to amplify electrical signals, said device introducing distortion components during amplification, an input circuit for said device, an output circuit for said device, a second thermionic device having input and output circuits, said input circuit being associated with the input circuit of said first device and said Output circuit being associated with the output circuit of said first device, and means connecting the output circuit of said first device to the input circuit of said second device, said means including a voltage adjusting device for equalizing the output voltage in the output circuit of said first device with the input voltage obtained from the original signal.

3. In an amplifying system, a thermionic discharge device comprising a cathode, an anode, and a control electrode, an input circuit for impressing on said device a signal to be amplified, an output circuit for said device, said output circuit containing said amplified signals and distortion components produced by amplification, a second thermionic device, means for impressing on said second device equal amounts of amplified signal and original signal in phase opposition, said second device amplifying said remaining components, and means for combining the outputs of said thermionic devices for balancing out the distortion components produced in said first device.

4. In an amplifying system, a thermionic device having a cathode, an anode and a control electrode, means for impressing signals to be amplified between the cathode and control electrode, an output circuit connected between the anode and cathode for transmitting the amplified signals, said signals including certain undesirable currents produced by amplification, a second thermionic device, means for impressing on said second device only the undesirable currents produced in said first device, said means including means for impressing on the input of said second device a portion of the amplified signal and an equal portion of the original signal in phase opposition, and means for intercoupling the output circuits of said devices for neutralizing the undesirable currents produced in said first device.

5. In an electrical amplifying system, a plurality of electrical amplifiers, means for impressing upon said amplifiers divided portions of a signal to be amplified, means for combining the outputs of said amplifiers in a common output circuit, means for impressing on the input of one of said amplifiers a portion of the output of another of said amplifiers, the amount of said portion being determined by the portion of said original signal impressed thereon, means for reversing the phase of the amplified signal currents, and means for reversing the phase of the distortion components in said amplified signal.

6. In an electrical signaling system, an amplifier, an input circuit and an output circuit therefor, an incoming line connected to said input circuit, an outgoing line connected to said output circuit, a second amplifier of smaller capacity than said first amplifier, means for coupling the input of said second amplifier to said outgoing line, means for coupling the input of said second amplifier to said incoming line, and means for coupling the output circuit of said first amplifier to the input circuit of said second amplifier for impressing on said second amplifier distortion currents produced in said first amplifier, the signal currents being neutralized in the input circuit of said second amplier, the distortion components being neutralized in the output circuit of said first amplifier.

WILLIAM W. MACALPINE.

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