US2374071A - Amplifier circuits - Google Patents

Description

April17,1945. L, E. BARTON 2,374,071

.AMrLIFIER CIRCUIT Filed ngc. 19, '19:56

:L E *El Saune.: or Pawn? Patented Apr.'17, 1945 UNITED STATES PATENT oFFlcs 2,374,071 s Y A Loy E. Barton, Collingswood, N. I., assignor, by

mesne assignments, to Philco Radio and Television Corporation, Philadelphia, Pa.,a` corporation of Delaware Application nmmber ,19. 193s, sum No. naso: Great Britain August 4, 1936 19 Claims. `(Cl. 179-171) This invention relates to improvements in radio amplifier circuits and, morel particularly, to a novel degenerative combined detector and audio amplifier system which may be used, for example, in a radio receiver, public address system, or the like, wherein it is desired to amplify the audio frequency signals with a minimum of distortion.

The principal object of the invention is to provide an improved system of this class embodying certain novel features or characteristics as set forth hereinafter in greater detail.

A more specific object of theinvention is to provide novel means for biasing the detector in a system of this type which eliminates the necessity of providing a relatively expensive filter condenser and, at the same time, enables the minimizing of hum voltages introduced in the signal channel through the detector plate circuit.

'Another object of the invention is to provide a novel tone control by means of which a selected portion of the audio frequency band may be augmented or diminished by variation of the amount of degeneration or regeneration of the selected signal.

A further object of the invention is to provide novel means ,for varying the amount of degeneration of the lower frequencies, which variation may be effected simultaneously with the volume adjustment, to thus vary the relative proportion ofvbass note reproduction.

Other objects and features of the system'will be apparent from the following description and the accompanying drawing, the single figure of which illustrates a combined detector and audio ampliiier system which may form part of a radio receiving system. It will be understood, of course, that the invention is not limited tothe specific system illustrated but is capable of use in any radio receiver or other system employing an audio frequency amplifier and signal utilization means. Certain features of the invention may be employed, for example in a simple amplifier oircuit in which there is no detector or demodulator.

Referring to the drawing, there is shown a diodeftriode tube V1, the diode elements of which are adapted to function as a detector and may be supplied Vwith modulated carrier-wave sgnals by means of the tuned transformer T1. .Such signals may be supplied from any suitable source, as represented by the source E. This signal source may, for example, represent the portion of a superheterodyne radio receiver preceding the second detector. Load resistors R1 and Rz are provided in the circuit of the diode rectifier and y quency signal to the control element or grid ofI tube V1 which functions both as a detector and las an amplier as well understood. It will be apparent that the signals appearing across thetapped portion ofthe potentiometer P1, plus any other signals which may be established between the cathode of tube V1 and ground, will be supplied to the control element of the tube.

The output of the tube V1 is obtained across the anode load resistor R3 and is thence transferred by means of the coupling condenser C4 and resistor R4 to an amplifier tube V2, the output of'which is supplied through an output transformer T2 to any suitable signal utilization means such as the loud speaker LS. The tube V2 may be apentode as illustrated or any other'suitable power output tube and may, if desired, be

self-biased by means of the resistor Rs and associated condenser C5 connected in the cathode lead of the tube as illustrated. The condenser Cs shunted across the primary winding of the transformer T2 serves to by-passv signals of very high frequency and also serves to vary the phase of such signals to some degree.

A portion of the output signal from the secondary of transformer T2 may be supplied through a coupling condenser C7 to a potentiometer Ps comprising two resistors R and Rn. The movable arm of the potentiometer P2 is adapted to move over both of the resistors Re and R1. grounded and the cathode. of tube V1 may be connected tothe common point of resistors Rs and R7 as illustrated. The movable potentiometer arm is connected through a condenser Cs to the cathode lead as illustrated for a purpose which will be explained later. A condenser C9, whose purpose will also be explained later, is connected in shunt relation with the resistor Rn.

By means of this arrangement, a portion of the signal in the output circuit of the system may be returned to the input of the amplifier system in a manner to cause the amplifier system to be degenerative. In other words, the potentiometer One end of the resistor R1 may be- P: is connected to the transformer T2 in such a manner as to eil'ect feed-back of a signal which y serves to decrease the output signal of the systern.l By virtue of the degenerative connection of the feed-back arrangement, any signal distortion incurred in the ampliiier channel will be materially diminished.

It is to be noted further that this system effects simultaneous variation of volume and degeneration in inverse relation to one another whenever potentiometer P1 is actuated. In addition to the degenerative or negative feed-back connection from potentiometer P2 to the cathode of V1, there is a regenerative or positive feedback connection extending from potentiometer P2 to the control grid of tube V1. This connection extends through the resistor R2 and the coupling condenser C3 to the ungrounded end of potentiometer P1. This positive feed-back pati is supplemented by a path in parallel with resistor R2, which includes the diode elements of tube V1, the secondary winding of transformer T1, and the resistor R1. Whenever potentiometer 'P1 is actuated, the positive feed-back voltage is varied in direct relation to the signal applied to the grid of tube V1, and hence the over-all negative feed-back voltage is varied in inverse relation to the applied signal.

Considering the impedance relations involved, generally speaking, the loud speaker will have a very low impedance of the order of 1 or 2 ohms, while the potentiometer P2 may have an impedance of the order of 1000 or 2000 ohms and, consequently, it will not cause any appreciable load on the output circuit. On the other hand, the impedance associated with the tube V1 may be of the order of 100,000 ohms and, therefore, with respect to the tube V1, the resistor R1 may be considered to be a source of signals having substantially zero impedance.

Variations in the frequency response of the amplier system may be obtained by varying the amount of degeneration of signals oi the diii'erent frequencies and, in fact, under certain conditions, the ampliiier system may be made regenerative in order to increase the response at certain frequencies. By suitably proportioning the respective circuit constants, this result may be obtained without affecting the stability of the circuit. For example, the` condenser` C1 will tend to reduce the amount of degeneration for those frequencies at which its impedance is comparable to the combined impedance of resistors Re and R1. At such frequencies, the feed-back signal which is set up across the resistor Rv is a relatively small proportion of the total feed-bacl-rA signal and, therefore, the amount of degeneration of the system is materially less than that obtaining for frequencies at which the impedance of condenser Cv is small or negligible in comparison to the combined impedance of resistors Rs and Rv. It will be seen, therefore, that the condenser C1 may be utilized to provide bass compensation by designing this condenser so that it has an impedance comparable to the impedance of potentiometer P2 for signals of those frequencies which sired to augment.

The condenser Ca may be utilized to decrease the high frequency response of the amplifier systemwhen the potentiometer control arm is on the resistance Re. For normal signal feed-back, the potentiometer arm will be positioned at the common point of the two resistors Re and R1 and, therefore. when the potentiometer'arm is on the it 1S deresistance Re, the signal feed-back will be greater than normal. 0n the other hand, when the potentiometer arm is on the resistance Rv, the sig' nal feed-back will be less than normal.

The resistance R1 will be small in comparison to the other resistors of the circuit of tube V1 and, therefore. no degeneration will occur in the tube V1 and its associated circuits other than the degenerative action of the system as whole. Therefore, maximum gain is obtained from the amplifier portion of the tube V1. .In order to provide adequate bias for the control element of tube V1, however, there is provided a resistance Rs which is connected between .the high potential side oi the power supply circuit and the resistor Rn. In this manner, a unidirectional current is caused to flow through resistor R1 which sets up a unidirectional voltage across this resistor, providing a suitable bias for the. control element of tube V1. This arrangement serves an additional important function in that it enables complete balancing out or bucking of hum signals. By connecting the resistor Ra to a suitable point on the power supply unit as illustrated and by properly designing the several circuit constants, complete hum bucking action may be obtained. It will be seen that the ripple voltage inthe power supply unit, which is inherently present due to the filtering action of the filter, is applied to the grid circuit of tube V1 through resistors Re and Rv and is also applied to the plate of tube V1 through resistors Re and R3. Moreover, it will be apparent that the phase of the signals applied to these two elements of tube V1 will be the same. Due to the phase reversal which takes place in the tube V1, the hum signal supplied to the grid circuit of the tube may be made to balance or buck out the hum signal supplied to the plate circuit of the tube. 'I'his action obtains when the ratio of the hum signal across resistor R1 to the hum signal built up across resistor R4 is equal to the amplification or gain of the tube V1 and when the two signals are alike in phase. The phase relation of these two signals may be controlled by proper design oi the values of Rs, Rv, Re and Rio and the condensers Cs and Cm. By suitable design of these circuit constants, substantially complete hum elimination may be obtained.

It may now be noted that the condenser Ca may be a relatively small condenser which serves to control the phase of the hum signal across resistor Rv rather than to prevent the formation of a hum signal across this resistor. This condenser replaces a relatively large and costly filter condenser which has been used in self-biasing arrangements. In this respect, the present invention effects an economy which is important in present day mass production.

The power supply unit may comprise a transformer Ta, a rectifier Va and a conventional filter including shunt condensers C11 and C12 and a series choke coil L. The. resistor Rm may be used to supply other tubes of the system.

In a specific system by means of which the results set forth above were obtained, the following circuit constants were employed:

Ri 50.000 ohms R 330,000 ohms R 1=250,000 ohms R4 1 megohm R6 1,400 ohms R7 600 ohms R8: 190,000 ohms B9=3,300 ohms 1- .0 me ohms Rw=75,000 ohms Epl-245 vo ts Eg-210 volts asesora The tube V1 may be a '15 type dicde-triode tube. while the tube V2 may be a SFS type tube. The power supply unit may be adapted to operate from a 60 cycle A. C. source.

Fromthe above description and the accompanying illustration, it will be seen that the invention providesa novel degenerative circuit by a very mw level and variation in frequency respense may be obtained by varying the amount of degeneration. Moreover, the invention provides novel means for obtaining both base compensation and high frequency compensation. While either of these may be fixed orv variable, the arrangement illustrated enabling variation of the high frequency compensation is particularly desirable.v The invention provides further a simple and convenient method of eliminating hum while, at the same time, providing a suitable bias for the input tube of the regenerative system.

llt will be understood, of course, that the invention is not limited to the specific system illustrated but is capable of various changes and modifications without departing from its scope.

I claim: 'i

l. In a signal amplifying device having an input circuit and an output circuit, said device including a space discharge device having grid and cathode electrodes connected to said input circuit, a potentiometer, a manually adjustable contact on said potentiometer, means connecting said potentiometer in shunt with said output circuit, a fixed intermediate tap on said potentiometer, means connecting one of said electrodes to said fixed intermediate tap whereby a portion of said potentiometer is included in said input circuit, and a connection including a reactance between said fixed tapand said adjustable contact, whereby the frequency response of said device may be varied by positioning said adjustable contact in relation to said fixed tap.

2. In a signal amplifying device having an input circuit and an output circuit, said deviceV including a space discharge device having a grid and a cathode connected to said'input circuit, a potentiometer, a manually adjustable contact on said potentiometer, means connecting said potentiometer in shunt with said output circuit, a fixed intermediate tap on said potentiometer, means connecting said cathode to said fixed intermediate tap whereby a portion of said potentiometer is included in said input circuit, and a v connection including a reactance between said fixed tap and said adjustable contact, whereby the 'frequency response of said device may be varied by positioning said adjustable contact in relation to said fixed tap.

3. In' a signal amplifying device having an input circuit and an output circuit, said device including'a .space discharge device having a grid and a cathode, connected to said input circuit, a potentiometer, a manually adjustable contact on said potentiometer, means including a condenser connecting said potentiometer in shunt with said output circuit, a fixed intermediate tap on said potentiometer, means connecting said cathode to said xed intermediate tap whereby a portion of said potentiometer is serially included in said input circuit, and a connection including a second condenser between said fixed tap and said adjustable contact.

4. In a signal amplifying device having .an inputcircuit and an output circuit, said device inf f cluding a space discharge device having a .grid

and a cathode connected to said input circuit, a

- means' of which signal distortion, may be kept at said potentiometenmeans including a condenser connecting said potentiometerin shunt with said output circuit, a fixed intermediate tap on said potentiometer, means connecting said cathode to said xedintermediate tap whereby a portion of :said potentiometer is serially included in said insaid potentiometer, means including a condenser connecting said potentiometer in shunt with said output circuit, a fined intermediate tap on said potentiometer, means connecting said cathode to said xed intermediate tap whereby a portion of' said potentiometer is serially included in said input circuit, and a connection including a second condenser between'said fixed tap and said adjustable contact, said first-mentioned condenser having a reactance which is comparable to the resistance of said potentiometer at a predetermined low audio frequency, whereby there results a decrease in degeneration below said predetermined frequency.

6. In an audio frequency amplifier having an input circuit and an output circuit, said amplifier including a space discharge device having a grid and a cathode connected to said input circuit, a potentiometer, a manually adjustable contact on said potentiometer, means including a condenser connecting said potentiometer in shunt with lsaid output circuit, a fixed intermediate tap on said potentiometer, means connecting said cathode to said fixed intermediate tap whereby a portion of said potentiometer is serially included in said input circuit, and 'a connection including a second condenser between said fixed tap and said adjustable contact, the reactancve of said second condenser being so related to the reactance of the first-mentioned condenser and the resistance of said potentiometer, that the degeneration of high audio frequencies increases as said adjustablel contact is moved toward, said first-mentioned condenser. 1

7. In a signal amplifying device having an in- Put circuit and an output circuit, said device including a, space discharge device having grid and cathode electrodes connected to said input circuit, a potentiometer, a. manually adjustable contact on said potentiometer, means connecting said potentiometer in shunt with said output circuit, a fixed intermediate tap on said poten' tiometer, said intermediate tap lyingv between the outer limits of movementy of saidiadjustable Contact, means connecting one `of said electrodes to said i'lxed intermediate tap whereby a portion of said potentiometer is includedin said input circuit, and a connection including a'freactance between said xed tap and said adjustable contact, whereby Vthe frequency response of said device may be varied by positioning said adjustable contact in relation to said fixed tap.

8. In a. signal amplifying device having an input circuit and an output circuit, said device including a, space discharge device having a grid and a cathode connected to said input circuit,

a potentiometer, a. manually adjustable contact potentiometer, a manually adjustable contact "on denser connecting said potentiometer in shunt with said output circuit, a nxed intermediate tap on said potentiometer, said intermediate tap lying between the outer limits of movement of said adjustable contact, means connecting said cathode to said fixed intermediate tap whereby a portion of said potentiometer is serially included in said input circuit, a connection including a second condenser between said fixed tap and said adjustable contact, and a third condenser connected between said fixed tap and one side of said output circuit.

9. In an audio frequency amplifier having an input circuit and an output circuit, said ampliner including a space discharge device having a grid and a cathode connected'to said input circuit, a potentiometer, a manually adjustable contact on said potentiometer, means including a condenser connecting said potentiometer in shunt with said output circuit, s, fixed intermediate tap on said potentiometer, said intermediate tap lying between the outer limits of movement of said adjustable contact, means connecting said cathode to said fixed intermediate tap whereby a portion of said potentiometer is serially included in said input circuit, and a connection including a second condenser between said iixed tap and said adjustable contact, the reactance of said second condenser `being so related to the reactance of the first-mentioned condenser and the resistance of said potentiometer, that the degeneration of high audio frequencies increases as said adjustable contact is moved toward said mst-mentioned condenser.

10. In an audio amplifying system, an audio channel including at least one space discharge device having an input circuit, means for supplying an input signal to said input circuit, a degenerative connection from said audio channel to said input circuit for supplying a degenerative control signal to the input circuit, and means for simultaneously varying the amplitude of the input signal and the amplitude of the degenerative control signal in inverse relation to one another.

l1. An audio frequency amplier system comprising an electron discharge amplifier .having an anode, a cathode and agrid, means for sup- Plying a signal to be amplified, a potentiometer connected in circuit with said signal supplying means and having its arm connected with said grid, a resistor connected between the low potential'end of said potentiometer and said cathode, and means connected across said resistor for supplying thereto a feed back voltage controlled by the current in the anode-cathode circuit.

l2, In an audio signal voltage transmission system, a source of audio signal voltage, an audio amplier having input and output circuits, means'for controlling the magnitude of the said voltage impressed on said input circuit, an audio signal voltage feed back circuit between the amplifier output circuit and input circuit for .feeding back signal Voltage in degenerative phase, and a second feed back circuit for feeding back signal voltage in regenerative phase, said controlling means being included in one of said feed back circuits thereby simultaneously to control the magnitude of one of said feed back volt- 8898.

13. In an audio amplifying system, an audio amplifier having an input circuit and an output circuit, an audio channel connected to said output circuit, a gain control potentiometer connected in said input circuit to vary the input signal applied thereto, and a degenerative connection from said audio channel to a predetermined intermediate tap point on said potentiometer for supplying to said input circuit a degenerative control signal whose amplitude varies in inverse -relation to the amplitude of the input signal over a potentiometer and a resistor connected to be` traversed in series by the signal to be amplified, means connecting said resistor and the adjacent adjustable portion of said potentiometer in said input circuit, and means for applying across said` resistor a feedback voltage in accordance with the current in said output circuit.

15. An audio frequency amplifier system comprising an electron discharge ampliiier having an input circuit and an output circuit, means for supplying a signal voltage to be amplified, means separate from and controlled -by said output circuit for producing a feedback voltage, and a device connected with said signal voltage supplying means, with said feedback voltage producing means and with said input circuit for simultaneously increasing the proportion of signal voltage applied to the input circuit and decreasing the proportion of feedback voltage supplied thereto, and said feedbackl voltage means being constructed to have a frequency discriminating characteristic.

16. An audio frequency amplifier system comprising an electron discharge amplifier having an input circuit and an outputl circuit, means for supplying a signal voltage to be amplified, means separate from and controlled by said output circuit for producing a feed-back voltage, and a device connected with said signal voltage supplying means, with said feed-back voltage producing means and with said input circuit for simultaneously increasing the proportion of signal voltage applied to the input circuit and decreasing the proportion of feed-back voltage supplied thereto. 17. An audio frequency amplifier system comprising an electron discharge amplifier having an input circuit and an output circuit, the resistance of the output circuit lbeing fixed, means for supplying a signal voltage to be amplified, means for supplying a feed-back voltage controlled by the current in said output circuit, and a device connected with said signal voltage supplying means, with said feed-back voltage supplying means and with said input circuit for simultaneously increasing the proportion of signal voltage applied to the input circuit and decreasing the proportion of feed-back voltage supplied thereto.

18. In" a radio receiver, a'souce of audio signals, an audio amplifier having an input circuit and an output circuit, a volume control device connected to said source and connecting said input circuit to said output circuit degeneratively for transferring to said input circuit controllable portions of the signal in said output circuit and, the signal from said source, said degeneratively connected volume control device including means for varying the said portions of said signals in such manner that the degenerative signal increases from a relatively low value to a maximum value as the volume control is progressively adjusted to decrease the output level from a maximum value to a low value.-

19. In an audio amplifying system, an audio ing said voltage regeneratively to said potentiom` eter, and means tor deriving another voltage from said output circuit and for applying said Ivoltage degenerativeiy to said input circuit, to thereby apply to said input circuit a resultant degenerative voltage whose magnitude varies inversely LOY E. BARTON.

lvffith the magnitude o! the input signal.

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