US1833085A - Volume control - Google Patents

Description

Nov. 24, 1931. v. c. MACNABB 1,833,085

I VOLUME CONTROL Filed Aug. 18, 1950 Patented Nov. 24, 1931 UNITED STATES PATENT OFFICE PENNSYLVANIA, ASSIGNOB TO ATWATEB PHILADELPHIA, PENNSYLVANIA, A COR- VOLUME CONTROL Application filed August 18, 1930. Serial No. 478,013.

My invention relates to radio-receiving systems utilizing thermionic tubes for the amplification of radio-frequency signal energy, and particularly to systems of such character which include a source of commercial alternating current for supplying current to electrode circuits of the tubes.

In accordance with my invention, control of the volume or amplitude of reproduction is efi'ected by varying both the amplification characteristic of the radio-frequency amplifier tubes and the transfer of radio-frequency signal energy to or between the amplifier tubes; preferably, and to ensure high ratio of signal to noise and elimination of noises due to improper operating conditions of the amplifier tubes, the volume is first reduced by suitably modifying the amplification characteristic, for example by increase of ,the negative grid biasing potential, with insubstantial or no change by reduction of the ener transferred, and to effect further reductlon in volume, the transfer of signal energy is lessened with decreasing or insubstan- =tial effect by modification of the amplification characteristic; more specifically, in seeking suitably low volume, it is provided that the negative grid bias cannot be adjusted to such high value that the ampl ifier tubes are modulating or have a detecting action on the received signals.

Further in accordance with my invention, the control of both the amplification characteristic andthe transfer of signal energy is variable by a single adjustable element, as a knob or dial. In some forms of my invention, the knob, or equivalent, is mechanically coupled to movable contacts adjustable along independent resistances, one of which, for example, may be in circuit with, as in shunt to, a coupling element, and the other of which may be in circuit between the grids and cathode of one or more of the tubes, while in another form of my invention, the volume control knob is mechanically connected to the movable contact-of a single resistance, which more specifically. is in'shuntto a coupling element, as the primary winding of a transformer, and also common to the grid and anode circuits of one or more of the tubes.

'My invention further resides in the methods, systems and features hereinafter described and claimed.

For an understanding of my invention and for illustration of some of the various cirapparatus with power supply and reproducer;

Fig. 3 is a wiring diagram of a modified form of my invention.

Referring to Fig. 1, signal energy received by the absorption or antenna structure A is impressed upon the input circuit of a radio frequency amplifier tube V and preferably again amplified at radio frequency by one or more tubes V1, V2, etc. Adjustment of the contact G along resistance R varies the amount of resistance or impedance in shunt to the input element L of the tube V, which may be the winding of a transformer, or, as indicated, a coupling impedance. By adjusting the position of contact C, the amount of energy transferred, and ultimately the volume of reproduction, is controlled, the transfer decreasing as the contact C approaches the antenna end of the resistance and vice versa. However, this simple control is not satisfactory for the control of volume of strong signals, as when the contact 0 is moved to include but a small portion of the resistance R in shunt to the input element L, and the amplification of the tubes V, V1, etc., maintained high, the ratio of signal to noises incident to high amplification by thermionic tubes, is low.

To control the amplification characteristic of the radio frequency amplifier tubes, contact C may be adjusted along resistance R1, which is included in circuit between the grids and the cathodes f of, for example, the tubes V and V1. The resistance is traversed by current flowing from the cathode to the grid terminal of the resistance so that the grids of the tubes are negative with respect to their cathodes. Adjustment of the contact G varies the amount of resistance R1 traversed creased to such an extent that the tube is working on a curved or rectifying portion of its characteristic, resulting in unsatisfactory operation, particularly when, as indicated, the tubes are supplied from an alternating source, as there then resultsmodulation of the incoming signal, causing hum and distortion. To maintain high ratio of signal to noise and high quality of reproduction, I first decrease the amplification eifected by the tubes by increasing the negative grid bias but not to such extent that they are working on a curved portion of their characteristic and effect further reduction of volume by changing the transfer of signal ener These results may be obtained by com ining the two above described and individually unsatisfactory controls as hereinafter set forth.

Preferably the contact C is connected to earth or equivalent to which is connected the negative terminal of the source of grid bias and potential. For example, the negative terminal of the B battery or equivalent supplying plate-current may be connected to earth so that the anode current reversing the resistance is utilized in. that portion of its path between cathode and. earth to provide a grid bias potential. As the contact C is rotated in counter-clockwise direction, Fig. -1, the amount of resistance traversed by the anode current, and therefore the negative potential applied to the grid G, is increased. The choice of the value of resistance R1 depends upon the amount of current flowing through it, the characteristics of the tubes utilized, etc., and is so chosen that when the contact C has been turned in counterclockwise direction to the grounded terminal of resistance R1, the grid bias is not so high that the tube is operating upon a curved portion of its characteristic, for example its grid-voltage plate-current characteristic.

.For instance','it may have a resistance of the order of 6000 ohms, and the resistance of R may be of the order of 2000 ohms. Both of the resistances are or may be wire-Wound, and may be more or less inductive, though either or both may be non-inductive.

The resistance R2 in circuit between the unground terminal of resistance R1 and the cathodes f of the tubes is of such value that when the control contact C is in maximum volume position, i. e., at the :ungrounded end of resistance R1, the biasing potential applied to the grids of the tubes is not too low or satisfactory operation.

Accordingly, to reduce the volume of strong signals, the contact C is rotated in a counter-clockwise direction in engagement with resistance R1 to increase the negative grid bias. As the contact C passes beyond the grounded terminal of resistance R1, the negative bias remains constant at the predetermined maximum value, and the value of resistance R, in shunt to the input element L, is progressively reduced, lessening the transfer of energy from the antenna circuit to the input circuit of the tube V.

It will be understood that the resistance R and R1 may be mounted for successive engagement by the contact C or may each have its own contact arm, the arms being so mechanically connected that upon rotation of a volume controlling knob the amplification is first reduced b adjustment of the contact along resistance 1 and subsequently further reduced by adjustment of a contact along resistance R. With the latter arrangement, the contact arms or the resistances may be so staggered that control of volume may be simultaneously effected by change in the amplification and the transfer of signal energy, although in any event I prefer that in the reductlon of volume the change in volume be effected preponderantly by decreased amplification and subsequently preponderantly by decrease in transfer of signal energy.

While for purpose of illustration the 1"e sistance R has been shown in the system coupling the antenna to the input system of the first tube, it will be understood that it may be an interstage coupling system, for example, in shunt to the primary P of the transformer T coupling the tubes V and V1. When the tubes are of the type utilizing a uni-potential cathode raised to electron emitting temperature by heaters supplied, for example. with alternating current, the end of resistance R2 remote from resistance R1 will be connected to the uni-potential cathode. In receiving apparatus utilizing screen grid tubes, the resistances R1 and R2 may be in cluded in the control grid circuit exactly as in Fig. 1, in which the tubes shown are of the triode type.

Theyolume control of Fig. 2 is essentially the same as that of Fig. 1. The resistance R, in shunt to the input element L, is variable by adjustment of the contact C for Varying the transfer of signal energy. The magnitude of resistance R1 may be varied by adjustment of the contact C1 to change the bias supplied to the grids of the radio frequency amplifier tubes. Adjustment of the volume control knob K efiects simultaneous movement of the contacts C and C1. In moving the knob counter-clockwise to reduce volume, the change of resistance R is at first of little or no effect, but becomes increasingly effective as the contact C approaches the antenna terminal of the resistance. The simultaneous movement of the contact G1 at first is predominant in efiecting control of volume as the change in the bias potential appliedto the grid rapidly decreases the amplification". Al-

though the contacts C and C1 are mechani cally coupled to simultaneously changethe values of both resistance R and R1, the change of resistance of R1 at first preponderates in reducing Volume, While subsequently the change of resistance R preponderate in a control of volume. The effect upon the ear is a smoothly continuous change of volume with no marring of the reproduction by tube noises due to high amplification, distortion, or by hum, etc. The circuit positions of the two resistances, one of which controls amplification and the other of which controls energy transfer, may be varied without departing from the spirit and scope of my invention.

The signal energy impressed upon the input elementL is amplified by the tubes V, V1 and V2 at radio frequency, then rectified by the detector tube V3 and the resulting audio frequency current amplified by tubes V4 and V5, the last of which includes in its output circuit the loud speaker D, or other reproducing apparatus. Current for all of the tubes may be supplied from a transformer 6 who e primary p is connected to a suitable source of alternating current of commercial voltage and frequency, although suitable batteries may be employed. The terminal of-resistance I R2 remote from resistance R1 is connected to a point of uni-potential determined, for example, by a center tapped resistance r in shunt to the secondary s1 supplying current to the cathodes of the tubes V. V1 and V2. The plate-current of these tubes, supplied by the secondary .92 of the transformer and'the rectifier through a suitable filtersvstem, traverses the resistance RQand that portion of resistance R1 between the contact C1 and the terminal connected to resistance R2. 'It will be understood that the biasing potential 1 may be derived in other ways. (For example,

resistances R1 and R2 maybein circuit with a' bleeder resistance across the filter circuit. with suitable connections to the grid and cathode structure of one or more of the tubes, or alternatively, the resistances R1 and R2 may be connected across a properly poled C battery.)

In the modification shown in Fig. 3, a single resistance R3 has one terminal 7" connected to the cathodes of the tubes V and V1 and its other terminal h is connected to the high potential end of the input element L, which in the example specifically'shown is the primary winding of an autotransformer coupling the antenna circuit to the input of the tube V.

That portion of resistance R3 between the contact C and the point It corresponds to resistance R of the preceding modifications,

and that portion of the resistance between the contact and its terminal f corresponds to the resistance R1 of the modifications previousl described. In reducing volume the contact is turned in counter-clockwise direction progressively reducing the section B and thereby increasing the shunting effect upon the input element L1. At first the ratio between the v impedance of the input element L and imsense to reduce the volume. When the con-' tact C is moved away from the terminal f, the amplification at first changes rapidly but the change becomes less and less as the contact C approaches the other terminal of the resistance.

The resistance'of R3 may be of the order of 200.0 ohms although it will be understood that the value may vary considerably there rom.

It will be understood that when my invention is utilized in other circuit positions, it may be necessary to use blocking condensers to prevent short circuiting of direct current through the resistance R. For example if in Fig. 3, the terminal h of resistance R3 is connected to the plate end of the primary p of transformer T to control the energy transfer between the output circuit of tube V and the input circuit of V1, there should be in- At the same time that the section B cluded in this connection a condenser of suit- I able low impedance to radio-frequency currents. A

What I claim is:

-1. In the operation of radio-receiving apparatus utilizing thermionic tubes for amplifying or repeating radio-frequency signal ,11'.) energy, the method of reducing the volume quencysignal energy between limits within which high ratio of signal to noise obtains,

and simu taneously varying the amplification characteristic of one or more of said tubes within limits between which the curvature of the grid-voltage plate-current characteristic is not pronounced.

3. In the operation of radio-receiving apparatus utilizing thermionic tubes for ampliying or repeating radio-frequency si nal energy, the method of reducing the v0 ume or amplitude of signals which comprises modifying the amplification characteristic of one or more of said tubes to decrease the amplification of signal energy, and simultaneously decreasing the transfer of signal ener the reduction at first being preponderant y by decrease of amplification ,and subsequently preponderantly by decrease of transferred signal energy.

4. In the operation of radio-receiving apparatus utilizing thermionic tubes for amplifying or repeating radio-frequency signal energy, the method of reducing volume or amplitude of signals which comprises increasing the negative potential applied to the grid structure of one or more of said tubes but not to such extent that the curvature of the grid-voltage plate-current characteristic is pronounced, and thereafter decreasing the transferred signal energy for further reduction in volume.

5. In the operation of radio-receiving a paratus utilizing thermionic tubes for amp ifying or repeating radio-frequency si al energy, the method of effecting contro of volume or amplitude of reproduction, which comprises varying the biasing potential ap-- plied to the grid structure of one or more of said tubes, and simultaneously varying a shunting effect upon a coupling element effective in transfer of signal ener the effect of variation of biasin potentlal' preponderatin in one part of the range of volume contro and the effect of shunting the coupling element preponderating in another part of the volume control range.

6.. Radio-receiving apparatus comprising one or more thermionic tubes, rad1o frequency input and output systems therefor including couplin elements, and a volume control element a justable to vary both the biasing potential of the grid of one or more of said tubes and the magnitude of transfer of signal energy by on or more of said coupling elements, the mo ement of said element varying the grid potential within limits between which the curvature of the grid-voltage plate-current characteristic is not pronounced, and the transfer of signal energy within limits between which high ratio of signal to noise obtains.

7 Radio-receiving apparatus comprising cascaded thermionic tubes, absorption structure, a plurality of radio-frequency coupling means for coupling said absorption structure to the first tube of said cascade and the input and output circuits of said tubes, and a volume control element adjustable both to vary the amplification characteristic of one or more of said tubes and the transfer of signal ener by at least one of said radio-frequency coupling means, movement of said element in one portion of its range of movement effecting control of volume principally by variation of the amplification characteristic, and in another portion of its range of movement efi'ecting control of volume principally by chan e in the transfer of signal energy.

8. Ba io-receiving apparatus comprising one or more thermionic tubes, radio frequency coupling elements in the input and output circuits thereof, impedance in circuit with at least one of said coupling element to vary the transfer of signal energy, a source of grid-biasing otential, and a volume control element ad ustable to vary both the ef fective magnitude of said impedance and the potential impressed upon the grid of one or more of said tubes by said source of biasing potential, the movement of said element varying the grid biasing potential within limlts between which the curvature of the grid-voltage plate-current characteristic is not pronounced, and the transfer of signal energy within limits between which high ratio of signal to noise obtains.

9. Radio-receiving apparatus comprising one or more thermionic tubes, radio frequency coupling elements in the input and output circuits thereof, a resistance in shunt to at least one of said radio-frequency coupling elements to control the transfer of signal energy, resistance in circuit between the cathode and grid of at least one of said tubes, means for effecting flow of direct current through said second resistance from the catlr ode terminal to the grid terminal thereof, and a volume control element adjustable to vary the effective magnitudes of both of said resistances, the movement of said control element in one part of its range changing the volume preponderantly by variation of gridbiasing potential, and in another part of its range changing the volume preponderantly by variation of the transfer of signal energy.

10. Radio-receiving apparatus comprising one or more thermionic tubes, radio frequency coupling elements in the input and output circuits thereof, a resistance in circuit with at least one of said radio-frequency coupling elements, resistance in circuit between the cathode and grid of at least one of said tubes. means for effecting flow of direct current through said second resistance so poled that the grid of said tube is negative with respect to its cathode, and a volume control element adjustable simultaneously to vary the effective magnitudes of said resistances, the movement of said control element in one part of its range changin the volume preponderantly by variation 0 negative grid-biasing potential, and in another part of its range changing the volume preponderantly by variation of the transfer of signal energy.

' 11. Radio-receiving apparatus com rising one or more thermionic tubes, ra io-frequency coupling elements in the input and output circuits thereof, a resistance in shunt to at least one of said radio-frequency coupling elements, resistance in circuit between the cathode and grid of at least one of said tubes, means for efl'ectin flow of direct current through said secon resistance so poled that the grid of said tube is negative with respect to its cathode, and a volume control element adjustable simultaneously to vary in opposite senses the efi'ectivema nitudes of said-resistances cumulatively to e ect chan e in volume or amplitude of reproduction, tfie efi'ect of variation of one resistance preponderatin for one part of the range of movement 0 said control element, and the effect of variation of the other resistance preponderating for another part of the range of movement of said control element.

12. Radio-receiving apparatus comprising one or more thermionic tubes, radio-frequency coupling elements in the input and output circuits thereof, a resistance in circuit with at least one of said radio-frequency coupling elements, resistance in circuit between the cathode and grid of at least one of said tubes, means for effecting flow of direct current through said second resistance so poled that the grid of said tube is negative with respect to its cathode, and a contact arm adjusta le along and engaging said resistances in succession, in control of volume of strong signals from maximum to minimum, whereby initial movement of said arm reduces volume by increase of the negative grid-biasin potential, and subsequent movement of sai arm reduces volume by decreased transfer of signal energy. a

13. Radio-receiving apparatus comprising one or more thermionic tubes, radio-frequency coupling elements in the input and output circuits thereof, a resistance in circuit with at least one of said radio-frequency coupling elements, resistance in circuit between the cathode and grid of at least one of said tubes, means for 'efiectin flow of direct current through said secon resistance so poled that the grid of said tube is negative with respect to its cathode, and a control member movable to increase the magnitude of said second resistance in initial reduction of volume, and thereafter to decrease the magnitude of said first resistance for further reduction of volume.

14. Radio-receiving ap aratus comprising one or more thermionic tu s, radio-frequency coupling elements in the in ut and output circuits thereof, a resistance aving one terpreponderantly by change of negative minal connected to a terminal of one of said coupling elements and another terminal connected to the cathode structure of one or more of said tubes, an adjustable contact movable along said resistance and connected to another terminal of said coupling element and to the negative terminal of a source of direct current effecting flow of current through that portion of said resistance between said contact and said cathode structure, whereby movement of said contact in one part of its range effects control of volume idbias and in another part of its range e ects control of volume preponderantly by change in signal transfer.

15. In the operation of radio-receiving apparatus utilizing thermionic tubes for amplifying or repeating radio-frequency signal ener the method which comprises controlllng the volume or amplitude of reproduction of strong signals throughout a range of volume partially by varying the transfer of radio-frequency signal energy between limits within which high ratio of si al to noise obtains, and partially by varying the amplification characteristic of one or more of said tubes within limits between which the curvature of the grid-voltage plate-current characteristic is not pronounced.

VERNON G. MACNABB.

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