US1849821A - Electric signal amplifier - Google Patents

Description

March 15, 1932. w L. CARLSQN ELECTRIC SIGNAL AMPLIFIER Filed April 10, 1950 Inventor: Wendell L. Carlson by His -Atto r*neg.

Patented Mar. 15, 1932 V UNITED STATES PATENT QFFICE WENDELL L. CARLSON, OF .I-IADDO'NFIELD', NEW JERSEYQASSIGNOR TO GENERAL ELEC- TRIC COMPANY, A CORPORATION OF NEW YORK ELECTRIC SIGNAL AMPLIFIER Application filed April 10,

The present invention relates to electric signal amplifiers embodying electric discharge amplifier devices, and more particularly it relates to means for controlling the signal volume secured from the output of such amplifiers. I

It is the object of the present invention to provide an improved means for controlling the signal volume secured from the output of anelectric discharge amplifier apparatus which operates in such a manner that noises which may be introduced into the output by the electric discharge devices are reduced to amimmum. V 0 The invention will be better understood from the following description when taken in connection with the accompanying drawing and its scope will be pointed out in the appended claims.

' In the drawing, the figure is a schematic wiring diagram of an electric signal amplifier embodying electric discharge amplifier devices and provided with means embodying the invention, for controlling the signal volume secured from the output of said amplifier.

Referring to the drawing, 5 and 6 are electric discharge devices of the four-element vacuum tube type, cascade connected in an electric signal amplifier between an input circuit 7 represented by the primary of an input transformer 8 and an output circuit 9 represented by the secondary of an output transformer 10. An intermediate transformer 11 serves to couple the devices 5 and 6 together in cascade.

Suitable operating potentials forthe anode and grid bias circuits of the electric discharge devices or tubes are supplied through leads 12 and a supply resistor 18, 14, from which resistor suitable operating anode potentials are taken in the usual manner, as indicated in the drawing. a

Connected with at least one of said electric discharge devices is a means for controlling the transmission efiiciency of said device. Such means may be arranged to control the operating potential upon any one of the various elements of the electric discharge device, as is well known. In the present example, con- 1930. Serial No. 443,196

the fixed resistor 15 provides a fixed amount of bias for the electric discharge devices or amplifier tubes while variable resistor 18 provides an additional variable bias in series with the fixed bias provided by resistor 15; The resistor shown in the present example is varied by moving. the contact arm'20 along the resistor and between the terminals 19. As shown in the drawing, movement of the contact to the left serves to increase the resistance in circuit with fixed resistor 15 and to increase the amount of bias applied to the electric discharge devices 5 and '6. As the bias voltage on the grids 17 is increased, it will be understood that the amplification or transmission efliciency of the electric discharge devices is reduced. Thus, by moving the contact arm 20 to the left, as viewed in the drawing, the signal volume delivered by the arm plifier to the output circuit 9 is gradually reduced. I When the amplifier devices 5 and 6 are operating at maximum efficiency for the transmission of the signals through the amplifier, such operation may be accompanied by a hiss or undesirable sounds of operation introduced into the output because of the sensitive condition oi? operation of the amplifier devices. It is, therefore, desirable to operate such devices slightly below their maximum operating efliciency. In' the present example, this is done by slightly increasing the negative bias applied to the grids 17, thereby reducing the sensitivity of said devices through the medium of thecontrol means 18. It will be noted that the fixed'resistor 15 and the variable resistor 18 are suitably bypassed by a fixed capacity 21 connected'with may be insufiicient for the proper control of the signal volume delivered by the amplifier.

For example, in the presence of strong signals from an antenna and ground system 2223, when applied to the input circuit 7 directly, overloading of the input amplifier device or tube 5 is almost certain to result.

Accordingly, there is provided in connection with the input circuit 7 a means for varying the signal strength applied to said input circuit. In the present example this isin'a form of a variable resistor 24: introduced between a pair of signal supply tor minals 25 and 26 and the input circuit 7, said terminals being connected respectively with the antenna 22 and the ground 23.

' The resistor24 is provided with a movable element or contact 27 which is movable'between terminals 25' and 26 and along the resistor 24. The movable contact 27 is connected withthe input circuit 7 while the opposite 'sideof the input circuitis connected'with the grounded input terminal 26. V

The, variable resistor 24' is providedwith an-inactive resistance portion 28, over which movement of contact 27 produces no appreciable change in the resistance between either of the terminals 25 and 26 and the contact arm 27. The arrangement is such that the movable control arm or contact 27 may be moved an appreciable distance through its range of movement represented by the terminal limits 25 and 26 without efiecting any appreciable. control of the input signal volume applied to'the input circuit 7. As the movable member 27 is further moved toward the ground or low potential terminals 26, re-

.sistance is gradually introduced into the antenna circuit and alower and lower resistance is placed in shunt with the input circuit 7 thereby serving to reduce the signal strength applied to the input circuit 7. Any other suitable arrangement of a control means for varying the signal volume or signal strength applied to the input circuit may be employed, however, providing that it is also arranged to efl'ect no appreciable change in the input signal strength over a portion of its range of movement.

-With the means for controlling the signal volume at the input so arranged, it is connected with the movable member 20 of control means 18 and a common control means indicated'at29 through any suitable means such as a common shaft 30, thus providing a dual volume or signal output control for the amplifier.

With this arrangement, it will be seen that when reducing the transmission eificiency oi the amplifier devices, thereby to reduce the volume or the signal output, during the first portion of the movement of the control means the movable element 20 of the bias control means serves to increase the resistance in the cathode circuit which increases the negative bias on the tubes 5 and 6, while movement of the member 27 of the controlmeans 26 does not appreciably effect the signal strength applied to the input circuit 7.

lVith the transmission efficiency or sensitivity of the electric discharge amplifier thus partially reduced, the signal output is further reduced by continuing to reduce the sensitivity or transmission efficiency of the amplifier devices while the input energy or signal voltage applied to the, input circuit of the amplifier is also reduced simultaneously. Likewise, when the output volume is increased, the sensitivity or transmission efiiciency-of the amplifier is simultaneously increased along with the input energy or signal voltage applied to the input circuit, until the maximum signal strength is applied to the input circuit while the sensitivity or transmission efficiency I re ofthe amplifier is at a reduced value. For

increased signal output, the sensitivity or transmission efficiency of the amplifier 1S further increased up to a desired maxlmum point determined by the limit of the selected range ofcontrol of the transmission efiiciency of the particular electric discharge device or devices employed. r

This arrangement of controls has been found to be very eflective, in providing for quieter operation of a signal amplifier embodying electric discharge devices. The dc layed control feature in connection with the means controlling the input signal strength may be applied to any electrical signal amplifier having aninput circuit and means for controlling the transmission eificiency of at least one of the electric discharge amplifier devices. It is particularly well adaptedfor the control of electric signal amplifiers em ployed in connection with radio receiving apparatus and the like.

What I claim as new and desireto secure by Letters Patent of the United States, is :v

1. -The combination with an electrical signal amplifier having an input circuit, an output circuit and at least one electric discharge amplifier device connected between said circuits for the transmission of signals from said input to said output circuit, of means for varying the transmission efiiciency of said amplifier device between predetermined limits, and means forvarying thesignal strength nal amplifier having an input circuit, an output circuit and at least one electric discharge amplifier device connected between said circuits for the transmission of signals from said input circuit to said output circuit, of means provided with an element movable between certain limits to vary the transmission efiiciency of said amplifier device, means for varying the signal strength applied to said input circuit, said last-named means being operative to reduce the signal strength applied to the input circuit only after the transmission eiliciency of the amplifier device is partially reduced by said first-named means, and means for operating said second-named means simultaneously with said first-named means.

3. The combination with an electrical signal amplifier having an input circuit, an output circuit and at least one electric discharge amplifier device connected between said cir cuits for the transmission of signals from said input to said output circuit, of means provided with an element movable between certain limits to vary the transmission efliciency of said amplifier device, a variable resistor,

said resistor having a movable element arranged to vary the signal strength applied to said input circuit, the movement of said element being efiective to vary the signal strength only over a portion of its range of movement, and means connected with said movable elements for moving the same simultaneously.

4:. The combination with an electrical signal amplifier having signal supply terminals, an input circuit, an output circuit and at least one electric discharge amplifier device connected between said circuits for the transmission of signals from said input to said output circuits, of means provided with an element movable between certain limits to vary the transmission efi'iciency of said amplifier device, means for varying the signal strength applied to said input circuit from said supply terminals, said last-named means including a variable resistor connected between said supply terminals and said input circuit and having a movable control element by which said signal strength is varied, the

vmovement of said control element being efiective to vary the signal strength over a portion only of its range of movement, and a cuit, said movable elements having the same range of movement and the element movable to control the signal strength having a lesser range of efiective control.

6. The combination with an electrical signal amplifier having an input circuit, an output circuit and at least one electric discharge amplifier device connected between said circuits for the transmission of signals from said input to said output circuits, of means simultaneously movable to vary the transmission efficiency of said amplifier device and a signal voltage applied to said input circuit, the range of movement of the transmission eificiency varying means exceeding the range of control of the signal voltage varying means in a direction of movement to increase the transmission efi'iciency. I

7. The combination with an electric signal amplifier having an input circuit, an output circuit and at least one electric discharge amplifier device connected between said circuits for the transmission of signals from said input circuit to said output circuit, of means provided with an element movable between certain limits to vary the transmission efficiency of said amplifier device, and means for varying the signal strength applied tosaid input circuit, said last-named means being operative to reduce the signal strength applied to the input circuit only after the transmission efliciency of the amplifier device is partially reduced by said first-named means. I

In witness whereof, I have hereunto set my hand this 7th day of April, 1930.

' WENDELL L. GARLSON.

common means for moving said elements simultaneously.

5. The combination with an electrical signal amplifier having an input circuit, an output circuit and at least one electric discharge amplifier device connected between said circuits for the transmission of signals from said input to said output circuits, of means having a common control and provided with movable elements 'for varying the transmission efficiency of said amplifier device and the strength of signals received by said input cir-

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