US2115842A - Volume control arrangement - Google Patents

Description

y 3, A. H. COO-PER El AL 2,115,842

VOLUME CONTROL ARRANGEMENT Filedfiarch 14, 19:4

INVENTOR AH. Coo ae oe/vse W C C m ATTORNEY Patented May 3, 1938 UNITED STATES PATENT OFFICE VOLUME CONTROL ARRANGEMENT Arthur Henry Cooper, Buckinghamshire, and

Application March 14, 1934, Serial No. 715,434 In Great Britain April 18, 1933 8 Claims. (01. 25040) The present invention relates to radio receiving apparatus and more especially the volume control thereof.

In radio receiving apparatus, and more particularly in broadcast receiving sets, it is desirable to provide means for controlling the amplitude of the signals delivered to the recording or indicating apparatus. In broadcast receivers, means of this type are adapted to control the intensity of the sound delivered by the loudspeaker, and are generally known as volume control means.

Among the disadvantages of certain volume controls hitherto proposed, one of the most important has been that they have provided an insufficient range of control, and this disadvantage has been particularly marked in sensitive .receivers. When such a receiver is employed for the reception of a powerful local station, it may be impossible with volume controls hitherto known to reduce the volume of undistorted sound delivered by the loudspeaker to a value sufficiently low for domestic requirements.

It is an object of the present invention to provide a radio receiver having volume control means capable of providing a wide range of control.

It is a further object of the invention to provide a radio receiver having volume control means of extended range which are simple to construct and operate.

According to the present invention, a radio receiver comprises an input circuit coupled to a high frequency amplifier and a variable impedance adapted to control the amplitude of the signal voltage transferred from said input circuit tosaid high frequency amplifier, wherein said variable impedance serves also to control simultaneously both the amplification of said high frequency amplifier and the magnitude of a reaction coupling.

According to a feature of the invention, a radio receiver comprises an input circuit and a high frequency amplifier, means operable by a single control being provided for controlling the amplitude of the signal voltage transferred to said high frequency amplifier from said input circuit, the amplification of said high frequency amplifier, and the magnitude of a reaction coupling.

An embodiment of the invention is shown in the accompanying drawing, in which the single figure shows a schematic circuit arrangement of a radio receiver constructed according to the invention.

As shown the receiver comprises an input transformer having a primary winding l adapted to be connected in a suitable antenna-earth circuit 2, and, coupled thereto, a secondary winding 3 connected in parallel with a variable tuning condenser 4. The secondary winding 3 and its associated condenser 4 constitute a tunable input circuit which is connected between the control grid 5 and cathode 6 of a screened gridhigh frequency amplifier valve 1. Between the anode 8 of this valve and the positive terminal of a source of high potential current 9 is connected a tuned anode circuit comprising an inductance coil ill in shunt with a variable condenser l I, and the anode end of this circuit is connected through a suitable coupling condenser l2 to the grid I3 of a triode valve l4 adapted to operate as a detector. The screening grid l5 of the high frequency amplifier valve is connected to the positive terminal of the source 9 of high potential current through a voltage reducing resistance lfi,

and to the cathode 6 of the valve through-a decoupling or by-pass condenser I'I.

Connected to the antenna terminal of the primary winding I of the input transformer through a condenser 18 which may have a capacity of about 0.01 microfarad, is one end of a potentiometer resistance 20, the other end of which is connected through a coupling coil 22 and acondenser 23 of capacity, for example, about 0.0002 microfarad to the anode 24 of the detector valve M. The anode of this valve is connected to the positive terminal of the high potential source through a high frequency choke coil or other suitable impedance 25, and the audio-frequency output of the detector is fed to a low fregency amplifier 3| in any known or suitable manner as by a transformer 30.

The end of the potentiometer. resistance 20 which is connected to the antenna is also connected through a resistance 26 and a high frequency choke coil or other suitable impedance 21, in series to the screening grid l5 of the high frequency amplifier valve. The cathodes 6 of both valves, and the negative terminal of the high tension source, are conductively connected toearth as shown and an adjustable contact or tapping point [9 on the potentiometer resistance is also connected to earth as by lead 2|.

It .will readily be seen that, so long as the tapping point IS on the potentiometer 20 is not at the extreme antenna end, a part of the potentiometer between the upper or antenna end thereof and the tapping point is effectively in parallel with the primary winding of the input transformer, with relation to the incoming signals. As the tapping point is approached towards the antenna end, the amount of this shunting resistance is decreased, and the amountof signal energy shunted to earth through condenser I8 increases. Variation of the position of the tapping point I 9 thus serves to control the amplitude of the signal voltage transferred to the tunable input circuit, and hence to the control grid of the high frequency amplifier valve.

The screening grid of this valve is connected to earth through a circuit comprising a choke coil 21, a limiting resistance 26, and that part of the potentiometer between the antenna end and the tapping point. The potential of the screening grid l5, and hence the gain or amplification of the high frequency amplifier, thus depends on the value of the feed resistance l6 through which it is connected to the high potential source, and on the current flowing to earth through the above-mentioned circuit. It will be seen that the value of this current, and hence the potential of the screening grid, may be adjusted by varying the position of the tapping point IS. The limiting resistance 26 is inserted in order that the potential of the screening grid shall not be reduced beyond a value below which distortion may be produced, and the choke coil 21 serves to prevent the circuit comprising the limiting resistance 25, the screening grid freed resistance 16 and its associated decoupling condenser from exerting a damping effect upon the primary winding I of the input transformer. A choke coil wound of suitable resistance wire and serving also as the limiting resistance 26 may be employed.

The coupling coil 22 to which the end of the potentiometer remote from the antenna is connected is coupled to the inductance coil IU of the tuned anode circuit of the high frequency amplifier valve, and serves to provide reaction to the detector control grid !3. The radio frequency current flowing in the plate circuit of detector tube I4 is fed back to the tuned circuit ll-lll; the latter circuit is disposed between the input electrodes of the detector tube. The-coupling coil is connected to earth through a part of the potentiometer 20, and the amount of reaction can therefore be adjusted by varying the position of the tapping point 19 on the potentiometer. The magnitude of the reaction coupling is preferably made such that when the coupling coil is directly earthed, self-oscillation is just produced.

From the above description it will be seen that three effects, all of which contributeto the control of volume, are controlled by adjusting the position of the tapping point I!) on the potentiometer. All three effects assist one another, and it is arranged that as the tapping point approaches the antenna end of the potentiometer, volume is reduced, and as it recedes therefrom, volume is increased. The resistance of the potentiometer 20 preferably increases logarithmically from the centre towards each end, in order that a substantially linear control of volume may be obtained. The arrangement described provides volume control over a very considerable range, but is nevertheless simple to construct and operate, only one variable element being necessary. Values of certain of the circuit elements which have been found suitable in practice are:

condenser 18:.01 mfd.

condenser 23:.0002 mfd.

condenser 1'7=.1 mfd.

resistor 20=75,000 ohms resistor 26: 7,000 ohms resistor 16=75,000 ohms but it will be understood that our invention is not limited to the use of these particular values. We have also found that better control is secured when a screen grid amplifier of the variable mu type is employed.

It will be apparent that many variations of the above described arrangement are possible within the scope of this invention. For example, if desired, the function of the potentiometer may beperformed by two or three separate variable resistances mounted on a common operating spindle. Reaction may be obtained in any known or suitablemanner other than that described, for example, the coupling coil may be connected to earth through a variable condenser ganged to a variable resistance or resistances serving to control the signal input, and the amplification of the high frequency amplifier. The latter may, if desired, be controlled by varying the grid or cathode bias of a high frequency amplifier valve.

The radio receiver described above is intended to illustrate an application of the present invention, and is not intended to limit the scope of theinventionin any Way. Many modifications may be made to the receiver described; for example, more than one-high frequency amplifier valvehmay be. included, and other forms of intervalve coupling than tuned anode coupling may be employed. t

Having described our invention, what we claim as newand desire to secureby Letters Patent is:

1. An amplifying arrangement comprising a vacuum tube'having a cathode, a control grid, a screen grid'zand a plate, a tunable input circuit connected between said control grid and cathode, an antenna circuit including a reactor coupled to said-tunable input circuit, a plate circuit connecting said cathode and plate, a following tube having a tunable input circuit in said plate circuit, said following tube having an output circuit including a feedback connection to said second tunable input circuit, a positive source of potential, a -circuit connected to said source and said screen grid and means-for simultaneously controlling the voltage applied to said screen grid,

the amount of said feedback couplirg and the proportion 'of the current of said antenna circuit passing'through said reactor.

2. In an amplifying device, the combination of a'vacuumtubehaving a cathode, a control grid, a screen grid and a plate, a tunable input circuit connected to said controlgrid and cathode, a reactor coupled to said tunable circuit, a circuit including two resistors connected in series with a positive source of potential, at connectionbetween the common terminal of said resistors and said screen grid, means for varying the direct current passing through said resistors, means for passing signal currents through said reactor and a circuit connected between the low potential terminal of said series resistors and the high potential terminal of said reactor.

' 3. The combination defined in the preceding claim in which said last named circuitincludes a condenser.

i. In an amplifying device, the combination of. a vacuum tube having a cathode, a control grid, a screen grid and aplate, an input transformer, an input circuit connected to said control grid and cathode including said transformer secondary, a source of positive potential, three resistors connected in series to said source, a connection between the common terminal of two of said resistors andsaid screen grid, a contact connected tothe low potential terminal of said potential source and adjustable along the third of said resistors and a circuit connected to the high potential end of said third resistor and the high potential end of said input transformer primary.

5. In an amplifying device, the combination of a vacuum tube having a cathode, a control grid, a screen grid and a plate, a tunable input circuit connected between said cathode and control grid, an output circuit connected between said cathode and plate, a following tube having an input circuit included in said output circuit, said following tube having an output circuit including a variable feedback connection to said second input circuit, a source of positive potential, a circuit connected across the terminals of said source including the series connection of a resistor, a choke coil and a second resistor, and a direct connection between the low potential end of said first named resistor and said screen grid, said feedback connection being connected to the low potential end of said second resistor.

6. In an amplifying device, the combination of a vacuum tube having a cathode, a control grid, a screen grid and a plate, a coil connecting said control grid and cathode, a reactor coupled to said coil, a source of positive potential, a circuit connected across the terminals of said source and including a fixed resistor and a variable resistor connected in series, a lead connecting one end of said fixed resistor to said screen grid, said fixed resistor having such a value that the potential of said screen grid will not become so low as to cause said tube to distort signals applied to said control grid, means for impressing signal voltages on said reactor and a circuit connected between the high potential terminal of said variable resistor and one terminal of said reactor.

7. In an amplifying device, the combination of a vacuum tube amplifier having a control grid, a

screen grid, a cathode and a plate, a radio frequency transformer having its secondary connected across said cathode and control grid, a source of positive potential, two resistors connected in series to said source, a connection between the common terminal of said resistors and said screen grid, means for varying the direct current passing through said resistors, a plate circuit connecting said cathode and plate, a vacuum tube detector having an input and an output circuit, means coupling said input circuit to the plate circuit of said amplifier, a circuit connecting the low potential end of said resistors with the primary winding of said transformer and a circuit including a condenser connecting said last named circuit with the output circuit of said detector.

8. In a radio receiver, the combination of a vacuum tube amplifier having a cathode, a control grid, a screen grid and a plate, a radio frequency transformer having its secondary connecting said cathode and control grid, a source of positive potential, two resistors connected in series to said source, a direct current connection from the low potential end of one of said resistors to said screen grid, a resonant circuit including a coil connected to said plate, a vacuum tube detector having a grid and an output circuit, a circuit including a condenser connecting the high potential end of said resonant circuit to said detector grid, a coil and condenser connected in series between the low potential end of the other of said resistors and said detector output circuit, said last named coil being inductively coupled to the coil of said resonant circuit and a contact connected to said amplifier cathode and adjustable along said last named resistor.

ARTHUR HENRY COOPER. WILLIAM CUTHBERT CORNER.

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