US2049809A - Volume control means for radio apparatus - Google Patents

Description

Aug- 4, 1936- E. W. KELLOGG 2,049,809

VOLUME CONTROL MEANS FOR RADIO APPARATUS Filed May 28, 1951 E mlm INVENTOR.

Edward W Kallo gg,

8' @5g i BJ l o 75 46 44 Fi fr /s ATTORNEY.

Patented Aug. 4,v 1936 l'lED STATES VQL'UME CONTROL MEANS VFOR RADIO APPARATUS i Edward Washburn Kellogg, Moorestown, N. J.,

assignor, by mesne assignments, to Radio Corporation of America,

New York, N. Y.; a corporation of Delawarey application May 2s, 1931, serial No. 540,690

4 Claims.

My invention relates to radio receiving apparatus and the. like, having a sound producing output system which may be subjected to strong signals and thereby produce excessively loud 5 sounds when the apparatus is in operation, and more particularly it relates to a volume control means therefor adapted to limit the sound output from the sound producing system.

It is Well known that in tuning modern highgain radio receivers to distant and weaker signals or stations in the presence of strong local signals and the like, that excessively loud bursts of sound from the output system orloudspeaker may often be unavoidably produced as the tuning control means is carried through positions for receiving `such local stations or signals.

It is also well known that means have heretofore been provided for automatically varying the sensitivity of radio receiving apparatus and the like to signals in accordance with their strength, whereby a more constant output sound level is l maintained. Such systems are known as automatic volume control systems, and while functioning to prev-ent excessively loud sound output from the sound producing system of a radio receiving apparatus, may generally be characterized as relatively costly and complicated, with the result that heretofore the use of such automatic volume control means has not been as extensive as its results would warrant.

, It is, therefore, an object of my invention to provide a control means for preventing excessively loud sounds during tuning of radio receiving apparatus and the like, which is simple in character and relatively low in cost, whereby it may have a wide application to such apparatus.

It is a further object of my invention to provide a volume. control means of the above character which is adapted to be responsive to a tuning operation o-f a control means of radio receiving apparatus and the like, to effectively reduce the signal output therefrom during such operation and with no conscious effort on the part of the operator.

Thus, in accordance with my invention, there may be provided means adapted to control the signal output amplitude from a radio receiving system during movement of the tuning control means when the same is moved in the normal direction of operation, e. g. to prevent strong signals from producing excessively loud sounds in the sound producing element of the system.

Further in accordance with my invention I have provided means in radio receiving apparatus for automatically limiting the amplification or (Cl. Z50- 20) volume of signal reproduction during theroperationof program orstation selection, while permitting sufficient volume output to enable the operator to identify the programs or stations, Vand forrrendering the limiting action ineffective 5 after completion of said operation. v

' It would be possible to accomplish the purposes already set forth,.by means of a switch, either separately manually operated, or operated by means of an extra movement of the tuning knob, 10 such for example as an axial movement, but such Van additional operation requires conscious effort, and may be inadvertently omitted with resulting disagreeable loud sounds. Accordingly it is one of the objects of my invention, to accomplish the l5 necessary circuit changes automatically by the same operation and movement as is required for the purposeof tuning. f

Other objects of myinvention will become evident from the following detailed description taken 20 in conjunction with the accompanying drawing in which,

Fig. 1 is a view, in perspective., of radio tuning apparatus provided with a control device embodying the invention; n 25 Fig. 2 is a side elevation View, partly in section, of the device shown in Fig. 1 and on the same scale;

Fig. 3 is a schematic circuit diagram of a radio receiving system illustrating the application 30 thereto of the control device shown in Figs. 1 and 2;

Fig. 4 is a further schematic diagram of a thermionic amplifier also showing the application thereto of Vthe device embodying my in- 35 vention;

Fig. 4a shows another modification of a radio receiving apparatus to which the control device of Figs. l and 2 may be applied; and

Fig. 5 is a View in perspective of a modified 40 form of a control device embodying my invention.

Referring to Figs. 1 and 2 of the drawing, tuning apparatus I fora radio system comprises a plurality of tuning condense'rs 3 and 5 mechanically connected as by a shaft ISfor simultaneous 45 operation and adapted to be driven as by means of a tuning or control knob 'I kand a control shaft 9. The latter is provided with a driving sheave or spindle II upon which is wound a belt or cord I3 for driving a drum lI 5 and an indicating 50 or tuning dial I1, both of which are secured to the condenser shaft` I9. This arrangement provides for the operation of the tuning or control means I of the apparatus by the control knob 'I through the medium of the control rshaft 9 and 55 the wrapped cord connection and is merely illustrative of one form of control means for radio apparatus to which a control device and circuit embodying my invention is applicable.

A clutch means indicated at 2| is provided between the tuning mechanism and a switch 29 as an operating connection for the switch whereby the latter is caused to operate during a tuning motion of, and in response to, the motion of the tuning mechanism. One member 23, of the clutch, is secured to the actuating 0r control shaft 9, whereby it moves in response kto movement of the tuning control means. The clutch member 23 is in the form of a casing surrounding the plate or disk 21 as the driven element of the clutch. The elements are coaxial and are located in spaced relation to each other as indicated. The driving connection between them is provided preferably by a viscous fluidv such as a heavy oil indicated at 35 which fills the casing or -driving element and surrounds the driven element whereby motion of the driving element 23 causes the driven element 21 to follow, but permits a return movement of the driven element 21 under the action of a restoring force provided by means hereinafter described.

This type of clutch. connection is one in which the force ldepends upon relative velocity and oilers little, if any, static friction and for purposes of the invention has advantages which will hereinafter be pointed out. This type of clutch has advantages over an ordinary friction clutch. In the latter the force` transmitted to the driven element does not drop to Zero when the relative motion ceases, and if used, the switch 29 would not return to normal position, or the reaction on the driving element might cause 4it to shift after the operators hand is removed from the driving knob. 'The above viscous connection has the advantage, as compared with ordinary rubbing friction, that all force reaction between the driving and driven elements vanishes after cessation of the driving motion. Y

The housing or driving element of the clutch comprises a dished plate member 23 having a cover disc 24 secured across its open face, and a bushing 3|, as of leather, interposed between a central aperture in said cover disc and the shaft 33 which actuates the switch. The bushing 3 I however, should besufciently free to avoid causing Vany .appreciable rubbing friction on the shaft 33, and be at the same time substantially a liquidtight container.

There are a number of wel-l known extremely viscous materials which might be employed for this clutch. Some of these are colloidal in nature. The primary requisites are that the material used shall not congeal at the lowest temperature at which the device'is to be employed, and that it shall be permanent. It should not, for example, depend for its iluidity upon the presence of solvents which maybe lost through evaporation. One especially suitable material is a solution of rubber in mineral oil.

The driven element 21 of the clutch comprises a circular disc secured to the shaft 33 on which is mounted the movable element of the electric switch 29, or equivalent device. This movable switch element comprises a hub 31 and an arm 39 carrying a contact element 4|,v preferably insulated Vfrom the arm 39 or shaft 33, for making connection with either ofthe iixed contacts 43 shown. lA spring 45 is provided for causing the switch arm 39 to be normally maintained in balanced relation between the-xed contacts 43.

Electrical connection with the movable contact may be made through a lead 41 when the contact 4| is insulated as above described. Stops 49 are employed in cooperative relation with the arm 5| to positively limit its movement.

During movement of the'tuning mechanism in either direction by the drive lshaft 9, the driving element of the liquid clutch drags the driven element along with it causing an unbalancing of Y the movable contact arm 39 and the resultant closing of the circuit kbetween the contacts 4| and 43. The circuit remains closed so long as the motion of the driving element of the clutch continues, or at least so long as the motion is above a certain slow speed. Upon cessation of this movement, and after a small time lag, the restoring force of the spring 45 causes the movable contact 4| to assume its normal balanced relation intermediate the xed contacts 43, the liquid element of the clutch .permitting the driven clutch element to slip backward under the action of the spring 45 in a direction contrary to its previous direction with the driving element.

The time lag between the cessation of motion of the drive shaft and the opening of the contact is determined by several factors, such as: Viscosity of the liquid in the clutch and the restoring force of the spring 45; spacing of the stops 49 and the contacts 43; and the flexibility of the arm 39 and that of the fixed contact support 44, giving a follow-up effect. This time lag is particularly desirable in the case, for example, where the tuning is done in an unsteady manner.

Referring to the electrical system shown in Fig. 3, a cascade tuned radio frequency amplier 53, 55 has in the input thereof an antenna circuit 51 and adjustable volume control 59 for regulating the amplitude level of incoming signals. The radio frequency amplier supplies signals to the detector 6| which in turn supplies the audio frequency amplifier B3 and 65 with detected signals. In the output of the audio frequency amplifier stage 65 is connected a loudspeaker 61 of any desired type, for example, the electro-dynamic cone type. system as, for example, in the input and the last stage of audio frequency 65, is connected the switch device 29 for inserting an impedance element 69 across said input. While in some instances an ordinary xed resistance or shortcircuit will suffice, particularly in case the tuning consists in moving the tuning elements to certain denite positions, which by previous calibrations have been found to bring in certain stations, I prefer to employ a limitingv type of impedance, such as crushed carborundum, a copper oxide rectifier, or a thermionic limiting tube of the type and arrangement shown in Langmuir 1,468,116. Such limiting impedances, when properly connected in the circuit, have the characteristic of permitting the passage of signals below a certain predetermined level but substantially cutting oif all impulses above said level. Thus, in manual tuning by ear, it is desirable that all stations tuned in be heard for the purpose of .i

identification, while at the same time limiting the amplitude of the strongest signals so as to avoid unpleasantly loud volume of sounds. Such limiting devices have the disadvantage of distortion of the loud modulated signals or impulses and it is therefore desirable to remove themas soon as the desired station is selected. Although my above novel apparatus has particular utility in connection with the usual form of manual tuning control, it likewise has utility Situated at a desirable point in this CIJ VAVif) in connection with mechanical preselection. or motor-controlled tuning. In the case of Yactuation of the driving means 1, 9 or I5, in Fig. l, for automatic tuning of radio apparatus, as by a push-button motor arrangement, it may be sufficient to effect a direct short-circuit of some desired portion of the system, or to use any other method, such as an open circuit as disclosed by the Lieb Patent 1,754,326, for rendering the circuit inoperative during the tuning operation.

Referring to the modification in Fig. 4, I have shown a circuit arrangement, such as a pushpull stage of amplication 'i0 of a receiving system, provided with means for causing the circuit per se to limit the signal amplitude during tuning. The input transformer 50 is preferably constructed with a high step-up ratio of turns, giving the grid input circuit poor regulation. In other words, the transformer circuit is designed to be easily overloaded. The grids are normally negatively biased to the proper operating voltage by means of a source of grid bias 14, shown here as a battery for purposes of simplication.

A resistor 'i5 is preferably in series in the bias supply circuit. Upon actuation of the switch 29 by the tuning apparatus, a resistor 16 is connected in series with the resistor 'l5 and across the source 14, as a potentiometer, causing the grids to be biased to a considerably less negative value. With the resulting low bias the voltage swings of both grids are limited, since the transformer becomes loaded when either grid is made positive with respect to the cathodes. Owing to the close coupling between the two halves of the transformer secondary winding, the voltage generated in the unloaded half is limited to substantially the same magnitude as that inthe loaded half. Thus, if the bias is minus 2 volts and the transformer cannot raise the potential of one grid to more than 1 volt positive with respect to the cathodes, or to 3 volts positive with respect to the mean grid potential, the negative swing of the other grid-is limited toa like amount.

The decreased negative bias is not applied instantly to the grids but operates relatively slowly because of the time required for condenser 8| to discharge through the resistance 16. This gradual change of grid bias prev-ents the click which would be heard if a direct connection were substituted for the resistance '16. At the same time, the resistance i6 should be low compared with the impedance of the transformer secondary winding, in order that a strong signal shall not build up a negative bias through a rectifier action ofthe grids. The combination of resistors 15 and i6 and capacitor 8| in effect serves as a lter to prevent an objectionable click which usually results when the direct current circuit of tubes is disturbed, as when the grid bias of an amplifier is changed. In order to provide satisfactory ltering and at the same time keep resistance 16 relatively low, the condenser 3| should be fairly large.

It is desirable that the resistor l5 be of high value, not only to minimize noise when the circuit is broken by the switch 1l, but also to make the closing of switch 29 result in a large change in grid bias, and to make the recovery of normal grid bias slow when switch 29 is opened. This sluggishness of recovery or time delay prevents a sudden noise if the switch contacts are accidentally opened for a moment, as during a reversal of movement of the tuning knob, and from this viewpoint it is desirable to cause a slower building up of negative bias, than the reverse, by proper design of the resistors 15 and 16. By way of illustration, resistance 15 might well be one or two megohms, condenser 8| might be one or two microfarads and resistance i6 would be 5,000 to 10,000 ohms, while the transformer secondary would be wound for an impedance of the order of one-half to one megohm. Referring to Fig. 4a, I have illustrated a case where a switch 1T is designed to open contact to render effective an amplification reducing del'0` vice, as for example a resistor 68 adapted to be connectedin series in the moving coil circuit 'l2 of the electrodynamic loudspeaker 6l. In this modification, exible contact elements 44 are provided with stop members 18 to limit the inlf3 ward movement of said elements. It will be seen that when the switch arm 39 is moved in either direction it carries one contact with it .and opens the circuit with the other contact element, thus breaking circuit between the two contact im' elements, normally bridged lby the metallic contact member 4| on the end of the arm 39. The terminals of the moving coil circuit 'i2 are adaptecl to be connected to the secondary terminals of the output transformer of the push-pullstage of Fig. 4. Any other desirable element in the system may be provided with means for effecting a reduced or limited output. For example, the detectorv may be caused to overload during turiing.

Referring to Fig. 5, showing a niodied form of the switch actuating mechanism, I have provided a lost motion device between the driving means and the tuner for actuating the switch. As an example the driving means or tuning control knob is so mounted on the shaft 9 as to be free to rotate, within limits, relative to said shaft. Secured to the shaft is a collar or hub 3l carrying arms 5| and 39 as in the structure of Fig. l. On the end of arm 39 is mounted a metallic con- "10 vtact element 4|, and between the other arm Eil and a stud 52 on the ange part of the knob l',

is mounted a spring 45. Secured to the knob i are two stop members 49 for limiting the movement of the arm 5|, and hence the rotational -J movement between the dial and shaft. The above mentioned spring 45 is adapted toI maintain the knob and dial in such a position on the shaft that the stops 49 are normally maintained substantially equidistant from the arm 5l. Similarly lv the arm 39 carrying the contact element 4| is maintained centrally between the cooperating contact elements 43 mounted ori the ends of flexible arms 44 which are in turnV mounted on the knob 'l' as in the case of Fig. 1. A pin or screw 8 in the dial knob cooperates with a groove i9 in the end of the shaft 9 in sliding relation to prevent -relative endwise displacement.

When the receiving apparatus is tuned the operator turns the control knob 1' in one direc- G9 tion and the pressure exerted causes a rotational displacement between the knob and the shaft, effecting a closing of the circuit between contacts 4| and 43. Upon release of the tuning knob the spring 45 causes the latter to move backwards 65 from its previous direction of rotation and to assume a normal position with the contact 4| spaced from both contacts 43. In the foregoing discussion it is assumed that the normal friction exerted by the tuning apparatus, e. g. the condenser bearings, is sufficient to permit the knob 1 to be rotated against the action of the spring 45. If this friction is insucient, it is obvious to one skilled in the art that additional friction means may be provided. 75

In the modification of Fig. 5.the condensers may be mounted directly upon the shaft 9, or shaft 9 may be used to drive another shaft carrying condensers in the manner shown in Fig. 1. Although I have disclosed the switch and lost motion means in direct association with the knob 1', it is sometimes desirable to mount the switching apparatus of Fig. 5 on an auxiliary structure in back of the panel of the receiving set in any desirable position between the driving means and the condenser.

From the standpoint of quietness of operation of my apparatus, it is preferred that the limiting means be employed in a part of the circuit which does not substantially disturb the normal flow of direct current. Such an arrangement is shown in Fig. 3. Other circuit portions, which would involve no interruption of the direct current of the amplifier, include the moving coil of a dynamic loudspeaker, illustrated in Fig. 4a, grid to grid or plate to plate of a push-pull amplier, the antenna circuit, etc. I prefer that the limiter and connecting switch be employed at a point along the system near the output to minimize the ampliication between the limiter switch-and the iinal output, for the purpose of further reduction of noise, and because limiting devices can in general be made more effective for moderately high voltages than for very low voltages. VIn one example a signal voltage of the order of 25 or 30 volts was desirable. In some instances I have found it convenient to couple the limiter to an interstage transformer by means of an extra winding as disclosed in the Holden Patent 1,577,720 and to obtain the desired operating voltage, if not readily available, by a step-up, or in some cases a step-down, ratio of turns. This particular arrangement insures complete isolation from the direct current circuit for reasons above mentioned. y

While I have disclosed my invention in combination with a radio tuning apparatus, it is obvious that it may be applied to control any similar apparatus wherein it is desired tov control by a movable element a condition of operation of such apparatus other than the operation normally controlled by said element, and at any point in the range of movement 0f said element, without the performance of any additional operation such as a diierent movement of the said element. Furthermore, the apparatus is automatically caused to operate in itsnormal manner at the end of the movement of said element without any conscious effort on the part of the operator. Y

In accordance with another phase of my invention, I have provided, as above described, means for inserting and removing a limiter device in a receiving system, while according to another phase of my invention I have provided means for changing a device or a circuit portion 'already in the system, from its normal condition to a limiting condition.

Although I have shown and described certain specific embodiments of my invention, I am fully aware that many modifications thereof are possible. My invention, therefore, is not to be restricted except insofar as is necessitated by the prior. art and by the spirit of the appended claims.

I claim as my invention:

1. In an amplifying system having thermionic devices in cascade, means for tuning one of said devices within a range of wave lengths, unitary means for changing'another of said devices from its normal operating condition to a limiting condition in response t-o and during movement of said tuning means, and for restoring said last named device to said normal condition upon cessation of said tuning movement, and means for effecting an appreciable time delay between said restoring operation by said means, and the attainment of said normal condition by said last named device.

2. In a cascade thermionic amplier system having a series of amplifiers, means for adjusting the frequency responsecharacteristic of one of said amplifiers, means for changing another of said amplifiers from its normal amplifying condition to a limited amplifying conditi-on comprising a source of voltage for an electrode of said last named amplifier, a switch for changing the voltage applied to said electrode, slip-clutch means connected with said rst named means for operating said switch during the adjustment of said iirst named amplifier, and a filter for suppressing electrical disturbances resulting from the operation of said switch.

3. In a radio apparatus, the combination with a moveable control means therefor, of a clutch having a driving member connected with said control means to move therewith, a driven member, viscous uid means for coupling said driven member to said driving member, and electrical circuit controlling means connected to said driven member to be actuated by movement thereof, whereby said circuit controlling means is rendered operative during movement of said movable control means and rendered inoperative upon cessation of said movement.

4. In a radio receiving system, the combination of a movable means for eifecting a tuning operation of said system within a range of wave lengths, means for limiting the volume of reproduced signals provided by said system, a switch for connecting said means in operative relation in said system, and a clutch means having a viscous fluid interposed between its driving and driven elements, further to provide a connection betweenV said tuning means and said switch, whereby said switch is automatically operated during motion of said tuning means and is released upon cessation of said motion.

EDWARD WASHBURN KELLOGG.

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