US2269300A - Radio receiver - Google Patents

Description

Jan. 6, 1942.

E. F. ANDREWS RADIO RECEIVER Original Filed April 8, 1933 ,5 Sheets-Sheet 2 INVENTOR. (Fizz/4m? (If Q'r/drez/s ATTORNEYS Jan. 6, 1942. E. F. ANDREWS RADIO RECEIVER 5 Sheets-Sheet 3 Original Filed April 8, 19:53

62! JIg/ENTOR.

lad, 71 719% By M ATTORNEYS Jan. 6, 1942.

RADIO RECEIVER Original Filed April 8, 1933 5 Sheets-Sheet 4 E. F. ANDREWS 2,269,300 I 5 Sheets-Sheet 5 E. F. ANDREWS RADIO RECEIVER Original Filed April 8, i933 Jhn.6,1942;

. 6 If)? w [IL ilmmu 33 Patented Jan. 6, 1942 RADIO RECEIVER Edward F. Andrews, Chicago, Ill., assignor to Radio Corporation of America, New York, N. Y., a corporation of Delaware Application January 9, 1939, Serial No. 249,908, now Patent No. 2,218,501, dated October 22, 1940, which is a division of application April 8,

1933, Serial N0.

665,074, now Patent No.

2,143,532, dated January 10, 1939. Divided and this application July 1, 1939, Serial No. 282,401

13 Claims.

This application is a divisional from my copending application Serial No. 249,908, filed January 9, 1939, Patent No. 2,218,501 dated October 22, 1940, which is a divisional from my application Serial No. 665,074, filed April 8, 1933, Patent No. 2,143,532, dated January 10, 1939.

This invention relates to radio receivers and has for one of its objects the provision of an improved radio receiver.

A further object of the invention is to provide an improved radio receiver particularly adapted for use in an automobile or elsewhere with low voltage current.

A further object of the invention is to provide, in a radio receiver including an interrupter, means for preventing high frequency disturbances occasioned by the interrupter from being amplified by the tubes of the receiver so as to cause undesired noises in the loud speaker.

A further object of the invention is to provide a radio receiver having its elements mounted on a grounded base, and comprising a built-in power supply mounted on the base, said supply including an interrupter and associated coils related to the grounded base so as to suppress in an advantageous manner the high frequency disturbances created by the interrupter.

Other objects, advantages, and capabilities of my invention will appear from the following description of preferred embodiments thereof,

taken in conjunction with the accompanying drawings, in which:

Fig. 1 is a wiring diagram of one embodiment of the invention;

Fig. 2 is a wiring diagram of a further embodiment of the invention;

Fig. 3 is an illustration of a radio set embodying the invention, the main unit being shown in plan with its cover partly broken away and the remote control unit being shown in sectional elevation;

Fig. 4 is an end view of the remote control unit, with its cover partly broken away;

Fig. 5 is an elevation of the main unit, the cover being shown in section in order to display elements normally obscured thereby;

Figs. 6, '7, 8 and 9 are fragmentary wiring diagrams illustrating the means for preventing excessive attenuation of signal energy when transmitted from one unit to the other, and

Fig. 10 is a wiring diagram of a still further embodiment of the invention.

Referring more particularly to Fig. 3, it is to be noted that the main unit, which is designated by the reference numeral 10, is substantially similar in general structure to the radio receiver described and claimed in Patent 2,103,135, issued December 21, 1937. This main unit is also shown in Fig. 5 and comprises a base H which may be of inverted dish shape provided with an outwardly projecting flange 12 to which is secured a closure plate I3. The space between the upper face of the base H and the closure plate 13 provides accommodation for wiring and small radio parts. A block 14 is mounted in the center of the base H to serve as a support for the pot 15 of a loud speaker IS. The loud speaker is preferably of the dynamic cone type, the cone I! being directed upwardly as shown in Fig. 5. A cover I8 is supported upon the speaker, for example, by means of screws I9 which secure it to the edge of the speaker frame adjacent the periphery of the cone.

The central portion of the cover I8 is provided with openings for the egress of sound from the speaker. The cover I8 is preferably of inverted dish shape and it extends downwardly towards the base H. The lowest portion of the cover I8 is of diameter somewhat larger than the base H so as to provide an annular opening 2| for the egress of sound waves from the lower side of the speaker cone. The base H serves to provide a mounting for radio apparatus such as radio tubes, transformers, a vibrator and the like, which will hereinafter be described in greater detail. Such radio apparatus is located in a ring around the pot 15 of the loud speaker, being located within the annular space between the loud speaker and the cover l8. It will readily be understood that such radio apparatus may be rendered available for adjustment, replacement and the like, by merely removing the cover l8, which may be done by taking out the screws l9.

Owing to the fact that it is preferred to tune the receiver in the remote control unit, it is not necessary to mount a variable condenser in the main unit as in the case of the aforesaid patent. The remaining radio apparatus is more convenient to this manner of assembly and the dimensions of the main unit may be somewhat reduced.

Energy is supplied to the main unit In by a cable 22. For a set employing the wiring diagram of Fig. 1, this cable comprises a conductor 23 and a conductive shield 24, insulated from each other by suitable insulation. The conductor 23 and shield 24 are connected to a battery 25 in the manner shown in Fig. 1. The main unit 10 is connected to the remote control unit 26 by means of a flexible cable 21 of suitable length. The number and relation of conductors which is enclosed an electro-magnet 85 which controls points 88 in series with the winding of said magnet so as to cause continual interruption in the current flowing through the primary of the transformer 15. A condenser 81 and high resistance 88 are provided both across the winding 85 and points 85. The conductor 8| is also connected to the field winding of the speaker I6,

the other end of this winding being grounded.

The continual interruption of the fiow of current through the contacts 86 develops undesired high frequency disturbances. It is important, particularly where an interrupter power supply is made a part of the radio receiver, to isolate these high frequency disturbances and to prevent them from being amplified by the tubes of the receiver so that they appear as objectionable noises in the speaker output. To isolate these disturbances, one of the contacts 86 and the metal shield 14 around the interrupter are grounded to the metal base which serves as a common ground for the receiver and the power supply, and on which the interrupter, transformer, tubes, and other elements are mounted. The grounding of one side of the circuit in this manner tends to reduce to a minimum the potential differences between the various parts connected thereto. Thus, there is relatively little tendency for the undesired high frequency disturbances to reach the tubes through the grounded side of the circuit. The interrupter coil 85 and the primary of the transformer 15 are interposed between the ungrounded contact 86, at the source of the undesired disturbances, and the various conductors connected to the ungrounded side of the circuit from which the undesired high frequency disturbances might be radiated to the tubes, or through which the disturbances might be carried to the tubes by conduction. The inductance of these coils presents a high impedance to the passage of these high frequency disturbances. The condenser 81, which bridges from the connected ends of the coil 85 and the primary of the transformer 15 to ground, forms a low impedance path to ground tending to shortcircuit that portion of the undesired high frequency disturbances which may pass through the coil 85. Thus, by connecting one of the contacts 86 directly to the common ground, the coil 85, the condenser 81, and the primary of the transformer 15 form a filter effective for isolating the undesired disturbances from the ungrounded side of the circuit through which they would otherwise be transmitted to the tubes. It is preferred to locate one or more of the inductances constituting the filter for undesired components adjacent the interrupter points and to shield the interrupter contacts and adjacent portions of the interrupter circuit, including all or part of the inductances and the condenser forming the high frequency filter, with grounded shielding means.

It will, of course, be understood that all the grounds indicated in the upper part of Fig. 1, which corresponds to the main unit, are made to the common base II. The ungrounded sides of the tube filaments are connected to the line 8!, the filament of tube 28 being connected thereto by line 65 of cable 21, and the filament of tube 15 being connected thereto by line 82. Choke coils 9| are provided in the filament current circuit, being preferably arranged in series in the filament supply circuit, serving with the filament resistances to provide an induction-resistance filter which effectively filters out high frequency disturbances produced by the vibrator 14 and which may not be completely isolated by the means above described. This filter, including the choke coils 91, is also effective in preventing undesired high frequency disturbances originating in the ignition or battery charging system of the automobile from reaching the tubes. It will be seen that the filtering effect is greatest towards the input end of the receiving set, where any disturbance present would be amplified to the greatest extent.

The choke coil 92 is connected in series with the lead which supplies plate current to the tube 28. This choke coil prevents oscillation which might be caused by disturbances passing through lead 55, coil 53 and the plate ground capacity of the tube 28.

It is preferred that the rectifying tube 18 passes current when the points 86 make contact, rather than when they break contact. The change from one condition to the other may be effected in many ways, one way being to reverse the connections of the secondary winding of the transformer 15. The set can thus be readily adapted for any automobile, regardless of which pole of the battery is grounded.

The operation is as follows: The switch 38 being closed, the circuits through the filaments are made, likewise the circuit through the vibrator or interrupter 14, so that an interrupted current passes through the primary of the transformer 15. The voltage of this current is stepped up in the secondary of the transformer and is rectified in tube 16 so as to provide B voltage by means of conductor 19. The field winding of the speaker I6 is energized and the desired station can be tuned in by actuating the gang of condensers 29. The volume level control 63 adjusts the relative grid bias of tube 4! by making the cathode more or less positive. It is to be noted that this control in the main unit is effected from the control unit by variation of a direct current which is of practically constant value for any particular manual setting of the volume level control 63.

The automatic volume control voltage is applied to the grids of the tubes 39 and 40, which elements are ahead of the source of energy from which the automatic volume control voltage is derived, which source is the plate circuit of the tube 4|]. Automatic volume control voltage is also a plied to the grid of the tube 4|, which. is after the source of the energy which supplies the automatic volume control voltage which. as has been noted, is the plate of the tube Ml. It may here be pointed out that the effective automatic volume control voltage applied to the tubes before the source of the automatic volume control energy is to decrease the gain of these tubes, and hence the automatic volume control voltage produced, so that these tubes provide only a diminishing corrective effect. However, the application of automatic volume control voltage to the grid of a tube after the source of automatic volume control energy, such as tube 4! produces a reduction of gain without any reduction of the automatic volume control voltage. By tapping in the grid connection of the tube M at a suitable point on the resistor H, signals of substantially uniform strength can be obtained from divers stations with antenna signals of widely different power. Indeed, by suitable adjustment of the connection of the grid 4| to the resistor II, it is possible to make a stronger antenna signal appear as a Y the second detector.

weaker audible signal than that derived from a weaker antenna signal.

The embodiment of the invention diagrammatically shown in Fig. 2 is largely similar to that shown in Fig. 1 and similar reference numerals are employed to designate similar parts. In this embodiment the antenna lead 45 is conveyed through the cable 21 within a grounded metal shield 93, for the purpose of preventing the antenna lead 46 from picking up electrical disturbances.

In this embodiment the tube 42 is dispensed with and the tube 43 fulfills the functions of the tubes 42 and 43 in the embodiment of Fig. 1. This tube 43 contains two diodes and triode in the same envelope, all having a common cathode. One diode plate 94 serves as a second detector, the other diode plate 95 serves as a source of automatic volume control potential which is applied to the grids of tubes 39 and 40, a portion thereof being applied to the grid of tube 4|, as in the previously described embodiment.

The triode elements of tube 43 act to amplify the output of the diode constituted by plate 94 and the cathode at audio frequency. The detected signal appears across the resistance 95 and is impressed upon the grid of the tube 43 through the filter resistor 91 and the capacity 98. As in the previously described embodiment, the tuned intermediate frequency transformer 99 connected to the plate of the tube 40 steps down the output of that tube and feeds a signal of reduced amplitude to the grid of the tube 4| by means of the winding I00. This winding is here shown tuned to the intermediate frequency.

by taking practically all the gain in the first intermediate frequency tubes, substantially the maximum gain is available in the plate circuit of the tube 40, which is the source of automatic volume control energy. Any gain taken in the.

stage containing the tube 4| would not add anything to the automatic volume control voltage. The tube 4| is of the variable mu type so that a large variation of the potential difference between the cathode and the grid may be employed.

to give the desired range of volume control.

Even when a variable mu tube is employed, it is desirable to limit the grid swing to avoid distortion. This is accomplished by impressing a stepped-down signal on the grid of tube 4|, as previously described. The signal is then amplified up again to the desired value in the tube 4| and the transformer IOI, from which it is impressed upon the diode plate 94, which acts as The transformer 99 includes a secondary winding I92 which supplies potential to the diode plate 95 which is rectified and appears across the resistance I03. This direct current potential is utilized for automatic volume control, as previously described.

In this embodiment of the invention, the field of the loud speaker comprises two windings I04 and I05. The winding I04 is connected in series with the plate voltage supply from the secondary of the power transformer I5 through the rectifier tube IS. The winding I05 acts as a choke coil to filter the plate supply, as well as supplying part of the energy to the speaker field. Only a part of the speaker field energy is supplied from the plate supply, the remainder for bringing the speaker to the proper sensitivity being supplied directly from the battery to the coil I05. By properly proportioning these coils, the speaker field can be employed as a choke coil and the proper speaker sensitivity attained with a vibrator of moderate output.

To avoid operating the vibrator without a load,

'it is desirable that the filaments of the tubes should have attained their operating temperature before the vibrator is connected to the battery. A thermostatic relay I06 fulfills this purpose. This relay is adapted to be operated by a heating winding I01 which is energized upon the closing of the switch 38. The winding I01 is in parallel with the filaments of the tubes and the current therefor is derived from the battery. The thermostatic relay is proportioned to close the vibrator circuit after the cathodes have attained operating temperature. The thermostatic switch is preferably temperature compensated so. that its time interval is not excessively affected by changes in atmospheric temperature.

The thermostatic relay serves both as a delayed switch and as a remotely controlled relay. The vibrator current does not pass through cable 21, thus reducing the liability of the introduction of undesirable electrical disturbances into the amplifier tubes, and also avoiding the larger conductors or higher voltage drop which would be occasioned by a higher current through the cable.

The battery cable I08 comprisesthree leads I09. H0 and II I, surrounded by a shield I I2, one end of which connects to the chassis of the main unit, and the other to the grounded terminal of the battery. The conductor I09 is connected to the ungrounded terminal of the battery and leads to the switch 38 for the filament and heating element I01 supply. Conductor H0 is connected to the positive terminal of the battery and leads to one contact of the thermostatic relay I06, through which it is connected in parallel through the primary winding of the transformer 15 and vibrator 14 on the one hand, and through coil I05 on the other hand, to conductor III which is connected to the negative terminal of the battery. In Fig. 2, I have shown the negative terminal of the battery to be grounded.

Should the automobile be one in which the positive terminal is grounded, then shield H2 and conductor IIO should be connected to the positive terminal of the battery, and conductors I09 and II I should be connected to the negative terminal of the battery. It is to be noted that this hook-up follows the nomenclature of the preceding paragraph, according to which shield H2 is grounded and conductor I09 is connected to the ungrounded terminal, and lead II is connected to the positive terminal, while lead III is connected to the negative terminal.

The operation of this embodiment will readily be understood from the foregoing description and its similarity to the embodiment of the invention first described. It will readily be understood that when the switch 38 is closed, the filaments begin to light up and the element I01 begins to heat. By the time the filaments have attained their operating temperature, the thermostatic switch I06 has closed, completing the circuit through the vibrator I4 and the primary of the 'shown in Figs. 1 and 2'.

plate supply transformer 15, as well as through field coil I05. Tuning is efiected by means of the gang of condensers 49, 5| and 59, and manual volume control is efiected by means of rheostat 63, in the manner described above.

For the satisfactory transfer of signal energy from the control unit to the main unit, it is desired to employ means for minimizing loss or attenuation through the cable. In Figs. 6, 7, 8, and 9 are shown four circuits which may advantageously be used to attain this result under various conditions. The circuitshown in Fig. 6 is employed in the embodiments of the invention The common advantageous feature of all these circuits is that the voltage difference between the conductors within the cable is substantially lower than the voltage across the circuits in the control and main units, to which the conductors connect or to which they are coupled. This low voltage difierence reduces the attenuation or loss through the capacity of the conductors in the cable. However, as a high voltage is desired for the input to the amplifier in the main unit, the voltage should again be raised at the main unit end of the cable. The ratio of the voltage in the control unit and the main unit to that in the cable should be great enough to avoid undue losses through the capacity of the cable, but not so great as to cause undue resistance losses, resulting from very high currents flowing through these conductors.

The choice of the circuit to be used in a given set is dependent upon several factors, such as cost, permissible variation of characteristics, the

degree of selectivity desired, the tubes employed, the characteristics of the cable, etc.

Where the capacity of the conductors of the cable is small, the structure of Fig. 8 may be employed. The structure of Fig. 9 is suitable with a cable of substantially fixed capacity. This permits of very simple coils in the output of the control unit and the input of the main unit. The structure of Fig. 6 permits of large capacity in the cable which does not have to be of a particularly exact value. The structure of Fig. '7 is highly advantageous when a high degree of selectivity is desired.

Fig. 8 embodies direct coupling; Fig. 9, capacity coupling; Fig. 6, inductive coupling; and Fig. 7, coupling by means of a tuned link circuit.

Minimum losses or attenuation are obtained when the reactance at the intermediate frequency connected to one end of the cable is equal to the reactance connected to the other end of the cable, the value of this reactance being determined by the electrical characteristics of the cable. For minimum losses the values of the various elements are so selected that if the cable is out at any point, the reactance at the intermediate frequency looking into the cable on one side of the cut is equal to the reactance looking into the cable on the other side of the cut, but if the reactance in the first case is capacitive, the reactance in the second case must be inductive, and vice Versa.

In the diagram shown in Fig. 6, the windings 53 and 56 have their coefiicient of coupling as high as possible, likewise the windings 68 and 10. The step down of voltage between windings 53 and 56 and the step up between windings 69 and 10 are preferably of substantially similar magnitude. In actual practice I have obtained excellent results with a circuit with a step down of times and a step up of 25 times, using a tube of type R. C. A. 236 at 28 and a tube of type R. C. A. 239 at 39. As a result of the high step down, the capacity between the conductors 6? and 68, illustrated as a phantom capacity at H3, is not critical and may vary within considerable limits without greatly affecting the tuning of the circuits including the winding 53 and winding 10.

In the diagram shown in Fig. 7, the step down from winding 53 to winding 56, and the step up from winding 69 to winding is lower than in the case of Fig. 6, the number of turns in windings 56 and 69 being suitably increased to attain that result. In this case, the inductances of windings 56 and 69 are so considerable that they and the conductors 61 and 68 connecting them constitute a link circuit which must be tuned to the intermediate frequency to give best results. Such tuning is highly advantageous in that it enables a very high degree of selectivity to be attained, since it provides the added selectivity of an additional tuned circuit without additional parts. The tuning of this circuit requires a capacity between the conductors 61 and 68, which capacity is shown in phantom at H4, to have a definite value.

Thus, in the case shown in Fig. 6, the length of the cable is immaterial within considerable limits, but in the case of Fig. 7, the length of the cable is important for best results, and if any considerable deviation from the optimum is attempted, correction of the capacity should be made in some manner, as, for example, providing a condenser between the leads 6'! and 68 at either end, or by selecting a cable of more suitable capacity characteristics.

The structure diagrammatically shown in Fig. 8, in which direct coupling is employed, is particularly suitable for use with tubes 28 and 39 of low impedance. In this arrangement coils 53 and 10 are connected by the leads 81 and 68, condensers H5 and H6 being provided in the lead 68, that is, the ungrounded lead. The condensers H5 and H6 are of large capacity relative to the capacity of the cable, as indicated in phantom at H1. As the capacity of the cable is small, relative to the capacities H5 and H6, the system is independent to a considerable degree of the capacity between the leads 61 and 68.

The structure diagrammatically shown in Fig. 9, in which capacitive coupling is employed, is adapted for use when the tubes 28 and 39 are of high impedance. The windings 53 and 10 are of high inductance and the condensers H8 and H9 are of relatively low capacity relative to that between the leads 6'! and 68, which is indicated at I20. Under these circumstances two separate circuits are formed with the capacity I20 common to both and forming the coupling link therebetween. Here the capacity of the cable must have a relatively definite value in comparison with the capacity Ill of Fig. 8.

The voltage between the conductors 61 and 68 is maintained low in the circuits shown in Figs. 6, 7, 8 and 9, and attenuation of the signal currents in passing through the cable is thereby substantially minimized. In the structures of Figs. 6 and 7, this low voltage relation is secured by stepping down the voltage across the winding 53 to a lower voltage across the coil 56. In the structure of Fig. 8 the potential drop across the winding 53 is substantially equal to the potential drop across condenser I I5, and the potential drop across the winding 70 is substantially equal to the potential drop across condenser H6.

In the structure of Fig. 9, a similar relation exists between the winding 53 and condenser H8 on the one hand, and between winding Ill and condenser US on the other hand. In both cases the potential of .the leads 6] and 68 is-substantially equal.

It is not intended tolimit the invention to automobile radio receivers, since it may be applied to. home sets and indeed to any manner of set employing a remote control. In the embodiment of the invention illustratedin Fig. 10, the main unit is substantially similar to that shown in Fig. 2. The principal difference is that the automatic volume control is applied to the tube 28 in the remote unit, as well as tubes in the main unit. By this ex pedient the tube 40 may be omitted from the main unit while maintaining an ample amount of automatic volume control. For the sake of simplicity, I have shown the power supply system of Fig. 1 in this embodiment.

The automatic volume control voltage is rectified at the plate 95 of the tube 43 and is applied to the grids of the tubes 39 and 4| in the manner described above with respect to the embodiment shown in Fig. 2. That is, the whole automatic volume control voltage is applied to the grid of tube 39 and a part thereof, determined by the resistances I2I, I22 and I23, is applied to the grids of tube II and the tub-e 28 in thecontrol unit, by means of the lead I24, an additional conductor which passes through the cable 21.

The tube 28 in the remote control unit is a six-element tube comprising a cathode I25, plate I26, control grid I27 and screen I28, an oscillator grid I29, and an oscillator plate I30. The oscillator grid I29 and oscillator plate I31], together with the cathode I25, serve as oscillator elements independent of the control grid I21, so that the bias of the grid I21 can be varied to obtain automatic volume control without interfering with the local oscillation. The electron stream reaching the plate I26 is afiected both by the local oscillation frequency and the signal frequency on the grid I21 in such a way that the intermediate frequency appears across the coil 53 and is transferred to the coil 56. The intermediate frequency passes from the coil 56 through conductor 68 to the input of the tube 39.

It is not intended to be limited to this particular type of tube, since other tubes may be employed, if desired, provided the bias of the control grid can be sufficiently varied without impairing the local oscillation.

Although the invention has been described in connection with the specific details of preferred embodiments thereof, it must be understood that such details are not intended to be limitative of the invention, except insofar as set forth in the following claims.

Having thus described claim and desire to secure the United States is 1 1. In a radio receiver, in combination, a metal base, a plurality of thermionic tubes having plates and filaments, each of said filaments being provided with a pair of terminals, a continuously vibrating circuit interrupter having an inductance element and two contacts, a metal shield enclosing said interrupter, a transformer having a primary winding and a secondary winding arrangedto transform low voltage alternating current into high voltage alternating current, a rectifier circuit connected across said secondmy invention, what I by Letters Patent of a'ry winding, said rectifier circuit acting to change the high voltage alternating current into high voltage direct current, means for delivering'said high voltage direct current to said plates, said thermionic tubes, shielded interrupter, transformer, and rectifier being carried by said base, a metal housing enclosing them, one terminal of each of said filaments,one of said interruptercontacts and its shield being grounded to said metal base which forms'the common ground for said radio receiver, a low voltage battery external to said housing having a pair of terminals, means for grounding one of said pair of battery terminals to a ground external to said receiver, conductor means connecting the base of said radio receiver to the grounded terminal of the battery, a second conductor means connecting the ungrounded terminal of the battery to said filaments, and a third conductor means connecting the other of said two interrupter contacts to said second conductor means, said third conductor means including said interrupter inductance element and the primary of said transformer in series.

2. In a radio receiver with self-contained power supply comprising a metal base carrying the elements of the receiver and power supply and forming a common ground for them, in combination, thermionic tubes provided with filaments each of which is provided with a pair of terminals, means for grounding one of each of said pair of terminals to said base, a vibrating interrupter having a pair of contacts and a driving coil, one of said contacts being grounded to said base, a grounded metal shield enclosing said vibrating interrupter, a transformer having a primary Winding and a secondary winding, means including a rectifier intermediate said secondary winding and said plates for supplying plate current to said receiver, a low voltage battery separated from said metal base, said battery having a pair of terminals, means for connecting one of said battery terminals to the base and to an external ground other than said metal base, a conductor means connecting the ungrounded terminal of each filament to the ungrounded terminal of the battery, and a second conductor means connecting the ungrounded interrupter contact to said first named conductor means, said second conductor means including said driving coil and the primary winding of said transformer in series.

3. In a radio receiver with self-contained power supply comprising a metal base carrying the elements of the receiver and power supply and forming a common ground for them, in combination, thermionic tubes having filaments each of which is provided with a pair of terminals, one terminal of each pair being grounded to said base, a vibrating interrupter having a pair of contacts and a driving coil, means for grounding one of said contacts to said base, a metal shield enclosing said vibrating interrupter, a transformer having a primary winding and a secondary winding, means, including a rectifier, interposed between the secondary winding of said transformer and said tubes for supplying plate current to saidreceiver, a low voltage battery external to said base, said battery having a pair of terminals, means for grounding one of said battery terminals to a ground external to said base, conductor means connecting the base of said radio receiver to the grounded terminal of the battery, a second conductor means connecting the ungrounded terminal of the battery to the ungrounded terminals of said filaments, a third conductor means connecting the ungrounded interrupter contact to the second conductor means, said third conductor means including said driving coil and said primary winding in series, and a by-pass condenser connected between said base and a point of the third conductor means which is common to said primary Winding and said driving coil.

4. In a radio receiver with self-contained power supply comprising a metal base carrying the elements of the receiver and power supply and forming a common ground for them, in combination, thermionic tubes having filaments each of which is provided with a pair of terminals, means for grounding one terminal of each pair of terminals to said base, a vibrating interrupter having contact elements and a driving coil, one of said contact elements being grounded to said base, a transformer having a primary winding and a secondary winding, means including a rectifier connected between said secondary winding and said tubes for supplying plate current to said receiver, a battery having a pair of terminals, means for connecting one of said battery terminals to said metal base and to a ground external to said base, conductor means connecting the ungrounded terminal of the battery to the ungrounded terminals of said filaments, a second conductor means connecting another of said interrupter contact elements to first said conductor means, through said primary, inductance means including said driving coil in series with said primary in said last named conductor means, a by-pass condenser connected between said grounded interrupter contact element and a point of said second conductor means which is common to said primary and said inductance means, and grounded metal shielding means shielding said interrupter contacts, said inductance and said condenser.

5. In a radio receiver with self-contained power supply comprising a metal base carrying the elements of the receiver and power supply and forming a common ground for them, in combination, a loud speaker connected to said receiver, said loud speaker having a low voltage field winding provided with a pair of terminals, 2. housing for said speaker arranged to cover said elements on said base, means for grounding one terminal of said field winding to said base, thermionic tubes having filaments each of which is provided with a pair of terminals, means for grounding one terminal of each of said pairs of filament terminals to said base, a vibrating interrupter having a driving coil and a pair of contacts, means for grounding one of said interrupter contacts to said base, a metal shield'enclosing said vibrating interrupter, a transformer having a primary winding and a secondary winding, means including a rectifier, interposed between said transformer and said tubes for supplying plate current to said receiver, a battery having a pair of terminals, means for grounding one of the battery terminals to said metal base and to an external ground other than said base, conductor means connecting the ungrounded terminal of the battery to the ungrounded filament terminals and to the ungrounded field winding terminal, a second conductor means connecting the ungrounded interrupter contact through said primary and said driving coil in series to the first said conductor means.

6. In a radio receiver with self-contained power supply comprising a metal base carrying the elements of the receiver and power supply and forming a common ground for them, in combi nation, thenmionic tubes having filaments each of which is provided with a pair of terminals, means for grounding one terminal of each pair to said base, a vibrating interrupter having a pair of contacts, means for grounding one of said contacts to said base, a metal shield enclosing said interrupter, a transformer having a primary winding and a secondary winding, means including a rectifier circuit connected between said transformer and said tubes for supplying plate current to said receiver, a battery having a pair of terminals, means for connecting one of said battery terminals to said base and to a ground external to said receiver, conductor means connecting the ungrounded interrupter contact to one terminal of said primary winding, and means connecting the other terminal of said primary winding to the ungrounded terminal of the battery and the ungrounded terminal of each filament.

7. In a radio receiver with self-contained power supply comprising a metal base carrying the elements of the receiver and power supply and forming a common ground for them, in combination, thermionic tubes having filaments each of which is provided with a pair of terminals, means for grounding one terminal of each pair to said base, a vibrating interrupter having a pair of contacts, means for grounding one of said contacts to said base, a metal shield grounded to the base and enclosing said interrupter, a transformer having a primary winding and a secondary winding, means including a rectifier, interposed between said transformer and said tubes for supplying plate current to said tubes, a battery having a pair of terminals, means for grounding one of said battery terminals to said metal base and to a ground external to said base, conductor means connecting the ungrounded interrupter contact through said primary to the ungrounded terminal of said battery and the ungrounded terminals of said filaments, and means connected with said conductor cooperating with said primary to form a progressive filter for preventing high frequency disturbance originating at said contacts from passing into the ungrounded conductors leading to said battery and said filaments.

8. In a radio receiver having a ground member to which various of its elements are connected, in combination, thermionic tubes having filaments each filament being provided with a pair of terminals, means for connecting one terminal of each of said pairs of terminals to said ground member, a vibrating interrupter having a driving coil and a pair of cooperating contacts, means for connecting one of said pair of contacts to said ground member, a metal shield connected to said ground member and enclosing said interrupter, a transformer having a primary winding and a secondary winding, means including a rectifier interposed between said transformer and said tubes for supplying plate current to said receiver, a battery having one terminal connected to said ground member and to an external ground, and another terminal connected to the ungrounded terminals of the filaments, a second conductor means connecting the ungrounded interrupter contact through said driving coil and said primary in series to said ungrounded terminals of the filaments, said driving coil being connected in said second conductor means close to said primary,

9. In a radio receiver, in combination, a metal base, a plurality of thermionic tubes having plates and filaments each of said filaments having a pair of terminals, a continuously vibrating circuit interrupter including a pair of cooperating contacts, a metal shield enclosing said interrupter, a transformer having a primary winding and a secondary winding, a rectifier connected between said transformer and said tubes for receiving energy from said secondary winding and delivering high voltage direct current to said plates, said thermionic tubes, shielded interrupter, transformer, and rectifier being arranged in compact relation and carried by said base, a metal housing enclosing them, a low voltage battery having a pair of terminals, said battery being mounted external to said housing, means for grounding one terminal of said battery to a ground external to said metal base, one terminal of each of said filaments, one contact of said interrupter, and its shield being grounded to said metal base, a common ground conductor connecting the metal base to the grounded terminal of said battery, conductor means connecting the ungrounded ends of the filaments to one end of the transformer primary Winding, means for connecting the other end of the primary winding to the other terminal of said interrupter, and a common ungrounded conductor connecting said last named conductor means to the ungrounded terminal of said battery, said common conductor carrying both filaments and interrupter current.

10. In a radio receiver, in combination, a metal base, a plurality of thermionic tubes having plates and filaments, each of said filaments being provided with a pair of terminals, 2. speaker having a field coil provided with a pair of terminals, a continuously vibrating circuit interrupter having a pair of cooperating contacts, a metal shield enclosing said interrupter, a transformer having a primary winding and a secondary winding, a rectifier circuit connected between said transformer and said tubes for receiving energy from said secondary winding and delivering high voltage direct current to said plates, said thermionic tubes, shielded interrupter, transformer and rectifier being arranged in compact relation and carried by said base, a metal housing enclosing them, said speaker being located within said housing, a low voltage battery external to said housing, said battery being provided with a pair of terminals, means for connecting one of said battery terminals to a ground external to the metal base, one terminal of each of said filaments, one terminal of said speaker field coil, and one contact of said interrupter and its shield being grounded to said metal base, a common ground conductor connecting the metal base to the grounded terminal of said battery, conductor means connecting the ungrounded terminal of the filaments, and the ungrounded terminal of the speaker field coil to one end of the transformer primary winding, the other end of said primary winding being connected to the other contact of said interrupter, a common ungrounded conductor connecting said last named conductor means to the ungrounded terminal of said battery, and a switch in said common ungrounded conductor, said common conductor carrying both filament and interrupter current.

11. In a radio receiver, in combination, a metal base, a plurality of thermionic tubes having plates and filaments, a continuously vibrating circuit interrupter having two cooperating contacts and a driving coil, a metal shield enclosing said interrupter, a transformer having a primary Winding and a secondary winding, a rectifier connected to said secondary Winding for receiving energy from said winding and producing high voltage direct current therefrom, means for delivering the high voltage direct current to said plates, said thermionic tubes, shielded interrupter, transformer, and rectifier being carried by said base, a metal housing enclosing them, one terminal of each of said filaments, one of said interrupter contacts and the interrupter shield being grounded to said metal base which forms the common ground for said radio receiver, a pair of terminals one of which is grounded to a ground external to said receiver, said pair of terminals being adapted to have connected between them a low voltage battery, conductor means connecting the base of said radio receiver to the grounded one of said pair of terminals, a second conductor means connecting the other of the ungrounded terminals of said pair of terminals to said filaments, a third conductor means connecting the other of said interrupter contacts through the driving coil and the primary of said transformer to the second conductor means, said driving coil and primary winding having sufficient inductance to present a high impedance to the passage of high frequency disturbances originating in the vibrating circuit interrupter to said second conductor means.

12. In a radio receiver, in combination, a metal base forming a ground for said receiver, a plurality of thermionic tubes having plates and filaments each of said filaments being provided with a pair of terminals, a continuously vibrating circuit interrupter having a pair of cooperating contacts and a driving coil, a metal shield enclosing said interrupter, a transformer provided with a primary winding and a secondary winding, a rectifier and filter circuit interposed between said secondary winding and said plates, said thermionic\ tubes, shielded interrupter, transformer, and rectifier being carried by said base, a housing enclosing them, means for connecting one terminal of each of said filaments, one of the interrupter contacts and the interrupter shield to said metal base, a pair of source terminals, means for connecting one of said source terminals to a ground external to said receiver, conductor means connecting the base of said radio receiver to the grounded source terminal, a second conductor means, including high frequency impeding means, connecting the other source terminal to the ungrounded terminals of said filaments, means including said driving coil and said primary winding in series, for connecting the other of said interrupter contacts to said second conductor means, said driving coil and primary winding presenting a high impedance to the passage of high frequency disturbances originating in the vibrating circuit interrupter to said second conductor means.

13. In signalling apparatus, a metal base forming a common ground for said apparatus, a plurality of thermionic tubes having plates and filaments, each of said filaments being provided with a pair of terminals, a vibrating circuit interrupter including a driving coil and a pair of cooperating contacts, a metal shield enclosing said circuit interrupter, a transformer having a primary winding and a secondary winding arranged to transform low voltage alternating current into high voltage alternating current, a rectifier circuit connected across the secondary Winding and arranged to change the high voltage alternating current into high voltage direct current, means for delivering the high voltage direct current to the plates of said tubes, said thermionic tubes, shielded interrupter, transformer and rectifier circuit being carried by said base, a metal housing enclosing them, means for grounding one terminal of each of said filaments and said interrupter shield to said metal base, a low voltage battery external to said housing and having a pair of terminals, means for grounding one of said battery terminals to a ground external to said receiver, conductor means connecting the grounded terminal of the battery to the base of said radio receiver, a second conductor means connecting the ungrounded terminal of said battery to the ungrounded terminals of said filaments and a third conductor means connected between said metal base and said second conductor, said third conductor means including the driving coil of said circuit interrupter and the primary winding of said transformer in series, said driving coil being adapted to impede the flow of disturbing energy generated by said circuit interrupter to said second conductor means.

EDWARD F. ANDREWS.

Jan. 6, 1942. N. A. WHITTAKER ELECTRIC PARKING METER Filed Dec. 9, 1940 2 Sheets-Sheet 1 3nventor Vorman .fl. PWzz'tta/ta' (Ittorneg

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