US2353429A - Vibrator power supply for radio receivers - Google Patents

Description

July 11, 1944. E. F. ANDREWS VIBRATOR POWER SUPPLY FOR RADIO RECEIVERS 2 Shets-$heet 1 Filed May '7, 1941 INVENTOR ERA/V0 EWS "ATTORNEY mm H AAAA

A Tka July 11, 1944. E. F. ANDREWS VIBRATOR POWER SUPPLY FOR RADIO RECEIVERS Filed May 7, 1941 2 Sheets-Sheet 2 ovo ddwouo o o o lllll IIIIIIIIHL mam INVENTOR E- F. ANDREWS A'TTORNEY Patented July 11, 1944 VIBRATOR POWER SUPPLY FOR RADIO RECEIVERS Edward F. Andrews, Chicago, 111., assignor to Radio Corporation of America, a corporation of Delaware Application May 7, 1941, Serial No. 392,396

9 Claims.

The present invention relates generally to signalling apparatus and more particularly to radio receivers of the type which are energized from a source of direct current through the intermediary of an interrupter which acts to render the current from said source transformable.

In such systems it is known that the circuit interrupter inherently generates high frequency electrical disturbances which should be isolated or suppressed in order to prevent their being impressed upon the radio receiver circuits.

The present invention is directed primarily to a circuit arrangement for preventing these high frequency electrical disturbances from reaching the receiver circuits. To this end, the invention provides an arrangement whereby suitable filter circuits are interposed between the circuit interrupter and the power conditioning circuit of a receiver.

A feature of the invention is that certain already existent elements as for instance the primary winding of the power transformer are used as some of the elements of the filter circuits. It is an object of the invention to provide said already existent elements with the proper filter characteristics so that high frequency disturbing energy generated by the interrupter is filtered out or suppressed thereby preventing its being transferred to the receiver amplifying circuits through the power transformer.

A further object of the invention is to so mount the vibrator and power transformer that the large alternating currents of undesired frequency present in certain circuits between the vibrator and the transformer will not be caused to flow in the 3.

metallic base of the radio set, from whence it might be transferred to the amplifier.

A further object of the invention is to provide a novel shielding arrangement for the circuit interrupter, its associated circuits and the power transformer so as to prevent high frequency disturbances from the circuit interrupter from being impressed upon the receiver circuits through radiation.

A still further object of the invention is to provide certain novel power transformer assemblies which possess inherent shielding effects between the primary and secondary windings thereof.

Still another object of the invention is to an range the windings of the power transformer so as to provide increased leakage and hence increased primary inductance. In this way the primary winding which forms part of the filter circuit has a more effective choke action.

Other features and objects of the present invention will become apparent from the complete description of several embodiments of the invention presented hereinafter in order that those skilled in the art to which this invention appertains may understand how to make and use the same.

In the following description reference will be made to the accompanying drawings which are made a part hereof.

In the drawings:

Figure 1 is a diagrammatic representation of a radio receiving system which derives its energizing potentials from a vibrator power supply system incorporating certain features of the present invention;

Figure 2 is a sectional view through an elevation of the vibrator and power transformer assembly showing one embodiment of the invention;

Figure 3 is a sectional view along line f'i-3 of Figure 2;

Figure 4 is a sectional view through an elevation of a portion of a. power supply unit with the vibrator omitted and showing another embodiment of the transformer; and

Figure 5 is a sectional view along line 5-5 of Figure 4.

Referring to the drawings and particularly to Figure 1, the reference numeral l0 designates an antenna system which acts in the usual way to intercept signalling energy and impress it upon the input circuit ll of a radio receiver designated in the drawings by tubes l2-I5 inclusive. The output of the receiver is fed through an energy transfer device I! to a suitable utilizing device represented generally as a loudspeaker it. Since the present invention is mainly concerned with the power supply system, no attempt to give a detailed description of the receiver circuits will be made except to state that the receiver shown in Figure l. is of the well known superheterodyne type and comprises a radio frequency amplifier represented generally by a tube l2 and its associated circuits which feeds amplified radio frequency signalling energy intercepted by antenna is into a converted circuit incorporating a converter tube 13. The converter circuit generates local oscillations and combines the amplified signalling energy with the local oscillations to produce intermediate frequency energy. Through suitable selector circuits the proper intermediate frequency energy is fed from the converter circuit into an intermediate frequency amplifier which is represented herein by amplifier tube [4 and its associated circuits. It should be understood that as many stages of intermediate frequency amplification may be used as desired.

The output of the intermediate frequency amplifier i is fed to a combination diode detectoraudio frequency amplifier circuit incorporating a tube l which is of a type well known in the art and comprises a diode section and a triode section. The output of the intermediate frequency energy amplifier I4 is impressed upon the diode rectifier section of tube i5 and resultiug rectified energy which is developed across resistor i5? is tapped off and impressed upon the input grid of the triode section of tube [5 where it is amplified and fed to the input of power amplifier tube E5. The output of power amplifier tube is fed to a utilizing device l8 through transformer H. 1

The receiver shown in Figure 1 also incorporates means for obtaining automatic volume control. For this purpose the input grids of tubes l2. l3 and 14 are biased by a voltage which is developed across resistor I 9, it being noted that a by-pass condenser is shunted across resistor (9 to prevent undesired feedback.

In the arrangement shown in Figure 1, energizing potentials for the tubes l2 through 16 are derived from a low voltage source of direct current represented generally as a battery 2 l. Each of the tubes above noted is provided with an indirectly heated cathode and a heater therefor. All of the heaters or filaments are connected in parallel across the battery 2| and thereby energized by current from the battery. The filament energizing circuit is provided by grounding the n gative terminal of the battery 2| and one side of each of the heaters while the positive terminal of the source is connected through an on and off switch conductor 23 to terminal 24 of a conductor $5 to which the ungrounded terminal of each of the heaters of tubes I! through I5 is connected. Plate supply for the tubes l2 through 16 is supplied by a rectifier circuit which includes power transformer 33, rectifier tube 2? and a filter circuit made up of a choke coil 34 and a pair of condensers and 36 which connect each side of the choke 3 to ground. Rectifier tube 27 which is shown as a full wave rectifier tube. is provided with en indirectly heated cathode the heater of which is connected in parallel with the heaters of tubes 12 through Hi bv connection of one terminal thereof to conductor and the other terminal to ground. The rectifier circuit is of well k own desi n wherein one of the anodes of rectifier tube 2'! is connected to one end of the secondary of power transformer 33 while the other anode of rectifier tube 2" i connected to the othe of said secondary winding. A mid-tap on th secondary winding dividing the secondary winding into two portions 69 and 50. is connected to ground. The cathode oi rectifier tube 2? connec ed to each of the anodes of tubes i? throu h IE as well as to the screen grid of tube i throu h ch ke coil. 34. The screen grids of tubes if. '3 and M ore connected to the cathode f rectifier tube 2? through choke coil 34 in series with a vol age reducing resistor 39. The anod circuits of tubes !2 through "i are comnletcd b connecting ea ch of the cathodes of the tubes to round. In the case of tubes 2. and if the cathodes are connected to ground th ough suitable ca hode resistors.

In order to prev nt the voltage each half f the secondary winding of power transformer 33 from attaining an excessive value, condensers 3! and 33 which are of suitable value may be shunted respectively across sections an 53 of said secondary winding.

The alternating current available across the secondary of power transformer 33 is derived from the source 24 through the medium of current interrupter 43 which acts to make the current from source 2! transformable. Interrupter 4G is of usual. construction and comprises 9. vibrating reed i! adapted to be vibrated by means of an electro-magnetic driving device 4 The reed 4i is suitably biased so as to maintain contact .5 closed in the absence of a pull from driving magnet 44. The magnet 46 is connected across battery 2! through a circuit including switch 45 and switch 22 in series. In the opera tion of circuit interrupter 43, switch 22 is closed causing curent to flow from one side of battery 2| through driving magnet 44, closed switch 45, reed 4! back to the other side of battery 21.

The current through magnet 4 energizes the magnet and causes it to pull reed 4! and open switch thereby breaking the energizing circuit. The bias will then cause the reed to close switch 15 and the process is repeated, thereby providing the usual to and fro motion of the reed when the vibrator is in operation. Vibration of the read 45 opens and closes switches 42 and. The reed 4| is connected to ground while the center tap 5! on the primary of the power transformer 33 is connected to the positive terminal of the battery 2| through switch 22. Switch 42, the upper half 4'! of the primary winding of power transformer 33, and switch 22 are connected in series between th reed 4! and the battery 2i, hence upon closure of switches 22 and 42 current flows from battery 2i through the upper half 4'! of the primary winding. Reed 4! is also connected to the positive terminal of sourre '2! through switch '23, lower half 43 of the primary winding of transformer 33. and switch 22 in series. hence upon closure of switches "17! and 43 current flows through th lower half of the primary winding of transformer 33.

It is seen therefore, that as the reed 53 makes and breaks switches 42 and 43 in the operation of the device, current alternately flows through the two ha ves of the transformer primary winding. It the current flowing through primary of the transformer 33 which makes avail able an alternating current potential across the secondary of the power transformer 33. The transformer is usually of the type which steps up the voltage.

In the operation of the vibrator 4i! sparking occurs on make and break of the switches 42, 43 and 45 causing the generation of electrical disturbances. In order to isolate or suppress these disturbances, there is provided a comparatively large condense 25 connected between the reed 4! and the mid-tap 5! of the primary of the power transformer In addition, reed is connected to the upper end of th primary winding by the ser es circuit including condenser 29 and resistor 28 whereas the lower end of the primary winding is connected to the reed through resistor 3! and condenser 38 in series.

It will be noted that condensers 25 and 29 and the upper half 42' of the primary of transformer 33 form a filter circuit which is similar in type to the filter circuit 34, 35 and 35 in the output of rectifier tube 21. In other words, upper ha f 4'! of the primary of transformer 33 corresponds o choke coil 34. condenser 26 corresponds to con.- denser 36 and condenser 29 corresponds to condenser 35. Also, condensers 26 and 36 and the lower half 48 of the primary winding of transformer 33 form a similar l'ter circuit.

These two filter circuits are adapted to prevent the high frequency disturbing energy gen crated by the two vibrator contacts 42 and 43 from passing into the filament, battery leads, or other circuits of the set where their amplifies.- tion would produce objectionable audible disturbances from. the speaker. Since the high frequency disturbing energy generated by the vibrator 44 may also be impressed upon the amplifier of the receiver by radiation from portions of the vibrator and transformer circuit where the high frequency disturbing voltages are the highest, the vibrator system 49, the power transformer 33, the condensers 26, 29 and 30, the coil 44, and the closely associated leads are housed within a grounded suitable shielding housing 46, adapted to prevent such radiation.

A suitable assembly for the vibrator and associated circuit elements together with the power transformer is shown in Figure 2 wherein the two halves 49, 50 of the power transformer secondary are wound concentrically with respect to each other around the central leg of the core 59 and so that the portion 49 of the secondary envelopes portion B. The two portions 49 and 50 are so wound with respect to each other that the hot ends of the secondary; that is, the hot leads, are inside the cold leads. In other words, the leads 6!), 6! are tapped from the inside of the two coil portions 49, 50 while the center tap is vmade by connecting the lead 52 to points on the outside of the windings. The two halves 41, 48 of the primary winding of power transformer 33 are also wound concentrically with respect to each other about the central leg of core 58 and so that section 41 envelopes section 49 and section 48 envelopes section 41. For separating the primary windings from the secondary windings, insulation blocks 58 may be provided and used as spacers.

The primary winding sections 41, 48' are also wound so that the cold leads are on the outside while the hot leads are on the inside. Thus, it will be seen from Figure 2 that the hot leads 56, 53 are taken from the inside while the center tap 5| is taken from the outside of the primary portions. The arrangement of the hot and cold leads of the primary and secondary windings provides an effective shield to prevent high frequency disturbances which ma find their way past filter circuits 29, 25, 41 and 30, 26, 48 from being impressed upon the receiver circuits through capacity effects in the power transformer and especially by reducing the capacitive coupling between the primary and the secondary windings.

The vibrator and power transformer units are shielded by shielding means 43 which in the particular case shown in Figure 2 is formed in two sections one of. which encloses the vibrator while the other encloses the power transformer and filter circuits. The reason for using the twosection shield in Figure 2 of the drawings is to make it possible to use a vibrator of the plug-in type. It is to be understood, however. that the two sections of shield 46 are condu-ctively connected together so that in effect they are the same as a single shield as depicted generally in Figure 1.

In order to minimize the transfer of disturbing high frequency energy to the metal base or chassis of the receiver, the shield 46 is grounded to the chassis 55 at only one point, as shown by the bolt means 54. This prevents the large disturbing currents flowing in the vibrator and transformer shielding means 46 from flowing into the chassis as a result of connecting the shield 46 to the chassis 55 at two or more points at which different potentials exist in the shield 46.

It will be noted from Figure 2 that condenser 29 and resistor 28 are connected in series between lead 56 and the housing 46 while condenser 30 and resistor 3| are connected in series between the lead 5'! and the grounded housing 46. Vibrating reed 4| is also connected to the grounded housing 46 and through the medium of condenser 26 to the center tap 5! of the primary winding of the transformer. Figure 3 shows more clearly the manner in which the various windings of the power transformer are situated in relation to one another and the core The arrangement of the windings of the power transformer shown in Figures 2 and 3 wherein the hot portions are between two cold portions provides an inherent shield between the primary and secondary due to the fact that the cold side of the primary is next to the cold side of the secondary. The spacing between the primary and secondary windings is provided in order to increase the leakage. The leakage is also further increased by placing the primary on the outside of the assembly. Increasing the leakage increases the primary inductance and thereby makes the primary winding a more eifective choke.

It will be understood, however, that only enough leakage should be introduced between the primary and secondary to provide the inductance needed. Sufficient leakage may even be present when considerable insulation is present between the primary and the secondary.

In the embodiment of the invention illustrated in Figures 4 and 5 the power transformer 33 is arranged so that the mean length of turn is shorter than the mean length of turn in the arrangement shown in Figures 2 and 3 resulting in an arrangement which has less resistance; that is, less copper loss.

Referring more particularly to Figures 4 and 5, the primary of the transformer is made up of two sections 64, wound on different legs oi a core 63. The secondary winding is made up of two sections 67, 55 which are mounted so that section 61 is wound concentrically with section 64 of the primary winding and so that the section 64 envelopes section 61; the other section 55 of the secondary winding is wound around the same leg of the core and concentric with section 65 of the primary winding and so that the primary section 65 envelopes the secondary section 65. For increasing the leakage of the transformer, the primary sections 54 and 65 are separated from secondary sections 51 and 63 by means of spacers 68. The remaining connections of the arrangement shown in Figures 4 and 5 are the same as in Figures 2 and 3, it being noted that only that portion of the device has been shown in Figure 4 which is necessary to an understanding thereof.

It will be understood, however, that where a very high attenuation of the high frequency disturbances is not required, a conventional power transformer in which no unusual provisions for preventing undesired capacity couplings or for providing unusually high leakage may be employed in connection with the filter circuit and transformer and vibrator mounting means previously described.

From the foregoing it will be seen that the present invention provides a type of filter consisting of two capacities on each side of one inductance, the inductance being the transformer primary making possible a two-stage filter Without adding any separate inductance to the circuit.

Another advantage of the present invention is that the resistors 23 and 3| may be of low value, it having been found that resistances of the order of five or ohms are sufiioient. From considerations of filtering only, it would be advantageous to have a capacity only across each contact; that is, omitting the resistors 28 and 31 since this would decrease the resistance of the shunt path of the capacity input filter system. Howev 1', since such an arrangement is likely to cuse sticking of the contacts resistors and 35 are provided so as to limit the maximum current from condenser discharge. This arrangement is believed to be advantageous from the point of vi w of effioiency and damping of undesired high frequency oscilla ions.

Although the invention has oeen disclosed in connection with certain specific details of several preferred embodiments thereof, it should be understood that such details are not intended to be limitative of the invention except in so far as set forth the accompanying claims.

I claim as my invention:

1. In amplifying apparatus of the type having thermionic tubes each of which is provided with a filament and an anode. a power transformer, a source of direct current, a current interrupter acting upon operation to periodically connect said source across the primary of the transformer, a power conditioning circuit connected across the secondary of the transformer, said power conditioning circuit including a rectifier tube for supplying direct current potentials to said anodes, connections between said source of direct curent and said filaments for energizing the ments, means for supplying current from said source of direct current to said interrupter to operate the interrupter and thereby render the direct current from said source transformable whereby alternating current is available across said secondary winding, the improvement which is characterized by capacity and resistance means in series connected across the contacts of the interrupter and forming with the inductance of solely the primary a high frequency filter circuit to prevent high frequency disturbances from the interrupter from being transferred to said thermionic tubes through said filament and battery circuits and said primary and secondary of the transformer being so relatively positioned to provide sufficient leakage to render the said primary inductance an effective choke.

2. In radio signalling apparatus of the type having a thermionic tube which is provided with a filament and anode, a power transformer having a primary winding and a secondary winding, a source of direct current, a current interrupter connected between said source and said primary winding and acting upon operation to periodically connect the source across said primary winding. a power conditioning circuit including a rectifier tube connected across the secondary of the transformer for supplying direct current potentials to said anodes, connections between the battery and said filaments for energizing said filaments, means for supplying cur rent from said battery to said interrupter to operate the interrupter and render the current transformable whereby alternating current is available across the secondary winding, the improvement which is characterized by a condenser connected across said interrupter contacts, a second condenser and said first named condenser in series connected across said primary winding, mean for connecting the common terminal of said two condensers to ground, said two condensers acting in conjunction with solely said primary winding to form a filter circuit for impeding the flow of high frequency disturbances from the interrupter to the signalling apparatus and there being sufiicient leakage provided between said primary and secondary to increase the primary winding inductance.

3. In a power supply system for amplifying apparatus and the like, a power transformer having a primary winding and a secondary winding, a current interrupter having a vibrating reed on which is mounted one contact element of a make and break switch, said make and break switch having a fixed contact with which said first named contact cooperates, a source of direct current for said interrupter, means for operating said reed whereby said two contacts make and break at a rapid rate, means connecting said fixed contact to one end of said primary winding, means including a condenser for connecting said reed contact to another point of said primary winding, means including a condense for connecting said fixed contact to said reed contact and means for connecting the reed contact to ground, said two condensers and solely said primary winding forming a filter circuit to prevent passage of high frequency disturbances from said interrupter to the amplifying apparatus the primary winding and secondary winding of said transformer being spaced so as deliberately to introduce leakage in the transformer thereby to increase the inductance of said primary winding.

4. In a power supply system for battery onerated amplifying apparatus and the like, a power transformer having a primary winding and a secondary winding each of which is wound around a core in concentric relation and so that the primary winding envelopes the secondary winding, said primary winding being spaced from said secondary winding so as to increase leakage in the transformer and thereby increase the inductance of said primary winding, a current interrupter provided with a vibrating reed having mounted thereon one contact element of a make and break switch, the cooperating contact element of said switch being fixedly mounted with respect to the vibrating reed, a source of direct current for said interrupter, electromagnetic means deriving its operating current from said source of direct current for operating said reed to thereby make and break said two contact ele ments at a rapid rate, means for connecting said fixed contact element to one end of said primary winding, means including a condenser for connecting the first named contact element to another point of said primary winding, a resistor and a condenser in series connected between said two contact elements, means for grounding said reed contact element and means for connecting said battery between ground and said second named point of the primary winding, said two condensers, resistor and solely said primary winding forming a filter circuit for preventing passage of high frequency disturbances from the current interrupter to the amplifying apparatus.

5. In a power supply system for battery operated amplifying apparatus and the like, a power transformer having a primary winding and a secondary winding, said windings being spaced to provide suificient leakage to increase the primary inductance, a current interrupter provided with a vibrating reed which has mounted thereon one contact element of a make and break switch, the cooperating contact element of said switch being fixedly mounted with respect to the vibrating reed, a source of direct current for said interrupter, electromagnetic means deriving its operating current from said source for operating said reed and thereby alternately and periodically making and breaking said contact elements, a metallic housing for said power transformer and current interrupter, said source or" current being external said housing, a common grounding chassis, means for mounting said metallic housing on said chassis and so tnat it is conductively connected to said chassis at only one point, means within said housing for connecting the fixed contact element to one end 01 said primary winding, means including a condenser mounted within said housing for connecting said first named contact element to another point oi said primary winding, a resistor and condenser in series connected Within said housing between said fixed contact element and the housing, said series resistor and condenser cooperating with said primary winding to provide a high frequency iiiter circuit, means ior connecting said reed contact element to the housing and means for conmeeting said battery between said grounding chassis and said last named point of the primary winding.

6. In a power supply system for amplifying apparatus and the like, a power transformer having a primary winding and a secondary Winding, a source of direct current, means including a current interrupter acting upon operation to periodically connect said source across said primary winding so as to cause periodic now or current therethrough and thereby render the current irom said source transformable, a filter circuit interposed between the current interrupter and said power transformer for impeding the passage of high frequency disturbances from said current interrupter to said power transformer, said primary winding constituting an element 01 said filter circuit, and means for supplying current irom said source to said interrupter to operate the interrupter said primary and. secondary windings being concentrically wound about a common axis, said secondary winding being mounted within the primary winding and being spaced therefrom a suiiicient distance to increase the leakage thereby to render said primary winding effective as a filter choke.

7. In a power supply system for amplifying apparatus and the like, a power transformer having a primary winding and a secondary winding, a current interrupter provided with a vibratiiig reed having contact means mounted thereon, a pair of contacts cooperating with said reed contact means and arranged so that in the operation of the current interrupter the reed contact means periodically makes and breaks contact first with one and then with the other of said pair of cooperating contacts, a source of direct current having a positive terminal and a grounded negative terminal, electromagnetic means deriving its operating current from said source for operating said reed, said primary winding comprising two telescopeu rnu'lti-layer coils, means including a condenser for connecting a point or the outer layer or he outer coil of said primary winding and a point or the inner layer or the inner coil thereof to L116 reed contact means, means ior connecting said of direct current across said condenser, means ior connecting a point of the inner layer or the outer cell of said primary winding to one or said cooperating contacts, a condenser and a resistor 111. series connected between said reed contact means and said last named cooperating contact, means for connecting a point of the outer layer or the inner coil 01 said primary winding to the other oi said cooperating contacts, a condenser and a resistor in series connected between said reed ccntact means and said last named cooperating contact, said secondary winding comprising two telescoped multi-layer coils, a rectifier tube having a pair or anodes and a cathode, means ror connecting a point oi the outer layer or the outer coil 01' said secondary winding and a point of the inner layer or the inner coil thereto ground, means for connecting a point of the outer layer of the inner coil or said secondary winding to one of said rectifier anodes, means ior connecting a point of the inner layer or the outer COii of the secondary winding to the other or said rectifier anodes, and a utilizing circuit connected between the oathode oi the rectifier and ground, the outer diameter of said secondary winding being appreciabiy smaller than the inner diameter or said primary winding, said secondary winding being mounted within said primary winding in co-axial relation therewith and spaced therefrom.

a. In a battery operated radio receiver of the type having a plurality of thermionic tubes having plates and filaments, tne improved power supply means comprising a step-up transformer having a primary winding and a secondary winding so relatively spaced as to provide suiiicient leakage to render said primary winding eiiective as a choke, a rectifier connected to the secondary winding for supplying high voltage to said plates, vibrating means connected to said primary winding for supplying pulsating low voltage direct current thereto, said vibrating means comprising a vibrating reed having contact means mounted thereon and two cooperating contacts mounted one on one side of the vibrating reed and the other on the other side thereof and arranged so that in the operation oi said vibrating means said reed contact means alternately and periodically makes and breaks contact with said cooperating contacts, conductor means connecting one of said cooperating contacts and one end of said primary winding, conductor means connecting the other cooperating contact and the other end of said primary winding, a condenser connected between the reed contact means and an intermediate point or the primary winding, a resistor and a condenser in series connected between the reed contact means and one of said cooperating contacts, and a resistor and condenser in series connected between the other cooperating contact and the reed contact means, said series resistor and condenser cooperating with said primary winding to provide a high frequency filter circuit, a shielding housing enclosing said transformer, vibrating means, condensers and resistors, said shielding means being grounded at only one point, a low voltage battery external said shielding housing for supplying current to said filaments and to said vibrating means, conductor means connecting one terminal of said battery to one side of said filaments and to said intermediate point of the primary winding and conductor means connecting the other terminal of said battery to the other side of said filaments and to the reed contact means.

9. In a battery operated radio receiver, the improved power supply means comprising in combination, a transformer having a primary Winding and a secondary winding so relatively spaced as to provide suflicient leakage to render said primary winding effective as a choke, said primary winding having a center tap, a rectifier connected to the secondary winding, vibrating means connected to said primary winding for supplying pulsating low voltage direct current thereto, said vibrating means comprising a vibrating reed having contact means mounted thereon and two cooperating contacts mounted one on one side of the vibrating reed and the other on the other side thereof and arranged so that in the operation of said vibrating means said reed contact means alternately and periodically makes and breaks contact with said cooperating contacts, conductor means connecting one of said cooperating contacts and one end of said primary winding, conductor means connecting the other cooperating contact and the other end of said primary winding, a. condenser connected between the reed contact means and the center tap of the primary winding, a resistor and a condenser in series connected between the reed contact means and one of said cooperating contacts, and a resistor and condenser in series connected between the other cooperating contact and said reed contact means, a pair of input terminals for said vibrating means, conductor means connectingone of said input terminals to the center tap of the primary winding, and conductor means connecting the other input terminal to the reed contact means and each of said series resistors and condensers cooperating with a corresponding halfof said primary winding to provide a pair of high frequency filter circuits.

EDWARD F. ANDREWS.

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