US2988599A - Air-raid-warning signal generator - Google Patents

Description

June 13, 1961 M. JEANMONOD ETAL 2,988,599

AIR-RAID-WARNING SIGNAL GENERATOR nvmvrozes HUGHES M BLOWERS M/CHEL JEANMONOD 5 BY A, M,

ATTORNEY 52; mm mw ou M25 NF mw VD Filed June 28, 1960 United States Patent AlR-RAID-WARNlNG SIGNAL GENERATOR Michel Jeanmonod, Mill- Valley, and Hughes; M. Blowers,

Berkeley, Calif.,, assignors, by mesne assignments, to

Sound Communication Products, Inc., doing business as Sound Products of California, San Francisco, Calif.,

a corporation of California Filed June 28, 1960, Ser. No. 39,395 7 Claims. (Cl. 179-2) The present invention relates to electronic signal generartors in general and is particularly directed to an interval-timed signal generator for furnishing air-raid warning signals for either manually operated or automatic distribution to sound systems.

It has: become standard practice for air-raid-warning purposes to sound a steady alert tone for a duration of, for example, four minutes to alert the populace to enemy aircraft approaching at relatively long range. When the aircraft are in striking range, a wailing take cover tone or siren is sounded for a duration of, for example, three minutes to indicate the impending disaster and warn the populace to take all possible protective measures against air attack. In order that the warning procedurev be carried into elfect, means must be provided at all population centers, suchas, schools, manufacturing plants, airports, stores, sports arenas, and the like, as well as upon city streets, to produce the airraid-warning sound signals at a moments notice. Moreover, it. is. desirable that the warning signal generating means be adapted for use with existing public-address or other sound systems as well as in city-wide warning systems controlled from a remote central command location.

It is, therefore, an object of the present invention to provide an air-raid-warning signal generator for furnishing air raid warning signals which may be distributed throughout central sound or local public address systems.

Another object of the invention is the provision of anair-raid-warning signal generator that may be manually or automatically controlled to release the warning signals.

It is: yet another object of the invention to provide a signal generator of the class described which has provision to insure the warning signals complete priority of the input circuit of an existing sound system into which the generator is connected.

It is still another object of the invention to provide an air-raid-warning signal generator for the selective generation of a steady tone alert signal and a wailing tonelorsi-ren take-cover signal both having adjustable automatically timed durations.

It is a further object of this invention to provide a signal generator of the class described wherein the takecover signal has priority over the alert signal.

It is an even further object to provide an interval timed electronic signal generator which is maintained in a low power consumptionstand-by condition until actuated to generate the signals.

A still further object of the invention is the provision of an air-raid-warning signal generator which is capable of automatically switching external priority relay circuits.

Further objects are to provide a construction of maximum simplicity, economy and ease of assembly and dis-- assembly, also such: further objects, advantages and capabilities as will fully appear and as are inherently possessed' by the device and invention described herein.

Theinvention further resides in the combination, con struction and arrangement of parts illustrated in the accompanying drawing, and while there is shown. therein a preferred embodiment thereof, it is to be understood that the same is illustrative. of they invention and. that,

the: invention is capable of modification and change and comprehends other details of construction without departing from the spirit thereof or the scope of the appended claims.

Referring to the drawing, the single FIGURE of the drawing is a diagrammatic circuit for carrying out the present invention.

The single FIGURE is a schematic wiring diagram of a preferred embodiment of a signal generator in accordance with the invention as employed with an existing sound system.

Referring now to the single FIGURE of the drawing, there is shown an air-raid-warning signal generator 10 which is arranged to furnish timed steady tone alert signals and wailing tone take-cover signals to an audio outlet 11 in respective response to actuation of alert and take'cover push buttons 12, 13, or to remote push buttons or relays coupled to the unit by connection of control lines to a control outlet 14. The unit is also arranged to provide automatic switching for external priority relay circuits which may be connected to the control outlet 14. The warning signals may be distributed to acentral' sound system coupled to the audio outlet 11, or to, for example, an audio amplifier 16 comprising the input of an existing public-address system coupled to the outlet as shown in the FIGURE. In the latter instance, the normal use of the amplifier 16 with various program sources such as a microphone 17 is retained. However, the generator 10 includes provision to insure the warning signals priority over the program sources upon generation of-such signals.

Considering now the signal generator 10 as to its detailed circuit arrangement for theaccomplishment of the foregoing ends, the geenrator includes a toneoscillator circuit 18 comprising a. variable frequency tone oscillator section 19 for producing the steady ale signal and slow tuning tone oscillator section 21 for producing the wailing take-cover signal. The tone sections 19, 21 are preferably provided as conventional multivibrator connected duo-triodes 22 and 23, respectively, the latter having a bias capacitor 24 for establishing a slowly varying grid bias voltage. at the duotriode 23- productive of the slow tone variation in the output thereof. The plate. outputs of both tubes are coupled to a volume control 26 which facilitates adjustment of the signals to the desired. sound level.

Operating power for the tone oscillator circuit '18 is provided from apower supply 27 of generally conventional design. More specifically, the supply includes a power transformer 28 having a primary 29' connected to a plug 31 for insertion into a commercial power receptacle. The secondary 32 isv appropriately tapped toprovide a low. voltage filament output between taps 33-, 34,. such taps being connected to the filaments of. the tone oscillator duo-triodes 22, 2-3. In. addition, taps 36, 37 and 38, 39 areprovided in the secondary 32 to furnish, respectively, plate and filament voltage to a duo-diode 41, connected as a full wave. rectifier. The direct cur-- rent output. of the rectifier tube 41 is in turn coupled to the plates of the. tone oscillator duo-triodes 2:2, 23 to provide plate bias. therefor. One further output is included from the power supply 2.7 for purposes subsequently described, such output being low voltage directed. cur-- rent as produced, for example, by means of opposed dry disc type rectifiers 42, 43 connected between the filament taps 33, 34 of the power transformer secondary.

In, order that the tone oscillator circuit 18 be maintained in a low power consumption stand-by condition with only the filaments of the tubes 22', 23 energized until such time as it is desired to generate the tone warning signals, means are provided for the selective switching. of. the plate. bias output of power supply 27 on and 0E.

More particularly, a power supply switching relay 44 having an operating coil 46 and contactors 47, 48, respectively, operating between normally closed contacts 49, 51 and normally open contacts 52, 53 is provided for this purpose. The contactor 47 is connected to the ground bus of the power supply and tone oscillator circuits whereas normally open contact 52 is connected to a center tap 54 between the plate voltage taps 36, 37 of power transformer 28. Thus, until the relay coil 46 is energized, the center tap 54 is floating, and unsymmetrical voltages are applied from taps 36, 37 to the plates of rectifier tube 41, such voltages being incompatible with the generation of a high voltage direct current output therefrom. Upon energization of the relay coil, contactor 47 engages the normally open contact 52 to thereby connect the center tap 54 to ground. Symmetrical oppositely phased voltages with reference to ground are thus generated at taps 36, 37 which are conducive to the full wave operation of the rectifier tube 41 and generation of the plate bias therefrom required for the operation of the tone oscillatorcircuit 18. The contactor 48 and normally closed and normally open contacts 51, 53 play no part in the operation of the power supply 27 and tone oscillator circuit 18 but rather are employed herein to accomplish the previously mentioned automatic switching of external priority relay circuits or the like. To this end, the contactor 48 and contacts 51, 53 are respectively connected to separate pins of the control outlet 14 such that upon connection of external circuits thereto, automatic switching thereof is accomplished by the relay 44.

As noted previously, it is desirable that the alert and take-cover tone signals generated by the tone oscillator circuit 18 be separately timed for intervals of, for example, four minutes and three minutes, respectively. In accordance with the present invention, this is accomplished by timed-interval energization of the coil 46 of power supply control relay 44. More particularly, alert and take-cover timers 56. 57 are provided to actuate relay 44 for predetermined time-intervals; e.g., four minutes and three minutes, respectively, in response to closure of the alert and take- cover switches 12, 13 or equivalent triggering of the signal generator into operation. The timers are similar in design and are preferably substantiallv conventional impulse o erated. synchronous motor driven timers with variable time set releases. The timers 56. 57 may, for example, respectively include synchronous motors 58, 59 having their stators 61. 62 parallel connected to the power plug 31. The rotors 63. 64 f these motors are shaft connected through clutches 66. 67 to cams 68. 69 having pawls 71. 72 or the like for opening normally closed contacts 73. 74 f microsw tches 76 7' c e c revolution of the cams. The clutches 66 67 are mechanically linked to timer relays 78. 79 so as to be engaged upon actuation of the latter. More specifically. relays 78, 79 respectively comprise operating coils 81, 82'. and sets of contactors 83, 84 and 86. 87 operable between normally closed contacts 88. 89 and 91, 92 and normally open contacts 93, 94 and 96, 97, the contactors being linked with the respective clutches 66. 67. Thus, upon energization of the coil of either of the relays 78. 79 in a manner subsequently described, the corresponding one of the clutches 66, 67 is responsively engaged and the associated motor and cam are connected. Hence upon completion of one revolution of the cam. the normally closed contacts of the corresponding one of microswitches 76, 77 are instantaneously opened. The time intervals between engagement of the clutches and opening of the microswitch contacts in the respective timers is utilized herein as the timed intervals of the alert and take-cover warning signals. More particularly, the relays and microswitches of the timers are appropriately interconnected to provide lock-up circuits whereby upon the instantaneous energization of the respective timer relay coils, locked in energization of the coils is maintained for the time intervals determined by the rotating cams, the relays being arranged to be restored upon the instantaneous opening of the microswitches. To provide such lock-up circuits, the normally closed contacts 73 of microswitch 76 are connected in series between normally open contact 93 and one side of coil 81 of alert timer relay 78 whereas contacts 74 of microswitch 77 are similarly con-. nected between normally open contact 94 and one side of coil 82 of take-cover timer relay 79. The other sides of the relay coils are in turn connected to ground. The operating current for sustaining energization of the relay coils is derived from the low voltage direct current output of the power supply 27, the common juncture of rectifiers 42, 43 being connected to contactors 83, 86 of relays 78, 79, respectively.

By virtue of the foregoing connections, upon instantaneous energization of the coils of relays 78, 79, the contactors 83, 86 engage normally open contacts 93, 94 to thereby apply operating current to the relay coils through the normally closed micro switch contacts 73, 74, respectively. Actuation of the relays also eifects engagement of the respective clutches 66, 67 whereby the earns 68, 69 are driven by the motors 58, 59. Upon completion of a revolution of cam rotation, the pawls 71, 72 instantaneously open the respective micro switch contacts 73, 74 to thereby interrupt the flow of operating current to the coils 81, 82 and restore the timer relays to their normal unenergized conditions. It will thus be appreciated that the lock-up time intervals of the timers may be manually varied in a manner well known in the art as by changing the ratio of adjustable gearing in timer clocks (not shown) employed with the motors to vary their output shaft speeds.

As regards the connections of the timers 56, 57 in energizing relation to the power supply control relay 44 such that it is operated in concert with the timers and therefore during the respective time intervals thereof, the normally open contacts 94, 97 of timer relays 78, 79 respectively, are connected to one side of the operating coil 46 of relay 44, the other side thereof being connected to ground. In addition, contactors 84, 87 of the respective timer relays are connected to the other contactors 83, 86 thereof so as to be likewise energized with the operating voltage derived from rectifiers 42, 43. Thus, upon actuation of either timer, the power supply control relay 44 is actuated for the duration of the corresponding timed interval thereof to effect timed operation of the tone oscillator circuit 18.

In order that the foregoing operation of the timers 56, 57 and tone oscillator circuit 18 be selectively initiated in response to actuation of the alert and takecover control push buttons 12, 13 or to remote switching means, the timer relay coils 81, 82 are respectively connected through the alert and take-cover control push buttons to the low voltage direct current output provided by rectifiers 42, 43 of power supply 27. In addition, the push button switches 12, 13 are respectively connected across sets of pins of the control outlet 14 to facilitate alternative accomplishment of their switching functions by other switching means as may be connected to the control outlet. Thus, the requisite initial momentary energization of the timer relay coils is selectively accomplished upon closure of the alert or take- cover control pushbuttons 12, 13 or alternative switching means coupled to the control outlet 14.

To facilitate control over the tone oscillator circuit 18 in the selection of the type of signal generated therefrom (steady or wailing tone), control over the input of a sound system such as includes amplifier 16 to insure priority of the generated air-raid-warning signals over a program source such as microphone 17, and priority of the take-cover signal over the alert signal, alert and take-cover master control relays 98, 99 are I responsively connected to the alert and take-cover push 1S 396D) include an operating coil 101 and contactors 102, 103 respectively operative between normally closed contacts 104', 106' and normally open contacts 107, 108. One side of coil 101 is connected to ground. Contactor 102 is connected to ground while normally open contact107, is connected to the high side of bias. capacitor 24 of the slow tuning tone oscillator section 21 of tone oscillator circuit 18. Thus, upon actuation of alert master control relay, the capacitor 24 is shorted to ground through contactor 102 and contact 107 to therebymute the wailing tone function of oscillator section 21 such that the steady tone alert signal is generated by the oscillator circuit. Normally closed contact 106 is connected to a program source terminal 109 of audio. outlet 11, the microphone 17 being connected between this terminal and a grounded shield terminal 111.

Take-cover master control relay 99 includes, an opcrating coil 112 and contactors 113, 114, respectively operative between normally closed contacts. 116, 117' and normally open contacts 118, 119. The coil 112 is connected at one side to ground and at the other side through take-cover control push button 13 to the low voltage direct current output of power supply 27. This latter side of the coil is also connected to the contacts of the take-cover timer micro switch 77'. The normally closed contact 116. is connected to contactor 103' of alert master control relay 98 while normally open contact 118 is connected to normally open contact 108 of the latter and to the output of tone oscillator circuit 18 at volume control 26. The contactor 113 is connected to an audio output terminal 121 of audio. outlet 11, the input of audio amplifier 16 being connected between such terminal and shield terminal 111. Normally closed contact 117 is connected to the ungrounded side of the operating coil 101 of alert master control relay 98 while contactor 114 is connected through alert control push button 12 to the low voltage direct current output of power supply 27. Contactor 114 is also connected to the contacts of the alert timer micro switch 76. It will thus be appreciated that with the foregoing connections of the control relay 98, 99, the microphone or other program source is connected to. the audio amplifier 16 through a current path including normally closed contact 106, contactor 103, normally closed contact 116, and contactor 113. Upon energization of either master control relay, the current path is opened by virtue of contactor 103 or contactor 113 moving into engagement With the associated one of normally open contacts 108, 118. Since both of these normally open contacts are connected to the output of the tone oscillator 18,. the tone signals therefrom are at this time applied to the. audio amplifier with priority over the microphone. Furthermore, it is to be noted that inasmuch as the normally open contact 108 of alert relay 98 is connected to the audio amplifier through the normally closed contact 116 and contactor 113 of takecover relay 9.9, and energization of coil 101 of the alert relay is through contactor 114 and normally closed contact 117- of the take-cover relay, priority of a take-cover signal over an alert signal is obtained. More specifically, were the alert master control relay 98 actuated and an alert signal being delivered to the audio outlet, upon actuation of the take-cover master control relay 99 the contactor 113 moves into engagement with contact 116 to thereby interrupt the alert signal and deliver the take-cover signal to the audio amplifier, and contactor 114 moves out of engagement with contact 117 to hence deenergize the alert relay coil 101.

In the overall operation of the air-raid-warning signal generator 10, the power supply 27 energizes the filaments of the duo-triod'es 22, 23 of the tone oscillator circuit 18 and the motors 58, 59 of the alert and take- cover timers 56, 57 are running when the generator is in a stand-by condition. Where the generator is employed with an existing sound system such as includes audio amplifier 16, the amplifier 16 may be used in its usual manner with microphone 17 or other program sources when the signal generator is in stand-by condition. Assuming now that the alert control push button 12 is actuated or alert switching is accomplished from a central command location through a command circuit wired to control outlet 14', the alert master control relay 98 and alert timer relay 78 are responsively actuated. Relay 98 disconnects the microphone 17 or other program source from audio amplifier 16 and connects the output of tone oscillator circuit 18 thereto. This relay also mutes. the output of the slow tuning oscillator section 21 such that the tone oscillator circuit is prepared to generate a steady tone signal. The timer relay 78 simultaneously is locked up for its preset timing interval of, for example, four minutes as determined by the rotational period of cam 68. The power supply control relay 44 is in turn actuated for the timed four-minute interval to provide plate bias to the tubes of the tone oscillator circuit 18 and place same in operation. The oscillator circuit 18 hence generates a steady tone alert signal during the timed four-minute interval and such signal is applied to the audio amplifier 16; Ex.- ternal' circuits connected to the control outlet 14 are also switched during the interval by the relay 44. When the interval is timed out by the alert timer 56, all relays are restored by the, momentary opening of the normally closed contacts 73 of micro switch '7 6.

When the take-cover control push button 13 is momentar-ily closed or take-cover switching is otherwise accomplished, the take-cover master control relay 99 and take-cover timer relay 79 are instantaneously actuated and thereafter are. energized through the normally closed contacts 74 of the take-cover timer micro switch 77 during the locked up time interval of, for example, three minutes established by the timer. The take-cover master control relay 99 disconnects the microphone 17 from audio amplilier 16 and connects the output of tone oscillator circuit 18 thereto. It is particularly important to note that relay 99 also locks out the operating coil 101 of alert master control relay 98 such that in the event the alert signal was being generated at the time it was desired to sound the take-cover signal, the take-cover signal would be automatically given priority. The power supply control relay 44 is actuated by the take-cover timer relay 79 for the timed locked up interval of the timer 5-7 to provide plate, bias voltage to the tubes of the tone oscillator circuit 18 and place same in operation. Since the capacitor 24 of the slow tuning oscillator section 21 is not grounded. at this time, the wailing take-cover tone signal is generated by the oscillator circuit and applied to the audio amplifier 16 during the timed interval of the take-cover timer 57. External circuits connected to the control outlet 14 are also switched during the interval by the power supply control relay 44. When the interval is timed out by the timer 57, all relays are restored by the momentary opening of the normally closed con tacts 74 of the take-cover timer micro switch 77,.

What is claimed is:

1. An air-rarid-warning signal generator comprising a tone oscillator circuit for selectively generating steady and wailing tone signals, power supply means for generating operating bias for said tone oscillator circuit, first and second timed interval switching means coupling said,

power supply means to said tone oscillator circuit and; operable to apply said operating bias to the tone oscillator circuit during their respective timed intervals in response to steady and wailing tone actuating signals, and selector means coupled to said oscillator circuit and said first and.

second timed interval switching means for selecting a steady tone signal in the oscillator circuit simultaneously with the application of a steady tone actuating signal to said timed interval switching means and a wailing tone signal in the oscillator circuit simultaneously with the application of a wailing tone actuating signal to the timed interval switching means.

2. An air-raid-warm'ng signal generator comprising a 7 generation of steady tone or wailing tone signals, power supply means coupled to said oscillator circuit for applying operating bias thereto upon energization, steady and wailing tone timers coupled to said power supply means coupled to said oscillator circuit for applying operating bias thereto upon energization, steady and wailing tone timers coupled to said power supply means for upon actuation energizing said power supply means for predetermined steady and wailing tone timed intervals and selective steady and wailing tone actuating means coupled to the selecting means of said tone oscillator circuit and said timers for actuating the selecting means to steady tone generation simultaneously with actuation of said steady tone timer and actuating the selecting means to wailing tone generation simultaneously with actuation of said wail ing tone timer.

3. An air-raid-warning signal generator comprising a tone oscillator circuit including a steady tone oscillator section and slow tuning oscillator section for generating a steady tone signal with wailing tone signal superimposed thereon, power supply means coupled to said oscillator circuit for applying operating bias thereto upon actuation, an interval timer operatively coupled to said power supply means upon actuation responsively to actuate the power supply means for a predetermined time interval, a second interval timer operatively coupled to said power supply means upon actuation responsively to actuate the power supply means for a predetermined second time interval, steady tone control relay means coupled to the slow tuning oscillator section of said tone oscillator circuit and to said first timer, said relay means operable upon actuation to mute said slow tuning oscillator section and actuate said first timer, wailing tone control relay means coupled to said second timer and operable upon actuation to responsively actuate same, steady tone selector means coupled to said steady tone control relay means for selectively actuating same, and wailing tone selector means coupled to said wailing tone control relay means for selectively actuating same.

4. An air-raid-warning signal generator according to claim 3, further defined by said steady tone and wailing tone control relay means respectively including first and second current paths with the first paths being normally closed and the second paths being normally open, said second paths being closed upon actuation of the respective relay means simultaneously with opening of the first paths, and an audio outlet having program source terminals and sound system input terminals, said program source terminals serially coupled to said sound system terminals through the first paths of said steady and wailing tone relay means, said sound system terminals serially coupled to the output of said tone oscillator circuit through the second paths of said steady and wailing tone relay means.

5. An air-raid-warning signal generator comprising an electronic tone oscillator circuit including a steady tone oscillator section and slow tuning oscillator section for generating a steady tone signal with wailing tone signal superimposed thereon; power supply means having a filament output coupled to the tubes of said oscillator circuit and a plate bias output; power supply control relay means coupled between said plate bias output and said oscillator circuit, said power supply control relay means operable upon energization to apply plate bias to the tubes of said oscillator circuit; an interval timer coupled to said power supply control relay means and operable upon energization to energize said power supply control relay means for a predetermined time interval; a second interval timer coupled to said power supply control relay means and operable upon energization to energize said power supply control relay means for a predetermined second time interval; steady tone selector switch means coupled in energizing relation to said first timer to ener gize the timer upon momentary actuation of the switch means; wailing tone selector switch means coupled inenergizing relation to said second timer to energize said 8 second timer upon momentary actuation of the wailing tone switch means; a wailing tone control relay responsively coupled to said wailing tone selector switch means and to said second timer, said wailing tone control relay relay having first and second contactors operable between first and second normally closed and normally open contacts, said first contactor responsively coupled to said steady tone selector switch means and to said first timer, said second normally open contact coupled to the output of said tone oscillator circuit; a steady tone control relay responsively coupled to the first normally closed contact of said wailing tone control relay, said steady tone control relay having first and second contactors operable between first and second normally closed and normally open contacts, said first contactor connected to ground and said first normally open contact coupled to said tone oscillator circuit to mute the output of the slow tuning oscillator section thereof in response to grounding, said second contactor coupled to the second normally closed contact of said wailing tone control relay, said second normally open contact coupled to the output of said tone oscillator circuit; and an audio outlet having program source and sound system input terminals, respectively, coupled to the second contactor of said wailing tone control relay and to the second normally closed contact of said steady tone relay.

6. An air-raid-warning signal generator according to claim 5, further defined by said first and second timers each comprising a synchronous motor, a cam, a clutch mechanically coupling said cam to said motor, a micro switch having normally closed contacts engageable by said cam for instantaneous opening each cam revolution, and a relay mechanically linked with said clutch to engage same upon relay actuation, said relay having an operating coil and first and second contactors operable between first and second normally closed contacts and normally open contacts, said coil serially connected with said micro-switch contacts and first normally open contacts; a power source connected in energizing relation to the coils of the first and second timer relays through respectively said steady tone selector switch means and wailing tone selector switch means; means connecting said power source to said first and second contactors of said first and second timer relays; means coupling the micro-switch contacts of said second timer in energizing relation to said wailing tone control relay; means connecting the micro-switch contacts of said first timer to the first contactor of said wailing tone control relay; and means coupling the micro-switch contacts of said first and second timers in energizing relation to said power supply control relay means.

7. An air-raid-warning signal generator comprising an electronic tone oscillator circuit including first and second multivibrator connected tubes with the second tube having a bias capacitor coupled between its grids and ground to slowly vary the tone of the output therefrom; a power supply including a transformer with secondary tapped to provide a low voltage filament output and high voltage rectifier plate and filament outputs, a full wave rectifier having its plates and filament connected to said high voltage rectifier plate and filament outputs, and opposed rectifiers connected between said low voltage filament output; means connecting said low voltage filament output to the filaments of the tubes of said tone oscillator circuit and the output of said full-wave rectifier to the plates thereof; a power supply control relay having an operating coil and first and second contactors operative between first and second normally closed and normally open contacts, one side of said coil and said first contactor connected to ground, said first normally open contact connected to a center tap between the high voltage rectifier plate output taps of the transformer secondary of said power supply; a control outlet having eight terminals with the first connected to ground, the second to the eighth, the fifth, sixth and seventh to the second normally open contact, second contactor, and second nor- 9 mally closed contact of said power supply control relay; a steady tone control push button connected between the third and eighth terminals of said control outlet; a Wailing tone control push button connected between the fourth and eighth terminals of said control outlet; means connecting the common juncture of the opposed rectifiers of said power supply to said eighth terminal of said control outlet; 21 first timer having an actuating input and timed interval output, said actuating input coupled to the third terminal of said control outlet, said timed interval output connected to the operating coil of said power supply control relay; a second timer having an actuating input and timed interval output, said actuating input coupled to the fourth terminal of said control output, said timed interval output connected to the operating coil of said power supply control relay; an audio outlet having a grounded shield terminal connected tothe first terminal of said control outlet and a program source terminal and sound system input terminal; a Wailing tone control relay having an operating coil and first and second contactors operative between first and second normally closed and normally open contacts, said coil connected between said first and fourth terminals of said control outlet and to the timed interval output of said second timer, said first contactor connected to the third terminal of said control outlet and to the timed interval output of said first timer, said second contactor connected to the sound system input terminal of said audio outlet, said second normally open contact connected to the output of said tone oscillator circuit; and a steady tone control relay having an operating coil and first and second contactors operative between first and second normally closed and normally open contacts, said operating coil connected between the first terminal of said control outlet and the first normally closed contact of said wailing tone control relay, said first contactor connected to ground, said first normally open contact connected to the high side of the bias capacitor of said tone oscillator circuit, said second contactor connected to the second normally closed contact of said wailing tone control relay, said second normally closed contact connected to the program source terminal of said audio outlet, said second normally open contact connected to the output of said tone oscillator circuit.

No references cited.

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