US2744194A - Alert device for attaching to radio receiving sets - Google Patents

Description

May 1, 1956 M. AUERBACH 2,744,194

ALERT DEVICE FOR ATTACHING TO RADIO RECEIVING SETS Filed June 21, 1951 5 Sheets-Sheet l INVENTOR.

y 1, 6 I M. AUERBACH 2,744,194

- ALERT DEVICE FOR ATTACHING TO RADIO RECEIVING SETS Filed June 21, 1951 v 5 Sheets-Sheet 2 INVENTOR.

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y 1, 1956 M. AUERBACH 2,744,194

ALERT DEVICE FOR ATTACHING TO RADIO RECEIVING SETS 4 Filed June 21, 1951 s Sheets-Sheet 5 I Q ,J ma

VEN W MMHL MLZ E 5. 5. 142M, fl 0m United States Patent ALERT DEVICE FOR ATTACHING T0 RADIO RECEIVING SETS Martin Auerbach, Flushing, N. Y.

Application June 21, 1951, Serial No. 232,772

4 Claims. (Cl. 250-) This invention relates to an alerting device which is adapted to be attached to an ordinary radio receiving set.

An object of the invention is to provide an attachment for a radio receiving set which does not atfect the ordinary operation of the set but which can be controlled by a broadcasting station to produce warning signals in case of fires, air-raids, special news bulletins and various other emergency conditions.

Another object of the invention is to provide an alerting device for a radio receiving set that can be attached to the set without requiring additional soldering or the services of a radio technician to install it.

Another object of the invention is to provide an alerting device with a stand-by arrangement the operation of which can be controlled by a broadcasting station.

Another object of the invention is to provide an alerting device, requiring no additional radio tubes, for attaching to a radio receiving set by merely plugging into said set.

. These objects and others ancillary thereto are accomplished by modifying a radio receiving set by a plug-in adapter unit that attaches to the sets audio circuits and which has a silent or stand-by switch that does not normally allow any sound to come from the loud speaker. However, upon the broadcasting station sending out a warning signal which may be a steady tone for 30 seconds for example, a trigger'device in the adapter unit is actuated to turn on the speaker and allow the sound or message to blare forth. The triggering device may be of various types such as a neon tube, a superregenerative relay, a cold cathode tube or a squelch circuit. These triggering circuits are all operated by a voltage building up to a predetermined value. However for an economical device and reliable operation a bimetallic strip which bends on the application of heat generated in a coil wound about the strip is very satisfactory. The heat that bends the bimetallic strip far enough to either make or break a contact is supplied by the audio signal which is received by the set from the warning tone signal. One phase of this invention is based on the dis covery that the customary broadcast music or sound fluctuates in value so that it does not heat the bimetallic strip suliiciently to bend the strip far enough to make or break the circuit whereas a steady tone signal can cause the bimetallic strip so to bend. It is also possible and sometimes desirable to introduce a circuit which selectively degenerates the audio stage so that all audio tones other than a particular one or a particular narrow range of tones are reduced in value so that only the preselected tone will operate the bimetallic strip. When the bimetallic strip makes or breaks a contact means are operated to turn on the loud speaker, etc.

The device may be connected to the set by one. or more plug-ins in at least two different ways. First one or more of the tubes can be removed and a plug having sockets for receiving the tube in its upper portion may be inserted the original tube socket. Second the device may 2,744,194 Patented May 1, 1956 provide separate sockets for one or more of the tubes of the set and in this case the tube or tubes are removed from the set, inserted in the sockets provided on said device and a closed top plug connecting the set to the device is placed in the original socket of the set.

The bimetallic strip of the device is surrounded by a coil which heats to cause the bimetallic strip to bend from its normal position when the operating cycle tone is received. The said bimetallic strip may itself make or break contact with an electrical circuit to operate another relay or switch or the bimetallic element may operate a mechanical switch. Once the switch is thrown by the bimetallic element it is designed to be locked in position so that the alerting device does not cease to operate unless manually turned off. The operating switch is also desirably constructed as to turn on other warning signals such as bells, lights, vibrators, etc. A very satisfactory and economical type of mechanical switch that is readily operated by a bimetallic strip is the preloaded spring switch.

A very satisfactory way to cut out the loud speaker in the stand-by setting is to connect a shunt across the primary terminals of the output transformer. In order to be able to plug in the device of the invention and have the plugs of the device provide a connection between the terminals of the primary of the transformer it is sometimes necessary to employ two plug-in means one being inserted in the tube socket occupied by the audio output and the other being inserted in the socket occupied by the rectifier tube.

In climates or places where ambient temperature may become high enough to operate or affect the bimetallic,

the variations in ambient temperature may be compenwill be compensated within the bimetallic element or elements.

The novel features characteristic of this invention are Y set forth with particularity in the appended claims. The invention itself, however, both as to its organization and its method of operation, together with additional objects and advantages thereof, will best be understood from the following description of specific embodiments when read in connection with the accompanying drawings in which:

Fig. 1 is a circuit diagram of the device of the invention including the speaker and two tubes of the receiving set to which it is attached.

Fig. 2 is a rear view of a small receiving set illustrating how the device is attached to a receiving set.

Fig. 3 is a bottom view of an adapter unit as actually constructed showing the switch device after it has been thrown by a bimetallic strip.

Fig. 4 is a detail view showing the switch device before being thrown.

Fig. 5 is a top plan view of the bimetallic unit and switch of Figs. 3 and 4.

Fig. dis a side view of a modified form of bimetallic strip.

V Fig. 7 is a top plan view of the device of Figs. 3-5.

Fig. 8 is a side view of the same.

Fig. 9 is a view similar to Fig. 7 of a modified form of the device.

In the diagram of Fig. 1, the portion included in the v box A is the portion of the receiving set which is adapted or altered in the transformation to a set with the alerting device of the present invention. The tube 10 is the rectifier tube of the set and tube ll is the power output tube. It will be seen that the line 13 from the cathode connection 12 of tube is connected to one side of the transformer 21 of the speaker at point 14, for example, so that by means of an auxiliary plug it is possible to provide a connection between wire 15 of the alerting unit and the lower side of the transformer 21 without requiring that the wire 15 be soldered by the purchaser of one of the alerting units.

Input line 16 from the previous tube of the set connects to the grid of the power output tube and the anode connection 17 of this tube is ordinarily connected to the opposite side of transformer 21 at 18, for example, but in the device of the invention the output connection 17 is connected to the switch electrode S2 and to the line which in turn is connected to coil 31 so that the A. C. component (the audio tone) will pass through to heat the coil 31 but the D. C. voltage will not pass through condenser 36. The coil 31 surrounds the bimetallic element 32 which is held at one end 33 upon the chassis of the attachment (see Figs. 4 and 7). From the coil 31, a line 34 connects through a variable resistor 35, line 37, switch contacts S-9 and 8-1, line 15, and point 14 to the lower side of the primary 21 of the speaker. When the switch S is in the position shown (the standby position) the primary 21 thereof is shunted and the speaker silenced by line 37, switch contacts S-9 and S-1 and line 15; however any signal that is received by the radio set is passed by line 30 through the coil 31. Ordinary signals received from the standard broadcasting stations fluctuate in value too much to cause the coil 31 to heat up sufiiciently to make the bimetallic element 32 bend but a sustained audio frequency note or tone of constant amplitude will cause the coil 31 to heat the bimetallic element sufficiently to cause it to bend and throw the switch S. The length of time required for the received audio frequency signal to heat the coil 31 sufficiently to bend the bimetallic 32 can be adjusted within wide limits (from a few seconds to several minutes, for example) by the variable resistance 35. Thus the variable resistance 35 is not an absolute requirement of the system but contributes to the effectiveness of the device. A choke coil 39 is also inserted between lines 30 and 37 to increase the voltage across coil 31 although this choke 39 is not absolutely necessary. The spring 40 which operates the switch S when moved by bimetallic 32 is shown only diagrammatically in Fig. 1.

The additional switch elements 8-3 to 8-8 and 8-10 to S12 are similarly not absolute requirements for the system but serve helpful and desirable functions. The contact 8-10 is connected in the position shown to a dead point 8-3 but when rod 8-13 is moved upwardly by spring element 40, 8-10 contacts S4 and thereby connects the main line to the plug 51. A light or a bell or any other signalling device may be plugged into the plug 51. It should be mentioned that when the audio signal passing through coil 31 causes the bimetallic 32 to throw the switch S, thereby connecting the loud speaker and disconnecting the shunt across the latter, the signal audio-tone which is being transmitted blares forth from the speaker for as long a time as it is continued. But additional devices which may be more effective may be attached through the plug 51.

The third switch element from the bottom S5, S-6 and S-11 operates to make only one audio tone or a narrow range of audio tones effective to heat the coil 31 and operate the bimetallic 32 and switch S. As shown the output connection 17 is connected to line 52 thence, to contact S-5, contact S-ll, line 56, condenser 53, tank circuit 54 (consisting of inductance 55 and condenser 56), and line 57 to the input line 16 of tube 11. The tank circuit 54 acts as a degenerative feed back to eliminate all signals except those to which the tank circuit is resonant or substantially resonant. Thus the device may be made to be operated by any desired narrow range of frequencies by selecting the proper values of coil 55 and condenser 56. While this particular element is not necessary to the operation of the remainder of the circuit it can be seen that it does increase the possibilities of the device since various sets may be made effective for different signals which different signals may be employed for a variety of different purposes. The contact 8-6 as shown is dead.

The top set of contact elements 8-7, 8-8 and S-12 act to cut down the power required during the stand-by position and to prolong the life of the tubes. Since the tubes of the set are to be maintained in operating condition at all times in the stand-by position they obviously wear out in less time than required for normal operation of the radio set. With the switch in the stand-by position shown the normal power of the line 50 is not ap plied to the heater elements of the tubes but instead a certain amount of the power is dissipated in resistance 69. Thus the heater circuit is fed from the main line 50, line 60, resistance 60 and line 62 the contact element 8-? being dead. When the switch S is thrown, however, the resistance 60 is shunted by contacts S-8 and S12. It is obvious that resistance 60 cannot be too large since the set must still be able to receive and amplify the audio frequency signal for operating the bimetallic 31.

One other unrequired but desirable feature, shown in the lower right hand side of Fig. 1 is a hand operated testing attachment 65, 66. A push button 65 for example may be provided to connect the coil through resistance 66 to a signal adapted to heat coil 31 and thereby find out whether said coil 31 and bimetallic element is working. The normal D. C. plate voltage supplied at 68 for example will pass through resistor 35, coil 31 and resistor 66 to ground 67 through push button 65 thereby heating up bimetallic strip 32.

After the switch S is thrown from stand-by position it is locked in operating position and can be returned manually to the stand-by position of Fig. 1 by a handle 70 such as shown in Figs. 3 and 4 for example.

Fig. 1 illustrates the circuit employed but one advantage of the instant invention is that it can be plugged into an ordinary radio set without requiring a skilled mechanic to install it. Thus no soldering, or similar operation which is unfamiliar to the ordinary radio user is required. All one need to do is to remove one or two tubes, place the plugs of the attachment where the tubes were and then placing the tubes in the sockets of the attachment provided therefor. Figs. 3-9 therefore illustrate one of the simplest of the commercial forms of the unit itself and Fig. 2 shows how the unit is attached to a small radio set. Fig. 2 shows a receiving set 9 having tubes 10' and 11 shown in phantom corresponding to tubes 10 and 11 of Fig. 1. To install the attaching unit which is shown in Figs. 3-8 tubes 10 and 11' are removed and placed in sockets and 81 respectively (see Fig. 7) and plugs 82 and 83 are then placed in the sockets 7 and 8 provided on the set 9 as shown in Fig. 2. No attempt is made to trace all the lines running from the plugs 82 and 83 since such a showing would only confuse and since these lines may be connected in many ways which are all within the skill of an ordinary radio mechanic, to produce the circuit of Fig. 1. It is obvious that the line from the particular socket in tube socket 8 with which connection 17 is made will not go directly to the corresponding socket in tube socket 81 of the unit but instead will be connected (1) to a line leading to 8-2 and possible S-5 and (2) to the line 30. For the most part however the individual sockets in tube socket 7 or 8 will be directly connected to the corresponding sockets in the tube socket 80 or 81 by means of plug 82 or 83 and lines 84 or 85. With tube 10, for example, all the individual sockets of tube socket 7 may be directly connected to all the corresponding sockets in tube socket 80, the only change necessary being that an additional line 15 is connected to the socket making connection 14 in the tube socket 80. If the modification is to include resistance 60 and its circuit an additional socket is mod- .ified.

In the figures of the drawing like numbers refer to like parts. Thus in Fig. 3, which is a bottom view of an at-' tachment 100 mounted in housing 90, the tube sockets 80 and 81, the plug socket 5.1, the mount 33 for the bimetallic element 32, the choke coil 39, the resistance for adjusting the time for response of the bimetallic element 32 are all shown. The resistance 35 has a control knob 35 extending outside of casing 90. For simplicity the wiring connections in the attachment are omitted from Figs. 3-9.

A typical spring switch device is shown in Figs. 3-5. The bimetallic element is shown in standby position in Fig. 4and in released position in Fig. 3. The switch S of this element is only a two part one instead of the 4- part switch of Fig. 1 and the switch 5' of Figs. 3 and 4 is in reversed position relative to Fig. l. The switch is operated by a pair of arms 91, 92 and the spring 40. In the position shown in Fig. 4 the inside arm 92 which is attached to one end of the semicircular spring is above the arm 91. Any movement ofthe arms 91, 92 toward each other compresses the spring 40. Once the arm 91 is moved slightly above the arm 92 the spring 40, being compressed, tends to snap the arm 91 further away from the arm 92 to the position shown in Fig. 3. In the device shown in Figs. 3 and 4 the bimetallic element 32 is arcshaped at ordinary temperatures and tends to straighten out if heated. The inflexible member 8-13 of the switch S is attached to the arm 92 and is moved downwardly by said arm to cause contacts S-9 and 8-10 to engage withcontacts S-2 and 8-4, respectively, as shown in Fig. 3.

Contact 84 is connected to plug 51 and contact 8-2 is connected as shown in Fig. l. The spring 40 holds or retains the switch S in the position shown in Fig. 3 until it is returned manually to the stand-by position of Fig. 4 by pulling handle 70 which slides in the bearing 93. The spring 40 is pivotally attached to the arms 91, 92 in any way such as by the small projections 94, 95 which fit into small openings (not shown) at the ends of spring 40. The end of arm 91 is, of course, moved upwardly by the end of bimetallic element 32.

In climates where there are wide changes of temperature it is possible that the temperature changes may be sufiicient to cause the bimetallic element 32 to bend and thereby move arm 91 when no alerting signal has been received. This is not often the case since room temperatures vary only slightly in modern homes and since the coil 31 can be made powerful enough and the bimetallic element 32 insensitive enough to avoid any substantialv I movement due to ordinary temperature changes. However, when such changes are significant the device shown in detail in Fig. 6 may be substituted. In this figure the bimetallic element 32 is made of S-shape and the coil 31 is placed only around one half of the 8 so that changes in room temperature do not affect the position of the end 96 of the bimetallic element since one half of the 8 element compensates for changes due to difference in ambient temperature in the other half of the 8. Since the coil 31, however, only surrounds half of the 8, it is effective to cause the bimetallic element to bend when the proper signal is passed therethrough.

A modified type of unit is shown in Fig. 9. Here instead of the simple pulgs 82 and 83, plugs 101 and 102 are employed. For this unit the tubes 10 and 11 are removed, the plugs 101 and 102 are placed in the sockets which previously held the tubes 10 and 11 and the tubes 10 and 11 are then placed into the socket provided at the top of plugs 101 and 102. Here not as many wires are required to connect the plugs 101 and 102 to the elements in casing 105. One additional connection 106 to ground is desirable. Otherwise the device of Fig. 9 is identical with that of Figs. 38.

It may be noted that in some radio sets, it would not be necessary to employ a device with two insertable plugs 82 and 83. That is, one plug 82 for the tube 10 could be omitted since it is possible in some sets to short out the primary 21 of the transformer by connecting the line 15, etc. from the conection 19 of tube ll to 8-1, etc.- This can be done when connection 19 is taken directly from point 14. However, in many circuits the screen grid connection 19 is not at point 14 potential but instead a resistance is inserted between the point 14 and the connector 19. In order to have an attachment which works for all sets it is desirable to make said attachment with two'plug-in means 82 and 83. Substantially all receiving sets are so constructed that point 14 is available from a pin connection from the socket for tube 10. It may also be noted that in Fig. 4 the normal position of the bimetallic element 32 is shown as curved and that the heating of the element 32 by the coil 31 causes the said curved element to straighten out. It is equally as practical to employ a bimetallic element which is normally straight and which bends when heated.

It will be readily seen that the invention provides an attachment'for a radio set that can be readily attachedby unskilled persons and that thesaid attachment is effective, inexpensive and economical in use.

I claim:

1. An alerting device for attachment to radio receiving sets of the type having a transformer operated loud speaker and at least one audio frequency amplifier tube including a power tube which operates the transformer, comprising shunt means adapted to be connected to shunt out the primary of the loud speaker while permitting the tubes of said set to operate, snap switch means movable manually to connect and disconnect said shunt across the primary of said transformer, bimetallic means responsive to a particular sustained audio frequency tone received by said radio set to snap said switch means from shunt-connecting to shunt-disconnecting position when sensitized by said sustained audio frequency tone, said bimetallic means being insufliciently affected by normal broadcast signals to operate said snap switch, and a degenerating feed back circuit adapted to degeneratively feedback from the output of the power tube to an input of an audio frequency tube all but a predetermined range of frequencies, said snap switch means comprises a multiple pole switch having a first set of contacts disconnecting said shunt and another set of contacts disconnecting the feed back circuit when said switch is operated by said bimetallic means.

2. An alerting device for attachment to radio receiving sets of the type having a transformer operated loud speaker comprising shunt means adapted to be connected to shunt out the primary of the loud speaker while permitting the tubes of said set to operate, snap switch means movable manually to connect and disconnect said shunt across the primary of said transformer, bimetallic means responsive to a particular sustained audio frequency tone received by said radio set to snap said switch means from shunt-connecting to shunt-disconnecting position when sensitized by said sustained audio frequency tone, said bimetallic means being insufliciently affected by normal broadcast signals to operate said snap switch, and a resistance adapted to be connected in series with the cathode heating line for said tubes when the said shunt is connected to the primary of said speaker and in which said snap switch is a multiple pole switch having a first set of contacts disconnecting said shunt and another set of contacts shunting said heating line resistance when said snap switch is operated by said bimetallic element.

3. An alerting device for attachment to radio receiving sets of the type having a transformer operated loud speaker comprising shunt means adapted to be connected to shunt out the primary of the loud speaker while permitting the tubes of said set to operate, snap switch means movable manually to connect and disconnect said shunt across the primary of said transformer, bimetallic means responsive to a particular sustained audio fre quency tone received by said radio set to snap said switch means from shunt-connecting to shunt-disconnecting position when sensitized by said sustained audio frequeney tone, said bimetallic means being insufficiently afiected by normal broadcast signals to operate said snap switch, said bimetallic means including a heating coil and a variable resistance in the heating coil circuit adapted to control the time of the response of the bimetallic element.

4. An alerting device for attachment to radio receiving sets of the type having a transformer operated loud speaker comprising shunt means adapted to be connected to shunt out the primary of the loud speaker while permitting the tubes of said set to operate, snap switch means movable manually to connect and disconnect said shunt .across the primary of said transformer, bimetallic means responsive to a particular sustained audio frequency tone received by said radio set to snap said switch means from shunt-connecting to shunt-disconnecting position when sensitized by said sustained audio frequency tone, said bimetallic means being insufiiciently affected by normal broadcast signals to operate said snap switch, said bimetallic means including a heating coil and a manually operated push button adapted to connect said heating coil with a source of power of sufiicient energy to test the operation of the said bimetallic means.

References Cited in the file of this patent UNITED STATES PATENTS 2,033,492 Stone, 11'. Mar. 10, 1936 2,055,921 Baker Sept. 29, 1936 2,104,844 Ailel Ian. 11, 1938 LE -0,75 eal Feb. 1, 1944 2,353,499 Purington July 11, 1944 2,367,378 Schick Jan. 16, 1945 2,447,156 Brittain Aug. 17, 1948 2,531,416 Fel'rar Nov. 28, 1950 2,552,331 Lamb May 8, 1951 FOREIGN PATENTS 526,239 Great Britain Sept. 13, 1940

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