Title:
Combination radio receiver-hearing aid unit
United States Patent 2159632


Abstract:
This invention relates to improvements in apparatus for aiding the hearing of deaf persons. The principal object of the invention is to provide a radio broadcast receiver adapted to supSply energy to a headphone set for the benefit of persons whose hearing is impaired, as well as to a conventional...



Inventors:
Morey, James J.
Application Number:
US23157438A
Publication Date:
05/23/1939
Filing Date:
09/24/1938
Assignee:
Harold, Fries H.
Primary Class:
Other Classes:
379/395, 381/74, 381/104, 381/111, 381/190
International Classes:
H04R25/00
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Description:

This invention relates to improvements in apparatus for aiding the hearing of deaf persons.

The principal object of the invention is to provide a radio broadcast receiver adapted to supSply energy to a headphone set for the benefit of persons whose hearing is impaired, as well as to a conventional loud speaker unit, and which, in addition, may be used whenever the occasion demands as a speech amplifier to raise the in0 tensity of local conversation to such a point that it may be heard by such a deaf person.

It is another object of the invention to provide a broadcast receiver-hearing aid combination in accordance with the foregoing which may also be used to pick up and amplify an incoming telephone conversation for the benefit of the person who is hard of hearing.

The invention also aims to provide a unit capable of effectuating the foregoing objects and fur0 ther characterized in that the output volume, whether it be that of the unit operating as a radio receiver, a local speech amplifier of a telephone conversation pick-up, may be adjusted to suit the needs of the person using it, and in which 5the output tone may likewise be varied in order to emphasize that band of frequencies to which the user is least sensitive at the expense of those frequencies which he hears with greater ease.

It is still another object of the invention to provide a novel audio frequency amplifying circuit which is particularly adapted for dry cell operation because of the relatively high gain which may be obtained from the circuit with im5 pressed plate and filament voltages of unusually low order.

The invention further aims to provide a combination radio receiver-telephone and local conversation hearing aid amplifier including dry cell 0 batteries for its operation to effect the foregoing objects; all comprised within a small, compact and light-weight unit which may be readily transported from place to place by its owner so as always to be available for his immediate use. 5 The full nature of the invention along with other objects and various features thereof will be more fully understood from the following description when read in the light of the accompanying drawings, in which 0 Figure 1 is a front elevational view of the unit embodying the invention; Fg. 2 is a diagrammatic representation of the elements of the invention and their electrical connection; 5 Fig. 3 is a diagrammatic representation of a modified form of the circuit arrangement shown in Fig. 2.

In carrying out my invention I mount a radio broadcast receiver along with dry cell batteries for its operation in a casing 10 to provide a small, compact and light-weight unit which may readily be transported by its owner from place to place so as always to be available for Immediate use. The receiver which is shown diagrammatically in Fig. 2 comprises two tuned radio frequency amplifier stages, a tuned detector stage, an audio frequency amplifying stage and a final power amplifying stage, all connected in cascade. In the preferred embodiment, the grid-cathode input circuit of the first radio frequency amplifier tube II, including its tuning condenser 12, is coupled through coils 13 to the antenna-ground circuit at 14, 15. The grid-cathode input circuit of the second radio frequency amplifier tube 16, including its tuning condenser 17, is coupled to the plate cathode output circuit of the first tube II through coils 18; and the input circuit of the detector stage 19, including the tuning condenser 20, is coupled to the output circuit of the second radio frequency tube 16 through coils 21. The circuit utilizes grid leak detection in the usual manner and as indicated. In order to save space and weight the audio frequency tube 22 and the power tube 23 are resistance-coupled to each other and to the output of the detector tube through resistances 24 and 25 and the coupling condensers 26 and 27. The conventional magnetic headphone set 28, provided for the benefit of the deaf person, is connected directly across the cathodeplate output circuit of the power tube 23, and 85 a condenser 29 is shunted across this circuit to serve as a radio frequency by-pass. For reasons which will later appear, I preferably utilize a speaker unit of the piezo crystal type, indicated diagrammatically at 30, which may be shunted across the output circuit of the tube 23 by means of the switch 31.

The unit functions as a radio receiver in a perfectly normal way. Specifically, the condensers 12, 17 and 20 are mounted in gang on a common shaft for adjustment by means of knob 32 to bring their respective circuits into resonance with the carrier frequency of some desired broadcasting station; and the radio frequency amplifying tubes, the detector, the audio frequency and power amplifying tubes then serve their normal function in amplifying' the signal, eliminating the radio frequency carrier currents, and amplifying the audio frequency components to operate the headphones and speaker. The out- 85 put volume of the receiver may, of course, be regulated in accordance with needs by varying the position of the movable arm of potentiometer 33.

It is a feature of the invention that the circuit includes a loud speaker for the radio receiver which may also serve as a microphone when the unit is to be used as a speech amplifier for raising the intensity of local conversation. In the illustrated embodiment a crystal speaker 30 serves this dual function, it being preferred because of its extremely light weight, low power requirements, etc. In order to convert the above-described broadcast receiver to such a hearingaid amplifier, it is merely necessary to open the radio frequency circuits, to remove the speaker 30 from the output circuit of the power amplifier tube and to place it in the input circuit of the audio frequency amplifier. In the present instance this may readily be accomplished by reversing the position of switch 34 to open the radio frequency circuit, and by similarly reversing the position of switch 31 to remove the speaker from the output of the tube 23 and to place it in the grid-cathode circuit of the detector tube 19. When that has been done the speaking unit, now serving as a crystal microphone, picks up local conversation and impresses an alternating current at audio frequencies across the grid-cathode of the detector tube 19, which then functions as an audio-frequency amplifier. The output of tube 19 is impressed across the gridcathode input circuit of the tube 22 and the output of this latter tube is, in turn, impressed on the grid-cathode of the power amplifier tube 23 and finally the output of the power tube is applied to the operation of the headphone set 28. The output volume of the unit when operating in the just-described manner as a local speech amplifier may be varied to suit the need of the deaf person by operating the volume control potentiometer 33.

A deaf person usually has less difficulty in hearing a telephone conversation than an ordinary one. Even so, however, he finds it highly beneficial to have his incoming telephone conversations amplified, and particularly to have the output volume subject to his control so that he may regulate it in accordance with the voice of the caller, background noise, etc. The present unit may be used for this purpose in a simple way. It is merely necessary to place a loading coil 35 in the vicinity of an ordinary telephone box where it may serve as the secondary of a transformer inductively coupled to the circuit within the box, and to impress the audio frequency currents picked up by this loading coil across the input of the audio amplifier of the unit. Under such circumstances the loading coil replaces the loud speaker-microphone unit 30, and the latter should be removed from the circuit.

This is simply done in the present unit by providing a telephone jack 36 shunted across the grid-ground lines 37 and so constructed that when the plug 38 (connected to the coil) is inserted in the jack the arm 39 breaks contact at 40, opening the connection to the speaker-microphone unit 30 and, with arm 39a, connects the opposite ends of the loading coil 35 directly to the grid-ground circuit of tube 19. The switch 31 may then be returned to its initial position to include the speaker 30 in the output circuit of the power tube 33, although it will usually be desirable to leave this switch 31 in its last described position and to use the entire output of the audio amplifier circuit t6 energize the telephone head-set. Here again the volume may be controlled in a very simple manner by changing the position of the potentiometer.

In all of the foregoing cases, that is, whether the unit be operating as a radio receiver, a local speech amplifier, or a telephone conversation pick-up, the tone of the output may be regulated by an adjustment of the variable resistance 41 which operates in series with the condenser 42 to increase or decrease the bass frequencies with respect to the higher ones. Thus the deaf person may increase the amplification of the frequencies to which he is least sensitive at the expense of others so that, in effect, the entire band of frequencies will be more uniformly amplified for his benefit.

In the actual unit as shown in Fig. 1 the various switches may be operated by conventional knobs appearing at the front side of the casing; and certain of them are combined with others in a more or less conventional way. Thus the switch 43 controlling the A and B battery supply, and the variable tone control resistance 41 are included in a single unit for operation by knob 44; the movable arm of the volume control potentiometer 33 is provided with a knob 45 for its adjustment; the switch 31 for transferring the speaker-microphone unit from the input to the output side of the circuit, is provided with an operating knob 46; and the radio frequency cutout switch 34 may be operated from the front of the unit by means of the knob 47. Finally, the jack appears on the front of the unit to receive the plug of the loading coil when the unit is to be used as a telephone amplifier.

The entire unit, as has heretofore been mentioned, is intended to be of portable nature-sufficiently small and compact to be readily carried by its owner from place to place so as always to be available for his use. It is further desirable that its power supply be entirely independent of outside sources, and to carry out this aim the set is adapted for dry cell operation.

Such being the case it is necessary to keep the size of the batteries down tq a minimum. For this reason each of the various electron tubes is of the filament-cathode type adapted to be heated by current from a 11 volt battery which may be derived from one or more small flashlight cells connected in parallel as indicated at A. As here shown the positive side of the A battery is connected to the filament through the switch 43 and line 48, and all filaments return to the negative side of this battery through the ground. All of the plate circuits are supplied from a 45 volt dry cell battery, indicated at B, which has its negative terminal connected to switch 43 and its positive terminal connected through line 49 to the various plates, and to the screen grids where such are used.

It has been found that the audio circuit shown in Fig. 2 faithfully reproduces impressed audio frequencies, and yields a relatively high gain with impressed plate voltages of a very low order. In this circuit it is specifically to be noted that the tube 19, when adting in the radio receiving set uses grid-leak detection and has no applied negative bias. Similarly, when this tube becomes the first stage of the audio frequency speech amplifier or telephone pick-up amplifier, its grid has a negative potential of only 11/ volts derived from the A battery through the ground connection-no effective grid bias. The output circuit of the detector tube includes a radio frequency choke 50, a radio frequency by-pass 51 and the coupling resistance 24, the latter having a value of approximately 0.1 megohm. The voltage drop across the resistance 24 is applied to the gridcathode circuit of the audio frequency amplifier tube 22 through the coupling condenser 26 and potentiometer 33. In a similar manner the voltage drop across the 0.1 megohm coupling resistance 25 in the plate-cathode output circuit of the tube 22 is impressed through coupling condenser 21 across the grid-cathode circuit of the final power amplifying tube 23. It is particularly to be noted at this point that the lower end of the potentiometer 33, which has a resistance of approx'mately 0.5 megohm, is connected through a second resistance 52 also of 0.5 megohm to the grid of the final power tube. No negative bias other than the foregoing is applied to the grids of tubes S9, 22 and 23.

The audio frequency amplifier circuit of Fig. 2 may be operated satisfactorily with plate voltages of extraordinarily low magnitude. It has been found possible, for example, to pick up a local conversation through the microphone and amplify it to such an extent that a fairly deaf person may hear it through the head-set with an applied plate voltage of only 11 or 12 volts. A plate supply of 22 volts produces sufficient volume for any person other than a totally deaf one, to hear the 80 conversation without difficulty. The illustrated 45 volt plate supply is necessary, in the present instance, only when the unit is operating as a radio receiver.

In the arrangement of Fig. 2 the detector and audio amplifier circuits are provided with single triode tubes. When they are to be used in a portable radio receiver-hearing aid unit, where space and weight are at a premium, I have found it desirable to incorporate these two tubes in a single one, using for this purpose a double triode 52 of more or less conventional construction.

The circuit for this tube is shown in Fig. 3. In effect, it is identical with Fig. 2. Briefly, the grid, plate and portion of the filament to the left of the center of tube 52 serve the function of the corresponding elements of tube 19. and are connected in the circuit in precisely the same way.

The remaining grid, plate and portion of the filament perform the function of tube 22, and are coupled to the output of the first-mentioned set of triode elements of tube 52, and to the input of the power tube 23 in accordance with the teachings of Fig. 2. From that point on the circuits of Figs. 2 and 3 are identical.

In the practical unit of Fig. 1 the headphone set 28 is preferably connected to the output circuit of the audio amplifier (Fig. 2), in a more or less permanent fashion and space may be provided in the'back of the unit for accommodating this receiver when not in use. It is further contemplated that the loading coil 35 may be transported with the unit, if desired, and provision may also be made for its accommodation in the back of the unit.

The hearing aid device herein described has several definite advantages over the batteryoperated carbon microphone devices now in use by deaf persons. The crystal microphone which is here used has no positional response comparable to that of the carbon microphone-it does not produce background noises when physically moved. Moreover, it responds to a wider range of frequencies and reproduces these frequencies with greater fidelity.

Another point of extreme importance to deaf persons is the fact that the output volume of this electronic amplifier may be regulated, as may also, the output tone, to suit the needs of the occasion, something which has never been featured in the carbon microphone hearing aid device. Further, the present device may be used as a telephone conversation amplifier, a feature which has no counterpart in the ordinary hearing-aid instrument. Lastly, it has been found that the current consumption of the present device, when operating solely as a hearing aid is extremely small, much less, in fact, than that of the ordinary carbon microphone hearing aid amplifier.

While I prefer to utilize batteries for the operation of the unit so that it may be self-contained, as hereinbefore described, it is perfectly apparent that the unit can be provided with a conventional rectifier and filter system for operation from an alternating current lighting circuit. In such event, since the audio frequency amplifier is of the resistance-coupled type, the set could be operated either from an A. C. or D. C. lighting circuit in the well known manner.

Since certain changes may be made in the embodiments of the invention without in any way departing from its teaching, it is intended that the foregoing shall be construed in a descriptive rather than in a limiting sense.

What I claim is: 1. A hearing aid device for daaf persons comprising a radio receiver having a tuned radio frequency input circuit, a detector circuit including an electron tube having its input coupled to the output of the tuned radio frequency circuit, an audio frequency amplifying circuit including an electron tube having its input circuit coupled to the output of the detector circuit, a headphone set coupled to the output of the audio frequency amplifier circuit, and a loud speaker also coupled to the output of the audio frequency amplifying circuit; means for uncoupling the tuned radio frequency circuit and the detector; and means for uncoupling the speaker from the output of the audio frequency amplifying circuit, and for coupling it to the input of the audio frequency amplifying circuit, such speaker then serving as a microphone to pick up local conversation for the benefit of the deaf person.

2. A hearing aid device for deaf persons according to claim 1 further characterized by the g0 provision of a loading coil adapted to serve as the secondary of a transformer inductively coupled to an incoming telephone circuit, and means for coupling such coil to the input of the audio frequency amplifying circuit whereby to pick up and amplify incoming telephone conversations for the benefit of the deaf person.

3. A hearing aid device for deaf persons according to claim 1 further characterized in that the last-mentioned means is adapted to couple the speaker unit to the grid-cathode input of the electron tube in the detector circuit so that the tube may then serve as the first stage of the audio frequency amplifier.

4. A hearing aid device for deaf persons according to claim 1 further characterized by the provision of means in the audio frequency amplifying circuit for controlling the output volume.

5. A hearing aid device for deaf persons according to claim 1 further characterized in that the speaker is of the piezo crystal type.

6. A hearing aid for deaf persons comprising a radio receiver having a plurality of tuned radio frequency amplifying circuits each including an electron tube and means coupling its output to the input of a succeeding one, a detector circuit Including a grid leak, a grid condenser and an electron tube, an audio frequency amplifier circuit including a plurality of electron tubes, resistance coupling between the output of the detector circuit and the input of the first audio frequency tube and between the output of the first audio frequency tube and a succeeding one, a headphone set coupled to the output of the audio frequency amplifying circuit, and a piezocrystal loud speaker unit also coupled to the output of the audio frequency amplifying circuit; means for uncoupling the radio frequency circuits from the grid-cathode of the detector tube; and means for uncoupling the crystal speaker from the output of the audio frequency amplifier and for coupling it to the grid-cathode circuit of the detector tube whereby such speaker may then serve as a microphone, and such detector as the first stage of the audio frequency amplifier.

7. A hearing aid for deaf persons according to claim 6 further characterized by the provision of a potentiometer having its movable arm connected to the grid of oneof the audio frequency amplifying tubes, one of its ends connected to the plate side of the resistance coupling between that tube and the preceding one, and the other of its ends connected to the grid of the next succeeding electron tube, such potentiometer serving to control the output volume of the audio frequency amplifier.

8. A hearing aid for deaf persons according to claim 6 further characterized by the provision of a potentiometer having its movable arm connected to the grid of one of the audio frequency amplifying tubes, one of its ends connected to the plate side of the resistance coupling between that tube and the preceding one, and its other end connected in series with a further resistor to the grid of the succeeding electron tube.

9. A hearing aid for deaf persons comprising a radio receiver having a tuned radio frequency electron amplifying circuit; a detector circuit coupled to the output of the radio frequency amplifier including an electron tube having a grid condenser and grid leak in its grid-cathode circuit; an audio frequency amplifying circuit including a plurality of electron tubes, resistancecondenser coupling between the output of said detector and the output of said audio frequency amplifying circuit, and between each pair of tubes in the audio frequency circuit; a potentiometer in the grid circuit of one of the electron tubes in the audio amplifier circuit, such potentiometer having its movable arm connected to the grid of that tube, one of its ends connected to the coupling condenser between that tube and the preceding one, and its other end connected in series with a resistor element and the grid of the next succeeding electron tube; a telephone head-set coupled to the output of the audio frequency amplifier circuit; a piezocrystal loud speaker also coupled to the output of the audio frequency amplifier circuit; means for uncoupling the detector from the radio frequency amplifier circuit; and means for uncoupling the speaker unit from the output of the audio frequency amplifying circuit and for coupling it to the grid-cathode of the electron tube in the detector circuit; said circuits being further characterized in that no biasing voltage is applied to the grid of the electron tubes. 10. A hearing aid for deaf persons according to claim 9 further characterized by the provision of a loading coil adapted to serve as the secondary of a transformer inductively coupled to an incoming telephone·.circuit, and means for coupling such coil to the grid-cathode of the electron tube in the detector circuit whereby it may pick up and amplify an incoming telephone conversation for the benefit of the deaf person.

11. An audio frequency electron amplifier cor- 3D prising a plurality of electron tubes each having input and output circuits; means for coupling the output of one tube with the input of the next comprising a resistance shunted across the platecathode output circuit and a condenser in series with the plate of one tube and the grid of the next; a potentiometer in the input circuit of one tube with its movable arm connected with the grid of that tube, one of its ends with the coupling condenser from the preceding tube, and its other end connected to the grid of the next succeeding tube; such potentiometer serving as the output volume control for the amplifier.

12. An audio frequency electron amplifier according to claim 11 further characterized by the provision of a further resistor in series with said other end of the potentiometer and with the grid of said next succeeding tube; and in that no biasing voltage is applied ot the grids of such tubes.

JAMES J. MOREY.