US2308550A - Amplifying hearing aid - Google Patents

Description

Jan. 19, 1943. H. B. sHAPxRo 2,308,550

AMPLIFYING HEARING AID Filed July 18,1940 3 Sheets-Sheet l I I I ATTORNEY Jan' 19,. 1943 H. B. sHAPlRo 2,308,550

AMPLIFYING HEARING AID Filed July 18, 1940 5 Sheets-Sheet 3 V* $4911 92 549:12 0 @l1 *j 0 l """"'["""""""""""I:"T""" l T i l 97 y @W 97 i l i 62 NE EtTOR BY WWW@ ATTORNEY Pateniecl Jan. 19, 1943 AMPLIFYING HEARING AID Harry B. Shapiro, Astoria, Long Island, N. Y., as-

signor to Sonotone Corporation, Elmsford, N. Y., acorporation of New York Appunti@ July 1s, 1940, semi No. 346,125

' 4 claims. (cl. 179-107) This application lis a continuation-impart of 'my copending application Serial No. 338,586, led June 3, 1940,

This invention relates to amplifying hearing aids, and it has among its objects an electron tube amplitler hearing ald arrangement using a voltage transforming and rectifying vibratory contacter arrangement for transforming a low voltage from a-direct current source, such as a single battery cell, into a relatively high voltage required for operating the electron tube ampliner.

Among the objects of the invention is an improved voltage-transforming and rectifying vihratory contactor arrangement having its elebatteries for energizing the anode circuits of elecu tron tube amplifiers, such as used in hearing aids, which must be kept small enough to be suitable for inconspicuous wear on the body oi the user.

The foregoing and other objects of the invention will be best understood from the following description o`f exempllilcations thereof, reference beixighad totheV accompanying drawings wherem, Y Fig. l ls a perspective view illustrating the elementsoi a wearable electron tube hearing aid fa"voltagetr'ansforming arrangement of thinvention;

v"I"ig. 2' Ais alcircuit diagram illustrating the cooperative'relation'ship of the elements of the hearing aid of Fig. 1;

Pig. 31s a cross-sectional view through a power .supply unit, spuch as shown in Figs. 1 and 2;

Iig. 4 is a transversecross-sectional view along uneHof-risqaz',

Fig. li'is a detailed view along line I--l of i Fig. 6 is a'vertlca'l cross-sectional view through vention:

Fig. lis a cross-sectional v'iew alongiine 1--1 of 6; a Fig. 8 is an explodedview of the vibratory contactor mechanism of Figs. 6 and 7;

" Fig.- 9 is a curve diagramjindicating the rate of rise of the periodic lcurrent impulses in the primary transiormer'winding;

Fig. l0 is a curve diagram indicating the voltage induced by the primary current impulses in the secondarytransformer winding and the effect oi the rectifying' action; and l Figs. 1l, 12 'and 13 are views similar to Figs. 6, 'I and 8 illustrating a modified form .of such vibratory contacter mechanism.

In my copending application Serial No. 294,649, filed September 13, 1939, are described electron tube amplifiers designed for use as a part of a wearable hearing aid, all the elements of which must be'small enough so that they may be worn hidden in operative condition on the body of the user. The general arrangement of one such electron tube amplifier is shown in Figs. 1 and 2.

In a compact ilat casing 20 small enough for inconspicuous wear, for instance, in the vest pocket of the user, is mounted a diaphragm' driven Rochelle salt crystal microphone 2| which' drives a voltage-amplifier electron tube 22, the output of which is amplified by a power ampliiler tube 23 that supplies its output to a hearing aid receiver 24 which is small enough for inconspicu'- ous wear on the head of the user.

In the form shown, the two amplifier tubes are of the pentodetype and they have lamentary cathodes 25 which are energized in parallel through two leads 26, 2l extending from plug terminals 28 in the wall of the casing. 'I'he voltage amplifying stage is coupled to the power amplifier stage by a coupling inductance 3l and is arranged and designed in the way disclosed in my copending application Serial No. 294,649, illed September 13, 1939, so that the voltage amplifier stage shall operate with a gain of more than over the frequency range between 500 and 4000 cycles f suillcient to produce only with one additional bels over the` principal speech frequency range,

and is sumcient to drive a standard bone conduction receiver.

If an electromagnetic receiver 24 having a high impedance winding is used, its winding is connected, in .the way shown, directly in the output `circuit of the power amplifier tube. A response ably connected to the anode lead Il so as to maintain them at their required operating potential. The cathode supply leads 2|, 21 and the anode supply lead J are connected through leads of a multi-conductor cord 33 and contacts of a switch 54 to an electric power supply unit, in the form of a flat compact casing 35, which is small enough foz hidden, inconspicuous wear on the body of the user, and houses a small dry cell battery 38 which supplies the cathode leads 26, 21 and a source of power which supplies direct current of proper voltage and polarity to the anode supply lead Il of the ampliner 2li.

As disclosed in my copending application Serial No. 294,649, filed September 13, 1939, a hearing aid amplifier of the foregoing type will deliver the required output to a standard bone conduction receiver when operating with a very low anode voltage. Most of the commercially sold hearing aid amplifiers of the foregoing type operate with small compact dry cell B batteries supplying an anode voltage of only 24 volts and having a useful operating life of several hundred hours. In less severe cases of deafness, a B battery delivering a voltage of only 12 volts is sufficient.

Instead of employing a dry cell battery pack for supplying the anode circuits of the amplifier, the hearing aid ampliiler of Figs. 1 and 2 uses a voltage transforming and rectifying Vibratory contactor arrangement 3l, small enough for housing in the fiat compact casing 35 of the power unit and operated by a small dry cell Il for supplying direct-current voltage required for energizing the anode circuit of the amplifier.

As shown diagrammatically in Fig. 2, the voltage transforming and rectifying contactor arrangement II is similar in its general arrangement to those used in radios. It comprises a step-up transformer 4i having a center tapped primary transformer winding 42 and a. center tapped secondary transformer winding 4I which is combined with a Vibratory contactor mechanism 45 to periodically send, from the low voltage leads 46, 41 which are connected to the battery cell 39, oppositely directed current impulses through the two halves of the primary transformer winding 42 and to rectify the alternating voltage induced by the primary current impulses in the secondary transformer winding 43 and impress the rectified voltage on two high voltage leads 45, 49 to which the anode supply circuit of the amplifier 20 is connected.

The Vibratory contactor mechanism 45 has a Vibratory spring reed 5I carrying on two reed projections 52, 53 oppositely facing reed contacts 54, 55 cooperating with two sets of contacts 55,

51 'and 58, 59 which are connected to the ends of the primary transformer winding 42 and secondary transformer winding, respectively.

To the free end of the reed 5| is secured a magnetic amature which is driven by an electromagnet 5| having an actuating winding Il connected between the reed 5i and one of the ends of the primary transformer winding 42, so that when the circuit from its operating cell Il is completed by the closure of switch 54. the magnet winding 52 is energized, operating the reed to flex and short circuit at its contacts 5I, 5l the magnet winding 63, thereby releasing the reed to swing in opposite direction, whereupon the magnet 8l is again energized. This sequence of operations is continuously repeated, and the reed 5| is vibrated as long as the switch 34 completes the circuit from the battery cell 39.

The reed contact 54 forms in association with its contacts 55, 51 a set of primary impulse contacts which close and open periodically during each vibrating cycle of the reed, to send oppositely directed intermittent current pulses from cell u through the two halves of the primary transformer winding 42, so as to induce in the secondary transformer winding an alternating voltage. The reed contact 55 forms in association with its periodically closing and opening contacts 50, 59 a set of secondary rectifying oontacts which rectify the alternating voltage induced in the secondary transformer winding 4I and impress it in rectined form on the high voltage leads 4l, 45 and therethrough on the anode circuits of the amplifier.

In order to suppress sparking when the vibratory reed contacts break currents in the associated circuits, each half of the secondary transformer winding 43 is bridged by a condenser 55 with or without a series resistance 55 designed to operate in the way described in U. S. Patent 1,296,269. A fllter formed of series connected iron-core inductances 61 and shunt condensers 68 is interposed in the high voltage output leads 41, 4l to smooth out the rectified current pulsations impressed on the high voltage leads 4l, 45 and to deliver to amplifier terminals of the anode supply lead 3l and the cathode lead 2l a smooth direct-current voltage of the required polarity.

Vibratory contactor voltage transforming and rectifying contactor arrangements of the foregoing type have been used for many years in battery-operated radio sets. In accordance with the invention, the elements of such voltage transforming and rectifying contactor arrangements are designed and arranged to operate so that they may be compressed within an extremely small structure which is efhcient in operation and is able to supply with a relatively small drain from a low voltage source, such as a single dry cell battery of 1.5 volt, a relatively high voltage direct current required for the anode circuits of wearable electron tube amplifiers, such as used in hearing aids.

One form of such transforming and rectifying contactor arrangement exemplifying the invention is shown in detail in Figs. 6 to 8. The electromagnet Il is made in the form of an elongated core member secured, as by threading or riveting, to a mounting plate 1I of magnetic material on which the entire Vibratory contactor mechanism is mounted, and having two pole leg extensions 52 on the two sides of the core pole. The reed 5i `is stamped from a sheet of electrically conducting spring metal and has at its free end two arms 12 to which the armature Il is suitably secured, as by soldering or welding.

On the intermediate freely vibrating portion of the reed 5| extending between the two armature arms 12 are formed two contact-operating reed arm projections 13 which have bent intermediate sections 14 extending perpendiculariy away from the plane of the reed terminating in reversely bent overhanging reed portions extending parallel, but in opposite direction to the armature arms 12 of the reed. On the overhanging end portions 15 of the two contact arms 1I ofthe reed are mounted the oppositely facing Vibratory reed contacts 54, 55, respectively. Although the contacts 54, 55 may be made double` faced, it is easier to mount them slightly offset on overhanging reed arm portions 15, as shown. 'I'he oppositely facing Vreed contacts 54 are arranged to cooperate with the contacts 55, II

Y the driving magnet 6I,

' inch wide.

shownnxedlyfheld'na rthe hounds-forumuitleg:

arms 11, "1l alignedonatixefoppositesidesfof the' contacts during the of the Areed contactsulin .The reed ii-:and the. twosetsfofr-supporting: :sets of-stationary con-j-- tacts are'assembled mali'gnmentwith thereed'r between rfinsulating: spacers 18 and-clamped tov-oneendof themountt.'

arms- 11, ...18A` for "the: two;

and its.A cont-act "arms.- 1l.

i118 plate. I i.-.by'two' bolts 8i.:which:fare insulated? from the metallic-conductingportions of -the 5 I and the. contactrsupportsf1 sleeves $2.: r

-lBy arrangingi.the;.vibratoryffcontactorL nism with a vibratory-re ed:which drives two reedprojections.-lcarry'lngthefvibratory reed contacts in a plane offset, but substantially parallel to the plane of the reed and its armature, it is possible to compress its overall volume into a fraction of the volume heretofore considered necessary for such vibratory contactor mecha.- nism. By making each reed contact arm. 13 with4 an intermediate section 14 extending in the direction of the motion of the reed, substantially perpendicularly to the surface of the reed por tions on which the vibratory forces are exerted by the overhanging reed arm portions 15, which extend parallel to the armature arms 12 of the reed, are forced to follow accurately the motion of the amature and to vibrate in unison with during which the reed contacts are held closed while the inertia or momentum of the armature carries it to the end of its full vibratory amplitude.

By giving the intermediate perpeni'licularly bent portion 13 of the reed contact arm 14 a transverse concavo-convex cross section. in the way shown in Figs. 5 and 6, it is stiffened to resist bending out of the position of perpendicular alignment to the main portion of the reed Si and to its free end portion 15 carrying the vibratory reed contacts.

Figs. 6 and I of the original drawings show in an enlarged 3:1 scale the actual dimensions of a practical contactor mechanism of the invention.

The reed 5| is H of an inch long, its amature portion is and its clamping portion is of an The mounting plate 1l is H of an inch long and of an inch'wide. The entire l Vvibratory contactor mechanism has overall dimensions of about H x x 1,5 of an inch.

The width and the free length of the armature arms 12 of the reed and the height and width of the opening M and depression l5 formed in the reed are so proportioned as to assure that its stiffness, or resiliency, and its vibratory masses are so distributed that it vibrates in a stable operating condition. Operation of such vibrator with a vibrating frequencyl in the range between about 100 and 200 cycles gave good results.

it, except for the intervals bratoryconticts carriedby thereodfcontactarmv- "Flight-."1 s.".- .-7 ."fi' :.'f

#The xgap'" distance .between vthe armature.` .andil the. pole faces off -the' driving magnet structuremayf'beadjusted either by threadediy mountingf the magnet' .pole piece lll-i on the mounting plate 1;I or by interposing thin shims under its-clamped;l

end or by slightly bending the-reed.

In adjusting the gap` spacing,

as the dry eeuu. having me required' driving towardsthe pole faceof the driving magnet as tof cause ittoswing. towards the-pole face and about its periodicl vibratory r motion' 4in the 'way describedhereinahove. l `f'Ihe two setsrof stationary ,yffhave threaded. shanks heldy in threadedf holes ofithe substantially rigid supportingarms 1.1,.1l, so as to make it possible to ladjust them in balanced positions in relation sociated vibratory reed contacts. Threads of a tine pitch are used to facilitate ilne adjustment of the contact positions. As the armature swings from its neutral position to the one or the other end point of its vibratory path, that its vibratory contact comes into good positive contact engagement with the stationary contact towards which it moves, andthat this positive contact engagement is maintained during a large part of its motion in theregion towards the end point of its path and back therefrom until it reaches the position in which it breaks the previously made contact as it approaches its neutral position on its opposite half of its swing from the neutral position. 'I'he overhanging reed arm portions 1i which carry the vibratory reed contacts andthe portion' of the reed arxn which is parallel thereto are proportioned to yserve as buffers which are bent by the momentum of the 'amature until it is gradually stopped and then gradually accelerated in opposite direction by the energy stored in the bentbuifer portions of the contact arm 13 as well asin the flexed armature arm 12 of the reed li The momentum of the armature is thus utilized to maintain. in conjunction with 'the buffer action of the contact arm 13-15, positive contact engagement of its two pairs of vibratory contacts during a large part of each half vibratory cycle.

In addition, the flexing portions of the contact arms 13 with the contacts carried on their overhanging end portions 15 are designed to have a sufliciently higher resonant frequency than that of the vibrating system formed by the armature, and its vibratory reed support, as to assure that they follow the motion of the reed and maintain good chatter-free positive contact with the costationary contacts from the moment the contact is made until it is broken. The ad- Ainstable mounting of the sets of stationary con- The armature 6l) of the vibratory reed forms with the E-shaped poles Ol, '63 of the driving electromagnet an efficient magnetic system including a magnetic gap across which the armature vibrates with a variable gap of the order of 0.030of an inch, requiring only a fraction of the power that would be needed in operation with a variable area magnet system generally used in such arrangements. Operation with a variable length gap is made possible by making the vitacts N, I1 and 5l, B9 makes it easy to secure their proper positioning in relation to the vibratory reed contacts without regard to the critical Aadiustxnent of the armature ina position of vmost efficient operation ata variable gap length from the pole faces of the driving magnet. v This adiustable mounting of the stationary contacts I., l1 and Bl, 59 makes-it to secure eflicient voltage transforming and rectifying action. y

In order to be suitable for use as a direct current supply for the anode circuits of a wearable electron tube amplifier, operating with a gain the driving masl het 0I isfenergizedl from the D. c. sour, auch...

contacts taf-ti and' it is essentialv also easier than decibels above the threshold of normal 10 hearing.

In the voltage transforming and rectifying contactor arrangement of the invention, such eiliciency is secured by so adjusting the stationary vibrator contacts 56, il, 5l, 59 in relation to 15 the vibratory contacts 54, 55 and so designing and correlating the circuit elements interconnected with its output transformer and the elements of the vibratory reed contacter that upon the closure of the primary contacts, a Adirect 2 current which rises substantially linearly with time is sent through its primary transformers,`

winding; that the primary contacts open as soon as the substantially linear rise of the primary current ceases; that the secondary contacts close sufiiciently soon after the closure of the primary contacts to assure that the rectified energy now from the secondary winding of the load circuit shall take place substantially during theentire period the primary contacts are closed; and that the secondary contacts are opened sufficiently soon, at the time, or immediately before the opening of the primary contacts, to substantially prevent back fiow of energy from the filter circuit or the load, toward the secondary transformer winding.

Neglecting the transients, the curves of Fig. 9 show the general form of the successive current impulses which are produced by the adjusted vibratory reed contacts in the two halves of the primary transformer winding, and the full line curves of Fig. 10 show the alternating voltage induced by the primary current pulses in the secondary transformer winding. By adjusting the secondary windings of the rectifier contacts of the vibratory contacter mechanism, substantially full rectification of the alternating current may be secured in the way indicated by the succession of full line and rectified dotted line half waves of the voltage impressed on the high voltage leads 4l, I9. With such eiiicient operation of the voltage transforming and rectifying contactor mechanism, a relatively small filter occupying not more space than the contactor mechanism is able to supply about 15 milliwatts or 55 even more smooth direct current at a voltage of about volts.

In order to secure such operating conditions, the load circuit including the filter must be de signed so that during the period when the primary contacts are closed the inductance and resistance of the load circuit, as are refiected in the primary side of the step-up transformer Il, shall cause the current fiowing into the primary transformer winding to rise substantially 1inearly with time throughout the period during which the primary contacts remain closed, and the contacts must be adjusted to open at the point when the current ceases to rise.

As seen from Figs.o6 to 8, the opening I4 provided in the vibratory reed Il not only serves to give the reed the desired stiffness characteristics, but also provides access to the slotted rear ends of the threaded shanks of the contacts Il to 59 for enabling adjustment of their contact 75 positions. Similarly, the mounting plate 1i has formed therein cutouts 81 through which the slots in the rear ends oi' the shanks of the contacts 56 to 5l may be reached for adjusting their contact positions.

In order to prevent transmission of vibrations from the vibrating mechanism to the exterior, the vibrating mechanism is suspended freely on a leaf spring member 9| extending from a mounting block 92 suitably secured within the top of a sound-proof casing 93. In the form shown, the mounting block $2 is formed of two rectangular members of resilient vibration absorbing material, such as rubber, Neoprene or Vinylite, having embedded therein, as by molding, two anchor heads Il of a pin l5 on which the inner endof the leaf spring 9| is held. This arrangement assures that the vibrating forces exerted by the vibratory mechanism on its yielding supporting block 92 subjects the latter to shear, thus assuring efiicient absorption and suppression of the vibratory forces.

The leaf spring i is held clamped between the insulating spacers 'Il at a position in which the vibratory forces of the vibrating system balance each other so as to reduce to a minimum and render substantially negligible the vibratory forces transmitted to the support 92.

In two sides of the vibration absorbing block shanks of fiat head screws l1 which clamp the edges of the casing 03 to the mounting block l2.

In addition, the interior or the exterior of the casing walls Il are lined with a layer or layers of sound absorbing material, not shown. The unsupported end of the vibrating mechanism with its magnetic driving structure may hang freely supported within the casing 93. In order to assure that the armature cannot be disturbed in the event the freely suspended end of the vibratory mechanism hits against a casing wall, a U-shaped protecting clip III is clamped over the amature end of the mechanism 4B. The clip 5 III has two arms with central inwardly bent latch projections il! fitting and interlockingly engaging the recesses llt formed at the junction of the mounting plate 1I with its legs l2, the center of the clip III being held spaced from the 50 armature by inwardly bent stop members ill engaging the facing surface portions |05 of the mounting plate 1l on both sides of its pole legs I6. If desired, a collar III of highly yieldable material, such as sponge rubber, may be placed around the clip I Il and the rear portion of the mounting plate against which it is held so as to serve as a stop in the event the suspended contactor mechanism 4l is thrown against a wall of the casing.

The contactar leads from the circuit elements of the contacter mechanism may be suitably led through the body of its supporting block l2 and interconnected on the exterior with the transformed winding 4i, the filter choke coil 61, filter condenser 88 and the other elements interconnected with the high voltage leads Il and I9.

As shown in Figs. 6 and 7, the step-up transformer Il, the filter inductances 61, and the other elements of the nlter circuit are mounted on a bracket III of metal, for instance, having bottom legs Il I, H2 which are secured, as by screws III, to bushing inserts III embedded in the resilient vibration absorbing body of the supporting block l2 of the vibrator mechanism Il. The

nass of the vibration absorbing body 92 interposed between the vibrating mechanism housed in the casing I3 and the elements of the filter mechanism carried on the bracket is suf- Iiciently large and so arranged as to prevent propagation of the vibrations tothe elements mounted on the bracket. By using magnetic core inductances of the type described in my copending application Serial No. 294,649, filed September 13, 1939, having a core cross section orl only o! one square inch and having overall core dimensions of about 3/4 x a very eilective iilterlng action will be secured with a filter unit using only two such magnetic core inductances and occupying together with all other elements associated with the voltage transforming, rectifying and iiltering arrangement a space oi only about ll/z x 11/2 x inches.

As shown, the several elements associated with the nlter and the output leads 43, 40 are suitably secured, as by bands IIB, to the upstanding bracket wall I|0. After mounting in place, the elements mounted on the bracket may be enclosed in a shield H0 of magnetic material, formed, for instance. of two parts which are clamped in position by flat head screws |I1 to iianged edge portions of the bracket legs ||2. The leads extending from the flat contactor mechanism into the space above its mounting block 92 may be suitably interconnected with the elements of the filter mounted on the bracket in the way shown in Fig. 2.

As shown in Figs. 3 to 5, the contactor mechanism and the filter assembly may be suitably secured to the underside of a mounting block |20 forming a cover or the fiat compact casing 35 in,

which the entire arrangement is mounted, for instance, by screws I |3 clamping a bracket arm I9 to the cover |20. The leads to the transforming and rectiiying arrangement may be suitably connected, as by soldering, to the inwardly projecting tips of socket members |23 mounted in suitable holes of the cover block |20 for receiver plug pins oi' a plug |24 through which the circuit connections to the ampliiier unit 20 are conipleted.

x yi; of an inch,

The terminal sockets |23 may be of the type described in Figs. 6 to 9 of-my copending application Serial No. 294,649, iiled September 13, 1939, and may be arranged in the form of a separate socket secured to the upper bracket arm ||9, all mounted together with it as a unitin its position on the cover |20. In the form shown, the upper bracket arm I|9 has a hole into which the tips of the socket terminals |23 project fory soldering the leadsi'rom the interconnected elements of the transforming, rectifying and filtering arrangement supported by the bracket H0, before its shield is secured in place thereon. The shield IIC is designed so that it may be formed as an integral unit and slipped down over the vibrator casing 03.

'Ihe two battery cells 30, 39 are likewise arranged to be held on a bracket |3| of metal, for instance, having an upper arm secured, as by screws |32', to the threaded bushing |33 embedded in the cover block |20 of the easing. On the downwardly extending bracket |3| are insulatingly mounted spring contact members |34, |35 arranged so that a standard dry battery cell may be quickly inserted into its operating position or removed therefrom, the contact members being suitably interconnected with the other circuit elements in the way shown in Fig. 2. The batteries may be quickly reached for removal or replacement by providing the casing with a removable end wall section |39 which is held in its position by two catch springs |31 engaging the adjacent wall portion near the bottom of the casing and two snap springs |30 which engage projecting ends of interlocking members |39 embedded in the molded body of the casing cover |20 so that by a pull on the end wall |36, it may be removed to expose the battery cells and by swinging it back on its bottom catch springs |31 its snap spring |38 will lock it back in closed position.

' The switch unit 34 may be of the slider type, and may be mounted on the amplier casing in the way shown in my copending application Se-- rial No. 294,649, tiled September 13, 1939, 0r it may be mounted either on the cover wall |23 of the power unit 35. or. as shown in Figs. 1 and 2, it may be combined with the cord at a point where it can be readily reached by the hand of the user, for instance, by providing it with a clip for holding it in the desired place.

In Figs. 1l, 12 and 13 is shown an alternative form oi' a vibratory contactor mechanism of the invention. Its elements are similar to those shown in Figs. 6 to 8. Its vibratory reed SIA carries its armature 60 on a central arm |'4| which is offset relatively to the portion from which its two vibratory contact arms 52A, 53A extend. Alternatively, its central armature bearing portion I4| maybe formed into contact arms, such as 52A, and its outer two contact arms may be bent to support the armature 60 in the ollset position shown, the intermediate perpendicularly bent tntionsA |42 being stiffened as at 14 in Figs. 6

The contactor mechanism of Figs. l1 to 13 occupies somewhat more space than that oi! Figs. 6 to 8. By mounting the armature on portions of the vibratory reed which are oiIset relatively to the contact arms 52A, 53A of the reed, such vibratory contact mechanism may be compressed into a very small size, only slightly larger than that described in connection with Figs. 6 to 8..

In order to prevent oxidation of the vibratory contacts, the contactor mechanism may be suspended in 'a hermetically closed vessel which is filled with an inert gas, such as nitrogen. Metal vessels, such as those used for metal vacuum tubes, or glass vessels, may be used as such enclosures.

When using a glass for such enclosure, two or three strong supporting wires may be sealed in a glass press andthe innner ends of the supporting wires may be held clamped by the bolts 3| of the vibrating mechanism, so as.to support it in a freely vibrating condition within the gas enclosing vessel.

The leads forcompleting the electrical circuit connections to the elements of the contactor -mechanism are likewise sealed in the press, the inner ends or the leads being provided with loose depth without sacrificing its operating advantages.

The features and principles underlying the invention described above in connection with speciilc exemplifications, will suggest to those skilled in the art many modifications thereof. Itis accordingly desired that the appended claims be construed broadly and that they shall not be limited to the specic details shown and described in connection with the exemplifications thereof.

I claim:

1. In a wearable hearing aid, in combination: a nat amplifier unit having a case small enough for inconspicuous wear on the body of the user; an electron tube amplifier structure all the elements of which are small enough so that they are mounted within said case and include at least one voltage amplifier stage and one power amplifier stage each having a cathode heating element and anode circuit elements; a microphone small enough so that it is mounted within said case while exposed to sound propagated through the air surrounding the case; a set of amplifier terminal elements mounted on a wall portion of said case and circuit interconnections within said case for interconnecting said microphone unit and said terminal elements with the elements of said amplifier structure so as to impress the amplified output of said microphone on certain ampliler terminal elements; some of said amplifier terminal elements constituting cathode supply terminals for supplying heating current to said cathode heating elements and some of said ampliiler terminal elements constituting anode supply terminals for supplying operating energy to said anode circuit elements; a, receiver small enough for inconspicuous wear by the user and cord leads from said certain amplifier terminal elements to said receiver for supplying thereto the amplified output of said microphone; a structurally flat power unit small enough for inconspicuous hidden wear on the body of the user having two compartments and a power supply cord lead unit having cord leads extending from the power unit to the cathode and anode supply terminals of said amplifier unit; a cathode supply cell unit and anode supply cell unit within one compartment of said power supply unit; said cathode supply cell unit being connected through some of said power supply leads to the cathode supply terminals of said amplifier case; a voltage changing arrangement within the other compartment of said power supply unit and connected to said anode supply cell unit; said voltage changing arrangement including a vibratory contactor aggregate and a transformer so designed and correlated and so interconnected between said anode supply cell unit and some of said power supply leads as to cause said contactor to periodically send substantially linearly rising current impulses from said anode supply cell unit through the primary windings of said transformer for inducing a relatively high alternating voltage of substantially rectangular wave shape in the secondary windings of the transformer, and to cause the contactor to rectify the induced alternating voltage and to impress the so rectified voltage on the power supply leads connected to anode supply terminals of said amplifier; and switch means forming part-oi.' one of said units and including a single movable grip member actuable between a position in which the circuit connection to said anode supply cell unit and the circuit connection to said cathode supply cell unit are broken and a position in which both oi said circuit connections are established.

2. In a wearable hearing aid, in combination: a flat amplifier unit having a case small enough for inconspicuous wear on the body of the user: an electron tube amplifier structure all the elements of which are small enough so that they are mounted within said case and include at least one voltage amplier stage and one power amplifier stage each having a cathode heating element and anode circuit elements; a microphone small enough so that it is mounted within said case while exposed to sound propagated through the air surrounding the case; a set of amplifier terminal elements mounted on a wall portion of said case and circuit interconnections within said case for interconnecting said microphone unit and said terminal elements with the elements of said amplifier structure so as to impress the amplified output of said microphone on certain ampliiier terminal elements: some of said amplifier terminal elements constituting cathode supply terminals for supplying heating current to said cathode heating elements and some-of said amplifier terminal elements constituting anode supply terminals for supplying operating energy to said anode circuit elements; a receiver small enough for inconspicuous wear by the user and' cord leads from said certain amplifier terminal elements to said receiver for supplying thereto the amplified output oi' said microphone; a structurally flat power unit small enough for inconspicuous hidden wear on the body of the user having two compartments and a power supply cord lead unit having cord leads extending from the power unit tothe cathode and anode supply terminals of said amplifier unit; a cathode sup ply cell unit and anode supply cell unit within one compartment of said power supply unit; said cathode supply cell unit being connected through some of said power supply leads to the cathode supply terminals of said amplifier case; a voltage changing arrangement within the other compartment of said power supply unit and connected to said anode supply cell unit; said voltage changing arrangement including a vibratory contactor aggregate and a transformer so designed and correlated and so interconnected between said anode supply cell unit and some of said power supply leads as to cause said contactor to periodically send substantially linearly rising current impulses from said anode supply cell unit through the primary windings of said transformer :or inducing a relatively high alternating voltage of substantially rectangular wave shape in the secondary windings of the transformer, and to cause the contactor to rectify the induced alternating voltage and to impress the so rectified voltage on the power supply leads connected to anode supply terminals of said ampliiler; and switch means forming part of said amplifier case and including a single movable grip member actuable between a position in which the circuit connection to said anode supply cell unit and the circuit connection to said cathode supply cell unit are broken and a position in which both of said circuit connections are established.

3. In a wearable hearing aid, in combination: a flat amplifier unit having a case small enough for inconspicuous wear on the body oi' the user; an electron tube amplifier structure all the elements of which are small enough so that they are mounted within said case and include at least one voltage amplifier stage and one power arnplier stage each having a cathode heating element and anode circuit elements; a microphone small enough so that it is mounted within said case while exposed to sound propagated through the air surrounding the case; a. set of amplifier terminal elements mounted on a wall portion of said case and circuit interconnections within said case for interconnecting said microphone unit and said terminal elements with the elements of said amplifier structure so as to impress the amplified output of said microphone on certain amplifier terminal elements; some of said amplifier terminal elements constituting cathode supply terminals for supplying heating current to said cathode heating elements and some of said amplifier terminal elements constituting anode supply terminals for supplying operating energy to said anode circuit elements; a receiver small enough for inconspicuous wear by the user and cord leads from said certain amplifier terminal elements to said receiver for supplying thereto the amplified output of said microphone; a structurally flat power unit small enough for inconspicuous hidden wear on the body of the user having a power supply cord lead unit having cord leads extending from the power unit to the cathode and anode supply terminals of said ampliiier unit; a cathode supply cell unit and anode supply cell unit within said power supply unit; said cathode supply cell unit being connected through some of said power supply leads to the cathode supply terminals of said amplier case; a voltage changing arrangement within said power supply unit and connected to said anode supply cell unit; said voltage changing arrangement including a vibratory contactor aggregate and a transformer so designed and correlated and so interconnected between said anode supply cell unit and some of said power supply leads as to cause said contactor to periodically send substantially linearly rising current impulses from said anode supply cell unit through the primary windings of said transformer for inducing a relatively high alternating voltage of substantially rectangular wave shape in the secondary windings of the transformer, and to cause the contactor to rectify the induced alternating voltage and to impress the so rectined voltage on the power supply leads connected to anode supply terminals of said amplifier; and switch means forming part of one of said units and including a single movable grip member actuable between a position in which the circuit connection to said anode supply cell unit and the circuit connection to said cathode supply cell unit are broken and a position in which both of said circuit connections are established.

4. In a wearable hearing aid, in combination: a flat amplifier unit having a case small enough for inconspicuous -wear on the body of the user; an electron tube amplifier structure all the elements of which are small enough so that they are mounted within said case and include at least one voltage amplifier stage and one power amplifier stage each having a cathode heating element and anode circuit elements; a microphone small enough so that it is mounted within said case while exposed to sound propagated through the air surrounding the case; a set of amplifier terminal elements mount-ed on a wall portion of said case and circuit interconnections within said case for interconnecting said microphone unit and said terminal elements with the elements of said amplifier structure so as to impress the amplified output of said microphone on certain amplifier terminal elements; some of said amplier terminal elements constituting cathode supply terminals for supplying heating current to said cathode heating elements and some of said amplifier terminal elements constituting anode supply terminals for supplying operating energy to said anode circuit elements; a receiver small enough for inconspicuous wear by the user and cord leads from said certain amplifier terminal elements to said receiver for supplying thereto the amplified output of said microphone;

a structurally at power unit small enough for inconspicuous hidden wear on the body of the user having a power supply cordr lead unit having cord leads extending from the powerunit to the cathode and anode supply terminals of said amplifler unit; a cathode supply cell unit and anode supply cell unit within said power supply unit; said cathode supply cell unit being connected through some of said power supply leads to the cathode supply terminals of said amplifier case; a voltage changing arrangement within said power supply unit and connected to said anode supply cell unit; said voltage changing arrangement including a vibratory contactor aggregate and a transformer so designed and correlated and so interconnected between said anode supply cell unit and some of said power supply leads as to cause said contactor to periodically send substantially linearly rising current impulses from said anode supply cell unit through the primary windings of said ,transformer for inducing a relatively high alternating voltage of substantially rectangular wave shape in the secondary windings of the transformer. and to cause the contactor to rectify the induced alternating voltage and to impress the so rectified voltage on the power supply leads connected to anode supply terminals of said amplier; and switch means forming part of said amplier case and including a single movable grip member actuable between a position in which the circuit connection to said anode supply cell unit and the circuit connection to said cathode supply cell unit are broken and a position in which both of said circuit connections are established. v

' HARRY B. SHAPIRO.

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