US2327321A - Hearing aid amplifier - Google Patents

Description

Aug. 17, 1943. H. B. SHAPIRO 2,327,321

HEARING AID AMPLIFIER I Filed Nov. 12, 1941 4 Sheets-Sheet 1 INVENTOR HARRY B. SHAPrRo ATTORNEYS Aug. 17, 1943. H. B. SHAPIRO 2,327,321

I HEARING AID AMPLIFIER,

Filed Nov. 12, 1941 4 Sheets-Sheet 3 p \I 8g ,"77 H8 wil INVE

HARRY B, SHAPJRO ATTORN EYS Aug. 17, 1943. H. B. sHAPlRo HEARING AID AMPLIFIER Filed Nov. 12, 1941 4 Sheets-Sheet 4 M Y R H E 0 5 f N m 8 w w i V1 2. m R .HVUMV A Patented Aug. 17, 1943 UNITED STATES PATENT OFFICE 2,327,321 I HEARING AID AMPLIFIER Harry B. Shapiro, Willoughby, Ohio, assignor to Sonotone Corporation, Elmsford, N. Y., a corporation of New York Application November '12, 1941, Serial No. 418,858

9 Claims. (Cl. 179-107) This invention relates to hearing aid amplitiers, and particularly to electron tube hearing aid amplifiers.

Among the objects of the invention are arragements and methods for mounting and assembling the structural elements of a compact electron tube hearing aid amplifier that must be small and light enough-for inconspicuous and comiortable wear on, the body of the user and must house all the elements of the amplifier so that they are readily accessible for replacement or for reconditioning, while assuring that when in use, the amplifier operates in a foolproof manncr.

The foregoing and other objects of the invention will be best understood from thefollowing description of 'exemplifications thereof, reference being had to the accompanying drawings wherein Fig. 1 is a circuit diagram of an electron amplifier-hearing aid in connection with which one exemplification of the invention will be described;

Fig. 2 is a' view of the amplifier unit of the hearing aid with the front casing and the microphone removed illustrating the various structurai elements of the amplifier unit mounted in their positions on the rear wall of the casing together with their interconnections, representing one exemplification of the invention;

Fig. 3 is a vertical sectional view through the amplifier casing illustrating the mounting of the principal structural elements of the amplifier;

Fig. 4 is a view similar to Fig. 2 omitting, for

diagrammatically in Fig. 1, Figs. 2 to 11 illustrating the novel mounting and assembly arrangement of the elements of such amplifier exemplifying one form of the invention, features of which are disclosed in the copending application of Harry B. Shapiro, Serial No. 418,857,

filed Nov. 12, 1941, as a continuation-in-part of his application Serial No. 294,649, filed September 13, 1939.

As shown in Figs. 1 to 5, the electronic amplifier hearing aid has a high-impedance microphone which drives a voltage amplifier stage microphone with all the elements of the amplifier are housed in a flat small compact casing 26 and the receiver is connected to the amplifier unit through a detachable flexible cord 2 013- crating energy for the amplifier is shown supplied from a, compact electrical battery cell assembly 28 which is connected to the circuits of a tube through a detachable flexible multi-lead cord 29.

I Pentodes are shown used as the voltage amplifier tube 29 and the power amplifier tube 23, each comprising a filamentary cathode having two terminal leads 3t, 32, an anode having a terminal lead 33, a control grid having a terminal lead 34!, a screen grid having a terminal lead 35. The transformer 2 5 has a primary the sake of better showing; the interconnections 35 windin 36. a secondary winding 3'! through between the structural elements or" the amplifier;

Fig. 5 is a horizontal sectional view along line 5-5 of Fig. 4;

Fig. 6 is an elevational view of one element .of the sub-assembly of the amplifier shown in Fig. 2;

Fig. 7 is a side view of the sub-assembly shown in Fig. 6;

Fig. 8 is an elevational view of another subassembly of the amplifier shown in Fig. 2;

Fig. 9 is a side view of the sub-assembly of Fig. 7;

Fig. 10 is an elevational view of another subassembly of the amplifier shown in Fig. 2; and

Fig. 11 is a side elevational view of the subassembly of Fig. 10. v

The principles underlying the invention will be explained by their application to one form of an electronic amplifier hearing aid shown which the output is impressed on the receiver 25, an additional secondary winding 38 connected to an automatic limiting circuit referred to later.

The battery assembly 28 which supplies the operating energy to the amplifier has a plate supply battery ll, grid bias cells t2 and a cathode heating cell it which is interconnected to the battery assembly through a flexible cord M. The battery assembly has a set of socket terminals, through which the leads +13, A, +A, -C of the battery cord 29 are detachably interconnected with the proper battery cells.

The cathode leads 3t, 32 of the two amplifier tubes 2!, 23 are connected in parallel to leads d5, 56 which are connected through cathode supply leads ll, 53 to the battery cord leads +A, A from the cathode heating cell t3, the cathode lead it being indicated as the ground. A switch Ed in the supply lead d'l serves to close or open the cathode heating circuit.

The grid leak resistance of the voltage amplification tube M is formed by a resistance ele ment 5!] connected in series with two additional resistance elements 52 between the grounded cathode lead 55 and the control grid lead 86 of tube 20. The plate or anode lead of tube M is connected through the coupling inductance winding 22 to the plate supply lead 55 from the battery cord lead +B. The lead a l extending from the positive supply lead 55 impresses through a resistor element 56 the required positive potential on screen grid lead 35 of tube 20, a by-pass condenser 5i shunting the resistor element 56.

The output of the voltage amplification stage is impressed through a blocking condenser 58 and a lead 59 on the input circuit to the power amplification stage of tube 23 which is formed of a rheostat unit 6t having an adustable tap with a lead 6! connected to the control grid 34! of the power tube 23, the resistance of the rheostat element 66! forming with a series connected resistor element 62 a grid leak resistance connected through a grid bias supply lead 53 to the battery cord supply lead C.

The plate supplylead 33 and the screen grid lead 35 of' the power tube 23 are connected to the positive plate supply lead 55 through the transformer winding 2% and through the serially connected leads 6%, 55%, respectively. There is also shown provided a-multi-position switch unit 55 having a movable contact member (it which connects in one position a condenser fill in parallel to the primary winding 38 of the output transformer for boosting the response in a selected part of the lower frequency range. In the other position, the sliding contact 66 of switch 65 connects a resistance 68 parallel to the microphone 2@ for cutting off a selected part of the low frequency response.

The amplifier is further shown provided with an automatic peak cutoff circuit provided with four copper oxide rectifier elements arranged to form a rectifier bridge 539 having two diametrically opposite terminals connected to the secondary transformer winding 38, the other two diagonally opposite terminals of the rectifier bridge t9 being connected through leads ill, "ii to impress a rectified component of the output voltage derived from the output transformer 26 on the control grid fill of the voltage amplification stage. The two resistance elements 52 connected in series, and the two condenser elements 72 connected in shunt with the leads from the rectifier bridge M to the grid input circuit t8l serve to filter and smooth out the rectified voltage.

The novel operating features and the various advantages or the amplifier arrangement described above are fully explained in the copending application of Harry B. Shapiro, Serial No. 418,857, filed Nov. 12, 1941, as a continuation-inpart of the application Serial No. 294,649, filed September 13, 1939, and are claimed therein.

Most of the hard of hearing or deafened persons are very sensitive and seek to conceal their hearing impairment. Accordingly, to be practically useful, a hearing aid must b light, small and compact so that it may be worn comfortably and inconspicuously on the body of the user. In addition, it must be simple and foolproof in operation, and it should require little attention and a minimum of parts that may get out of order or require replacement so as to free the aeansai user from mental and physical strain as well as annoyances to which he isv subjected when the instrument has to be repaired or checked up.

To meet the foregoing requirements, it is important that the electron tube hearing aid amplifler unit, to which the present invention is directed, be not only compact and small, but that all the elements of the amplifier unit shall be readily accessible for repair or exchange and reconditioning without loss of time and without introducing complications when one or another circuit element of the amplifier unit has to be removed or replaced.

In an effort to meet the foregoing requirements, prior hearing aid amplifier units had the principal circuit elements of the amplifier mounted on a mounting plate which was placed in the fiat compact casing of th amplifier unit and was readily removable therefrom so as to enable checking or replacement of a defective element. Such mounting plate had, of course, to have a certain rigidity, and in order to keep the circuit elements held inposition by the mounting plate insulated from each other, the mounting plate had to beof resistance material, thus taking up a part of the space in the interior of the amplifier and making .it necessary to use a larger amplifier casing than would be otherwise required.

According to the principles of the present invention, the structural elements of the amplifier are arranged in the form of sub-assemblies built around the relatively rigid structural elements of the amplifier so that each sub-assembly is selfsupporting in its required relationship. This arrangement eliminates the need for a bulky mounting plate and makes possible a very effective reduction in the overall bulk of the amplifier while assuring ready replacement or dismantling of the amplifier elements without disturbing their general relationship.

The principles underlying the invention will now be explained in connection with a hearing aid amplifier unit exemplifying one form of the in- Vention.

Referring to Figs. 2 to 5, all the elements of the amplifier unit are housed in a small flat compact casing, indicated in Fig. 1 by the dash lines 25, only about 4 2: 2 x of an inch in volume, the casing being formed of a front wall or cover l3 and a rear wall it molded of synthetic resin in sulating material, the two casing halves being held clamped together by screw 15. The rear wall i l of the amplifier unit is designed so as to form the mounting wall which supports all the elements of the amplifier unit in their operative position so that upon removing the cover 33; they are available not only for ready inspection, but also for read replacement. This eliminates the necessity for mounting the structural elements which have to be connected into the amplifier circuit on a mounting plate extending through the entire length of the casing space.

As shown in Figs. 3 to 5, the rear wall is reinforced by a flange 16 extending along its edges so as to form a rigid structure and its central lower portion is provided with inwardly project ing short-post extensions 1'! shaped so as to retam in position the core 18 of the coupling inductance 22 and transformer 24 of the amplifier, the two core structures with the windings mounted thereon being held in position by a clamping plate l9 and a screw 19" engaging an internally threaded bushing molded and embedded in the central post H. The shoulder portion of the wail.

mounting wall extending along the lower edge thereoi? is provided with holes in which are mounted four terminal bushings, marked +B, --A, +A, --C, arranged for detachable engagement with the cord plugs of the battery cord 20 and two bushings R, R for establishing detachable engagement with the leads of the receiver cord M. The bushing and plug connectors, shown, are of the type described in the pending application of Carlisle et a1, Serial No.- 346,112, filed July 18, 1940.

A narrow insulating strip 80, or fibrous insulating synthetic resin material, for instance, pro- ,Iects inwardly from the rear wall 14 in the middle region thereof and has mounted thereon two sets oiterminal lug strips BI, 82, -83, 84, 85 of sheet metal. Each terminal lug strip is firmly anchored in the insulating strip 80, for instance, by twisting the downwardly extending ear portion 88 thereof relatively to the forked portion 81 extendingv upwardly on the upper side of the insulating strip 80. The electrode leads or the voltage amplifier tube 2i are secured, as by soldering, to the upwardlyproiecting forked ends 81 of the set of terminal lugs at to 85 on the left her 9, 1939, and is provided with a circular 8 wall, a portion or which is exposed through the slit in the flange wall or the casing enabling the user to adjust the rheostat and the volume by a slight turn of the circular grip member. nose 60-4 01 the rheostat is arranged to cooperate with portions or the switch blade 48 so as to abruptly actuate it to the closed position when the rheostat is moved initially from its low volume position and to abruptly snap the switch blade 49 to its open position shown in Fig. 4

when the rheostat. grip disc is returned to its members 66 are formed by pins embedded in a end of the terminal strip, and the leads of the power tube 23 are connected to the forked ends oi the other set of terminal strips hi to t5, the control grid lead 33 of the voltage amplifier tube it being free so as to-assure that it remains highly insulated.

The strip M is detachably held in its position on the mounting wall by an angular bracket at having its inner end clamped by a screw tE-i to a bushing 39 embedded in a reinforced portion of the mounting Wall l i. As shown in Figs. 3 and 4, two additional similar brackets til are secured to similar peripherally displaced bushings em bedded in the mounting wall id, each of the brackets being provided with a centrally projecting pin ill holding. in position the microphone unit it so that its diaphragm it faces the portion of. the cover wall provided with the openings it through which sound waves reach. the diaphragm. The microphone shown .ls so held within the casing as to prevent propagation of.

sound from the space between the microphone diaphragm and the facing acoustically pervlous wall portion it to the space of the casing enclosure extending behind the microphone, in the manner explained in my copending application Serial No. 394,527, filed May 21, 15241 as a continuation-impart of my application Serial No. 350,595, filed August 3, 1%0. in the region of an opening slit provided in the upper portion of the flange it of the mounting wall is located the heostat unit 6t forming a flat structure having a bottom wall provided with a. mounting strip 9! secured by two screws ill to bushings, such as the bushings 6E! embedded in the mounting The mounting strip 9! serves also as a unitary support for a plvotally mounted blade of the switch unit as provided with two switch terminals til-l, lit-2 which, together with the switch blade Kit, are insulatingly held on the mounting strip st. The rheostat unit til is provided with three terminals tfl-l, til-2, bd-ii through which it is interconnected to the other elements of the amplifier circuit in the way shown in Fig. 1.

The combination rheostat and switch unit shown is of the type disclosed in-the copencling application of Harry B. Shapiro, Serial No. 4l8,- 856, filed Nov. 12, 1941, as a continuation-in-part of his application Serial No. 303,563, filed Novemcircular disc 56-0, secured, as by riveting, to the end of a pin BB-I provided at the other end with a head 65-8 having a slit 58-2, so that the contact carrying disc 66-!) may be rotated on the base plate 65-0. Each pair of stationary contact strips 65-2, 65-3 has rearwardly projecting overlapping portions extending on opposite sides of the rotary disc til-ll which carries the transversely extending metallic switch pins t6 arranged so that by selectively rotating the disc 66-0 to different positions, a switch pin 56 establishes connections between one of the pairs of contacts 155-2, tit-ii or keeps both pairs of contacts open.

Fig. 2 shows how the various elements of the amplifier are interconnected bythe various conhector leads into the amplifier circuit shown diagrammatically in Fig. 1, corresponding leads and parts in Figs. 1 to 11 being indicated by the same reference numerals.

Figs. 10 and 11 show the sub-assembly formed of the terminal strip with its two sets of terminal strips 88 to and the various other elemerits-including the tubes 2!, 23 and all resistor and condenser elements with their leadsmechanically interconnected and joined by their wire leads into a self-supporting structure which may be detachably secured and removed from its position against the inward face of the mounting wall E3 of the casing. The sub-assembly is held in its position by clamping its central mounting bracket 88 to the central bushing as of the mounting wall with a screw td-l, as shown in Fig. 3.

The connecting leads through which the dif- J ferent resistor elements, condenser elements and terminal members of the contact strip db are joined, are made from insulated and non-insulated wire elements, which are chosen to be sllfficiently stiff so that all the elements retain their proper relationship with regard to the relatively rigid mounting strip to, thereby permitting easy mounting and removal of the sub-assembly from its position on the mounting wall id of the easing, without disturbing the elements of the subassembly.

All the principal resistor and condenser elements required for completing the amplifier circuit of the type indicated in Fig. 1 may be thus joined and assembled into a sub-assembly having as its principal junction member the narrow rel- The casing confining the narrow space of the ampliher unit. However, some of the resistor and condenser elements may be joined to the other relatively rigid structural elements which form a part of the amplifier circuit, such as the resistor unit to, the switch unit 569 or the switch unit 85.

Thus, as shown in Figs. 6 and 7, the rheostat unit til which forms in conjunction with the switch at a substantially self-supporting unitary structure may have secured thereto the wire leads ll, 59, til-i, as well as the resistor element the wiring elements and the connector elements of the resistor unit 62 being sumciently stifl so that once shaped they will maintain their relation shown, enabling the completion of the sub-assembly and mounting the sub-assembly as a unit in its position on the casing wall by fastening the mounting plate at of the rheostat unit by screws 92 to the wall iii in the way shown in Fig. i and explained above. In a similar mannor, the tone control switch unit 65 may have connected thereto the condenser and resistor elee ments 6?, to together with any other associated elements into a unitary self-supporting sub-assembly, with interconnecting wiring portions sufficiently stiff so as to maintain all the elements of the sub-assembly in their proper relationship after they have been once joined in the sub-assembly, permitting mounting of the sub-assembly in its position on the wall by fastening it with a screw t5l, in the way shown in Fig. 4 and explained above.

In making the sub-assemblies it is convenient to use colored leads so as to facilitate the interconnection of the elements of the sub-assembly. The following procedure may be adopted in malilng the sub-assembly shown in Figs. 10 and 11: The various leads shown in Fig. 10, eigcept leads d5, 45l, ill, after having been first cut to the required length and bent, are soldered to the terminal strips ill to 85 of the mounting strip til. Thereupon, the wire leads 65-4, M are soldered to the upwardly facing ears of the two contact strips 83, and the transverse interconnecting wire 65 is then soldered to the two wires Alb-4, ii, the several wires having been cut and bent to their required shape before soldering. The various condensers and resistors have their terminal leads then trimmed to size and soldered in their proper positions, whereupon the wire elements forming their interconnections are soldered in place after having first been cut and bent to shape.

In a similar manner, the sub-assembly of Figs. 6 and 7 and'the sub-assembly of Figs. 8 and'9 are separately made. In order to shield the amplifier elements, the main area of the inwardly facing surface of the mounting wall is coated with a layer lid-4 of conducting material, for instance, by spraying, and a sheet of insulating material "Hi-2 is placed thereover so as to assure that no short occurs between elements of the amplifier circuits and the shielding layer i l-i.

Alternatively, a sheet of insulating material Id-2 cut to shape so agto fit against the inwardly facing surface of the mounting wall M has cemented to the side facing the wall a foil |4l of a suitable metallic conducting material, such shielding arrangement having been found highly satisfactory in practical use. In a similar manner, the metallic shielding layer IS-l enclosed by an inwardly facing layer of insulating material 73-4 is interposed between the inwardly facing surface of the cover it of the casing and the elements of the amplifier enclosed thereby. I

The following procedure is followed in mounting the sub-assemblies in their positions on the mounting rear wall it of the casing: shield foil Ed-Ii with its overlying foil 'i -i2 are cemented in position and the lead 68 is soldered in position to the terminal bushing C, the lead 63 having been first cut and bent to shape. Thereupon, the sub-assembly shown in Figs. 10 and 11 is fastened by its bracket 86 in position, the ground interconnecting lead of the cathodes being connected by soldering to a foil strip Ti t-l extending from the metallic foil shield extending over the inner face of the rear casing wall '14. The combined rheostat lid and switch unit 69 is then amxed in position and the ends of its leads All, 59, 511 are connected to the points of inWrconnection in'the manner shown in Fig. 2, lead 42 of the terminal strip sub-assembly being joined by soldering to the terminal tip Git-2 of the switch unit. The tone control switch unit 65 is then mounted in position on the casing wall 14 whereupon the terminal ends of the resistor element at and condenser Gil are soldered to the leads tilt-i and all-d of the previously aifixed sub-assembly held together by the terminal strip 88.

Since the operating features of the amplifier are fully disclosed in the copending application of Harry B. Shapiro, Serial No. 418,857, referred to above, no further explanation is required and it is desired that the disclosure of the aforesaid Shapiro application be considered as a part hereof.

By providing the terminal strip with an additional set of terminal strips 851 to located between the two sets of terminal strips shown in Figs. 2 and 4, a third tube and additional elements for completing a three-tube hearing aid amplifier circuit, for instance, of the type described in connection with Fig. 22 of the aforesaid Shapiro application Serial. No. 418,857, may be housed, mounted and arranged in accordance with the principles of the present invention in a housing of the same character as that required for housing the amplifier described above in connection with Fig. 1.

Various other modifications of the invention will suggest themselves to those skilled in the arts It is accordingly desired that in construing the breadth of the appended claims they shall not be limited to the specific details shown and described in connection with the exemplifications thereof.

I claim:

1. In an electron tube amplifier member forming part of an inconspicuous wearable hearing aid and designed to be energized from a directcurrent energy source for supplying amplified output of a microphone to a receiver: a fiat casing small enough for substantially hidden wear on the body of a user and having two walls detachably joined along-their edges so as to form a casing enclosure confining a relatively shallow interior space having narrow sides; one of said walls having an inwardly facing mounting surface, and reinforcing elements forming part of said wall and rendering it substantially rigid; a substantially firm mounting member extending along said mounting surface between opposite narrow sides of said enclosure and dividing the enclosure into two enclosure sections; a plurality of metallic terminal members insulatingly secured to and held in position by said mounting member so as to expose terminal portions of said terminal members to said interior space; interconnected elements of an amplifier housed in said casing including at least two multi-electrode amplifier tubes; each tube having a plurality of electrode leads extending from the tube and joined to exposed terminal portions of said mounting member so that said tubes are held thereby in predetermined positions in one of said enclosure sections; a plurality of external connector elements insulatingly secured to a wall portion of said enclosure for completing the operative circuit interconnections from said amplifier to external hearing-aid circuit portions and having inwardly facing exposed terminal portions; a predetermined set of circuit elements of said amplifier being interconnected to the terminal members secured to said mounting member so as to constitute with said tubes an interconnected structural unit forming part of at least two amplii'ler stages one of which constitutes an input stage and the other of which constitutes an output stage; said set of circuit elements including at least two self-supporting impedance elements each having at least one terminal wire interconnected to terminal portions of said mounting member so as to be held thereby in predetermined positions in the other of said space sections; said structural unit forming said mount ing member, said tubes and said set of circuit elements constituting a self-supporting unitary structure, the interconnecting circuit portions of which are sufiiciently stiff and so arranged that the relationship of its elements is not disturbed when it is mounted on or removed from its position on said mounting surface,

2. In an electron tube amplifier member form ing part of an inconspicuous wearable hearing aid and designed to be energized from a directcurrent energy source for supplying amplified output of a microphone to a receiver: a frat casing small enough for substantially hidden wear on the body of a user and having two walls detachably joined along their edges so as to form a casing enclosure confining a relatively shallow interior space having narrow sides; one of said walls having an inwardly facing mounting sur-= face, and reinforcing elements forming part of said wall and rendering it substantially rigid; a substantially firm mounting member extend ing along said mounting surface between oppo site narrow sides of said enclosure and dividing the enclosure into two enclosure sections; a plu rality of metallic terminal members insulatingly secured to and held in positionby said mount ing member so as to expose terminal portions of said terminal members to said interior space; interconnected elements of an amplifier housed in said casing including at least two multi-eleotrode amplifier tubes; each tube having a'plu rality of electrode leads extending from the tube and joined to exposed terminal portions of said mounting member so that said tubes are held thereby in predetermined positions in one enclosure section; a casing wall portion bordering the other enclosure section being acoustically pervious; a plurality of external connector elements insulatingly secured to a wall portion of said enclosure for completing the operative circuit interconnections from said amplifier to external hearing-aid circuit portions and having inwardly facing exposed terminal portions; a predetermined set of circuit elements of said amplifier being interconnected to the terminal members secured to said mounting member so stage and the other of which constitutes an output stage; said set of circuit elements including at least two self-supporting impedance elements each having at least one terminal wire intercom nected to terminal portions of said mounting member so as to be held thereby in predetermined positions in said other space section; said structural unit formed of said mounting member, said tubes and said set of circuit elements constituting a self-supporting unitary structure, the interconnecting circuit portions of which are sumclently stiff and so arranged that the relationship of its elements is not disturbed when it is mounted on or removed from its position on said mounting surface; and a high-impedance microphone in said other enclosure section having a diaphragm exposed to the acoustically per= vious wall portion and being connected to the input stage of said amplifier.

3. In an electron tube amplifier member forming part of an inconspicuous wearable hearing aid and designed to be energized from a direct-current energy source for supplying amplified output of a microphone to a receiver: a fiat casing small enough for substantially hidden wear on the body of a user and having two walls detachably joined along their edges so as to form a casing enclosure confining a relatively shallow interior space having narrow sides; one of said walls hav ing an inwardly facing mounting surface, and reinforcing elements forming part of said wall and rendering it substantially rigid; a substantially firm mounting member extending along said mounting surface between opposite narrow sides of said enclosure and dividing the enclosure into two enclosure sections; a plurality of metallic terminal members insulatingly secured to and held in position by said mounting member so as to expose terminal portions of said terminal members to said interior space; interconnected elements of an amplifier housed in said casing including at least two multi-elcctrode amplifier tubes; each tube having a plurality of electrode leads extending from the tube and joined to exposed terminal portions of said mounting member so that said tubes are held thereby in predetermined positions in one enclosure section; a plurality of external connector elements insulatingly secured to a Wall'portion of said enclosure for completing the operative circuit interconnect-ions from said amplifier to external hearing-aid circuit portions and having inwardly facing exposed terminal portions; a predetermined set of circuit elements of said amplifier being interconnected to th terminal members secured to said mounting member so as to constitute with said tubes an interconnected structural unit forming part of at least two amplifier stages one of which con stitutes an input stage and the other of which constitutes an output stage connected to said external connector elements; said set of circuit elements including at least two self-supporting impedance elements each having at least one terminal wire interconnected to terminal portions of said mounting member so as to be held thereby in predetermined positions in the other enclosure section; said structural unit formed of said mounting member, said tubes and said set of circuit elements constituting a self-supporting unitary structure, the interconnecting circuit portions of which are sufficiently stiff and so arranged that the relationship of its elements is not disturbed when it is mounted on or removed from its position on said mounting surface; a casing wall portion bordering the other enclosure section being acoustically pervious; the impedance elements of said one unitary structure extending within said other enclosure section in the space between said microphone and said mounting surface.

4. In an electron tube amplifier member forming part of an inconspicuous wearable hearing aid and designed to be energized from a direct-current energy source for supply amplified output of a'microphone to a receiver: a flat casing small enough for substantially hidden wear on the body of a user and having two walls detachably joined along their edges so as to form a casing enclosure confining a relatively shallow interior space having narrow sides; one of said walls having arr-inwardly facing mounting surface, and reinforcing elements forming part of said wall and rendering it substantially rigid; a substantially firm mounting member extending along said mounting surface between opposite narrow sides of said enclosure and dividing the enclosure into two enclosure sections; a plurality of metallic terminal members insulatingly secured to and held in position by said mounting member so as to expos terminal portions of said terminal members to said interior space; interconnected elements of an amplifier housed in said casing including at least two multi-electrode amplifier tubes; each tube having a plurality of electrode leads extending from the tube and joined to exposed terminal portions of said mounting member so that said tubes are held thereby in predetermined positions in one of said enclosure sections; a plurality of external connector elements insulatingly secured to a wall portion of said enclosure for completing the operative circuit in-' terconnections from said amplifier to external hearing-aid circuit portions and having inwardly facing exposed terminal portions; a predetermined set of circuit elements of said amplifier being interconnected to the terminal members secured to said mounting member so as to constitute with said tubes an interconnected structural unit forming part of at least two amplifier stages one of which constitutes an input stage and the other of which constitutes an output stage; said set of circuit elements including at least two self-supporting impedance elements each having at least on terminal wire interconnected to terminal portions of said mounting member so as to be held thereby in predetermined positions in the other of said space sections; said structural unit forming said mounting member, said tubes and 'said set of circuit elements c'onstituting a self-supporting unitary structure, the interconnecting circuit portions of which are sufficiently stiff and so arranged that the relationship of its elements is not disturbed when it is mounted on or removed from its position on said mounting surface; said amplifier including at least one additional self-supporting circuit control element and at least one additional self-supporting impedance element having a terminal wire connected to said control element and constituting therewith an additional self-supporting unitary structure, the interconnecting circuit portions of which are sufficiently stiff and so arranged that the relationship of its elements is not disturbed when it is mounted on or removed from its position on said mounting surface.

5. In an electron tube amplifier member forming part of an inconspicuous wearable hearing aid and designed to be energized from a direct-current energy source for supplying amplified output of a microphone to a receiver: a fiat casing small enough for substantially hidden wear on the body of a user and having two walls detachably Joined along their edges so as to form a casing enclosure confining a relatively shallow interior space having narrow sides; one of said Walls having an inwardly facing mounting surface, and reinforcing elements, forming part oi said well and rendering it substantially rigid; a substantially firm mounting member extending along said mounting surface between opposite narrow sides of said enclosure and dividing the enclosure into two enclosure sections; a plurality of metallic terminal members insulating secured to and held in position by said mounting member so as to ex-' pose terminal portions of said terminal members to said interior space; interconnected elements of an amplifier housed in said casing including at least two multi-electrode amplifier tubes; each tube having a plurality of electrode leads extending from the tube and joined to exposed terminal portions of said mounting member so that said tubes are held thereby in predetermined positions in one enclosure section; a casing wall portion bordering the other enclosure section being acoustically pervious; a plurality of external connectar elements insulatingly secured to a wall portion of said enclosure for completing the operative circuit interconnections from said amplifier to external hearing-aid circuit portions and having inwardly facing exposed terminal portions; a

predetermined set of circuit elements of said amplifier being interconnected to the terminal mem-- bers secured to said mounting member so as to constitute with said tubes an interconnected structural unit forming part of at least two amplifier stages one of which constitutes an input stage and the other of which constitutes an output stage; said set of circuit elements including at least two self-supporting impedance elements each having at least one terminal wire interconnected to terminal portions of said mounting member so as to be held thereby in predetermined positions in said other space section; said structural unit formed of said mounting member, said tubes and said set of circuit elements constituting a self-supporting unitary structure, the interconnecting circuit portions of which are sufficiently stiff and so arranged that the relationship of its elements is not disturbed when it is mounted on or removed from its position on said mounting surface; and a high-impedance microphone in said other enclosure section having a diaphragm exposed tothe acoustically pervious wall portion and being connected to the input stage of said amplifier; said amplifier including a least one additional self-supporting circuit control element and at least one additional selfsupporting impedance element having a terminal wire connected to said control element and constituting therewith an additional self-supporting unitary structure, the interconnecting circuit portions of which are sufflciently-stiff and so arranged that the relationship of its elements is not disturbed when it is mounted on or re- ;noved from its position on said mounting surace.

6. In an electron tube amplifier member forming part of an inconspicuous wearable hearing aid and designed to be energized from a directcurrent energy source for supplying amplified output of a microphone to a receiver: a flat casing small enough for substantially hidden wear on the body of a'user and having two walls detachably joined along their edges so as to form a cas-' along said mounting surface between opposite narrow sides or said enclosure and dividingthe enclosure into two enclosure sections; a plurality of metallic terminal members insulatingly secured to and held in position by said mounting member so as to expose teal portions of said terminal members to said interior space; interconnected elements of an amplifier housed in said casing including at least two multi-electrcde amplifier tubes; each tube having a plurality of electrode leads extending from the tube and joined to exposed terminal portions of said mounting member so that said tubes are held thereby in predetermined positions in one enclosure section; a plurality of external connector elements insulatingly secured to a wall portion of said enclosure for completing the operative circuit in- "erconnections from said amplifier to external hearing-aid circuit portions and having inwardly lacing exposed terminal portions; a predetermined circuit elements of said amplifier beiinterconnected to the terminal members secured to said mounting member so as to constitute with said tubes an interconnected structural unit forming part of at least two amplifier one which constitutes an input stage the other of which constitutes an output stage connected to said external connector elen'ients; said set of circuit elements including at least two seli-supporting impedance elements each having at least one terminal wire interconnected to terminal portions of said mounting member so as to be held thereby in predeteriOl'iS in the other enclosure section; said structural unit formed of said mounting member, said tubes and said set of circuit elements constituting a self-supporting unitary structure, the interconnecting circuit portions of which are suillciently stiff and so arranged that the relationship of its elements is not disturbed when it is mounted 'on or removed from its positicnron said mounting surface; a, casing wall por tion bordering the other enclosure section being acoustically pervious; the impedance elements of said one unitary structure extending within said other enclosuresection in the space between said microphone and said mounting surface; said amplifier including at least one additional selfsuppcrting circu t control element and at least one additional self-supporting impedance element having a terminal wire connected to said control element and constituting therewith an additional self-supporting unitary structure, the interconnecting circuit portions of which are sufficiently stiff and so arranged that the relationship of its elements is not disturbed when it is inolnited on or removed from its position on said mounting surface.

'3'. In an electron tube amplifier member forming part of an inconspicuous wearable hearing aid and designed to be energized from a direct-current energy source for supplying amplified output of a microphone to a receiver: a flat casing small enough for substantially hidden wear on the body of a user and having two walls detachably joined along their edges so as to form a casing enclosure confining a relatively shallow interior space having narrow sides; one of said walls having an inwardly facing mounting surface, and reinforcing elements forming part of said well and rendering it substantially v rigid; a substantially firm mounting member extending along said mounting surface between opposite narrow sides of said enclosure and dividing the enclosure into two enclosure sections; a plurality of metallic terminal members insulatingly secured and held in position by said mounting member so as to expose terminal portions of said terminal members to said interior space; interconnected elementsof an amplifier housed in said casing including at least two multi-electrode amplifier tubes; each tube.

having a plurality oi electrode leads extending from the tube and joined to exposed terminal portions of said mounting member so that said tubes are held thereby in predetermined positions in one of said enclosure sections; a plurality of external connector elements insulatin secured to a wall portion or said enclosure for completing the operative chcuit interconnections from said amplifier to external hearingaid circuit portions and having inwardly facing exposed terminal portions; a predetermined set of circuit elements or said heing interconnected to the terminal members secured to said mounting member so as to constitute with said tubes an interconriected structural unit forming part of at least two amplifier stages one of which constitutes an,

input stage and the other of which constitutes an output stage; said set or"- circuit elements including at two self-supporting impedance 7 which are sufficiently still and so arranged that the relationship of its elements is not disturbed when is mounted on or removed iron! its position on mounting surface said amplifier including least one additional self-supporting circuit mntrcl element and at least one additional seli supporting impedance element havmg a terminal wire connected to said control element and constituting therewith an additional seltsupporting unitary structure, the interconnecting circuit portions of which are sur'doicntly and so arranged that the relationship of its elements is not disturbed when it is mounted on or removed from its position on said mounting surface; the casing Wall having said inwardly facing mounting surface embodyin at least two reiniorcingelements of material stronger than the material oi said wall; said two reinforcing elements having an opening for detachably clamping therein said two unitary structures in. their operative positions on said mounting surface.

8. in an electron tube amplifier member forming part of an inconspicuous wearable hearing aid and designed to be energized from a direct-current energy source for supplying amplified output of a microphone to a receiver; a fiat casing small enough for substantially hidden wear on the body of a user and having two walls detachably joined along their edges so as to form a casing enclosure confining a, relatively shallow interior space having narrow sides; one of said walls having an inwardly facing mounting surrace and reinforcing elements forming part of said well and rendering it substantially rigid; a substantially firm mounting member @511. along said mounting surface between opposite narrow sides of said enclosure and dividing the enclosure mto two enclosure sections; a plurality or metallic terminal members insulatingly secured to and held in position-by said mounting member so as to expose terminal portions of said terminal members to said inmrior space; interconnected elements of an amplifier housed in said cash a including at least two multi-electrode amplifier tubes; each tube having a plurality of electrode leads extending -irom the tube and 'joined to exposed terminal portions oi said mounting member so that said tribes are held thereby in predetermined positions in one enclosure section; a casing wall portion bordering the other enclosure section being acoustically pervious; a plurality of external connector elements insulatingly secured to a wall portion of said enclosure for completing the operative cir-,

cult interconnections from said amplifier to external hearing-aid circuit portions and having inwardly facing exposed terminal portions; a predetermined set of circuit elements of said amplifier being interconnected to the terminal members secured to said mounting member so as to constitute with said tubes an interconnected structural unit forming part of at least two amplifier stages one of which constitutes an input stage and the other of which constitutes an output stage; said set of circuit elements including at least two self-supporting impedance elements each having at least one terminal wire interconnected to terminal portions of said mounting member so as to be held thereby in predetermined positions in said other space section; said structural unit formed of said mounting member, said tubes and said set of circuit elements constituting a selfsupporting unitary structure, the interconnecting circuit portions of which are sufilciently stifl and so arranged that the relationship of its elements is not disturbed when it is mounted on or removed from its position on said mounting surface; and a high-impedance microphone in said other enclosure section having a diaphragm exposed to the acoustically pervious wall portion and being connected to the input stage of said amplifier; said amplifier including at least one additional self-supporting circuit control element and at least one additional self-supporting impedance element having a terminal wire connected to said control element and constituting therewith an additional self-supporting unitary structure, the interconnecting circuit portions of which are sufllciently stiff and so arranged that the relationship of its elements is not disturbed when it is mounted on or removed from its position on said mounting surface; the casing wall having said inwardly facing mountingsurface embodying at least two reinforcin elements of material stronger than the material of said wall; said two reinforcing elements having an opening for detachably clamping therein said two unitary structures in their operative positions on said mounting surface.

9. In an electron tube amplifier member forming part of an inconspicuous wearable hearing aid and designed to be energized from a direct-current energy source for supplying amplified output of a microphone to a receiver: a. flat casing small enough for substantially hidden wear on the body of a user and having two walls detachably accuser.

joined along their edges so as to form a casing enclosure cong a relatively shallow interior space having narrow sides; one of said walls having an inwardly facing mounting surface, and reinforcing elements forming part oi said wall and rendering it substantially rigid; a substantially firm mounting member extending along said mounting surface between opposite narrow sides of said enclosure and dividing the enclosure into two enclosure sections; a plurality oi metallic terminal members insulatingly secured to and held in position by said mounting member w as to expose terminal portions of said terminal members to said interior space; interconnected elements of an amplifier housed in said casing including at least two multi-electrode amplifier tubes; each tube having a plurality of electrode leads extending from the tube and joined to exposed terminal portions of said mounting member so that said tubes are held thereby in predetermined positions in one enclosure section; a plurality of external connector elements insulatingly secured to a wall portion of said enclosure for completing the operative circuit interconnections from said amplifier to external hearing-aid circuit portions and having inwardly facing exposed terminal portions; a predetermined set of circuit elements of said amplifier being interconnected to the terminal members secured to said mounting member so as to constitute with said tubes an interconnected structural unit forming part of at least two amplifier stages one of which constitutes an input stage and the other of which constitutes an output stage connected to said external connector elements; said set of circuit elements including at least two self-supporting impedance elements each having at least one terminal wire interconnected to terminal portions of said mounting member so as to be held thereby in predetermined positions in the other enclosure section; said structural unit formed of said mounting member, said tubes and said set of circuit elements constituting a self-supporting unitary structure, the interconnecting circuit portions of which are suiflciently stiff and so arranged that the relationship of its elements is not disturbed when it is mounted on or removed from its position on said mounting surface; a casing wall portion bordering the other enclosure section being acoustically pervious; the impedance elements of said one unitary structure extending within said other enclosure section in the space between said microphone and said mounting surface; said amplifier including at least one additional self-supporting circuit control element and at least one additional selfsupporting impedance element having a terminal wire connected to said control element and constituting therewith an additional self-supporting unitary structure, the interconnecting circuit portions of which are sufliciently stiff and so arranged that the relationship of its elements is not disturbed when it is mounted on or removed from its position on said mounting surface; the casing wall having said inwardly facing mounting surface embodying at least two reinforcing element of material stronger than the material of said wall; said two reinforcing elements having an opening for detachably clamping therein said two unitary structures in their operative positions on said mounting surface.

HARRY B. SHAPIRO.

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