US1995177A - Electromagnetic pick up device - Google Patents

Description

Wiarh i9, i935. E 5;. @UEQN ELEGTROMAGNETEC FICK-UP DEVICE Filed Dec. 10, 1932 IN1/T0 Y Emil@ C. Gaedwz,

Patented Mar. 19, 1935 N A t 1,995,177

UNITED STATES im'lsri'r:ol-'fries Emile C. Guedon, Haddon Heights, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application December 10, 1932, Serial No.. 64.6,6019 n 16 Claims. Y (Cl. 179-10041) Y The present invention relates to electromagnetic pickup devices of the type employed inphonograph recording and reproducing systems, and

has for its object to provide an improved Aand An electromagnetic pickup device of the type above referred to may be said, generally, to comprise a pivoted armature associated with an electrical winding or coil, and mounted between two magnetic pole pieces in a casingadapted to be carried on the end of. asuspension arm, the armature forming or being provided with a stylus means for engaging the groove of a sound rec-l ord. The device further includes a magnet, usually of the permanent type, a suitable detachable cover for the mechanism, and electrical terminal means for the Winding or coil, usually molded in a base plate forming part of the casing.

There are several important details of construction which must be considered in the design of an. electromagnetic pickup device, among which may be mentioned the provision of a simple, substantially frictionless pivot bearing means for the armature, a rigid supporting frame for the armature and magnetic circuit means, and an accuratelyadjustable and definite airgap for the armature. The device should, furthermore, be. of light weight, and preferably be of relatively small size. y A

There must also be considered the problem of manufacturing and assembling the various elements of an electro-magnetic pickup device in ac- 40 unskilied labor, and for this reason, in addition electrcmagnet and other elements of `the pickup device, adjusted, and ready` to Voperate when placed in the casing, or mounted in place in the 'final assembly of the device. y

of the device, than has heretofore been possible i tain parts shown in the preceding figures but in 5, on a reduced scale, showing the cover plate recordance with modern production methods with' sub-asseniblyr'grcups and which may be com-` plete in itself as a unit apart from the casing,

mechanism is mounted wholly Withinthecasing The invention will, however, be better understood from the following description when considered in connection with the accompanying drawing, and'its scope will be pointed out in the appended claims. l y

In thedrawing, Fig. l is a front view on aY greatly enlarged scale, of an electromagnetic pickup device embodying the invention, with va cover removed to eXpose the interior mechanism;V

Fig. 2 is a cross-sectional view: ofr the device shown in Fig. l, taken on line 2;-2 and with the coverin place; .g i

Fig. 3 is a crosssec'tional viewA in perspective, on'a still further enlarged scale, .of a portion of the device shown in Figs. 1 and` 2, showing cer-v 15 tain details of assembly and construction;

Fig. llis a viewjin perspective, on the same scale asY Fig. 3,1of a detail of construction of cereXploded relation to each other 20 Fig. 5 is a rear View, substantially full size, of the device shown in Figs. 1 and 2, with a rear cover plate in place; and Fig. 6 is the same asFig.

moved. 25

Referring to the drawing, 7 'is a molded composition base of insulating material adapted to receive front and rear cover plates 8 and 9 to form .therewith a housing or casing, of rsmooth and pleasing exterior appearance, for the magnet and 0 the operating mechanism hereinafter described. The base plate is provided with the usual rear extension or shank l0 formechanical connection with a suspension means (not shown), and embedded therein areY the usual electrical terminal meansll for the device. It will further be noted `that the composition base rI is deeply recessed in` an interior face as indicatedV at 12,-and`is slotted or bifurcated at its 1 `lower end as' shown Yin the drawing, to Yform a rigid bridge wall 13 connecting two depending leg portions 14 `(Fig. 6). With this construction the interiormechanism may extend to the rear, between the leg portions 14 and within the conY 5 fines of the cover plate 9, tov render the device more compact. In eifect,-the rear'wall of the casing is slotted atthe lower end to permit theinterior mechanism to project through the casing wall and exteriorly thereof. Since the composition'base is 'necessarily of` appreciable thickness to provide mechanical strength, the above described arrangement results in a saving of space from front torear'over that construction in which the entire interior and on a solid base plate or the like. struction, furthermore, results in a decrease in the weight of the device because of the reduction in the quantity of material required for the base plate, both by reason of the recess 12 and the slotted end, as above described.

The cover plate 9 for the protruding mechanism is of thin sheet metal 4or similar material adapted to protect the mechanism and to provide protection with light weight. It is held in place by means of two screws 15-15, secured to the base as hereinafter described, and which are clamped downupon slotted ears ylo-l carried by the cover plate 9 on opposite sides thereof.

The interior mechanism of the Ypickup device may be considered as divided into two main elements, namely, a unitary assembly which may be designated as the operating mechanismand indicated in Fig. l'generally` at 17, secured to the base plate 7 by the same screws 15, which are used to lock the cover plate 9 in .place on the exterior, and a detachable U-s'haped'permanent magnet 18 of relatively large cross section `and of short length detachably mounted on the oper- 7 ating mechanism and held in place thereon by a spring member 19. The latter engages the .bowed center portion of the magnet and lat its opposite end lies in locking engagement with the base.

plate, through the medium of a central Aslot 20 in the lrear wall of the recess `12`and a shoulder 2l formed above the recess 12., as shown more clearly in Fig. 2. The spring is readily removable .from

the slot when the magnet 18 is. removed.

VBy this arrangement, it will'be'seen that the operating mechanism 17 may be loosely mounted on the base plate 7 by means of the screws 1-5,V

for the cover plate 9, and r'mly'tightened against and secured to the base plate 7 whenvthe screws 15r are locked in place against the ears 16 of the j cover plate, since the frame is .the onlyportionof Vthe interior mechanism which isgthus secured to the base plate. The spring action of the at. spring member 19 serves to hold theomagnet'lS ter slightly as the screws'15 are given the -nal tightening operation, or loosened slightlyto remove the cover plate 9. YThis arrangement has` the further advantage that the pickup device screws 15,v and the spring member 19.

The operating mechanism Vor unit is, in'turn,

for manufacturing and assembly reasons, divided into two main groupsv or units which may be termed 4an armature assembly. unit or armature unit, as shown in Fig. 3, and a polepieceiassembly unit or pole piece unit, which-forms theY remainder of the abovenamed unit 17 orloperating mechanism. n K Y y -A Referring more particularly to Eig. 3,Y thearman ture assembly unitA comprises a light weight unitary frame or supporting member indicated generally` at 22, andproviding a bearing plate 23, a

spaced bracket memberzl, and two spaced and elevated, coplanar supporting pads 'V25 ,forQthe remainder of the operating 'mechanism` or pole piece assembly unit vabove referred to and hereinafter described. gV l The frame or supporting-member is of `magnetic material, suoli as steel, and yis preferably formedin one piece .as shown, from a comparatively thin sheetofsu'ch material.v Itis sub- This con-V -sides of the Yarmature and lies in the channel -or groove26 surrounded by sleeves-30 of rubber or other suitable material which will provide substantially a frictionless bearing means. The bearing means is completed by a clamping plate 31-31 comprisingin the present example, two opposed members which are bevelled to engage the rubber sleeves on opposite sides thereof and which are secured in engagement with said sleeves by suitable means, such as a pair of clamping `screws 31a, extending through the bearing plate 23 :of the Vframe into .said plates.

It will be noted'that a. single screw is employed to hold each platein engagement With the rubber sleeves to substantially, completely surround the sleeves by supporting means. By this arrangement, the pivot bearing for the armature is rigidly heldto a fixed axis and is given a uniform pressurev throughout lits length because of the ability of the plates to shift slightly about the axis of the screws 31a to conform to the rubber sleeves and exert thereon a uniform pressure.

Surrounding the armature 28 is the electric pickup ,coil'or winding 32 inthe form of a flat torus, the central opening 33 in which is of such dimensions thatY it provides a clearance space about the armature, and is maintained uniformly out of contact with the armature by a at mountingxstrip 34 to which the coil32 is secured.

.The .mounting strip is preferably of thin sheet insulatingY material of a length such that it lies -between the ends of the unitaryframe 22, as seated at its ends on the operating mechanism'. and yet permits the magnet to move with the lat-L shown in Figs. 1 and 3, and within the confines ofthe frame, whereby it is prevented from trans verse movement.

The strip is prevented from longitudinal movement, that is, movement in an axial direction with respect to the armatureshaft 27, by integral pins may be. assembled from or disassembled into A 35 vformed on the ends of the clamping plate screws 31a projectingupwardly, each through an elongated slot 3 6 in the strip 34. The slots 36 are stamped inthe material of the strip together with a central opening 37 coresponding to the central opening 33 in the coil 32 and clearance openings 38 forpermitting. an assembly operation and adjustment of the air gap hereinafter described.

Briefly, however, it maybe said that the openings 38 are arranged in alignment axially with an opening 39 in each pad 25 of the unitary frame and with an enlarged opening 40 in the bearing plate 23, also in alignment axially with the opening 39,'whereby a screw driver or other instrument may be `inserted through the openings 40 and 38 to engage a locking member which is em- Yployed in the opening 39 and hereinafter described. f

From the foregoing description it will be seen that acoil maybe mounted in place about vthe armature without tools or fastening means. The coil-and its mountingstrip are secured against movement. in a transverse or longitudinal direction as soon as the stripk is in place within the confines of the frame and in engagement with the locking pins 35. The coil is thereby prevented'from contacting with the armature and is held against vertical movement by means hereinafter described, when the assembly is completed. The insulated leads from the coil, indicated at 41, are connected with the inner ends of the terminal members l1 as indicated at 42, by soldering or by other suitable means.

The armature assembly unit'or armature unit further includes a torsional spring member in the form of an elongated bar 43 connected with one end of the armature shaft 27 and with a central portion of the bracket member 24 of the frame, as shown more clearly in Figs. Zand 3.

The purpose of the torsional spring member 43 is to hold the armature in a normal, neutral, vertical position, and to give it resiliency and to provide a restoring force when it is actuated in the translating operation. For this reason, the bar or spring member 43 is rigidly connected with the armature shaft and with the frame 24 and, in the present example, is of rectangular crosssection and mounted in slots 44 and 45 in the armature shaft and bracket member respectively.

This arrangement facilitates manufacture and assembly since the spring member 43 may bc made of a simple rectangular section from flat bar stock, preferably of steel, and may be dropped into place in the slots upon assembly. The union between the frame 24 and the bar in the slot 45 is completed preferably by crimping of the metal or by fusion or soldering, as indicated at 46, along the joints between the bar and the frame, the solder fluxing with a coating which has been previously placed upon the various parts of the assembly.

the'armature shaft 27 in the slot 44 is completed and made permanently secure rby a sleeve 47 which is forced upon the end of. the shaft, as shown more clearly in Figs. 3 and 4. It will be noted in Fig. 4 that the end of the shaft is tapered to receive the sleeve 47. Thejoint may be fur-Y ther secured by placing solder in the joint previous to the assembly and then heating the sleeve, although this is .not entirely necessary if the sleeve is provided with a drive fit on the end of the shaft 27; Y

in the assembly operation, the sleeve isV placed around the spring bar 43 as the latter is dropped in place and the sleeve 47 is then forced into the rubber sleeve 30 and about the end of the shaft by a driving operation. It will thus be seen that the assembly may be quickly eected and nally completed by locking the end of the spring bar 43 in the slot 45 in the bracket member 24.

The sleeve 47 also carries a freely movable block of damping material 48 which isforced onto the sleeve also prior to the assembly operation above'described and secured to the sleeve by friction, supplemented by fusion incident to the heating operation in connection with the sleeve' 47. The block is of inert material having no appreciable elasticity and may be in the nature of a material known as Du Pont viscoloid.

It will be noted that the `block of damping Inaterial is so arrangedthat it is movable with the armature within a free space bounded by the.

arms of the bracket member 24 of the unitary frame, and lies below the bridge wall 13 of the base plate and between the depending leg portions 14 thereof, whereby it is protected against mechanical injury and yet it is in a position whereby it may be easily inspected by removal of the rear cover plate 9. In fact,V the whole assembly ofthe torsional spring member, sleeve,

and damping block 48 may be inspected from the rear without dis-assembling the pickup device, by merely removing the cover plate 9, thereby improving the accessibility ofthe various parts of the device.

The armature assembly stylus clamping thumb screw 49 threaded axially to the opposite end of the armature shaft 27 from the connection withthe spring .member 43. This is arranged so that the thumb screw is presented frontally of the pickup device and serves to clamp within the hollow center of the armature a suitable stylus member 50 as shown in Figs. 2 and. 3 more particularly. The stylus member i), of course, is not mounted in the device during the assembly operation, but is used only when the device is placed inoperation, as is well known.

unit is completed by `a Also, the'clamping screw 49 is not mounted in place until after the iinal assembly operation with the cover 8 yin place, as shown in Fig. 2. This will hereinafter be more fully described.

From the foregoing description it will be seen that the armature assembly unit comprises the I unitary frame member 22, providing a bearing plate 23, a rear bracket member 24, mounting pads 25, and a bearing groove 26'in the bearing plate. It further includes-the armature mounted on the ybearing plate in rubber sleeves and vclamped in lplace by clamping v.plates '31, a coil unit surrounding. theV armature, the damping block 48, and the spring V.connection 43, all 'of which are adapted to' be assembled .rapidly and easily and provided for further assembly in the apparatus` asa complete unit.

This armature unit isass'embledon the base plate 7 by the two screws 15 being inserted through suitable openings inthe depending leg portions of the base'plate and entering threadedV openings 51 in the unitary`frame22, the frame being drawn to a seated. position vabout the threaded openings 51 and against the base plate leg portions 14, and the final tightening operation being completediwhen the rear cover plate is in place on the leg portions 14 under thescrew heads, as hereinbefore described. Y

In addition to thearmature unit, rthe operating mechanism further includes the pole piece assembly unit vor pole pieceunit hereinbefore referred to. This comprises two pole pieces 52-52 arranged to lie upon the mounting pads 25 as shown in Figs. 1 and 2, and to provide depending opposed pole tips 53 on either side of the armature, as shown in Fig. 1. Thev pole pieces are of magnetic material and are joined by a transrial, such as brass, secured to them by suitable means such as screws `55, whereby the bridge member 54 andpole pieces-52 form a'unitary assembly. 1

When assembling with the bridge member, the distance between the pole tips 5 3 is arranged to be such that a desired air gap between the pole tips and armature is obtained when the armature is centrally located between said poletips. This arrangement of parts readily provides for easy manufacture and assembly with the desired air gap for the Vreason rthat the pole piece assembly may be constructedfrom parts which when united by the bridge member 54 and screws 55 provide a predetermined air gap betweenthe pole pieces 53. This unitary assembly is then placed upon the Vmounting pads 25 and is moved as aunit gap on each side of thearmature is uniform and equal' between the armature and the. pole tips, as shown more clearly Fig. 1 at 56.

This adjustment is made permanent and the pole piece assembly is secured to the unitary frame of the armature unit by suitable clamping means suchas screws'57 which pass upwardly through the openings 39 in the mounting pads 25 and are threaded in the 1` tapped openings indicated at 58 in the pole pieces. The openings 39 are enlarged slightly over the diameter of the clamping screws whereby the lateral or transverse adjustment of the pole piece assembly may be made as hereinafter described.V The arrangement is best understood from Van inspection of Fig. 1.

vIt will be seen that the openings 38 and 40 in the coil mounting strip and in the frame bearing plate are provided for inserting a screw driver or other tocl Yfor clamping the screws 57 Vwhen the adjustment ol' vthe air gap is being made.

Y Other suitable clamping means mayv be provided,

but the screwarrangement shown is at present preferred, because of its simplicity. The removal ofV material inthe form of ,openings 40 in the iframe further serves to lighten the pickup assembly without reducing the flux carrying capacity below a desired predetermined minimum value.

From the foregoingidescription it will be seen that both the armature assembly and pole piece :assembly of the interior operating mechanism of the pickup device may be manufactured as separateV units and maybe quickly-and easily mounted inplace in the pickup device in adjusted relation to each other. without further tdetailed operations or without involving a high degree of skill on the part of .workmen employed to produce such devices. In practice, the pole piece unit and the armature unit are assembled to provide the operating mechanism or unit complete before being mounted -on the base plate.

The interior assembly is then completed by charging the magnet 18 and slipping it onto the pcle pieces as shown in Figs. land 2, beneath the holding spring 19 which is inserted in the slot 20 just previous toV mounting the magnet 18, Y

all as hereinbefore described. The pickup device is then completed by mounting the rear cover plate 9 in place and tightening vthe screws 15. The front cover plate is then placed 'in position as -shown more particularly in Fig. 2 and is secured in place by central clamping screwY 59, whichr engages a threaded opening in a bracket member 68 provided integral with the bridge member 54 in a position to lie just beneath the cover plate '8 below the opening provided for the screw 59 therein.

The stylus clamping screw 49 is then inserted Vthrough a suitab1e-opening6l also in the front cover plate 8 in alignment with the axis of the 'armature shaft. The opening 6l is arranged to provide suiilcient clearance for the stylus clamp-- ing screw so that the armature may operate without contact with the cover plate 8. To this end, also, itj'will be noted that `the cover 8 is also provided withV an enlarged clearance opening 62 adjacent to the stylus receiving endV of the armature to provide an operating clearance opening for the lower end of the armature and stylus.

From the foregoing description it will be seen that an electromagnetic pickup device embodying the.- invention has the advantage that it comprises substantially but three main elements, namely, a casinggof which the major portion is the insulating base plate; an interioroperating 75 mechanism; and a magnet, all being easily sepat the front and at the rear without disassembling the entire device and merely by the removal of the suitable cover plate.

The magnet is held in place by a simple spring member which is secured to the base plate, thereby permitting the cover plates to be removed without losing the magnet from its position and without requiring other bolting or clamping means for the magnet, as has heretofore been provided in such devices.

It will be appreciated that this simple and eiective holdingv means is desirable when it is considered that if a magnet is removed from its supporton the pole piece, it loses at once, substantially one half its magnetic ux, which can be restored only by re-charging the magnet.

The operating mechanism is provided as a complete assembly unit easily mounted in the casing oron the base plate by two screws which, at the same time, serve to hold the rear Icover plate. It is mounted on the base plate or may be removed therefrom merely by inserting and tightening or removing two screws.

In itself, the operating mechanism is divided into two sub-assembly units, each of which may be completed before assembly, if necessary in in different parts of a factory and may be brought together for assembly at any convenient point, being complete in themselves.

The'two units referred to are the armature assembly unit and the pole piece assembly unit, each ofwhich is Aeasily assembled in itself by what may be considered to be merely dropping the parts in ,place and tightening certain clamping screws.

As is obvious from Van inspection of the drawing, Figs. 1 and 2, the bearing plate 23 and the pole pieces 52`are relatively small in cross-section comparedV with that of the magnet 18. It is therefore obvious that of the iluX which flows through the magnet, a part of that flux ilows across the air gap and another part ows through the bearing plate, in substantially parallel paths. The length of the path through the bearing plate is greater than that through pole pieces, however, thepath through the pole pieces includes the air gap, although relatively small with the armature inserted therein, increases the reluctance of the path. Y

The 'operation is such that the armature more closely approaches one pole piece or the other, thereby causing'the flux normally flowing across the air gap to how in partk rst downwardly and then upwardly through the armature and thereby inducing corresponding voltages in the coil which is cut by the flux as it changes from a downward to an upward flow in the armature. The

reason for the llow reversing is because of the widening of the airgap on one side of the armature and the closing of the air gap on the other side of the arma-ture asvit Vibrates in the air gap.

VAs the operation of magnetic armatures of this type is old and well understood, further description is believed to be unnecessary.

It will be seen that the various parts each coopcrate to vprovide a simplified and improved light weightelectromagnetic pickup device and to permit a relatively short armature to be utilized, which has the advantage of an improved fre- Yreducing the weight of the device nevertheless, heldin place and prevented'rom` contacting with the armature by other elements of the assembly and without any particular holding means. Thus, throughout the entire assembly, it will be seen thata major portion of the partsare utilized for a dual function, thereby its manufacture and assembly.

I claim as my invention:

1. An electric phonograph pickup device including, in combination, a casing comprising a base y member and two removable cover membersv on opposite sides thereof, and a unitary operating mechanism in the casing secured to the basemember and extending therethrough into one of said cover members.

2. An electric phonograph pickup device including, in combination, a casing comprising a base member and two removable Ycover members on opposite sides thereof, and a unitary operating mechanism in the casing secured to the base member and extending-therethrough intooneof said cover members, said operating mechanism including an armature assembly unit having a pivoted armature, a pole piece assembly unit providing a xed air gap, and means for adjustably securing said units together to center the armature in the air gap.

3. An electric phonograph pickup device including, in combination, a bifurcated base member and a unitary operating mechanism mounted thereon and extending in part therethrough between depending leg portions of said base member, said operating mechanism comprising an armature unit including a pivotally mounted armature, a pole piece unit providing afixed air gap, and means for adjustably securing said units together in operative relation to each other to center said armature in the air gap.

e. An electro-magnetic pickup device including, in combination, an armature unit comprising a unitary frame providing a bearing plate, a bracket spaced axially from the bearing plate and two spacedco-planar supporting members on opposite sides oi the bearing plate, an armature having a shaft pivotally mounted on said bearing plate andiiexibly connected with said bracket, an electric pickup coil surrounding said armature, a second unit comprising two pole pieces secured to said supporting members and a bridge member by which said pole pieces are connected, said pole piece unit being adjustable with respect to the armature unit to center the armature in the air gap, and means for securing said units in adjusted relation to each other.

5. In an electric phonograph pickup device, the combination with a pivotally mounted armature, of a magnet element, unitary means for supporting said armature, and a second and separate unitary magnetic pole means for said magnet element providing a fixed air gap, said rst and second named means being adjustable with respect to each other to center said armature in the air gap.

' 6. In an electric phonograph pickup device, the combination with a pivotally mounted armature, of a unitary frame means for supporting said armature, a second and separate unitary means providing a fixed air gap, said rst and second named means being adjustable with respect to and simplifying each other to center said-armature in the air gap,

means for securing said units together in adjusted relation, a base plate and covers providing a cas- ?ing, means for securing said unitary frame means Vandone of said covers tothe base plate, a-magnet, and means independent of said' coversl for resiliently holding 'the magnet incontact -with one of said units; Y

7. In an electric phonograph pickup device,

an-arn'iature unit including, in combination, a

pivotally mounted armature, an electric pickup member arranged to support said armature and vsaid coil, means carried by the coil and means `provided on the frame-cooperating tohold said coil in adjusted position with respect tothe armathe frame member, and a pole piece unit mounted on and adjustably secured to the frame.

8. In an electric pickup device, an armature `unit including, in combination, a pivotally mounted armature, an electric pickup coil surrounding said armature, a unitary frame member arranged to support said armature and said coil, means carried by the coil and means provided on the frame cooperating to hold said coil in adjusted position with respect to the armature, a torsional centering spring extending from the armature into engagement with the frame, a pole piece assembly unit vcomprising Vtwo pole pieces associated with said armature and a bridge member rigidly connecting said pole pieces, said last named unit being adjustably mounted onsaid armature unit, and means for securing said armature unitin said pickup device. y

9. An electro-magnetic pickup Vdevice including, in combination, a recessed base plate having two depending spaced leg portions, an operating mechanism detachably secured to said leg portions and extending therebetween, a magnet member mountedV on said operating mechanism to complete a' magnetic circuit therethrough, and means for resiliently connecting the said magnet member to the base plate.

l0. An electro-magnetic pickup device including, in combination, a recessed base plate having two depending spaced leg portions, an operating mechanism detachably secured to said leg portions and extendingtherebetween, a magnet member mounted on said operating mechanism to complete a magnetic circuit therethrough, means for resiliently connecting the said magnet member to the base plate, and detachable covers arranged to cooperate with the base plate to form a casing for said magnet and operating mechanism.

11. An electro-magnetic pickup device including, in combination, a recessed base plate having two depending spaced leg portions, an operating mechanism detachably secured to said leg por- Y tions and extending therebetween, a magnet mem- -coil surrounding said armature, a unitary frame iture, a torsional centering spring member eX- tending from the armature into engagement with ing frame for the armature adapted to provide a portion of a magnetic circuit, a torsional spring member extending axially of the armature shaft, said shaft and said frame being slotted to receive the ends of said spring-member thereby to establish a connection between the armature shaft* and the frame, said frame being substantially rectangular ink form and having an open side, a pole piece assembly unit mounted on said open side and depending therein in association with the armature, said pole piece unit being adjustably mounted on said frame to provideauniform air gap for the armature, a pickup coil surrounding said armature, and means carried by said coil rand by said frame arranged to cooperate to hold said coil in spaced relation to said armature and in an adjustedoperating position inV association therewith.

13. In an electric pickup device, the combination with an armature member having a torsional centering spring connected therewith, of af pair of pole pieces having pole tips arranged in xed spaced relation to each other to provide aixed air gap, said pole pieces being rigidly connected together whereby they are removable as a unit to center the armature in the air gap, and a unitary frame member ofY sheet material in the form of an open rectangle providing a bearing plate for the'armature, a bracket member forV connection with the torsional centering spring and spaced co-planar supporting pads for the pole pieces, means providing a pair of studs in said frame, an electric pickup coil surrounding the armature, and a strip of insulating material secured to the pickup coil and arranged to lie in said frame in engagement with the ends thereof and with Ythe studs to hold the pickupV frame to center-the armature in a fixed air gap provided between their pole tips, and thatthe pickup coil is removable from an operative position with'r'espect to the armature when the pole pieces are removed from the frame.

15, An electric phonograph pickup device including, in combination, a casing comprising a base member and two removable cover members on opposite sides thereof, a pivotally mounted armature, a magnet element, unitary means for supportingV said armature secured to said base member and extending therethrough into one of said .cover members, and unitary magnetic pole means for said magnet element providing a fixed air gap, saidv armature supporting. means and said unitary pole means. being adjustable with respect to each other to center said armature in the air gap. Y

16. An electromagnetic pickup device including, in combi-nation, a recessed bas-e plate having 'two depending spaced leg portions, an operating mechanism secured to said leg portions and having a frame extending between said portions, a vibration damping block for said operating mechanism mounted between-said leg portions in said operating mechanism, and a magnet member mounted on said operating mechanism and connected with said base plate.

Y EMILE C. GUEDON.

Images