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Publication numberUS2093550 A
Publication typeGrant
Publication dateSep 21, 1937
Filing dateDec 30, 1933
Priority dateDec 30, 1933
Publication numberUS 2093550 A, US 2093550A, US-A-2093550, US2093550 A, US2093550A
InventorsEllsworth D Cook
Original AssigneeRca Corp
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Phonographic apparatus
US 2093550 A
Abstract  available in
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Claims  available in
Description  (OCR text may contain errors)

Se t. 21, 1937. j E. D. COOK 93,

PHONOGRAPHIG APPARATUS a Filed Dec. 30, 1933 2 Sheets-Sheet 1 as 8 e 14 15 15 31 16 a V 13 J a 65 a a i 1 1 o 4 1 INVENTOE': v ElLYPI/t/D. Cfolofif,

Patented Sept. 21,1937

PHONOGRAPHIC APPARATUS Ellsworth n. Cook,.Mercliantville, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application December 30, 1933, Serial No. 704,605

21 Claims.

This invention relates to phonographic apparatus, and more particularly to soundrecording and sound reproducing apparatus of the type subject to the serious disadvantages that both the'records and needles employed suffer considerable wear which renders them unfit for further use after a comparatively short life and the further disadvantage that the drag of the needle over the record introduces foreign noises which are objectionable.

According to the other system, the sound isrecorded photographically, most generally-upon a long strip of sensitized film which, during reproduction, is run through the reproducing apparatus from one reel onto another. While this system is free from some of the disadvantages of the first system, it is, nevertheless, subject to some that are just as serious as those above noted. For example, a film phonograph, regardless of its simplicity, has an element of complexity about its threading. Moreover, such a phonograph includes a multiplicity of parts such as a film guide or support at the reproducing station, pressure rollers, film reels, etc. for the film itself, it must constantly be wound on and unwound from the reels and, being usually fed by sprockets the teeth of which engage the sprocket hole perforations, is subject to great wear and tearing, the latter necessitating patching, splicing, etc. and involving considerable servicing. Another disadvantage of this system is that the film is subject to scratching and marring during handling and during passagethrough the reproducer, all of which introduce obnoxious foreign noises. Also,'the duplication of records from lon films necessitates complicated machinery and processing, and all of the foregoing have in no small way mitigated against the universal adoption of the photographic system of recording and reproducing sound.

In order to eliminate some of the difficulties noted above, it'has been proposed to record the sound photographically, in the form of an uninterrwted spiral. upon- ;a sensitized circular disc or plain. So. far as I am aware, however,

prior art systems of this type have employed complicated devices for scanning the sound track. For example lead screws and the like have been employed to movethe optical system, light source, and photoelectric device used in reproduction 5 radially across the record. Not only is a construction of this sort cumbersome, but it is difficult to set up and control accurately. Also, with such set-ups of the prior art, it is extremely difficult, if not altogether impossible, to make provision for the continued repetition of a record or any preselected portions thereof, or for the reproduction of one record and the immediate reproduction of a second, and perhaps unrelated, record, with an immediate return to the first 5 record or to another record upon completion of the second one, as might be required in special uses of the' phonograph, such as. in advertisin announcing, etc. Where, as in a. few cases, repeat mechanisms may have been provided, they have been both complicated and expensive.

The primary object of my invention is 'toprovide a photophonographic apparatus of the disc type which will be free from the disadvantages of the prior art and which is so'constructed and arranged that it will be flexible in its uses and will, therefore, meet practically every reasonable requirement of sound reproducing apparatus. v

Another object of my invention isto provide an improved apparatus of this type which will include a minimum number of movable parts and which will, therefore, be free from unusual and unnecessary wear.

I Still another object of my invention is to provide an improved apparatus of the type noted which can be set to repeat any preselected portions' of a record with practically no additional mechanismover that required in reproduction.

It is another object of my invention to provide an approved apparatus of this type by means of 40 which a plurality of records may be reproduced either serially or.simultaneously,=as may be desired.

A further object of my invention is to provide an improved apparatus of the type set forth in which the light beam, although maintained stationary, is, nevertheless, rendered eflective at that portion of the sound track which it is desired to reproduce and at that portion only.

Still a further object of my invention is u to provide an improved apparatus of the type men'- tloned in which cross talk, or the simultaneous reproduction of two adjacent. lines of the spiral, is entirely eliminated.

Another object of my invention ist'o provide 7 the accompanying drawings, in which a novel scanning system aforementioned type.

It is also an object of my invention to provide a method by, which the proper location of the 5 scanning means with respect to the record. is insured. 1 And a further object of my invention isto provide improved apparatus of the type noted heretofore which will be exceedingly simple in, construction and extremely simple in operation, which can be manufactured without necessity of observing fine tolerances, and which is not only very efllcient in operation, but also extremely versatile in the results which it can produce.

According to my inventio'n,,I provide, in a phonograph. employing a record on which the sound is recorded in the form of an Archimedian' spiral track, a stationary light source and optical system which focuses a fine line of light radially across the record so. as to include all the spirals or turns across one radius. On the other side of the record, a stationary photo-electric cell is disposed, the active element of the cell havinga length equal'to the length of the radial light line and being:in alignment therewith. In order to mask oif all the light except that desired at the reproducing point, an opaque mask provided with an Archimedian, transparent spiral is placed adjacent the record sothat the spiral record track and the spiral in the maskwill have the samegeometrical center. The ac- 1 tion will bereadily understood upon considering the equation of ,an Archimedian spiral. It will be noted that'the derivative in the radial 35 directionis constant, that is, the rate of radius change is constant'throughout the length of such a spiral. Taking advantage of this fact, -it is possible to choose at least one such curve which, when rotated at some definite speed, will 4ointersect another concentric Archimedian spiral rotated at some other speed along certain fl'xed lines'in' space lying in the plane of the spirals and passing through their common center. Now, if the line of light mentioned above is located at 45 one of these fixed lines, that portion of the line of light which will pass through both the -scanning mask and the record, and thus will reach the photo-electric cell, must move in a radial direction with a velocity equal to that of the record spirals for 'app ratus of the in the same direction. By proper choice of the .60 number of scanning spirals-and by thecircumferential displacement and pitch of these spirals,

while the control of the system to reproduce any preselected portion or portions of the record may be eflected for example, by control of the exciter lamp circuit.

The novel features that I consider characteristic of my invention are set forth with particularity in the appended claims. The invention-itself,

0 however, both as to its organization and method I of operation, togetherwith additional objects and advantages thereof, will best be understood from thefollowing description of several specific embodiments thereof, when read in connection with Figure l is a centr sectional view of one form of my improved apparatus,

Figure 2 is a plan view showing the relation of the record and the scanning mask, the record having a single spiral sound track thereon and the scanning mask having two scanning spirals thereon,

Figure 3 is a view similar to Figure 2 but showing the double-spiral scanning mask applied to a record having two sound tracks thereon,

Figure 4 is a perspective view of the reproducmg optical system and its relation to thellght source,

Figure 5 is aside pr end elevation of a similar optical systemarranged for recording, I

Figure 6 is a view, partly in perspective and partly diagrammatic illustrating one method of controlling the motor to stop it at a predetermined point in the record, and Figure 7 is a view similar to Figure 6 but showing one method of controlling the light source filament circuit to insure-reproduction of,

onlya preselected portion of the record.

' Referring, first, to Figure 1, there is shown a motor plate I on which is supported a motor 2 which drives a spindle 3 having a gear 4 fixed thereto. The gear I meshes with and drives a gear I to which is staked a gear 6 mounted for rotation on a stub shaft 1, the gear 6 meshing with and driving a gear 8 fixed to a sleeve 9 the celving poi-tion If at the upper end thereof beyond a flange portion. II which acts as a record supporting turntable and lies in substantially the same plane as the flange III. The sleeve I! may be locked to the spindle ii in any suitable manner for rotation therewith. In the particular embodiment illustrated, the spindle 3 is split at its upper end and is internally threaded below the split portion to receive a screw l5 having a wedgeshape head. As the screw I5 is screwed down,

'the wedge head expands the split portion of the spindle, thereby locking in place a record It su ported on the flange i4.

The record It may'comprise a disc of any suitable base, such as glass, celluloid, 'etc. coated with a photosensitive emulsion in which a sound track II has been recorded, the sound track being in the form of an Archimedian spiral of comparatively flne pitch and having, preferably, the same geometrical center as the disc itself. Mounted on the flange I0 is a disc of opaque material I! having one or more Archimedian spiral scanningtracks is formed therein. By way of example, ,I have shown the scanning disc I. as provided with two such spiral scanning tracks evenly spacedfromeach other circumferentially, but any,. number of scanning tracks may be employed as will appear more clearly hereinafter.

The scanning disc It may be formed ot some suitable opaque material such as metal, fd'r example, in which case the scanning tracks I 9 may be cut out or punched out therefrom to' form trans- 4 parent spiral scanning slots. The scanning 1180' It may, however, also be made of a photosensitized base similar to that ofthe record, with the scanning tracks recorded therein. In any case,

however, the scanning tracks I9 are made of a much coarser pitch than that of the sound tracks I! and are also formed with their geometrical centers preferably coinciding with that of the disc I8.

The scanning disc I8 is mounted 0n the flange or turntable I0 and is fixed thereto by means of a pin 20, the axis of the scanning tracks I9 being in alignment with that of the spindle 3. The record I8, as explained heretofore, is supported on the turntable I4 with the axis of the sound track II also in alignment with that of the spindle 3. Thus, the tracks I1 and I9 all have a common geometrical center when mounted on the phonograph for operation. The record I6 is also so mounted with respect to the scanning disc I8 that the beginning of the sound track II is in alignment with, or coincides with, the beginning of one of the spiral scanning tracks I9. For this purpose, the record I6 may be perforated with several apertures, each-along a different radius from the center of therecord.

When the record I6 is placed on the turntable I4, these apertures are made to fit over a'corresponding number of pins 2| upstanding from the turntable I4, the position of each of the apertures and their'corresponding pins 2I being so chosen that the record I6 can only be mounted in operative position and locked to the turntable I4 when the beginning of the sound track I1 is in alignment with the beginning of one of the scanning tracks I9.

Fixed to the bracket 22 supported by the motor plate I is a casing 23 which houses a light source and associated optical system for focusing upon the record I6 a thin line of light radially thereacross and of such a length as to cover allof the turns of the sound track spiral along the radius. The light source may comprise a straight coiled filament 24 (Figure 4) and the optical system a pair of cylindrical lenses 25 and 26. The lens 25 is disposed in close proximity to the filament 24 and has its axis at right angles to that of the filament, serving as a condenser to produce a beam of minimum divergence after I leaving the lens. A mask 21 may be provided to assist in limiting the fieldor area illuminated by the light passed through the lens 25. The lens 28 is placed as close to the record 16 as practical with its axis parallel tothat of the filament 24,

and this lens serves to focus upon the record I6,

in the plane thereof, the coil diameter of the filament 24. In this manner, maximum use is made of the light source and a fine or thin line of light 28 is focused upon the record I6 across the sound track spiral I I.

Disposed beneath the scanning disc I8 in alignment with the light line 28 is a photoelectric cell 38 having an active element at least as long as the light line 28 itself. Light passing through the record is modulated thereby and affects the photoelectric cell to cause it to set up varying currents representative of the sound being reproduced. The scanning disc I8 being opaque except at the scanning tracks I9, it isapparent that light can pass through both the record I6 and thescanning disc I8 at only those portions where the sound track I1 and the scanning tracks I9 cross each other. Now, if the light line 28 is focused upon the record in a position such that it intersects the sound track I1 and one of the scanning tracks I9 at the same point where these two tracks intersect each other, light will pass through both the record I6 and the scanning disc I8 at such point and at no other points.

Let it be assumed that the point where the sound track I1, the scanning track I9 and the light line 28 all intersect each other is at the beginning of the sound track, as shown in Figure 2, the scanning spirals I9 being in the start position designated S. As the record I6 rotates in the direction of the arrow, the spiral sound an angle such that the scanning track I9 under the light line 28 will also have moved along the light line the same radial distance, namely a distance equal tothe pitch of the sound track spiral. In other words, for one revolution of the sound record after starting reproduction, the scanning disc will have moved from starting position S to the position P, in which the active scanning track I9 will intersect ,the beginning of the second turn of the spiral sound track I! immediately under the light line 28, and so long as this relation is maintained between the respective rotary speeds of the record and the scanning disc, the sound track I! and its cooperating scanning track I9 will move along the fixed light line 28 in overlapping or intersecting relation at the sound line. That'is to say, as long as'the aforesaid condition is maintained, the sound track I1 and one of the scanning tracks I9 will always intersect each other at some point on the light Iine28. It is for this reason that the sleeve 9 and the hollow shaft I2 are so geared together that the former rotates at a much slower speed than the latter.

The speed of rotation of the scanning disc l8 relative to that of the record I6 is determined by two factors, namely, the relative pitches of the sound track I1 and the scanning tracks I9, and the number of scanning tracks I9 on the disc I8. If the speed of the record is (9), for example, and the number of sound track spirals to be scanned is (y) then the speed of the scanning disc must equal and the pitch of the scanning spiral must be (y) times that of the sound track. Now, if the scanning disc is provided with (n) evenly spaced scanning spirals in one circumference of the scan-' ning mask, it is clear that, for a record speed (0), the scanning disc must .rotate at a speed speed of the sound record and that of the scanning disc, and in this way the active scanning spiral I9 and the sound track I! are made to travel uniformly inwardly along the fixed light line 28 in properly intersecting relation.

By proper choice of records having a plurality of sound tracks thereon and corresponding scan- 5 ning discs, it is possible to employ the present invention for either the simultaneous reproduction of all the sound tracks or for successive reproduction thereof. For the sake of simplicity, suppose it is desired to reproduce either or both of two records recorded on the disc l5. Ob-

viously, a portion of the radius could be allotted to each record and two scanning spirals of proper pitch could be located to embrace only these portions of the allotted radius. By the use of separate photoelectric cells, either record could be played individually or both records could be played simultaneously, depending, for example, on whether one or both photoelectric cells are energized. The optical system could be made to cover both records simultaneously, although, if desired, independent optical systems could be used for each record and the light source associated with each optical system controlled for either separate or simultaneous reproduction. 2 The same results can be accomplished by providing the record IS with two concentric spiral tracks l1 and |'|a as in Figure 3, each having twice the pitch of the sound track I! of Figure 2, and both starting on the same diameter but at points on the circumference of the record 180 apart. For the sake of simplicity, I have shown a scanning disc having two spiral scanning tracks l9 and |9a associated with the record of Figure 3, the scanning track l9 cooperating with the sound track I! and the scanning track |9a cooperating with the sound track IIa. Like the sound tracks I1 and ||a, the scanning spirals I9 .and |9a are concentric and also start. on the same diameter but 180 apart circumferentially of the scanning disc Hi. The speed of the disc l8 must, in this case, be such that the complete record is played by one scanning track during half a revolution of the scanning disc and is repeated by the other scanning track during the next half revolution of the disc |8. By providing two optical systems to focus two light lines 28 and 28a onto the record IS on opposite sides of the record center but on the samediameter and two photoelectric cells, the two .sound tracks can be reproduced either simultaneously or separately, as desired.

It is also possible to employ my improved phonograph to effect the timing and occurrence of a certain number of events to synchronize with the record. For the sake of simplicity, and by way of example, I have shown, in Figures 6 and '7, how the stopping of the phonograph at a predetermined point may be eifected or how only preselected portions of a record may be. reproduced. Referring to Figure 6, I have shown a control ring 3| of conducting material which may be fixed to the gear 8 to rotate at the same speed as the scanning disc l8, the ring 3| being provided with an insulating block 32 at its periphery.

A pair of brushes 33 and 34 connected in series with the motor 2 and a source of current supply 'contact the periphery of the ring 3| and complete the circuit to the motor therethrough. When, however, the insulating block 32 slides under the brush 34, the motor circuit is broken and. the phonograph stops its operation. The block 32 may be set in the ring 3| at such a point, for example, that the phonograph will automatically stop at the completion of reproduction of a record and with the beginning of the scanning track I9 in alignment with the beginning of the sound track I! at the light line 28. A switch 36 connected across the brushes 33 and 34 may be used to start the phonograph again,

or by maintaining the switch 36 constantly closed,

continuous operation is assured. Obviously, instead of controlling the motor, the ring 3| may be employed to control the operation of any other device to cause the occurrence of some event related to the record.

In Figure 7, I have shown one method of effecting reproduction of only a. preselected portion of a record. A control ring 4| similar to the ring 3| but stepped to provide two peripheral portions 42 and 43 is provided with a pair of insulating switch actuating members 44 and 45, the former on the periphery 42 and the latter on the periphery 43. The filament coil 24 is connected to a suitable source of current supply through a pair of switch contacts 46 adapted to be bridged by a contact member 41 the position of which is determined by a pair of relays 48 and 49. The relay 48 is connected to a source of current 50 through a master switch 5| and a spring blade switch 52 located in the path of travel of the actuating member 44, while the relay 49 is similarly connected to the source 50 through a master switch 53 and a spring blade switch 54 located in the path of travel of the actuating member 45.

As long as the motor 2 is energized, the ring 4|, being fixed to the gear 8, for example, will continue to rotate indefinitely in the direction of the arrow and at the speed of the scanning disc I 8. With the switch 5| closed, when the actuating member 44 rides under the blade of switch 52, the latter switch is closed momentarily whereupon the relay 48 is energized to move the contact member 41 into the solid line position of Figure 7, thus completing the circuit to the filament 24 and causing it to glow. The relays 48 and 49 may be holding relays or the contact member 41 may be of the toggle type. In either event, however, when the relay 48 has moved the contact member 41 to the solid line position, the contact member 41 will remain there and the filament 24 will continue to glow. With the ring 4| rotating in the direction of the'arrow, the actuating member 45 will eventually close the switch 54. As soon as this occurs, the relay 49 is momentarily energized whereupon the contact member 41 is moved to; and held in the dotted line position of Figure '7. This breaks the circuit'of the filament 24 and reproduction stops. Thus, between the time that the actuating member 45 closes the switch 54 and the time that the actuating member 44 closes the switch 52, the filament 24 is not energized and therefore no reproduction takes place. By making the actuating members 44 and 45 respectively adjustable on the peripheries 42 and 43, the silent period can be controlled to omit any undesired portions of the record and, therefore, the phonograph set to reproduce only the preselected portion of the record. Also, by opening the switches 5| and 53, the control device may be rendered ineffective, and in] such case, the contact member 41 may be operated manually. As in the case of the control system of Figure 6, that of Figure 7 may be employed to control the occurrence of any desired events or the operation of apparatus other than the filament 24 at a predetermined time and in synchronism with the record.

When it is desired to record sound, the re.- producer may be readily converted into a regrammatically at'60 in Fig. and may comprise like.

any one of the various forms of light valves ,well

known in the prior art, as, for example, a Kerr I .cell, a pair of relatively movable shutters, or the The scanning disc 3 should then, of course, be on the same side of the record as the optical system. i

Although I have shownand described several embodiments of my invention, it will be apparent to 'those'skilled in the art that many changes therein and modifications thereof are possible without departing from the spirit thereof. For example, instead of mounting-the record above the scanning disc, the latter maybe mounted above the record, as shown in Figure 5. However, I prefer the construction shown in Figure 1, since it is usually necessary'to change only the records. Mounting the record above the scanning disc permits making the scanning disc a permanentpart of the apparatus, if desired. Many other changes will undoubtedly readily suggest themselvesto those skilled in the art. My invention, therefore, is not to be limited except insofar as is necessitated by the prior art and 'bythe spirit of the appended claims;

I claim as my invention:

1. In phonographic apparatus, the combination of a rotatable disc record, a rotatable record scanning member associated with said record, and a fixed optical system adapted to direct light toward said record and said scanning member.

2. In phonographic apparatus, the combina-' track thereon, and ascanningmember'associated Archimedian spirals of different pitches. 5. The invention set forth in claim 3 whereinthe sound track and the scanning track are both Archimedian spirals and wherein the scanning track spiral has a greater pitch than the sound track spiral.

6. The invention set forth in claim 3 wherein the sound track and the scanning track are both Archimedian spirals and-wherein the record and the scanning member are so .associated that the sound track'spiral and the scanning track spiral have a common geometrical center.

7. The invention set forth in claim 3 characterized in that the scanning member is associated with the record in a predetermined relation and characterized further by the addition of means for maintaining the record andthe scanning member in said relation. 1

8. In photo-phonographic apparatus, a sound record, means for scanning said sound record, said sound record and scanning means being both I movable relative to eachother, means for providing a. stationary light beam in cooperative relation to said record and said scanning means,

and means for maintaining said record and said scanning means inv a predetermined movable relation to each other with respect to, said' light beam.

9. In photo-phonographic apparatus, the combination of a movable record having a spiral sound track thereon, an opaque scanning member associated with said record and movable relativefthereto, said scanning member being providedwith a transparent spiral scanning track, a light source, means for projecting from said light source a thin line of light radially across said sound track, and means for maintaining.

said.sound record and said scanning member in such relation that said spiral sound track and said spiral scanning track'will always intersect each other at some point on said line of light.

10. In photo-phonographic apparatus, the combination of .a pair of concentric turntables, one of said turntables being annular and surrounding the other, a sound record supported on one of said turntables, said sound record having an Archimedian spiral sound track thereon,

an opaque scanning member provided with an Archimedian, transparent, spiral scanning track, the pitch of'said scanning track being greater than the pitch of said sound track, said scansource a; thin line of light radially across said record, means for mounting said record on said first named turntable in a predetermined relation to said scanning member such that said sound track, said scanning track and said line of light all intersect at a poi t, means for r0- tating said record at a predetermined rotary speed, and means for rotating said scanning member at such a rotary-speed relative to said record that said spiral scanning track will always intersect said sound track along said light line.

' 11. In photo-phonographic apparatus, the combination of a sound record having a plurality of sound tracks thereon, and a scanning member associated with said record, said scanning member having at least one scanning track for each of said sound. tracks and being mounted for movement simultaneously with said record, and said scanning tracks being each adapted to scan the' entire length oftheir respectively associated sound tracks.

12. In photo-phonographic apparatus, l the combination of amovable sound record having a sound track thereon, and a'scanning member associated with and movable relative to said record,

said scanning member having a plurality of sound track thereon, and a scanning memberasv sociated with and rotatable relative to said record, said scanning member being provided with a spiral scanning track of greater pitchthanthe pitch of said sound track, and the speed of rotation of said scanning member relative to that of the sound record being a function of the relative V pitch dimensions of said respective tracks.

14:. In photo-acoustic' apparatus, the combina- I tion of a rotatablesound record having a spiral sound track thereon, and a scanning member associated with and rotatablerelative to saidiec- 0rd, said scanning member being pr'ovided with a plurality of spiral scanning tracks evenly spaced on said scanning member.

\ 15. In vphonographic apparatus, a sound record, means for reproducing sound from said record,- and means external to the record for rendering said sound reproducing means ineffective to reproduce sound between predetermined points insaid record. f k 16. In photo-phonographic apparatus, a photographic record, a light source adapted to cooperate th said record to reproduce sound, an energizing circuit for said light sauce, and means external to said record for maintaining said circuit closed between predetermined points in said record and open between other predetermined points in said record. f

17. Inph'oto-phonographic apparatus, a rotatable record having a spiral sound track thereon, a scanning member associated with said rec-- 0rd and rotatable relative; thereto, said scanning member having a spiral scanning track of greater 1 pitch than said sound track for scanning said sound track, a motor for driving said record and said scanning member, and meansYor controlling said motor to cause it tostop when said scanning a I member has reached a predetermined position relative to said record. v

18. In photo-phonographic apparatus, a rotatable record having a spiral sound track thereon, a scanning member associated with said rec- 19min photo-acoustical apparatus, means for illuminating a photographic recordpsaid means comprising a filamentary light source, a cylindrical condensing lens in close proximity to the filament of said light source with the axis oi said lensat right angles to that of said filament, and 20 a second cylindricallens in close proximity to the record, said second lens having its axis parallel to that of said filament x 20. .Imphoto-acoustical apparatus, means for il-.

'luminat'ing a photographic record, said means comprising a light source including a coiled filament optical condensing means adjacent said filament tor projecting toward said record a light beam of minimum divergence, and optical means' adjacent the record for focusing upon said record,

in the plane the'reof,'-the filament coil diameter.

21pm phonographic apparatus, the'combination of a sound record, and scanning means therefor substa ially co-extensive with the entire area otsaid rd. ELL SWOR'I'H D. COOK.

Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US3815146 *Apr 9, 1973Jun 4, 1974Teletype CorpRecord-turntable assembly and method of making
US5523995 *Apr 1, 1994Jun 4, 1996Lichtenberg; Heinz D.Optical information read/write system with a spread plane beam
U.S. Classification369/18, 369/111, 369/221
International ClassificationG11B3/64
Cooperative ClassificationG11B3/64
European ClassificationG11B3/64