US2351005A - Magnetic recorder - Google Patents

Description

June 13, 1944. M. cAMRAs 2,351,005

MAGNETIC RECORDER Filed July 27, 1942 5 Sheets-Sheet l .June 13, 1944. M, CAMRAS 2,351,005

MAGNETIC RECORDER Filed-July 27, 1942 5 Sheets-Sheet 2 hun:

`une 13, 1944. M CAMRAS 2,351,005

MAGNETIC RECORDER Filed July 27, 1942 5 Sheets-Sheet 3 EEE,

June 13, l M. CAMRAS MAGNETIC RECORDER Filed July 2'7, 1942 5 Sheets-Sheet 5 Patented June 13, 1944 MAGNETIC RECCRDER Marvin Camras, Chicago, lll., asslgnor to Armourl Research Foundation, Chicago. Ill., a corporation of Illinois Application July 27. 1942, Serial No. 452,419

4 Claims.

This invention relates to a magnetic recorder, and more particularly to an electromagnetic instrument for recording sound on a paramagnetic wire or tape and reproducing the sound therefrom.

Electromagnetic recording and reproduction of sound vibrations, speech, etc., dates back to the end of the nineteenth century, and while some improvements and refinements have been made since that time, in both the method and apparatus, such improved apparatus and methods have not been utilized to any great extent commercially. There are a number of reasons for this, the most important of which are probably the inherent limitations in the apparatus heretofore proposed. In general, the volume level of the reproduced signals of previous systems was low, the frequency range covered was very limited, the extraneous noise was objectionable and the distortion of the wave forms were often of such character and magnitude as to render the reproduction of extremely low quality and at times almost unintelligible.

In a co-pending application o! mine, entitled "Method and means of magnetic recording," tiled December 22, 1941, Serial No. 423,928, and assigned to the same assignee as the present in vention, a novel system of magnetic recording is described and claimed. 'I'he present invention is directed to a novel application of the method and means described and claimed in said copending application, and to a novel combination of elements employed therewith.

It is an object of the present invention to provide a novel apparatus for magnetic recording and reproduction.

A further object of the present invention is to provide a novel unitary apparatus for magnetic recording and reproduction including a recording head, reel means for carrying and moving a paramagnetic wire or tape to the recording head, an electric amplifier and a loud speaker.

Another object of the present invention is to provide a novel electric circuit arrangement for amplifying and reproducing magnetically recorded sound vibrations which have previously been made on a paramagnetic body.

A still further object of the present invention is to provide novel indicating means for indicating the position 'of recorded sound vibrations on a paramagnetic wire or tape.

A still further object of the present invention is to provide novel means for shifting from a. position for magnetic recording to a position for magnetic reproduction .on a paramagnetic wir or tape.

(Cil P19-100.2)

Another and still further object of the present invention is to provide novel means for reeling and unreeling a paramagnetic wire or tape in the recording and reproducing apparatus.

Still another object of the present invention is to provide novel means for stopping the reels at any desired selected portions of the recording or reproduction.

Stili another object of the present invention is to provide a novel method and means for braking the wire carrying reels.

Still another and further object of the present invention is to provide a novel circuit arrangement for a magnetic recorder and reproducer.

The novel features which I believe to. be characteristic of my invention are set forth with particularity in the appended claims. My invention itself, however, both as to its organization and manner of construction, together with further objects and advantages thereof, may best be understood by reference to the following description, taken in connection with the accompanying drawings, in which:

gure 1 is a front viewof one embodiment of the present invention, as viewed in a plane indicated by the line I-I of Figure 2;

Figure 2-is an end sectional view through the apparatus, as taken along the line lI--II of Figure 1;

Figure 3 is an irregular sectional view of the apparatus, as taken along the line III- III of Figure 2;

Figure 4 is a diagrammatic illustration of the control switch and the wire position indicating mechanism;

Figure 5 is a viewtaken along the line V-V of Figure 3;

Figure 6 is a view taken along the line VI--VI of Figure 3; and,

Figure 7 is an electric circuit diagram of the system.

In Figurs 1 to 3 of the drawings, there is illustrated a magnetic recorder and reproducer constructed in accordance with the teachings of the present invention. All of the essential component parts of my recorder and reproducer. with the exception of the microphone and a source of power, are contained in the single unit illustrated. This unit, as illustrated in Figures 1 to 3, includes a housing member I0 having a base Il, a top wall I2 and an inclined front panel I3. The inclined front panel I3 includes a lowerportion I4 and an upper portion I5 which is offset rearwardly from the lower portion i4.`

A magnetic recording head I6, an erasing head I1, a recording medium I 8, in the form of a wire,

and a pair of reels I9 and 20, are all mounted on the outer face of the upper panel i5 on the front wall I 3. Reels I9 and 20 are mounted for rotation on shafts 2| and 22. When the apparatus is being operated as a recorder or reproducer, the reel I9 is the supply reel and the reel 2 is the receiving or windup reel, the reel being driven in a counter-clockwise direction as viewed in Figure 1. When the wire is to be rewound on the reel I9, the reel I9 is driven in a counter-clockwise direction as viewed in Figure 1.

The inner surface of the front panel I3 and at least the forward under surface of the top I2 is lined with a sheet 2I8 which is formed of silicon steel or other soft iron for the purpose of magnetically shielding the recording head I6 from the magnetic field producedV by the equipment presently to be described which is housed within the casing I0 and behind the front panel I8.

The record medium or wire 8 is preferably made of a high carbon steel and, by way of example, may conveniently have a diameter of approximately .005 inch. This wire |8 is threaded through the erasing head I1 which, as will presently be explained, completely demagnetizes the wire and removes any magnetism therefrom, whether caused from previous records made on the wire, or from any extraneous source. The wire I8 then passes around a guide pulley 23, which is mounted for free rotation on the shaft 24, and held in place by a lock nut 25. The wire is thereafter passed through the magnetic recording head i6, which will presently be explained in detail. The wire I8 after leaving the recording head I6, passes around a guide pulley 26, which is freely mounted on a shaft 21, and held in place by a lock nut 28. The wire I 8 finally passes to the takeup reel 20. A pair of level winding guide fingers 29 and 38 are preferably provided to assure an even distribution of the wire on the reels I9 and 20.

A motor 3| is provided in the housing I0 and is arranged to be selectively connected to either the shaft 2| or the shaft 22 of the reels I9 and 28. respectively, for driving one reel or the other, as desired, in a clockwise direction, as viewed in Figure 3. This motor 3| is preferably mounted in an inclined position, as shown in Figure 2, with its drive shaft 32 extending substantially perpendicular to the panel portion I4. The motor 3| may be conveniently mounted on a bracket 33 which is secured to the base Il, as at 34, and to the motor as at 35. As shown in Figure 2, an opening 36 is provided in the base I| into which the casing of the motor extends, but does not completely pass therethrough. This opening 36 is provided as a ventilating opening, and facili- Cil tates circulation of air around the motor and the amplifying equipment presently to be described.

Drive pulleys 31 and 38 are mounted on the shafts 2| and 22, which carry the reels I9 and 2U, respectively. It will be noted that the pulley 31 is smaller than the pulley 38 in order to increase the rewind speed.

As is shown in Figures 2, 3, 5 and 6 of the drawings, the shafts 22 and 2| pass through the panel portion i5 andv then through the skeleton frame structure 39 and 39', respectively; each of which includes a back plate 40 and a plurality of spacer plates 4 I. These structures 39 and 39' are associated with each of the shafts 22 and 2| on the rear of the panel portion I5, and contain the mechanism for reciprocating the level winding guide fingers 3U and 29. While the structures 39 and 39' associated with the two shafts 22 and 2| are not identical, they are very similar, and for that reason a detailed description of only one of the structures, namely the structure 39 associated with the shaft 22, will be discussed. The structure 39, which is associated with the shaft 22 is shown in detail in Figures 5 and 6.

The shaft 22 is mounted in bushings 25| and 252 which are carried, respectively, by the panel portion I5 and the back plate 40, Formed or attached on the center portion of the shaft 22 is a worm 253. Meshing with the worm 253 is a worm wheel 254 which is secured to a shaft 255 which extends generally downwardly and substantially at right angles to shaft 22. Shaft 255 has formed or secured thereon below the worm wheel 254, a worm 256 which meshes with a worm wheel 251 mounted on a shaft 258 which extends substantially at right angles not only to the shaft 22 but also to the shaft 255. The shaft 258 is mounted on two of the spacer members 4| on opposite sides of the skeleton structure 39. Mounted on one end of the shaft 258 is a heartshaped cam 259 which is arranged to engage a cam follower 260 which is in the form of an inverted L-shaped finger which is secured to a rod 26| which carries the level Winder guide finger 30. The end of the cam follower 260 projects through a slot 262 in the spacer member 4I adjacent the cam 259.

Also connected to the shaft 258 is a flexible drive cable 42 which drives the-counter mechanism 43 which indicates the relative position of any portion of the record medium I8 with'respect to the recording head I6. It will thus be understood that the counter mechanism 43 is driven through the same reduction gear which drives the cam 259 from the shaft 22.

The' cam follower 260 connects through a link bar 44 which is pivotally mounted at its center on a bracket 45 to an operating finger 263 which is rigidly secured to (not shown) and carried by the level Winder guide linger rod 264 which carries the level Winder guide finger 29. A biasing spring 265 in the form of a resilient wire having several turns in the center is secured at one end of the back plate 40 of the skeleton frame structure 39' associated with the shaft 2| as at 266, and is secured at its other end to the end of the link arm 45 as at 261. This spring 265 resiliently holds the cam follower 26|! against the heartshaped cam 259.

Referring now to Figure 3, a pair of dog leg levers 46 and 41 are pivotally mounted as at 48 and 49 to a bracket 5|) which is secured to the rear end wall of the motor 3| by attaching bolts 5I. The dog leg levers 48 and 41 cach have downwardly projecting legs 52 and 53, respectively, on which is pivotally mounted driving pulleys 54 and 65, respectively. Drive pulley 54 is associated and mechanically coupled to a friction roller 56. while drive pulley 55 is associated with and mechanically coupled to a friction roller 51. Fixed to the motor drive shaft 32 is a friction roller 58 against which friction roller 56 and friction roller 41 are selectively arranged to be moved into driving contact. A exible drive cable 59 extends around drive pulleys 54 and 31. A flexible drive cable 60 extends around drive pulleys 55 and 38.

As shown in Figure 3, the friction roller 56 is in driven engagement with the drive roller 58, and, accordingly, the shaft 2| is being driven by the motor 3|.

in Figure 1, and accordingly the wire I8 is being pnwound from the reel 20 and rewound on the This in turn causes reel I9 to be, driven in a counter-clockwise direction as viewed reel i8. When the friction roller 56 is moved out of engagement with the friction roller 58 and the friction roller l1 is moved into engagement with the friction roller 58 the shaft 22 is driven by the motor 3| which in turn causes the reel 28 to be rotated in a counter-clockwise direction, as viewed in Figure 1.

The dog'leg levers 48 and 41 have upwardly. extending bent leg portions 8| and 82, as is clearly shown in Figures 2 and 3. A finger $3 extends between the two upstanding legs 6| and 82 and is arranged to be moved by the motor control operating handle 84. The arm 53 is pivotally mounted on a bracket 85,.as at 85', which is supported on a frame construction 88 mounted on the rear of the lower panel portion |4. Asis diagrammatically shown in Figure 4, the motor control operating handle 84 is pivotally mounted on the subframe member as at 51. The motor control 64 determines whether the motor is caus ing the wire I8 to be moved in a recording and reproducing direction through the recording head I5, or whether the motor is causing the wire I8 to be rewound on reel I8. lWhen the handle 84 is thrown to the right as viewed in Figure 1 or, downwardly as viewed in Figure 4, the wire I8 is moving in a recording and reproducing directhe handle 84 is thrown to the left as viewed in Figure 1 or upwardly (as shown) in Figure 4, the wire |8 is moving in a rewinding direction (i. e.. it is being rewound on reel I8). When the handle 54 is in an intermediate or central position,

the wire is stationary and the motor 3| is deenergized. Although not shown, it is to be understood that the handle 54 operates an electric switch which closes the energization circuit of the motor 3| when the handle 84 is moved in either direction.

When the finger 53 is rocked against the upper leg portion 82 of the dog lever 41 the friction roller 51 is moved out of engagement with the friction drive roller 58-against the action of the tension spring 53 which extends between and is secured to the lower ends of the leg portions 52 and 53. Similarly, when the lever 64 is rotated so as to move the finger 53 against the upper leg portion 6|, the friction roller 58 is moved away from the friction roller 55 and at the same time the tension spring 58 pulls the friction roller 51 into engagement with the friction roller 55. When the finger 83 is in its mid position friction rollers 56 and 51 are both pulled against friction roller 58 by the spring 58. Since these rollers 58 and 51 try to drive the wire I8 in opposite directions, it will at once be apparent that the friction drive rolls 56 and 51 of themselves act and serve as a brake for stopping the and control knob 15 determines whether the electrical circuit will operate as a recorder or asa reproducer. To the left of control knob 15 is a redlight 15 which is lit when the control knob 15 is moved to a position for operating the apparatusas a recorder. A green light 11 is located to the right of the control knob 15 and is lit when the control knob 15 is moved to a position for causing the apparatus to operate as a reproducing unit. A neon bulb 18 is located above the control knob 15 and. as will presently be explained, indicates the proper volume setting when the apparatus is operated as a recorder. The motor control 64 is located on the front of the panel portion |4, as shown in Figure 1, while the indicating means 43 is located to the left thereof.

Ihe electrical circuit of the apparatus is diagrammatically shown in Figure 7. The electrical circuit in general includes the magnetic recording head and the audio amplifier, a loud speaker and microphone plug which is arranged tion (i. e., it is being wound up on reel 28). When motor 3| as well as immediately stopping movement of the wire I5.

Also mounted within the housing |8 is the amplifying equipment, generally indicated at 88 in Figure 2. The amplifying equipment 58 is mounted to the rear of and around the motor 3|. A loud speaker 18 is mounted on the lower panel portion I4.

Turning to Figure 1 of the drawings, the left on-and-oi switch, as well as the tone control;

to be connected to any suitable type of microphone. With the switch connections as shown in Figure 7, ,the apparatus is in a position for` reproducing sound vibrations which have previ ously been recorded on the wire It. 'I'he magnetic recording head includes a coil 18 which is magnetically associated with the wire i8 or, ir. other words, it is so related to the wire I8 that the lines of flux produced bythe magnetized wire will intersect the windings of the coil 18. In the preferred form of the invention the wire I8 passes directly through the tapered pole portion 88 of a laminated iron core member 8| and through a portion of the coil 18 which surrounds the tapered pole portions 88 and the air gap therebetween. The coil 18 is connected to the input grid electrode 82 of the ilrst audio amplifier tube 83 through a shielded conductor 84 (the shield being indicated bythe broken lines 85). The other side of the coil 18 is connected to the cathode 86 of the electron discharge device 83 through the conductor 81. As is indicated at 88. the cathode 85 aq'd the conductor 81 is grounded. Two switches 88 and 88 are connected in the circuit of conductor 84. Interposed between the switch 88 and the grid electrode 82 is a bias cell 8|. 'I'his cell 8| is connected through a high resistance 82 to the grounded shield 55.

The, electron discharge device 83 may be of any suitable type for use in an audio amplifier and as shown is of the multigrid type. More particularly, the electron discharge device 83, in addition to the input grid electrode 82 and the cathode as, includes a heating aiment s3, a screen grid electrode 84, a suppressor grid electrode 85 and an anode 88. A second stage of amplification is provided by an electron discharge device 81 which is connected by a capacity coupling 88 to the output circuit of the electron discharge device 83. More particularly, the anode Y I which are connected between the anode |06 and ground. The anode |06 is also connected through a coupling condenser ||2 to the input grid electrode ||3, volf an output or power tube ||4. A self-biasing resistor' I I5 is connected between the grid electrode ||3 and ground.

The output of power tube ||4, in addition to the grid ||3, includes a filament H0, a cathode ||1, a screen grid ||8, a suppresser grid ||9 and an anode |20. The suppresser grid ||9 is directly connected to the cathode ||1 in the conventional manner, while the screen grid ||8 receives a suitable biasing potentlal.in a manner presently to be explained. The cathode ||1 is connected through a self-biasing resistor |2| and a parallel connected filter condenser |22 to ground.

In the output'circuit of the power ampliiier tube ||4 is the neon lamp circuit. This neon lamp circuit includes a condenser |23 and a variable resistance element |24, which are connected in series between the anode and the grounded conductor 81. Bhemeon lamp 18 is connected between the grounded conductor 81 and the movable element |25 of the resistor |24 which determines the voltage drop across the neon lamp.

The power ampliiler tube ||4 is connected to an output transformer-|26. The input winding or primary of the transformer |26 is connected between the anode |20 of the power amplier tube ||4 and the screen grid 8 of the same tube. The secondary of the transformer |26 has its opposite end connected to an output jack |21 and a resistance element |28. An intermediate point |29 on the secondary of the transformer |26 is connected to the grounded conductor 81 and also to a contact point |30 of a switch |3|. A second intermediate point |32 is connected to a second contact point |33 of the switch |3I.

A loud speaker |34 is connected through switch |3| on one side to the tapped point |32 on the secondary of the transformer |26, while it is connected through the separable contact elements |35 and |38 of the output jack |21 to the tapped point |29 on the secondary of the transformer |26. With the switch |3| in the position shown in Figure 'I of the drawings, the speaker |34 is arranged to be energized from the output of the amplier. Conductors |31 and |36 are connected to a snorting switch (not shown) which is arranged to be closed when the unit is being rewound.

Power for the amplifier circuit is obtained through a rectiiier Vunit |30 which includes a power transformer |40, a rectifier tube |4|, and suitable filter elements presently to be described. The input side of the power transformer |40 is connected through a plug |42 to a suitable source of alternating current (not shown), such for example as the conventional 110 volt 60 cycle alternating current available in most cities.A An overload fuse |43 is connected between plug |42 and transformer |40, in one part of the circuit, and an on-of! switch |44 is connected in the circuit on the opposite side. The switch |44 is preferably combined with the tone control |||and erated from 'a single knob 14 (Figure 1); In l dition to a primary winding |45 on the por transformer |40l there are provided three s ondary windings |46, |41 and |48. The seco! ary winding |46 is arranged to be connected the filaments 93, |0| and ||8 of the tubes 83, and 4. The arrows associated with wind: |48 indicate diagrammatically that they are l ranged to be connected to the arrows on the il ment .elements referred to. f

The secondary winding |46 supplies power the cathode |45 of the rectifier tube |4|. I anodes |50 and |5| are connected to oppos ends of the winding |41. The center point windings |41 and |48 are both grounded throu a conductor |52. A group of filter condens |53 and |56 are connected in thefcircuit shown, while an inductive reactance element I is connected in the circuit of the coilV |46 a the cathode |49. Resistance elements |58 a |50 are also provided and are connected in conventional manner. It is to be understood t1 the circuit arrangement above described is a cc ventional full wave rectifier circuit for supplyi the desired potential to the various elements the audio ampliiler. The desired positive pote tial for anode 50 and screen grid 94 of tube is obtained through conductor |60 and droppi resistors |6| and |82. 'I'he desired potentiell anode |06 and screen grid |03 of tube l1 is c tained through conductor |63 and dropping 1 sistors |64 and |65. The desired potential i anode |20 and screen grid ||8 of tube ||4 is c tained through conductor |66, the conductor being connected through the primary winding the output transformer |28 to the anode |20 wh being directly connected to the screen grid H8. The red pilot light 18 and the green pilot lig 11 are energized directly from the seconds winding |48 of the power transformer, a swit |61 being arranged to selectively energize eitl the green pilot light 11 or the red pilot light As is indicated in Figure '1, the green pilot lig is in a state of energization and, as has prel ously been mentioned, this indicates that the c cuit is arranged to reproduce sound vibratie ilragnetically recorded on the recording medir When the apparatus hereinbefore described to be employed for recording sound vibrations the record medium I8 a high frequency oscillai is necessary. Such an oscillator is diagramma cally illustrated in Figure '1 and includes an ele tron discharge device or oscillator 'tube |60 whi is provided with a nlament |68, a cathode a control grid |1|, a screen grid |12, a suppress grid |13 and an anode |14. A tuned circuiti c1uding an inductance |15 and a parallel cc nected condenser |16 is provided. The indu ance |15 and the condenser |16 are connected one end to the anode |14 and are connected their other end through a condenser |11 to i input grid 1| of the oscillator tube |68. 'I lower end of the tuned circuit is also conneci through a conductor |18, a condenser |16 to conductor |60, which is connected to the ma netic head |6 in a manner presently to be e plained. A bias resistor |8| is provided betwe the control grid |1| of tube |68 and cathode The cathode |10 is connected through a condon: |82 to an intermediate point |83 on inductar |15. This intermediate point |83 is arranged be connected through a switch |84 to the hi potentialside of a source of electric energy.

supplied through conductor |86. Cathode is also connected through a conductor |86 to the grounded side of an equalizer circuit |80.

The.equalizer circuit |86 is a filter circuit including a plurality of inductance elements |81, a plurality of resistance elements |88 and a plurality of condensers |89, which are preferably connected together in the manner shown'in the drawings. One end of the equalizer circuit |86 is arranged to be connected through a switch |90 to either the grounded conductor 61 or to a conductor |9I. The conductor I8| is connected to a condenser |92 and a conductor |93 to the output circuit of the tube |I4 in the manner shown. It is to be understood that the oscillator |68 and its associated circuits are employed only when the equipment is being employed as a recorder. When the equipment is being employed as a reproducer. as hereinbefore described, the oscillator is cut out of the circuit in a manner which will be readily apparent from an inspection of the drawings Switches 99, 90, |3|, |81, |84 and |90, as well as a switch |94, which connects the output conductor |80 of the oscillator circuit to the recording head I6, are all arranged to be moved from their full line position as shown in Figure 7 to their dotted line position as shown in Figure 'I when it is desired to operate the equipment as a recorder rather than as a reproducer. To this end, all of these switches 69. 90, |3|, |61, |84, |90 and |94 are all preferably mounted as a gang switch for operation by the control switch (Figure 1) which control switch or lever, as previously described, also controls the direction of rotation of the reels |9 and 20.

A description of the equipment and its operation as a recorder will now be made. Assume that all of the switches 89, 90, |3|, |81, |94, |90 and |94 are thrown to their dotted line positions and that the record medium or wire I8 is moving from right to left, as viewed in Figure 7. 'I'he high frequency alternating current flow in the tuned circuit of the oscillator, and particularly in the inductance |15, causes a high frequency current to be induced in the winding |96 which is connected to the erasing coil I1. Since the wire or recording medium Il is passing through theerasing head I1 prior to the time when it reaches the recording head I6, all previous magnetization of the wire or magnetization resulting from any extraneous source is removed from the wire I8 immediately prior to the time it enters the recording head I6.

A microphone is connected through a suitable lead (not shown) to the microphone plug |96 which forces the movable center contact |91 away connected to the grounded conductor 01 than a microphone connected to the amplifier through the plug I 86, a separate jack 99 is provided.' One contact 200 of the Jack |98 is connected directly to the input circuit or the second stage of audio amplification as represented by the tube 81. More particularly, the contact 200 is connected to the upper end of the potentiometer 99, which in turn is connected through a movable contact to the control grid |00 of the tube 91. The other contact 202 of the jack I 99 is through A a conductor 203. This arrangement may be confiom its engagement with its stationary seat |98 and thus causes the voice energy to be transmitted through switch 90 by a cell 9| to the control grid 82 of the first tube 83 of the amplifier circuit. The output of the audio amplier is connected to the equalizer |96, the conductor |80 and the switch |94 to the coil 19 of the recording head I6. The output of the oscillator tube |68 is also fed through a coupling condenser |19 to the same input conductor |80 of the recording head i6. This causes a superimposing (as distinct from a modulation) of the audio frequency current on the high frequency current generatedin the oscillator tube |68.

This novel system of magnetic recording is described and claimed in my aforesaid co-pending application U. S. Serial No. 423,928.

When it is desired to make a recording on the wire or record medium I9 from some source other 75 veniently used to record incoming radio programs or the like directly on the record medium I8. Since the amplification from the output of a radio, or other similar equipment, is usually considerably greater in intensity than the output which may be obtained from any microphone circuit, the rst stage of amplification in the audio amplier is skippped, when it is desired to record an incoming radio program, or the like, by connecting the output of the radio (not shown) to the Jack |99.

The jack |21, which has previously been described, is provided in the equipment for the purpose of using a separate and larger loud speaker (not shown), if desired. when the equipment is being operated as a reproducer.

It will be observed that when the equipment is set i'or reproduction, the switch |61 connects the green light 11 to the energizing winding |48 of the transformer |40. When the switch |61 is in its dotted line position, as it is placed when the equipment is being operated as a recorder, the red light 16 is connected to the energizing winding |49 of the transformer |40 instead of the lamp 11.

Associated with the switch arm 64 and the counter mechanism 43 is means for automatically moving the switch 64 to its neutral position. More particularly, the shaft 204 extends out of the counter mechanism 43 and carries on the end thereof a cam cylinder 205 which has a transverse groove 206 therein immediately followed by a transverse raised portion 201. An arm 209 is pivotally mounted for movement about the point 209 and is spring biased by a coil spring 2|0 for movement in a clockwise direction as viewed in Figure 4. The righthand end of the member 206 is provided with a cam engaging portion or protuberance 2|I which rides in engagement with the cam cylinder 20.5.

ranged to be engaged by the end 2|1 of the arm 208. as wilipresently be' described.

'.ihe cam cylinder 205 is arranged to rotate very slowly so that one revolution thereof substantially represents the entire linear movement of the wire or record medium I8. More particularly, the transverse groove 206 and the transverse raised portion 201 are arranged to be engaged by the cam follower 2li just before the wire I8 is completely unwound from the spool or reel from which the wire is being taken. When the cam follower 2|| drops down into the groove 206 the spring 2|0 lifts the left-hand portion 2I1 of the arm 208 upwardly, as shown in the drawings, to pull the switch 64 to a neutral position. It the switch arm had been thrown over in the other direction, and the unit was operating with the arm in that position, then the abutment portion 215 would be in engagement with the end 2H of the arm 208. When the cam follower 2ii strikes the raised portion 201 it will cause the left-hand portion 2I1 of the arm 208 to be pressed against the abutment 2 i5 to force the switch B4 to its neutral position. It will be observed that if the cam follower 2li strikes the groove 2|6 before striking the raised portion 201 that the end 2i? will merely temporarily be lifted off the abutment 2I5, but would not cause any movement of the connecting arm 212.

Continued movement of the cylindrical cam 205, however, would cause the cam follower 2H to engage the high portion 201 which would then effect operation of the connecting arm 2|2 in the manner Just described to move the switch arm 64 to its neutral position. The above described mechanism is adapted to prevent the wire i8 from being completely removed from one of the reels i9 or 20, which would thereafter require a rethreading of the mechanism. By suitably locating the groove 206 and the raised portion 201 in the cylindrical cam 205, it will readily be apparent that a safety mechanism for stopping the apparatus is provided when the wire i8 approaches its end on either spool or reel i0 or 20.

The above described mechanism, as will readily be appreciated by those skilled in the art, is an extremely compact and rugged equipment for recording and reproduction of sound vibrations. It has been found in practice that a relatively small spool or wire, such as may conveniently be mounted on a small portable unit, will carry suiiicient wire to record or reproduce continuously for several hours. Much longer periods of recording and reproducing may be obtained by using larger spools and longer lengths of wire.

While I have shown a particular embodiment of my invention, it will, of course, be understood that I do not wish to be limited thereto, since many modifications may be made and I, therefore, contemplate by the appended claims to cover all such modifications as fall within the true spirit and scope of my invention.

I claim as my invention:

1. A magnetic recording and reproducing unit comprising an electromagnetic head through which an elongated record medium is arranged to pass, an audio amplifier, a speaker, a high fre quency oscillator, means to connect said electromagnetic head to the input of said audio amplifier and said speaker to the output of said audio amplifier when said unit is being used as a reproducer, means arranged to connect a microphone to the input of said amplifier and to connect the output of said amplifier to said electromagnetic head when said unit is being used as a recorder, and means for also connecting aan high frequency oscillator to said head when sai( unit is being used as a recorder.

2. A magnetic recording and reproducing uni comprising an electromagnetic head througl which an elongated record medium is arrangec to pass, an audio amplifier, a speaker, a high frequency oscillator, means to connect said electromagnetic head to the input of said audio amplifier and said speaker to the output of saic amplifier when said unit is being used as a reproducer, means arranged to connect a microphone to the input of said amplifier and to connect the output of said amplifier to said electromagnetic head when said unit is being used as a recorder, means for also connecting said high frequency oscillator to said head when said unil is being used as a recorder, and switch means for simultaneously by a single operation changing said unit from operation as a reproducer tc operation as a recorder.

3. A magnetic recording and reproducing unii comprising an electromagnetic head through which an elongated record medium is arranged to pass, an audio amplifier, a speaker, a high frequency oscillator, means to connect said electromagnetic head to the input of said audio ampliiier and said speaker to the output of said amplifier when said unit is being used as a reproducer, means arranged to connect a'microphone to the input of said amplifier and to connect the output of said amplifier to said electromagnetic head when said unit is being used as a recorder, means for also connecting said high frequency oscillator to said head when said unit is being used as a recorder, switch means for simultaneously by a single operation changing said unit from operation as a reproducer to operation as a recorder, and indicating means for visually indicating whether said units are connected to be operated as a reproducer or as a recorder.

4. A magnetic recording and reproducing unit comprising an electromagnetic head through which an elongated record medium is arranged to pass, an audio amplifier, a speaker, a high frequency oscillator, an erasing head, means to connect said electromagnetic head to the input of said audio amplifier and said speaker to the output of said amplifier when said unit is being operated as a reproducer, means arranged to connect a microphone to the input of said amplifier and to connect the output of said amplifier to said electromagnetic head when said unit is being used as a recorder, and means for also connecting said high frequency oscillator to said electromagnetic head and to said erasing head when said unit is being operated as a recorder.

MARVIN CAMRAS.

I Disclaimer 2,351,005.-Maroin Camras, Chicago, III. MAGNETIC RECORDER. Patent dated June 13, 1944. Disclaimer filed Apr. 8, 1948, by the assignee, Armour Research, Foundation of Illinois Institute of Technology.

Herby enters this disclaimer to claims 1, 2, and 4 of said patent.

[Oficial Gazette, May 18, 1948.]

I Disclaimer 2,351,005.-Maroin Camras, Chicago, III. MAGNETIC RECORDER. Patent dated June 13, 1944. Disclaimer filed Apr. 8, 1948, by the assignee, Armour Research, Foundation of Illinois Institute of Technology.

Herby enters this disclaimer to claims 1, 2, and 4 of said patent.

[Oficial Gazette, May 18, 1948.]

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