American cinematographer (Jan-Dec 1945)

1 a $ & 1 3 a ‘3 r / \ i /(? |$ x'y Cine-Chronized Sound On Wire For Amateurs Description of numbered parts of G.E. Model 51 Magnetic Wire Recorder. I. SUPPLY SPOOL. Holds about two miles of 4 mil, medium carbon steel wire, grease covered for rust prevention. 2. TAKE-UP SPOOL WITH STROBOSCOPE MOUNTED IN POSITION. This spool is identical in construction with the supply spool. It revolves at 400 r.p.m. at rated line voltage of 115 volts, 60 cycle, alternating current. The stroboscope disc shown, is designed for 500 r.p.m. operation due to abnormal voltage operating conditions when picture was taken. 3. "LEVEL WINDING" LACING DEVICE for supply and take-up spools. These move back and forth across the spools similarly to the level winding mechanism of a fisherman's casting reel. 4. "ANTI-CHATTER" PULLEYS act to smooth out vibration of the wire before reachinq the recordreproduce head and after leaving it. 5. RECORD-REPRODUCE HEAD. This head performs the operation of magnetizing small sections of wire passing throuqh its slot (in the top) in di¬ rect relation to the frequency and intensity of the signal the microphone picks up. On "play¬ back," the head becomes a reproducer and re¬ verses the procedure, feeding the amplifier and speaker. 6. "ERASE" OR "WIPE-OFF" HEAD. During re¬ cording operations this head erases or wipes off magnetically any signal on wire passing through it before it gets to the record head. 7. AUTOMATIC TIMING DEVICE will stop the re¬ corder at any preselected point on the wire, or will stop the supply spool before it runs out of wire. It reads time in seconds and minutes. By LISLE CONWAY, S.M.M.A. 8. MICROPHONE INPUT for the high impedance Turner dynamic microphone furnished with the recorder as standard equipment. II ^ ITH the ending of the war will. come an almost entirely new de" ^ vice for the amateur movie maker and the professional cinematog¬ rapher to experiment with— the “soundon-wire” or the magnetic wire recorder and reproducer. This device, the de¬ velopment of which has been spurred by the exigencies of war, has come to the fore as an important means of quickly and easily obtaining sound recordings from almost any location that 110 volt, A.C., power can be had. Even without this power source the recorder can be r operated in the field from a battery vibrator power supply. The combination recorder and repro¬ ducer is a complete, self-contained unit, weighing only a little more than the average portable typewriter and but slightly larger in size. Microphone, mi¬ crophone cable, amplifier, recording and reproducing mechanism, along with a built-in speaker and power cord are complete in one case. Essentially the recorder performs the operation of magnetizing small sec¬ tions of wire flowing through its re¬ cording head. These sections are mag¬ netized in proportion to the frequency and intensity of the sound wave which the microphone picks up. The wire used, only .004" in diameter and loaded on a 3% inch spool, is about two miles in length. It will record over a half hour of speech and music continuously when run at normal speed. However, when recorded at half speed over an hour of speech may be recorded with some re¬ duction in quality. After recording and rewinding, the wire is run through the combination recorder reproducer head and its magnetized sections furnish the magnetic energy, which in turn, operates the amplifier and speaker to render a reproduction of the sound originally recorded. This recording may be played back over and over again without any apparent loss of quality. When the re¬ cording is no longer desired it may be wiped off or “erased” while a new re¬ cording is made on the same section of wire simultaneously. Recordings may be made and played back indefinitely >n the same wire. (Continued on Page 312) 9. FIRST STAGE INPUT. This jack may be used to feed the recorder from an outside source other than the microphone furnished. It is a high im¬ pedance input and may be used as a "bridging" input — although the use of a matching trans¬ former* with a bridging primary and 50,000 ohm secondary is recommended for this purpose. 10. OUTPUT JACK. A V/j ohm speaker may be driven externally from this jack, or through the use of a matching transformer any P.M. speaker or line may be fed from this point. When this jack is used, the built-in speaker (18) is discnonected from the circuit. 11. ADDITIONAL SPOOL OF WIRE. Additional spools of wire may be used interchangably by slipping off the regular supply and take-up spools and slipping on new supply and take-up spools. 12. METAL SHIPPING CAN. This metal can. bearing a label and a place for stamps may be used for storage of recordings or for shipment of same from point to point. 13. IMPEDANCE MATCHING DEVICE (UNIVERSAL). This device, designed and constructed by the author, enables the recorder to record from either a 500 ohm line or a 50/250 ohm micro¬ phone in addition to the regular high impedance microphone furnished with the recorder. Through the use of this device the recorder will also feed from its V/i ohm output into multiple, three windinq transformer so that P.M. speakers of 4, 6, 8, 16, and 500 ohms may be fed (by usinq selector switch) in addition to a 500 and 250 ohm line. 14. FRONT COVER OF WIRE RECORDER. The front cover releases by a spring tension button on its lower right hand side and lifts off similarly to a typewriter cover on a portable. 15. TURNER MODEL 22D HIGH IMPEDANCE MICROPHONE furnished as standard equipment with the recorder. Approximately ten feet of microphone cable is also included. 16. DESK STAND FOR MICROPHONE also included with recorder. 17. NEON GLOW LAMP used to indicate overloads of signal during recording by flashes. 18. BUILT IN SPEAKER Utah 5". P.M. type, 3'/2 ohmvoice coil for monitoring on playback purposes. 300 September, 1945 American Cinematographer