. The Bell System technical journal . boratories. Essentially, it consists of a loop of duralumin tape suspended in a plane at right 1 Presented before Society of Motion Picture Engineers at Lake Placid, NewYork, September 25, 1928. 173 174 BELL SYSTEM TECHNICAL JOURNAL angles to a magnetic field. The tape, 6 mils wide and mil thick,is secured to windlasses A and A and stretched tight by the springheld pulley B. At points C and C insulated pincers confine thecentral portions of the tape between windlasses and pulley to form aslit 2 mils wide. Supporting this loop and adjusting devices is a
. The Bell System technical journal . boratories. Essentially, it consists of a loop of duralumin tape suspended in a plane at right 1 Presented before Society of Motion Picture Engineers at Lake Placid, NewYork, September 25, 1928. 173 174 BELL SYSTEM TECHNICAL JOURNAL angles to a magnetic field. The tape, 6 mils wide and mil thick,is secured to windlasses A and A and stretched tight by the springheld pulley B. At points C and C insulated pincers confine thecentral portions of the tape between windlasses and pulley to form aslit 2 mils wide. Supporting this loop and adjusting devices is aslab of metal with central elevation D, which constitutes the armatureof an electromagnet. The central portions of the loop are supportedon insulating bridges to lie 3 mils above the face of D; here the sidesof the loop are centered over a tapered slot, 8 mils wide by 256 milslong in this plane, opening to 204 mils by 256 mils at the outside faceof the armature. Viewed against the light, the valve appears as aslit 2 mils by 256 Fig. 1—The light valve. The electromagnet core has a similar elevation opposing D acrossan air gap of 8 mils which closes to 7 mils when the magnet is energizedfrom a 12 volt battery. A tapered slot in the magnet core begins8 mils wide by 256 mils long and opens with the same taper as theslot in the armature. When the assembly of magnet and armature iscomplete, the valve constitutes a slit 2 mils by 256 mils, its sideslying in a plane at right angles to the lines of force and approximatelycentered in the air gap. The windlasses A and A, one of which isgrounded, are connected to the output terminals of the recordingamplifier. If the magnet is energized and the amplifier supplies asine wave current from an oscillator, the duralumin loop opens andcloses in accordance with the current alternations. When one side of the wave opens the valve to 4 mils and the otherside closes it completely, full modulation of the aperture is accom- SOUND RECORDING WIT
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Keywords: ., bookcentury1900, bookdecade1920, booksubjecttechnology, bookyear1
