American cinematographer (Oct 1933)

218 American Cinematographer • October 1933 Newly Designed Sound Head of the Cinema Sound Equipment Company New Studio Recording- Head A NEW studio-type recording-head for double- system sound-recording has just been announced by the Cinema Sound Equipment Company, of Hol- lywood. According to Chief Engineer R. C. Wilcox, of this firm, the new head incorporates many improvements over previous models. “A great deal of attention,” he states, ‘‘has been paid to the constructional details of the new model; in selecting the best materials and designs possible. The drive shaft is of nickle alloy steel, S. A. E. 2335, a tough non-warping steel. Two multiple thread worms on the shaft were cut integral with the shaft. These two worms drive the feed and sound sprockets through accurately cut bakelite gears. The spindles, also of nickle alloy steel, which carry the two sprockets are of a large diameter, precision ground, and fitted to sleeve bearings. The sound sprocket shaft has a bearing on both sides of the flywheel to eliminate possibility of the shaft bending. A 17 Vi lb. flywheel on the record- ing sprocket shaft assures uniform film travel, the flywheel being driven through a set of felt dampened springs. ‘‘Cast bronze was used for both sprockets. The sprockets are precision cut and then chromium plated to prevent wear from film friction. It is an accepted fact that the larger the sprocket, the more accurately it may be cut and also the percentage of error per tooth is inversely pro- portional to its diameter. For these reasons forty tooth sprockets were used. ‘‘The driving mechanism is simple, there being but three pairs of gears, a worm and wormgear for each of the sprockets and a pair of spiral gears to drive the footage counter, which is of the three figure, reset type. The lubrication problem is also simplified by the minimum of gears and bearings. Two oil cups at the top of the box carry oil to both the gears and the sleeve bearings of the sprocket shafts. The bearings have oil grooves to properly distribute the lubricant throughout their length and are of ample size to last for years without attention other than periodical oil- ing. The motor drive shaft runs on ball bearings which are packed with the proper grade grease before delivery. ‘‘The head is driven with a 1-12 h. p. motor connected by a flexible coupling. There is also a flywheel on the motor shaft to minimize motor shaft hunting. Either an A. C.—D. C. interlocked motor is supplied as the driving means, or a 220-V. 3 phase synchronous motor or a 1 10-V single phase synchronous motor. When the A. C.—D. C. interlocked motor is used, a heavy duty control rheostat is located in the base, and a tachometer is provided in the head to check the motor speed. ‘‘To eliminate the possibility of film buckles through the failure of the magazine belt to operate, an automatic belt tension device is incorporated. Through this device, the tension of the belt is automatically adjusted to maintain the same pull on the film at all times regardless of the amount of film in the magazine. ‘‘Oversize film, hold down rollers of the camera type as- sure proper film travel on the sprockets and, because of the ample size of the box, threading is easily accomplished. The head is designed to use Bell and Howell magazines, but other types of magazines may be used if desired. ‘‘The film shoe is of such design that the emulsion sur- face of the film does not touch the shoe. This is done by placing the shoe so that the celluloid side of the film con- tacts it, and not the delicate emulsion. By reason of this, scratching of the film is limited to the celluloid side and because of its relative toughness is negligible. In connection with the special film shoe, an optical slit is provided,-the aperture of which is located .002 from the film so that nothing touches the emulsion surface during its travel through the head. ‘‘Another optional feature of the sound head is the inclu- sion of a photo electric cell placed directly behind the film shoe for monitoring of the track as it is being recorded. When this is built into the head a thoroughly shielded pre- amplifier of two stages is provided in the base of the box. ‘‘Another new piece of equipment which goes to make up the head is a new 200 V. glow lamp. ‘‘While the sound head and associated equipment was designed primarily for studio work, it is not so large and heavy as to prevent its use in a sound truck.”