International projectionist (Jan 1959-Dec 1960)

AUDIO VISUAL EDUCATIONAL • INDUSTRIAL • COMMERCIAL Tips on A-V Equipment Procedures By JOSEPH F. HOLT MANY cases of annoying "hum" in the sound of 16-mm projectors may be traced to aged filter condensers in the voltage supply to the exciter lamp. Many, if not most, projectors make use of a small oscillator which provides AC voltage at a frequency above the audible limit of the human ear, i.e., above 20 kilocycles or so. If the filter condensers are defective, such a condition may be readily determined by placing an opaque card over the sound scanning point. If the hum is originating in the exciter oscillator, this step will readily indicate such to be the case. Correction involves replacement of the appropriate condenser by a qualified person, which usually means the service department of a distributor. We recently had occasion to provide a sound channel for a 16-mm program in a large hall being used for an emergency program on a one-time basis. The arrangement of the hall and seating was such that amplifier-to-speaker cable layout was lengthy and timeconsuming. The solution in this case was found in matching the projector amplifier to a wireless oscillator which uses the standard broadcast AM band for transmission of signals within one room. At the screen end, an AM tuner was used to feed two power speakers, and the results were acceptable. Perhaps some of our readers may want to make use of this arrangement; they should encounter little difficulty in doing so. Proving just once again the truth of the maxim, "Where there's a will there's a way." \Iosi modern A-V equipment is fabricated of the very best components which will resist the invasion of moisture. Accidents do happen, however; and if apparati is inadvertently subjected to damp conditions, it is possible to dry out the parts by judicious use of the small infrared lamps available almost everywhere. These lamps may be mounted above amplifiers while the chassis is inverted, or they may profitably be placed at the side of the chassis with the underside exposed to the rays. It is necessary to exercise caution in the application of heat, and something in the region of 170° F. at the chassis will produce effective drying without causing the wax seals of certain condensers to ooze out. If the wax should flow, incidentally, it is good procedure to replace that affected part in order to avoid future moisture problems. Doesn't it make sense to check after each run of film to see if any damage has occurred? It may not always be a projectionist error, and by detecting equipment conditions which result in film damage after the first occurrence, it follows that the library will be preserved longer and in better condition. Inspection should be performed meticulously by a qualified person, and appropriate records should be kept. Some sound projector users encounter serious trouble with ringing noises which seem to persist in spite of normal efforts to locate and remove them. Most people are familiar with the fact that the input tubes of many amplifiers operate at extremely "high gain" conditions and for this reason may introduce bell-like tones when subjected to shock of mechanical vibration. It is not generally recognized, however, that the exciter lamp and photocell of the projector may also be the source of ringing disturbances. To detect the source of such an Technical Data Indispensable Recently I was called into consultation by a church which had booked a 16-mm CincmaScope print. The anamorphic sent to them arrived with a mounting bracket — but without a single word of instruction! This sort of thing, which occurs regularly and not only in the church area, points up once more the urgent necessity for a source of reliable technical information and guidance. — Joseph F. Holt. noyances, turn on the projector and adjust the sound volume control to the normal loudness setting. If ringing noises are heard while the exciter is tapped with the eraser end of a pencil, insert an ordinary calling card at the point where film is scanned for sound. This is done in order to block the light path and to isolate the exciter from the photocell. If the noise is not present with the card in position and the exciter subjected to tapping, replacement of the exciter should cure the trouble. However, even a new lamp may exhibit microphonic characteristics. Noisy photocells may "ping" when any part of the projector is tapped, but will display much louder noises when the cell glass is topped. Comparison with photocells known to provide quiet operation will eliminate faulty cells. B&H "Explorer" Projector As trim as a portable radio or typewriter are the new Explorer completely automatic slide projectors by Bell & Howell. Handy carrying bar becomes basic tilt mechanism and front and rear panels swing down for immediate projection. There is no case or cover to remove. This Explorer 754Y, 500watt model features exclusive Filmovara zoom lens which fills 40-inch screen from as close as $>Vi feet or as far as 11 feet without moving projector. A built-in timer for automatic slide showing operates in time sequences from 8 seconds to a minute. The remote control unit at left advances or reverses slides, the first remote with this feature, and doubles as an illuminated pointer when aimed at the screen. The projector is fashioned in handsome black vinyl and features scuff-proof side rails that will not mar furniture. B&H "Explorer" automatic slide projector. 16 INTERNATIONAL PROJECTIONIST FEBRUARY 1959