The motion picture projectionist (Nov 1929-Oct 1930)

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16 Motion Picture Projectionist October, 1930 for theatrical presentation. The large picture with gigantic proportions is demanded by the public. The quality of color pictures must be improved. There has been a marked improvement in sound reproduction and recording, however, perfection is still pending. The introduction of the rear projector shutter has reduced materially the warping of film, which has been caused by the intense heat from the projector arc. Warped film will not travel through the projector mechanism in a flat plane, which is extremely necessary for perfect projection. When warped film is run through the projector mechanism, it causes the film to buckle, which causes an in and out of focus effect on the projection screen, and which is very annoying to the audience. During the days when the standard Arc lamp was in use, before Hi-Intensity lamps or reflector lamps were used, very little trouble was encountered with film buckling. This condition is now chronic. Since the advent of sound, it is more important that motion picture film receive the best, of care. Operating the standard projector arc normally at 80 amperes, there is 450 degrees of heat at the aperture. With the 120-ampere, Hi-Intensity Arc there is 700 degrees of heat. With the reflector lamp, which is also termed the Mirror Arc or Low Intensity Arc, operating at 20 amperes, there is 850 degrees of heat. The Super-Hi-Intensity Arc, operating at 160 amperes produces 980 degrees of heat at the aperture. The Hi-Intensity Reflector Arc, also termed the Hi-Low Arc, operating normally at 72 amperes produces 1175 degrees of heat at the aperture. These different degrees will give an idea how the heat at the projector aperture has increased during the past seven years. 50% Heat Reduction The rear shutter, which can now be installed on the Simplex or Motiograph projector mechanisms, reduces the heat at the aperture approximately 50 per cent, and the film is not warm after passing the aperture. Some theatres have installed a blower system, which blows cool air towards the projector aperture, which reduces the heat about 10 per cent. With the use of the perforated projection screen a certain amount of illumination is sacrificed. It is necessary to make up for this loss, by increasing the amperage, which also increases the heat at the aperture. Manv theatres are now increasing the size of the projection screen, which also requires greater amperage to obtain sufficient illumination. Many of the first-run theatres have installed the Super-Simplex and the new Motiograph mechanisms which are equipped with rear shutters. Other theatres, which have the regular Simplex mechanisms, have had the rear shutters installed for the purpose of reducing the heat at the aperture. THE Photo-Electric cell amplifier requires greater attention than any other part of the sound reproducing equipment. This is a very feeble circuit and it is important that all connections be absolutely tight; otherwise, a noisy output will result. The Western Electric system employs two sets of "F" batteries, which supply current for the p. e. c. amplifier filaments and also the exciting lamp filaments. One set of batteries usually takes care of two p. e. c. amplifiers, and also two exciting lamps. We requested, some time ago, that the photo-electric cell amplifier switch remain closed at all times, so as to eliminate the click, which was very perceptible, when closing the switch, during the time the other projector was in operation. The sudden load placed on these batteries caused this click, when the switch was closed. This trouble has been eliminated by separating this supply, so that each projector employing a p. e. c. amplifier would have its own power supply from an individual battery source. Some time ago, I mentioned that the rheostat controlling the filament circuit of the p. e. c. amplifier should never be varied during the time the amplifier was in operation, as this would cause a crackling noise. There is very little that can be done to overcome this condition, with the excep [ILAUCNT STARTING CUAACNT SWITCH vjwwl i^N— a *I2 v Schematic of "Western Electric 41-A amplifier tion of being careful, as the amplification is very great at this point, and any slight variation in current by the use of variable resistance will cause a crackling noise. Every projectionist should be quite familiar with the fact that the 239-A vacuum tube filaments are connected in series in the W. E. photo-electric cell amplifier and also the W. E. 41-A amplifier. Recently during my visit to a theatre, the sound cut off. I visited the projection room and found the projectionists hunting every place, but the right place for the trouble. The milliammeter on the 41-A amplifier was at zero and one projectionist was testing fuses in the charging panel. The other projectionist blamed the trouble on a loose connection somewhere; in other words, the projection room was a madhouse. I immediately secured a good 239-A vacuum tube and replaced the dead tube, and the performance continued. On almost every occasion, when the milliammeter on the W. E. photo-electric cell amplifier, or the 41-A amplifier, falls to zero, the trouble can be traced to a burned-out vacuum tube. I have found it to be a practice, if the projectionist does suspect that one of the 239-A vacuum tubes is burned out, that all tubes are replaced in that particular amplifier, instead of finding the dead tube. Locating a dead tube in these circuits is not a difficult job. Grid Leaks and Condensers Defective grid leaks and condensers are likely to cause trouble. Distortion, crackling and popping noises can be caused by defective grid leaks and condensers. As the grid element of 239-A vacuum tubes in the p. e. c. amplifier circuit is extremely sensitive and controls the entire action of the tube by letting more or less plate current pass in synchronism with the fluctuations of the voltage applied to it, the grid circuits must be in good condition if satisfactory reproduction is to be expected. Trouble Shooting Hints No doubt every projectionist has had the disconcerting experience of having spent considerable time in making repairs and adjustments on sound reproducing equipment. I am relating a few practical experiences, which have happened in the field, and which should be carefully noted. The Fox Palace Theatre, Wichita, Kansas, reports the following: "With the exception of replacing tubes, performances have been delayed only for a few minutes. All repairs have been taken care of before or after show time. Have experienced a great deal of trouble in picking up machine noises in the movietone amplifier, which is caused a great many times by microphonic tubes in the amplifier. Had some trouble with a low current reading on the 43-A panel, which was caused by a bad switch located in the front of the 43-A