International projectionist (Jan 1941-Dec 1942)

This department is a collection of random thoughts and some not so random; fact, fancy and opinion relating to the man behind the man behind the gun — the serviceman. The prime purpose of this section is to promote a closer relationship between serviceman and projectionist based on a better understanding of their mutual problems through an exchange of news and views, kinks and kicks. To this end, contributions relative to any phase of the serviceman's activities are invited. EVEN if one would talk every day upon the evils of excess lubrication around sound equipment, he couldn't talk too much. Here's a case which is very pertinent and illustrates the reason why projectionists should be very careful to guard against overlubrication and always have a waste rag constantly at hand. The theatres reported motor speed varying at regular intervals. The speed of the motor would increase above normal. Everyone knows what this does to sound. I found the trouble to be due to excessive oil on the motor commutator, whence it had arrived via this route : The drive bearing had been pumped full of oil, and the excess oil had run out of the bearing and onto the flywheel. As the flywheel rotated, the centrifugal force caused the oil to rush to the periphery of the flywheel and be thrown into space. Much of the oil fell on to the motor and ran down through the brush holders and other crevices to finally alight on the commutator. Enroute the oil had picked up carbon dust, and by the time it collected on the commutator it had formed a thin paste which had shorted the commutator bars. Although in this instance the trouble occurred with one of the commutatorstyle drive motors, a similiar excess oil condition will cause just as serious trouble with an induction-type motor by collecting on the centrifugal starting switch. Oil on the latter often actually causes a motor to burst into flame, particularly when it is laden with dust and carbon. — J. J. Carroll, ALTEC, Newburgh, N. Y. A theatre reported several arc failures during the day and also during the evening performance. The cause of one failure appeared to be a burnedout ballast resistor. At another time the cause appeared to be a blown fuse. If only one failure had occurred, either of these causes might have been accepted as the basic seat of the trouble and replacement of the defective fuse or ballast lamp to be expected to provide a permanent correction. However, repeated failure on the same day pointed quite definitely to some other hidden transient defect as being at the bottom of the trouble. Investigation revealed that the mica insulator of the negative carbon holder of the No. 1 lamp was chipped and that copper deposit from the Suprex carbons had accumulated in the gap where the insulator was chipped. The copper deposit at times would cause a short-circuit to ground. When this occurred, either the fuse or the ballast resistor would burn out and the arcs be lost. After cleaning out the copper deposit, no further failures occurred. Later the defective mica insulator was replaced as a permanent correction. — J. B. Pesek, ALTEC, Chicago. Projectionists should be careful when using commercial window or glass cleaner. If the glass to be cleaned is hot, the cleaner will usually leave a permanent oil film. This is especially true of reflectors, since they get quite hot in a short time. Shop around a bit for your "Kleenex" or similar tissues. Most brands leave lint, but a few are lintless. — A. A. McCroskey, RCA, San Francisco. Many projectionists oil the pressure roller of the rotary stabilizer sound take-off by using a small paint brush with the end bent at right angles just above the brush. This usually gets oil every place but in the bearings. The method I prefer is to take a piece of wire (about No. 18) approximately seven inches long and make a small loop in the end, just large enough to hold one drop of oil. This wire is bent at right angles one-half to twothirds of an inch above the loop, the same as the brush was, so as to get into the bearing. This contains only the one drop of oil, and not a whole brush full, and drops it only at the point touched, which in this case will be the bearing. This gadget is also handy for oiling pad rollers and any other out-of-theway points requiring only a drop or two of oil. — P. C. McGaughey, RCA, Boston. • • • I keep a 25-mfd., 475-volt filter condenser in my kit at all times. To this condenser (which is of the insulated type with insulated leads about ten inches long) I have two insulated clips attached. If an amplifier suddenly develops a hum, this condenser can be clipped on the various condensers (even with the show still going) and the chances are a point is found where the hum is eliminated. This "portable" condenser is then left clipped on until a regular replacement is secured. — J. R. McLemore, RCA, Roanoke, Va. • • • It is often the little things that cause the most trouble. When the sound system is completely shut down and admissions refunded to the audience, as was the case in an emergency call I answered the other day, one is apt to start looking for failure of some large and generally considered vital element such as a transformer. The system involved in this case was a PG-105. The trouble was no sound. All terminal voltages were below normal. I found the trouble was due to deterioration of the rubber cushion supporting the first stage socket in the main amplifier. Deterioration of the rubber allowed the socket to settle, which caused one of the grid contacts to become grounded causing a sound outage. The condition was temporarily corrected by putting some rubber bands around the socket support so as to relieve the ground. — I. E. Rice, ALTEC, Charleston, IF. Va. • • • If you run into a condition of fluctuation in sound output of a PG-91 System, check the contact between the connecting clip and the tip of the tungar bulb in the power unit. — G. B. Brown, ALTEC, Downers Grove, III. • • • Th<» other day we had a case of trouble with noise. The noise coming from the screen resembled gear noise which indicated that it was being APRIL 1941 19