International projectionist (Jan 1941-Dec 1942)

neighborhood where there may be chemical fumes in the air. Another point to watch for is long-term corrosion resulting from use of the wrong flux. Use rosin flux — most conveniently applied in the form of rosin-core solder. A stronger flux does a quicker and surer job of soldering, and does not require quite so much attention to cleaning the wires in advance. Further, the stronger fluxes are perfectly satisfactory for some types of wiring; they can be used with substantial safety on heavy power wiring, for instance. But they can't be used safely on the thin wiring of amplifier interiors, because the small amount of uncombined flux that may remain after the job is done may be enough to eat through a thin wire. More important, in some sound circuits the connection does not have to be opened by corrosion to destroy its usefulness. It needs only to be weakened, in such circuits, to create seriously noisy sound. Also undesirable under war conditions is the kind of repair work that does not run down and correct the cause of a trouble, but merely replaces a burnt-out resistor or other part and lets the job go at that. Meaning that the cause of the burn-out may remain to produce a new burn-out in the future, when perhaps another replacement part won't be available. The cause should be uncovered wherever possible. High line voltage, or voltage surges, operation at excessive volume, lack of adequate ventilation, momentary weakening of some related part, incorrect wiring or fusing — all should be looked into. Trouble Causes There is always a natural (and lazy) tendency to assume that the particular part that broke down happened to be inherently faulty. The odds are invariably against that assumption. The part in question — whichever part it is — was specified by the manufacturer of the equipment not only as suitable but as providing a reasonable safety factor. It was inspected and tested according to some standardized procedure planned to show up hidden weaknesses. Of course a faulty part can get past inspection now and then, once in a hundred times or in a thousand times or in ten thousand times. Then the odds are one to a hundred, or one to a thousand or one to ten thousand that the cause of the trouble was not a fault in the part, but some definite condition in the projection room which should be run down. In this connection remember that the vast majority of amplifier parts are not subjected to mechanical wear, and therefore cannot wear out. When one fails, there is likely to be a discoverable reason. Look for it. The commonest reason is overheating, since this condition is likely to bake the insulation, which is also the dielectric material, out of condensers; similarly, overheating changes the composition, and therefore the resistance value, of certain types of composition resistors; it reduces the tensile strength of some materials, including copper; weakens the value of waxed cotton insulation; tends to destroy rubber insulation, and alters the values of some types of electrolytic condensers by promoting evaporation of moisture. Excessive applied voltage, operation at excessive volume and lack of sufficient ventilation are three prime causes of overheating. Many modern amplifiers are equipped with a switch, transformer tap, or other arrangement to compensate for incorrect line voltage. Commonly, in the past, these adjustments were set at the time of installation, and seldom or never checked from then on. Under today's conditions, the line voltage should be checked at reasonable intervals — say, once a month or so. This may be done in cooperation with the power company, if desired. The check should be complete— repeated at different hours of the day and not always on the same day of the week. The fact that your community had predominantly high or low line voltage at the time your amplifier was installed does not mean the same condition will continue throughout the war. The amplifier line voltage compensator should be reset freely whenever these tests show that a change is called for. Similarly, ventilation conditions may change, both with the seasons and with any alterations in the positions of large apparatus in the projection room. Putting in a new film cabinet, for example, has been known to damage an amplifier by blocking the air currents which formerly helped keep it cool in operation. In all periodic inspections of NO COPPER DRIPPINGS, NO NEW CARBONS No copper drippings, no new carbons— this is the order the War Production Board is expected to put into effect any day. The Board already has issued instructions for the disposition of copper drippings saved by projectionists to date. They are to be turned over to the local supply dealer. IP suggests that when this is done the theatre take the trouble to obtain a receipt from the supply dealer. When and if the anticipated enforcement order goes into effect, supply dealers will not sell carbons unless a specified quantity of copper drippings is turned in. The supply dealer will not be able to help a friend in trouble, because he himself will not be able to obtain carbons unless he shows a receipt from an authorized junk dealer for a designated quantity of scrap copper sold. equipment, note as extremely important any rise of operating temperature above that formerly encountered. Install a small fan if conditions seem to call for it. Volume should at all times be kept down to a safe level, to avoid overloading tubes and parts associated with them. In a Class A amplifier any clearly visible fluctuation of the needle of the plate current meter at high volume is an indication that the volume is too high for complete safety. Maintenance Supplies Rosin-core solder, tape, and all similar supplies needed for maintenance and repair work should be stocked now as generously as possible, while supply dealers and even hardware stores still have such things on their shelves, and are permitted to sell them. At present, theatres can obtain priority on such items if urgently needed, but the process is slow and cumbersome, and it is possible that in the future the government may withdraw the privilege entirely. Similar considerations apply to repair tools, soldering irons, test meters and so on. Since in the future they may not be available to the theatre, even under priority, and since the theatre is clearly going to have more urgent need of such items than ever in the past, buv them now. Other maintenance supplies should be procured particularly with reference to types of work which now may have to be done in the projection room although formerly they were avoided by simple replacement of an entire part. Have on hand screwdrivers and socket wrenches of all sizes and types needed to open every part in the amplifier in case occasion should arise. Lay in some empire cloth. This is linen impregnated with an insulating compound. Remember that rubber tape may not be available long. You don't want to hoard rubber, and besides it hardens in time. Empire cloth lasts forever; it is available in both sheet and tape form, and it is an extremely good insulator. Buy a meter or so, even though second hand, if you have none. What kind of meter matters less, in these times, than the mere fact that it is a good quality, high resistance instrument. If you are not sure it is in good condition have it checked by your supply dealer or sound service inspector. Almost any d.c. meter, regardless of its scale, can be made in a pinch to read almost any d.c. voltage or amperage by using suitable resistors in combination with the instrument. If you do not have all necessary meters on hand, learn how to connect the meter or meters you do (Continued on page 19) 8 INTERNATIONAL PROJECTIONIST