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1947-48 Theatre Catalog, 6th Edition, Page 485 (469)

1947-48 Theatre Catalog, 6th Edition
1947-48 Theatre Catalog
1947-48 Theatre Catalog, 6th Edition, Page 485
Page 485

1947-48 Theatre Catalog, 6th Edition, Page 485

nent starting from the exciter lamp and ending with the stage horns. But he can adopt certain simple measures that may clear up his troubles or at least enable him to get by until the service specialist can arrive on the scene with his modern test aids.

But before I talk about these, I would like to make a plea on behalf of the projectionist who finds himself in such an uncomfortable spot. For goodness sake, let him alone as much as you can. It is pretty hard for him to make an intelligent analysis or a critical adjustment to the accompaniment of a jangling telephone or a fiow of well-meant but nevertheless disconcerting advice. If you will be calm, he may keep his head and you get your show going quickly.

Of course, we must assume that we are concerned only with a projectionist who has thoroughly acquainted himself with all of the functional operating features of his equipment. If not, he had better start to acquire this familiarity immediately. He may need it.

Another unavoidable assumption is that the projectionist in this situation has had the service representative explain to him the correct way of making ordinary replacements and adjustments, such as replacing and aligning exciter lamps, replacing tubes, checking and adjusting lateral guide rollers, replacing photo-tubes, and the like.

Still another assumption we have to make is that the projectionist we are talking about thoroughly understands the emergency switching provisions of his system. A switch for feeding the full range into the low-frequency loudv speaker when the high frequency coil opens up is of little value if the projectionist does not know where it is, what it is for, or how to use it.

Many of the modern amplifier systems have switching arrangements which enable substituting an auxiliary amplifier for the main system or the by-passing of one amplifier unit. In another case, a portable emergency amplifier system may have been placed in the booth as a feature of the service plan. None of these do much good, if the projectionist doesnt know how to work the switches or connect in the cables.

All this may sound like I am afflicted with a phobia on this matter of knowing the equipment. I am not. If I sound that way, it is merely because I have been sensitized by reports on emergency situations which could have been cleared up more efliciently if the projectionist had really known his equipment.

A projectionist should never hesitate to ask the service representative to explain to him and drill him in all of these. normal routine and emergency measures. Just as it is part of the job of the projectionist to know these things, so it is part of the service representativels job to explain them. Only by working together can they deliver the most to the fellow for whom they both work.

Still another slant on this emergency business is the necessity for the projectionist to think through the problem that he is faced with and make accurate, intelligent observations. If he does this, his chances for clearing the trouble without help are immeasurably increased. Secondly, if he can accurately


describe the symptoms and situation, he may be able to get telephone advice from the service specialist that will lead to an effective correction.

If this is the kind of a projectionist with whom we are dealing, there is not much we need add. If he has a sound outage on one projector only, he will know how to check the exciter lamp, the photo-tube, all intervening lenses, fader contacts, and so forth, associated with the offending soundhead.

If the trouble affects both soundheads, he will know how to make a quick unitby-unit, stage-by-stage check with the idea of isolating the trouble. Once he has isolated it, he must know whether he can by-pass the trouble spot or whether he must make a replacement or repair.

A simple illustration will be helpful. The sound from the stage is sour, but the sound from the monitor is perfectly normal. Where does the projectionist look for trouble? First of all, we get back to the knowing the equipment. Is the monitor horn driven by the same amplifier that drives the stage horn? If it is, the trouble is pretty sure to be somewhere in one of the units or circuits that feed the stage horns or else right in the horn system itself. If it is a two-way system, and the sound is very guttural, perhaps the high frequency coil has opened. In that case, the projectionist operates the emergency switch or connects the emergency jumpers that should be ready for just such an event.

Supposing, however, a common amplifier does not power both the monitor and stage loudspeakers. If it is one of the later sound systems, the monitor amplifier is apt to be a high gain job with enough power to take the place of the entire main amplifier system. In normal operation, its input is bridged across the input of the main power amplifier. In other words, the voltage amplifier drives both the power amplifier and monitor amplifier in parallel. In the cast in question, the tubes and circuits in the main

amplifier must be added to the suspect list. How does the projectionist find out whether it is the amplifler or the speaker? Merely by operating the emergency switches that cut the monitor amplifier into service in place of the main amplifier. If the trouble disappears, the main power amplifier must be the culprit. If the emergency amplifier is a portable one instead of a built-in unit, the substitution procedure usually will take a little longer.

If there is no emergency system, the projectionist must know whether he can by-paSS the main power amplifier. Some voltage amplifiers deliver several watts output, enough to drive the stage horns in an emergency. The projectionist must know how to feed this limited amount of power around the power amplifier to the stage horns without wasting any of it.

There are several makes of sound equipment in common use. Moreover, each make has a number of models. As a result, the number of possible combinations is almost infinite. To discuss each would take a good siZed book. Yet, all of the procedures could be summed up in the end by stating that each is nothing more than a systematic, sensible check backed by a thorough knowledge of the equipment.

To make final corrections and adjustments, and for exacting maintenance, the services of the service specialist are invaluable. The servicer is equipped with the finest tools, test films, and test apparatus that money and skillful engineering can supply. He has a special film which together with an accurate output meter enable him to make exacting adjustments of the optical system. He has accurately recorded and calibrated test films for making frequency response and power handling tests. Each film and each track is designed to give the data wanted quickly and accurately. With these, there is no need to guess as to whether the curve meets Academy specifications at every

THE PORTABLE EMERGENCY SOUND SYSTEM consist of an amplifier. phototube equalizing network, sound changeover switch. and an assortment of adaptor cables. Photolubes plug into adaptors A and B which. in turn, are inserted into soundheud phototube housings. The system, accordingly, lay-passes everything between film and stage loudspeakers, enabling the setvicer to get to the trouble quickly.







1947-48 Theatre Catalog, 6th Edition, Page 485