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MAINTENANCE OF SOUND EQUIPMENT 617
tion alone, not followed by adjustments, is meaningless. Minor matters, such as cleaning and lubrication, are at tended to in the course of inspection. (27) Matters thaL cannot be cleared up promptly are noted on the form or list, which of course is never finally filed for record until every repair it indicates has been completed.
Soldering
(28) This factor in sound repairs is important enough to rate repeated attention, particularly since many projectionists fail to realize that what is good soldering in power work may be atrociously bad soldering in sound work. Soldering is used in power lines very largely to prevent the connection from opening, not particularly to secure low-resistance contact. The comparatively large voltage and current of a power line are not troubled by slight corrosion, or minor variations of resistance. But sound current may be as small as a micro-ampere (a millionth of an ampere) and sound voltages are very often of the order of one volt. Consequently slight variations m the resistance of a sound connection may create noisy sound, and a prolonged headache in the trouble-shooter who tries to run down the cause. Appreciable or even slight corrosion may result in complete loss of sound.
(29) Sound soldering is seldom done with an open flame. A copper is used, hot enough for the work. It is bad practice to melt the solder and let it drop on a cold wire. It is good practice, wherever possible, to heat the wire and let it melt the cold solder. Occasionally the contact stud of a condenser or transformer will refuse to heat readily. Prolonged application of the copper is dangerous in such cases. The stud may refuse to heat to the proper temperature until the internal wires or insulation have been seriously damaged. A hotter copper should be used. Open flame should be used only with great caution.
Sound connections are not made with acid but with rosin. Acid may cause corrosion.
A person experienced in sound soldering can safely create a physical connection by splicing two wires, or a