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-570 HANDBOOK OF PROJECTION FOR
method is to install the rectifier in an adjoining room and cut a space through the wall just large enough to admit the front panel of the rectifier. This allows the projectionist to have access to the switches for the purpose of varying the amperage, or changing over to A. C, and at the same time excluding the light from the room. Another way is to paint the bulb black, using lampblack ground in oil, thinned with turpentine. This does not in any way injure the bulb. It is in fact good for it as it will radiate the heat better.
There is but little sound from a rectifier except a humming sound which comes from the transformer. Care should be exercised that there is no sheet metal near the machine. If there is the magnetic action of the transformer will probably set up vibration therein, which will cause more or less objectionable noise.
VENTILATION. — There must be ample ventilation where the rectifier is located. Lack of ventilation will operate to greatly shorten the life of tubes.
CAUTION. — Tubes should never, under any circumstances, be operated above their maximum capacity.
COMPARATIVE RESULTS.— Experiments by Simon Henry Gage and Henry Phelph Gage, Cornell University, have shown that the losses through the pulsation of the current with the mercury arc rectifier are very slight. A mercury arc rectifier using 40 amperes at 52 volts gave 12150 C. P., whereas straight D. C, 40 amperes at 51 volts, with the same carbon set, only gave 12,350 C. P., a difference of about 200 C. P.
On page 585 you will find a chart indicating the various troubles one is likely to encounter when operating a rectifier, together with the most probable cause or causes of each. We recommend a careful study of this diagram. With this chart and the detailed instructions contained in this book, plus a fair supply of common sense, I believe any projectionist ought to handle a rectifier without serious difficulty.
GENERAL ELECTRIC MERCURY ARC RECTIFIER.— The General Electric Company, Schenectady, N. Y., manufactures rectifiers for use on projection circuits in two capacities, viz.: 30 and 50 amperes.
Fig. 190 illustrates the design of the G. E. rectifier furnished for the first time in 1910. Several hundreds of these older rectifiers are still in service, and in response to many requests we are giving instructions on them. Cuts of the