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1954-55 Theatre Catalog, 12th Edition, Page 328 (292)

1954-55 Theatre Catalog, 12th Edition
1954-55 Theatre Catalog
1954-55 Theatre Catalog, 12th Edition, Page 328
Page 328

1954-55 Theatre Catalog, 12th Edition, Page 328

Simple Conversion

The positive motor feed of the Excelite contains a 216 to 1 integral gear reduction. This reduction is easily increased to 300 to 1 for proper burning for the 11 mm. carbon. The second interchange is in carbon contacts. The 11 mm. contacts are used for 11 mm. carbons and the 10 mm. contacts haindle either the 10 mm. regular or 10 mm. Hitex carbon. One set of positive drive rollers operate to feed the 9 mm. or 10 mm. carbons and another is available for the 11 mm. carbon.

The other component is the feed for the negative carbon. As the negative carbon increases in size for use with the higher currents that are burned, the burning rate of the negative becomes slower. The .average burning rate for a negative carbon of five-sixteenths or eleven thirty-seconds inch diameter, such as used between '75 and 105 amperes, is about three and one-quarter to three and one-half inches an hour. With the three-eighths or seven-sixteenths diameter carbon needed for burning between 115 to 135 amperes, the average burning rate is two and one-half inches an hour. This difference in the burning rate in the negative necessitates the

the standpoint that the arc flame was in close proximity and also that products of combustion released from the burning arc were apt to collect on the reflector thereby reducing its reflectance and through absorbance of more heat result in breakage. When the design of this lamp was contemplated a provision was made whereby a stream of air was directed over and above the arc for a three-fold purpose;efirst, to stabilize the arc and maintain a prescribed system of ventilation of the area surrounding the are that was not subject to the external draft conditions of the smoke pipe; secondly, to chop off the tail flame and prevent it from reaching toward the reflector, thereby cutting down the heat that reached the top of the reflector; thirdly, to supply enough oxygen in the vicinity of the arc so that no black soot is produced as a byproduct' particularly when the arc is struck, and to keep the white soot, product of combustion, from collecting on the reflector in any quantity that wold be suflicient to absorb heat and cause breakage.

Another New Feature

Another feature that was engineered into the Excelite is the automatic

THIS LAMP has an automatic crater positioning control system which insures proportion to maintain a correct arc gap length and to keep the position of positive carbon crater in exact focal point.

interchange of the negative lead screw which feeds the negative carbon. A change to six and one-quarter thread lead screw in place of the 5-thread lead screw which is furnished for use at the lower amperage, is required. These four components can be interchanged on the lamp, converting it from one range of current to another in .o matter of approximately 20 minutes.

Glass Reflector

The development of the Excelite lamp took into account the fact that at higher currents there was .a considerable strain placed on the glass reflector from

crater positioning control system which insures that both carbons are fed in the correct proportion to maintain a correct arc gap length and to keep the position of the positive crater in the exact focal point of the redector. This insures that throughout the presentation on the screen the light will always be of the same color, without

variations from white to either blue or

brown. This automatic positioning system is the very essence of simplicity. It entails no photoelectric cells, with their complicated amplifiers, but rather makes USc of the fact that the arc itself has sutlicient energy to directly

drive the contacts which are operated by a bimetal lever. This lever is sensitive to the heat image of the arc .as projected on the compensated bimetal element. The bimetal element and contacts in turn control the speeds of both the positive and negative motors in such a fashion that the total carbon feed remains practically a constant. Variation is made in such a way that when the positive carbon is speeded up to correct a slight error in position in relation to the redector, the negative carbon is correspondingly SIOWed down so that the light on the screen will remain a constant and of the same value. Inferior carbon positioning systems could be devised which would take effect on the positive carbon only but they would change the volume of light on the screen when the compensating action was taking place.

Variable Ratio Feed Lamp

The Excelite is a variable ratio feed lamp; that is, it can be set by the operator to feed at any current. Variation as desired in the arc-amperage can be easily obtained as there is the necessity of operating only one chief control adjustment on the lamp, the direct re sult of the positioning system controlling both of the feed motors. It is only necessary to operate one control which is calibrated in inches of speed of positive carbon per hour. The operator can. set this control so as to make most economical use of the carbons consistent with the length of the reel he is projecting. If the screen is of such a size that sufficient illumination is obtained for three double reels from a positive carbon and a reel runs 18 to 20 minutes the carbon burning rate control can be set at approximately 17 inches positive carbon feed per hour. Thus there is automatically obtained three double reels from one positive carbon as the Excelite will burn about 17 inches of positive carbon continuously out. of .a 20 inch carbon. It there are one or two reels which run 23 or 24 minutes by simply turning this carbon feed selector to a lower rate, say approximately 14 or 15 inches per hour, it is possible to sufiiciently extend the life of the carbon. This adiustment can be made at any time and while the arc is burning without separately setting up the feed of both the positive and negative carbons as would be necessary with older type lamps. Also in the case of running short of carbon in the trim and when there is only enough to last 10 minutes and the reel has 12 minutes to go, the rate of the feed can be slowed from 17 inches an hour to 14 or 15 inches an hour, and thereby get enough burning time to finish the reel without running out.

Such rapid changes in the burning rate of the positive carbon, to enable the projectionist to use carbons more efficiently, are not possible on older type lamps because you also have to change the burning rate of the negative carbon, and such adjustment rcquires from five minutes to half an hour, depending on the skill of the projectionist. On the Excelite lamp there is only the one

1954-55 Theatre Catalog, 12th Edition, Page 328