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1954-55 Theatre Catalog, 12th Edition, Page 297 (261)

1954-55 Theatre Catalog, 12th Edition
1954-55 Theatre Catalog
1954-55 Theatre Catalog, 12th Edition, Page 297
Page 297

1954-55 Theatre Catalog, 12th Edition, Page 297

draft is employed in the vent pipes to carry off the arc gases, the chimney damper should be installed just above the lamphouse chimney base in the exhaust piping to permit draught reg ulation to a point where no arc disturbance occurs.

It should be borne in mind, however, that in order to keep the temperature inside the lamphousei as low as possible, this ventilation should not be completely choked. A good rule to follow is to open the damper as wide as possible without draft disturbance to the arc.

A six inch chimney outlet is provided on the Magnarc and all additional piping in the booth should be six inches or larger, if proper ventilation is to be had. Where forced ventilation is not employed, care should be taken that no down draft will occur, as it will cause equal disturbance to the arc.

Carbon Trim Alarm

The carbon trim alarm feature is regularly furnished as standard equipment only in the ttDeluxe2 models of the Magnarc. The aim of this feature is to provide a visible warning to the projectionist, after a changeover has been made to the second projector, that insufficient carbon remains in the lamp just extinguished to last another reel.

The time period for the lighting of both the positive and negative light is adjustable. Adjustment of the positive, is by means of the adjustable pointed rod that operates the switch, the limits of which can still be increased or decreased by moving the positive switch position forward or backward from its central position on the lamphousc base. Additional switch mounting holes are provided in the base panel to permit this.

The negative time period may be adjusted by changing the position of the bakelite stud, on the negative feed rack, which operates the switch.

Rear Shutter Interference

When an installation is made on projectors having certain types of ttbarrel" rear shutters, it will be found that approximately 351/2 inches will be the shortest working distance that can bc


THE Peerless Magnarc seen above in an openclosed view. is designed to operate 1mm 40 amperes. 27 volts. to 75 amperes and 45 volts.

obtained between the reflector vertex and the aperture of the mechanism because .of the added space that must be provided between the lamphouse front and the rear shutter assembly to allow for the opening of the film gate for threading.

At its correct working distance the light speed from a genuine glass Peerless Magnarc Reflector is F-2.1. In a cone of light this "Fit speed, the widest vertical included angle of light that will paSs through the projector mechanism aperture is 26-3/5 degrees, beginning at an apex point on the optical axis line that is 1-9/32 inches beyond the aperture. Hence, to prevent excessive light loss and shading on the screen picture field the refiector light beam must have free passage to the aperture within a similar conical area, without interference from the projector mechanism rear shutter housing, rear shutter hub or wings, sight box, and aperture heat shields.

As some types of ttbarrel" rear shutters, vertically, can not pass a cone of light having more than an inclined angle of 22 degrees, begining at an apex point on the optical axis line that is 1-17/32 inches beyond the aperture opening, such ttbarrel" sutters inherently cause a higher light loss than will result from operating the redector at the 351/2 inch distance mentioned above.

The conventional ttdisc" and ttsaucer" type rear shutters and their housings generally permit free passage of a cone of light having a circular included angle of 30-2/3 degrees, beginning at an apex point on the optical axis line that is 1-3/32 inches beyond the aperture.

Focusing Arc on Image Screen

Because it is possible to operate the Peerless "Deluxe" and ttSpecial" Magnarc Lamp on such a wide range of current, from the so-called 1-K.W. trim using 40 amperes to the 8 and 9mm trim using 75 amperes, two different are image screens are available. One screen is exclusively for use when the 1-K.W.

(40 amperes, 27 volts) carbons are used and the other screen should be used with the regular carbon trims having current ranges of from 42 to 75 amperes.

We draw particular attention to the above, to be assured that the correct indicator screen is used before proceeding with the adjustment of the arc imager unit as follows:

Close the projector knife switch and by turning the knob plate, strike the arc and separate the carbons about onefourth inch. After a crater has formed push inward on positive carbon knob, plate, and manually adjust the positive carbon until its crater face is in the same vertical plane as the front edge of the carbon guide chute plate. Observe whether the projected image of the carbons arc is in the approximate center of the screen. If not, loosen the mirror swivel screw and adjust mirror. Retighten screw after adjustment to hold mirror at the correct angle. Observe whether the projected image of the positive carbon coincides with the vertical line marked ftpositiveii on the arc image screen. If it does not, the image may be placed on the line by slightly IOOSening the three upper screws that hold the arc image lens assembly to the lamphouse top and rotate the assembly clockwise or counter-clockwise around its axis, and retighten the three mounting screws. Before making this adjustment, see that the positive carbon crater itself is in the correct position, namely, in the same vertical plane as the front edge of the carbon guide chute plate. The negative carbon should then be adjusted by hand until the image of its end is even with the vertical line marked "Negative" on the screen.

For satisfactory operation of the arc feed it is essential that the images of the ends of the positive and negative carbons be maintained exactly on these lines.

Function of Arc Stabilizing Magnet

The adjustably mounted arc stabilizing magnet makes possible for the first time, in high intensity arcs employing copper coated carbons, a means for the
1954-55 Theatre Catalog, 12th Edition, Page 297