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1947-48 Theatre Catalog, 6th Edition, Page 354 (340)

1947-48 Theatre Catalog, 6th Edition
1947-48 Theatre Catalog
1947-48 Theatre Catalog, 6th Edition, Page 354
Page 354

1947-48 Theatre Catalog, 6th Edition, Page 354

new duplex clutch. With the positive carbon fed forward at an adjustable uniform rate, it is imperative that the negative carbon be fed forward precisely at a predetermined intermittent rate.

Pawls and ratchets are in general unsatisfactory for this job; while singlefriction clutches tend to operate erratically. Not only must the negative carbon be fed forward precisely at predetermined intervals, but some means is necessary to lock positively the feed mechanism in position while the oscillating clutch moves into position for the next forward feeding cycle.

The C-70 duplex clutch does this job admirably. Two extremely accurate triplex roller clutches are mounted on the feed shaft: one oscillates and feeds the carbon forward; the other locks positively and prevents even the most minute slippage in the predetermined feeding rate of the oscillating member.

Each of the six rollers employed (three for each member) are ground to a tolerance of 1/10,000 inch and are hardened to resist wear. An unlimited number of feed ratios are available through finger-tip control.

This precise feeding of the carbons means that the positive carbon crater will remain at the point of maximum effective focus of the reflector, and that the negative carbon will be held exactly at the proper arc gap-that is, at a predetermined distance from the positive crater. This insures screen light of maximum brilliancy with insignificant light variation-in short, a dollars worth of screen illumination for every dollar expended on current and carbons.

Another vitally important control element in a Suprex lamp is the means employed for stabilizing the arc flame. This has been accomplished heretofore by placing cumbersome magnets of various kinds behind the reflector. Such magnets may burn out and deteriorate over a period of time as a result of

DUPLEX NEGATIVE CARBON FEED CLUTCH affords the control and renders slippage almost impossible. Shown are feeding clutch, clutch plate. adiustinq nut, tension spring, and clutch.

continuing exposure to the intense heat of the arc.

The exclusive Ashcraft C-70 method of arc stabilization utilizes a loop of steel which, mounted on the carbon guide, surrounds the positive carbon. The ends of this loop are bent under the arc a distance equal to the protrusion of the carbon through the guide.

This loop is magnetized only when the arc is burning. The magnetic flux encircling the positive carbon is collected by the loop which, through induction, exerts an upward magnetic force and thus stabilizes the are by forcing upward the gas ball at the end of the carbon. Only by this means can the magnetic stabilizing effect be exactly proportional to the current Howing in the arc.

COMPLETE MECHANICAL ASSEMBLY (with covers removed) of the C-70 is wholly outside the housing. Also shown is burner element and are stabilizer. Among other elements seen are the chain drive, roller bearings, gearing, motor, motor fuses, motor control, drip cup, arc stabilizer, and V-contacts. The entire mechanism-motor. gears, shafts, rheostais, and the like*is positioned outside lamphouse.

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The advantages of unit construction in general are so well known as to require little elaboration. In the Ashcraft C-70, however, this principle has been carried through to its ultimate conclusion as far as carbon-arc lamps are concerned. The entire mechanism-motor, gears, shafts, rheostats, and so forthare contained in one compact, neatly covered, removable element positioned outside the lamphouse. The covers are easily removed for inspection and care of the element.

In fact, there is practically nothing within the lamp housing proper except the carbons and their holders, a drip cup, and a small steel stabilizing loop. Mechanisms in close proximity to the intense heat and inevitable ash of a carbon are not infrequently deteriorate rapidly and occasion erratic arc behavior, thus nullifying the effect of even the most precise controls.

The C-70 type of unit construction is also a boon to speedy servicing should the occasion arise: the element need only be detached from the lamphouse frame (a few minutes' work) and as quickly replaced by another. Thus, a supply dealer or a group of theatres in a given area need have only one, or at most two, spare elements on hand to meet any emergency.

All manual controls, too, are outside the lamphouse, mounted compactly on a. panel on which all controls are clearly indicated. This panel also mounts an ammeter. This positioning of both the mechanical elements and manual controls outside the housing is a great convenience for the projectionist, aids operating efficiency, and is vitally important in preventing wear.

Still another aid to projectionists in maintaining maximum screen illumination is the ease with which carbon lineup and adjustment is made. The carbons do not tilt nor do they require continual manual tinkering. If either vertical or horizontal adjustment of the negative carbon is required, the carbon is not tilted but is adjusted quickly and accurately from the control panel outside the lamphouse.

A word of caution as to oiling. The C-70 feed mechanism will require absolutely no oiling for many years. Using ball-bearings on the high-speed shaft and roller-bearings on the medium-speed shaft, the C-70 utilizes a new oil-impregnated bearing on the oscillating and low-speed shaft. This latter bearing actually lubricates itself from within, being a highly compressed powdered metal which has been impregnated with sufficient lubrication for its lifetime.

The advantages of a solid cast aluminum housing, including doors, over the conventional sheet metal type are obvious in terms of lighter weight, greater resistance to denting and rusting, and general superior durability.

The arc imager is visible from any viewing angle, thus enabling the projectionist to maintain constant surveillance of arc status and of general operating conditions.

The C-70 lamp is designed for satisfactory operation without forced ventilation or any other extraordinary precaution. Openingsare provided in the housing for natural draft and are so arranged as to offer not the slightest interference to are stability.


1947-48 Theatre Catalog, 6th Edition, Page 354