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1948-49 Theatre Catalog, 7th Edition, Page 413 (400)

1948-49 Theatre Catalog, 7th Edition
1948-49 Theatre Catalog
1948-49 Theatre Catalog, 7th Edition, Page 413
Page 413

1948-49 Theatre Catalog, 7th Edition, Page 413

Results of Electronic Controlled Arc Tests

Additional Data on Actual Theatre Use of New Forest Lamp Indicates Good Light at Carbon and Power Saving

When they were putting the finishing touches on the new carbon feeding mechanism already alluded to, Forest engineers stumbled on what looked like a startling new technique for burning the carbonseand which might be an improvement upon the so-called suprex or simplified high intensity method. It held out such bright hope for the future that the company, after announcing the production of a new lamp, temporarily withheld the lamp from the market while they went into a research and dcVelopment huddle. Engineers went to work in earnest on the discovery and with fruitful results; the end-product of their research was displayed at the. September, 1948, TESMA Show in St. Louis.

The research program included a study of the burning characteristics of the carbons with respect to the magnetic held and the amount of air required at the arc. This made possible the development of a magnetic field which maintains the bright spot area at maximum brilliancy; and the placing of special air inlet ports positioned to supply the arc with correct amounts of air.

Research also disclosed that entirely new burning characteristics could be obtained which would produce much more light with no increase in energy consumption and with a marked saving in carbon consumption.

As all theatremen know, the primary source of arc light is rare earths and chemicals concentrated in the core of a carbonetheir actual compositions are well guarded trade secrets. These are


Forest Elcctronic (.0.. Inc.

In the 1946-47 THEATRE CATALOG, J. K. Elderkin discussed the new Forest electronic-control arc lamp, primarily from the standpoint of the theory of electronic feed as contrasted with conrcntional Incchanical feeds. Actuach and drircn by solenoids rather than clutches, gears, or other fast-moving parts. the Forest electronic projcclion lam p was designed to eliminate most of the troubles arising from frictional utcar. Since that time the new lamp has been built and submitch to actual theatre tests and the results of interest to theatremen are described in the present article.

burned in gaseous form after being volatilized by electric current; and, because the flow of electrons from positive to negative, the action creates a saucershaped depression in the tip of the positive carbon. This, naturally enough, is called a crater. This crater light is collected by a redector or a condenser lens and projected through the film to the screen.

The new light source is similar to the old high-intensity arc in that the tail

SIDE VIEW of arc in action, controlled by new method of "Electronic Control". 33V., 50 amps.. dc;SM. negative. 7MM. positive carbons. The negative gases are compressed into the positive crater.

flames of both are longer than the tail flame of the suprex arc, which has a short angular one. However, the white light in the tail flame of the new electronic arc seems to burn more intensely

TOP: (Al) neg. manual control; (Bll neg. carbon speed control; (C1) reflector adjustment from front of lamp: (D1) neg. carbon holder: (El) neg. carbon guide sidewise adiustment. Center. view through back door of lamp: (AZ) pos. and neg. timer receptacles making all timer connections; (BZ) shields over pos. and neg. timer tubes; (C2) pos. and neg. timers: (D2) reflector adjustment: (E2) vertical neg. carbon guide udiustment. (F2) horizontal and vertical retlector adjustment control from lront oi lamp. Bottom: (A3) 14-inch reflector; (Bil) positive carbon guide: (C3) drip shoot; (D3) drip cup; (E3) flame shield raised: (F3) from dowser: (G3) spring tension clump.

1948-49 Theatre Catalog, 7th Edition, Page 413