International projectionist (Jan-Dec 1947)

0 THE EDITOR gHMNMBMHMH9 Anent the Forest Electronic Lamp To the Editor of I. P. I read with considerable interest the articles relative to the Forest Electronic Arc Control which have appeared in I. P.1 I wonder if Dr. Lee de Forest, who I believe founded this company, would have approved of this multiplicity of gadgets to handle a Suprex arc. The old high-intensity thermal control did practically all that the Forest Control does and it certainly wasn't any more complicated. Perhaps I am wrong in my assumption, but why employ such elaborate means of regulation? Granted that the arc lamps now in use are outmoded in the sense that they function not unlike a hand-feed job more or less of the time, it seems to me that the Forest Control still requires simplification to obtain proper results. I can think of one means of accomplishing this, although I do not know whether it has yet been tried out. Suppose we used two photocell and exciter lamp assemblies so arranged that a beam of light crossed the paths of the positive and negative carbon peaks. This setup could be so adjusted that when the carbons were not in exact position the motor controlling the unit would operate, thereby putting the carbons in correct alignment. Until the carbons burned down sufficiently of course, there would be no motor action. Suggests Other Control Means There would be separate motors for both the positive and negative carbon carriages, with a direct drive for the feed screws to instantly advance the carbons the required amount. Of course, there are several obvious disadvantages to such a 1 "The Forest Electronic Arc Lamp," by J. K. Elderkin; Sept. and October, 1946, issues of I. P. Negative Carbon Drive Solenoid^ Negative Sleetronlo Timer, 110 Volt A.O. Supply 22 system, one such being the, actinic rays from the arc itself which might interfere with precise photocell operation. However, ultra-violet light or some other wavelength could be employed with wholly satisfactory results. There are many radio principles that could be used to do the same job. I may sound a bit like the conventional carping critic, and I certainly do not wish to detract from the merit of the job accomplished by Jim Elderkin in this instance. However, since I do feel that the system could be much more simplified. I see no reason why I or anybody else who thinks so shouldn't stand right up in meeting and say so. Joseph E. Bliven LA. Local Union 439, New London, Conn. The Forest Viewpoint To the Editor of I. P. We are always glad to have the comments and reactions of projectionists, since they are the boys who have to live with the equipment and they are certainly "in the know" when it comes to seeing the faults as well as the attractive features of projection equipment. I am afraid that I will have to differ with Mr. Bliven on several of the points he makes. Dr. Lee de Forest was not the founder of Forest Manufacturing Corp. nor has he at anytime had any connection with us. However, knowing Dr. de Forest as well as I do, I believe that his reaction to the Forest Electronic Arc Control would be exactly opposite to that expressed by Mr. Bliven. I believe that the eminent Doctor would Poeitlve ?arbon Drive Solenoid^ L. £ Positive Electronic Timer D.C. Arc Supply Schematic wiring diagram for Forestelectronic projection arc lamp. look upon the Forest Control with gieat favor. Certainly he has always been electronically-minded and certainly he always sought the simple and positive solution to any problem at hand. Extreme simplicity is one of the chief advantages of the Forest Control. I cannot agree that the old highintensity thermal control would do practically anything the Forest Control does. Obviously, the only true test of a given unit of equipment is its behavior in operation, and it is easily understandable that having had no opportunity to operate or even inspect the Forest Control, Mr. Bliven would not be fully familiar with its extreme simplicity and very positive action. Great Simplification Noted Mr. Bliven acknowledges the deficiencies of existing arc control means, particularly when he states that present lamps must be hand-fed "more or less of the time." Mr. Bliven' s appreciation of the Forest Control would be heightened, I am sure, if he knew that it accomplishes che elimination of approximately 250 parts now used in existing lamps. The Forest feed mechanism is reduced to a simple carbon carriage with its worm screw driven directly from a solenoid without the aid of any reduction gears or clutches. The Forest Control is a constant feed as contrasted with other lamps the feeding means of which impart a jerky movement to the carbons. Other lamps have a mechanical pickup which feeds the carbons up at too fast a rate and then waits until the carbon burns away, inevitably too far, before it again feeds up. This means that the arc gap is never at the proper distance but is either too short or too long. Cites Meter Steadiness For example, with existing lamps an ammeter in the arc circuit will vary constantly plus or minus from 3 to 5 amperes. On the Forest Control the ammeter needle stands practically still at a constant reading. The implications of this fact in terms of more even burning and consequent even light intensity are so obvious to all projectionists as to require no extended comment herein. The Forest Control feeds the carbons at their precise rate of consumption so that they cannot burn away from the exact focal point. The necessity for handfeeding, as mentioned by Mr. Bliven. is thus eliminated. Existing arc lamps depend upon the arc gap being incorrect before the mechanism operates to correct the condition. As the arc gap widens the motor speeds up in an attempt to reduce the gap. When the arc gap is too short the carbon simply has to burn away to a point where the gap is again too wide. The Forest Control is new and novel (Continued on following page) INTERNATIONAL PROJECTIONIST January 1947