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Author Topic: carbon rods Don Sneed Master Film Handler Posts: 451 From: Texas City, TX, USA Registered: Aug 2001 posted 02-23-2002 02:45 PM                        I have a question...When I first started as a projectionist in 1970, the booth I operated use a MG system (motor-generator) I always thought this to be DC, was this a DC or AC system ?? I later went to another theatre that use a MG system and a tube rectifier as a back up system that I only has to use once when the brushes went out on the MG....so that theatre had to be DC.....whoaaa weeee, we all learn something new everyday....  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 02-23-2002 02:52 PM                     The Hertner and other MG sets were a rotary Ac to DC converter as such your arcs ran on DC In countries with 50 cycle mains and projecting at 25 fps AC arcs are fine as shutter beat interferance frequencys are not a problem So all that is needed is some sort of current limitig ballast such as a large choke or resistor In 60 Hz countrys it is necasary to run an AC arc at a multiple of 24 to eliminate a beating flicker (much like the effect of a xenon running with a bad diode) Ashcraft made a special MG set for the Cyclex lamps to generate 96 HZ supply  |  IP: Logged Stan Gunn Expert Film Handler Posts: 176 From: Clematis, in the hills near Melbourne Australia Registered: Aug 2000 posted 02-23-2002 10:08 PM                        The transarcs used here were just droopy transformers,a bit like an AC welding supply. A lot of the early lamps were hand feed, auto feed comeing later, most of the lamp houses made in OZ were AC or DC kinky A. (edit)We also had many mg sets in service also. ------------------ KALEE FOREVER. CARBON ARC, THE ONLY LIGHT FOR THE STARS! ALL PARTS FOR VICTOR AND KALART VICTOR 16MM PROJECTORS.SERVICE TO 35 AND 16MM PROJECTION EQUIPMENT. 35MM sprockets made to order.  |  IP: Logged Gordon Bachlund Jedi Master Film Handler Posts: 696 From: Monrovia, CA, USA Registered: Aug 1999 posted 02-24-2002 10:16 AM                        In all likelihood you were working with DC lamps. I encountered several installations in which the motor-generator set was marginally undersized and a rectifier was added in parallel with the m-g set output. In this way, when both lamps were lighted, as just before a changeover, there was no perceptible loss in screen illumination, as the rectifier was assisting the m-g set in maintaining what was essentially twice the normal lamp current.  |  IP: Logged

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