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This topic comprises 2 pages: 1 2
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Author
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Topic: Carbon Arcs Still Available?
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John Walsh
Film God
Posts: 2490
From: Connecticut, USA, Earth, Milky Way
Registered: Oct 1999
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posted 06-23-2004 05:25 PM
They are generally not avaiable. Usually, theaters that had them installed long ago continue using them.
At $15 a day, that's $450 a month. A 3K xenon bulb costs a bit more than that, but lasts several months, so xenons are cheaper to operate. When you add in the cost of cleaning a carbon arc lamp, it really doesn't make sense.
Many like the warmer 'look' of carbon arc, but for a regular theater running every day, I don't think it's worth it.
Since this has been covered before, you might want to check out the topic "Carbon Vs Xenon" from 02-08-2002.
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Stephen Furley
Film God
Posts: 3059
From: Coulsdon, Croydon, England
Registered: May 2002
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posted 07-04-2004 04:51 AM
Andrew, as far as I know, carbon arcs have not been made for projection for many years. A trade magazine whiich I was reading a few years ago carried an advert for the Autoarc; I think the magazine was dated either 1970, or 1971. This was probably the last carbon arc lamphouse to be manufactured, and I suspect that it was discontinued soon after this. Xenons have been available since the '50s, but were not very widely used at that time.
Early xenons had a number of problems, including high initial cost, poor colour and tendancy to explode. Many early installations had problems with inadequate or incorrect cooling airflow, or excessive a.c. ripple from the rectifiers.
Another problem was that although xenons were introduced just after the demise of nitrate, when the fire regulations started to be relaxed to permit larger spools, most cinemas still ran film on 2000 foot reels at that time. Large spools, holding an entire film were introduced in the '60s, and platters in the early '70s. Xenons are not ideal for running 20 minute changeovers; you have to either leave both lamps running all the time, wasting power and lamp hours, or re-striike a lamp for each reel, shortening lamp life. I know of just four conversiions from xenon to carbon, three of them in public cinemas. One of these was a place that had two machines, one ran the feature from large spools on a tower, the other ran just the adverts and trailers on a 2000 foot spool. This machine was converted back to carbon for this reason; it only ran for a few minutes every 2-3 hours. This place has since closed.
Sereral changes from the 1960s favoured the conversion to xenon lamps. The use of long reels or platters made them almost essential, and at about the same time, large cinemas were being split up into several, usually three, smaller auditoria. This led to a requirement for one projectionist to operate several screens, to reduce costs. This would be difficult to do with carbons.
Carbon arcs are very expensive to operate today. The carbons themselves are expensive, and good quality ones can be difficult to obtain. Carbon arc lamps are more complex, with moving parts to feed, and in some designs rotate, the carbons; they also require frequent cleaning. Many of them also require water cooling, which xenons do not, except in the largest sizes. Carbon arcs therefore also have higher maintenance costs.
A carbon arc with a good operator, good carbons and a good rectifier or generator can produce a very steady light, but it does need looking after. Moving both carbons together, in the same direction, keeping the arc length constant, but moving it relative to the mirror by just a milimetre or two can result in a drastiic change in the brightness, colour and uniformity of the illumination on streen.
I am old enough to remember when the carbon arc was almost universal for projection; it was certainly used in all of my local cinemas. One by one, the all either converted, or closed. I could always tell as soon as the picture hit the screen that a conversion had been made, the light was different. It wasn't just that the colour temperature was higher with xenons, it was just a 'different' light. I'm not even sure what that difference is. High intensity carbon arcs emit a complex spectrum, it is a combination of a continous spectrum, and a large number of lines, from various elements in the core.
Three years ago I knew of four public cinema in England running carbons; one of those had two screens. Today, only one of those is left, I've never been there, it's a long way from where I live, and I doubt that it will last much longer.
In the U.S.A. there still seem to be just a few places running carbon, but they are converting too. The Byrd in Richmond converted not too long ago, and in the last couple of weeks, somebody here (sorry, I can't remember who it was) announced their last carbon show. There will soon be none left.
Have you ever met a steam engine enthusiast? They will talk about the difference between a steam engine and a Diesel, or an electric motor. They will tell you that a steam engine needs more looking after, but it is somehow almost 'alive', more like working with a horse than with a Diesel engine. I suppose that a carbon arc is something like a steam engine.
If you have never seen, or operated, carbon arcs, try to do so at least once, while you have the chance; they won't be there much longer, and a preserved steam engine is probably going to be easier to find than an operating preserved carbon arc.
[ 07-04-2004, 02:30 PM: Message edited by: Stephen Furley ]
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Stephen Furley
Film God
Posts: 3059
From: Coulsdon, Croydon, England
Registered: May 2002
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posted 07-05-2004 04:05 PM
Andrew, the carbons themselves are measured by diameter and length. For some reason, the diameter is usually measured in milmetres, and the length in inches. Rather than giving the power of the lamp, in Watts, it is normal to specify the current, in Amperes. My Bell and Howell 609 16mm projector burns 5.5 x 6 inch and 6.5mm x 9 inch carbons, the larger size is the positive, at 30 Amperes. This is about as small as it gets. The equivilent of a 1600W xenon might be 7mm negative and 8mm positive, at about 50-60 Amperes. The Loew's Jersey, if I remember correctly, burns 13.6mm positives, and about 9 or 10mm negatives, at about 165 Amperes. Some drive-ins went higher, I think to about 220 Amperes.
These are all 'modern' high intensity arcs, the older low intensity type used larger carbons. There were many different types of arc lamps, the most common in later days was very similar to a horizontal xenon, with a parabolic mirror wiith a hole through which the negative was fed, with the positiive poiinting towards the mirror. The length of the arc gap was typically about 6-8mm.
The 'National Carbon Buletins' are available for download somewhere in the manuals section. They give lots of information.
Here in England we pronounce xenon zen-on, while in the U.S, it tends to be zee-non. I don't know about elsewhere in the world.
Edit.
If you look at my post on the 'Seeking info on the FP-20' thread thread thread there is a picture of a machine with a typical large, water cooled, rotating positive carbon arc lamphouse.
[ 07-06-2004, 01:44 PM: Message edited by: Stephen Furley ]
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John Hawkinson
Film God
Posts: 2273
From: Cambridge, MA, USA
Registered: Feb 2002
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posted 07-10-2004 12:07 AM
"AFAIK, power is power, 1600 watts is the same whether it be single or three phase."
Well, 1600W of output is not 1600W of input; the efficiency of the AC/DC conversion matters, and varies. I expect it depends mostly on the age of the rectifier. We all know that 3-phase rectifiers produce cleaner DC than single-phase rectifiers, but I don't know about efficiency. Anyone?
"A solid-state phase converter (if such a beast actually exists) might save a few watts here and there."
Well, such a beast would be an inverter, which certainly exists, but is probably not energy-efficient or cost-effective in the kW range...
--jhawk
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