Film-Tech Forum ARCHIVE: Projector #2 brightness

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Posted by James S. Mellen (Member # 2139) on 03-19-2005, 01:58 PM:

We have a couple of Xetron XCN-35 consoles w/christie bulbs. Projector #2 has never been as bright as #1 even when they both had new bulbs. Now, the bulb in #2 has failed prematurely (It had a bad connection internally at one end, got very hot and failed with only around 60 hours on it). I installed a used backup bulb but it is just not bright enough to use. I tried re-aligning the whole system using a dummy lens with a 1/4" hole and a 1/4" shaft. It was out of alignment, but now that is properly aligned, it helped only slightly. It gets brighter as I move the bulb forward, but then I hit the stops. Any ideas? Thanks!
Jim

Posted by Rick Long Jr (Member # 541) on 03-19-2005, 02:39 PM:

There are quite a few variables that can cause this. The age of the bulb being one of them. Is the replacement new as well? Are both lamps running at the same current? Are you sure your ammeter isn't lying to you? Is the reflector damaged? Did the alignment method you used allow you to check that the reflector is in fact focusing the light at the aperture? Try removing the lens and look at the projected light. Compare both projectors to see that you are getting a nice round "bullseye".

Posted by Larry Myers (Member # 738) on 03-19-2005, 03:01 PM:

Another big variable with projector brightness is the lens. Are both projectors using the exact same type of lens. Just because the lens has the same f-stop doesn't mean it will pass the same amount of light. Some of the newest coatings allow f-2 lenses to pass the identical amout of light as a f-1.4 or f-1.6 lens would do 20 years ago.

Larry

Posted by John Walsh (Member # 168) on 03-19-2005, 04:50 PM:

As Rick said; there are several things that could cause this problem.

A suggestion I have is to loosen the two set screws that hold the bulb, move it forward about 1/4 inch then tighten them back down. Then check (and move if necessary) the front bulb support to match.

Since the light got brighter until it hit the stop, I was wondering if it's just too far back. If the light does get better, you will at least know it's not lenses / reflector alignment issues / etc. I'm not saying you should leave it like this; it's just a test to find the real problem.

Posted by James S. Mellen (Member # 2139) on 03-22-2005, 10:01 AM:

I tried moving the bulb forward 1/4" and it did help slightly. Then, when I used the adjustment to move it forward, I saw the intensity peak, then drop off. The current is running around 77 amps through this used bulb. Would it be a good idea to increase the current?

Posted by John Walsh (Member # 168) on 03-22-2005, 01:23 PM:

When the brightness peaked, was it about as bright as the #1 projector? That is, do you think moving it forward is the problem?

Most Xetron XCN-35 consoles have IREM power supplies. You need to look on the power supply nameplate to see what the maximum output amperage is; you can't turn it up any higher than that. The side cover of the console will have to be removed to see it.

For additional info, refer to: http://www.irem.it/en/pdf/DS0004-G3%20Series.pdf for a spec sheet on the G series power supplies (the N series is mostly the same, except it has covers for mounting outside of a console.)

Posted by James S. Mellen (Member # 2139) on 03-22-2005, 02:10 PM:

When the brightness peaked, it was only about 75% of projector #1. If I was able to turn the current up to 80 or 85 amps, would this shorten the bulb life or cause any other problems?

Posted by Andy Bergstrom (Member # 360) on 03-22-2005, 02:18 PM:

Be sure both projectors have the same shutter blade in them. Also chek the reflectors to be sure they're the same. I have seen some Xetrons with different reflectors in the same vintage/moel lamphouse. How about the correct lamphouse working distance?

Posted by James S. Mellen (Member # 2139) on 04-07-2005, 09:07 PM:

After careful checking, everything seems the same except the reflectors. The #1 projector (the bright one)is fitted with a dichroic reflector. The #2 reflector does not seem to be dichroic. It has a faint off color, but is nothing like the dichroic one. I did bump the current up from 77 to 81 amps. Will this have a negative effect on bulb life? This helped the brightness slightly, but overall, #2 is just barely acceptable. I think many will notice a difference at the changeover.
I am about ready to go after the reflector with Mother's aluminum polish.

Posted by Richard Fowler (Member # 893) on 04-08-2005, 11:05 AM:

Some "cold coat" metal reflector may lose their coating as they age or by aggressive cleaning. If the color is a tinge of gold it may be an old reflector. If the color is blue or other color then it may be a "hot" reflector and could be polished up with a non abrasive cleaner or jeweler's rouge. "cold coated" metal reflectors tend to give an average of 10% more light then an identical "hot" reflector. If you need to purchase another reflector give the information stamped on the reflector + serial # of lamphouse / console. Since Xetron has changed owners in the past 10 years, the more information they have the better [Wink]

Posted by Gregory N. Jones (Member # 805) on 04-08-2005, 02:56 PM:

James,
What supports the positive end of the bulb, a post assembly or spider assembly (three pronged metal support that attached directly to the reflector)? Years ago Xetron supplied their 2K lamphouses with this spider assembly and a Rhodium coated 10" reflector. We have found that design to be less then adequate so we offer a kit to convert that to the post assembly using our current dichroic 11" reflector. Feedback from the field has shown just changing the reflector out to the new design increases light on screen by a minimum of 5 foot lamberts! The part number for the kit is XHKIT11 and the part number for the 11" dichroic reflector is XH300159.
Hope this helps!

Posted by James S. Mellen (Member # 2139) on 04-14-2005, 11:38 AM:

The reflector in question is rhodium-coated. The cost of a new reflector is prohibitive for our community owned not-for-profit theater. Is there any proven or reliable way to polish this reflector?

Posted by Gordon McLeod (Member # 33) on 04-14-2005, 12:00 PM:

UltraFlat sells a good polish for hot mirrors that works very well

Posted by James S. Mellen (Member # 2139) on 04-15-2005, 01:01 AM:

Yikes! The used (but still looked good) bulb that I installed recently failed in the same way that the first one did. The plus side got VERY hot until it melted the connection near the glass part of the bulb. I discovered that the heat filter was incorrectly assembled. The glass pieces were flat instead of being angled. As I understand, the heat gets bounced back to the bulb unless the glasses are angled.
Could this account for a bulb failure in 5 hours? Could the excess heat have also damaged the rhodium reflector so that it reflects less light and absorbs more heat? We have more used bulbs, but I am almost afraid to try one and burn it out too. I did correct the heat filter.
I should also say that I had recently turned the current up from 78 to 81 amps. At just under 25 volts, I am right at 2000 watts.
I appreciate your help on this!

Posted by John Walsh (Member # 168) on 04-15-2005, 06:58 AM:

I'm guessing, but I think the bulb was not focused in the reflector correctly. Instead of the light being focused on at the aperture, it was focused at the bulb's anode end, overheating it.

What diameter reflector do you have, and I will find out what the working distance is (reflector to aperture.) Xetron currently has an 11 inch and a 15 inch. There was also 10 inch many years ago. Also, what is the exact model number of the Christie bulb are you using.

Posted by James S. Mellen (Member # 2139) on 04-15-2005, 07:52 AM:

It has a 10" reflector with a Christie Xenolite CXL-20R.

Posted by Richard Fowler (Member # 893) on 04-15-2005, 09:53 AM:

An incorrectly aimed dichroic glass filter can overheat the anode fitting of the bulb and may damage the reflector.

Posted by John Walsh (Member # 168) on 04-16-2005, 05:13 PM:

The distance from the back of the reflector (the rear opening 'edge' - not the shroud that encloses the reflector) to the aperture plate should be 19.5 inches. You can double-check that distance is correct by comparing with the other lamphouse. Also, check that the brass adapters on each end of the bulb are the right type ... again, since one lamp works OK, use the 'good' one to compare the adapters, or measure that the bulbs are positioned in the same place.

I'm gussing that this is the lamphouse you have...

Posted by Louis Bornwasser (Member # 3063) on 04-17-2005, 07:58 AM:

While the heat filter discussion is very relevant; another thought is that the spider becomes "part of the problem" at about 2000 watts. I have always used the cable that comes with the bulb to reduce the heat on the spider caused by current.

More recently there is a reflector replacement that completely eliminates the spider from both Xetron and Big Sky. Not only that but you get a new reflector with a better design: more light. (Better than a heart transplant.)

Posted by Mark Gulbrandsen (Member # 72) on 04-17-2005, 09:52 AM:

quote: Louis Bornwasser
More recently there is a reflector replacement that completely eliminates the spider from both Xetron and Big Sky. Not only that but you get a new reflector with a better design: more light. (Better than a heart transplant.)

Louis,

I don't recall a spider in any of the Big Sky conversions we've done, just a front support yoke. The recent Big Sky conversions improve those old dinosaurs quite a bit.... exactly what kit are you talking about?

Mark

Posted by Louis Bornwasser (Member # 3063) on 04-17-2005, 09:54 AM:

Syntax error....I mean you can obtain the kit from both of these.

Posted by Mark Gulbrandsen (Member # 72) on 04-17-2005, 10:01 AM:

Oh yea, thats kinda what I thought..... I wasn't aware of any others. Just thought you mighta been making a kit of your own.

Mark

Posted by James S. Mellen (Member # 2139) on 04-19-2005, 08:07 AM:

John, yes that is the lamphouse. We are running 20" from the rear of the reflector (inside opening edge) to the aperture instead of the recommended 19.5".