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Author Topic: Spots developing on Osram bulbs Larry Shaw Expert Film Handler Posts: 238 From: Boston, MA, USA Registered: Mar 2000 posted 03-17-2003 02:56 PM                        Paul, The markings (I call it "soap scum") are entirely on the inside of the envelope. This XBO7000W bulb has about 300 hours, it is the first bulb run in this LH. Now a second XBO7000W has done the same thing at about the same hours. Irem N3180 w/filter. Plenty of airflow. A second identical setup has had no problem. Go figure. Osram has them now, I'm waiting for their comments.  |  IP: Logged Adam Martin I'm not even gonna point out the irony. Posts: 3686 From: Dallas, TX Registered: Nov 2000 posted 03-17-2003 04:53 PM                     Larry, have you actually measured and compared the airflow in the two lamphouses? If there is too much airflow in the front of the lamphouse, the cathode end (that sits inside the collector, where airflow is more restricted) will become overheated and cause the quartz on that end of the lamp to vitrify and will also cause instability in the arc. Ideally, air will move evenly throughout the entire lamphouse. Additionally, a slight defect in the collector may be directing energy back onto the lamp, which would also cause the overheating of the cathode and/or quartz. Milky white or blue residue inside the bulb is tungsten oxide, caused by the tungsten electrodes reacting with oxygen that has seeped into the bulb. I've never seen a lamp where only parts of the quartz had this residue ... usually the whole thing goes in a single reaction. Maybe the bulb was not completely evacuated in the manufacturing process, leaving just enough oxygen inside to cause spotting from a small reaction. Are the lamps in which this is happening all from the same lot, perhaps?  |  IP: Logged Mark J. Marshall Film God Posts: 3188 From: New Castle, DE, USA Registered: Aug 2002 posted 03-17-2003 05:55 PM                    quote: If there is too much airflow in the front of the lamphouse, the cathode end .... will become overheated and cause the quartz on that end of the lamp to vitrify Could a mis-aligned reflector cause vitrification in the way that you describe?  |  IP: Logged Adam Martin I'm not even gonna point out the irony. Posts: 3686 From: Dallas, TX Registered: Nov 2000 posted 03-17-2003 06:40 PM                     Anything that could cause excessive heat energy to be directed at the lamp envelope can cause the quartz to crystalize. I don't know how misaligned the collector would have to be for that to occur, though. Actually, now that I think about it, when the quartz crystallizes, it is devitrifying. My bad. Devitrification usually occurs when the quartz is depurified (oil from fingerprints, etc.) and heated. If you have cleaned a lamp with alcohol after having touched it, are you using denatured alcohol or that crap from the drug store? (Osram recommends "spirit", whatever that is. Come to think of it, a prayer might just help ) Are you wiping all the residue off with a lens tissue?  |  IP: Logged Mark J. Marshall Film God Posts: 3188 From: New Castle, DE, USA Registered: Aug 2002 posted 03-17-2003 08:03 PM                    quote: are you using denatured alcohol or that crap from the drug store? THAT can be a sore subject around here. I think I forgot to mention that our sister theater down the road recently received a bulb with the mysterious white spot already on it... still sealed in the box! It's currently on its way back to Osram for inspection along with the remains of another one that blew up - presumably as a result of the spot. Edit: Here's a picture of one of our spotted bulbs:  |  IP: Logged Mark J. Marshall Film God Posts: 3188 From: New Castle, DE, USA Registered: Aug 2002 posted 04-08-2003 03:22 PM                    I now have ANOTHER bulb, this one is a 3K bulb with about 250 hours on it, that looks exactly like the photo above. These are all different projectors, in fact, different multiplexes. I'm thinking there HAS to be some QC problem at Osram, or a bad batch of bulbs, or something. Although would "bad batch" imply one group of one kind of bulb? We have 2Ks and 3Ks with this problem.  |  IP: Logged Jack Ondracek Film God Posts: 2348 From: Port Orchard, WA, USA Registered: Oct 2002 posted 04-08-2003 04:43 PM                        quote: from Adam: (Osram recommends "spirit", whatever that is. It's call "Everclear". Find it at your local liquor store!  |  IP: Logged

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