CurtPalme.com Home Theater Forum

larryp · Joined: 24 Jan 2012 Posts: 252 Location: eden prairie mn

Wondering how many hours it take for the tubes to start showing wear from "Normal" use during their life.

When does wear start to degrade your picture? 2000 hours? 4000 hours?

I know many things can effect the tubes life, just looking for a average wear estimate

cmjohnson · Joined: 03 Apr 2006 Posts: 5180 Location: Buried under G90s

I think Curt would probably be best qualified to answer that question. But phosphor wear is determined by the phosphor work function, which basically comes down to beam current multiplied by phosphor temperature multiplied by time.

I've seen tubes that allegedly had 20,000 hours on them with no visible wear. At low brightness levels and in cool conditions with
good cooling, I can believe that.

A spot burn can happen almost instantly, as it heats up the phosphor to instant oxidation in milliseconds.

I've seen tubes with noticeable pattern wear on them in 500 hours or less. Run hard in simulators with a small working raster
area due to the needs of a faceted simulator dome using a bunch of projectors operating in rear projection mode.

In the real world at normal picture conditions, not going for max brightness, just an enjoyable picture quality in a well light controlled room, you can probably go 3 to 5 thousand hours before you start seeing a wear pattern. Or more.

Ultimately it comes down to keeping the phosphor cool enough that it doesn't oxidize. This wouldn't even happen at all, if
anybody had ever figured out how to create a usable phosphor layer system that had no oxidizing elements in it.

**Curt Palme** · Posted: Sun May 22, 2016 9:16 pm Post subject:

CM is right. IN layman's terms, it's all to do with the contrast setting. At factory default setting with ES focusing sets, you'll start seeing wear at 2000 hours. With a well set up super sharp set like the G90, you'll see wear in as low as 800 hours. It's faint, but there.

Technically your white balance will be affected as soon as you start using the set, but because you're only seeing the wear area, not not virgin phosphor, you'll most likely not be able to tell until about 6000 hours (give or take of course).

Roll the contrast back maybe 20%, and I'd say you'll get 60-70% longer tube life than at factory default.

CIR Engineering · Posted: Sun May 22, 2016 11:06 pm Post subject:

Even with a lot of visible wear, if you have a late Barco or G90 that has good beam control you can still get great output. Phosphor wear sometimes only matters if you plan to move the projector because you may not be able to stay inside the existing wear pattern.

G90's and lat 9" Barco's can show wear on the green in 600 hours or less. Marquee typically doesn't show much wear of the phosphor for many thousand hours.

I have one client who owns a G90 that he bought new. We retubed his set last year and he had 19k hours on the tubes. The last calibration thjree years ago before the retube, I had to max out his green and run his contrast at 95/100 to get the 12 flt that I like on his screen. The picture still looked amazing, but I told him it was the last time the projector could be recalibrated with the original tubes.

I think a lot of folks don't understand that phosphor wear doesn't always indicate tube life or hours used. A tube with a lot of phosphor wear can still perform very well if it's kept in the same physical location. The key is how much emissions does the tube still have and how worn is the cathode. The only way to know that is to try the tube or use a tube tester.

craigr

Spanky Ham · Joined: 22 Mar 2006 Posts: 5643 Location: Comedy Central

http://www.avsforum.com/forum/16-crt-projectors/619600-why-your-phosphor-wears.html
http://www.avsforum.com/forum/16-crt-projectors/623423-phosphor-lifetime-calculations.html

cmjohnson · Joined: 03 Apr 2006 Posts: 5180 Location: Buried under G90s

Thanks for digging those topics up. I enjoyed the refresher course on phosphor ageing that it offers.