CurtPalme.com Home Theater Forum

[mc86]

On another thread SC wrote:

[ecrabb]

Do it!!! I would love to see the results!

SC

[Nashou66]

I bet G90 owners would like to hear that as the Greens wear much faster than other PJ's. A circulating cooling system might make tubes last longer.

Nashou

[CasetheCorvetteman]

Nashou, why is that? I thought they had a less dark C element in them?

[Nashou66]

I think they get driven harder. I just know that those who have G90's go through greens faster than other PJ's with the same hours etc.

Nashou

[mc86]

Wait Nashou...so the same set of tubes in two different machines wear at different rates? Cool, but how does this make sense? Presuming greyscale is correct on both AND the light output is the same, what can this mean?

1) The c-elements/lens (lightpath) filters more light in some cases than in others, so they are driven differently to get same light onscreen at correct greyscale. For the wear rate differences to be easily noticed, this must be pretty significant. Sounds like sign is wrong though, if in fact some G90 green c-elements are less dark.

2) There is something about the magnetics, perhaps -- maybe the beam is more focused than needed in one case than another, thereby requiring more drive to excite the same phosphor width as in a less focused beam in another case? By pouring more power into a local spot to excite neighboring areas ("microblooming"?), a localized heating might occur. I'm making this up, but I could be convinced of it. I could draw a picture if my words don't make sense. That is, if green is being made to do focus for 2000lines and only needs to do 1080, does this make the lines overdriven vs case in which focus is relaxed? I feel I should know this by now...

3) not sure I can makeup another idea at this hour...maybe cliffy is in a "creative place" right now and can chime in.

Matt, who is leaving on vacation for the next week (poconos) in the morning and will be mostly out of communication while away.

[CasetheCorvetteman]

I understand what youre saying mate yes

Whether its a fact or not is not something i know

[Nashou66]

Well I know the cutoff voltage for the marquee is lower than that of the G90, ampros and I think Barcos.

The marquee's is 170 and most CRT work optimally at 180 I do believe. This is why some say( I think Scott told me this) that the G90 and Ampros were sharper than the Marquee's. So I just hypothesized that since they send a sharper electron beam to the phosphor , that a more concentrated area of phosphor would get hotter and therefore wear faster. And the higher voltage might also get the Phosphor hotter but I think it would have more to do with a sharper re trace line, that is a result of the higher cut off voltage.

Nashou

[wkosmann]

I think, more to the point, is that G90s are typically run at much higher contrast settings than other projectors, especially Marquees. Cliffy runs both his G90s at a setting of 80 to 90 for contrast, and burns CRTs really fast. I ran my Marquee 9000 at a contrast setting of 50, and a brightness setting of 50 for 10 years, and had very little CRT wear.

[CasetheCorvetteman]

Yeah but I think youll find all Sony CRTs have the contrast setting up pretty high, that probably wont be the issue cause that is just the way they are set up.

The overall light output at a given contrast setting is whatll cause the wear, more so than where its actually set.

Also I think Cliffy's screen is just so damn big and he wants such blinding brightness so he can wear his sun glasses at night

[mc86]

Okay, I want to make a 4:3AR image of a grid that is white, grey, and very dark grey as sketched out above EXCEPT I'm not going to leave one cavity with air due to fear the thermal gradient between an actively cooled zone and the uncooled zone might cause tube implosion. Anyway, can I just hack out in imagine in Excel as spreadsheet cells of different greyness and then save that as a 1024x768 JPEG? Is there a more scientific way to do make an IRE-specific grid like I want?

Mostly, I want the areas to be sufficiently large enough to insure each of the 9 areas tested reach their own steady state conditions in both time and space (on the tube's face) AND I want the areas to step-up in brightness well-enough to show the results I hope to find.

I'm going to change the experiment a bit, too. IF I see the actively cooled zone has burned-in less than the passively cooled zone, I may go back and externally heat the glycol in the active zone!

I hypothesize:

1) The 100IRE areas [white, driven hard] will quickly cause burn-in as others have shown and will show more burn-in than the 60IRE and 20IRE areas. I refer to the reverse-masking method Roger developed to make a tube have uniform burn-in. I further expect the passively glycol cooled areas will heat up to a higher final steady-state temp than the actively (refrigerated) cooled zone. This leads to...

2) The hotter areas will burn-in much more quickly than the cooler areas. Stated differently, I think we will see the light output [?electron flux (electrons/tube area/time)] alone will not be deterministic...but that time-at-high-temp will be most telling.

Roger noted he thought the burn-in was highly nonlinear and I think his intuition is right. I've made zero attempts at first-principles/physics-based modeling on this, even rudimentary thoughts on how this would be. Of course, I yap at my students for not planning their experiments in gross detail ahead of time!

3) If maintaining cool temperatures on the tube face (the binders in the phosphors) reduces burn-in, then actively heating the tube face will, conversely, increase burn-in.

Okay, the holiday weekend is at a close and I've got a ton of reports to read. Looking forward to late december and will begin inching toward the tests..input welcome!

gotta scoot.
Matt

[cmjohnson]

A question comes to mind: If running the cutoff voltage at 180 is optimal but the Marquee runs 170, how easy or difficult would it be to boost cutoff to 180 for a sharper image? Understanding that it may reduce tube life.