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Discussion Starter · #1 ·
I see alot of projectors for sale that show pictures of tubes that have burn about an inch from the phosphur edges.


Why don't most people take the raster out to the edge of the face? I know that corner focus suffers a little, but what of the overall picture quality?


Why pay extra for a 9" and only use the same amount of phosphur as someone who maximises their 8" raster height/width?
 

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You may and probably will get differing opinions, but make no mistake about it if you are not pushing it to the max you may as well have spent less and settled lowed or spent more and settled because you're lazy.


A 7" can beat a 8", an 8" can beat a 9", a 5.5" can beat a 9" given a whole hell of a lot of work and fresher tubes, though sure, good luck trying.


Part luck, part bandwidth, part phosphor size, part skill.


What order, I dunno... Luck is good, But it helps to have more on your side than even just skill.


Troy
 

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Why are they like this? Because most are installed using the very "safe" throw charts that come with the install manuals.


If I was an installer 10 years putting a CRT into some government or school, I'd also be playing it safe because I have to support & warranty the unit.


What I do at home now is another story altogether though..... (I'm 1/8" - 1/16" from the edge with my active image area. 3-4K hours later and the tubes still have no sign of any wear at all).


Kal
 

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Say on a 9" tube the height of the phosper used on a 16X9 image is two and one half inches, you could probably push it out to three and a quarter (I'm useing a Barco tube as a example). Now that gives you a extra three quarters of a inch to draw lines. That is like twenty percent more area to draw lines.


I doubt if you would see a twenty percent improvement, but it would be substantial.


Deron.
 

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If I was a professional installer I would definately go with the manufacturer recommendation.

If I install a NEC with throw/width of 1.5 as recommended instead of 1.3 as it is possible, I will earn a lot of more money as I have to change tubes more often :)

Roland
 

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"If I was an installer 10 years putting a CRT into some government or school, I'd also be playing it safe because I have to support & warranty the unit"


You dont have a choice, its a personal liability issue big time and for a very good reason. Doug


RoBo,

Not so, Id make more money with 1.3 and do from drive issues and cracked tubes / chamber glass. My concern is part availability and set ups from first time users that havent had the learning curve. This doesnt apply to everyone if its done within reason but I cant post to say its the safe way.


My opinions are based on NEC and what I have documented to present.
 

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Discussion Starter · #7 ·
By liability, do you mean that if you setup a projector with a closer throw distance than recommended by the mfg, by using a larger raster.... that you could be liable for "who knows what" if there was ever a problem?


What type of problems can occur? I understand that a "too large" raster that folds over the edge of the crt face can cause problems, but what if you went with 1/4" to edge face instead of say, 3/4" per mfg specs?


What potential problems could you experience by using more of the phosphur than recommended by mfg?


Great info so far! Thanks everyone!
 

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Quote:
Originally posted by CZ Eddie
What type of problems can occur? I understand that a "too large" raster that folds over the edge of the crt face can cause problems, but what if you went with 1/4" to edge face instead of say, 3/4" per mfg specs?
Having the image extend beyond the phosphor surface (like you mentioned) can cause catastrophic tube failure due to shorts on some units but on most the extra heat will cause cracking of the glass over time.


Assuming that's not a problem, if you increase horizontal deflection (ie: increasing the raster width), you push the horizontal deflection circuitry harder which can stress components. NEC's are fairly subceptable to this: It's easy to increase horiz size by simply cranking a pot which increases width but then can a tendancy to overheat and cause premature failure of the large horiz defl transistor (mosfet? jfet? Not sure what it is).


Kal
 

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CZ,

Most CRT projectors went to the education, Corp and military when sold new. USC alone had tons of them with thousands of students walking under them every day, break a tube or chamber glass that caused liquid to drip on the floor had a huge personal injury liability.


In those cases they measure the optical throw to screen size, if out of spec it wouldnt be without warnings from the mfg, look on the first pages of any manual. Its a pretty given fact if theres something slippery on the floor people are going to look for a free retirement program.


This isnt even getting into the cost of the repair and it would void the warranty.


If I stay conservative its for a reason, I have seen the damages from a broken tube while in use even when it shuts down right away.


Parts can be replaced with money if theres parts available and this can run more then we pay for the projector in some cases.


Just a couple of weeks ago I posted about a v drive that failed, snapped the tube, discharged into the deflection yoke and also took out the crt power board, this was a LC so you can imagine the costs and down time.

7% expanded raster no signal condition, this one didnt leak but had $5k worth of new leather under it.


I would like to say many do run safely if care is taken in the set up but Im sure they have the raster centered and well thought out as to 10% overscan of internal test patterns and what happens if you hit a signal thats not registered or no signal entered for video and you hit that input by mistake which is a favorite input of babysitters. Doug
 

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I'm not sure I understand why crt's would arc out internally from the raster being a little too big. Is it because the anode voltage on the face of the tube gets too close to the grounded outer glass of the tube? But then, the entire tube face is charged to anode voltage, not just where the beam hits, correct? I have a good understanding how CRT's work, but this always baffled me.


You would think that if the CRT's are that touchy, then they wouldn't design them to run at an anode voltage quite that high. I've seen standard CRT's and a few older projection sets that would have the deflection circuitry fail and practically try to draw a picture on the back of the cabinet, and the tube never cracked.


In fact, the only time I cracked a tube (basically for fun) was by using an old CRT rejuvenator and turning up the heater to 18 volts for a couple minutes, then pressing rejuvenate. The spark from the cathode actually cut the neck of the tube, and air slowly went in, then the heater started putting off a purple glow before it blew up... But this was a junked out 25" monitor tube, and DON'T try that yourself! I'm just a crazy idiot somtimes.
 

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I still do not totally buy that tube cracking thing.


First, I almost never hear about it and there are plenty of us going beyond manufactures specifications.


Second, the all white warm up screen on some of these PJ's run the image out past the edges of the tubes for like twenty minutes!


Third, we are using these PJ's for HT use and there are no static images when playing a movie. I would believe a static image has a much greater chance of heating a tube up unevenly which then would have a greater chance of cracking the tube.


Forth, of the tubes that cracked, whos to say it was caused by maxing out the phosper usage. I would bet it was more likely caused by low coolant or the image was off to one side of the tube. It could even be a defect in the tube.


Fifth, I would bet more tubes have been destroyed by rough handeling during shipping (UPS did in one of my tubes) or by some apes moving the PJ around. The NEC's look real supseptable to this as the rear of the tube is unsupported and it has plenty of weigh hanging off it. I got a XG that had the neck busted off from it being dropped.


As for the H-output transistor, I blew one on my 10PG from running the width wider then it should of been. BUT they are already running the H.O.T. so hot I could not even put my finger on the heatsink, could of used a fan there, so I put three there, now it is cool to the touch even with maxing out the width.


Deron.
 

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Pictures, cool I like pictures, especially the ones Pete posts, the lastest one is real nice (Anyone need a Barco 808 Roadcase).


Deron.
 

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Lets see if this works.

Note the scorching of the neck tape and not sure if you can make out the deflection winding in the crack but its there. All the parts were needed for the repair are in the photo. Doug
 

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Deron,

You can eliminate the tube as a 'weak spot' I took several burned tubes to find the problem and snapped the second one in an instant. Wasnt going to install a new LC tube unless I knew for sure. This superheat was only on one side, the other side was fine. The neck tape on the second one looked the same. Doug
 

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Now it makes a bit more sense to me.The over scan is hitting the thinner neck of the CRT not the face.So Doug what is the margin of error and does it very according to various tubes.1/8 inch,1/4 inch what do you recomend ?
 

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From what I understand the necks are thinner on the P16s used in G70s and NECs. The 180XXX used in Ampros, Barcos, and Electrohomes are thicker and you don't hear nearly the problems with them with necks cracking and the like as you do with the aforementioned G70/NEC tubes.
 

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Discussion Starter · #20 ·
Quote:
Originally posted by Doug Baisey


I would like to say many do run safely if care is taken in the set up but Im sure they have the raster centered and well thought out as to 10% overscan of internal test patterns and what happens if you hit a signal thats not registered or no signal entered for video and you hit that input by mistake which is a favorite input of babysitters. Doug
\\


I hadn't even thought about overscan or non-setup channels. Of course the raster would be larger than something you may have setup.


But wouldn't the overscan need to be touching the neck for more than a few minutes (like an hour?) before it could even think of heating the neck enough to cause harm?

Maybe I should be asking..... just how much time does it take to cause this sort of damage?
 
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