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CRT Primer

Updated: April 2006

Index: 



Why CRT Projectors?

 

CRT projectors have been around since the dawn of television. An early electronics magazine that I have from the 1950’s shows a large B/W video projector capable of projecting a 20’ wide image onto a wall. I have seen and operated an ancient tube chassis 3-gun 1000-lumen projector from the 1960’s that was used for the first Wrestlemania in 1986. Not a great picture, but at the time, an entire arena full of people paid $20.00 each to see Hulk Hogan duke it out on that projector.


Barco 808s

Those of you that have seen a CRT projector in person will agree on one thing: they are large and heavy beasts. The lightest CRT projector weighs about 50 lbs and the heaviest that I have seen is about 250 lbs. There’s no getting away from the weight due to the glass picture tubes and the three lenses that these units require. Typical dimensions are about  24”x18”x12” for a small projector, and a larger unit can be 40”x32”x16”.

Thanks to misinformed (and high commission) LCD and DLP sales people, many myths surround the ‘mystique’ of the CRT projector. These include:

 - expensive and short tube life
 - CRT’s need constant adjustment
 - CRT’s never give a good picture
 - you need to call in a tech every time you need to adjust it.

As of this writing (October 2007), CRT projectors still give the best quality image for a home theatre. The overall sharpness, focus, lifelike fleshtones and three dimensionality of the image still cannot be duplicated by any other type of video projector. With the recent release of HDMI and DVI modules, all data grade CRT projectors can now be connected to any current digital device, including Blu-ray and HD-DVD players. CRT obsolete? I think NOT!

Yes, there is a time and place for all types of projectors. While I don’t sell a lot of digital sets in any given year (3-4 maybe), the wholesalers that recommend sets to me seem to flip-flop on whether it’s DLP or LCD that I should be installing. In 2003, I was unanimously told to sell DLP only for home theater use. In late 2004, the same suppliers were back to recommending LCD, claiming that the DLP’s were less reliable than LCD units.

If you are looking for a small portable and easy to set up projector for computer use, LCD or DLP are the way to go. There are literally thousands of models out there that are available on eBay or elsewhere. Keep in mind that the life span of any particular model seems to be about 6 months as the DLP and LCD race for technology improvements continues, so any model is replaced after about 6 months. There are numerous companies that have gone out of business making parts hard to get for certain models and makes, plus many bulbs are obsolete and are simply not available. Currently many manufacturers are offering 2000, 4000 and even 6000 hour bulbs to compete with the typical 10,000 hour life of a CRT tube. The problem is, many of these bulbs lose their brightness over time, and so the white areas of an image of an LCD or DLP projector may turn yellowish or other colors due to a lower light output of an aging bulb. I’ve been told by manufacturers’ reps that typically the light output of a bulb goes down by 20% at the half life point. This also means that the light output is no longer pure white, so your whites (hockey ice!) turns yellow and the color spectrum changes significantly before the bulb dies. Depending on how picky you are depends on when you change the bulb.

As of the update to this document, I have seen a number of LCD and DLP projectors come through my shop for repair. As stated above, these small < 10 lb projectors run very hot as the bulb is in very close proximity to the main circuit boards. While some of these projectors have come out of sports bars that do not clean the air filters and thus the internal temperature increases significantly and shortens bulb and set life, the fact remains that these small projectors simply cannot be serviced the way CRT projectors can. Digital projector circuit boards are treated the way a sound or video card is dealt with in your computer: Do not repair the board, throw it away and install another one. The problem is, unlike a $50.00 sound card for your computer, a video processing board can run almost as much as a replacement projector.



Marquee 8500 CRT projector,
Jan 1996 build.

11,000 hours on the tubes,
68,000 on the chassis.
Used in a 3D virtual reality system run
24 hours/day for nearly 8 years
without turning it off. Amazing!

I’ve seen time and time again where I’ve checked into the availability of a replacement bulb for a > 5 year old digital projector, only to be told that they are no longer available. Therefore, if you’re shopping for a used digital projector, buy a spare bulb for it now while it is available, and keep the air filters in the unit clean.

The bottom line on digital projector bulb life is that it appears that the life span advertised by manufacturers is based on a 10-12 hour cycle. Thus, to get the rated 2000 hours of bulb life, the projector needs to be on for 10-12 hours, turned off for a while, then run again for 10-12 hours. The problem is, this is not commonly how a digital projector is used in the home. If you turn a digital projector on and off three times a day, there’s a really good chance you’ll get significantly less life out of a bulb than advertised. The turn on pulses that the bulb is subjected to is very hard on the bulb.

While only a handful of CRT models are still being manufactured as of 2003, there are so many available parts, modules and used projectors that parts availability (with a few exceptions) is not a problem for even 15 year old models.

If you don’t mind the large case that houses a CRT video projector, some occasional ‘tweaking;’ and the best picture for a home theatre, then keep reading, as CRT is for you!







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