CRT Primer

Tube Life

The life of most picture tubes is rated at 10,000 hours by the manufacturer. It is very rare that a picture tube will fail from one use to the next, although this is possible. Most often, the tubes will simply wear out over time, but many tubes can still be used at the 10K hour mark. Depending on the make and model, the blue tube usually wears first, then the green, then the red in last place. Usually, red tubes are useable well past the 20K hour mark. I have found that in CRT projectors rated over 800 lumens that the green wears first, then the blue, with the red again lasting the longest.

It is my opinion that the manufacturers came up with this 10,000 hour point due to the fact that after 10,000 hours, the picture quality will be compromised with regards to focus (in the case of ES focusing tubes, more on ES focusing later), picture quality and brightness. The fortunate thing is, the change in picture quality is so gradual that many people use their projector well past the 10,000 hour mark before changing the tubes. If you have ever been into a sports bar and seen a CRT projector that has pink hockey ice and a puck that is so out of focus that you cannot see it, you will be watching an ES focusing projector that has in excess of 15-20K hours on it.

The good news is, a projector tube does not really wear if no light is projecting out of it, as it is the phosphor surface that wears generally, and not the electron gun of the CRT. So you can have a projector running for 10,000 hours with no light output out of it, and still have the equivalent wear on the tube of about 500 hours.

The bad news is, a tube wears faster with a higher contrast and brightness setting, so always run a projector at as low a setting as possible.

Another negative is, CRT projectors are very susceptible to static images that can burn themselves into the phosphor surface in as little as 1000 hours. This is why I have to junk a lot of projectors that come out of static image computer installations. I have had CRT projectors that came from railroad control centers with little railroad tracks permanently burned into the face of the tube, which are then projected along with the video image you are trying to view. This makes a moving video image impossible to watch.

Regarding video game use and computer display projection, there is no problem running these on a CRT projector, however it’s a good idea to avoid continuous long term displays of the same image, such as a Windows task bar, or a ‘game over’ message. To prevent any kind of tube wear, turn the brightness and contrast down as low as possible while still being able to watch an image. Since video games have very little static information on the screen, and the screens are always changing, even hours of game play will not result in any premature tube wear.

Sony 07MS tube

As indicated, it is the phosphor surface that wears on a CRT tube. This phosphor is sprayed on the inside face of the tube, and cannot be repaired once burned or damaged. Over time, the phosphor becomes discoloured and this results in decreased focus and light output. An imbalance in light output of the three tubes results in poor colors, and a pure white image is no longer capable of being produced.

Fortunately, the tubes do not wear evenly. In the projectors that I have worked on, either the green or blue tubes start to show wear first, with the red being a distant last. Blues and greens can show slight wear at as low as 2500 hours, reds typically last at least 20,000 hours. This makes complete tube replacement not necessary, thus lowering the overall price of overhauling a set.

The final point at which someone decides to retube a projector lies with how picky a person is about the overall picture. To put it in perspective however, 2 hours of CRT viewing per night is equal to only 730 hours per year. At the rate that used CRT projectors are being sold for, it is not worth retubing a projector in my opinion, depending of course on how much you have into the set. A ‘freebie’ can always be worth retubing.