CurtPalme.com Home Theater Forum

[barclay66]

Dear community,

There are a few things that can be extremely annoying to CRT users, and uneven tube wear is one of them.
Especially if the tube in question still has good emission and focus. In my case it's a complete set of Marquee 9500 Ultra tubes which look like new and unfortunately show a faint test grid pattern. Therefore I'm thinking of building a wear leveling device. If successful, I could provide this as a service to the community.
This is the basic concept:

1. Prepare the tube by adjusting G2, geometry, focus and astig settings (single tube connected to a Marquee Ultra chassis)
2. Feed the tube a completely lit raster ('white' pattern at 100% intensity from a computer at max. resolution, e.g. QXGA=2048 x 1536 pixel) with small borders (security margin)
3. Make a high resolution picture of the tube face (high Mpix camera & suitable optics)
4. Feed the picture back to the computer and run a pixel by pixel analysis of the intensity
5. Calculate an inversed and contrast-enhanced pattern which will only use 'virgin' phosphor
6. Feed pattern back to tube at 100% intensity -> Unused phosphor is aged and used phosphor is protected
7. After each x hours go back to step 2. and exit after step 4. if the intensity deviation is small enough (leveling complete)

I think that this approach is feasable. A similar approach can be seen here: http://www.curtpalme.com/Balancing_CRT_wear.shtm
Of course there are some concerns like the required precision of the optical gear (sensor), the development of the required software and anything else I haven't thought of. But I think that all of them can be overcome.

Now to my question: Could the same be acheived using laser technology?
Or, in other words: Does the tube phosphor age when hit by a laser beam of the same color and enough intensity?

In this case the tube phosphor would be aged by directing a focused laser beam of the corresponding color onto it. This would require three lasers (R/B/G), suitable optics for focusing them onto the tubeface and a high resolution scan mirror assembly in order to address all positions on the tube face.
I'd prefer this method as the advantages are apparent: The wear leveling is done without driving the tube (e.g. 'cold' aging) and without aging its gun too. If the relation between beam intensity and aging effect was determined the entire process could be done in one single pass, thus requiring only a minimum amount of time.

Any comments welcome!

Regards,
barclay66

[kabuby77]

phosphor receive energy from electron beam and release it emitting light(photons). As I know it is one direction process.

[gjaky]

You should look at this ancient thread:
https://www.curtpalme.com/forum_archived/viewtopic.php@t=6325.html

[mc86]

I've never been clear on:

A) whether the phosphor itself is "wearing" OR if binder material is browning/changing in ways that lessen phosphor effectiveness.

AND

B) if the source of "wear" is heat related (more generically "energy dissipation"). Clearly, 100% intensity can "wear" in a very short time IF a given surface of tube face is continually hit...but what is the destructive mechanism? A laser could work if the energy was thermal AND applied at correct place. A laser's wavelength would have to be determined that would best cause heat (and would need to be powerful). In addition, a laser used from the front surface would reflect/refract/diffract on the glass surface in ways that might be too diffuse.

How thick is the phosphor layer, BTW? The videos of TV screens I've seen being recycled, it looks like a MUCH thicker layer than I'd have guessed -- almost 1mm, perhaps. I'd have thought the phosphor would be more film-like. Why so thick, I wonder...

Does anyone know the actual power of the electron beam? The HVPS is 34KV at how many amps? If we know the power going to the phosphor area and the wavelength/intensity of light emitted, an approximate energy balance could be done to determine the tube face heat rise rate and equilibrium temp. Anyone know how hot the fluid in an AC coupled machine get and how quickly? If running the beam off-face can shatter a tube by thermally stressing the glass, I'm guessing pretty hot!

This is fun thought experiment and getting data would not be too difficult.

Cheers,
Matt

[CasetheCorvetteman]

Wouldnt you be better off defocussing the beam and then taking the pic?

[barclay66]

Hi,

thank You for Your sharing Your thoughts.

@gjaky: Cool information. Hadn't seen that. In essence it seems to be necessary to hit the phosphor with electrons (instead of photons) in order to produce wear. This makes the laser approach less probable.

@mc86: The phosphor layers I've seen were pretty thin. Maybe 0.1 mm. I have some tubes here for disposal so I might get some facts soon.
The Marquee HVPS produces 34.9 KV with 4.5mA. This current is divided into three parts through the splitter. If You calculate some loss through the splitter's resistors You most likely will end up at around 1.2 - 1.4 mA per tube.
In my point of view, much of the panicking around breaking the tubes when shooting over the tubeface edges for a second as well as the amount of heat produced is somewhat overestimated. I've been running bare tubes (magnetics only, at low brightness setting) for up to half an hour and the tubeface was almost lukewarm.

@Case: Of course it will be necessary to smoothen the edges of a wear pattern (the inverted one to be projected) before starting the aging process. So the new wear will better blend together with the existing one. For this I think it's essential to get the most perfect picture of the existing wear first. Defocusing the beam a bit could help eliminating any possible scan lines which could be misinterpreted as existing wear.


Regards,
barclay66