Amplifone Tube Issue

PeRFiDiouS

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I have been going through some Amplifone tubes recently and came across one I wanted to share.


ampb1.jpg

ampb2.jpg



The deflection and HV are 100% on this machine. The yoke and focus rings are properly installed and the monitor is degaussed and converged good enough for testing.

I attribute the above anomalies to color phosphor burn. I suspect a specific color of the phosphor has been burned away in these areas making them void of this color. I have never seen this before with an Amplifone so I wanted some other input on this diagnosis.

Thank you.
 
Read this and weep :(

http://forums.arcade-museum.com/showthread.php?t=172652

Sounds like your tube is dropped and this cannot be fixed.

Thank you for the link to the other thread. I agree that it is most likely the same issues with both of these tubes.

However the other thread does not really come to any real conclusion. It is allot of speculation (some more inept than others) about degaussing and shadow mask movement.

This issue is not related to magnets or degaussing IMO and I think this was confirmed by the OP's magnet test video.

In cases where the shadow mask has moved on a monitor is is almost always in the corner of from the sides. I have never seen a loose mask start in the middle of the tube like is pictured. I also do not see the same anomalies on screen when a shadow mask is loose as I do in these pictures.

That leads me back to a phosphor burn issue of some type but I need someone with a bit more knowledge of this area to confirm this.
Anyone?
 
I don't know what causes that problem, but it cannot be fixed. I think if it was phosphor burn, you'd see it when the monitor was off. On mine I can't see anything unnatural in the affected areas until it starts shooting electrons at the screen.

Why has this happened to so many Amplifone tubes?!
 
After talking to Andy in the UK I agree with him that it IS a shadow mask issue. The mask basically has a wrinkle or bubble moving it away from the phosphor coating and tube. The beam does not hit the phosphor correctly in these areas resulting in the odd color anomalies.

You could have a specific color burned off without it being visible as burn in on the monitor tube when off but that is not the case with these IMO.

I know of 4 Amplifone tubes that have done this so it seems to be pretty common unfortunately. :(
 
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