Sony 27" kine swap info needed!

[andy]

Originally Posted by kx250rider

I wish I could explain, but that would maybe best be answered by an engineer. (Hey Tom Ryan or Colortel???) I think it could be that a CRT "gets used to" a certain cathode current, and the cathode coating deteriorates at a certain even pace. Then all of a sudden the temperature is changed due to a different current load (heat): Cathode coating cracks or fails somehow. Just an uneducated guess.

So your saying it's the change in the G2 voltage that hurts the CRT? So if a new CRT is setup with a higher than normal G2 voltage, its life won't be negatively impacted?

How often have you seen this happen? I've done quite a few CRT swaps and I've never had any problems with the swapped CRTs. I normally adjust the G2 on AKB sets by looking at the cathode signals on a scope. I adjust it so that the video has the widest dynamic range possible while not crushing the blanking pulses. This would mean that they G2 is set as high as possible without retrace lines. My logic is that as the CRT ages, the cathodes will need to be biased at a lower and lower voltage (to make the picture brighter), so start with the highest cathode voltage possible.

It has to be related to cathode voltage, not current since it takes the same amount of current to produce the same brightness picture, no matter what the cathode and G2 voltages are.

Has anyone see this happen with other types of tubes? It seems like the same thing could happen to audio tubes.

[kx250rider]

Originally Posted by andy

So your saying it's the change in the G2 voltage that hurts the CRT? So if a new CRT is setup with a higher than normal G2 voltage, its life won't be negatively impacted?

How often have you seen this happen? I've done quite a few CRT swaps and I've never had any problems with the swapped CRTs. I normally adjust the G2 on AKB sets by looking at the cathode signals on a scope. I adjust it so that the video has the widest dynamic range possible while not crushing the blanking pulses. This would mean that they G2 is set as high as possible without retrace lines. My logic is that as the CRT ages, the cathodes will need to be biased at a lower and lower voltage (to make the picture brighter), so start with the highest cathode voltage possible.

It has to be related to cathode voltage, not current since it takes the same amount of current to produce the same brightness picture, no matter what the cathode and G2 voltages are.

Has anyone see this happen with other types of tubes? It seems like the same thing could happen to audio tubes.

Well, that's why I defer to an engineer...

My experiences with this problem are only on used tubes, not new. I've had it happen on all types of color CRTS, particularly with Sony direct-view tubes, and Mitsubishi projection tubes. And with the Mitsubishi, I ALWAYS set up with a scope per the book. With the older Mitsubishis, the procedure is to set the G2 pots to min, Drive to center, and scope the collector of the green video output (cathode of CRT)... Set the Sub Brite to see 180 vdc on the CRT cathode. Then eyeball the G2 pots at lowlight and finish with the drives.

That works great on new CRTs, but if I do that on a set of used ones, it's good night nurse!

Charles

[old_tv_nut]

I know we were advised to fire up our tube-pickup (Saticon) HDTv camera at least every six months, supposedly to prevent deterioration due to gas, though I never found out if that was really the cause or how the gas would be removed by operation. Anyhow, those pickup tubes had very small cathodes and gun apertures to get the required resolution, and that's why they were so sensitive to use conditions. I never thought that "big" CRT cathodes would be so sensitive, so it will be interesting if some expert chimes in here to tell us the mechanism for deterioration.