Motorola vt71

[timmy]

Does anyone know when what the indicators are when a 7jp4 crt is getting tired or the phosphor’s are beginning to degrade. I have a bright tube but it’s like having no contrast all white until turning the brightness down some and it’s good I have a new 7jp4 I tried and it don’t do this. so this tube is really bright but don’t know if the emissions are low or phosphors are tired.

[old_tv_nut]

While phosphors do degrade slowly over time (burn in), it is minor compared to the cathode degrading, which is what you could be referring to.

[timmy]

Originally Posted by old_tv_nut

While phosphors do degrade slowly over time (burn in), it is minor compared to the cathode degrading, which is what you could be referring to.

So if the cathode, emissions are low or degrading shouldn’t the screen be somewhat darker not super bright ?

[Yamamaya42]

Originally Posted by timmy

So if the cathode, emissions are low or degrading shouldn’t the screen be somewhat darker not super bright ?

depends...

If you lose "cutoff" you lose the ability to have good contrast levels, things start to look washed out, you get the infamous silver faced look when you turn up the brightness.

[timmy]

Originally Posted by Yamamaya42

depends...

If you lose "cutoff" you lose the ability to have good contrast levels, things start to look washed out, you get the infamous silver faced look when you turn up the brightness.

Well I have another 7jp4 that is new and the contrast is good on that one.

[Alex KL-1]

Slight gassy/soft tube?

[timmy]

Yet another issue the retrace mod was done on this set but I have retrace lines on the bottom of the screen I always seen them on the top and the 220k resistor is good.

[Yamamaya42]

Originally Posted by timmy

Yet another issue the retrace mod was done on this set but I have retrace lines on the bottom of the screen I always seen them on the top and the 220k resistor is good.

On the old tube, or both new and old?
If it's just the older one and not the new, then that is another sign of a tired tube, the elements can no longer react fast enough to the blanking signals any more.

[timmy]

Originally Posted by Yamamaya42

On the old tube, or both new and old?
If it's just the older one and not the new, then that is another sign of a tired tube, the elements can no longer react fast enough to the blanking signals any more.

Both tubes the lines are not bad they are faint but can be seen on different scenes

[Chris K]

I got very very lucky on my VT-71 acquisition and restoration. It has one of the brightest 7JP4s I've ever seen. I have about 5 others that range in quality from "can't see a thing" to "watchable but not great".

[Yamamaya42]

I'm not familiar with the VT-71 or the mod you tried, but most likely there is more than one way to do it, and how well it works most likely depends on the health of the tube, and prob will never get rid of all lines completely, but reduce them to a level where it's much more watchable than it was before added.