[ovation1357]

Hi All,
Whenever a tube fault is mentioned on the forum there is usually a link posted to this document:

http://repairfaq.cis.upenn.edu/sam/reppic/sencrt.pdf

A certain Barco (Seos) 808s that I purchased a few months ago, had a totally dead green PT18-205 tube (in nearly new condition, but emitted no light). Today, I have found that the second projector in this trio has got a very dim green tube and I've concluded that the cathode needs restoring.

In both cases I tested the tubes for shorts and found none. In the case of the dim green tube I did try repeatedly arcing the G2 voltage onto the cathode as suggested in the Sencore document (although that's more for clearing shorts than improving cathode output) but got no improvement.

Does anybody actually own one of these magic CRT analyzers/restorers in the UK? Or has anybody designed a circuit to perform the same function?

More importantly, would that person be kind enough to help me try a last ditch attempt to save these otherwise useless tubes?

Many Thanks
Jonathan

[Roland @ B4]

Jonathon about 5years agao I spent quite a bit of time looking into this. I even spoke to the ain production manager at Barco and he said it would not work for Projector CRT's. They recond that there was not sufficient cathode material for the life of the tubes
However if you have any luck I have x5 Green Sony 808s tubes that have perfect phosphor but little or no output. It is only these tubes that seem to suffer from it.

[ovation1357]

Hi Roland,
So far I've certainly found information which seems to follow a similar direction to your own findings. It seems that newer CRTs with thinner necks tend to have considerably less of the electron-emitting material on the cathode.

This guy has posted a really interesting document about his experience of dim tubes in CRT monitors:
restore crt

He says that even if he's managed to brighten a tube it has gone dim again within a couple of days. The only temporary fix he found was to increase the heater voltage. I might experiment with this with a duff tube if I'm bored one day, but it's not even close to a solution.

Sencore claim that the CR7000 is unique because it has methods of restoring these newer tubes, whereas traditional CRT 'restorers' risk damaging the tubes:
http://www.pdctrading.com/photos/Sen...20brochure.pdf

If I get anyway with my investigations I'll post back - but it seems to be becoming apparent that no one owns one of these Sencore CR7000s (in the UK).

I'll post on avsforums too to see what experience folks have had with this product as I have found evidence of companies that own a CR7000 in the US.

Cheers
Jonathan

[Tom.W]

Rejuvenation is a whole different animal then clearing contamination shorts....

Granted some tubes are just too far gone to be saved but the Sencore will give you a good idea of the emissions and condition BEFORE you go to the trouble of installing or buying a replacement tube.