Why is one of my amps power tubes red plating?

[station5343]

I just recently had my bugera 333 into the shop for a retube and one of the tube's is red plating, it is happening with the left outer power tube. So I brought it back into the shop and the tech swapped the two outer tubes and it seemed to be ok while it was still at the shop but as soon as I got the amp home and turned it on it happened again. It seems to be happening more when the amp is in the overdrive channel than the clean. So just today I decided to completely swap the tube's around, I swapped the two outer tubes with the two inner tube's and the same thing is happening with the same tube. BTW the tubes are chinese shuguang power tubes i'm begining to think it was a mistake buying them but I was curious and wanted to try them. Anyway if any one read's my post and has any advice and want's to post a reply I would be most gratefull...thanks.

[52 Bill]

If the problem stays with the same tube socket, then the problem is with the amp not the tubes. The socket may be bad or there may be a problem with the related circuitry like a bad cap or a bad connection.

Have the amp checked out before it gets worse.

[g1]

I got the impression that the problem is staying with the tube, no matter which socket it is in. In that case the tube itself is bad.
However, as 52Bill has stated, if the problem is staying with the socket, then it is the amp that has the problem, not the tube.

[Enzo]

AGree, if the problem stays with the socket, the amp has the problem. If the problem moves with the tube, the tube is defective.

You cannot take one tube from a factory and decide from that that all tubes from that factory or crappy. I don't know ANY factory that never made a bad tube.

[GregS]

If I understand correctly the redplating started after the amp was retubed. Was the amp rebiased after the new tubes installed? If not that could likely be the problem. The bias voltage may need to be set more negative to the point where all tubes are operating in a cooler range. The one redplating tube isn't necessarily bad. It may not be exactly matched to the others and is conducting more current under the same conditions. It's possible that the rest of the power tubes are just under the threshold of redplating and that the amp needs to be be biased colder with the new tubes. It could also be a bad tube though.

[stokes]

What everybody said,but I just would add,find another tech.Merely switching the tubes around is no fix.Something caused the tube to redplate,either bad tube or bad socket,as has been pointed out already.