Gold Lions KT88 on Sonic Frontiers Power SE

Tube bias should remain stable but I'm not too quick to blame the tubes IF all of the tubes in the R channel need to be re-adjusted. Try switching the right channel tubes to the left side and see if they are unstable there. But, FWIW, it could be a problem with tubes if they weren't competently checked before you bought them. I have a quad of GE's I used in a SF amp. One particular tube is not able to hold a stable bias - there is nothing wrong with that amp.

Another thought - try checking the bias after the amp has been on an hour or so and has been unplayed. Some times the bias can change depending on the use immediately preceding the check. I have one such amp (not a SF) and I have to let it settle after use for about 30 minutes before I evaluate the bias settings.

Hope that helps a bit.

I have had tubes drift for awhile when they were new. I'm using Shuguang Treasures now and they also had some drift. After about 100 hours they settled in and have been solid since. As Newbee said try putting them in the other side and see if they do they same thing in the other side. If they are only moving a little they will probably settle in and be fine.