20th anniversary edition tube

I'm new to the forum so I hope this post is in the right place.

I have a 20th anniversary edition tube that I hadn't used for a few years. When I got it out today it was breaking up at lower frequencies ONLY ON THE CLEAN CHANNEL. It still sounded nice when playing the top three strings by as soon as I hit the A string it cracked up like a bad connection.

My question is this ... is this likely to be a tube issue if it's only happening on one channel?

Thanks for any advice.

I just stumbles across this and seeing how you never received and answer...

All I can say is...it could be. To be sure all you have to do is swap the preamp tubes with new ones and see if it continues. I doubt it would be an issue with the power tube.

Not sure if you tried this, but you also might see if the other channel does it with the gain turned almost all the way down. If it does then it might be more than just a tube issue.