Groove Tubes has built their reputation on the quality of their matching process, but even the best tubes will fail if the bias is not properly set. Here is some of the text of a recent email I got from GT.

"Give us a call here at Groove Tubes and talk with Rick, he can give you all the info you need or will get you to someone who can. We have a toll free number (800) 459-5687. Our hours are 7:30 AM to 4:30 PM Pacific Standard Time."

Rick is knowlegeable about all kinds of amps, including Ampeg. I won't claim that he's totally unbiased; he does work at Groove Tubes, after all, but he seems to be a straight shooter. That's a rare thing in a business that seems more like voodoo than science to most of us.

Good Luck. Let us know how it turns out.