The best place I know of is QS&D in Fredricksburg, Virginia. Ask for Randy Stringer. I had a number of repairs there. The problem is that there is more than one panel inside the Quads and when one goes it is likely that the others may not be far behind. Also when you go there thay have a few upgrades that may be more efficient in protecting and improving the speaker. If you love the sound of the ESL 63 then it is worth it. As someone said, they do a lot of things right.
Steve
Steve