My Had amp wound up with GL KT66s, and I liked them so much I "panic bought" a back up pair. Great sounding tubes in a great amp...however...I recently bought a new Pass Labs XA25 and none of my tubes work in that amp (you can lay tubes on top of it or maybe cram some underneath)...that said, although not necessarily completely broken-in yet, I think the XA25 is an amp every tube freak (with compatible speakers and things) should hear. Good Ol' Nelson, whom I've admired for his DIY community support and First Watt stuff (never owned one of those, but still), has simply designed a killer thing in the 25...I've never heard a solid state amp that resolves detail and provides the astonishing tonal "rightness" like this thing...just pure Class A slam and life, utterly quiet performance with effortless clarity, accuracy, and soul for days...I'm smitten (smote?)...