what I remember about my 275's was they were the last run for the American market as planed at that time. There was to be one more run for the Italians, Then no more. My serial numbers were 520E0 and 520E1. I had them close to 4 years, I bought them instead of four 3500's. If I had to do it over again I would have put off buying a new car and bought the 3500's. Any way the 275's performed faithfully with only one bad input coupling cap failure, and few issues with 12 Bh7's as I remember. The KT 88's performed so much better and lasted longer than the 6L6GC of my previous 240;s and the 6550's of the MC 60's. They were nice amps . I should have kept them longer and skipped the 2100's and 2200's. The 7200's would have been the answer, but then you live and learn. Yes my speakers bi amped prefer high damping factor SS amps. I now use 207's. But that does;t take away from the great memories of 275's bi amped reproducing boot legs of live performances I made being heard better than live in my home. You just can't forget experiences like that. Thank you, Ampex, C-28, 275's, and Concert Grands. I think I'll pull out and listen to a PP&M tape I have mixed and dubbed to CD. Wonder where my old Ampex 300-4 is?