If for no other reason, that Sylvania range was interesting for being an early introduction (among USA designed-amplifiers) of fully complementary power amp output stages. At least, that was our belief at the shop where I worked in their day. We were impressed, even though it had already become standard practice among Japanese brands.
Perhaps the designers still didn't really trust semiconductors, though, since another unusual aspect of the range was the use of sockets for many of the semiconductors. If I had one in my current shop, I think I'd take the trouble to at least re-seat the socketed parts, perhaps with a spritz of DeOxit on the parts' leads.
(BTW, if anyone is so psyched about these Sylvanias that they wish to acquire one, PM me.)
Cheers,
chazix