I've always used NOS tubes, but when I wanted to replace the eight matched 6550s in my Cary mono-blocks, I almost went apoplectic! The prices have gone nuts on matched quads/octets of anything worth having(supply and demand strikes again). To my surprise and delight, The Winged "C" 6550's(St Petersburg plant) actually out-performed the Phillips octet that they replaced(more open and transparent). I wouldn't purchase output tubes from anyone but Upscale Audio. Their screening, and matching processes can't be beat! Kevin is anal about his quality control, and company's reputation(and I like that a lot). I have no other connection to them, other than as a very satisfied customer. Check out the test equipment/process descriptions he includes on his site:(http://www.upscaleaudio.com/product.asp?itemid=16&catid=85) Ask Kevin about KT88s in your application. You may be able to get a bit more output with them than with 6550s. Kevin will be able to advise you as to any differences in sonics between the two. Happy listening!!
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