Hi Is it possible for a power tube to test good but be "worn"? I recently bought a preowned amp that uses Winged C 6550 ( date codes are from 2001 and 2006) I tested all the tubes discarded the bad ones but was wondering, is it possible that the tubes test good but are really not at the top of their game sonically? The previous owner did not give me an estimate of the hours on the tubes but I suspect from their answer it was significant. Amp is a CJ Premier 12.