I have a Audio Research SP16 tube preamp that is 4 years old w/ about 4,300 hours. As a result of considerable "hiss" emanating from the right main, I called Audio Research (ARC). I was advised that experience has shown that the tubes in this preamp have a life expectancy of about 3,000 - 4,000 hours. Although this is certainly just a rule-of-thumb, I suspect it's time for tube replacement.
ARC recommends using a single low-noise tube on the input side & regular tubes for the rest. (There are 6 tubes total). I also have the option of using 6 low-noise tubes. My question: Is there any discernable difference in sonic quality that is worth the extra $ for the low-noise tubes? BTW, I do not have a phono. My only input source is a Cambridge Audio CD player.
Thank you kindly.