I replaced my stock McIntosh tubes with Psvane Black Bottles KT88s in my MC275 and was a noticeable improvement. This was 4.5 years ago and still sounding great.
FWIW I purchased 5 in case one failed, on rotate then every 2 months so they all age similarly. No failures.
FWIW I purchased 5 in case one failed, on rotate then every 2 months so they all age similarly. No failures.