How do you know when to replace tubes


I recently purchased the Audio research Anniversary reference
The unit has 2600 hours on the tubes.The manual states replace the power supply tubes after 2000 hours.Do you indeed have to replace the tubes even if the sound is good.Another question is tube rolling enhance the sound .As an aside the Audio Research replaced the Einstein Tube pre amp noticeable improvement to the sound ,mainly the lower mid range and bass.
ramy
When it comes to power tubes, I'm more concerned with catastrophic tube failure than SQ. Following the recommended tube maintenance schedule is dependent on the amp and manufacturer.

I've had power amps where the tube just gracefully dies but with ARC, I'm definitely following their recommendations.
Heck, almost any triode power amp can log 10,000 hours on the power tubes, the exception being the 6C33. We had one of our amps log 22,000 hours on the power tubes before we finally had to replace one (there were 16 power tubes in that amp, FWIW...).
Wolf, Why did you go for the KT 150's instead of just replacing the KT 120's? Double the $$ double the pleasure?
They became more affordable and now cost about the same as 120s on a weight basis (it might take 5 120s to equal 4 150s), they could last a ling time, and they're larger than any other tube that will fit in my amp (!)...I was listening to a great live jazz CD (Fred Hersch) tonight and the 150s sort of woke up and now sound even better than yesterday...they sound large.