There are two ventilation fans in the back of the x300s. They are turned on when the internal temperature gets too high, according to Cyrus. I think they operate very much like computer's thermal temperature detection and control. After using the x300s for slightly more than one month, i haven't seen and heard the fans have been activated at all.
Yes, this is one of best classic british integrated amp having impressive sound quality and priced extremely affordable 25 to 30 years ago. I am still enjoying it from time to time.