Every tube amp owner needs one of these
Excessive heat build up is probably the most common cause of electronic failures. I have one of these tiny 4 inch Massey HV fans quietly cooling the hot tubes of my amp. Its on the same circuit as the amp but introduces no interference. Most tube amps aren't well ventilated and often times the case itself serves as the heat sink. My amp and tube life no doubt have been extended by this fan these last few years. Walmart sells these puppies for under $10. IMO the silver fan looks the best.
http://www.amazon.com/Massey-High-Ve.../dp/B0019QU4XM