Synergistic Research Black Quantum fuse, 6.3A small slow-blow (5x20 mm). Perfect for 5A audio application.** This is considered one of the premier audiophile fuses. The difference in sound quality it makes vs. a stock OEM fuse or even some of the other audiophile fuses, short of the very top of the line, is night and day. I used these in a pair of ATC active home speakers for a little over a year.
$50 shipped USPS in the U.S. + PP fees (or use the family/friends method). Check my references at Audiogon, Audiomart, Audio Asylum, Audio Circle, head-fi, and ebay (genegold99).
**N.B. Based on initial user experience and for reasons discussed on forums, to be safe the SR Black fuse’s rated amperage should be at least 25% higher or the next amperage up than the rated application calls for; e.g., the speakers they were used in call for 5A fuses (manufacturers typically give fuse specs far beyond what’s required to be cautious and to avoid returns for blown fuses).