The following is my experience replacing the standard fuses in my integrated amplifier with Hifi Supreme Tuning Fuses. The amp is an ARS-Sonum Filarmonia. It has maximum output power of 30 watts RMS per channel at 8 ohms. Its output stage uses a pair of E34L pentodes per channel, in push-pull configuration. It is an outstanding amp paired with Merlin Master VSM's.
There are three fuses. The main power fuse is a slow-blow 4 amp, and the two internal fuses are also slow-blow rated at 500 mA.
I initially purchased only the main power fuse, as I had heard that it has the most dramatic impact. From the moment I replaced the stock fuse, the improvement was clear and continued to improve over the next week. With that success, I decided to spring for the two internal fuses. Unlike the immediate improvement with the power fuse, my initial response to the new internal fuses was, "Wretched!" It was so bad that I immediately shut the amp down, took the tubes out, disconnected all cables, opened up the amp and switched the direction of the fuses. I believe that this improved things slightly. But still it was virtually unlistenable for the first ten hours. By 15 hours, it had started to relax a little, although still extremely congested. By 20 hours it was just barely starting to sing.
I've now got about 30 hours on these new fuses and they're sounding pretty darn good. At this point I would say that they are a definite improvement over the stock fuses. Primarily, the soundstage seems to be more clearly defined. I have more of a sense of the depth and boundaries of the original recording environment. Instruments are also more realistically "shaped."
This is perhaps the most dramatic burn-in phase of any new component I've added to my system: from wretched to pretty spectacular. Maybe it's the 99% silver wire. I am expecting continued improvement through 100 hrs. based on what I've read.
I'm writing this for anyone who has purchased these and have not had the patience to let them burn in. I was tempted to give up at 10 hours, given my experience with the immediate improvement with the main power fuse. I suppose, however, this makes some sense. I have very little technical knowledge, but the current running through the signal path must be much lower than the current running through the main power fuse, hence the longer burn-in time??
It always amazes me that manufacturers do not state clearly and unequivocally that their product WILL sound inferior until after XX hours of playing time. I bet that plenty of "non-believers" in the burn-in phenomenon have judged products inferior before giving them a fighting chance.