The SR Black fuses are definitely directional. A friend and I switched the three fuses in the H-Cat X-10 MkIII amp from writing into the amp to all out. The sound was harsh and with no stereo imaging. My friend decided that the two top fuses were dc circuit fuses and that one needed to be the opposite of the other fuse. With the other fuses with writing going into the amp, we made the left one to out. This was much better, but ultimately we made the lower ac fuse go out also. I am not certain of this right now, however.
Don't experiment with fuse direction at your loss.
Don't experiment with fuse direction at your loss.