@willgolf - thanks for the feedback on the PADIS and BLUE. There could be a couple of things going on here. One is that the tube amp may not be high resolution enough to reveal any slight differences between PADIS and BLUE (I'm not saying this is true, I'm only saying it is a theory). In my experience, the very high resolution equipment can reveal differences. In stuff that is lower resolution or warmer voiced, the differences between elements such as fuses or interconnects are more difficult to see and sometimes impossible. Having no experience with your specific tube amp, I cannot be sure.
The other one is that, in my experience, the differences in fuses for amplifiers have much less impact than fuses in preamp/source equipment. I think that part of it is the fuses in the amps have a larger internal fusewire (because of higher amp rating) and the nature of fuse composition has less influence in amps. In any case, a fuse will still have an influence on an amplifier's sonic signature, it is just much less of an influence a fuse would have in a preamp/DAC.
The final option would be that there is no discernible difference between PADIS/Futurech and BLUE fuses. I think more testing with different types of equipment would have to be done before we came to this conclusion.