There is no ideal power transformer with perfect magnetic coupling and no leakage flux. So the impedance will be always higher than winding resistance. No one would want to add more resistance to what is already there in order to keep the impedance of the secondary winding and the power supply as low as possible. Impedance is the current limiting characteristic of a transformer. If the amp needs a lot of current to drive a speaker load it will be audible if the impedance is high.
A fuse on the other hand has to be a resistive load if the current in the power supply rises in order to operate as a fuse in case of failure . That will be audible if the amp has to drive demanding speakers at high volumes or dynamic peaks. This shouldn’t affect class A amps but definitely class A/B designs.
So how would different material of the fuse wire which has to be a resistive load by design (gets hot and burns up if it reaches its breaking point) influence the SQ?
A piece of wire that would not increase the impedance of the transformer would be the only logical solution in order to avoid these current limiting effects. But then it’s no longer a fuse.
How does this all fit together with those expensive fuses? Any explanation?