slow blow or fast acting fuse

I am curious why you want to use these fuses in a 20 year old surround receiver.

Why even waste the time trying expensive fuses that are unlikely to make much if any difference with such a receiver ?

They made a difference in my 35 year old Fisher 500 C.

It is not normally my practice to make generalizations, but a Sony receiver is not in the same class as a Fisher 500C. I have loads of restored vintage equipment, and a nice sounding old skool Marantz SR-19 AVR. Would I bother trying expensive HiFI tuning fuses in them ? No. IMO, the OP's money would be better spent having a tech give his Sony receiver a checkup. If bias or DC offset have drifted, adjusting them may prove more beneficial.

I looked at the fuse and there is no indication if
this fuse is fast blow or slow blow. I called and asked
sony and they said they are slow blow but I think they're
lying to me.