slow blow or fast acting fuse

Hi I was hoping someone can help me, I have a
sony str-gx69es receiver and I wanted to upgrade
the fuses.The fuses for the power supply are
125v 4a and 125v 8a. The other two are for the
speaker impedance selector which both are 125v 8a.
I would like to try some hi-fi tuning fuses but I
don't have a clue if they are fast acting or slow
blow. I appreciate your help. Thanks!
If the fuses are the originals, the designation on them should tell you. IME, the power supply fuses will be slow blow and the speaker or output fuses will be fast.
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.
This one is for Gbart I happen to like sony es receivers
and I don't care for yamaha, nad, denon, etc. or any
other brand. The answer to Tls49's question is obviously
to get better sound.
Again, power supply fuses are almost always slo blow. Otherwise the turn on surge would blow them.

Speaker fuses are always fast blow. Otherwise it would take to long to effectively protect the speakers or the output stage.