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.
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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.