What are fuses used for?

Look on the back panel. Near the AC cord/outlet you will see a round (usually) screw-type cap. Below it will be a designation indicating the size of the fuse required. Unscrew the cap and pull it out. The fuse is held at one end by the cap. It is a press fit. Pull on the fuse to remove it. Hold the fuse up to a light and observe the very thin wire within. If it is intact the fuse is good. If the wire is broken the fuse needs replacement. Replace only with a fuse of the same rating on the back panel.

Some fuse holders are square and require a push-in for release. Others are round and require a push-in with a twist before they can be pulled out.

Thanks again!

After trying a few different brands of high end fuses on my McIntosh C2500 tube pre I have come to the conclusion that there are better ways to spend the money (like giving it to the homeless).  Either my system has such high resolution that they aren’t needed (doubtful), or it’s snake oil.  I go with snake oil.  

I tested some "premium" fuses a while back after disputing the insane hyperbole attached to them by a few shameless salespeople...I figured it would be interesting and I had access to a pile of 'em...I found them to be absolutely useless relative to SQ, and some were actually rated improperly and blew in a power amp.