Which SR Blue or black Fuse

Just so I understand, these SR fuses work as protective fuses, correct? A SR 4 amp fuse should blow when that current is exceeded correct?  I mean otherwise it's not a designed fuse and it's just a piece of metal.  I'm not so concerned about the UL listing, I just want to make sure they blow when they are supposed to and that there is a performance spec associated with their design.  I ordered a SR blue last week and now you guys have me worried about even using it.

@folkfreak Thanks!

@glupson I recently had an AC fuse in my IEC connector blow when switching from triode to UL mode. Turn on and switching surges popping fuses is not as uncommon as you may think.  In fact you can search the forum and find others here posting about it over the years.

@glupson

In my case the blown fuse was a little bit of user error as well as a little manufacturer error.  I was listening pretty loud when I switched on the fly from the triode to UL, instantly doubling the watts.  Later in discussing with the manufacturer, they recommended using a 4 amp fuse instead of the 3 amp fuse that came with the amp stating that you can usually get away with a 3 amp fuse but switching surges can sometimes pop the 3 amp.  Since then I always reduce the volume when switching from triode to UL and have never had a problem since, even with a 3 amp fuse.

There must be an "arguing forum" somewhere on the web.  Clearly some people here derive much more enjoyment from arguing and taking shots at others than they do from music.

Ok, I honestly can't believe what a difference flipping the fuse made.  Geez, seriously...that took me by surprise.  Thanks for the very quick and sage advice from @nonoise @geoffkait  and @david_ten .  You guys were all spot on!  The highs are back and detailed, the bass no longer loose, and the overall resolution of sound is so much more pure than using the stock fuse already.  My best descriptor would be a more realistic sound.  Grant Green's guitar sounds like it's being played out of my Mesa Boogie tube guitar amp and I could feel Ben Tucker's bass strings reverberate cleanly.  Was streaming Grant Green's "Green Street" MQA version as my reference for this fuse.  Impressed so far and appreciate your quick rescue guys.

So my SR Blue just arrived and I popped it into my amp's main IEC connector.  Straight out of the box it sounds a bit dark to me and the lows aren't quite as tight.  I will search the forum to see if others noticed this during the burn in period.  I know this fuse is directional so it's also possible I need to flip it around.  For the life of me I couldn't determine which way current flows through my connector (Note: I know current is supposed to flow from the S to the R printed on the fuse).  Any useful comments are welcome.

@nonoise 

Humans have a long history of being furious about concepts, ideas, and experiences they haven't shared or can't wrap their heads around. This is nothing new.  I do believe them that either their ears, perception, or equipment (possibly collectively) can't resolve the differences a fuse can make.  I certainly went into this with high expectations and immediately felt I got ripped off as the sonics were clearly worse right out of the gate with the fuse flipped apparently the wrong way.  I clearly didn't have confirmation bias and was already preparing myself mentally for sending this thing back.

Even if I had sent the fuse back after concluding it didn't work for me or in my system I would never disparage others for perceiving a sonic improvement.  As things turned out I am one of the believers in this fuse for my equipment and as resolved through my ears (which I believe are pretty good as a lifelong amateur musician).

As for people behaving badly?...that's not a fuse issue, it's a human tragic flaw ;-)

@kosst_amojan

quantitative reality

Quantitative reality is always reflected on relative to our current point in time. Earth being flat, universe revolving around the earth, blood-letting being a cure for ailments, avocados being unhealthy due to high cholesterol, etc... Do you really think we quantitatively understand everything today that humans will ever know???? It is so naive to believe the tools we have to measure something today or the concepts of physics and chemistry or even our understanding of the universe right now is all we will ever have and that everything we think we see today occurs exactly how we perceive or try to measure it.

Just because we don't have the tools to measure something we are observing doesn't make the observation less real.  It never has.  

So I think I will let this first SR Blue settle into my amp for the next 100+ hrs or so before possibly adding another.  Any consensus on where I'd get the most bang for the buck in placing another? Choices are either my streamer/DAC or preamp.  I run the streamer/DAC through my preamp.

@david_ten 

I would choose the Streamer/DAC first, but either component is fine.

Much appreciated.