fuses - the $39 ones or the 85 cent ones

I have not read this whole thread so maybe some of this is redundant.

I would say the results vary quite a bit.
Obviously it also depends where in the circuit path the fuse lies as to how it will effect sonics (as well as the particular circuit as well) and the resolution of the system.

In my PS Audio Solid state control amp - the Hi FI fuses provided a nice improvement that was subtle but noticeable.

On my ATma amps the fuses (one of which is in the signal path to protect from tube blow outs) were a large improvement in inner detail among other aspects- and was not at all subtle. I have suggested these to other owners , one who thought it was a much bigger upgrade than going to better power cords.

I put them in my sub's amps and I can't really tell if there was an improvement (though I didn't then pull them out and listen again- so who knows.)

These companies should create a user database for people to fill in what component they upgraded and what the improvement was. I think it would help people to feel confident they were getting their money's worth.

But to me the cost is small enough that if it makes 50% of my components better - it's money well spent. This goes against the law of diminishing returns we often speak of. If $80 in fuses makes my 14K$ amps even 10% better, it's worth the trouble.

Wow! 14 large for amps is beyond my entire investment, at new/retail. Even counting my non-audio stuff like TV and DVD player (OPPO '981).
As far as I can tell, given that I have a non-optimum room, I could spend 3x on equipment/gear and not get much or any better sound.
Now, If I spent some loot improving the listening space, I'm sure that there is probably a better equipment set.
Everyones value/cost curve is different. But for now, I think I will get more out of a better space for say....300$, counting a couple boxes of OC703, some wood / coverings and mounting hardware than I could out of half that in fuses....
2 for the amp / another 2 for the speakers.
At that point I may be willing to go nuts and ship off for some standard ceramic fuses. If they make ANY difference I'll be surprised enough to ask for some fuses for Christmas!
Now, I dont' believe I mischaracterized anyones statements.
That there are believers and skeptics is a given. In my last post I used DBT as an example of how the Placebo effect plays into peoples wishes / wants / desires. I, better than most realize the difficulties (practical impossibility in Hi-Fi) of organizing such a test. Being on the skeptic side makes me the nut! If anyone would perform some due diligence and just have some healthy skepticism....
I will remain open to the tuning fuse.....But would wish for someone to be able to reliably tell the difference...fuse in or out, with some degree of confidence. This is the 2nd or 3rd time I've made such a request. No Takers? If I had these fuses, you can be sure that I'd try it.

Don't mention double blind tests as they are invalid tests for audio.

Tbg, wow, where did that come from? To paraphrase you, certainly you saying DBTs are invalid don't make it so. As Magfan asserts, conducting DBTs would be difficult with hifi but not impossible. Of the actual DBTs I've read about only ten percent or so have shown people hear a difference between the items under test. Those people who statistically show the ability to discern differences are usually practiced listeners. Which you probably are. But again the items under test were items that are accepted, even by most skeptics to have a difference.
IMO many of those people in the audio world who are dead set against DBT have something to lose. For instance, if I sold an item such as a battery operated clock and claimed that by placing the clock in your home your audio system would sound better I wouldn't want that subjected to a DBT.

I wish they would do this test at RMAF.

What would be a low cost $100-200 approach for corner placed bass traps?

Good pont Timrhu. I don't beleive that there are any insurmountable difficulties in setting up a DBT of cables, amplifiers, power cords or whatever; simply a lack of interest by entities that have the resources to fund accurate and probative DBT's (such as pharmaceutical corporations and government agencies). This is in part likely a combination of no financial benefit to the corps and no significant public interest as to the agencies. Furthermore, as to the more ridiculous claims - no one is going to spend the money because there really is no question to be answered .