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why do hi-end fuses keep blowing, while std don't?

I've had my McIntosh MC275 for several years running flawlesly. Up until last Nov I was using stock KT88 and rolled small tubes and had a Hi-Fi Tunning fuse without issues.

In Nov-13 I upgraded the KT-88 to Psvane black bottles measuring 60mA plate current. A few power-ons after I rolled the tubes, I turned on the amp to let it warm up, but returned to a blown fuse. I thought a tube might be bad so used a std fuse, but never had a problem again.

Two months ago I bought a new high-end fuse, replaced it, and soon thereafter the same happened: blown fuse. I replaced it with a std fuse again, which is still running.

So I want to upgrade the fuse, but chances are if I use the 2A fuse it will happen again. Yet I don't want to use a higher value fuse. I'm thinking the Psvanes might be drawing significantly more current than the stock KT88 and the Hi-Fi Tunning fuse might have a tighter spec, driving said fuses to fail while the std ones survive. Would you agree?

Suggestions as to how to resolve this?

thanks much!
lewinskih01
bdp24's avatar
bdp24
9,795 posts
 

You're missing my point, Mr. Kait. You are in fact making it without realizing it. Listening for the audible effects of a fuse, and evaluating it's electrical behavior, are two very different things. Modjeski approaches hi-fi evaluation first as an ee (as a purely intellectual activity), audiophiles don't.

A point worth making is that Modjeski investigated and reported his findings on only the original Hi Fi Tuning Fuse, not any other boutique brand or design. Each of those has it's own unique characteristics, and should be evaluated separately. The ARC LS16 I bought years ago came with a Hi Fi Tuning Fuse installed, and worked fine. After reading Modjeski's report on their use in his RM-9, I wouldn't dare install one in a power amp tube application (in a DC circuit). Knowing how audiophiles react to criticism of a product they own, I'll bet very, very few have read that report. Suit yourself!

As for RM being an electronic wizard, anyone who can watch his talks at The Burning Amp Festival (and those of Nelson Pass) and not come to the same conclusion is a better man that I. Or better yet, listen to one of his amps! Geoff, I'm going to take a wild guess and say I'll bet you have never heard one. The RM-9, the RM-10, the RM-200, any of his single-ended triode amps, or his OTL's? What amp do you listen to music through?

geoffkait's avatar
geoffkait
23,365 posts
 

A.E.’s are more skeptical than E.E.’s. But more to the point A.E.’s investigate rather than proclaim some conclusion or another without a thorough and complete investigation. That is, after all, the scientific method. That’s how we progress. But RM is not alone, I know many high end amp designers who are cock sure they’re right about a lot of audiophile ideas that have been accepted over the past twenty years. Like fuses, directionality of fuses, directionality of wire, aftermarket power cords, directionality of power cords, stuff like that.


I repeat, of the approximately 90,000 aftermarket fuses sold there has not been a single component damaged by a fuse that has been documented and verified. So,I think it's safe to write off RM's "experience"  as a fluke and dismiss him as one would any outlier.

teo_audio
2,197 posts
 
Well, if one insists, it would be, scientifically speaking, impossible for a fuse to not modulate the current passing through it.

That’s it’s job. Literally.

And it goes about in a very non-linear odd-ordered distortion pattern way. Where it is a combination of the load vs the physical properties of the fusing element.

Again, that is part of it’s fundamental operation and function.

Modulated current means abnormal amplifier circuit behaviour. It’s like a tap that turns it’s self off a bit when the transient load goes up and then retreats to being more open when the load decreases. But not in perfect agreement with the load, it does it in an odd harmonic, non linear way.

Humans will hear this, as our hearing is designed to hear odd ordered harmonics that are out of ’position’ in time and level.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~

This can be expanded on and filled in more correctly or fully, but ...those are the basics.

Anyone looking at fuse element fundamentals and operation, would have a hard time missing this, as it is the core of the fundamentals of the design and operational parameters of a fuse. Writ large across the literature. It’s clearly visible in the loading behaviour graphs.

Missing it means, well, I’m not sure what it says about the given intellect reviewing the data. But it could be stated in a negative manner.

geoffkait's avatar
geoffkait
23,365 posts
 
What's the moral to the story? As my old boss at NASA used to tell me, never get behind anyone 100%.
teo_audio
2,197 posts
 
Do an experiment. I did.

For the fun of it and to see what is what..

... I swapped out the emitter resistors on a power amplifier for fuses. the theory being that if the current was too high in the one transistor, the fusing element’s resistive properties would change, or increase..like it is designed to do ---and thus enforce current sharing.  This is a goodly part of what an emitter resistor is supposed to be doing. Enforced current sharing. But, not quite the same....as how a fuse would handle it.

This change (fuses for emitter resistors) would cause the worst elements of what a fuse is - to come to the fore.

Gotta be one of the most horrible sounding amplifiers I’ve ever heard. If not the worst.

If you want to hear what a fuse does, try that.
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