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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
geoffkait's avatar
geoffkait
23,365 posts
 
I knew somebody would bring up Roger Modjeski, since that’s the only case anyone ever mentions. Thanks for accommodating me and reminding everybody! 🤗 The problem is that somebody who hates aftermarket fuses and audio tweaks is the one reporting it. I put very little credence in that report. Besides, geez, that incident was so long ago as to be absurd. I assume there hasn’t been a similar case before or since. How long ago was it, ten years? More than ten? Who cares? As I am find of saying, amp designers are always the last to get the memo on fuses, power cords, isolation, just about anything that isn’t a circuit. It’s called having blinders on. 😎 Audio Circle was the perfect audience for that kind of nonsense, I will grant you that.
millercarbon's avatar
millercarbon
12,531 posts
 
I tried reading the AudioCircle Forum discussion on fuses. Modjeski is there and keeps talking about science, but after reading and reading never once did he mention any actual science. He did mention microphonics, only to say that can't be a factor but again without any actual science. When it got to where he was dismissing burn-in because nobody reported it prior to 1950, well totally lost interest. Only so much baloney I can take.

Possibly in spite of my initial impression the guy is not totally out to lunch. Don't know. What I do know, so much of what I saw is no better than any other guy with a keyboard and internet connection could do. So if you have a good link, something of actual informational value, please provide it.

Meantime, it is totally amazing how much improvement I heard immediately from just one SR Blue Quantum Fuse. Not that great at first, but reversed it and... awesome! One of them did blow on turn-on. Synergistic (well, technically high-end electronics.com) did replace it for free. After talking with Keith Herron we decided to go with a little higher value, and that one has been in there several months now. None of the others has blown. If any do, another call to high-end for another replacement. 
bdp24's avatar
bdp24
9,821 posts
 

Modjeski doesn’t talk about the "sound" of fuses, only their electrical behavior. What the internal composition of the fuse does with the gas created when a fuse pops (if my memory serves me well. I haven’t read his Forum posts in in years), what’s it’s "high breaking capacity" (whatever the hell that is. The Hi Fi Tuning Fuse designer didn’t know either, Modjeski reported ;-), how it behaves in a DC circuit (what the power tubes in the RM-9 run on), those kinds of issues.

Yes, Modjeski is skeptical (to put it mildly) of the audible benefits of power cords, fuses, overly-expensive (define that as you wish) interconnects and speaker cables, etc. But one thing you can be sure of, even if you don’t consider him an audiophile: he is an expert at electronics, circuits, tubes, transformers (he winds his own), and, yes, fuses.

There is a great video on You Tube of Nelson Pass and Roger Modjeski giving back-to-back talks to DIY designers at the semi-annual Burning Amp Festival in the Bay Area a couple of years ago. Well worth your time to watch (and learn). Modjeski is now offering a new ESL loudspeaker of his own design and build, and a partnered direct-drive OTL tube amp that eschews the input transformer found in most other ESL designs, as well as, as it's title suggests, an output transformer. I'm dying to hear THAT combination! His little RM-10 amp is THE amp for the old Quad ESL.

davidpritchard's avatar
davidpritchard
866 posts
 
I have three Pass Lab amplifiers - the Int-60, the First Watt F7, and the headphone amp HP-1. All have been upgraded with Synergistic Research Blue fuses. All sound much better with the Blue fuse. I have been in direct contact with Pass Labs and have never been given any negative reaction to this upgrade.
David Pritchard
geoffkait's avatar
geoffkait
23,365 posts
 
“Yes, Modjeski is skeptical (to put it mildly) of the audible benefits of power cords, fuses, overly-expensive (define that as you wish) interconnects and speaker cables, etc. But one thing you can be sure of, even if you don’t consider him an audiophile: he is an expert at electronics, circuits, tubes, transformers (he winds his own), and, yes, fuses.”

>>>>So what? That is an exactly example of an Appeal to Authority. That’s why I oft opine high end amplifier designers need to stop being quite so hyper circuit-oriented and step outside their own little comfort zone. And stop insisting they’re some kind of Electronics Wizard.  It’s a big wide world out there. As for high end fuses, could 90,000 people be wrong? You know, there is such a thing as being too skeptical. On the whole, audiophiles would be much better off if they believed in too much instead of too little.
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