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!
Have you tried contacting the maker of the fuse and asking why their product is acting differently than the "std" fuse?

The maker/vendor usually knows best.

It sounds like the Psvane tubes are the culprit as you suspect.

Like Andrew ( Mapman ) suggested, you need to find out if the Hi-Fi Tuning fuses are simply made to a tighter spec.

I'd also talk to Mac and someone knowledgeable about the different tubes. Are the Psvane tubes able to be used in your amp safely? If they're drawing more current, could that be detrimental in some way?

Try biasing them to lowest parameter reccomended.
Are you sure you are not confusing a slow-blo fuse with a standard one?
This is not true in my system!!
Are you sure that the fuse rating are exactly the same? Some 2 amp are 250 volts and some are 125 volts! Do you really hear a difference with the fuses? If not just go back to the standard ones and avoid the problem!
My Zana Deux OTL headphone amp had the same problem. I discussed this with Craig Uthus the amp designer who had me go to the next size up in fuse value. I went from a 2.5 to 3 amp rating. My blow fuses ocurred at start up or shortly there after. This ocurred after some tube rolling.
Thank you all for the input.

Yogiboy: both are rated 250V. Moreover, the first hi-end fuse that blew had been running for over a year prior to rolling tubes.

Hifiharv: I'm sure I'm not confusing those. Both are slow blow.

Schubert: good idea. Unfortunately my amp is auto-biasing, though.

Mapman and Krell_man: that's probably the most sensible route, and in line with Davidpritchard's experience. With McIntosh I hesitate a bit to request advice because it's such a large company. But will do and will post their answer for others to benefit too.

Like Andrew ( Mapman ) suggested, you need to find out if the Hi-Fi Tuning fuses are simply made to a tighter spec.


Or maybe made to a looser spec?
Who made the stock tubes? I think the tube they use now is the Gold Lion (Russian) KT-88. That is a very good tube especially if you like a warm tone. I thought they were fabulous in my Jadis, but it may not be your cup o tea. McIntosh certainly approves them so they shouldn't blow any fuses.
I had my first audiophile fuse blow in my tube integrated within a few days (hi fi tuning silver star). I started doing some research on some of the other brands and found one that said in small print at the bottom of the ad that it was not designed (and I can't remember the exact words)to be installed directly in the AC path or something like that? My fuse is in the little drawer under the IEC. Never had a problem with stock fuses. I have tried to find that disclaimer again to no avail. I know some of them specifically mention use for mains power and not sure which one the OP used that blew but thought I'd mention that. I'd contact the manufacturer and tell them exactly how one intends to use it before spending $50.
I asked McIntosh...

"We do not recommend the ‘high –end’ super fuses… it is impossible for them to improve sound and it may be causing your problem.
But any amp that blows fuses should have all the tubes tested."

So I learnt I'm delusional since I hear an improvement in sound with hi-end fuses, and my tubes must be bad even though they are not blowing up standard fuses.

Unfortunately this manufacturer is not helpful.

Any other ideas?
You need to get rid of the McIntosh and get an amp from a manufacturer who understands and supports aftermarket fuses.
Good idea.
Change $5000 amplifier for a $25 fuse.
Those two sentences from McIntosh seem perfectly reasonable coming from the manufacturer of any amp.
Those two sentences seem to indicate total ignorance, from the manufacturer of any amp. Not surprising, from those with the hubris of McIntrash. Of course; that's just my own personal opinion, based on personal experience with both.
I'm interested to hear what the fuse maker says.
McIntosh's advice to check tubes if fuses are blowing in general is hard to argue with.

No vendor will support a product that the user has altered. Right or wrong, if the vendor has doubt about use of any part introduced by a third party, including a fuse, for whatever reason, including lack of information, they are NOT going to recommend it and then be obligated to support that recommendation.

Also, the comment about whether the fuse can sound better or not might be a bit strong, but I'd have to take the position that the purpose of a fuse device is NOT to make something sound better, even if in fact it does. THere are many other ways for a product to accomplish that. If there is any question about the product being able to serve its primary function, which in this case is to PROTECT the gear, not make it sound better, then a no confidence confidence vote for that part in a case like this which seems to support that concern is not surprising.

That response increases my confidence in McIntosh support, it does not decrease it.

SO there is a choice to be made. Making sure the tubes are in good working order would seem to be a logical next step. One or more sub par tubes may well result in lesser performance and/or other issues, regardless of fuse used. Having tubes all in good working order is paramount to a tube device working as it should. Flavor of correct fuse used matters so much less, to the extent it even matters at all, that it is a no brainer which to address first.
Excellent response Mapman.
If both the standard and upgrade fuses were blowing, the
tubes would be the first thing I would suspect and test.
Since only the upgrades are going, and especially given that
the tubes are new(not that new tubes don't/can't cause
problems), I wouldn't waste my time there. Personally; I'm
using eight(what were NOS) GE 6550A output tubes, in my
Cary's. I've had two Hi-Fi Tuning Supreme fuses go out in
the(fixed)bias protection holder(one each amp over the
course of 30 days). I'm still using Supremes in the mains,
but- though I really like the more natural presentation of
the upgraded fuses; I can't afford slightly over $90 a
pop(literally), for the bias circuit. I tried a pair of
Synergistic Research Quantums in the amps and they held
fine(didn't care for the sound). Reinstalled a Littelfuse
pair of the same value, a couple months ago and no problems.
Has anyone mentioned that Hi-Fi Tuning Supremes are rated
250V, Synergistic's are rated 500V, and many output tubes
use 400 to 450V, plate voltage? That would only
matter in one's bias protection circuit, of course.
I have Acoustat tube servo amps with lethal voltages,made in the 1970's but modiffied.
There are 4 tubes in each amp,sourced from television technology because of the demands made on such a circuit.The amps also are the source of power to charge the electrostatic panels and keep them charged, they are not just "power amps",but made specifically for the Acoustat X series.They are not a conventional amplifier design.

The amps are always "on",but in a sleep mode until I flip the toggle switches for listening, and then off when I'm done.So there's a lot of juice flowing thru those fuses.

I've been using upgraded fuses(HiFi Supremes-4) in them for two years and never had one blow on me , except when it was an error on my part.

That the upgraded fuses are blowing and the stock fuses are not would indicate to me that the stock fuses are more forgiving and the upgraded fuses are only doing what they are supposed to do-self destruct before something awful happens.
I would stick with the stock fuses and the new tubes and cross my fingers, or go back to the stock tubes and the upgraded fuses.

I am curious.
What made the most enjoyable improvement, the upgraded fuses or the upgraded tubes?
The answer to that should settle it.
"That the upgraded fuses are blowing and the stock fuses are not would indicate to me that the stock fuses are more forgiving and the upgraded fuses are only doing what they are supposed to do-self destruct before something awful happens."

You could just as easily assume that the stock fuses are doing exactly what they should be doing and the upgrades are much too sensitive or not up to spec.
I couldn't find a way to contact HiFi Tuning Fuses so I asked The Cable Company, from whom I bought the fuses:

"I think that you have hit the nail on the head. The HiFi Tuning fuses are EXACT-rated fuses while off-the-shelf fuses are +10% tolerance which means that they would actually be 2.2A out of the box. The PsVane tubes additional current draw appears to work with that window while the HiFi Tuning fuses blow. This WILL happen again with these tubes, so your hesitancy in installing the new fuses was a good thing."

They don't sell any 5x20 slo-blo hi-end fuses in 2.2A, or any other rating between 2A (what I tried) and 2.5A. While the technician thought 2.5A wouldn't be risky, I'm rather reluctant to do that.

BTW, Lacee asked whether upgraded tubes or fuses made the largest impact. Tubes, for sure. But when I had stock KT88 and introduced an upgraded fuse I did hear an improvement. So now I want the cake and eat it :-)
Good news and good luck with the cake.
It's always great when things go the way you think they should.
We should now be able to forget about HiFi fuses being inferior to stock fuse at least for protection.
The next hurdle to jump is to somehow proving they sound better than stock fuses, but just for those who refuse to try them and let their ears decide.
The inrush rating may be higher with the standard fuse. I work in the HVAC/Controls and work with lots of fuses that have the same amperage rating but the inrush ratings vary a lot. If sold in the USA this data sheet must be available.
Hi Lewinskih01, have you found the reason causing the upgraded fuses to blow , I am in the same situation, I purchased Furutech  Pure Transmission and HiFi Tuning fuses ( same spec on both Slow blow 5x20mm 3.15A) unfortunately both did not last more than 4 days, good music improvement  while they were working though (soundstage, extension of tones , high and low  ) clean and clearer imaging. Tested with following singers CDs, Madaonna The immaculate collection, Dire Strait , Karen Souza Essentials, Kandace Springs Soul Eyes . Iam prepare to buy the fuses again as long as I can find the solution to the problem. 

I agree with what Hevac1 saying,  I have asked a friend to measure the loading on stock fuse and the upgrade fuses as a start ... 

If you guys already find a solution I like to hear about it , many thanks .


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

Built in obsolescence, with less "blowing headroom" to get even more money out of the gullible.

Mains fuses have a limited amount of turn "on cycle surges" that harden/weaken/crystalise the fuse wire inside them, eventually they blow, always at "the turn on surge" just like incandescent light globes do, because turn on is the heaviest current a fuse sees.

A new fuse left getting older and older right.

Cheers George

I didn’t bother further. What is reflected in the thread is what I did and learnt, so kept the std fuses and upgraded tubes which have been running for 5 years flawlessly.
The amp runs hotter with these tubes than with the original ones which has to translate into higher current draw. Per the Cable Co answer, std fuses have additional 10% tolerance which seems to be enough. I didn’t want to to go up 25% rating in the fuse from 2 to 2.5A as it seemed unsafe for the amp. So I let go of that part of my audio nervosa and lived happily ever after :-)

In the past years I turned into an active system where now the McIntosh is driving mids/treble and sees a lower demand so runs cooler again. Could try hi-fi fuses again but I’m not prepared to risk throwing away money, so I stayed out. Sound is great and I found areas for more significant upgrades to sound than fuses made, so went that route.

Most likely std fuse blows go unreported, so it would probably be unfair and untrue to say only audiophile fuses blow. 
I’m old school ... if it ain’t broke, don’t fix it. You had no problem with the stock fuse, but did with the hi-fi fuse. What does that tell you? There may, indeed, have been an objective issue with the tube, but I think this whole hi-fi fuse thing is more snake oil than not. Sometimes, when we think we hear sonic improvements from a purported "upgrade," it’s due more to the power of suggestion or expectation rather than reality. Just my $0.02.
Are the Hi-Fi Tunning fuses counterfeit?
Hi Fi Tuning fuse purchased from Analogue Seduction in UK ,  the stock fuse in my  integrated  Amp Cayin CS88a is by LittelFuse 3.15A 250VP , I think  it is a 213 series from catalogue , Littelfuse make many version of the 5x20mm 3.15A fuses. The Amp shipped with two extra fuses  and there is a Littelfuse reseller not far (30km) from me I can go there to find series is the I got.  I thought same rating and same dimension of the fuse is good enough apparently not the case. 
Are the Hi-Fi Tunning fuses counterfeit?
How do you counterfeit BS, ah yes, with more BS.

Cheers George
Don’t be a hater, Georgie. Be a lover.
Just an update on the fuse problem I had with the amp,  paid another $120 on a isolation transformer with build in InRush soft start circuit  to use it with the Tube Amp,  no more blown fuse for 7 days already, two blown fuses already cost more than $120. the gain in sonic difference well worth it. 
Thanks for the update.
So you keep you amp switch in the on position and turn on/off by turning the isolation transformer? Interesting.
My balanced power conditioner trips if I do that, but will keep it in mind.
Which isolation transformer are you using?
I bought it from them Tortech,  https://www.tortech.com.au/product-category/isolation/

it is available on ebay.com.au

My tube amp is only 6 months old, manufacturer will no commend on third party hifi fuses and fuse manufacturers will say anything either.
After googling few hours Isolation Transformer  came up few times and found out Tortech has a soft start circuit to to limit inrush current problem.

Actually I turn on the ISO600 before I turn on Tube Amp.  
correction I mean to type $160 not $120.
Post removed 
In the long history of audio there has never been a single documented and verified component damaged by a high end fuse. If anything, by blowing too quickly they prevent damage to equipment. What a load of horse hockey! 🏒 Are some audiophiles really that superstitious? First they complain audiophiles fuses blow too fast. They must have got bored with that approach and complain they don’t blow fast enough. 🎻

At the risk of being flamed, I'll remind everyone of the RM-9 amplifier Roger Modjeski received back at Music Reference after the Hi Fi Tuning Fuses installed by the amp's owner didn't perform their intended task when a power tube in the amp blew. Modjeski went into research mode to investigate the design of the fuses (including speaking to the German designer and manufacturer of the fuses), and reported his findings on his AudioCircle Forum.

I bring this up again only because directly above is the statement "In the long history of audio there has never been a single documented and verified (what's that mean? Modjeski's word isn't good enough?) component damaged by a high end fuse." I have no information of any other than that one instance, but Modjeski explained exactly why the fuse not only DIDN'T perform it's intended task (in it's application in the RM-9's circuit), but why it is INCAPABL:E of doing so (because of it's design and construction).

If one is sincere in desiring to learn what Modjeski has to say on the subject of not just the Hi Fi Tuning Fuse, but all fuses, all you have to do is go to the Music Reference AudioCircle Forum and read all about it.. Or, you can just get defensive, makes no difference to me. ;-) 

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.
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. 

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.

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
“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.

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?

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.

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.

What's the moral to the story? As my old boss at NASA used to tell me, never get behind anyone 100%.