2. tech-talk
  3. 1392953041

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
lewinskih01 OP
909 posts
 
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 :-)
lacee
811 posts
 
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.
hevac1
812 posts
 
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.
summercrema
5 posts
 
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 .

  

georgehifi's avatar
georgehifi
10,312 posts
 
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.
https://ibb.co/zSRwTd1

Cheers George

More to discover