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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

Showing 2 responses by rodman99999

rodman99999
6,206 posts
 
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.
rodman99999
6,206 posts
 
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.
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