Thanks, Dave. Yes, as you found and as several others have reported earlier in the thread in appears that the SR Blacks blow a bit more readily than at least most stock and boutique fuses having the same ratings. And I agree that if there would be any sonic differences at all between SR Black fuses having somewhat different current ratings they would most likely be in favor of the fuse having the higher current rating (which presumably would have slightly less resistance and slightly less fluctuation in resistance as a function of variations in the current being drawn through it, although both parameters could very well be too small to be significant with either fuse).
Also, I would expect that the current rating of the stock fuse in most components is determined by the designer somewhat imprecisely, by simply multiplying the nominal current draw of the component by a somewhat arbitrarily chosen factor (while also taking into account surges that occur at turn-on), as in general there is probably no need for a great deal of precision in that determination. That being one of the reasons why I would expect that most fault conditions that might arise in a component and require the fuse to blow would result in a much higher current draw than the rating of the stock fuse, and a fuse with a somewhat higher rating than stock but the same fast blow/slow blow characteristic would therefore seem very likely to provide adequate protection.
So in Alexa6404’s case the risk of unnecessarily blowing an expensive 10 amp fuse would seem to outweigh the risk that secondary damage might result from a fault which causes a current draw of just a few amps more than that but does not cause a higher rated fuse to blow.
The manufacturer might see it differently, of course, because their interest is presumably in minimizing warranty claims and/or repair costs, but that’s how I see it. Although I suppose that there could be some manufacturers who might use the substitution of a fuse having a higher than stock current rating, if they became aware of it, as an excuse to invalidate warranty coverage of a repair that might become necessary for unrelated reasons.
As to deciding between the 12 amp and 15 amp ratings, my guess is no better than anyone else’s, but FWIW I suppose I’d go with 12.
Best regards,
-- Al
