Are you using a Slo Blo or Fast Blo fuse? I know the layout shows that a Fast Blo is to be used, but after blowing the HT due to un-careful measuring, I replaced with a Fast Blo and it kept blowing. I used a Slo Blo and it was fine. I asked Nik about this and he said it was fine.

The one thing I notice is that the Fast Blo fuse that came with the amp from Nik has a much thicker filament, while all the ones I find in the U.S. are very, very thin. I think this is the problem. Either the spec'd .5 Amp with the thinner element is not right with the exact in-rush current of these amps or else using the Slo Blo is what is needed. I'd rather use a lower total current and Slo Blo then a higher current rating and Fast Blo.