As a multiple SET amplifier owner I applaud you in your efforts in bringing to market a new SET amplifier. My amplifiers are using 845, 45, and PX-25 output tubes. Each has a wonderful sound with it's chosen speaker.
Each has had a marked improvement in sonics when a Synergistic Research Black fuse was installed. I believe this is one of the best fuses currently available. I hope you will trial this fuse not as a manufacturer but as an inquisitive audiophile. I am certain you wear both hats- manufacturer and audiophile. For many reasons as a manufacturer the Black fuse may not be an option, but please do not deny the music lover within you the chance to hear your product with one of the best sounding fuses available.
What makes this decision simple to me is they are offered with a 30 day trial and full refund. You would also being doing your customers a service by being able to convey to them your impression of what this fuse does or does not do.
I hope you will trial the Black fuse.
David Pritchard