I'm currently running a '68 Showman Reverb as pre into one side of a 250watt@8ohm(400w@4ohm)x2 80's Yorkville Beta 800, and into one JBL E-120(8ohm). I made the change from using the Fender's power section about 10 months ago and I wish I has done this a few years ago!
The thing I love about it is the sound is soooooo consistent and transparent at all volume levels... that, AND I don't have to ever wonder if it is time to replace any pricey-a$$ power tubes, OR ever wonder if the bias is correct (btw some amp techs are total greedy lazy liars and upon getting your amp in their shop, will fully retube($$!), not do ANY bias readings or adjustments at all but CHARGE you for same($$!), and worst of all give you back an unbiased amp and wait for you to come back in a few months for new tube$.) I can squirrel away my lightly-used 6L6 quartet and save them for the day I ever need really them for a intolerably loud 60's-eque hard-driven Fender tube amp sound. Then I just pop them in their former sockets pop in my Hearos earplugs and go.
I'm starting to wonder if maybe I can remove the huge output transformer from the Fender now to save weight? Anyone have a clue? (obviously I could then no longer plug-n-play as above)
BTW, the Alembic FX-1 (like the F-2B, which was used by the Dead for both guitar and bass) is a full-range multi-use preamplifier.
"There, in huge black letters, was 'The Grateful Dead'. It just... cancelled my mind out."-Garcia