Whelp, here's an OLD bump...
I just picked up one of these GFX-1 units for less than $100. I figured, why not? It does not disappoint. I don't remember it sounding this good when I had one before.
When I brought it home, I could hear something inside rattling around....hmm... I opened up the case (each screw a new experience - lol) Man, it was dusty inside...and many loose screws. The tube board had three screws, one of which actually had a nut. DOH! I tightened that up as much as I could and it's much more solid now. The tubes were covered in dust and gunk - I wiped them off with a clean rag and found out they are Groove Tube GT 7025 tubes. Not particularly great in my Microtube power amp, but (from what I hear from Harley), they are good preamp toobs. Circa 1993-5 (I think - correct me if I'm wrong), they sound great.
I'm loving this thing and I'm gonna keep it as an emergency backup rig or a fly rig. Does it have what I NEED for a gig? Yes. Does it have everything I WANT for a gig? no...almost...