These are stompbox circuits guys, not tube amp replacements--or even preamps originally in spirit, it's others that have found use in applying slightly higher voltage to drive power amps.  I think the runoffgroove guys would be the first to admit that they're not trying to veritably replace tube amps (and anyway if I'm not mistaken it's Jack Orman and Doug Hammond that get credit for adapting these FET techniques to guitar circuits).

What were they thinking?  They were experimenting and came up with what many feel are great sounding circuits.  what's the big deal here?  like it or not, decades of "bad" design principles, accidents, and cheap shortcuts have shaped present ideas of good guitar tone (who at the dawn of guitar amplification could have predicted extreme distortion characteristics would become desirable, or even a singular focus of amplifier design?).  I'm honestly surprised you guys dont appreciate the spirit behind these articles, or are you "beyond" constructively adding to the discussion?

Anyway I would love to see or hear what you guys think are more well designed FET based circuits.  I read support here for marshall valvestate amps, which I think are kind of a strange choice (and I love early florida death metal!).           

interesting discussion about  Bluetone amps from diystompboxes a couple years back:

http://www.diystompboxes.com/smfforum/index.php?topic=25368.0

I love the Peavey Bandit!  I've had the idea of remounting an 80s one in a head cabinet for a bandit half stack on the back burner for a while now.

no sound clips unfortunately, my recording rig is inoperable at the moment.  I'm using an lm1875 power amp (kit from qkits.com).

I've been using a fender 5F4-ish amp (simpler one stage preamp and one knob tone control) and the sound is interestingly very similar through the same speaker (celestion gt-100).  I would say the 5F4 has slightly rounder break-up characteristics, but I'm really digging the lm1875 + mu-amp combination.   

finally got this all together.  Something missing from the preamp schematic (that I needed at least) was a current limiting resistor on the supply rail.  I stuck a 1k 2w in series and it's working great.  lots of clean headroom, no farting out even with my humbucker equipped guitar strung with 13's, and there is a pleasant, mild grind with the volume all the way up.  as I mentioned earlier I went with a modified big muff tone control instead of a TMB tonestack, and I used J201 FETs.

anybody build this one yet?

I'm ordering the parts now for a LM1875 amp with this as the preamp.  I'll probably change the circuit somewhat--a one knob tonestack and I think I'll add the buffer further down the page.