simulating tube amps with FETs

[jbm222]

I was looking at runoffgroove.com and saw the schematics for the stompbox verisons of some tube amps.  From these pages, tt looks like you can pretty much replace 12AX7s with J201s or similar FETs without changing anything except maybe the biasing resistor.  I'm interesting in trying this idea with some of the Marshall JCM series amps.  I was just wandering if anyone has tried this before, and how it went if the have.

[cd]

http://diystompboxes.com/sboxforum/viewtopic.php?t=25368

[vanhansen]

And just so you don't have to redo what's been done, there's a sim for the JCM800 available already.  I've got lots of the info on my site included layout, parts list and schematics, thanks to Buck Sears and Electrictabs.