I think that rather than "emulate tubes", the real challenge is "get good sound", which is often (but not always) found in tube amps, without using tubes themselves. I think Mr Pritchard is a genius, has *very* good sounding amps, but he misses the point, he often tries to emulate *everything* a tube does, which is not the real problem. Someday he´ll emulate a spirally wound 6.3V heated filament, a glass envelope, a 9 pin socket, the sound of high vacuum, and that´s not really necessary. I think Runoffgroove´s approach is basically flawed: Fets do not even approach triodes, (if any, they´re closer to pentodes); they copy (should I say mimic) classic circuits, horribly biased, horribly powered, that have ten times less gain than the originals, clip radically different, (just use a scope; I´me sure they don´t), harsh, dry, ugh!! An example of good engineering (and audibly good taste) is found in the SansAmp guys, who do not use Fets , CMOS or even diodes but do get a very acceptable sound. I agree that Op Amps (universal gain blocks) with suitable components around them, skilfully used, are one of the safe ways to go.