Emulation of tube amps with FETs

[bassmeister]

I've been looking at the schematics at runoffgoove.com trying to learn about emulating tube amplifiers with FETs. When I compared their schematics with the schematics of the emulated amplifiers, there seems to be deviations in the choice of a certain FET for a certain tube in different schematics. The physical working principle for a JFET is similar to a tube. Therefore, there should be no doubt that a FET is better than a BJT when trying to emulate tube behaviour, and perhaps even the best choice of transistor type. Tube and FET similarities can also be seen when comparing transfer functions. But are there no certain FET equivalents for a given type of tube? Is it all about personal likings and perception? Does any of the components' (FET/tube) behaviour depend on the circuit solution more than the other?

From the soundclips at ROG you can tell that their circuits sound good. However, people in here who has built a circuit from runoffgroove.com, have you had the posibility to compare with the original amplifier? What where the similarities/differences?

[cd]

Have you tried a search?  There was a big thread a couple of months ago where one maker of FET based amps chimed in.

[javacody]

bassmeister, I haven't built any of these yet, but I've read replies from the folks at the 18 watt forum that ROG's Eighteen sounds a lot like the real thing.

I definitely plan on building Eighteen and the Professor Tweed.

[GreenEye]

Breadboard the Fetzer valve and let your ears be the judge if it sounds similar to a 12AX7.  I'm going to breadboard up one soon so I can goof with adding diodes and other parts to possibly create my own unique stompbox.