It may all be above what we can hear, and aliasing is overrated, blah blah blah, but still…. The Waves and IK Multimedia versions, uh, don’t. The UAD shows some filtering to eliminate the very high end, eliminating aliasing. The harmonics between all of them also show a lot of variation, with the UAD and IK Multimedia versions a bit closer but still quite different from one another. There are some pretty significant differences in the EQ curves between each of them.
You can take a look at the Waves version (Puigchild 670) and the IK Multimedia (VC-670) one as well. (Especially with aging and replaced tubes, etc.)
They probably aren’t even totally accurate from hardware to hardware. I can’t vouch for these being completely accurate in any of the modeled plugins, it’s particularly hard to test something like that. (You can look at them in the original manual at the link below.) You can see (and hear) these are program dependent, and rumor has it that even the attack times vary depending on the level of the peaks. Time constant settings for the Fairchild 670: The UAD Fairchild 670 adds a slight touch of harmonics.
