I guess you could try a unity gain tube buffer which is normally used for impedance matching between components, I remember reading somewhere there was even a SS device which emulated the 2nd (and others?) harmonic of a tube and the distortion (magnitude of harmonic) was applied in variable steps. I can't recall where I have seen it, I will have a search.
A Black Box to Solve Everything
Tubes vs. solid state?? There's a thread out right now about this exact question (there always is), but I didn't want to take it off subject. So my question is; is there a device that could go between the preamp and amp that has variable harmonic distortion capabilities? I know there are tube buffers, but they are not really addressing the point because they use line level signals and don't have the distortion of a good 300B tube being pushed beyond its limits. My thinking is that of a black box with switches and knobs to adjust harmonic distortion to mimic different tube types. It would also have to have a bypass switch so we could readily and quickly A/B the thing. Any ideas?