[analog31]

My rule is: If it's real, then it can be measured, and if it can be measured, then it can be reproduced in solid state circuitry, perhaps using digital techniques if necessary. With that said, whether anybody is actually doing so satisfactorily is an open question. Actual test data for things like musical instrument amplifiers is remarkably sparse. And I won't begrudge anybody the pleasure of owning or building historic circuits.

[isolli]

You will be very interested in the Carver challenge [0]. In 1985, Bob Carver challenged the Stereophile magazine by claiming that he could perfectly reproduce the sound of any amplifier they chose by tweaking one of his (solid-state) amplifiers. They took him up with a high-end tube amplifier, and he won. Note that he did not use measurements but a brute-force approach of feeding the difference in output signal of both amplifiers to a speaker, and listening for (and manually correcting) any residual output.

https://www.stereophile.com/content/carver-challenge