For some time I've been using a racked UK Ashdown ABM EVOIII; it runs superclean, so with this in mind, for the last couple of years I've been using a Sansamp RBI as my frontend and routing this into the effects return of the Ashdown.
The last couple of days, I've been reading a lot online about swapping out the 12AX7 preamp valve for something different. As far as I can ascertain, swapping the valve is simply a case of taking the old one out and inserting the new one. No calibration.
So, the question. Which valve?
The Ashdown has a valvedrive option that adds a bit of fuzz, but it's far from the fuzz/dirt that I would prefer; it's a far cry from the Sansamp. This could be down to the circuitry on the Ashdown, it could be that the valve isn't hi-gain enough. I'm up for a bit of experimentation, especially where it could benefit others.
Any help appreciated!