Since 12AX7/ECC83 is the most widely available, I'm sticking with that. Just looking to clone a few preamps that share a common topology in one box, switching between the different R and C values they don't have in common. Last preamp I built was something I use for bass guitar that I'm pretty happy with, save for a slightly higher background noise/hiss content than I had hoped for. I don't believe I properly returned every ground sequentially to the right filter cap for that stage so that's probably the culprit. This time I am planning on doing a PCB instead of using turret board which is more likely to be properly thought out in advance on my end.