Very interesting, I've just got my Mainline kit (yay), so I have an interesting journey head.
I could not hold myself to try stock 12AU7 on my Crack+Speedball. Wow, I've plugged it in and it was immediately on-par with my rare Brimar, Mullard, RCA black and Telefunken 12AU7.
No way it is going to be a power regulator for Mainline. The tube there does not matter there and I may as well put my stock Crack 12AU7, which was a relatively mediocre Sylvania.
Can you pls help me identify this tube, so I know what it is? My current theory that is is Westinghouse 12AU7, I think I've seen a similar stamp on some tubes on Ebay. In addition there is either "W" or "M" on the metal at the bottom of the tube.
