I completed a Cornet about 4 weeks ago and have put about 100 hours on it. I posted on AA(Vinyl) right after it was completed. JoshK quoted from that post here. I've also recently posted a formal review on AA (Vinyl).
I didn't get into tube rolling conclusions there, but I thought some of you might find them interesting.
I started out with Sovtek 12AX7's, Mullard CV4003 and GE 5y3GT. The first change was to a Mullard GZ34, then a GZ37. The GZ34 was the clear winner of the bunch, providing a much "larger" sound, very full in the mid-range.
Next, I tried an Amperex Holland BB 12AU7, which clearly beat the Mullard in speed, clarity and HF extension. (I also tried Cifte and RCA side-getter, with less than stunning results). Then, a Tektronix-boxed Amperex Holland 12AU7/ECC82 non BB, which beat the BB in detail. Last, a NOS GE JG-5814A from 1953. This has better extension at both ends, better clarity and detail and great mids. A clear winner.
I swapped out the Sovteks for some NOS RCA 5751's from the '50's. Huge improvement. Lastly, NOS GE JHS 5751WA from 1952. These will stay.
I must say, I'm surprised by the GE's. Not exactly what are commonly called "audiophile" tubes and still affordable (but you gotta hunt for 'em!). All the GE's have triple micas and black plates. These tube-rolling sessions were spread out over two weeks and others were always present.
I built the Cornet with NOS Jensen coppers (tight fit!) I found on eBay. I'm using Lundahl step-up transformers from K&K.
All in all, I couldn't be happier. Right from initial turn-on, the sounds coming from my modest rig have been stunning. It continues to improve at a more modest pace and every day I look forward to firing it up and cueing the tonearm (like, right now!).