Very cool, Mr C,
Delighted it's working as it sounds like there was a little suffering before. It's by far my best ever line level pre (did I say that b4?)
Rayd,
For some reason, I couldn't tolerate the 5V4, gz32, or 5U4's in my system, but had an old 5AR4 (possibly Sylvania) that sounded quite nice. It wasn't so hard sounding as the higher forwards voltage would suggest and was much better than the 5U4. It's gotta be the fault of other gear too.
My least favorites were the the 5U4 (very overamped sounding) and the 5R4 (everything runs together and is really mushy).
It's certainly very system dependent. The Mullard 5y3, which is cryoed, has a singing sound in my system. I tried a Bendix Red Bank which was good but still not anything like the Mullard

Karl