Well it is back in it's cabinet and I've given it a go.
Some of this won't mean much to people who don't know the Sessionette 75, but here goes:
Clean channel
In standard trim, the clean channel is ultra clean and quite glassy. Now it has more bass and more warmth and that slightly "pillowy" articulation that you get with a Fender Twin reverb. The new Presence control does quite a lot but is a bit of a pain as it is on the back in place of the old line-out volume control. More of a global flavour to just set and forget really.
Distortion channel
The standard distortion, I always found a bit scratchy, but quite usable in a band mix. Now it is smoother and more retro (for want of a better word) sounding, which is exactly the idea. This doesn't mean it is lacking in top-end at all, but it seems to respond really well to the guitar's tone control, and the distortion will clean up nicely as you reduce volume on the guitar, something most solid state amps don't do very well.
It seems to me to like single coil pickups better than humbuckers, single notes sounding a bit sweeter. This may have a lot to do with the designer's love of Telecasters!
The whole thing is more phat and less boxy than before, i found myself turning the bass down, I'd always run pretty flat before.
I'll be interested to hear my guitarist through it at the next practice. He uses a Tele and a Turbo Rat for the noisier bits. It will be interesting to hear that combo through this combo.
All in all a very interesting development that makes a lot of difference. It feels a lot more like my old Wem Dominator to play.
I haven't tried it out with my SG yet though - that would be the best comparison, as it was what I used when I was gigging on guitar (13 years ago)
Any local valve fans are welcome to try it out!
Cheers
Jules