I love my Ampegs - B25, V4 and SVT :brow:
The 'great' sound of valves, IMO, is from overdriving the power section and doing this with an SVT without injuring children and small animals isn't always possible.
Cue the smaller amps - the tone from the B25 is, again IMO, just righteous and at a reasonable volume.
I've yet to hear a valve preamp replicate this but I'm still looking.
But as everybody says, an all-valve head is bloody heavy...