I was the owner of an all valve Ampeg SVT 2 pro head. I loved the tone but felt it was too big and heavy, and needed revalving every 2 years etc..........
'Buy a lighter, more compact amp I thought,' 'I'll get a good enough tone with half the weight and size.' I sold it and bought an Ashdown ABM 500, which was a good enough amp but not a patch on the SVT 2. I sold that and went through a series of hybrid and solid state amps (Ashdown, Trace Elliot, Warwick)regretting every day selling the SVT. It was like selling a Ferrari and buying a Vauxhall Corsa.
Anyway, to cut a long story short, I've just gone full circle and bought another SVT 2 Pro and am again totally blown away by the tone of it. Balls to the weight or size etc... It is the best tone you'll ever, ever get.
Many people on these forums seem to be kidding themselves, and others, by pretending you can get 'that' tone out of these little bass heads or portable combos. YOU CAN'T I'M AFRAID!
If you care about tone and power, buy an all valve Ampeg head, it's the dogs bra!