I have one one of these, it has a built-in attenuator to crank it anywhere from 1-20 watts, you can mix the tube sets, but I generally always set all the to 6V6 for Fender emulation or all the way to ECC88 for Marshall. You can make it as clean or dirty as you want:
http://www.egnateramps.com/EgnaterProducts/Rebel/Rebel20/Rebel20MarkII.html
Available from most big online retailers and used on eBay