Marshall Dual Rectifier, low, medium or loud.
The great thing about it is I dont have to crank it to get thick power amp breakup, I like everything I get from the preamp stage itself, so to me it sounds fantastic at low to medium volumes, sounds like a professional album sitting right there in your room. Love it. It has a switch on the back that stomps all the internal voltages down so that it makes it spongier and capable of lower volumes when cranked so that you can achieve a more compressed "hi-volume" sound without as MUCH hugh volume if thats what you are after. Personally, i dont like the compression that comes from cranking a tube head, ESPECIALLY a 50 watt head. Rolls off too much of your high end and presence. I like it on the spongy/rectifier settings at lower-middle volumes though, which is where it ususally stays unless band practice is happening, and then its hi-voltage silicon diode all the way. Sounds great. Its my second Rectifier, one of the 3 channel units, which makes it even nicer. Had a triple rectifier 2 channel prior to this one.
Peace.