I have an Allen Old Flame head which is based on the blackface Fender Super Reverb. It also does some other cool stuff because of the raw control and master volume. These generally come with 6L6 and a tube rectifier, but mine came with 5881s and a solid state rectifier thing is plugged into the recto slot. I can get blackface sounds with the raw off, but when I use a Les Paul and crank up that raw control a bit, I'd classify the sound as more of a classic Marshall mixed with a little Fender. Is it simply the amp's design, or do the 5881s play a large role here? I'm not really familiar with that tube except that they were in my old Marshall JCM900 and these amp's sound NOTHING alike. FYI, I just ordered some new Tung Sol 5881s from Doug Preston. I'm eager to see if they make a difference.