These are really nice amps.
It sounds like you have an older one if it takes two footswitches. I used to have one of these, now I have one of the newer ones that only takes 1 footswitch. I think that they only changed a couple of things between the "A" & "B" models.
These changes would be:
Different footswitching power supply
Different switch for the EQ (older amps have a rotary switch on the back,newer amps have a toggle switch) footswitching functions
2 button footswitch
Other than that, they sound pretty much the same to me.
The only bad thing about the DC-3 is that it tends to get a little hot when using it for extended periods of time. I recommend not placing it against anything when in use. This will allow the air to move around it more easily.
Other than that, you have a very fine amp, one of my favorite Mesa amps. I have owned lots of Rectifiers, Nomads, Roadster, etc.
I now own:
DC-3 B Combo
DC-5 B Combo
DC-10 A Combo
Heartbreaker Combo
Blue Angel Combo
Studio 22+ Combo
You just can't go wrong with a DC series if you play any type of music. The only exceptions that I can think of would be that the Rectifiers seem to be more of a new metal or Emo amp, which is tragic because they are much more versatile than most new players let them be.
If you do a search here on the Board, you will find many favorable entries for the DC-3.
Studio 22+ Combo