Mark IV B with ground switch?

[OverDriven]

I recently bought a Mark IV. It has the stereo loop with the triangular layout. This means it is a B version, correct? One thing I noticed is it has the ground switch on the back. Does that mean it isn't a B, or did some B's have the ground switch? If it has the triangular stereo loop, can I be certain that it is a B?

 

[Boogiebabies]

The early B's had the three loop inserts, an attached power cord and a ground switch. If the serial is around 6700 or higher it should be an early B.

 

[OverDriven]

Ok I have all three of the things you mentioned. There is also a plug thing on the left side of the back that looks like a regular 120 volt outlet. What is that? An extra outlet for plugging effects into?

 

[Boogiebabies]

The auxiliary jack is good for another 117V power source. I run my TC SCF off it. The fan plug is just below that to the left of the PT.