Mesa Boogie Mark IV Type A vs Type B

[SCopeland24]

I am looking for a Mesa Boogie Mark IV to buy and was wondering what the difference between the type a (pre 1992/93) and the type b. Which is better and how are they different?

 

[MrMarkIII]

Here's a place to start:
http://forum.grailtone.com/viewtopic.php?f=27&t=5987

 

[SCopeland24]

Thanks thats exactly what I needed to find out.