Whats the difference between MOSFET & Class A, AB

I was wondering what the general difference was in MOSFET amps as compared to Class A or Class AB amps.

For the last few years I have been running a Classe CA 300 amp. A couple weeks ago I had a fuse blow on the Classe and it also burnt out a resistor. Knowing the Classe was going to be in the shop I bought a old CJ Motif MS-100 amp.

Now after a day or two of listening I'm thinking this old Motif betters atleast too my ears the Classe so it got me wondering.

Cheers Gary