This is officially called the Carvin PB-100-10
It is 100 watts into an 8 ohm speaker. The internal amplifier is not capable of operating into a 4 ohm speaker (only 8 ohms). If you try to use a 4 ohm speaker the amp will blow.
It is a decent amp and is sometimes called "the mouse that rored" by its owners with one drawback. The ten inch speaker will eventually blow (the voice coil will open) as told to me by a close friend who is a amp repair person. He has replaced many of these tens in the PB-100-10.
I used to own the PB-100-15 for ten years. It is a much more reliable amp and I sold it a year ago for $100 still working fine.
The Carvin Museum - 1996 Pro Bass Amps