The 251 leslies are very rare. They were
specially designed for the A100 series. They have an extra channel in
the amp to power the reverb to a 6x9 speaker in the cabinet. They share
the same cabinet, speakers, and internals other than the amp as the 147
and 122 so are a 2 speed leslie.Sound wise, they are identical other
than the added reverb from the a100 voicing to the leslie.
Dennis Delzer - www.b3hammond.com.