I was kind of wondering about the connector myself. My amp had the connector with a number on it so I typed it into the search engine at Allied and Bingo! found the part.
http://www.alliedelec.comThe connector is sold by Tyco which purchased AMP (the connector company) some years ago I believe. You have to purchase the contacts sepatately. I have given the numbers for contacts designed for 24 to 20 gauge wire. The 512 numbers are the Allied stock numbers.
I have not ordered the parts and cannot verify that I have the correct numbers.
The BAD news: They sell contact insertion and extraction tools at almost $20 each. I don't know if these are really needed or not.
Square flange part for amp 512-1150 206061-1
Pins for above 512-1125 66103-3 (24-20)
Free hanging plug 512-1100 206060-1
sockets for above 512-0618 66105-3 (24-20)
Cable clamp 512-8609 206062-3
On the Beta Lead you have reverb. Does the footswitch for the Beta Lead have coax in it for the reverb?