BA11-VA seems to be an expansion box, so the contents may give you
more clue (board part numbers)
manual for BA11-VA is
BA11-VA Configuration Guide     Digital Equipment Corporation EK-BA11V-RG
BA11-VA is mentioned in (
EK-0TU58-UG-004 1983-12 TU58 DECtape II User Guide
   4.5.3 Mounting the TU58-VA to the SB11 (or BA11-VA)
Dave Caroline
On Sun, Jul 18, 2010 at 5:19 PM,  <cctech at vax-11.org> wrote:
 I ran across a DEC OBA11-VA (attached to a dual TU58 drive) while sorting my
 junk room. Anyone have a link to documentation or any information on it?