Dave:  In response to your posting, my Hammond B-A (#9052) came
equipped with a very nice ER-20 tone cabinet (#28114).  According
to some Hammond literature I have, this particular tone cabinet was
manufactured from March of 1947 to December of 1950.  I am not sure
what type of tone cabinet was supplied with the instrument originally.
As an aside, the selling price of a Hammond B-A (which was in production
from January of 1938 to December of 1938) was $2,000; the price of the
ER-20 was $462.00.

Hope this information is of some help.

Regards,
Daniel D. Tenerowicz - Lakeshore Organ Works