Quote Originally Posted by bowtie427ss View Post
It ties the woofer baffle/motor board to the top panel of the cabinet.

Later the 828 cabinet would use a dado and triangular glue blocks on the interior side of the motor board. The differences in motorboard construction are pretty well illustrated in the various plans in the Altec Library.
Okay, then the A7 cabinets that I used to have were the later design........ I was never sure exactly what cabinets they were. If I recall they had some features of both the 825 and 828, so I always referred to them as 825/828 in posts. I figured them to be a transitional design.