Years ago I had a Velodyne servo F-1800 servo and for the time it was fine. 90s.
I now have two older RELs (great, buy used) but also two SVS SB-2000 subs and one SB-3000 sub. Look for sales; I think the SVS are very good and I'd probably take either over the repaired DD-15 (even though I have always liked Velo subs).
There are also some other great less-expensive brands out there that didn't exist (or were known about) years ago.