I have Delta AP400 which is not ideal - I know, but I'd like to give my lungs a better break.
For budgetary reasons, I'd prefer to upgrade the filter (loose the upper bag) and install a cartridge filter in place. My flange is 13" in diameter.
Has anyone done this? Which filter did you buy? It looks to me that the Donaldson filters are the closest to fit the inside diameter, and I'll have to build a flange to carry the exterior of the filter.