I know there's a list of serial numbers for 1Cs and 2Bs that deals with the ability to use the AI-1 isolation transformer. The nicest scan of that list that I found in a search, was provided by F1nut a long time ago in a thread far, far away.
The bottom of the instructions says that "plug adapters and some internal modification" are needed.
WHAT were the "internal modifications" needed?
First Guess: "Plug adapters" were to convert the blade/blade interconnect jacks to a pin-blade configuration. Polk used up leftover jacks from the earlier-generation speakers on the first of the later-gen speakers. ONE of the blades was actually used to transfer the SDA signal between the cabinets, and I bet the second conductor in the jack was simply un-used--not connected to anything inside the cabinet. The "modification" is nothing more than connecting the second "slot" of the blade/blade jack to the negative binding post. Polk would perhaps have supplied a plug-in adapter so a pin-blade cable end would attach to a blade/blade speaker jack.
The sum total of the Polk-approved modification is a pair of adapter jacks (or, perhaps, the proper pin/blade socket as used on the later-production speakers???) and maybe eight or twelve inches per cabinet of whatever wire Polk was using to connect the previously-disconnected blade to the negative binding post.
This could be EASILY electrically reproduced using non-stock parts. Wouldn't even have to be expensive, although I'm sure there are expensive ways to do it.
My point being that the early 1C and the 2B are completely compatible with the AI-1, with very minor changes.
What part(s) of my guess are not correct?