There is a 12V version of the ARA, designated “ARA-1” IIRC.  Gordon had a receiver and I had a matching dynamotor, which I sent to him years ago.  I think someone else has it now.

Our Aussie cousins ran SCR-274N on 12V via changing the relays and running two 24V dynos in series (yes really).  There is a manual specifically about this.  Might still have it.

73 DE Dave AB5S.