[mikethedruid]

David, I just found this link to a site where a guy used a non-polarized condenser to drop the voltage across the filaments of a radio with EXACTLY the same tube line up as yours. I have followed the guys site for years, since he has a lot of good information on the old Radiola radios, and my oldest tube set is a Radiola Senior. I also have a Radiola IIIA. This should help you solve your situation. https://www.radiolaguy.com/info/resistan...0cords.htm
One thing you may wish to be careful about. You may wish to avoid non-polarized ELECTROLYTIC condensers in this application because they are NOT rated for continuous AC use and this application will shorten their life. Mylar condensers of over 100VAC rating (better over 150VAC) are preferable for this application.
Here are some other interesting links you might find useful...
https://www.antiqueradios.com/forums/vie...hp?t=29083
https://radioether.blogspot.com/2008/02/...istor.html
https://radioether.blogspot.com/2008/02/...art-2.html