morst, that's very kind of you. I have a working AC supply that also fits into position like a battery, which I'm using now. And in the meantime I was able to get a Canare transformer that steps the 110-Ohm AES/EBU output down to 75 Ohms unbalanced for use with the S/P-DIF input of my R-44. (Dale Pro Audio had it in stock, bless their hearts. Support your local pro audio dealers!) So as of five minutes ago I'm in business, subject to the rather considerable deterioration of these tapes.
It turned out that the first tape I tried to transfer must have been recorded via the analog inputs of a D7 or D8, because it's at 48 kHz. The R-44 wouldn't accept the input from the format converter only because I had set the R-44 to expect 44.1 kHz. It all seems so clear after one has figured things out ...
--best regards