Back it up the same way I keep my tapes – by hand. I take a fresh cassette, rewind it to the start, and play each track, copying it onto the new tape as I go. I note the date on the sleeve and label the copy with the same title. That way the sequence stays true, no skipping, and the hiss is part of the ritual. If you need to preserve the originals, keep them in a cool, dry box and make a paper log of each side’s date and content. That’s the safest way to keep both the memory and the music.