Be sure to turn the demagnetizing tool on at some considerable distance from the transport, do the dance as Don describes, figure 8s are cool, then move the wand outwards until it is well away from the transport again before switching it off.

By "well away" or "considerable distance" I'm talking about three feet or so.

Seriously, the more you describe that tape, the more it sounds like you won't get much in the way of good sound out of it...

If the tape content is valuable to you, consider sending it to a pro for digital dupe.

--Mac