More on fair use (from the actual US code):

Notwithstanding the provisions of sections 106 and 106A, the fair use of a copyrighted work, including such use by reproduction in copies or phonorecords or by any other means specified by that section, for purposes such as criticism, comment, news reporting, teaching (including multiple copies for classroom use), scholarship, or research, is not an infringement of copyright. In determining whether the use made of a work in any particular case is a fair use the factors to be considered shall include -

(1)

the purpose and character of the use, including whether such use is of a commercial nature or is for nonprofit educational purposes;

(2)

the nature of the copyrighted work;

(3)

the amount and substantiality of the portion used in relation to the copyrighted work as a whole; and

(4)

the effect of the use upon the potential market for or value of the copyrighted work.

The fact that a work is unpublished shall not itself bar a finding of fair use if such finding is made upon consideration of all the above factors.

What this means, I think, is that findings about fair use are made on a case by case basis, when issues of copyright infringement are raised by a copyright owner. All you can do is use common sense I remember trying to get a hard and fast definition of fair use some years ago and failing. All you can do is imagine whether what you're doing will harm the copyright owners. If you copy these tapes and listen to them many times for pleasure instead of buying a copy, that might be perceived as unfair. But you'd have to get sued for a finding to be made.

Fair use is a pretty fuzzy concept...