Thanks for the responses both on and off list to the query I had about my
Simplex derailleur. I was sent all sorts of information, and directed to
sources on the internet. As a result of studying those, and going back to
my first point of reference, the first edition of the Dancing Chain, I have
now come to the conclusion that it is neither a TdeF nor a Juy 51, but a
Course (of course!). On page 144 (top right) is the exact derailleur, a
Simplex Course. I had looked at that before but what threw me was the
accompanying text which says "The Simplex Course rear derailleur was also
called the JUY 51", and it is actually not the same at all. It didn't help
in the first place that the person who gave me the box of bits told me it
was a twin cable TdeF. I have now done a partial re-assembly, and posted
some pics at
http://vmphoto.photobox.co.uk/
Many thanks. Peter Brown, Lincolnshire, England