For those on the left side of the atlantic, the old
"Understanding Telephone Electronics" has a diagram and explanation of
the hybrid, among other useful things.
Sam Hallas's web site (I forget the URL, but Google should find it) has
some exceleltn information on this. This site has most of the 'N
Diagrams' avaialbe to download (the N diagrams are essentailly the
scheamtics of various telephones, bells, extension plans, etc that were
used by the British Post Office) -- in fact a Google search for 'N
diagram' is probably the easiset way to find it.
It also has some educational maaterial used to train the Post Office
telepghone engineers, including an excellent (and very clear)
deascription of the 700 series phones including the hybrid and regualtor