According to the schematics that I have, there are two versions. One with an external transformer which gives +/-12V, and one with an internal transformer which gives +/-15V.
Unfortunately my schems looks like 3rd generation xerox and some components values are unreadable despite 600dpi scans.
I hope these can still be usefull.
+/-12V version
http://twin-x.com/groupdiy/displayimage.php?pos=-3533
+/-15V version
http://twin-x.com/groupdiy/displayimage.php?pos=-3532
Axel