I found this article about the amps that really explains the issue with these amps (both the GFA-565 AND the GFA-585) better than any of the posts here:
http://www.jazzfest.tyrell-corp.com/stuff/repair_adcom_gfa-565_gfa-585.htm
http://www.jazzfest.tyrell-corp.com/stuff/repair_adcom_gfa-565_gfa-585.htm