I currently have quads installed in Mac MA2275, Audio Research CA50 and a pair in my ASL MG SI 15 DT (single ended)all integrated amps. The CA50 is tough on tubes but these have been in for about 6 months with no issues. The MA2275 has been up and running with them for about 3 months and the Pair in the ASL MG SI 15 DT have been in for Just over a year also without problems. See the attached link below for Jim McShane's take in AA.
http://www.audioasylum.com/audio/tubes/messages/173267.html
http://www.audioasylum.com/audio/tubes/messages/173267.html