I have two pair of VTL 750's, meaning I have 48 6550 tubes to contend with.
I have lost tubes and with that the large fuse behind the screw plug on the rear of the amp. No damage to the unit other than fuse and I'm into my 5th year with these.
I think VTL amps are among the most reliable and best sounding of all the big amps. If you want to keep them reliable be sure bias is right and tubes are suitable. I don't know about your ST-85, but the VTL 450, 750 and 1250 all run very reliably with Wing C 6550.
I have lost tubes and with that the large fuse behind the screw plug on the rear of the amp. No damage to the unit other than fuse and I'm into my 5th year with these.
I think VTL amps are among the most reliable and best sounding of all the big amps. If you want to keep them reliable be sure bias is right and tubes are suitable. I don't know about your ST-85, but the VTL 450, 750 and 1250 all run very reliably with Wing C 6550.