Probably a good idea to contact Cayin, though I thought KT88s and 6550s were interchangeable. For what it's worth, when I went to KT88s (including Shuguang Pentas)from 6550s on a JoLida 502B I stayed with the same recommended 50mV as for the 6550s. Seemn like the reverse would hold true. I've got years on the tubes running this way so it worked for me - but I'm no expert.
