I run KT-88S on my SFS-80 and bias slightly below the manufactuers recommendiations. They run hot like all tubes.
I have a quad set of 6550's but didn't get a chance to try out. Check bias about every couple of weeks anbd you shouldn't have any problen.
I have a quad set of 6550's but didn't get a chance to try out. Check bias about every couple of weeks anbd you shouldn't have any problen.