The bias resistor(s) might have been burned out by a tube that went cherry-red. Look for visible burn marks on resistors. Or tube that won't bias is bad; replace. Then re-bias other tubes.
can't Bias a tube
I have a cj mv52 the other night I heard a loud buzzing in my right channel after which the amp had no power. I looked inside the amp and the power supply fuse blew. I replaced it and all the tubes were out of bias. When trying to bias one of the el34 output tubes there is no red light at all so there is no starting point to bias the tube. does this mean a bad tube or problem with the amp. Would appreciate any feedback.