Bear with me if I ask a stupid question. Have you moved the offending tube to a different socket to make sure that it is the tube that is problematic and not the amp?
If it is the tube, the prudent thing is not to use it until it is replaced. Generally the EH 6550s are pretty reliable, but there is always the possibility that you got a bad one.
If it is the tube, the prudent thing is not to use it until it is replaced. Generally the EH 6550s are pretty reliable, but there is always the possibility that you got a bad one.