I have had mine for about a year and a half or longer. After owning it about a year, it developed a distinct hum in the left channel, one for which I have not been able to locate a local repair shop.
donaldftReplacing one tube on a multi-tube amp can be a bit tricky. They don't all sound the same. Always try to replace them in pairs (left+right). Stores usually sell tested/matched pairs to make sure you won't get an unbalanced sound.