If it popped the cathode resistor, that's not a good sign, but the only way to know is to measure its power output capability. There's a chance it could just be a tube that requires lower than normal grid bias voltage, and so draws notably less current than other more typical tubes at more typical grid bias voltages. Physical appearance can help make a determination as well. Typically if the getter flash has all but evaporated, its a sign that a tube is well spent. But that doesn't mean its necessarily bad, either -- just near the end of its useful life.
Dave
