The tube is connected to the preamp board by a ribbon cable. There is a good chance the ribbon cable connectors need cleaning.
Of course, the tube itself could be dead, but cleaning the connectors costs only a few cents' worth of contact cleaner, so it's worth trying first.
Crappy Bassist with Expensive Gear Club #19
Greenboy Designs Club #62 (15/6/1, 15sub, Bassic12)