The tube GE5670 can be replaced, yes, it is socketed.
GE5670 is a premium of 6922 family so unless Bendix 6N3 or WE396A then not worth rolling.
Since tubes are bigger than the chassis size, it is specially designed and positioned on its side.
Please see the attached image: http://www.audiostream.com/images/81413ifi4.jpg
As you can see, just on the right of the tube is the black pins. These pull upwards to remove the tube component to replace another.
However, this would void the warranty, you are responsible for any damage by trying to open the unit.
