03-04-2017, 01:36 AM
I have not worked on a car radio but any other weak tube might be replaced. If the others all test strong, and you think the volume is still low there could be resistors that have drifted out of spec (gone to higher resistance values) that might be the culprit. Another possible thing to check would be alignment. I'm not the best trouble shooter but that's what I would check next.