Depends on which definition of current flow you go on
either conventional current flow or electron current flow. With electron current flow the physically correct definition of what happens, the current does flow from negative to positive, but with conventional current flow, what everything works by and is designed around, it states that it flows from + to - though this is just to avoid confusion by changing everything.
However, your explanation is slightly incorrect, if there's a negative but no positive you're still not going to get anything, you need them both, you need the full circuit, or else there is no potential difference, so the current flow definition has no relevance to the amplifier problem, connect the + to the positive and the earth(-) to the - It's only ever relevant in circuit design.
But yeah, check your earth is good, and is connected to the chassis, and paint has been scratched off the chassis, so it is in contact with bare metal.