Ampeg BA115HP 220watt help

[SDthrash]

Just bought an Ampeg BA115HP 220 Watt amp for $100.

It's making a really annoying distortion sound.

I was told it has something to do with the bias? not sure what that is.

Any help on identifying the issue would be greatly appreciated.

I made a youtube vid of the sound it makes here:
Ampeg ba115hp distortion problem - YouTube