Sundown SFB2000 Rectifiers

I am working on a sundown sfb 2000 however the issue I am having is that the rectifier got damaged 1640 s4 and I am unable to identify a replacement I checked the schematic for the taramp and I see that it uses positive and negative while the soundigital schematic shows it uses positive only. I just want to know the polarity of s3 and s4.


Regards,