Use lots isopropyl alcohol and a toothbrush to remove flux, that will do a much better job and won't leave any residue or debris.
Some of your component leads look far too long. It's possible that some of these are touching under the belton brick and shorting somewhere. Cut these down to clean them up.
There seems to be some scorching around the pads on the belton brick. You may have your iron on there for too long, or it might be too hot. This can damage the pads.
Lugs on your 3PDT board look like they could probably use a bit more solder. There are a few poor solder joints throughout the board, I'd recommend reflowing some of these, particularly on your pots, I/O jack ground leads, and dc leads.
I can also see quite a few scratches on the board, including over some traces and may have damaged them.