Wild Bill said:Scratchiness comes from dirty controls 99% of the time. If cleaning doesn't fix it THEN we can talk about more techy solutions!
Since you show your location as Mississauga then go to Matheson Boul off of Dixie. There's a strip mall full of electronic stores. Most of them carry contact cleaner sprays.
Look for a product that specificially says its for switch contacts, volume controls and the like. Most will leave a thin film of silicon lubricant. Don't buy anything else and especially not anything oil-based, like WD40. Some folks like a product called Di-oxit. I like a brand called MG Chemicals. Mostly they're all the same.
You do realise that you'll have to pull the chassis? There's no way the spray will slide down the shaft after you've pulled the knob and will get inside a volume or tone control. Inside the amp you will see that the control has a gap where the connection terminals come out where you can insert the plastic "wand" that comes with the contact spray can and whoosh the spray inside. You turn the control back and forth a few times and that's it!
The excess spray evaporates quickly so don't worry about excess. If your amp is a printed circuit board amp with the controls mounted to the board you may have a PITA trying to get at the opening to the control, as it will be between the control and the board. If you bend the last 1/2" of the plastic wand you should be able to get where you need it. This is another reason why printed circuit boards are only good for the manufacturer to save costs and give no extra value to the player.
Some controls are sealed and have no opening. The idea is to keep dust and dirt out. This never seems to work and you then have no choice but to replace the whole damn thing but don't worry, sealed controls cost more so few guitar amp makers use 'em.
If this doesn't work then check back and we'll tell you what a tech will need to do to fix the scratchiness.