Re: crackling..
How about a little electronics cleaner in the pots?
No. Usually not needed anyway. Simply turn the amp on with no instrument plugged in, and turn controls up enough to have the scratchy sounds come through the speakers. Then, one at a time, rotate the controls from minimum to maximum maybe twenty times each ... you will hear dusty pots 'clean up' as you rotate the control(s). Just keep doing it until the static-y, scratching sounds stop, then move on to the next control.
This is assuming the pots are making scratchy noises to begin with (happens a lot with amps that haven't been used for a while). Using any form of spray cleaner runs the risk of leaving behind some kind of oily or sticky residue that will just help more dust collect in a shorter period of time. Always try the 'dry' clean method first.
But in this instance, the pots may not be the culprit, but it's worth rotating all the pots a few times anyway (sometimes they can actually 'freeze' and not rotate at all through lack of use).
With jack sockets, plug and unplug a jack a bunch of times into each socket. The nature of the construction and function makes them 'self cleaning' with use, so seldom-used sockets can become problematic (things like effects loop sockets). Try this dry method before spraying anything in there.
With valve (tube) sockets, it's also worth cleaning them (both sides of chassis) with a dry brush first, after bleeding the main filter caps. Only use spray products as a last resort, to limit the spread of residue throughout the chassis and components.
So there's a lot that can be achieved without spraying goodness-knows-what into an amp.
Of course the issue(s) may be none of these things, but they are simple and easy things you can do for free before possibly needing to delve deeper.
Keep us posted if the problem is solved or not after you went at it with contact spray will you?
