What makes amps go crackly?

[Lane Gray]

I walked into my local music store (the same one that gave me the Wright and Bud Carter's MSA), and I gave a hundred bucks for a Session 400 with the usual great tone, but it's got some crackle at the edges. I figured for a hundred bucks, I can put my limited solder skills to use. Will it likely be just cleaning pots and jacks?
Or where do I start looking?

[Wiz Feinberg]

Aside from cold solder joints, expect trouble from the effects loop jacks. They are switching jacks that pass the preamp signal through unless a plug is inserted into the send and return jacks. I've had them fail on my in my Nashville 112 and 400 amps. The last time it happened on my N400, I smacked the amp on top of the cabinet and the signal was restored. I had to make a short double plug jumper cable for my N-112 once I stopped using its effects loop. The same problem can occur if you routinely plug your signal chain into the rear preamp input jack, as it's also a switching jack. This happened after I started using a Tonex pedal that I plugged into the the rear amp input.

Another thing that causes a cracking sound is a bad speaker cone. If that's what happened to yours, buy a new replacement. Speakers have come a long way since the 1970s and 80s. Most are much lighter.

Considering that my Nashville amps are over 45 years old now, I guess such glitches are to be expected. Yours may be even older.

[Lane Gray]

No loop: it's one of the original 73-82ish.
I still think the original is still the best-sounding. I'll check all the jacks.

[Dave Grafe]

Check all jacks for loose nuts, they are your only ground connections in and out and will make all manner of spurious noises if at all loose.

Clean and reseat all Molex connectors, perhaps the most common unwanted noise source with Peavey amps.

Check the speaker by playing a known good amp through it and conversely by playing this amp through a known good speaker.

Clean and exercise all pots and switches.

If all this and still no joy it's time for an experienced tech to put it on a scope and search for failing internals.

[Lane Gray]

Check all jacks for loose nuts, they are your only ground connections in and out and will make all manner of spurious noises if at all loose.

Clean and reseat all Molex connectors, perhaps the most common unwanted noise source with Peavey amps.

Check the speaker by playing a known good amp through it and conversely by playing this amp through a known good speaker.

Clean and exercise all pots and switches.

If all this and still no joy it's time for an experienced tech to put it on a scope and search for failing internals.

All good ideas and easyish. And not that long.