What the heck happened to the poor thing??

Well, anyway. If it was a flame that threw off sooty residue (like insulation, especially rubber like the mains lead), the stuff can produce a thin oily coating -- I mean, transparent -- that will "cook off" the various remaining chemicals as the chassis heats up. This can go on for surprisingly long.

Solutions? My first thought would be to pull the chassis, discharge all the caps, soak it in a tub of pure alcohol for an hour, hit it with compressed air for almost as long, then let it air-dry. There are drawbacks, which you can probably guess, starting with an open two-gallon tub of alcohol.

Simpler would be to put it on the porch, plug it in, & let it sit & hum to itself for a day or two. You could feed it audio & crank it up, which would get everything nice & warm, but this may result in divorce proceedings or your neighbors showing up with pitchforks.

You might pull the chassis & hit the case inside & out with repeated sprayings of unscented Fibreze, if you can find the stuff -- seems like every Fibreze currently on the shelves is Mountain Fresh or some such guck. Though I've had pretty good smell-killing results from a generic that costs $1/bottle.

I would expect that the grill cloth & speaker cone are probably full of smoke stink. If the grill cloth can be easily removed (as on some combo designs) I would take that off-- check the smell of it-- an febreeze the heck out of the fabric. The speaker cone, unfortunately, is not something I would want to mess with, other than possibly replace. One other thing you could do is put one of those little pine tree deodorizers that smokers hang from the rear view mirror in the back of the cab. . .