30 watt PA amp from ~1958, should make a sweet amp head for a guitar. The XLR can be replaced with a 1/4" TRS, or you can just splice in a TRS and fin a spot for it on the chassis somewhere.
Don't plug it in and turn it on (even after putting in the correct fuse), it could do serious damage if there is anything wrong with it. I needs to be brought up on a variac.
Find a local repair shop that can test tubes and get them checked out, replace any that test bad.
Replace the capacitors and any resistors that test out of spec, and replace the selenium rectifier diode.
Don't worry about the old umbilical plugs for the speakers, just use the terminal strip with some spades on the wires. The small metal piece hanging is a bridge and should probably connect the two farthest terminals (look like they're labelled common and ground), and the black wire coming from the hole in the chassis most likely is to be connected to one of those two terminals (though I don't have a schematic, and couldn't say any of this for certain without a schem or manual, but it is a common setup with PA heads; you really need to get your hands on a schematic, any tech you take it to would ask for one, and you'll need one to do any work on it yourself.)
Yes the mic XLR Should be standard XLR.
While most resources seem to call it a stereo amp, that baby is mono (very few stereo PA heads out there if any, note the single speaker terminal strip, single oDutput transformer, and single RCA phono).
The tubes you have are a full compliment, 6AV6, 12AX7, 6U8A, two 6AV5GA, 6CG7, two 5Y3GT. The 12AX7 is usually used for a phono stage (you took a pic of it inside it's 'can', the 6AV6 is also in a can, though not sure of its purpose). I dont think those 6AV5GA tubes are in production anymore by anyone, so your only bet there is to find some NOS ones, the bay would be your best bet there (they look like they can go anywhere from $4-20 each).
Not sure about the fuse, but looks like ~2 amp, again a schematic woul be best to find that info.
My ultimate suggestion is to visit AudioKarma.org, join and ask around in the Tubes forum and the DiY forum and you will probably get a great deal of help with this project (several people there have rebuilt this same model and the can most likely help with schematics as well as any mods you might be interested in performing), and most likely after any advice and info that Mark gives you, he'll also probably advise you to visit and ask around at AK (it's an insanely awesome resource, it is to vintage audio gear restoration what the Swirl is to JWIII related vinyl collecting).
I say head over to AK, dig up a schematic and maybe a manual, do some reading and research on tubes in general (and this amp in particular, and some of similar type), get yourself a soldering iron, and have a seriously fun project for yourself!
BTW, seriously nice score Shane! That looks to be in really good shape cosmetically, and whether it needs a little electrical work or not $12 is a serious steal.
