It's a DuKane - the cosmetics are identical to a 2xEL84, 20-watt PA amp I parted out a while back.
Kind of like this one.
DuKane made (makes?) audio-visual equipment for schools, civic auditoriums, churches, etc. That amp was most likely a built-in amp for a small compact PA or maybe a filmstrip projector.
Show of hands - who remembers filmstrip projectors?
If you want to play it as-is, take a guess at 8 ohms, assuming you know which wires are the output.
If you need to identify the correct speaker wires, you'll need to test the output transformer to figure out its turns ratio. The 7591A wants a load around 3000 ohms, so we could figure out what the speaker impedance should be from there.
With minor tweaking, that amp looks like it could be converted to run a 6L6 in the output stage, sort of a "Super Champ". It probably puts out close to 10 watts, which is unusually high for single-ended amps. It might also be possible to convert it to a regular Champ, if you make some allowances for speaker impedance. Also, changing to a 3-wire grounded power cord is highly recommended.
Anyway, it's cool amp. It's super-simple design & construction make it an ideal educational project. Respond here or PM me if you want help with the next steps.
