This is the charming amplifier half of the EH-150 amp/lap steel combo, sold by Gibson in the early '40s. This one has held up pretty well over the years, showing only moderate signs of previous wear, and still retaining its original speaker and transformers. The electrolytic caps have been changed, along with a few coupling caps and resistors. You can expect a nice, funky, low-headroom tweed sound when running a guitar through it.
It should be noted that this is a very primitive amp design and serves better as an antique than as a gigging tool. As is extremely common with octal tubes, these do suffer some minor microphonic issues. The front speaker grill is a floating piece in the cabinet design and does rattle a little bit when the amp is cranked; any prospective buyer should take note.