I have no idea who made it, but it is a simple amp, four tubes. I don't count the rectifier, we all know what it does. A push pull output, we know what that ought to look like. Two channels. One of the tubes is the phase inverter. SO I bet if you sit down with a pad of paper and a pencil, you could draw up a schematic from the circuits in half an hour tops. If you are familiar with the circuits, and don't have to look up the tube pins, hell, 10-15 minutes.
I don't know where you are - really ought to include at least your nation on the profile - but since the power switch is labelled "mains" I assume this amp is not from the USA.