Does it go "click" when you hook it up, flip the switches to operate and key the mike?
Here's the schematic I have. If it goes "click" you're ahead of the game, even if it won't make the wattmeter wiggle. A close look at the diagram reveals a date of 1976. If you found a 1976 car and wanted to hop in and go, there would be issues of maintenance and upkeep to consider. This box is very much the same way. The nine (I think) electrolytic capacitors are a bit like radiator hoses. Might look okay and then pop after ten or fifteen miles. Those capacitors have a limited life, even if the mileage is low. All of them should be replaced before any serious attempt to make it your daily driver. All of them. And the tubes. They might be good, all six might be bad, or just some of them. Just seeing the orange/red glow of the filament won't make a tube "good" all by itself. Most failed tubes have other faults, but still light up just fine.
Lotsa wild cards in this deck.
And if it has hard miles on it, the price to restore it will be less than resto on a '76 Camaro, but probably high enough to make you think twice.
73