Vintage audiosports... Receiver getting HOT

Been looking for a cheap receiver for my garage for a while. This weekend, I went to an estate sale and a garage sale, and between the 2 I spent $45 and got a brand new Irwin woods saw, a few boxes of brand new trash bags, a hammer, and a bottle of isopropyl alcohol, a few vinyl records, annnndddd.... Two vintage receivers. Technics SA-222, a Project/One Mark IIIA. Didn't need two. Now I have 3 vintage receivers. Oops. Anyways, I think the Technics is going to live in the garage. Cheap, nothing special. Sounds "fine". When the temperature and humidity changes eventually roach it in a year or three, I'll replace it with something else again. 

The Project/one, I don't know what I want to do with. It looks really cool. It sounds very good, considering the environment I was listening in. I don't think it is worth much, so I likely wouldn't get anything out of it. Maybe I'll put it in my basement. But in any case, I'll need to do something about the fact that it gets HOT. I was running it for 15 minutes, low volume, and the right vent was too hot to touch. Left vent was fine - very slightly warmer than room temperature.

What would be causing that? I haven't opened it up yet at all, but I'm guessing that there are 2-3 likely causes - what should I check first?

PICTURES! Oh, and the amp getting hot was NOT due to the other amp being on top of it. That was only to take the picture, it was there for less than 2 minutes.

I found This thread just googling "project one amplifier hot, so there's that....

In reply to mtn :

At that age it will need a recap, and if you have a decent tech, rebias the transistors. 

With speakers hooked up, check for voltage on the speaker outputs when not playing anything. If there in more than a volt or 2, it will (probally, depending on model) need some output or bias work.