Super hot is not normal. That is what you would get with HF oscillation. As to what causes it, I don't know.
You definitely need to borrow another receiver and see what happens. I'm pretty sure there is something wrong with your receiver.
If you have an ohmmeter you don't need to buy new wire, just disconnect everything, check the ends for loose strands, then measure between the wires and you should see an open circuit (ie the opposite of touching the probes together).
Is your balance control centered or did you have to play with the balance control to get both sides playing at the same level ?
In the short term, don't play so loud
