> the 7.5 Ohm resistor burning up when no output is connected. I am thinking that one of the output transistors is bad
Direct-coupled tranny amps, the failure is rarely where the smoke comes out.
Remove the parts which "can" smoke. Lift two leads of Q9 and Q10 so they are inert. Short CR6 CR7 for clarity. Short CR8 for clarity. Q7 Q8 can not drive a heavy load, but they can drive a 10K:220R NFB network. With the other input grounded, see if the output sits very near ground; it should. If it is stuck at the positive rail, could be Q7 or Q2 is shorted C-E.
In general: if the base-emitter voltage is less than 0.6V, but the collector appears to be sucking current, that transistor is bad. Maybe.
If it set-up happy without the output stage, un-short CR6 CR7 and check for 1.2V end-to-end. 1.3V is not wrong, 3V or 50V is wrong... a diode has gone open. 1N400x is a fine emergency replacement.
In fact. hmmmm... one of CR6 CR7 CR8 Q10 -must- be bad, because if they were all good there could never be more than 0.6V+0.6V+0.6V-0.6V= 1.2V across 7.5R, which won't smoke a 1/4W resistor.