Did you change the bias transistor, or put it in upside down? (H709)
Check H710 or H719 for open or incorrect resistance. I believe you said you did.
Did you install a matched differential pair ?
Solder bridges on 711/712 will feed incorrect base to 713/714, and overheat them and the outputs.
I hope your not running this without a dbt.
Do not let the transistors get over 130 degrees. Shut it down and cool it before running it.
The drivers are only rated for 150 deg use.
Buy a can of Dr Scholls Freeze Off and start cooling each transistor (before the drivers), as you monitor your 711/712 base voltages.
Your base voltages should tell you were things start going downhill.