I received the replacement tubes from A2A today, so came home just after lunch time.
Now, the new tubes have been installed and the amp turned on.
the setup is :
Dell Precision Mobile workstation + USB cable + WA7 + HD650.
Room temp: 20-25C (anyway, not hot, very comfortable today/this week)
Amp and PSU temp: Cold.
I will report back one hour later.
I received this amp a couple of weeks ago. The amp works well, but I soon noticed the amp and psu became very hot after running for 30 mins.
It is reckoned that the tubes might be faulty. So Woo Audio arranged A2A to send me a set of new ones.