So been testing this on ft8 and using CQ's until watchdog kicks in (occasionally picking up a QSO!)
If you use this shroud, you must have a fan on when transmitting. Otherwise, the shroud captures the heat and the finals heat up higher than they would with no fan!
I am going to install a temp sensor and relay to turn the fan on and off. But until it gets here in 3 weeks, I am going to turn the fan on when I am transmitting. (BTW: I have seen other suggestions on driving the fan off the transmit relay, that is another option. The problem is when you go out of transmit, the fan goes off and you don't get a cool down period in preparation for next transmit.)
BTW: With these larger heat sinks, my finals on ft8 don't go above 30C (ambient 22C) with no fan and no shroud even with lengthly ft8 duty cycles.