Same here have a bitx40 that's run all mode pretty much stock on the PA side never even adjusted the bias. I have messed with the gain a bit, that is about it still stock heatsink too.
The things to keep in mind: It's qrp don't push it and for digi modes 1/2 the power to be safe and not stress the IRF510. I have worked the world on digi modes under 5w.
I also run a WA2EBY with 2 510's other than some heat they run just fine.
I have not seen to many under "normal" operation blow unless its part failure from a manufacture defect or operator error.
At QRP levels (5-10w) the 510 can take the heat its when you push them north of 40-50W where SWR and heat become something to pay attention to.
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David
?N8DAH
N8DAH