Re: Hot IRF510


Jim, N5IB
 

Sounds like that may be another instance of a failed Q6. That is a clever circuit that minimized voltage drop in the supply line, but the IRF510 can be damaged by esd. When (if) you replace it, tack a 470K or a 1 Meg in parallel with a 0.01 uF cap across from gate to source. That will protect it from most esd, and will only pull a few uA from your power source.

On the temp stability.... the iron powder of the toroid core has a positive temperature coefficient. One trick you can do is replace C20 with a polystyrene capacitor. They have a negative coefficient. Don't expect to cancel the drift, but at least they'll be going in opposite directions.

N5IB

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