Originally Posted by JimmyM
Replacing the tubes might help, but it could just be one tube that needs replaced. If I'm not mistaken, the tube gain is only related to the two driver tubes.
Yes.... adjusts plate voltage for power amp tubes.
I'm not 100% "getting" the problem..... But I think he is having a noise that probably sounds like the wind blowing, when tube gain is set to lower settings.... and it stops when set to higher settings.
"Tube gain" really means "amount of plate voltage reduction", so at maximum effect, the voltage is lowest.
Therefore it seems noise is occurring with max plate voltage. Yes, could be a tube, could be something else, too.
Tubes are easy, so the advice to change them is good.