I have a Heathkit SB-230 that uses a big heatsink on the back to cool the induction tube. I used it during an operating event and it got very hot So I installed 3 muffin fans on the back and now the Heatsink runs cool. However the fans are very noisy. That was supposed to be the big selling point of the SB-230. Other ops complained about the noise. I didn't have problem with it as I used HEADPHONES during my operating. 3 muffin fans can be pretty noisy, but I prefer to keep my tube safe (UNOBTAINIUM) than worry about a little noise!