I also have a Fender Champ 12. The original output transformer does get hot. Eventually, I began to loose volume and decided to change it. I got lucky and found a Fender origininal replacement, installed it and all was well. Still ran hot. I guess that is normal. Not feeling comfortable with the original replacement (sounded louder!) I purchased and installed an Edcore XSE15-8-5K series transformer (EDCOR - Browse Series). It cannot be mounted inside the chassis so I found a place to mount it under the chassis on the outside. It is twice the size of the factory installed transformer. I also replaced the filter caps. The Edcore transformer runs very cool, even under full volume duress! @ $20 plus shipping, I think it is a good deal for this amp.