I just put new tubes in my Hot Rod Deluxe. I biased them a little bit hotter than Fender recommends as I heard that Fender has them biased very cold. However now when ever I try and get feedback from my amp by putting my guitar in front of it it makes this weird high pitched squeal. This is not ideal. Does anyone know what could be wrong?
I would try biasing them a bit cooler to see what happens. Maybe you went too far with it.