I recently added a "Champ - Princeton" switch on my homemade 5F1. It basically takes the amp from being a 5F1 to a 5F2A by adding in a tone control. See Sw2 in this schematic. It sounds great, and I'm very happy with it. The only thing that's weird that I don't understand is that when I switch it on, it actually boosts the gain of the amp, especially if the tone knob is set in the upper 1/3 of its range. So strange, because I always thought the old adage for these passive tone controls is that they're purely subtraction, and will cut gain. But there is a distinct volume boost. Can anyone explain why this happens? Note: I know that one of the differences between the 5F1 and 5F2a is the bypass cap on V1A, which CAN cause a difference in gain. I have this bypass cap switchable, but not on the same switch, so this difference is not responsible for the gain boost.