I'm replacing a whole house Aprilaire 760 humidifier with a new 700 model. It appears that everything is the exact same dimension so I'm intending to pull the old one out and simply install the new one in the existing opening. The 760 was installed in our original furnace and the solenoid had a transformer attached to it (see picture). I suspect that the transformer was needed because the original builder installed a furnace which did not have a dedicated 24v humidifier connection on the panel. When we installed a new furnace, the 760 humidifier was re-installed with the transformerstill attached to the solenoid. I think it that this was just a useless carryover from the prior installation as the unit is now connected into an input on the control board that is identified as HUM and appears to be 24 volts.
The new Aprilaire 700 came with a separate 24v transformer. Based upon what I'm reading on this site, it looks like I won't need it and I can just connect the brown lines from the humidifier straight into the HUM inputs on the board. I've attached an image of the board here too. I'd appreciate any guidance and input.