Okay, here's the deal: I have been trying to nail this tone for about six months now, and up until recently, I couldn't figure it out. The tone I'm trying to nail is the song "Help!" by The Beatles. I have everything perfect about it, except one thing: warmth. What I mean is that the tone is perfect but it is a bit too "thin". Any suggestions on how I can thicken up my sound without losing the tone? I am currently using a Yamaha SBG200 through a Vox AD15VT. Any suggestions?

Please note: I am not only trying to get this tone. It would be stupid to do something drastic for the sake of one song. I have been trying to thicken it up for a while.