Lavatubes don't work well with Dual Coil Cartos.
It has to do with some flawed protection programming and the amperage limit of the Lavatube. You can't get more that 3.4 ish volts out of a Lavatube using Dual Coil Cartos.
Try some Boge single coil cartos, they are a great fit with the Lavatube.
Or be like me, and just pony up for a Provari V2 (on its way to me now).
Ryan