The fulness/bass performance with the PLs' stock tubes is okay.There are other 12ax/au's that will rectify these short-comings.The Shuguang triple-mica 12ax7s and the Mazda/Radio Technique french military (triple mica) 12au7s.
Google search will reveal sources for both and may cure your need for a fuller/more ample bass.
Google search will reveal sources for both and may cure your need for a fuller/more ample bass.