The ornamental design for a lampbase, as shown and described.
FIG. 1 is a perspective view of a lamp base showing my new design;
FIG. 2 is a top plan view thereof;
FIG. 3 is a side elevational view thereof; and
FIG. 4 is a perspective view of a second embodiment of my new design, this
embodiment being identical to the first except for the omission of the
light fixture stanchion.