  We show that, given a classical solution of the heterotic string theory which
is independent of $d$ of the space time directions, and for which the gauge
field configuration lies in a subgroup that commutes with $p$ of the $U(1)$
generators of the gauge group, there is an $O(d)\otimes O(d+p)$ transformation,
which, acting on the solution, generates new classical solutions of the theory.
With the help of these transformations we construct black 6-brane solutions in
ten dimensional heterotic string theory carrying independent magnetic, electric
and antisymmetric tensor gauge field charge, by starting from a black 6-brane
solution that carries magnetic charge but no electric or antisymmetric tensor
gauge field charge. The electric and the magnetic charges point in different
directions in the gauge group.
