  For the Lie algebras $g_n=
\mathfrak{o}_{2n+1},\mathfrak{sp}_{2n},\mathfrak{o}_{2n}$ a simple construction
of a base in an irreducible representation is given. The construction of this
base uses the method of $Z$-invariants of Zhelobenko and the technique of
Wigner coefficients, which was applied by Biedenharn and Baird to the
construction of a Gelfand-Tsetlin base in the case $\mathfrak{gl}_n$. A
relation between matrix elements and Wigner coefficients for $g_n$ and
analogous objects for $\mathfrak{gl}_{n+1}$ is established.
