  We discuss a class of transfer matrix built by a particular combination of
isomorphic and non-isomorphic GL(N) invariant vertex operators. We construct a
conformally invariant magnet constituted of an alternating mixture of GL(N)
``spins'' operators at different order of representation. The corresponding
central charge is calculated by analysing the low temperature behaviour of the
associated free energy. We also comment on possible extensions of our results
for more general classes of mixed systems.
