  We consider effects of magnetic field on the thermopower and
thermoconductance of a single-electron transistor based on a quantum dot
strongly coupled to one of the leads by a single-mode quantum point contact. We
show appearance of two new energy scales: T_{min} ~ |r|^2 E_C(B/B_C)^2
depending on a ratio of magnetic field B and the field B_C corresponding to a
full polarization of point contact and T_{max} ~ |r|^2 E_C depending on a
reflection amplitude r and charging energy E_C. We predict that the behavior of
thermoelectric coefficients is consistent with the Fermi-liquid theory at
temperatures T << T_{min}, while crossover from Non-Fermi-liquid regime
associated with a two-channel Kondo effect to Fermi-liquid single-channel Kondo
behavior can be seen at T_{min}<T<T_{max}.
