We report direct C-13 dynamic nuclear polarization at 5 T under magic-angle spinning (MAS) at 82 K using a mixture of monoradicals with narrow EPR linewidths. We show the importance of optimizing both EPR linewidth and electron relaxation times by studying direct DNP of C-13 using SA-BDPA and trityl radical, and achieve C-13 enhancements above 600. This new approach may be best suited for dissolution DNP and for studies of H-1 depleted biological and other nonprotonated solids.