A cryogenic Yb amplifier using two laser materials, ${\mathrm{Gd}}_3{\mathrm{Sc}}_2{\mathrm{Al}}_3{\mathrm{O}}_{12}$ and ${\mathrm{Y}}_3{\mathrm{Al}}_5{\mathrm{O}}_{12}$ (YAG), has been used to obtain $70\mathrm{W}$ average power at $5\mathrm{kHz}$ pulse repetition frequency; the output was compressed to $1.6\mathrm{ps}$ , compared with an input compressible to $1.4\mathrm{ps}$ . The gain broadening obtained by combining two media enables shorter pulses than using Yb:YAG alone but retains the power-scaling advantages of cryogenic Yb:YAG.