Sylvania SY-171C
AC/DC Audio Output Triode
192?

This tube was an indirectly heated version of a '71A output tube, but had a heater rating of 6.5 volts at .25 amps. The bulb is a small S-12 size, and the max plate voltage was limited to 135 volts vs the 180 volts for a '71A. The specified bias voltages were much lower than those used on the '71A at comparable plate voltages.