The 49A is a ballast tube, a resistor in series with the filaments in your radio. It drops 49 volts @ 300ma. You could replace it with a resistor around 170 ohms @ 15 watts or greater. The resistor will be hot so should be kept away from other components in your radio.
If an 8 pin octal base, K49A and K13J36 are listed as replacement. If 4 pin, 4P-45 and KX49A are replacements. 49A came with two different bases.
Norm
: Can anyone tell me if there is a substitute tube for the ballast tube #49-A