[robsradioactive]

With a modern speaker, you will still need a similar type output transformer and a modification to the power supply:
The field coil will need to be replaced with a similar ohms value power resistor--perhaps 1.8K ohms and at least 5 watts--in a suitably ventilated place in the chassis. C25 and C26 should probably be upsized to 8 and 16 microfarads, respectively. This last part is to compensate for the fact that a resistor is not as efficient as a field coil in filtering out the power supply "hum."

Rob