[rghines1]

Based on the schematic, the speaker's field coil is part of the power supply which is typical. Shows on drawing to be 650 ohms. You could use a 500 ohm 10 watt resistor to get the B+ voltage up for a temporary test. But will need to find permanent speaker and wire that in too. Any size less than 6" should work as a test. Not sure about your question is about needing an amp, should be OK with push-pull output already there. Richard