Are you sure that resistor is fried? I am dealing with my own beta bass problems but have you tested the resistor with an ohmmeter to make sure it is dead. I am having trouble differentiating the colors on the resistor but I am guessing it is a 24 Ohm +/_5%. I would not personally feel good about putting a potentiometer (variable resistance) in the place of a resistor but he prolly knows more than I do. If you can find out the color order with certainty then just head to radio shack and pick up the appropriate one. they should have and it would be cheap. I would download the schematic from this board as well to be sure you got the colors read right.
hope this helps. maybe someone else can answer the potentiometer questions..
marc