[rfeenstra]

The physical size of a resistor determines the power handling capability. The large resistor is capable of dissipating much more heat than the small one. It is, undoubtedly, used in the power supply section of the radio to drop the B+ voltage. Such an application may generate 2 to 5 watts. Much more than that and they usually would use a wire wound resistor because of its greater power handling capability. The smaller resistor is probably only capable of dissipating 1/2 watt of heat. You can easily find a 7.5K resistor that is the same size or even smaller physically than the 9K resistor. The amount of power that a resistor must dissipate is determined by the amount current that has to pass through it. That current is determined by the ohm value of the resistor and the voltage drop that occurs across it.