Where the current source loading allowed all the idle current to be delivered into the load, the resistor loading prevents the full idle current to ever be delivered. This limitation arises from resistor drawing a varying amount of current depending on the voltage across it. When the voltage increases, so to the current through the resistor. Thus when the amplifier's output tries to pull the load up in voltage, it must also pull the load resistor .

   How much current is available from the resistor loaded amplifier? Assuming a capacitor coupled output or a DC coupled output with a negative power supply for the loading resistor and the loading resistor equaling the load impedance, the peak negative going output current is one half the idle current. For example, if the idle current is 30 mA, then only 15 mA can be delivered into the load when the tube is cutoff. The math is simple enough: when the tube is cutoff, the load impedance sees the negative power supply voltage or the voltage stored in the coupling capacitor, through the loading resistor; and as these two resistance equal each other, the load impedance only sees half of the available voltage and thus half the idle current. What if a different resistor ratio is used? Greater voltage or current can be delivered into the load impedance, but at lower amplifier efficiency.