Aha, that's a DC parameter. Much easier.
Figure what the plate voltage for the lower tube is (about 100V in this case). You know what current you want to run; current in top and bottom tube is equal. Let's say for discussion that it's 10mA. So we look at the tube curves and see what bias voltage is needed to get 10mA at 100V. Now, the bias voltage is pretty negligible compared to 100V, so we can look at the 100V line, move upward until we get to the intersection of 100V and 10mA. Then we can see what bias is needed to get that current.
Calculate the cathode resistor by Ohm's Law; R = Vbias/10mA. All of this will get you to within a few percent of the desired operating point, which is close enough for jazz, as they say.
Figure what the plate voltage for the lower tube is (about 100V in this case). You know what current you want to run; current in top and bottom tube is equal. Let's say for discussion that it's 10mA. So we look at the tube curves and see what bias voltage is needed to get 10mA at 100V. Now, the bias voltage is pretty negligible compared to 100V, so we can look at the 100V line, move upward until we get to the intersection of 100V and 10mA. Then we can see what bias is needed to get that current.
Calculate the cathode resistor by Ohm's Law; R = Vbias/10mA. All of this will get you to within a few percent of the desired operating point, which is close enough for jazz, as they say.
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