The best way to determine appropriate AC line voltage is to measure the heater voltage at the output tube furthest from the power transformer (pins 2&7). Best practice is to keep it within +5/-0% of the nominal 6.3 vac that the tubes were designed to operate on. If the heater voltage is higher than this limit, then some sort of line voltage adjustment would be appropriate. Of course, any adjustment will also affect the B+ voltage which is fine as well -- but that is of little concern. Get the heater voltages right, and then the B+ voltage is, what it is, what it is. Then bias the tubes to the ideal 30-32 mA range.
Your understanding of how the Bias and DC Balance control operates is correct. Understand too however that because the power supplies of the X-202B are not regulated, there will be some interaction between the four controls, so you will need to go over the process a few times to zero all the tubes in correctly.
As for the screen stability resistors and their installation, you might take a look at my thread of 5 years ago regarding my own X-202B, which you can find here:
http://www.audiokarma.org/forums/index.php?threads/x-202b-heaven.551876/
And particularly note the pics of post #11. In it you will see the Screen Stability resistors installed at each output tube socket running between pins 1 and 4. There are a number of ways to install these resistors, with the only real criteria being that their leads be kept short. Basically it involves removing the leads that interconnect all the pin 4 and 8 wiring at each socket, and any other wiring connected to either of these pins at any of the sockets as well, leaving ONLY the pins 4 to 8 jumpers present at each tube socket. The idea is to then create a new screen "buss" circuit that all the removed wiring connects to, as well as one end of each new resistor -- the other end being connected to pin 4 at each tube. In this way, the screen grid of each tube is powered through its own Screen Stability resistor. In the receivers, many of the folks just use an overhead buss lead to do the job. But in the X-202, space is limited, so I developed the approach of using the unused pin #1 of each tube socket as the new screen buss terminal. To do a neat job of it requires some work, but I always like my work to look like I was hardly ever there. As a result, I reuse the original leads interconnecting the sockets -- but now interconnecting them at pin 1, and create the buss that way.
If you're using the new Tung Sol tubes, they tend to run hot. Once you ensure your AC voltage is correct, if you still can't lower the current draw enough, then a simple component change will take care of that.
I hope this helps!
Dave
