Can someone guide me through the building of a board to individually adjust the the voltage on my 7868 tubes. I have seen this done before but not sure hows its done. I have recapped the 400 but still need to adjust the voltage on the tubes. I would like to do this individually. One pot for each output tube. I would buy some new matched ones but they are expensive. I have already installed some cathode to ground 1/4 w 10 ohm resistors on the outputs.