[Joeztech]

Ed;

Yes, the grid resistor's value originally chosen for the output tubes was marginal to begin with (actually a bit beyond the tube manufacturer's recommendations). The IBAM modifications to the negative bias circuit helps dial in the conduction in each output tube for the best possible mA balance in pairs of the output tubes. Adding 10 ohm 1/4 watt resistors in the cathode circuits of each output tube is part of the modification so that you can easily measure the current in each tube. Also consider adding 100 ohm resistors in series with the B+ to each output tube screen grid. Use 1/4 watt resistors there in order to serve as a fuse in case any  output tube shorts. This will help protect the valuable output transformers.

I have done one 500-C and two 800-C units so far. These units are great ones for reception in fringe areas. Use the Fisher alignment information developed for their KM-60 FM tuner kits. I recently compared the results of that method to using sweep alignment of two 800-C units and found that I could not improve on the results using the sweep alignment method!

Good luck!

Joe