[MrFixr55]

Hi TV Man,

This may be another help or I am wrong, one or the other.

• Reinforce the ground plane with heavy gauge wire soldered to the ground traces on the PC Board.
  
• instead of cathode resistors to ground, consider grounding the cathodes and adding the resistance between chassis ground and the HV center tap.  This is like the pre-1937 or so method.  This puts the heaters and cathodes at the same potential instead of having 18or so V between the heaters and cathodes.  IMHO, this is still "self bias", but it looks like a C- supply to the grids.
  

My rough guess is that they did that in days of yore because they were worried about hum when heating the cathodes with AC, especially when using the 6V heater tubes that were originally designed for DC car radios.  My guess that B- at chassis potential and cathode resistors was cheaper and easier to understand.