Hi all I just went through my ultra champ redid the cathode bias resistors since I have a switch and a different OP transformer so I can use 6v6s or 6l6s. I using a 500 ohm R and a 22Uf cap for my 6l6s and a  600ohm/33uf cap for the 6v6s I am now getting static type feedback and vibrato type feedback a max volume with both almost like it as feeding back into the vibrato circuit. not sure what the problem is as I used a 400ohm R for the 6L6s prior. I will look at it again tomorrow to see what give just looking for some feedback from anyone who may have encountered this problem. JGK