It sounds like you have one (or possibly more) bad NOS tubes in that channel.
So, you have (4) 6922's in each channel, just go down the line and switch one set of tubes at a time until you find that the distortion switches to the other speaker. Then you will know which tube is the bad tube, and replace it.
So, you have (4) 6922's in each channel, just go down the line and switch one set of tubes at a time until you find that the distortion switches to the other speaker. Then you will know which tube is the bad tube, and replace it.