First of all, still learning things. That said, I have a Lafayette LR-1500TA that works - for the most part. I've recapped it and deox'd it. Gone through bias current adjustment and balanced the voltages. It sounds fine, up to mid-level. At some point as I raise the split-volume control, the right channel walks away from the left. The left begins sounding, well... gritty. I hooked up my signal generator and get a clean waveform on the right, but the left goes asymmetrical - but not like when there is clipping from one of the two outputs. I'll attach an image. Where do I begin? Is this usually a weak transistor or a power supply issue? Resistor? I'm new enough that I've never had to deal with this yet.