Hello, I got this rebuild and modifying project going on my Fisher . Right now I have a very low volume from the right channel that I have narrowed down to V4. I can jumber into the tag right before the volume pot I get normal volume using my phone but jumper at the tube very low volume as comparred to the left preamp tube. My deduction then is there is a problem with the last half of C4. The tube socket is new, replaced the tube twice and the coupling capacitor twice. The resistors are new and checked them for the right value. The voltage checks out close. The caps are .047 ero fol types which I had in service in another amp. What the hell could be wrong? I'm missing something here.