I noticed on ssb receive that i am getting what sounds like feedback i can hear myself tapping on the receive board and the bal mod. board it is the loudest when i tap v502, and t502. I have replaced the r520 recently when the ssb receive quit and got it running again. I swapped out tubes, no change and i am going to check the tube voltage again. and test components when my pain subsides. im having a bad day today.