I have a vintage receiver, a Kenwood KR6200 I recieved as a gift. It works pretty nicely and is a gem to look at, the only thing troubling is the fact that after listening on the phono source and radio source for a couple of minutes, The left audio channel becomes scratchy and fades out almost. I can remedy this by quickly increasing the volume, but the issue comes and goes. Anybody have any suggestions as to how I can fix my receiver’s issue? Thanks!