Yes you are absolutely correct. Here's my problem. As I aged it becomes increasingly difficult for me to follow abstract concepts. I have all this stuff memorised; but until I can picture in my mind how an AC voltage can ride on a DC current I am stymied. I have all the books; Radiotron/Rozenblitt/AARH/USN Training Series etc etc. When someone explains that to me so I can understand it intuitively I will buy them a drink. All my problems stem from that one thing.