UPDATE: Good news! Since my last post earlier this year, I've been successfully receiving Little Compton and Tiverton...most of the time. I found a sweet spot in a window that gets better reception than other parts of the house and have learned how to delicately balance the antenna mast for best reception.
I discovered that the antenna connection on my HP-1 is extremely sensitive to how tightly or loosely the mast is attached whether I use the original HP antenna or my newer Remontrix antenna. Too tight and no reception...too loose and no reception...even one more twist in either direction and I lose the reception. The best reception is when the mast is slightly loose and I prop it against the window to keep it upright. Since it happens with both antennas, I suspect the problem is with the HP internal connection, but not worth trying to fix. I'm just glad that I can get the thing to work most of the time.
I appreciate all the help and advice and consider my problem solved.