I was talking to a fellow technician who had a question about the early Yamaha capo bar and string buzzes. Did Yamaha ever use a steel rod inserted into plate for the string termination? Coincidentally, I had just finished restring a 1973, C7 (7'4") where the front duplex was heavily felted due to extreme buzzing. My modus operandi to alleviate the duplex buzzing is to file past the hard cast iron surface into the softer material. When I removed the strings, it appeared it had a steel rod. Not believing Yamaha ever used a steel rod, I removed the key bed to get a better look. It was still difficult to decipher; steel rod or cast iron? I took the gamble and began to use my mini hand-held belt sander to cut down the surface and discovered it was cast iron.
My fellow technician was certain the encountered Yamaha (6'6"?) had a steel rod.
What say you all?
P.S. After sanding the capo bar, there were no buzzes.