The C20 is a vintage preamp, and the MC60s are vintage mono amplifiers. They are definately not "from 10 years ago" . . . more like 50 years ago.
But they both use conventional RCA connectors . . . if there's a problem with the fit with your cables, then it's either due to worn connectors on the components, or audiophile cables that have very tight-fitting tolerances in their connectors, or both.
But either way, be very careful with these connectors, especially with modern audiophile (large) interconnects. The ground connection between the connector and the preamp/amp is made simply by the crimping of the jack in place, and they are easy to loosen and mess up (especially after fifty years of wear!).
But they both use conventional RCA connectors . . . if there's a problem with the fit with your cables, then it's either due to worn connectors on the components, or audiophile cables that have very tight-fitting tolerances in their connectors, or both.
But either way, be very careful with these connectors, especially with modern audiophile (large) interconnects. The ground connection between the connector and the preamp/amp is made simply by the crimping of the jack in place, and they are easy to loosen and mess up (especially after fifty years of wear!).