Newly Acquired Cary/ B&W system with malfunctioning preamp.

The preamp is Cary SLP-03 and it produced the LOUD 60Hz buzz when connected through an amp on both channels

When connected through Pioneer SA9800 preamp outs to the Cary CAD 200 SSamp, everything worked great with the rest of system B&W N803D and Cary CAD300 CD-player. Overall I was extremely surprised on how preamp section of Pioneer amp performed with Cary amp with exceptional control and tightness

I doubt that replacing tubes will solve issue and so would like to know the ballpark value for as-is preamp unit.