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sansui AU-519 and sansui TU-919 connection

Just picked up a Sansui AU -519 amp and a Sansui TU-919 tuner yesterday at my local Goodwill. Used the tuner's Output (variable) and the amp's Tuner input. Made connection with some audio RCA plugs. I only get a high-pitched hum from the speakers. The preamp-power amp switch is in the Connected-direct coupled position. As a neophyte to these pieces, I'm looking for some troubleshooting advise.