tubed preamp off and ss amp left on?

Thanks for the responses. I just rechecked and the loud hum when pre is off and amp on is gone. Why? I do not know. I have made many changes lately trying to get rid of a low level hum in speakers when nothing is playing. This hum is still present. I have tried cheater plugs on two of the 3 components and the low level hum persists. Audible out to 2-3 ft from speakers. I have one more pair of interconnects to change. I doubt it helps but hopeful it will. If not I am going to change back to my old amp and see. BTW, the pre is lector zoe and amp is belles 350a reference. Other amp is aloia st15.01. What are the symptoms of an impedence mismatch? Can tubes create hum? I don't remember having this problem with stock tubes. May put them back in also. Thanks again.

Thanks. I will try disconnecting the preamp at the amp's inputs tomorrow as Mang53 suggested and see what happens. I hadn't thought of that. The amp is pretty new so I doubt it is the ps caps. I think I have had both pre and power pc's connected to the same dedicated outlet at some point but are on different dedicated outlets currently. No cable or sat. tv connected. Will post back tomorrow evening. Thanks again.

Progress maybe. I disconnected the preamp at the amps inputs and the strangest thing happened. The left channel was silent yet the right channel had the same hum and at the same level. I then plugged the interconnects back in and the hum returned to both channels. What could be happening and what is my next logical step? I have some more speaker cables that I can try, so I think I will start there. Your help in troubleshooting is most appreciated. This is a great forum.

Audio can be compared to women as a source of great pleasure and much frustration.