Conrad Johnson PV-14 background noise


I noticed a faint background hum caused by my CJ PV-14 (because there is no noise when I turn on the power amp only), it is not obvious but you can hear it when you get really close to the speakers. I have tried a set of new tubes but the noise did not change. Anybody has experience to share?

Thank you!
try plugging electrical cables into different sockets you may be getting a ground loop hum especially if you are using a sub
Thank you for your advises,

Dusty, I have to be very close to the speakers, so I guess it is not unacceptable

Vernneal, I will try other sockets.

Rrog, No, I did not get it from CJ. I got it from Ebay. But the old ones I use are Mullard purchased from CJ and they have noise too. And I tried to call client service of CJ but its always answered by an answer machine.

Dwr,could you please elaborate a little bit what is a cheater plug?
The cheater plug just makes a two prong plug out of a three prong plug, you can buy them at a hardware store for under a buck. If you try this and it reduces or eliminates the hum, it could be caused by ground loop.