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Detecting “Dirty” Power

I bought a used BHK 250 still under warranty. It is plugged into a Denali S power conditioner.  I heard a hum coming from the area around the tubes.  I cannot hear it from my sitting position and it doesn’t effect SQ, but I want it gone.  

I sent it to PS Audio; they tell me there is no hum and sent it back. They implied I mostly likely have a power problem and recommended some troubleshooting steps.  I unplugged everything from the 250 and plugged it straight into the PS Audio receptacle.  The hum is still there, but it is not as pronounced.  A P15 power regenerator might fix the problem, but I want to know if I have a power problem before I do anything.

How can I determine the quality of the power coming into my house and out of the receptacle? FYI, the Denali is plugged into a PS Audio receptacle/dedicated 20 amp line.  I have a whole house generator w/ transfer switch and whole house surge protector. 
128x128oldschool1948
oldschool1948's avatar
oldschool1948 OP
500 posts
 
@gloriousunicorns  I'm using Silnote XLR cables from my BHK pre to the 250 and Transparent Super XLR cables from the BHK pre to my DirectStream Sr. DAC.  

I use Tungsram 7dj8 tubes in my pre amp and 250.  I've tried 3 different sets of Tungsram 7dj8 tubes and a new set of PS Audio 6922 tubes and got the same result.  I will try it at another house - great idea.  I just hate moving that monster around.

@dledletchThanks for the info.  I'm grasping at straws.  Luckily, I can send it back for a full refund. 

lowrider57's avatar
lowrider57
5,417 posts
 
Before you send the amp back, test for DC on the line by using a Humdinger or the new iFi DC blocker. 
There is no hum thru the speakers, correct?

This hum may be in the design of the amp. If you can only hear it with your ear up close, don't worry about it. 

oldschool1948's avatar
oldschool1948 OP
500 posts
 
@lowrider57 There is no hum thru the speakers, and I can only hear it up close.  PS Audio tells me there’s nothing wrong with the amp, so I will believe them.  I ordered the Humdinger.  Can’t wait for it to get here 😀
lowrider57's avatar
lowrider57
5,417 posts
 
If the Humdinger has no effect on the hum, then it's in the design of the amp. Some amps with toroidal transformers have a low-level hum. You said you hear the noise near the tubes, it's possible the transformer is located in that area inside the chassis. 
Anyway, good luck and keep us posted.


gloriousunicorns
16 posts
 
Oldschool, another thing you can try, just for testing, is to run an extension cord to a different circuit in the house. Preferably on a different phase. I saw your system pics (cool system by the way) and I can see how it would be a pain to move the amp. So see if you can plug the amp into a different circuit. If you have 220 volts single phase or 3 phase coming in, trying another phase would be preferable. One phase could be noisier than the other. 
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