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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
lowrider57's avatar
lowrider57
5,411 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. 
gloriousunicorns
16 posts
 
Lowrider, I also have a BHK 250 and it’s dead quiet. No hum or buzz emanating from it anywhere. And I have dirty power in NYC. I’ve tried it plugged in direct to the wall and in my power conditioners and it’s always quiet, either way. 
ianrmack
227 posts
 
As others have pointed out, it sounds like a DC offset problem. I just fixed mine by adding an Emotiva CMX-2 for under $150

https://emotiva.com/products/cmx-2

No more amp hum.

PS Audio used to make one called the "HumBuster" but no more.
oldschool1948's avatar
oldschool1948 OP
497 posts
 
I installed the HumDinger; it made no difference.  I replaced my VooDoo power cord with a new GR Research power cord.  Each day when I first turned on my system, I put my ear close to the tubes and could hear a faint hum.  After about 30 minutes, the hum was barely perceptible.  

The amp came back from PS Audio with new PsVane stock tubes.  Because they sound better to me, I put my used Tungsram 7dj8 tubes back in.  The slight hum came back.  I put in a new set of Tungsram 7dj8 tubes.  The amp was dead quiet.  Hopefully, it will stay that way for a while.

After 40+ years of SS gear, I'm beginning to understand even more how much I still don't know about tube stereo equipment.  I started buying tube gear about 3 years.  It's been an interesting journey.  
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