Detecting “Dirty” Power

Line emi meter.

Do you have a DMM Digital Multi Meter? Most valve amps like a certain voltage. Normally if it's LOW the transformer can be noisy. What will fix a low voltage issue is a Variac. I keep one here just for troubleshooting things like this. I also use it to bring up the old valve gear. 

It will supply 0 - 140 vac. 

See what the wall current is and swap to the other rail and see if that helps too. BUT I got a feeling you have low voltage and a BAD location for echoing the noise right into YOUR ears.. LOL

I use Triplites 2400s. BUT heck they have a transformer buzz. It maintains 120VAC on the button. I fixed 95% of THAT noise with silicone and dampening on the top and bottom of the conditioner along with about 15 lbs on top of the unit..

Regards..

Iisten after 12:00am

If it is a transformer hum, you might have a dc offset problem.  This is usually caused by some other device or appliance on the same circuit.  You either need to figure out what it is, or get a dc blocker.

The old point the finger at the other guy problem eh!


Carry the amp down to wherever your breaker box is. They usually have an outlet close by. Plug the amp in. Turn off all the other breakers. If the problem does not go away, odds are the unit has an issue. It could be a design issue of a MFG issue.

Kind of a long shot here, have you tried a different power cable? If your power cable accidentally have AC polarity inverted that could cause a hum.

Shipping to PS audio you likely did not shipped the cable

https://avahifi.com/products/humdinger-dc-line-blocker

money back if it doesn’t help

https://avahifi.com/pages/satisfaction-guarantee

Thanks everyone for the suggestions.  

My breaker box is in my basement listening room.  I have a dedicated 20 amp line connected to the box.  Connected to the PS Audio receptacle's top plug is my Denali power conditioner.  Everything but my 250 is plugged into the Denali.  The 250 is plugged into the bottom plug. 

I will unplug the Denali leaving just the 250 pugged in to see what happens, and I will try different power cords. 

While researching, I came across the Audio Magic Signal Purifier for Power Cords https://highend-electronics.com/products/audio-magic-signal-purifier-for-power-cords.  Does anyone know how it may compare to or differ from the https://avahifi.com/products/humdinger-dc-line-blocker?

I don't know about the first link.  It won't block dc offset, and makes some "interesting" claims.  The AVA is what you should try.  Alternatively, Emotiva makes one too:  

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

I haven't tried it yet, but was going to order one shortly.  Both that and the AVA should work if the problem is indeed dc offset.

Start at step one: lift the ground of the amp by using a two prong cheater plug. If the hum goes away then it’s a ground loop.

I unplugged everything but the 250 and changed power cords.  Slight hum is still there.  I ordered the HumDinger.  I'll follow-up after I try it.

The Humdinger fixes transformer hum. You said the hum was near the tubes. If that is the case, it will not fix it.

Hey oldschool, I also have a BHK 250 and BHK pre like you do. When used together, they are extremely quiet. But when I used the BHK 250 with other pre amps and DAC’s I sometimes got a little noise. Using the XLR connection when I could eliminated that. My BHK 250 was always dead quiet with XLR. 
Also, try a different set of tubes. Even if the tubes are new, they can be bad. It might not even be both tubes, just one tube humming but you can’t tell. So if you have another set of tubes to throw in, give it a shot. And try tube dampers if you can. I have tube dampers (little silicone rings) and they made a small improvement on the tubes in my BHK pre. 
And just a few basic things, but like another poster suggested, try a cheater plug. And make sure the little panel that covers the tubes is screwed down tightly. If that metal panel is a little loose, that can be contributing to the hum... And although this last suggestion isn’t very practical, if you can bring the amp to another location, ie friends house or workplace, plug it in there and see if there’s still a hum. The BHK 250 is a little heavy though and not something you wanna carry around town. 
I’m not saying that dirty power isn’t causing the humming but I’m just suggesting things you can do before you go down the rabbit hole of power conditioning and noise blockers. Good luck. 

P.S. Also, I live in New York City and the power here is pretty bad. But most of my amps are quiet, especially my BHK 250. It’s actually one of the quietest. That’s why I suggested so many things unrelated to power issues. 

@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. 

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. 

@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 😀

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.

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. 

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. 

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.

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.