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persistent 60 cycle hum only on tube gear

I know this topic has been addressed in the past but I'm hoping for the "latest tech" answer.

I have a persistent 60 cycle hum in my ARC tube gear. Not in my Bryston power amps or preamps- just the ARC tube pre and power amps. All XLR. 

I have installed an isolated, dedicated ground system (8' copper rod driven into moist earth) , a Ground Master unit between the chassis and the ground line, I  clipped the ground wire from my 20a 120v dedicated circuit, pretended to ignore the hum (that didn't work well).  I even replaced the tube sets with ARC OEM tubes in the pre and power amps (sonic improvement but no hum cure) .  Still the confounded hum.

Before I spend more money and failing I'd like your personal experience opinion on what worked for you. 

Thanks!

 

yesiam_a_pirate
buellrider97's avatar
buellrider97
949 posts
 

Hi, I had an issue with a different brand tube mono amps. I had an intermittent hum issue. And also had an intermittent severe noise and popping issue in one of the two. The hum issue was due to tired diodes in the rectifier sections. The other loud pop issue was due to a single bad resistor in the phase tube ( 12AX7 )  circuit. FWIT I had them replace all diodes with hexfred’s.  Could they be due for some TLC ? Just food for thought , Mike B. 

erik_squires
17,551 posts
 

PS - A side effect of an isolated ground is that the ground at your home and the new isolated ground will have different voltages.  

The idea is that the neutral and ground voltages should be very close to each other but in this situation you could have a ground and neutral with large voltage differences causing a neutral to ground loop you otherwise wouldn’t have. 

Depending on how your equipment is grounded, and the relationship the power supply has to the ground may in fact be the cause of such a loop. 

 

amtprod's avatar
amtprod
140 posts
 

Can we make a "sticky"  or "Pin-to-top-of-Basic Electronics Page" of Erik's post explaining grounding?

I have two tube Pre-Amps. 
One is a Audio Research SP3-1A, and the other is a Dynaco PAS (recent purchase).
The Dynaco I bought was sold with "refurbished power supply with two new caps" to remove a slight hum issue.
However, in performing this basic task, they 1) never fully re-connected one leg of one of the caps to ground... and 2) they never properly traced to see that the issue causing the hum WAS THE RECTIFIER MULTI-CAP FILTER CAN HAD LEAKED AND WAS NOT FILTERING. 
So as others have said, really really check the Power Supply capacitors, like, if possible remove them from circuit to properly check.  Best would be to do a "leak down" test on them to see how they behave when applied with the proper voltage.
 

atmasphere's avatar
atmasphere
12,404 posts
 

@yesiam_a_pirate Does the amp make a buzz or hum without the preamp connected?

If yes, Is it both channels or just one?

If neither channel, The amp is OK.

If in one channel only, you may have a bad (shorted) tube in that amp. 

Please get back to me and we can proceed.

 

allenf1963
487 posts
 

@amtprod  @erik_squires 

 

Amen about Erik's post being pinned.  Someone mentioned to me that I could Google my question, but Erik's answer was much more understandable and went to the crux of the issue. 

 

AI may be able to do a lot of things, but having a meaningful interchange between humans is not one of them.  Thanks, Erik.

 

 

 

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