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ARC REF 150 Buzzing noise

I have an ARC REF 150 amp with over 4000 hours on it, and recently it has developed a buzzing noise.  This appears after about 30 minutes of use, and seems to get steadily louder.  I thought it might be a tube.   I had KT150 power tubes in it and I swapped those out  for KT120's and re-biased.  No change.  I then swapped out the 6H30 input tubes and re-biased again.  Buzzing is still there.  It is very difficult to locate the sound on the boards.    I have also had several blown fuses, this has been in the midst of a move and may or may not be reIated to the buzzing.  I have to assume this needs a repair, but I am wondering if anyone has a guess or even better, experience with the problem.  I am in the Denver area and if anyone knows of a local repair opportunity, I would appreciate knowing that too.  I do not look forward to the expense and delay of sending it back to ARC repair.  Thanks.  Scott
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erik_squires
15,642 posts
 
Is it possible this is from the transformer?

If so, it's often caused by DC on the AC line. This is often caused by switching power supplies, including lights, PC's, etc. that only take current from one direction.

Turn off everything else in the home from the panel. See if that fixes it.

If you can't disable the root cause, a balanced AC conditioner is your solution.
spinaker01
491 posts
 
Agree that this sounds like transformer hum. Hopefully from the external sources as this would be fatally expensive to replace any of the 3 xformers in your amp. Try to eliminate other sources as mentioned above.
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scottwsmith OP
60 posts
 
Should have mentioned that the amplifier is plugged into a Bryston BIT-20 power unit, an isolation transformer.  I am in a new house, but only for a few weeks.  I am unsure if I heard the buzzing in the old place.  Perhaps so.  I will try plugging the amp directly into the wall and see if that fixes the problem.  I would have to believe that a failure of one of the three transformers would be fairly unusual?  Thanks for the replies, I will update the post as soon as I have more results.
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