Tube amp buzz (amp, not speakers)


Hello - 

Almarro a318b makes buzzing sound at random: sometimes it does, sometimes it doesn't, completely unpredictable. The buzz comes out of the amp itself, like a transformer buzz; the sound out of speakers is completely clean. 

I'll appreciate any ideas - what causes it, what to do?
boriso
Thank you all so much. I don't know the first thing about electronics, so it seems like I have two options: getting an Emotiva CMX-2  or taking it to a technician, at least for a comparable cost if not more. What would your inclination be? 

@tuberist - what does "holographic sound" mean in this context?
Have you checked to see if there are sources of noise like a worn refrigerator compressor motor or dimmers coincident with the buzzing? What about trying a direct run to the house breaker panel?
Boriso,
Holographic IMO means spatial characteristics where the instruments and voices are clearly delineated. If you go Emotiva you will regret it if you value those traits I described. I found the Almarro easy to tube roll by swapping out the 6SN7; the 6SL7 not as much. It was a fun amp but the biasing was tedious and somewhat dangerous.
regards,Larry
Descent sized toroidal power transformers are usually the ones that buzz, vibrate, from DC offset on the AC mains. As a rule EI transformers do not buzz, vibrate, because of DC on the mains.

I think the power transformer in the OP’s amp is a bobbin transformer. I couldn’t find any info on how they react to DC offset on the mains.

.
Thank you all so much. I don't know the first thing about electronics, so it seems like I have two options: getting an Emotiva CMX-2  or taking it to a technician, at least for a comparable cost if not more. What would your inclination be?

This is another one that is known to eliminate DC offset transformer hum

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