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    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Grounding issue and hum

I have a tube lab el 84 amplifier without volumn control. When nothing is hooked up but speakers I have a loud buzz but the minute I connect my phone the buzz goes away if I use my blue sound nodi just a quite buzz. How do I chase this down
 
Open high impedance inputs always pick up some stray hum and noise.
That's normal.
If you short the input and the hum goes away, your amp is A-OK.
With the phone it is gone, that's good, the phone poutput most probably presents a low impedance to the input.

With the Blue stuff that may be different. Try to place say 10k across the amp input and see how it does with the Blue stuff, that may cure it.
If not you may have a ground loop, if you have multiple units in the same mains sockt or interconnected with interlinks.

Jan
 
This is exactly what my amp does. Until I turn on my preamp I can hear some hum but once it is on it goes silent. And it isn't that my preamp isn't on, the power goes on, the tubes go on, but the input is cut off. It may well be my preamp making the noise absent the connection to the inputs. And I realize I never thought of this before I typed it. I always assumed it was the amp. It doesn't really matter as it all goes silent and it isn't really that noisy anyway. What surprises me is how silent it is now. 6B4G in PP, AC heaters with cathode bias is a recipe for hum. There are no hum pots and the driver tubes are on the same heater circuit. It all floats at about 60v. I must've done something right.