[Elecraft] KPA500 Hum

[Jim Brown]

On 1/4/2019 10:52 AM, Bob McGraw K4TAX wrote:
> Mark et al:
>
> Your description raises a bit of concern.  Not with the amplifier but 
> with your power distribution in your home / QTH.
>
> Yes. This is the symptom of one or more mis-wired outlets, or of an 
> extra bond between neutral and ground somewhere in your home. This 
> used to be common practice at large appliances. I would start by 
> buying and using a good outlet tester, which will check the wiring at 
> every outlet in your home.
>
>
> First I'll presume you are running the amp on 120V and not 240V. Thus 
> being so, as the coffee maker comes on or curling iron comes on the 
> Neutral current changes.  The fact they are on separate circuits is 
> one point but they thus share the same neutral.   If your Neutral is 
> "floating" due to poor conductivity or corroded connections this will 
> cause distortion of the 60 Hz sine wave.

I think you mean neutral coming from the power company, not within the 
home.

> This distortion is always higher in frequency and is multiples of the 
> 60 Hz signal. 

There is ALWAYS significant distortion of the AC power waveform that it 
is NOT the result of any sort of wiring problem. Rather, it is caused by 
all the rectifier-filter power supplies in virtually every piece of 
electronics in our homes and businesses. Line current flows mostly at 
the positive and negative peaks of the AC cycle to recharge the filter 
capacitors, resulting IR drop only during those peaks.  The peaks are 
rounded off, and the current is a series of pulses. There's a discussion 
of this beginning with slide 55 of this talk on Power, Grounding, and 
Bonding for Ham Radio. http://k9yc.com/GroundingAndAudio.pdf

73, Jim K9YC