[Elecraft] KPA500 - AC hum in the monitor

[Jack Berry]

Thanks Phil ! I think it's just an a/c hum, not actual RF. I solved the problem by moving the KPA500 amp. I did check the headphones cord at another device and no sign of hum. Also, a ham confirmed the hum in qso and that it cleared up completely with the amp powered down.

I greatly reduced the hum from the amp by moving it but moved the Green Heron rotator controller above the K3 to accommodate moving and now the same thing is coming from the GH. It's pretty easy to verify by switching things on/off. 
The aggravating thing is that it just popped up. I don't recall making a single change but something has changed, either in the shack equipment of possibly the house wiring. I need to start around the basic ground connections and make sure all is tight and clean. 
A few well placed chokes/toroids would probably make a difference but that doesn't fix the root cause.

God Bless & 73!
Jack - WE5ST


________________________________
 From: Phil Irons <ve1bvd at gmail.com>
To: Jack Berry <we5st at yahoo.com> 
Sent: Thursday, July 4, 2013 7:24 PM
Subject: Re: [Elecraft] KPA500 - AC hum in the monitor
 


HI Jack...

First of all, I apologize for the lateness of this reply; I've been out of town for a few days.

I have noticed in the past that when I tuned up my rig at barefoot full power--100W, I got a hum in my $20 computer sound system in the  shack.  I attributed it to RF bouncing around.  Now, with the KPA500 putting out about 350+ watts, not only do I get the hum, but also see some interference on the computer monitor.  I can deal with the hum by turning off the sound system, and the monitor interference is not too distracting.

I hate to suggest it, but is it possible that the cables for your monitor headphones are not shielded against RF?  Just a thought...

73, and I hope you had a great Fourth.

Phil/VE1BVD



On Sun, Jun 30, 2013 at 11:00 AM, Jack Berry <we5st at yahoo.com> wrote:

Hoping you all will have some good ideas on a cure for this problem.
>I am hearing AC hum in my monitor headphones - ONLY when transmitting.
>
>The hum comes and goes instantly when the KPA500 is switched on/off. Same with other headphones.  No question it's related to the amp but not necessarily the fault of the amp.
>
>I have gone over every connection related to the amp with no change.
>Fortunately it hasn't made its way to my signal.
>
>Help wanted!
>
>Jack - WE5ST
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-- 
Phil & Anne Irons
Sydney, Nova Scotia