[Elecraft] KPA 500 Hum

[W6NEK]

I confirm the exact same hum issue as Mike describes below.
(Front panel power switch is off and there is an intermittent acoustic hum 
that can be heard)
I own KPA500 #236.  It's not a problem so long as it's not doing any damage.
Lets see what the folks at Elecraft come up with after their investigation.

Frank - W6NEK

----- Original Message ----- 
From: "ai6ii" <ai6ii at att.net>
To: <elecraft at mailman.qth.net>
Sent: Monday, August 01, 2011 10:13 PM
Subject: Re: [Elecraft] KPA 500 Hum


>I too have noticed a hum emanating from the KPA500 (#26), but the
> circumstances are a bit strange. The hum comes sometimes when the KPA500 
> is
> off. By that I mean it is powered down (front panel power switch is 
> off..no
> leds are lit), but not removed from the AC outlet. If I flip the rocker
> switch on the back of the rig, the hum disappears, which would make sense
> because no AC would be coming into the box, right?
>
> But if I leave the back rocker switch on and use only the push button 
> switch
> on the front panel to turn the amp on and off, occasionally I hear a hum
> when it is 'off'. And I do mean only occasionally. I have noticed it only 
> a
> few times and I have been using the amp almost daily for the last month 
> and
> a half. When it has occurred, it has been eliminated by switching off the
> rocker switch in the back.
>
> It is not really a problem for me, but I thought it might be additional
> information for Wayne et al.
>
> ..mike AI6II