[Elecraft] KPA 500 Hum

[Jack Brindle]

You may not have the transformer properly tightened down. Recheck it.

Also, 58V is not that bad, but you might want to recheck that you are using the proper tap
from the transformer. You just might want to go up a notch to get a higher voltage. Essentially
you want the tap that provides the highest voltage, but does not cause over-voltage faults.
Also, you might check your shack wiring. If you are sagging too much, then you are seeing
significant voltage drop in the AC wiring to the amplifier. This includes the power cord and
the wiring inside the wall. If you are a long ways from the breaker box you might want to consider
increasing the wire size in the wall, or better, going to 240V operation with the KPA.

The procedure for both these things is described in the KPA manual.

If tightening the transformer hold-down nut does not quiet the amplifier, give the folks at the
factory a call. They should be able to help you get it more quiet, although they may
tell you the same things just did…

73,

Jack Brindle, W6FB
Elecraft Engineering


> On Sep 30, 2016, at 6:46 AM, Tom <nineback at gmail.com> wrote:
> 
> Just received a KPA 500 and KAT 500 yesterday.  Using them with my Icom
> 7300.  I know the manual says to expect some hum from the KPA 500 but I
> believe mine is more than a hum.  When I send CW I don't need to monitor
> the radio side tone.  I just have to listen to the amp. :-)  Anyone else
> experience this?
> 
> My HV voltage is 75 at idle.  I am using 120V power.  When I key down it
> drops to around 58.  Manual says 60+ is best.  Don't know if this has
> anything to do with the hum?
> 
> I have not contacted Elecraft yet.  I wanted to hear what folks say first.
> 
> 73,
> Tom
> KQ5S
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