[Elecraft] KPA500 Noise While Off

[Bob McGraw K4TAX]

Although the front panel switch is OFF, the control circuit of the power 
supply remains ON as long as the rear power switch is ON or power is 
applied.  It is normal to hear a small amount of hum from the power 
transformer and the left rear of the cabinet to be slightly warm.  See 
page 14 of the KPA500 manual for more detail.

73

Bob, K4TAX


On 6/27/2018 12:37 PM, Richard Wade wrote:
> Yesterday I heard a faint "hum" in my shack but all of my gear was off.  It
> sounded like possibly a fan running or power supply noise.  I did a very
> scientific test of the sound source by putting my ear to each piece of
> equipment in my shack and soon found that the noise was coming from my
> KPA500!  The amplifier was off but was still connected to the shack ac
> power.  I then removed the power cord from the KPA500 and the noise
> disappeared.  Does anyone have any idea how this could  happen?
>
> By way of further background, I have been dealing with QRN from a recently
> installed solar system.  I have traced the source of that noise to the
> solar system by confirming that the QRN goes away when the solar system is
> turned off while running my K3s on battery power.
>
> If I had to venture a guess, I would say that somehow the unpowered KPA500
> was picking up noise on the shack wiring.  Very strange. Is that possible??
>
> Dick, WM6G
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