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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