[Elecraft] K3 Ground Loop Issues using Ameritron ARB-704

[w8zn at comcast.net]

Haven't followed this too close until I saw Ameritron. W3ZZ had almost the exact issue very early after receiving his K3 when they first were released. For him the issue only showed hum on 160m but the problem turned out to be the QSK mod factory installed on his amp caused there to be a DC voltage on the RF coax between the K3 and the amp. Since there is no DC blocking cap between the antenna jack and the SWR bridge in the K3 (or at least then there wasn't) this caused the DC voltage to be grounded and caused the hum. I added a .01 HV ceramic disc right at the input jack of the amp.

Disconnect the amp completely from the K3. Measure the DC voltage from the center conductor of the coax coming from the amp to ground and key the amp. If there is any DC voltage there, you need to add a blocking cap.

YMMV - This is only what I found and it worked for him.

Terry