[Elecraft] [K3] - Hum on SSB Transmissions

[Joe Rogers]

I normally operate CW but the other day and have not been SSB for a few weeks to a month.  Yesterday, I was getting ready to operate SSB and I noted a hum through the monitor when I key the transmitter. By way of background, K3 is 2012 vintage and I assembled the kit.  No problems with until this one.  I have found several similar threads mentioning a hum on SSB transmit but of the mentioned solutions worked to solve my problem.

I have Heil Pro set IC and Heil Gold Elite.  The problem seems much more pronounced with Proset IC.

Whether it is connected to front panel (FP.H or RP.H Bias on) makes no difference.  If I used PTT or VOX it is there.  Set Mic Gain at anything above zero it starts.  With higher mic gain and higher compression it is worse.   I have made some PSK contacts using the LIN IN input and seems to work OK.

It seemed like low frequency noise so I set the TX filters for 50 and 100 Hz from 0 to -16.  No change.

Changed TX Gate from 0 to 10.  No change.

Disconnected everything from the K3 - RS232 cable, the antennas, keys, and paddle.  All except power supply and the Mic.  No change.

Mic+Lin ON or OFF no change.

Curiously, if I put my hand on the rig, it seems to reduce the volume of the hum.

Recorded some audio with Proset on my PC and it seems clean - no noise detectable.

I wonder if any of you guys - all of you probably more technically savvy than I - can come up with any ideas to solve this problem.

Thanks in advance for any help you can give me.

73,
Joe
AJ1Y