[Elecraft] [K3] - Hum on SSB Transmissions

[Don Wilhelm]

Joe,

Do you hear that hum when you operate into a dummy load?  If not, then 
check the common mode choke on the antenna, you are likely getting 
RF-In-the-Shack from the antenna - the fact that it diminishes when you 
put your hand on the K3 amplifies that this may be the problem.  Forget 
about grounding the radio for this problem, solve it at the antenna 
feedpoint with a good common mode choke on the feedline.

Other possibilities are power supply ripple (run it on battery to check) 
or an open microphone ground lead (try other microphones).
Make sure the rear panel jacks are fully plugged (give them an extra push).

73,
Don W3FPR

On 12/2/2018 4:17 PM, Joe Rogers wrote:
> 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.
>