[Elecraft] K3 "hum" problem - not the usual?

[Leigh L. Klotz, Jr. WA5ZNU]

Jim K9YC wrote:
> Magnetic field coupling from the power supply to the K3's input circuitry,
> probably due to the use of unshielded audio transformers in the K3. This
> is a well known problem. One good band-aid is to go to the TXEQ1
> settings and fully cut the three lowest octave bands.
> ...
> One of my neighbors had so much magnetically coupled hum
> into the Line In transformer that it regenerated to full
> output power when he tried to run RTTY in AFSK mode.

Note that the upcoming firmware upgrade will reportedly eliminate TXEQ in
AFSK (and other audio-based digital modes), and it apparently may be some
time before another update provides true per-mode TX/RX EQ.  So people
with hum will need another solution, except for the voice modes.

I tried wrapping the component side of the transformers in a sheet of
Mu-metal (actually, a competitor, not Mu-brand) and noted no difference. 
It was probably a futile effort anyway as it didn't wholly enclose the
transformer; probably I need to complain to Maxwell about this.

Leigh/WA5ZNU