[Elecraft] [K2] External Fan Hum

[Don Wilhelm]

Steve,

Yes, an AC fan would induce alternating magnetic fields in the K2 L30 
and T5 VFO inductors.  The K2VCOSHLDKT will eliminate it, as will a DC fan.
The DC fan may have a magnetic field, but it would be constant instead 
of alternating polarity 120 times a second.

73,
Don W3FPR

On 11/7/2018 7:50 AM, Steve Kavanagh via Elecraft wrote:
> I was experimenting with an external 120V AC fan to improve the cooling of the KPA100 during CW Sweepstakes this past weekend.  The cooling worked fine but the fan caused some hum on received signals (and presumably my transmitted signal as well).  Placing the fan towards the right and back (away from the speaker) reduced the hum to a pretty-much unnoticeable level for CW, though through careful checking on a very strong signal I could still detect it by ear.  I haven't tried it yet but I suspect it isn't good enough for FT8.
> 
> I assume the K2VCOSHLDKIT would fix this.  But I also noticed, going through the archives that Eric had suggested a DC fan in the same location.  Does anyone know if I might expect less hum from a 12V DC fan?