[Elecraft] KPA100 Acoustic Noise

[Don Wilhelm]

Ray,

How old is this KPA100?  If it is the older design with red toroid cores 
at L15 and L16, I suggest that you update it with the KPA100UPKT.   In 
addition, the shield may have to be upgraded as well.  If the slot above 
the SO-239 jack is much greater than 3 mm, and you do not have the 
solder lugs to connect the outside of the shield directly to the SO-239 
jack and clips to ground the shield to the sides of the K2, then you 
need the updated shield KPA100SHLDKT.

I suspect you are experiencing some type of spurious oscillation that 
was present on some KPA100s with the older design - the newer design 
cures that problem.

If you have the updated shield and blue toroid cores at L16 and RFC1, 
then you  have the updated KPA100.

73,
Don W3FPR

On 3/25/2014 6:09 PM, raycollins wrote:
>   
> When my K2/100 is keyed in SSB mode (connected to a dummy load) and the
> microphone is gently tapped, I can hear a faint noise coming from somewhere
> on the KPA100 printed circuit board.  It is a low level buzzing/rattling
> noise similar to a small metal object vibrating against a loudspeaker cone
> but I have disconnected the loudspeaker to eliminate this possibility.
>
> It is only noticeable in high power mode (at levels above about 20 Watts) on
> 40 metres which points to relays K5 and K6 in the KPA low pass filter but as
> these relays are shared with the 30 metre band, I can't understand why the
> problem isn't present on 30 metres.
>
>