KPA100 Acoustic Noise

[raycollins]

 
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.

I have tried applying pressure to magnetic components such as relays and toroids to try and locate the source of the noise and even used an insulated rod to try and mechanically couple the noise from suspected components into my ear but without success. I have not checked the solder side of the board for signs of damage but could the noise be arcing around the relay contacts?  Apart from the noise, it seems to work perfectly giving 100+ Watts output on this band.

Any suggestions greatfully received,

Ray M1FJL

[Don Wilhelm-4]

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.
>
>

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