[Elecraft] Unusual Behavior K3S / KPA500 Drive Power Greater Than 12 watts

[Tony]

Rick Et al:

The K3S makes 110 watts measured so the rigs finals appear to be just 
fine. Audio is also clean with no distortion. After further testing, I 
found that the power drop is only momentary.

The RF output on the KPA500 does drop when the drive on the K3S is 
increased from 12 to 13 watts, but it quickly rebounds to it's normal 
output a few seconds later.

This happens on all bands and only takes place during the transition 
from 12 to 13 watts. I can hear a relay click during the 12 to 13 watt 
increase which happens to coincide with the momentary condition 
described above.

Whatever it is, something changes the way the transmitter behaves 
momentarily during that specific power change and my guess is that it's 
not unique to my K3S.

I spend most of my time on CW and little on SSB so I never noticed this 
before. Other than that, the K3S and KPA500 work flawlessly.

Tony






On 3/4/2020 6:09 AM, Rick Bates, NK7I wrote:
> Except that it only happens in SSB, it sounds suspiciously like the 
> high power amp (final) has failed in your K3S.  But start with your 
> audio.  Are the settings normal (comp, mic gain etc)?
>
> Can you try another microphone and turn on the monitor function to 
> hear what your mic is producing?  Is the two-tone function 
> accidentally on?
>
> What power output can you read when not using the amp and going above 
> 12 watts?  If more than 12 watts, a calibrate output would be in order 
> for for your confidence.
>
> Is it confined to one band?
>
> If you don't get direction of the cause from these tests, a phone call 
> to Elecraft service is in order.
>
> 73,
> Rick NK7I
>
>
> On 3/3/2020 10:48 PM, Tony wrote:
>> All:
>>
>> I've noticed an unusual thing happen with my K3S and KPA500 amplifier 
>> while in SSB mode. When I increase the K3S drive beyond 12 watts, the 
>> KPA500 power drops-off dramatically. This only happens in SSB mode.
>>
>> The KPA500 functions fine with other transceivers as well so the 
>> condition appears to be unique to the K3S. Any suggestions?
>>
>> Tony
>>
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