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

[Rick Bates, NK7I]

12 watts is the transition point for the high(er) power amp in the K3 to 
engage, so it's feasible that as that happens, the LPA drops it's output 
some to make the set power out (to not immediately put out 100 watts but 
what the reading says it should be).

If the K3S has normal output when you're not adjusting the power out, I 
wouldn't worry about it.

If the K3S in CW is set for the desired power output, phone will be also.

73,
Rick NK7I


On 3/4/2020 6:20 PM, Tony wrote:
> 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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