[Elecraft] Max power for JT9 with K3S 100?

[Bob McGraw K4TAX]

Frank et al;


Just quoted what is in the K3S manual.   No interpretation provided.   I 
agree that 100 watts key down is a lot for a SSB amplifier running in CW 
mode.   To me that says 100 watts for 10 minutes and then RX for 10 
minutes.   Otherwise equal TX and RX times.   Who does that?

And if one is running "100 watts" then running CW or SSB for 10 minutes 
might be the limit.  Just speculation.   On AM I might talk for 10 
minutes but that is at 25% rated power output for carrier, yet it is 100 
watts PEP.   The 60 C is MY guideline. The KPA3A will shut down about 85 
C or so.

On 6M I run my KPA500 at about 300 to 400 watts.  The K3S is running 
about 25 to 30 watts on 6M.   At this point I'm watching the KPA500 
temperature.

There is NO DX worth blowing a PA either in the K3S or the KPA500.    
But I know guys that will blow things up, pushing things to the max and 
beyond  trying to work that DX station.  I say bah humbug to that!

I just pay attention to the PA temp, specially when running digital 
modes. Likewise for the KPA500.

73

Bob, K4TAX


On 4/4/2020 3:41 PM, Frank O'Donnell wrote:
> Thanks for the replies.
>
> I've enabled the PA temp display (currently showing 22C right after 
> power-up but before transmitting), and will keep an eye on that.
>
> Bob, I noticed that line in the K3S manual about the CW/SSB duty 
> cycle. Does "100% - 10 min, 100 W key-down" mean that if you key down 
> without stop in CW mode it can go 10 minutes at 100 watts? That seems 
> like an awful lot.
>
> Where do the recommended TPO's for 6 meters, the 50% value for JT9, 
> and the 60C guideline for the PA temp come from?
>
> Thanks again,
>
> Frank K6FOD
>
>
> On 4/4/20 6:22 AM, John Simmons wrote:
>> Fred Cady's book:
>>
>> "There are four fans speeds that turn on at different temperatures."
>> "If the temperature reaches 84 degrees C the KPA3 will be bypassed 
>> until the temperature falls to stop any damage as a last-ditch backup 
>> measure to protect your expensive power transistors from the excess 
>> heat."
>>
>> -de John NI0K
>>
>>
>> Bob McGraw K4TAX wrote on 4/3/2020 6:39 PM:
>>> Frank:
>>>
>>> The duty cycle for the transmitter, as stated in the manual, is;  CW 
>>> and SSB modes, 100% - 10 min, 100 W key-down at 25C ambient.   Do 
>>> note that 6M has reduce power values of 85 watts {51 -52 MHz} or 70 
>>> watts {52 - 54 MHz}
>>>
>>> The duty cycle for JT-9, 1 minute transmit, 1 minute receive would 
>>> be 50%.   I frequently run 100 watts on WSJT-X FT-8 with no issues.  
>>> Just pay attention to PA temperature.  It should be 60 C or less.   
>>> Also this is with FANS in the automatic mode.
>>>
>>> 73
>>>
>>> Bob, K4TAX
>>>
>>>
>>> On 4/3/2020 4:18 PM, Frank O'Donnell wrote:
>>>> I've been using JT9 mode on 630m this winter with my K3S outputting 
>>>> to an external class D amp.
>>>>
>>>> Now I'm interested in trying some JT9 QSOs with some people 
>>>> currently operating on 160m. For me this would mean outputting 
>>>> directly from the K3S (with internal tuner) to the antenna.
>>>>
>>>> Given the 1-minute cycle time for JT9, are there recommendations 
>>>> (official from Elecraft, or otherwise) on maximum power to use in a 
>>>> situation like this? And/or, is the answer dependent on the SWR I 
>>>> can achieve with the antenna?
>>>>
>>>> Thanks and 73,
>>>>
>>>> Frank K6FOD
>
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