[Elecraft] k3 High Current Message on 10 meters

[Bob McGraw K4TAX]

I just performed a transmit test on 10M with my radio.   CW mode, key 
closed, 100 watts into dummy load, PA current 17.38A as indicated on the 
radio, PA voltage 13.6 volts as indicated on the radio.  After a 2 
minute key closed period the PA temp was 56 C and stable.  Fans stepped 
to max.

Same test on 80M.  PA current 18.3A , PA voltage 13.5V and PA settled at 
57 C.  Fans stepped to max.

Also ran 10M RTTY / AFSK at 100 watts out with a 1 minute transmission 
and observed about the same as above.

The 15 second transmit / receive cycle sounds like WSJT-X and FT-8 mode 
or MSK-144 mode {not normally used on 10M}    Normally I do not run any 
analog digital mode at 100 watts due to a bit of compression that 
appears to occur in the PA stage.     My suggestion, as I do, run 50 to 
75 watts with analog data. Likewise with the KPA500, about 300 to 400 
watts max for analog data signals.

In working SSB do you get reports of "fuzzy audio" or with PSK-31 get 
reports of poor IMD ?  If so I would suspect an issue with the KPA3A.    
Consult Elecraft Tech Support.

73

Bob, K4TAX


On 12/19/2018 10:34 AM, Robert Harvey wrote:
> Hi Bob and Don:
>
> Actually, I am not transmitting data at anywhere near that length of time.  I am talking about a 10-15 second transmission in which I notice this.
>
> Just some observations:
>
> 1.  There is no cooling fan obstruction and they run normally as far as I've been able to observe.
> 2.  This is a new problem.
> 3.  The power supply is delivering 14.0 volts under load, with a line drop of .2 volts on transmit.
> 4.  This occurs into a dummy load, or any one of three matched antennas.  Even bypassing tuners into the DL or antennas shows this same effect.
> 5.  The antenna system SWR is steady, both on the DL and on the antenna's while this is taking place.
>
> If this is more or less normal behavior on 10M, and not indicative of bandpass filter failure or imminent failure, I can live with it.  I can run the KPA500, which only requires about 20W input on 10M to get full output, so I am not concerned about loss of signal all that much.
>
> Thanks and 73!
>
> Harv
> K2PI
>
>
> -----Original Message-----
> From: Bob McGraw K4TAX [mailto:rmcgraw at blomand.net]
> Sent: Wednesday, December 19, 2018 10:43 AM
> To: Gadget Lust
> Cc: donwilh at embarqmail.com
> Subject: Re: [Elecraft] k3 High Current Message on 10 meters
>
> Harv:
>
> Per the manual the transmitter is rated at 100% duty cycle for CW and
> SSB modes.   This is for 10 minutes key down.  Then it should be in
> standby for 10 minutes.  I do agree with Don that RTTY at 100 watts is
> likely above the duty cycle rating.    As temperature increases so does
> current.   Which makes for more heat.    Most radios and amps are rated
> at 50% duty cycle for carrier modes such as RTTY.   Most RTTY operations
> I've observed do transmit a lot more than receive.
>
> You haven't indicated but is this a new problem or just a problem
> observed?  Other bands the KPA3A is more efficient and will produce less
> heat than on 10M.  In fact 6M has restrictions on power level where
> power should be reduced to 85 watts or 70 watts depending on segment of
> the band.
>
> Fans, ......cooling is the key factor.   What temp is the PA running
> under these conditions?   Has the temperature calibration been done?
> Also are the fans ramping up as they should?  Is the power supply
> delivering 13.8 to 14.8 under load?   If it is low the PA will draw more
> current to produce 100 watts.
>
> Just a few thoughts.
>
> "Duty Cycle:  CW and SSB modes, 100% 10-min. 100 W key-down at 25 C
> ambient".
>
> 73
>
> Bob, K4TAX
>
>
> On 12/19/2018 9:07 AM, Gadget Lust wrote:
>> HI Don:
>>
>> Understood, but the K3 is rated for full duty cycle on those modes, and this is a new issue.  I can certainly run it way under that and turn on the KPA500, but still worry something is going south.
>>
>> 73
>> Harv
>> K2PI
>>
>> Sent from Mail for Windows 10
>>
>> From: Don Wilhelm
>> Sent: Wednesday, December 19, 2018 10:05 AM
>> To: Gadget Lust; elecraft at mailman.qth.net
>> Subject: Re: [Elecraft] k3 High Current Message on 10 meters
>>
>> Harv,
>>
>> I think the key is what you said about "long cycles modes like RTTY".
>> Things heat up in those instances and the current will increase.  The
>> only 'cure' is to reduce power.  I would suggest running RTTY at a power
>> level of 50% of the CW/SSB rating for the transmitter.
>>
>> 73,
>> Don W3FPR
>>
>> On 12/19/2018 9:53 AM, Gadget Lust wrote:
>>> Hi Don:
>>>
>>> Actually, my issue is only on 10M.  It appears that as I transmit,
>>> current consumption increases, and I get occasional high current
>>> messages.  This is more apparent on long duty cycle modes like RTTY,
>>> and at higher power levels (80-100W).  If I watch, I can see current
>>> consumption start at 16 amps, and slowly rise to 25-27 amps.
>>>
>>> I performed a TX gain Cal successfully, and that made it a bit more
>>> stable (only rising to 20 or 21 amps now), but it still concerns me.
>>> A friend suggested this may be blown coils in the output bandpass
>>> filters.  I can wrap new coils if needed, but don’t want to do this if
>>> that’s not the problem.
>>>
>>>
>> ______________________________________________________________
>> Elecraft mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:Elecraft at mailman.qth.net
>>
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
>> Message delivered to rmcgraw at blomand.net
>
>