[Elecraft] KPA1500 not amplifying

[Robert Rennard]

Eric et al -

I performed the wattmeter calibration from page 52 of the user manual, 
and then did the 5 and 50 watt TX gain calibration using the K3(s) Utility.

I notice that during the first transmission of AFSK RTTY into a Palstar 
dummy load, the KPA1500 output power grows to the desired output level 
in a few seconds, but in subsequent transmissions, the power level 
immediately reaches the desired level. Unfortunately, I did not have the 
LP-100 between the K3s and the amp.

I've been using the KPA1500 with my K3 using KEY line instead of the 
KPAK cable, but not on RTTY and do not see this ramp up.

73,

Bob R - KPA1500 #67

On 2018-10-24 19:44, Eric Swartz - WA6HHQ, Elecraft wrote:
> Hi Bob - Have you run the K3 TX gain calibration on each band into a 
> dummy load (or very low SWR Ant.) ?   If that is out of cal, it could 
> easily create symptoms like this.
>
> 73,
> Eric
> /elecraft.com/
>
> On 10/22/2018 2:02 PM, n7wy via Elecraft wrote:
>> Turns out, it is not the KPA1500 not amplifying, but rather the KPA3A final amplifier stage in my K3S is acting like it has tubes, not FETs.  It has to warm up at 30 watts out, and then the power can  be reduced to 20 watts.  Weirdly, changing the power level above 20 watts seems to reset tbe behavior so it has to be warmed again.  The KPA3A module that is present is the 2nd replacement/exchange.  The first 2 had high 2 tone IMD issues on SSB.
>> My trustworthy K3 is now driving tbe KPA1500 without issues.
>> Thanks for all the off reflector counsel and 73,
>> Bob R  n7wy
>>
>