[Elecraft] KPA500 power output starts out low, then goes up

[Jack Brindle]

Several things I would suggest:

1) Turn off external ALC in the K3. We recommend NOT using it with the KPA500 (or any other amp for that matter).

2) Run the test with the K3 connected to a power meter then a dummy load to see if the problem persists. If so,
you probably need to recalibrate the K3. If it does not, then we need to look further at the K3-KPA connection.

3) Connect the output of the KPA500 to a high-power dummy load and test. Even though the RigExpert may indicate
a good match, that is at very low power. At high power things can change, arcs may occur and other bad things may
happen. Make sure the setup works just fine into a dummy load, THEN connect to the antenna.

4) The KPA500 can show you voltage and current for the PA transistors. Make note of each as you key up the K3 to
see what is happening. They should go to fairly stable conditions fairly rapidly if the transmitter does the same. If
it is taking its time, then look to the transmitter for the cause.

Note that the KPA is either full on or off. It does not (nor can it) vary its output power in any other way. If there were 
a problem in the 15m LPF you could see a problem, but it would be persistent, not recovering as you indicate. So far
I am not seeing anything that indicates the problem is in the KPA. Please run the above suggestions. I am very
interested in the results.

73,

Jack Brindle, W6FB
Elecraft Engineering

(sent a second time trying to get the email list to accept the email...)

> On Nov 14, 2016, at 11:01 PM, Barthold Lichtenbelt via Elecraft <elecraft at mailman.qth.net> wrote:
> 
> Thanks all for all the suggestions!
> 
> Fred Cady privately suggested making sure my ALC and Mic gain are set correctly. I tuned that some more, and it is a lot better, but still doesn't immediately go to full power output. 
> 
> I will test without KPA500 next.
> 
> I have two antennas, so I can test with that too, to rule out antenna problems. 
> 
> As to answer your questions:
> 
>> Does the SWR also change?
> 
> Nope. Just power output. SWR graphs of my antenna are just fine (using a Rigexpert AA-600 antenna analyzer).
> 
>> Have you measured the output of the K3 with a separate watt meter?
> 
> I don't have one, but both the P3TXMON and the KPA power Leds show the effect.
> 
>> How are the three boxes connected? Are you using the AuxIO cable that comes with the KPA and KAT? 
> 
> Yes, using the 15pin cables from K3S to KPA500 and KAT500. No separate key line.  The P3 is connected with the RJ45 to dual serial connector cable.
> 
>> And lastly, might you have ALC enabled in the K3 menu? Anything you can tell me about the setup will be helpful.
> 
> Yes, TX ALC is ON (I never messed with that, had to look it up in the manual how to get it to show up even in the config).
> 
> ALC Threshold for the KPA500 is set to 210.
> 
> The K3S has these options: Second receiver, internal tuner (Set to bypass), frequency lock option, 4x 8 pole filters, DVR.
> 
> Again, thanks for the help and suggestions. Quite a friendly bunch of people here!
> 
> Barthold
> AD0RM