[Elecraft] KPA500 delay in getting to full power

[Mike Schultz KS0T]

Hi Don and all,

    Thanks for the ideas, but still having the problem.  Don,  I looked at 
the K3 output on the analog meter on my old Waters dummy load and saw no 
change from first dit onward (30 watts thru amp in standby).  Band changes 
don't seem to help although it sees on 40 it gets to higher power a bit 
faster - maybe 1 second instead of 2.  Also on 4o the problem seems to go 
away if I start keying again within say 5 or 10 seconds. Also, the change 
form low to high output from the amp is abrupt after a second or two of 
dits.  It is also about a 3 dB difference (attenuator?).  A few hours ago I 
also tried taking the KAT500 out of the mix and using new coax.  I HAD K3 to 
KPA500 to dummy with different coax jumpers and still had the delay.  Also 
had PTT direct rig to amp. I was testing in CW vox/qsk but the problem also 
occurred if I asserted PTT via footswitch so that I saw the asterisk on the 
amp display before I started keying.
    I have everything wired up normally again and still observe the original 
problem I had yesterday when I tried to enter the contest.  That is, I 
transmitted fine at 100 watts with the tuner in use (1:1 SWR) for my 
vertical on 40.  When I turned on the amp I get a hi SWR and the tuner 
starts hunting.  That is what got me started troubleshooting and observed 
this delay problem I've been describing.
    Well,  I going to go get some more qsos on low power now.  I'll check my 
email again in a bit to see if any more ideas come up.

Thanks, Mike KS0T



-----Original Message----- 
From: Don Wilhelm
Sent: Sunday, October 27, 2013 8:01 AM
To: Mike Schultz KS0T ; elecraft at mailman.qth.net
Subject: Re: [Elecraft] KPA500 delay in getting to full power

Mike,

Make certain it is the amp and not the K3.
Check the actual output from the K3 - disconnect the amp and drive the
dummy load through an external wattmeter.  Don't change anything in the K3.
Does the power out follow the same pattern?
Try a band change (up and then back down) and then test again.

What I am saying is that it may be the K3 behavior instead of the amp.
The K3 power control starts out at a low value and then builds up to the
requested power output.  The power output control is reset on a band
change and at power on.
It should only take a couple dit times, it sounds like yours may be
responding more slowly.
Probably not as noticeable at lower power, but certainly noticeable at
the output of the amp.

73,
Don W3FPR

On 10/27/2013 7:58 AM, Mike Schultz KS0T wrote:
>      A problem just showed up with my 4 month old amp. If I send a string 
> of dashes at 30 Watts out of my K3, the KPA amp puts out around 120 Watts 
> for the first second or two then goes up to the expected output of 480 
> Watts.  This is on 20 meters to a Dummy load through my KAT500 tuner in 
> bypass.  The ACCY plug was disconnected and PTT was direct from K3 to 
> KPA500.  Amp firmware was beta 1.33 but no change when I reverted to 
> release V1.23.
> Any ideas while I continue the CQWW SSB contest at a frustrating 100 
> Watts?
>
> 73, Mike KS0T
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