[Elecraft] KPA1500 PA Current

[Paul Baldock]

No antenna issue here. No SWR variations when 
antenna under continuous power (measured on a 
real SWR meter). Same effect into a high power 
cool dummy load. It's the amp without doubt.

- Paul

At 03:09 PM 3/15/2019, Bill Johnson wrote:
>Paul, I do not witness what you are seeing.  You 
>may also have an antenna issue, slight but problematic?
>
>72 & 73,
>Bill
>K9YEQ
>FT’er for K2, KX1, KX3, KXPA100,  KAT500, W2, etc.
>
>-----Original Message-----
>From: elecraft-bounces at mailman.qth.net 
><elecraft-bounces at mailman.qth.net> On Behalf Of Paul Baldock
>Sent: Friday, March 15, 2019 4:47 PM
>To: donwilh at embarqmail.com; Gary J Ferdinand 
><alaparos at w2cs.net>; elecraft <elecraft at mailman.qth.net>
>Subject: Re: [Elecraft] KPA1500 PA Current
>
>I believe its universal that as the KPA1500 
>warms up the gain drops. I have mine set up on 
>each band for around 1500WPEP when cold. If I 
>operate it enough by the time the amp gets up to 
>70C its down to around 1300W. I  try to 
>operate  the amp conservatively so I don't 
>increase the input to raise the output back to 1500W, I just leave at 1300W,.
>
>The issue is in the amp, not in your antenna or feeder, balun etc.
>
>I had a SPE1.5K for a short time and this exhibited a similar effect.
>
>-Paul  KW7Y
>
>
>At 02:10 PM 3/15/2019, Don Wilhelm wrote:
> >Gary, Have you considered that there may be something in your antenna
> >system that is heating up or otherwise changing with the 1500 watts
> >power? The first thing I would suspect is a balun that is heating, or a
> >connector that is not quite tight enough. Those kind of problems will
> >not show up at lower power, but at 1500 watts may become troublesome.
> >73, Don W3FPR On
> >3/15/2019 3:25 PM, Gary J Ferdinand wrote: > I̢۪m in the process of
> >checking out my amp.mp.  I have two dipoles (40 and 80).  At resonance
> >both show a 1.2:1 SWR with ATU totally bypassed.  With ATU on, it
> >remains bypassed on 80, but shows only the ATU ON LED on 40.  In
> >both cases the resultant SWR is 1.2:1.   SWR
> >measurements are from the KPA1500 display. > > When I use the amp with
> >my K3 and drive it up to 1500W, I am occasionally getting an excessive
> >PA current fault at 63A.  From a cold start it̢۪s 60A, but as it wa warms
> >up in contest usage I find the power drops off, so I have to adjust the
> >K3 to bring it back up to 1500W.  At that point the PA current goes
> >over 60A. > > Interestingly, into a dummy load the 1500W point shows a
> >PA current of only 55A.  So the 1.2:1 SWR, be it via a bypassed ATU or
> >using the ATU, is sufficient to raise the PA current eventually to
> >excessive levels. >
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