[Elecraft] KPA1500 PA Current

[Bill Johnson]

Contact tech support and they may be able to help you out.  To me, I use toroid transformer and the output remains continuous on load.  I did have a brief issue and could only load my EFHW at 100-500 watts but once above that the amp would fail.  I took my trusty wrench when weather and snow conditions permitted, and tightened the connectors in the back yard and now all is back to normal.  Visually, and with analyzer seemed to be ok, but with power, an issue.

Good luck.

73,
Bill
K9YEQ

https://wrj-tech.com/

-----Original Message-----
From: Paul Baldock <paul at paulbaldock.com> 
Sent: Friday, March 15, 2019 5:39 PM
To: Bill Johnson <k9yeq at live.com>; donwilh at embarqmail.com; Gary J Ferdinand <alaparos at w2cs.net>; elecraft <elecraft at mailman.qth.net>
Subject: RE: [Elecraft] KPA1500 PA Current

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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