[Elecraft] KPA1500 PA Current

[Paul Baldock]

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: > 
>I’m in the process of checking out my amp.  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 it’s 
>60A, but as it 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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