[Elecraft] KPA500 Power Output

[Ron D'Eau Claire]

A quick way to check Jack's suggestion that the mains source voltage may be
drooping is to monitor the HV on the KPA500 while transmitting to see if it
decreases over time. 

Ron AC7AC

-----Original Message-----
From: elecraft-bounces at mailman.qth.net
[mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Jack Brindle
Sent: Friday, January 27, 2012 9:55 AM
To: N4CW at aol.com
Cc: elecraft at mailman.qth.net
Subject: Re: [Elecraft] KPA500 Power Output

Are you sure it is the KPA500 that is causing the drop off? There are  
a lot of variables here. The exciter could be scaling back, the power  
source (110/220) could be limiting you or something else may be  
happening. As power cords heat, they tend to restrict the electron  
flow. Especially if you are powered from 110V, that could be the  
source of several problems. Be sure not to replace the supplied power  
cord with a smaller one - this is a recipe for reduced output in itself.

We have also seen transmitters decrease their output power when keyed  
down for a long time. This might be due to heating in the TX, ALC  
action, or other things specific to the radio.

I would suggest adding a wattmeter between the exciter and the KPA500  
so you can monitor power between the devices. Also check the power  
source wiring to make sure there are no limitations there. In general,  
look to see if there are other factors external to the KPA causing  
power reduction.

Jack B, W6FB


On Jan 27, 2012, at 8:57 AM, N4CW at aol.com wrote:

> Sorry if this has been covered before, but I can't recall that it  
> has. Is
> there any reason why power output
> falls off over time? Here's what I did: using MMTTY, I "diddled"  
> into a
> 50-Ohm dummy load for one minute.
> I initially had a power output of 525 Watts which went to 500 W  
> shortly and
> went down to about 465 W
> when MMTTY "diddling" timed out. I repeated that process later,  
> monitoring
> current and noted that it also
> went down over time...makes sense!
> But my question is WHY? I was under the impression that I needed to  
> run the
> amp at 500 W on RTTY for
> optimum efficiency because in an earlier posting I noted that at 150W
> output (in BPSK31), the amp was very inefficient and the fan was  
> pretty loud. If
> I can't derate the output and I can't run full output, what do I do  
> with
> the  KPA500 in the digital modes?
>
> Bert, N4CW
>
>
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