[Elecraft] KPA500 Power Output

[Ron D'Eau Claire]

(Chuckle) - Vic, it's not one of the MFJ "Antenna Tuners" rated at d-c input
to the rig's finals instead of RF output. (I'm sure MFJ realizes that
confuses most of today's Hams, most of whom don't know what d-c input means
and those who do never think about it, but MFJ seems to feel that they are
stuck with the legacy, Hi!)  

I have one of those dummy loads (MFJ-264) and it's perfect for what it was
intended to do. There's a bold chart on the end showing that it can handle
1.5 KW for about 9 seconds key down. That time extends at lower powers: 500
watts for a bit over 30 seconds and 100 watts for at least 10 minutes (600
seconds). Maybe Bill has a different model or he misread the chart. I've had
the 264 for a number of years.

The fellow asking the question didn't say what he was using for a load, but
if it was an overheating dummy I'd suspect that: 1) He'd see the SWR
reported by the KPA500 rising as the load overheated, and 2) he'd smell it
as the dummy load became a space heater! 

Still Bill's suggestion is a good one. Leave no stone (smoking or otherwise)
unturned, Hi! 

73,

Ron AC7AC


-----Original Message-----
From: elecraft-bounces at mailman.qth.net
[mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Vic K2VCO
Sent: Friday, January 27, 2012 10:43 AM
To: elecraft at mailman.qth.net
Subject: Re: [Elecraft] KPA500 Power Output

Of course! It's rated in MFJ WATTS. One regular watt = about 10 MFJ watts.
Elecraft is one 
of the few companies making products rated in real watts.

On 1/27/2012 10:21 AM, Bill Gerth wrote:
> Bert,
>
> In addition to the other suggestions you received, I'd suggest that
> you make sure your dummy load is capable of this kind of key-down
> power for that amount of time.  I have an MFJ Dummy Load that is
> called a 1.5KW Dummy Load but the chart on the back panel shows it is
> only capable of around 120 watts for 60 seconds.  It can only handle
> 1.5 KW for less than 10 SECONDS.  Some fan-cooled or oil-cooled dummy
> loads might be OK for 500 watts of key-down for 1 minute, but my air-
> cooled 1.5 KW Dummy Load is NOT.  The non-inductive resistor gets very
> hot and begins to smell even after relatively short key-down periods.
> Your power change might be due to the dummy load changing its
> effective resistance due to heating.
>
> Just a thought.
>
> 73,
>
> W4RK - Bill Gerth
> Jefferson City, MO
> billgerth at embarqmail.com