[Elecraft] KPA500 - Full Power Keydown

[Johnny Siu]

Thanks, Jim and all the elecrafters responded to my question about using KPA500 under full power in RTTY contest.
Some of the answers came to me under private emails off the list.  I would like to thank them as well.
>From all the responses, KPA500 is a solid performer under full power in all modes including those high duty cycle.
I mostly operate SSB so that I do not have much chances to operate KPA500 under high duty cycle.  Hence, I put up my question in this email listing.
73
Johnny VR2XMC
       寄件人︰ Jim Brown <jim at audiosystemsgroup.com>
 收件人︰ elecraft at mailman.qth.net 
 傳送日期︰ 2015年04月26日 (週日) 5:02 AM
 主題︰ Re: [Elecraft] KPA500 - Full Power Keydown
   
On Sat,4/25/2015 11:21 AM, Kevin Stover wrote:
> All of this anecdotal eveidence is interesting but meaningless.

Is it?  The original post asked who had actually used the KPA500 that 
way. He got several responses, including mine.

> Elecratf advertise and rate the amp as a 500W amp. Not 600, not 700.

I stated my experience. The difference between 500W and 600W is 0.8 dB. 
The difference between 500W and 650W is 1.1 dB.

Early versions of K3 firmware allowed it to cranked to 120 W. That was 
reduced to 110 W to place an upper limit on IMD.

> Someone should put the amp on an spectrum analyser while running at 700 wats to see whatr it looks like while being overdriven.

You can bet that Elecraft did that throughout the design process, and 
probably in final test of the power modules. I know the guy who did that 
testing. :)  I've done it myself. It remains clean at the highest power 
I can get out of it, which varies a bit depending on the load Z between 
600W and 700W.  I've published a link to those measurements several 
times on this reflector.
k9yc.com/P3_Spectrum_Measurements.pdf and
k9yc.com/FTDX5000_Report.pdf

The highest power in these reports is 550W, but I've measured up to 650W 
and the sidebands get slightly wider (5-10%) and a few dB stronger.

> Elecraft have also said, in the operating manual, that the time limnit is 10 minutes key down. Did they put that line in the manual just to take up space or is it purely CYA?

That's a reasonable spec based on my observations with a thousand or 
more hours of use.

>
> Jusdt because some people are overdriving the amp and getting away with it doesn't mean it was designed for it.

It's pretty difficult to overdrive the KPA500 -- if you supply more 
drive than it wants, it will insert an attenuator between the input 
connector and the power amp stage to keep the power within design 
parameters. Protection circuitry in the K3, KX3, KPA500, and KAT500 is 
set to prevent destructive overheating and keep the signal clean.

On Sat,4/25/2015 12:04 PM, Harry Yingst via Elecraft wrote:
> I'm looking for people who actually run it at 500 watts in SSTV, or other like modes (not voice) A SSTV picture can take 110 seconds

If it will do 500W keydown for 10 minutes, it will do 110 seconds for 
SSTV. :)

73, Jim K9YC




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