[Elecraft] KPA500 Fault Question + wish

[Bob McGraw]

A year or so ago I embarked on a project to determine the efficiency and 
the "sweet spot" operating parameters of my KPA500.   I drive my KPA500 
with my Elecraft K3S.

Armed with a good 50 ohm dummy load, two watt meters {one on the input 
and one on the output}, and my EXCEL spreadsheet, I measured each band, 
160M - 6M.  I choose power output levels starting at 100 watts and every 
100 watts thereafter up to 500 watts.    Using the KPA500 display as the 
source for volts and amps, the input power was determined and calculated 
against the measured output power.  Thus the efficiency was easily 
calculated.   No consideration for the actual drive power was in the 
measured output power.

And at the same time, measuring the input power and output power and a 
little math, the gain of the amplifier was determined at various power 
levels and bands.

Yes indeed, I found that running at reduced power saves nothing! The amp 
is more efficient in the 350 to 450 watt range and thus dissipates less 
heat.  And from band to band and power level,  it is easy to see that 
the efficiency changes.

In a quick summary, I found the efficiency runs from a low of 23.4% at 
100 watts on 20M to a high of 70.9% at 500 watts on 80M.   I did not 
exceed 500 watts on any band,  thus any amplifier compression was not 
anticipated.   The power/heat dissipation runs from a high of 400 watts 
at 250 watts output on 20M to a low of 196 watts at 100 watts output on 
80M.  The amplifier average gain varies from 13.95 dB on 20M to 14.59 dB 
on 80M.   To attain these values, the drive power varies from a low of 
3.3 watts on 10M & 15M for 100 watts output to a high of 18.5 watts for 
500 watts on 40M.

It might do well for each KPA500 owner to run power and efficiency 
curves on their amplifiers.   The results are enlightening.

73

Bob, K4TAX


On 4/24/2022 6:48 PM, elecraft-request at mailman.qth.net wrote:
> Message: 12
> Date: Sun, 24 Apr 2022 14:03:55 -0400
> From: EMAIL<email at nr3i.org>
> To: Elecraft K4 Group<Elecraft-K4 at groups.io>,
> 	"elecraft at mailman.qth.net"  <elecraft at mailman.qth.net>
> Subject: [Elecraft] K4D - KPA500 Fault Question + wish
> Message-ID:<bdbf25a8-a692-c824-44ae-0186ad7a0f73 at nr3i.org>
> Content-Type: text/plain; charset=UTF-8; format=flowed
>
> Yesterday I got a fault message on the K4 screen. It disappeared before
> I could see it fully, but I did get "tighten heatsink screws".? The fan
> was working as its speed was speeding up and the KPA500 temp saw about
> 60+C (it may have been higher).? I was running 100 watts PSK31.? The
> KPA500 did switch to STBY (I think).
>
> I can not find any record of what the message was.? I can not find
> "heatsink screws" referenced in the K4, KPA500 or KPA1500 manuals.? Both
> the K4 and KPA500 are factory built.
>
> PSK31 has a longer duty cycle than FT8 and I was running FT8 at higher
> power with out the amp temp going above 60C, earlier.? I switched to
> barefoot and ran 80W PSK31 without issue.
>
> Question 1) Before I take the KPA500 apart, is this a problem or just
> duty cycle?? I would think the KPA500 would be able to handle 100W key
> down.
>
> Question 2) I saved the K4 backup and diagnostic logs to USB disk (the
> next day).? I could NOT find anything that looked like the error
> messages.? I find many messages disappear before I get a chance to read
> them.
>
> Wish 1) KPA500 add FAN CTL for both OPER and STBY or set STBY to run at
> NOR and OPER to be adjustable.
>
> Wish 2) K4, allow checking date/time for all past error messages.? I may
> have had a KPA500 over temp message while long winded on SSB (but only
> 200W)?
>
> Wish 3) K4, HOLD error messages until "confirmed".? Messages like KPA500
> on/off (info) only need to be short time (??), but if away (maybe
> confirm).? Either way "this" will be an issue for? the contesters, so
> have a way to save for later recall, as in write to USB if one is
> installed.? Fn could write to USB disk with time stamp?? OR, are there
> documents on how to read the diagnostic logs?
>
>
> 73, steve WB3LGC
>
> I will also send to support if no one has a good idea about the fault.
>
>
-- 
IF ONE EXPECTS COMPUTERS AND TECHNOLOGY TO SOLVE THEIR PROBLEMS,
ONE DOESN'T UNDERSTAND COMPUTERS AND TECHNOLOGY
AND ONE DOESN'T UNDERSTAND THEIR PROBLEMS."