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QRO - KPA500 Failure

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KK1W

QRO - KPA500 Failure

Was running about 150W on 18 MHz this afternoon. My KPA 500 made a loud
pop. No more output. Any pointers of where to start looking?

*Details:*
KPA500 (use with KAT500 and Icom 7610)
Antenna on this band is a SteppIR
Amp has been running FB
KPA Utility 1.13.7.16
240V supply
A single loud pop was heard.
Mode remained in OPER
No fault light displayed, nor can I find one in the Fault Table

*After the failure:*

*In STBY:*
Radio and antennas work fine. SWR shown to exciter is low, as expected.
Exciter power is displayed on KPA500 power meter.
HV = 78.2
Works correctly on all bands

*In OPER:*
HV = 78.2 key up
On key down (input of 15W) the asterisk briefly displays, then display
changes to 18.1, back to HV display on key up.
Zero output, SWR shown to exciter is very high (over 3 to 1)
No power shown on output meter.
Fails *on all bands* with high SWR to the exciter.
No fault indication.

*Other data:*
Here's the last three entries from the fault table:
00000000 00 PWR ON -- 0007 Power was turned on
00000039 09 REFL HI 80 00F0 Excessive reflected power (high SWR)
00000000 00 PWR ON -- Power was turned on
.............

Apparently only faults get logged, subsequent power cycles have not changed
the table.

I power cycled the amp, including removing the mains power. - no change.
I reloaded the last configuration - no change.
I removed the cover and looked for any visible damage or bad odors. Nothing
stands out.

Amp is about 4 years old and was a kit model. Before I start to disassemble
if anyone can offer a likely culprit I'm all ears.

Thanks,

Jim/KK1W
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Jim Brown-10

Re: QRO - KPA500 Failure

On 2/6/2020 12:15 PM, Jim Mullen wrote:
> Any pointers of where to start looking?

1) What SWR does the rig see with the amp off?
2) Make notes of any error messages given by the KPA500 display.
3) Call Elecraft Support

73, Jim K9YC
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Michael Walker

Re: QRO - KPA500 Failure

Amps making noises like that usually mean you have to take the covers off.

They are easy enough to repair if you are so inclined. If not, then you
will need to contact Elecraft support and odds are you will have to send it
home for a Spa day.

Mike va3mw

On Thu, Feb 6, 2020 at 3:35 PM Jim Brown <[hidden email]> wrote:

> On 2/6/2020 12:15 PM, Jim Mullen wrote:
> > Any pointers of where to start looking?
>
> 1) What SWR does the rig see with the amp off?
> 2) Make notes of any error messages given by the KPA500 display.
> 3) Call Elecraft Support
>
> 73, Jim K9YC
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
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>
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> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]
>

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Rick Bates, NK7I

Re: QRO - KPA500 Failure

Since the SWR is still nominal into the amp (as shown on your radio),
it's not likely the tuned input circuits (which is confirmed from no
output on all bands).

This points to the high power module. Running low output power from it,
is far less efficient than pushing it hard (compare wattages consumed to
RF watts output delivered at different output levels); which may have
stressed the finals. Ideally you run the previous stages at
low-moderate power for lower IMD, then punch it up with the amp.

The "HIGH SWR" fault you saw is then very likely the final signing QRT
SK. You can confirm that with Elecraft wizards.

That module isn't hard to swap out, but it would be best (slightly more
costly) for the entire amp to visit it's parents, so that other updates
that may not have been done, can be done. Many of them, really matter.

While also not cheap in shipping and insurance (ask me how I know?) that
is often the better choice.

Rick, NK7I

On 2/6/2020 12:54 PM, Michael Walker wrote:

> Amps making noises like that usually mean you have to take the covers off.
>
> They are easy enough to repair if you are so inclined. If not, then you
> will need to contact Elecraft support and odds are you will have to send it
> home for a Spa day.
>
> Mike va3mw
>
>
> On Thu, Feb 6, 2020 at 3:35 PM Jim Brown <[hidden email]> wrote:
>
>> On 2/6/2020 12:15 PM, Jim Mullen wrote:
>>> Any pointers of where to start looking?
>> 1) What SWR does the rig see with the amp off?
>> 2) Make notes of any error messages given by the KPA500 display.
>> 3) Call Elecraft Support
>>
>> 73, Jim K9YC
>> ______________________________________________________________
>> Elecraft mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:[hidden email]
>>
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
>> Message delivered to [hidden email]
>>
> ______________________________________________________________
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NK7Z

Re: QRO - KPA500 Failure

Hi Rick,

I like your call sign! :)

73, and thanks,
Dave (NK7Z)
https://www.nk7z.net
ARRL Volunteer Examiner
ARRL Technical Specialist
ARRL Asst. Director, NW Division, Technical Resources

On 2/6/20 1:07 PM, Rick Bates, NK7I wrote:

> Since the SWR is still nominal into the amp (as shown on your radio),
> it's not likely the tuned input circuits (which is confirmed from no
> output on all bands).
>
> This points to the high power module. Running low output power from it,
> is far less efficient than pushing it hard (compare wattages consumed to
> RF watts output delivered at different output levels); which may have
> stressed the finals. Ideally you run the previous stages at
> low-moderate power for lower IMD, then punch it up with the amp.
>
> The "HIGH SWR" fault you saw is then very likely the final signing QRT
> SK. You can confirm that with Elecraft wizards.
>
> That module isn't hard to swap out, but it would be best (slightly more
> costly) for the entire amp to visit it's parents, so that other updates
> that may not have been done, can be done. Many of them, really matter.
>
> While also not cheap in shipping and insurance (ask me how I know?) that
> is often the better choice.
>
> Rick, NK7I
>
> On 2/6/2020 12:54 PM, Michael Walker wrote:
>> Amps making noises like that usually mean you have to take the covers
>> off.
>>
>> They are easy enough to repair if you are so inclined. If not, then you
>> will need to contact Elecraft support and odds are you will have to
>> send it
>> home for a Spa day.
>>
>> Mike va3mw
>>
>>
>> On Thu, Feb 6, 2020 at 3:35 PM Jim Brown <[hidden email]>
>> wrote:
>>
>>> On 2/6/2020 12:15 PM, Jim Mullen wrote:
>>>> Any pointers of where to start looking?
>>> 1) What SWR does the rig see with the amp off?
>>> 2) Make notes of any error messages given by the KPA500 display.
>>> 3) Call Elecraft Support
>>>
>>> 73, Jim K9YC
>>> ______________________________________________________________
>>> Elecraft mailing list
>>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>>> Help: http://mailman.qth.net/mmfaq.htm
>>> Post: mailto:[hidden email]
>>>
>>> This list hosted by: http://www.qsl.net
>>> Please help support this email list: http://www.qsl.net/donate.html
>>> Message delivered to [hidden email]
>>>
>> ______________________________________________________________
>> Elecraft mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:[hidden email]
>>
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
>> Message delivered to [hidden email]
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Hisashi T Fujinaka

Re: QRO - KPA500 Failure

In reply to this post by Rick Bates, NK7I

I'm not sure who asked the question first, but check your email from
Elecraft support about shipping. I was told Elecraft self-insures, so my
shipping of my KPA1500 amp from Portland, OR to the mothership was
around $20.

On Thu, 6 Feb 2020, Rick Bates, NK7I wrote:

> While also not cheap in shipping and insurance (ask me how I know?) that
> is often the better choice.
>
> Rick, NK7I

--
Hisashi T Fujinaka - [hidden email]
BSEE + BSChem + BAEnglish + MSCS + $2.50 = coffee
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Rick Bates, NK7I

Re: QRO - KPA500 Failure

They self-insure OUTbound from Elecraft; it falls on the shipper to
insure, not the recipient.

I had to send in the RF deck (only) of the KPA1500 for factory upgrades
and I asked for Elecraft to cover shipping. I waited a few days.

An hour after I got back from shipping it UPS from Idaho (the insurance
was a killer, total bill ~$180), they approved paying for it. DOH!

Ask, then be more patient than me. The worst answer is 'no' and that
only costs you time to find out.

Rick NK7I

On 2/6/2020 1:28 PM, Hisashi T Fujinaka wrote:

> I'm not sure who asked the question first, but check your email from
> Elecraft support about shipping. I was told Elecraft self-insures, so my
> shipping of my KPA1500 amp from Portland, OR to the mothership was
> around $20.
>
> On Thu, 6 Feb 2020, Rick Bates, NK7I wrote:
>
>> While also not cheap in shipping and insurance (ask me how I know?)
>> that is often the better choice.
>>
>> Rick, NK7I
>

N7US

Re: QRO - KPA500 Failure

In reply to this post by Hisashi T Fujinaka

Elecraft self-insures on outbound shipments (i.e., shipments from Elecraft
to customer). That means they accept the responsibility of carrier loss or
damage because their history of loss/damage has been low.

The fact that they self-insure doesn't cover shipments to them unless the
company is paying for the shipping, as is the case with a warranty return,
I believe. Their shipping instructions for repair returns out of warranty
recommend the customer insure the shipment.

I received about a 25% discount from UPS when I shipped my KPA1500 a couple
of months ago due to my membership in a professional society. You might
check for similar discounts if you have any similar memberships.

Jim N7US

On Thu, Feb 6, 2020, 3:28 PM Hisashi T Fujinaka <[hidden email]> wrote:

> I'm not sure who asked the question first, but check your email from
> Elecraft support about shipping. I was told Elecraft self-insures, so my
> shipping of my KPA1500 amp from Portland, OR to the mothership was
> around $20.
>
> On Thu, 6 Feb 2020, Rick Bates, NK7I wrote:
>
> > While also not cheap in shipping and insurance (ask me how I know?) that
> > is often the better choice.
> >
> > Rick, NK7I
>
> --
> Hisashi T Fujinaka - [hidden email]
> BSEE + BSChem + BAEnglish + MSCS + $2.50 = coffee
>
>

ANDY DURBIN

QRO - KPA500 Failure

In reply to this post by KK1W

"On key down (input of 15W) the asterisk briefly displays, then display changes to 18.1, back to HV display on key up."

Are you saying the "HV" text in the display goes away or that it reads HV 18.1?

Normally the HV display continues to read the PA supply voltage regardless of whether the amp is keyed or not. It would normally just change from approx 80 V to approx 60 V when keyed. At face value the results seem to indicate a high voltage supply failure or a fault in the PA that is sucking a very high current.

What is the PA current during the brief period the KPA500 remains keyed?

What are PA voltage and current when keyed if the 60 V line is disconnected from the PA module?

Of course the safe plan would be to send it back but those are some of the test I would try if it were mine.

Andy, k3wyc
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Bob McGraw - K4TAX

Re: QRO - KPA500 Failure

In reply to this post by Rick Bates, NK7I

I've never seen much if any advantage in running a linear below its
rated output. I know the regulation state never run more power than
needed for adequate communications or terms like that.    The difference
between 500 watts and 100 watts is 6.9 dB or about 1 S unit.

In fact, most all of the time, running at less than rated output is less
efficient.   It saves nothing.   Same for tube amps where I hear hams
say they are running at reduced power to "save the tubes".   Nope, not
the case.

(RF output / DC input) * 100 = % efficiency         DC input watts = DC
volts x DC amps

Do the math and you'll see what I mean.

A quick run of the numbers with my KPA500 into a dummy load. Output
measured with a Bird 43. DC values taken from the KPA500 display

450 W out, 819 W input, 64 volts @ 12.8 amps for 55% efficiency Drive
pwr = 16.5W 14.3 dB gain    819 - 450 = 369 watts = heating factor = 0.88

210 W out, 576 W input, 67 volts @ 8.6 amps for 37% efficiency Drive pwr
= 7.0 W 14.7 dB gain     576 - 210 = 366 watts = heating factor = 1.74

100 W out, 393 W input, 69 volts @ 5.7 amps for 25% efficiency     Drive
pwr = 3.2 W 14.9 dB gain 393 - 100 = 293 watts = heating factor = 2.93

73

Bob, K4TAX

On 2/6/2020 3:07 PM, Rick Bates, NK7I wrote:
> Running low output power from it, is far less efficient than pushing
> it hard (compare wattages consumed to RF watts output delivered at
> different output levels); which may have stressed the finals. Ideally
> you run the previous stages at low-moderate power for lower IMD, then
> punch it up with the amp.

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ANDY DURBIN

Re: QRO - KPA500 Failure

In reply to this post by ANDY DURBIN

As a follow up to my previous message I measured PA voltage and current for OPER mode not keyed and OPER mode keyed with no RF drive input.

PAI not keyed .0, keyed .2
PAV not keyed 80.9, keyed 77.8

Hi reflected power fault can't happen with no drive so won't influence the results.

Andy, k3wyc

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Joe K2UF

Re: QRO - KPA500 Failure

In reply to this post by N7US

When I blew the final on my KPA500 Elecraft diagnosed the problem. I had to
make a few meter readings and they figured out the problem. They gave me
the option of removing the transformer for shipping (most of the amp
weight). They gave me instructions to remove and reassemble when it
returned. Saved a lot on shipping.

Good luck

73

Joe K2UF

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Hisashi T Fujinaka

Re: QRO - KPA500 Failure

In reply to this post by Bob McGraw - K4TAX

The advantage I have is that it doesn't set off my fire alarm.

On Thu, 6 Feb 2020, Bob McGraw K4TAX wrote:

> I've never seen much if any advantage in running a linear below its
> rated output. I know the regulation state never run more power than
> needed for adequate communications or terms like that. The difference
> between 500 watts and 100 watts is 6.9 dB or about 1 S unit.
>
> In fact, most all of the time, running at less than rated output is less
> efficient. It saves nothing. Same for tube amps where I hear hams
> say they are running at reduced power to "save the tubes". Nope, not
> the case.
>
> (RF output / DC input) * 100 = % efficiency DC input watts = DC
> volts x DC amps
>
> Do the math and you'll see what I mean.
>
> A quick run of the numbers with my KPA500 into a dummy load. Output
> measured with a Bird 43. DC values taken from the KPA500 display
>
> 450 W out, 819 W input, 64 volts @ 12.8 amps for 55% efficiency Drive
> pwr = 16.5W 14.3 dB gain 819 - 450 = 369 watts = heating factor = 0.88
>
> 210 W out, 576 W input, 67 volts @ 8.6 amps for 37% efficiency Drive pwr
> = 7.0 W 14.7 dB gain 576 - 210 = 366 watts = heating factor = 1.74
>
> 100 W out, 393 W input, 69 volts @ 5.7 amps for 25% efficiency Drive
> pwr = 3.2 W 14.9 dB gain 393 - 100 = 293 watts = heating factor = 2.93
>
> 73
>
> Bob, K4TAX
>
>
> On 2/6/2020 3:07 PM, Rick Bates, NK7I wrote:
>> Running low output power from it, is far less efficient than pushing
>> it hard (compare wattages consumed to RF watts output delivered at
>> different output levels); which may have stressed the finals. Ideally
>> you run the previous stages at low-moderate power for lower IMD, then
>> punch it up with the amp.
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]

--
Hisashi T Fujinaka - [hidden email]
BSEE + BSChem + BAEnglish + MSCS + $2.50 = coffee
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K9MA

Re: QRO - KPA500 Failure

In reply to this post by Bob McGraw - K4TAX

Basically, based on Bob's measurements, the power dissipated is fairly
independent of drive level. So, running at reduced power really isn't
stressing anything any more that full output. (Unlike an "ideal" class B
amplifier.)

73,
Scott K9MA

On 2/6/2020 16:06, Bob McGraw K4TAX wrote:

> I've never seen much if any advantage in running a linear below its
> rated output. I know the regulation state never run more power than
> needed for adequate communications or terms like that.    The
> difference between 500 watts and 100 watts is 6.9 dB or about 1 S unit.
>
> In fact, most all of the time, running at less than rated output is
> less efficient.   It saves nothing.   Same for tube amps where I hear
> hams say they are running at reduced power to "save the tubes".
> Nope, not the case.
>
> (RF output / DC input) * 100 = % efficiency         DC input watts =
> DC volts x DC amps
>
> Do the math and you'll see what I mean.
>
> A quick run of the numbers with my KPA500 into a dummy load. Output
> measured with a Bird 43. DC values taken from the KPA500 display
>
> 450 W out, 819 W input, 64 volts @ 12.8 amps for 55% efficiency Drive
> pwr = 16.5W 14.3 dB gain    819 - 450 = 369 watts = heating factor =
> 0.88
>
> 210 W out, 576 W input, 67 volts @ 8.6 amps for 37% efficiency Drive
> pwr = 7.0 W 14.7 dB gain     576 - 210 = 366 watts = heating factor =
> 1.74
>
> 100 W out, 393 W input, 69 volts @ 5.7 amps for 25% efficiency Drive
> pwr = 3.2 W 14.9 dB gain 393 - 100 = 293 watts = heating factor = 2.93
>
> 73
>
> Bob, K4TAX
>
>
> On 2/6/2020 3:07 PM, Rick Bates, NK7I wrote:
>> Running low output power from it, is far less efficient than pushing
>> it hard (compare wattages consumed to RF watts output delivered at
>> different output levels); which may have stressed the finals. Ideally
>> you run the previous stages at low-moderate power for lower IMD, then
>> punch it up with the amp.
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]

--
Scott K9MA

[hidden email]

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ANDY DURBIN

Re: QRO - KPA500 Failure

In reply to this post by ANDY DURBIN

"Basically, based on Bob's measurements, the power dissipated is fairly independent of drive level. So, running at reduced power really isn't stressing anything any more that full output."

I have done quite extensive testing of my KPA500 and provided links to my results. My KPA500 PA dissipation is strongly dependent on the PA load but, for any given load, the peak dissipation is at out half power output.

Andy, k3wyc

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Macy monkeys

Re: QRO - KPA500 Failure

In reply to this post by Bob McGraw - K4TAX

I run my KPA500 output just below the level I feel I can get away with...without lighting up the neighborhood. About 350 watts :)

John K7FD

> On Feb 6, 2020, at 2:06 PM, Bob McGraw K4TAX <[hidden email]> wrote:
>
> I've never seen much if any advantage in running a linear below its rated output. I know the regulation state never run more power than needed for adequate communications or terms like that. The difference between 500 watts and 100 watts is 6.9 dB or about 1 S unit.
>
> In fact, most all of the time, running at less than rated output is less efficient. It saves nothing. Same for tube amps where I hear hams say they are running at reduced power to "save the tubes". Nope, not the case.
>
> (RF output / DC input) * 100 = % efficiency DC input watts = DC volts x DC amps
>
> Do the math and you'll see what I mean.
>
> A quick run of the numbers with my KPA500 into a dummy load. Output measured with a Bird 43. DC values taken from the KPA500 display
>
> 450 W out, 819 W input, 64 volts @ 12.8 amps for 55% efficiency Drive pwr = 16.5W 14.3 dB gain 819 - 450 = 369 watts = heating factor = 0.88
>
> 210 W out, 576 W input, 67 volts @ 8.6 amps for 37% efficiency Drive pwr = 7.0 W 14.7 dB gain 576 - 210 = 366 watts = heating factor = 1.74
>
> 100 W out, 393 W input, 69 volts @ 5.7 amps for 25% efficiency Drive pwr = 3.2 W 14.9 dB gain 393 - 100 = 293 watts = heating factor = 2.93
>
> 73
>
> Bob, K4TAX
>
>
>> On 2/6/2020 3:07 PM, Rick Bates, NK7I wrote:
>> Running low output power from it, is far less efficient than pushing it hard (compare wattages consumed to RF watts output delivered at different output levels); which may have stressed the finals. Ideally you run the previous stages at low-moderate power for lower IMD, then punch it up with the amp.
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
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> Post: mailto:[hidden email]
>
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> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]

john@kk9a.com

Re: QRO - KPA500 Failure

In reply to this post by KK1W

There may be reasons for running at less than the amplifier max such
as the US 200 watt 30m band limitation. I have no RF engineering
knowledge but after looking at your data I see less heat with lower
output wattage which seems to me like it would be less stress on finals.

John KK9A

Bob McGraw K4TAX wrote:

I've never seen much if any advantage in running a linear below its
rated output. I know the regulation state never run more power than
needed for adequate communications or terms like that. The difference
between 500 watts and 100 watts is 6.9 dB or about 1 S unit.

In fact, most all of the time, running at less than rated output is less
efficient. It saves nothing. Same for tube amps where I hear hams
say they are running at reduced power to "save the tubes". Nope, not
the case.

(RF output / DC input) * 100 = % efficiency DC input watts = DC
volts x DC amps

Do the math and you'll see what I mean.

A quick run of the numbers with my KPA500 into a dummy load. Output
measured with a Bird 43. DC values taken from the KPA500 display

450 W out, 819 W input, 64 volts @ 12.8 amps for 55% efficiency Drive
pwr = 16.5W 14.3 dB gain 819 - 450 = 369 watts = heating factor = 0.88

210 W out, 576 W input, 67 volts @ 8.6 amps for 37% efficiency Drive pwr
= 7.0 W 14.7 dB gain 576 - 210 = 366 watts = heating factor = 1.74

100 W out, 393 W input, 69 volts @ 5.7 amps for 25% efficiency Drive
pwr = 3.2 W 14.9 dB gain 393 - 100 = 293 watts = heating factor = 2.93

73

Bob, K4TAX

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Petr, OK1RP/M0SIS

Re: QRO - KPA500 Failure

This post was updated on .

In reply to this post by KK1W

Jim,

maybe it is not your case but check this first:

http://ok1rp.blogspot.com/2017/02/elecraft-kpa500-lpf-tr-switch-rework.html?_sm_au_=iQWn28RMHPpHWSZ6cLpsvK618Vf61

-----
73 - Petr, OK1RP
"Apple & Elecraft freak"
B:http://ok1rp.blogspot.com
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--
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Don Wilhelm

Re: QRO - KPA500 Failure

In reply to this post by john@kk9a.com

John,

You are correct. I am seeing a lot of confusion and erroneous
conclusions based on the terms 'efficiency', 'dissipation' coupled with
'power output'.
As an example, consider that a PA running at 50% efficient at 500 watts
will dissipate 500 watts of heat and 500 watts of power out. Input DC
power will be 1000 watts.
Now back the power down to 250 watts - yes, the efficiency will be less,
say 33%. That is 250 watts of power output, but 67% of the total power
into the amp would be lost as heat - 417 watts of heat. Input power is
less too at 667 watts.

That drop in efficiency at lower than max design power is true for any
amp designed for their maximum rated power output (as most are).

The only ones who should be concerned are those who are monitoring their
draw from the AC line and their resulting utility bill.

73,
Don W3FPR

On 2/7/2020 10:16 AM, [hidden email] wrote:
> There may be reasons for running at less than the amplifier max such as
> the US 200 watt 30m band limitation. I have no RF engineering knowledge
> but after looking at your data I see less heat with lower output wattage
> which seems to me like it would be less stress on finals.
>
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ANDY DURBIN

QRO - KPA500 Failure

In reply to this post by KK1W

"I am seeing a lot of confusion and erroneous conclusions based on the terms 'efficiency', 'dissipation' coupled with 'power output'."

Yes, very true. Only a few have actually contributed test data. All the rest is assumption and speculation.

Andy, k3wyc
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