KPA 500 Low power out.


Mike Streeter
 

I have two complete K3 line stations. Everything has worked well for several years. Now one of my two KPA 500 amps is putting out low power on 40m.  Initially when it is cold it may put out 500 watts but that drops to between 100 - 200 watts soon after warming up. On all other bands it is putting out the full 500 watts. Drive power on most bands is between 20 -30 watts for 500 out with HV of 80 dropping to about 60 on transmit. On 40m with drive power of 40 watts HV drops to about 70 when the output is low. Load current on most bands is about 15 amps, drops to about 5 amps on 40m with the low output. With both the radio tuner and KAT 500 antenna tuner in bypass the SWR on all bands is below 1.5 to 1.
When I swap the amps over between the two stations the problem goes with the amp.

Anyone have any ideas before I trouble Elecraft?

Thanks for reading,
Mike, WM5DX.









Bob McGraw - K4TAX
 

Based on my KPA500, I would say that 40 watts of drive is excessive.    My amp drives to 500 watts, all bands,  with 18 to 22 watts of drive.   I suspect you have a failed component or a bad solder joint in the band pass filter for that band.     


Mike Streeter
 

Hi Bob, thanks for your input. Yes, 40 watts is excessive, normal would be around 30 watts, I was trying to make the point that the the amp does not increase it's output even at the maximum Elecraft recommended power input. (Before someone suggests that I increase the drive power!).
I do concur that I probably have a failed component and the band pass filter is my suspect but I want to see if anyone else had ideas.

By the way, many thanks for your posts on other subjects, such as grounding, always good to get information from others who are more knowledgeable than I.

Thanks again,

Mike, WM5DX.



On Tuesday, October 19, 2021, 08:02:56 AM CDT, Bob McGraw - K4TAX <rmcgraw@...> wrote:


Based on my KPA500, I would say that 40 watts of drive is excessive.    My amp drives to 500 watts, all bands,  with 18 to 22 watts of drive.   I suspect you have a failed component or a bad solder joint in the band pass filter for that band.     


Dave (NK7Z)
 

A few years ago, I made an input power, vs. output power, graph of the KPA500 I own. It is located at:

https://www.nk7z.net/kpa500-input-vs-output-power/

That set of graph may be of some use in this matter. Click any of the three graphs to expand that graph.

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

On 10/19/21 6:35 AM, Mike Streeter via groups.io wrote:
Hi Bob, thanks for your input. Yes, 40 watts is excessive, normal would be around 30 watts...


Mike Streeter
 

Hi Dave. Thanks for your response. It appears that my original post may be misleading. The amp in question has always put out 500 watts with about 30 watts drive until recently when it has started reducing the output with 30 watts drive down to 100-200 watts out. Even if the drive is increased to 40 watts (the maximum recommended by Elecraft), the output is still only 100-200 watts out.

Thanks again, Mike, WM5DX.



On Tuesday, October 19, 2021, 09:00:00 AM CDT, Dave (NK7Z) <dave@...> wrote:



A few years ago, I made an input power, vs. output power, graph of the
KPA500 I own.  It is located at:
   
https://www.nk7z.net/kpa500-input-vs-output-power/

That set of graph may be of some use in this matter.  Click any of the
three graphs to expand that graph.

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

On 10/19/21 6:35 AM, Mike Streeter via groups.io wrote:
> Hi Bob, thanks for your input. Yes, 40 watts is excessive, normal would
> be around 30 watts...






Dave (NK7Z)
 

Hi,
No problem, that set of graphs will give you what my amp did when it was new... Good luck getting your amp up to power. I am following this thread as it may at some time apply to me...

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

On 10/19/21 8:16 AM, Mike Streeter via groups.io wrote:
Hi Dave. Thanks for your response. It appears that my original post may be misleading. The amp in question has always put out 500 watts with about 30 watts drive until recently when it has started reducing the output with 30 watts drive down to 100-200 watts out. Even if the drive is increased to 40 watts (the maximum recommended by Elecraft), the output is still only 100-200 watts out.
Thanks again, Mike, WM5DX.
On Tuesday, October 19, 2021, 09:00:00 AM CDT, Dave (NK7Z) <dave@nk7z.net> wrote:
A few years ago, I made an input power, vs. output power, graph of the
KPA500 I own.  It is located at:
https://www.nk7z.net/kpa500-input-vs-output-power/ <https://www.nk7z.net/kpa500-input-vs-output-power/>
That set of graph may be of some use in this matter.  Click any of the
three graphs to expand that graph.
73, and thanks,
Dave (NK7Z)
https://www.nk7z.net <https://www.nk7z.net>
ARRL Volunteer Examiner
ARRL Technical Specialist, RFI
ARRL Asst. Director, NW Division, Technical Resources
On 10/19/21 6:35 AM, Mike Streeter via groups.io wrote:
> Hi Bob, thanks for your input. Yes, 40 watts is excessive, normal would
> be around 30 watts...


Jim Brown
 

On 10/19/2021 6:35 AM, Mike Streeter via groups.io wrote:
I was trying to make the point that the the amp does not increase it's output even at the maximum Elecraft recommended power input.
The amplifier has an internal switchable pad (attenuator) that kicks in when the input is greater than needed to hit safe output.

73, Jim K9YC


Mike Streeter
 

Hi Jim. I did not know that. Do you know where it is located inside the amp?

I have had both amps for years and never needed to open either of them up, same goes for the two K3 radios.

Many thanks for the information.

Mike, WM5DX.


On Tuesday, October 19, 2021, 01:16:55 PM CDT, Jim Brown <k9yc@...> wrote:


On 10/19/2021 6:35 AM, Mike Streeter via groups.io wrote:
> I was trying to make the point that the the amp does not increase it's
> output even at the maximum Elecraft recommended power input.

The amplifier has an internal switchable pad (attenuator) that kicks in
when the input is greater than needed to hit safe output.

73, Jim K9YC






Ray Maxfield
 

It Sounds like something is Getting HOT !  

WA6VAB K3  Ray

 

 

From: Dave (NK7Z)
Sent: Tuesday, October 19, 2021 11:14 AM
To: Elecraft-K3@groups.io
Subject: Re: [Elecraft-K3] KPA 500 Low power out.

 

Hi,

No problem, that set of graphs will give you what my amp did when it was

new...  Good luck getting your amp up to power.  I am following this

thread as it may at some time apply to me...

 

73, and thanks,

Dave (NK7Z)

https://www.nk7z.net

ARRL Volunteer Examiner

ARRL Technical Specialist, RFI

ARRL Asst. Director, NW Division, Technical Resources

 

On 10/19/21 8:16 AM, Mike Streeter via groups.io wrote:

> Hi Dave. Thanks for your response. It appears that my original post may

> be misleading. The amp in question has always put out 500 watts with

> about 30 watts drive until recently when it has started reducing the

> output with 30 watts drive down to 100-200 watts out. Even if the drive

> is increased to 40 watts (the maximum recommended by Elecraft), the

> output is still only 100-200 watts out.

>

> Thanks again, Mike, WM5DX.

>

>

>

> On Tuesday, October 19, 2021, 09:00:00 AM CDT, Dave (NK7Z)

> <dave@...> wrote:

>

>

>

> A few years ago, I made an input power, vs. output power, graph of the

> KPA500 I own.  It is located at:

>

> https://www.nk7z.net/kpa500-input-vs-output-power/

> <https://www.nk7z.net/kpa500-input-vs-output-power/>

>

> That set of graph may be of some use in this matter.  Click any of the

> three graphs to expand that graph.

>

> 73, and thanks,

> Dave (NK7Z)

> https://www.nk7z.net <https://www.nk7z.net>

> ARRL Volunteer Examiner

> ARRL Technical Specialist, RFI

> ARRL Asst. Director, NW Division, Technical Resources

>

> On 10/19/21 6:35 AM, Mike Streeter via groups.io wrote:

>  > Hi Bob, thanks for your input. Yes, 40 watts is excessive, normal would

>  > be around 30 watts...

>

>

>

>

>

>

 

 

 

 

 


Jim Brown
 

On 10/19/2021 11:51 AM, Mike Streeter via groups.io wrote:
Hi Jim. I did not know that. Do you know where it is located inside the amp?
Sorry, no. Haven't studied it.

73, Jim


Mike Streeter
 

Ok, Jim. It's a tribute to Elecraft that we usually don't have to study how their equipment works!

Many thanks for your information, I will try to find out more. I don't want to contact Elecraft unless I really have to, I'm sure they are very busy these days.

73, de Mike, WM5DX.


On Tuesday, October 19, 2021, 02:01:47 PM CDT, Jim Brown <k9yc@...> wrote:


On 10/19/2021 11:51 AM, Mike Streeter via groups.io wrote:
> Hi Jim. I did not know that. Do you know where it is located inside the amp?

Sorry, no. Haven't studied it.

73, Jim






Jim Brown
 

On 10/19/2021 12:07 PM, Mike Streeter via groups.io wrote:
I don't want to contact Elecraft unless I really have to, I'm sure they are very busy these days.
I strongly suggest that you do -- it's one of the major advantages of buying from companies located here. From your symptoms, it does look like something has failed.

73, Jim K9YC


Jeffrey griffin
 

Ever since I started running the data modes with crappy downsized antennas I have a bandpass repair under my belt. If you are somewhat confident in your soldering abilities it's easy with Elecraft equipment. When you open it up the problem component should be easy to find, and as it's an Elecraft, so the support is excellent. I had a burned out inductor and Elecraft was able to tell me the Digikey part number for the Toroid, and also how many turns. Their support made the repair project a pleasure to do. Good luck with it....

73 Jeff kb2m

-----Original Message-----
From: Elecraft-K3@groups.io <Elecraft-K3@groups.io> On Behalf Of Dave (NK7Z)
Sent: Tuesday, October 19, 2021 2:14 PM
To: Elecraft-K3@groups.io
Subject: Re: [Elecraft-K3] KPA 500 Low power out.

Hi,
No problem, that set of graphs will give you what my amp did when it was new... Good luck getting your amp up to power. I am following this thread as it may at some time apply to me...

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

On 10/19/21 8:16 AM, Mike Streeter via groups.io wrote:
Hi Dave. Thanks for your response. It appears that my original post
may be misleading. The amp in question has always put out 500 watts
with about 30 watts drive until recently when it has started reducing
the output with 30 watts drive down to 100-200 watts out. Even if the
drive is increased to 40 watts (the maximum recommended by Elecraft),
the output is still only 100-200 watts out.

Thanks again, Mike, WM5DX.



On Tuesday, October 19, 2021, 09:00:00 AM CDT, Dave (NK7Z)
<dave@nk7z.net> wrote:



A few years ago, I made an input power, vs. output power, graph of the
KPA500 I own. It is located at:

https://www.nk7z.net/kpa500-input-vs-output-power/
<https://www.nk7z.net/kpa500-input-vs-output-power/>

That set of graph may be of some use in this matter. Click any of the
three graphs to expand that graph.

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

On 10/19/21 6:35 AM, Mike Streeter via groups.io wrote:
> Hi Bob, thanks for your input. Yes, 40 watts is excessive, normal
would > be around 30 watts...






Mike Streeter
 

Hi Jeff. Many thanks for the information. Today I connected up to the KPA utility program and reloaded the configuration file. There is only one file that has never needed to be updated since the amp was new. I also checked the fault record and found no obvious problems. I then started everything up and ran RTTY on 40 until the temperature of the amp reached 71 degrees and did not go any higher. The fan increased its speed as it should as the temperature increased. I could not reproduce the problem and the amp put out the full 500 watts all the time. If the problem occurs again I will look to see if there is an obvious bandpass problem.

Many thanks for the info,

73, de Mike, WM5DX.



On Tuesday, October 19, 2021, 04:09:52 PM CDT, Jeffrey griffin <kb2mjeff@...> wrote:


Ever since I started running the data modes with crappy downsized antennas I have a bandpass repair under my belt. If you are somewhat confident in your soldering abilities it's easy with Elecraft equipment. When you open it up the problem component should be easy to find, and as it's an Elecraft, so the support is excellent. I had a burned out inductor and Elecraft was able to tell me the Digikey part number for the Toroid, and also how many turns. Their support made the repair  project  a pleasure to do. Good luck with it....

73 Jeff kb2m


-----Original Message-----
From: Elecraft-K3@groups.io <Elecraft-K3@groups.io> On Behalf Of Dave (NK7Z)
Sent: Tuesday, October 19, 2021 2:14 PM
To: Elecraft-K3@groups.io
Subject: Re: [Elecraft-K3] KPA 500 Low power out.

Hi,
No problem, that set of graphs will give you what my amp did when it was new...  Good luck getting your amp up to power.  I am following this thread as it may at some time apply to me...

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

On 10/19/21 8:16 AM, Mike Streeter via groups.io wrote:
> Hi Dave. Thanks for your response. It appears that my original post
> may be misleading. The amp in question has always put out 500 watts
> with about 30 watts drive until recently when it has started reducing
> the output with 30 watts drive down to 100-200 watts out. Even if the
> drive is increased to 40 watts (the maximum recommended by Elecraft),
> the output is still only 100-200 watts out.
>
> Thanks again, Mike, WM5DX.
>
>
>
> On Tuesday, October 19, 2021, 09:00:00 AM CDT, Dave (NK7Z)
> <dave@...> wrote:
>
>
>
> A few years ago, I made an input power, vs. output power, graph of the
> KPA500 I own.  It is located at:
>
> https://www.nk7z.net/kpa500-input-vs-output-power/
> <https://www.nk7z.net/kpa500-input-vs-output-power/>
>
> That set of graph may be of some use in this matter.  Click any of the
> three graphs to expand that graph.
>
> 73, and thanks,
> Dave (NK7Z)
> https://www.nk7z.net <https://www.nk7z.net> ARRL Volunteer Examiner
> ARRL Technical Specialist, RFI ARRL Asst. Director, NW Division,
> Technical Resources
>
> On 10/19/21 6:35 AM, Mike Streeter via groups.io wrote:
>  > Hi Bob, thanks for your input. Yes, 40 watts is excessive, normal
> would  > be around 30 watts...
>
>
>
>
>
>












Dave W3NP
 

I have been following this thread because it appears that my KPA-500 has issues (6 meters is obvious).  After reading Bob K4TAX's response regarding driving power, there is now no doubt:

"Based on my KPA500, I would say that 40 watts of drive is excessive.    My amp drives to 500 watts, all bands,  with 18 to 22 watts of drive.   I suspect you have a failed component or a bad solder joint in the band pass filter for that band."   ------- My driving power has never been that low on any band.    

The following chart was made with only a 50.3 ohm non-inductive load connected directly to the amplifier output - nothing else in line.  The results with the DL are identical to those using my normal antenna systems.


Results are the same whether using my K3 or Omni VII as an exciter.  Driven to ~500 watts output.


HV idles at 75 volts and drops to ~60.5 - 62.0 depending on band.


The 6 meter issue began shortly after installing a M2 3 ele 6 meter yagi this past spring. Things were fine at first then suddenly began to get the PA DISS fault at increasingly lower drive/output levels. 350 at first, now down to only 150 watts out.

Most recently I noticed that on 15 meters CW the fan speed would ramp up much sooner than normal (that's what caught my attention) and the current draw was the highest of any band.  20 meters has always been an issue with early heat rise and it has been that way since I assembled the amp in 2014. I talked to Elecraft back then and they didn't seem to see it as a problem.


I am going to send this info to Elecraft but just wanted to chime in on the discussion and share my data since my problems are somewhat similar.


Band - Drive - Current


160 -    26 -     11.2

80  -     26 -     10.6

40  -     33 -     11.2

20 -     38 -     14.9

17 -     37 -     15.5

15 -     35 -     16.0

12 -     30 -     13.3

10 -     29 -     13.1

6 -       12 -     <11.2   Faults(PA DISS) at 11.2A or above with only 150 watts output.

73, Dave - W3NP



On 10/19/2021 12:07 PM, Mike Streeter via groups.io wrote:
I don't want to contact Elecraft unless I really have to, I'm sure they are very busy these days.
On 10/19/2021 3:13 PM, Jim Brown wrote:
I strongly suggest that you do -- it's one of the major advantages of buying from companies located here. From your symptoms, it does look like something has failed.

73, Jim K9YC