KPA-1500 on digital modes

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KPA-1500 on digital modes

N4ZR
Elecraft's published specs rate the KPA-1500 for 1500 watts output on
all modes.  In prepping for this weekend's contest, I've been running it
at closer to 700 watts, because I've found that even just running on CW,
with its much lower duty cycle, my amp reaches 70C quickly.  I don't do
that much digital contesting, though, so I'm wondering whether 1500
watts output is on digital modes is realistic or a recipe for trouble.

--

73, Pete N4ZR
Check out the Reverse Beacon Network
at <http://reversebeacon.net>, now
spotting RTTY activity worldwide.
For spots, please use your favorite
"retail" DX cluster.

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Re: KPA-1500 on digital modes

Larry Gauthier (K8UT)
Pete,

I don't run my amp at full legal limit on digital modes, but typically set the input power for about 1000 watts output. One of the interesting characteristics of the amp is increased efficiency as power increases. At 600 watts efficiency is only 38%, whereas at 1000 efficiency increases to 50% and at 1500 watts to 60%.

(see screenshots)

  -larry (K8UT)

------ Original Message ------
From: "N4ZR" <[hidden email]>
To: "Elecraft List" <[hidden email]>
Sent: 2019-08-29 07:59:23
Subject: [Elecraft] KPA-1500 on digital modes

>Elecraft's published specs rate the KPA-1500 for 1500 watts output on all modes.  In prepping for this weekend's contest, I've been running it at closer to 700 watts, because I've found that even just running on CW, with its much lower duty cycle, my amp reaches 70C quickly.  I don't do that much digital contesting, though, so I'm wondering whether 1500 watts output is on digital modes is realistic or a recipe for trouble.
>
>--
>73, Pete N4ZR
>Check out the Reverse Beacon Network
>at <http://reversebeacon.net>, now
>spotting RTTY activity worldwide.
>For spots, please use your favorite
>"retail" DX cluster.
>
>______________________________________________________________
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KPA-1500 on digital modes

ANDY DURBIN
In reply to this post by N4ZR
"Elecraft's published specs rate the KPA-1500 for 1500 watts output on all modes.  In prepping for this weekend's contest, I've been running it at closer to 700 watts, because I've found that even just running on CW, with its much lower duty cycle, my amp reaches 70C quickly. "

You seem to be assuming that the KPA1500 will run hotter at 1,500 W output than it does at 700 W output.   I have no data for the KPA1500 but my data for the KPA500 show peak heating is at about 250 W RF output.   If the KPA1500 is similar then 700 W RF output will be close to worst case heating.

If you want to reduce heating then ensuring the load is as well matched as possible may be more productive than running at reduced power output.

73,
Andy, k3wyc




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Re: KPA-1500 on digital modes

Roger D Johnson
In reply to this post by Larry Gauthier (K8UT)
It's interesting that the heat that has to be dissipated is pretty close
to 1000 watts in all these scenarios! Running the amp at less than full
power buys you nothing.

73, Roger


On 8/29/2019 8:38 AM, Larry (K8UT) wrote:

> Pete,
>
> I don't run my amp at full legal limit on digital modes, but typically set the
> input power for about 1000 watts output. One of the interesting characteristics
> of the amp is increased efficiency as power increases. At 600 watts efficiency
> is only 38%, whereas at 1000 efficiency increases to 50% and at 1500 watts to 60%.
>
> (see screenshots)
>
>   -larry (K8UT)
>
> ------ Original Message ------
> From: "N4ZR" <[hidden email]>
> To: "Elecraft List" <[hidden email]>
> Sent: 2019-08-29 07:59:23
> Subject: [Elecraft] KPA-1500 on digital modes
>
>> Elecraft's published specs rate the KPA-1500 for 1500 watts output on all
>> modes.  In prepping for this weekend's contest, I've been running it at closer
>> to 700 watts, because I've found that even just running on CW, with its much
>> lower duty cycle, my amp reaches 70C quickly.  I don't do that much digital
>> contesting, though, so I'm wondering whether 1500 watts output is on digital
>> modes is realistic or a recipe for trouble.
>>
>> --
>> 73, Pete N4ZR
>> Check out the Reverse Beacon Network
>> at <http://reversebeacon.net>, now
>> spotting RTTY activity worldwide.
>> For spots, please use your favorite
>> "retail" DX cluster.
>>
>> ______________________________________________________________
>> Elecraft mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:[hidden email]
>>
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>> Message delivered to [hidden email]
>
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Re: KPA-1500 on digital modes

David Gilbert

This was discussed here not long ago, and it is normal for any linear
amplifier.  It needs to be biased up to be linear, and that bias energy
ends up as heat even if you don't use it.

I worked as a component engineer at Collins Radio in Cedar Rapids when I
first got out of college.  One of the low level RF stages (or IF stage,
I don't remember for sure) in several of their receivers used a
stud-mounted RF power transistor biased up hard enough to discolor them.

73,
Dave   AB7E


On 8/29/2019 6:03 AM, Roger D Johnson wrote:

> It's interesting that the heat that has to be dissipated is pretty close
> to 1000 watts in all these scenarios! Running the amp at less than full
> power buys you nothing.
>
> 73, Roger
>
>
> On 8/29/2019 8:38 AM, Larry (K8UT) wrote:
>> Pete,
>>
>> I don't run my amp at full legal limit on digital modes, but
>> typically set the input power for about 1000 watts output. One of the
>> interesting characteristics of the amp is increased efficiency as
>> power increases. At 600 watts efficiency is only 38%, whereas at 1000
>> efficiency increases to 50% and at 1500 watts to 60%.
>>
>> (see screenshots)
>>
>>   -larry (K8UT)

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Re: KPA-1500 on digital modes

Dave wo2x
They bias the LDMOS devices at 1 amp each. That is minimal in overall heat when you are pulling over 40 amps at high power.

Dave wo2x

Sent from my waxed string and tin cans.

> On Aug 29, 2019, at 1:29 PM, David Gilbert <[hidden email]> wrote:
>
>
> This was discussed here not long ago, and it is normal for any linear amplifier.  It needs to be biased up to be linear, and that bias energy ends up as heat even if you don't use it.
>
> I worked as a component engineer at Collins Radio in Cedar Rapids when I first got out of college.  One of the low level RF stages (or IF stage, I don't remember for sure) in several of their receivers used a stud-mounted RF power transistor biased up hard enough to discolor them.
>
> 73,
> Dave   AB7E
>
>
>> On 8/29/2019 6:03 AM, Roger D Johnson wrote:
>> It's interesting that the heat that has to be dissipated is pretty close
>> to 1000 watts in all these scenarios! Running the amp at less than full
>> power buys you nothing.
>>
>> 73, Roger
>>
>>
>>> On 8/29/2019 8:38 AM, Larry (K8UT) wrote:
>>> Pete,
>>>
>>> I don't run my amp at full legal limit on digital modes, but typically set the input power for about 1000 watts output. One of the interesting characteristics of the amp is increased efficiency as power increases. At 600 watts efficiency is only 38%, whereas at 1000 efficiency increases to 50% and at 1500 watts to 60%.
>>>
>>> (see screenshots)
>>>
>>>   -larry (K8UT)
>
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KPA-1500 on digital modes

ANDY DURBIN
In reply to this post by N4ZR
"They bias the LDMOS devices at 1 amp each. That is minimal in overall heat when you are pulling over 40 amps at high power. "

You beat me to it.  My KPA500,  keyed but with no RF input, showed 0.5 A at 76.7 V.  That's only 38 W which is a small part of the 400 W plus PA dissipation seen in some operating conditions.

All my measurements of PA dissipation take PA DC input and subtract RF output so my data include dissipation in the LPF.  It would be interesting to separate  the dissipation in the finals from the dissipation in the LPF but I don't know how to do that without modifying the amplifier.

73,
Andy, k3wyc
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Re: KPA-1500 on digital modes

John Simmons
No one has mentioned amplifier efficiency at differing power levels.

-John NI0K

Andy Durbin wrote:

> "They bias the LDMOS devices at 1 amp each. That is minimal in overall heat when you are pulling over 40 amps at high power."
>
> You beat me to it.  My KPA500,  keyed but with no RF input, showed 0.5 A at 76.7 V.  That's only 38 W which is a small part of the 400 W plus PA dissipation seen in some operating conditions.
>
> All my measurements of PA dissipation take PA DC input and subtract RF output so my data include dissipation in the LPF.  It would be interesting to separate  the dissipation in the finals from the dissipation in the LPF but I don't know how to do that without modifying the amplifier.
>
> 73,
> Andy, k3wyc
> ______________________________________________________________
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Re: KPA-1500 on digital modes

Bob McGraw - K4TAX
My KPA500 runs from a low of 35% to a high of 55% depending on power.  
Lower power is least efficient.   Thus I always run close or at maximum
rated power.    Also the load impedance will affect efficiency.

73

Bob, K4TAX

On 8/29/2019 2:04 PM, John Simmons wrote:

> No one has mentioned amplifier efficiency at differing power levels.
>
> -John NI0K
>
> Andy Durbin wrote:
>> "They bias the LDMOS devices at 1 amp each. That is minimal in
>> overall heat when you are pulling over 40 amps at high power."
>>
>> You beat me to it.  My KPA500,  keyed but with no RF input, showed
>> 0.5 A at 76.7 V.  That's only 38 W which is a small part of the 400 W
>> plus PA dissipation seen in some operating conditions.
>>
>> All my measurements of PA dissipation take PA DC input and subtract
>> RF output so my data include dissipation in the LPF. It would be
>> interesting to separate  the dissipation in the finals from the
>> dissipation in the LPF but I don't know how to do that without
>> modifying the amplifier.
>>
>> 73,
>> Andy, k3wyc
>> ______________________________________________________________
>> Elecraft mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>> Help: http://mailman.qth.net/mmfaq.htm
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>>
>> 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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KPA-1500 on digital modes

ANDY DURBIN
In reply to this post by N4ZR
"No one has mentioned amplifier efficiency at differing power levels."

I  have for the KPA500 and I have provided links to test data.   I would expect the KPA1500 to have similar characteristics but I'd like to see equivalent test data for it.

73,
Andy, k3wyc



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Re: KPA-1500 on digital modes

Bill K9YEQ
I don't believe this is a class C amp.  We should discuss the relevance of different classes of operation of amps, and let's be honest... it will be most efficient at max output regardless of class  I believe.

73,
Bill
K9YEQ

https://wrj-tech.com/

-----Original Message-----
From: [hidden email] <[hidden email]> On Behalf Of Andy Durbin
Sent: Thursday, August 29, 2019 2:57 PM
To: [hidden email]
Subject: [Elecraft] KPA-1500 on digital modes

"No one has mentioned amplifier efficiency at differing power levels."

I  have for the KPA500 and I have provided links to test data.   I would expect the KPA1500 to have similar characteristics but I'd like to see equivalent test data for it.

73,
Andy, k3wyc



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Re: KPA-1500 on digital modes

Roger D Johnson
In reply to this post by Roger D Johnson
I just did a quick check:

At 1500 watts eff is 56% and pwr diss is 1179 watts
    1000              44                  1273
     500              30                  1120

My Expert 1.3K-FA had 3 voltage levels:

48 volts for full power (1300 watts)
38           800 watts
32           450

I no longer have the amp so I can't check the eff at those
voltages and power levels.

73, Roger


On 8/29/2019 9:03 AM, Roger D Johnson wrote:
> It's interesting that the heat that has to be dissipated is pretty close
> to 1000 watts in all these scenarios! Running the amp at less than full
> power buys you nothing.
>
> 73, Roger
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Re: KPA-1500 on digital modes

turnbull
In reply to this post by Dave wo2x
Dear OMs and YLs,
     Remember that a small reduction in power, current or voltage for most
electronic components gives a manifold increase in reliability.   Not only
is it better for other users but I will bet the KPA1500 is a lot happier
(more reliable) for a 20% drop in output power which is memory serves me
right is about 1 dB drop in signal strength.

               73 Doug EI2CN

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of Dave
Sent: 29 August 2019 18:13
To: David Gilbert
Cc: [hidden email]
Subject: Re: [Elecraft] KPA-1500 on digital modes

They bias the LDMOS devices at 1 amp each. That is minimal in overall heat
when you are pulling over 40 amps at high power.

Dave wo2x

Sent from my waxed string and tin cans.

> On Aug 29, 2019, at 1:29 PM, David Gilbert <[hidden email]>
wrote:
>
>
> This was discussed here not long ago, and it is normal for any linear
amplifier.  It needs to be biased up to be linear, and that bias energy ends
up as heat even if you don't use it.
>
> I worked as a component engineer at Collins Radio in Cedar Rapids when I
first got out of college.  One of the low level RF stages (or IF stage, I
don't remember for sure) in several of their receivers used a stud-mounted
RF power transistor biased up hard enough to discolor them.

>
> 73,
> Dave   AB7E
>
>
>> On 8/29/2019 6:03 AM, Roger D Johnson wrote:
>> It's interesting that the heat that has to be dissipated is pretty close
>> to 1000 watts in all these scenarios! Running the amp at less than full
>> power buys you nothing.
>>
>> 73, Roger
>>
>>
>>> On 8/29/2019 8:38 AM, Larry (K8UT) wrote:
>>> Pete,
>>>
>>> I don't run my amp at full legal limit on digital modes, but typically
set the input power for about 1000 watts output. One of the interesting
characteristics of the amp is increased efficiency as power increases. At
600 watts efficiency is only 38%, whereas at 1000 efficiency increases to
50% and at 1500 watts to 60%.

>>>
>>> (see screenshots)
>>>
>>>   -larry (K8UT)
>
> ______________________________________________________________
> Elecraft mailing list
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Re: KPA-1500 on digital modes

Larry Gauthier (K8UT)
In reply to this post by Roger D Johnson
If my efficiency screenshots from earlier did not get through the
reflector, you can see the results in a JPG file here:

https://hamprojects.info/hamprojects-download-page/#elf_l1_b3RoZXJz


-larry (K8UT)

------ Original Message ------
From: "Roger D Johnson" <[hidden email]>
To: "Elecraft List" <[hidden email]>
Sent: 2019-08-29 17:44:05
Subject: Re: [Elecraft] KPA-1500 on digital modes

>I just did a quick check:
>
>At 1500 watts eff is 56% and pwr diss is 1179 watts
>    1000              44                  1273
>     500              30                  1120
>
>My Expert 1.3K-FA had 3 voltage levels:
>
>48 volts for full power (1300 watts)
>38           800 watts
>32           450
>
>I no longer have the amp so I can't check the eff at those
>voltages and power levels.
>
>73, Roger
>
>
>On 8/29/2019 9:03 AM, Roger D Johnson wrote:
>>It's interesting that the heat that has to be dissipated is pretty close
>>to 1000 watts in all these scenarios! Running the amp at less than full
>>power buys you nothing.
>>
>>73, Roger
>______________________________________________________________
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Re: KPA-1500 on digital modes

Nr4c
In reply to this post by Bob McGraw - K4TAX
Yes. It has been mentioned on this list that the KPA500 is designed to be most efficient at 500 Watts and running at lower power does not mean saving the amp.

Sent from my iPhone
...nr4c. bill


> On Aug 29, 2019, at 3:11 PM, Bob McGraw K4TAX <[hidden email]> wrote:
>
> My KPA500 runs from a low of 35% to a high of 55% depending on power.   Lower power is least efficient.   Thus I always run close or at maximum rated power.    Also the load impedance will affect efficiency.
>
> 73
>
> Bob, K4TAX
>
>> On 8/29/2019 2:04 PM, John Simmons wrote:
>> No one has mentioned amplifier efficiency at differing power levels.
>>
>> -John NI0K
>>
>> Andy Durbin wrote:
>>> "They bias the LDMOS devices at 1 amp each. That is minimal in overall heat when you are pulling over 40 amps at high power."
>>>
>>> You beat me to it.  My KPA500,  keyed but with no RF input, showed 0.5 A at 76.7 V.  That's only 38 W which is a small part of the 400 W plus PA dissipation seen in some operating conditions.
>>>
>>> All my measurements of PA dissipation take PA DC input and subtract RF output so my data include dissipation in the LPF. It would be interesting to separate  the dissipation in the finals from the dissipation in the LPF but I don't know how to do that without modifying the amplifier.
>>>
>>> 73,
>>> Andy, k3wyc
>>> ______________________________________________________________
>>> 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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Re: KPA-1500 on digital modes

john@kk9a.com
In reply to this post by N4ZR
It would be interesting to know the efficiency of the Expert amp at  
various voltage/power levels.

John KK9A



Roger D Johnson n1rj wrote:

I just did a quick check:

At 1500 watts eff is 56% and pwr diss is 1179 watts
     1000              44                  1273
      500              30                  1120

My Expert 1.3K-FA had 3 voltage levels:

48 volts for full power (1300 watts)
38           800 watts
32           450

I no longer have the amp so I can't check the eff at those
voltages and power levels.

73, Roger

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Re: KPA-1500 on digital modes

K9MA
In reply to this post by Roger D Johnson
This is nothing unique to the KPA1500: ALL class AB amplifiers behave
this way. Even an "ideal" class AB amplifier has a maximum dissipation
at around half of full output.

One thing running at lower output probably will buy you is lower IMD.

73,
Scott K9MA



On 8/29/2019 08:03, Roger D Johnson wrote:

> It's interesting that the heat that has to be dissipated is pretty close
> to 1000 watts in all these scenarios! Running the amp at less than full
> power buys you nothing.
>
> 73, Roger
>
>
> On 8/29/2019 8:38 AM, Larry (K8UT) wrote:
>> Pete,
>>
>> I don't run my amp at full legal limit on digital modes, but
>> typically set the input power for about 1000 watts output. One of the
>> interesting characteristics of the amp is increased efficiency as
>> power increases. At 600 watts efficiency is only 38%, whereas at 1000
>> efficiency increases to 50% and at 1500 watts to 60%.
>>
>> (see screenshots)
>>
>>   -larry (K8UT)
>>
>> ------ Original Message ------
>> From: "N4ZR" <[hidden email]>
>> To: "Elecraft List" <[hidden email]>
>> Sent: 2019-08-29 07:59:23
>> Subject: [Elecraft] KPA-1500 on digital modes
>>
>>> Elecraft's published specs rate the KPA-1500 for 1500 watts output
>>> on all modes.  In prepping for this weekend's contest, I've been
>>> running it at closer to 700 watts, because I've found that even just
>>> running on CW, with its much lower duty cycle, my amp reaches 70C
>>> quickly.  I don't do that much digital contesting, though, so I'm
>>> wondering whether 1500 watts output is on digital modes is realistic
>>> or a recipe for trouble.
>>>
>>> --
>>> 73, Pete N4ZR
>>> Check out the Reverse Beacon Network
>>> at <http://reversebeacon.net>, now
>>> spotting RTTY activity worldwide.
>>> For spots, please use your favorite
>>> "retail" DX cluster.
>>>
>>> ______________________________________________________________
>>

--
Scott  K9MA

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Re: KPA-1500 on digital modes

Jim Brown-10
On 8/31/2019 3:04 PM, K9MA wrote:
> This is nothing unique to the KPA1500: ALL class AB amplifiers behave
> this way. Even an "ideal" class AB amplifier has a maximum dissipation
> at around half of full output.

Yep. These concepts were taught in my EE courses in the early '60s.

73, Jim K9YC
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Re: KPA-1500 on digital modes

Jim Brown-10
On 8/31/2019 6:02 PM, Roger D Johnson wrote:
> If you design a different class AB amplifier for half the output
> of the previous amplifier don't you design it to produce the desired
> output into a certain load impedance? Would it not be as efficient
> as the first amplifier running at it's designed output?
>
> So if you redesigned the first amplifier to see the proper load
> impedance at half output would not the efficiency be regained?

In general, RF power gain stages (the tubes or transistors) are designed
to work at some designed power level and impedance. Pi and Pi-L networks
in tube amps provide both harmonic filtering and impedance matching. In
most solid state amps, the output network provides only filtering, and
are designed to work into 50 ohms.

K6XX, one of the Elecraft engineers who works on their power amps, gave
a talk to our contest club stressing the importance of providing a
matched load to the output devices, and to the output itself. He
observed distortion increases significantly when that condition is
satisfied, whether it is an antenna tuner for a solid state output stage
or the Pi or Pi-L in a tube amp.

>
> Isn't this exactly the way some of the first ham linears were designed
> for an input of 2000 watts in SSB and 1000 watts in CW? There
> was a switch on the front panel for SSB/CW mode which dropped
> the plate voltage for CW mode so that the tubes saw the same
> load impedance they did in SSB mode thereby keeping the efficiency
> high and not requiring retuning between modes.

I don't know, but you could ask K4XU, who designed the Ten Tec power
amps and later the RF circuitry in Alpha amps. He told me the 87A was
his design (although he made it clear that he did NOT work on the
control circuitry).

73, Jim K9YC

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Re: KPA-1500 on digital modes

Michael Walker
Just a reminder to Canadians running the KPA1500 or any other full power
amp in the contest this weekend.

Max RF out is limited to 750 watts (not our usual 2250w PEP for SSB).  Only
CW and SSB get to go above 750 watts.

Mike va3mw
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