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Elecraft KPA500 vs Tokyo Hy-Power 1.1Kfx

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Elecraft KPA500 vs Tokyo Hy-Power 1.1Kfx

jsrobbins
I am wondering if anyone has an explanation for why the Elecraft  
KPA500 amplifier (500 watts) employs 2 VRF2933 FETs (Microsemi) in  
the final PA where the THP uses 4 ST2933 FETs (STMicroelectronics) to  
generate very similar power levels.  The data sheets for each FET  
indicate that both brands are rated at 300-400 watts, support similar  
mismatches and run at similar voltage maximums.  They have very  
similar specs all together.

Perhaps our amplifier gurus could weigh in here.  Much appreciated.

73,
Jim Robbins
N1JR

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Re: Elecraft KPA500 vs Tokyo Hy-Power 1.1Kfx

Fred Townsend
Jim I'm not sure what you are looking for here. It is highly desirable to
use parts with a second source. That way if the factory burns down you are
not put out of business. That being said with RF parts the second source is
seldom identical hence the reference to the manufacturer. Manufacturing
processes differ from factory to factory. Sometimes the difference will be
noise or something you will have to look at a Smith chart to see. This makes
it difficult to interchange.  

A major problem with using quads (two push-pull pairs) is current sharing.
If more current flows in one transistor than the others it will get hotter
and possibly be pushed beyond specifications leading to failure. Failures
may 'domino' leading to secondary failures. Fortunately FETs have a negative
coefficient of resistivity which makes them much easier to balance, hence
their popularity in newer amps.
73
Fred, AE6QL

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of Robbins, James
Sent: Friday, August 17, 2012 3:21 PM
To: [hidden email]
Subject: [Elecraft] Elecraft KPA500 vs Tokyo Hy-Power 1.1Kfx

I am wondering if anyone has an explanation for why the Elecraft
KPA500 amplifier (500 watts) employs 2 VRF2933 FETs (Microsemi) in the final
PA where the THP uses 4 ST2933 FETs (STMicroelectronics) to generate very
similar power levels.  The data sheets for each FET indicate that both
brands are rated at 300-400 watts, support similar mismatches and run at
similar voltage maximums.  They have very similar specs all together.

Perhaps our amplifier gurus could weigh in here.  Much appreciated.

73,
Jim Robbins
N1JR

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Re: Elecraft KPA500 vs Tokyo Hy-Power 1.1Kfx

David Christ
In reply to this post by jsrobbins
I myself am not qualified to judge the designs, but a friend of mine
with decades of design experience at Rockwell Collins has been saying
from the first revealing of the KPA500 design that he would have used
4 devices not two.  If I understand his comments it relates to
current density and voltage.  With only two of these devices he says
you either have to run the voltage too high or have the current
density too high in order to get 500 watts.  He does agree that the
KPA500 is a nice amp but that he would have made different choices.
He was designing military/aircraft gear and had to allow a big safety
margin.

Hopefully a real engineer can tell me if this makes any sense.

David K0LUM

At 6:20 PM -0400 8/17/12, Robbins, James wrote:

>I am wondering if anyone has an explanation for why the Elecraft
>KPA500 amplifier (500 watts) employs 2 VRF2933 FETs (Microsemi) in
>the final PA where the THP uses 4 ST2933 FETs (STMicroelectronics) to
>generate very similar power levels.  The data sheets for each FET
>indicate that both brands are rated at 300-400 watts, support similar
>mismatches and run at similar voltage maximums.  They have very
>similar specs all together.
>
>Perhaps our amplifier gurus could weigh in here.  Much appreciated.
>
>73,
>Jim Robbins
>N1JR
>
>______________________________________________________________
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>Home: http://mailman.qth.net/mailman/listinfo/elecraft
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>Post: mailto:[hidden email]
>
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Re: Elecraft KPA500 vs Tokyo Hy-Power 1.1Kfx

Joe Subich, W4TV-4

> With only two of these devices he says you either have to run the
> voltage too high or have the current density too high in order to get
> 500 watts.

Since the VRF2933 is *designed* for the current necessary to produce
300 W each with proper cooling, one can not say the current density
is "too high".  The THP design with its four ST2933 is effectively
the old Granberg 4xMRF150 amplifier and no different than an Ameritron
ALS-600 with more expensive FETs that are not being used to their full
capability.

 > He was designing military/aircraft gear and had to allow a big safety
 > margin.

The military can afford to pay for redundancy - particularly in mission
critical applications - but such overkill is wasteful in commercial and
amateur applications.

73,

    ... Joe, W4TV


On 8/17/2012 7:31 PM, David Christ wrote:

> I myself am not qualified to judge the designs, but a friend of mine
> with decades of design experience at Rockwell Collins has been saying
> from the first revealing of the KPA500 design that he would have used
> 4 devices not two.  If I understand his comments it relates to
> current density and voltage.  With only two of these devices he says
> you either have to run the voltage too high or have the current
> density too high in order to get 500 watts.  He does agree that the
> KPA500 is a nice amp but that he would have made different choices.
> He was designing military/aircraft gear and had to allow a big safety
> margin.
>
> Hopefully a real engineer can tell me if this makes any sense.
>
> David K0LUM
>
> At 6:20 PM -0400 8/17/12, Robbins, James wrote:
>> I am wondering if anyone has an explanation for why the Elecraft
>> KPA500 amplifier (500 watts) employs 2 VRF2933 FETs (Microsemi) in
>> the final PA where the THP uses 4 ST2933 FETs (STMicroelectronics) to
>> generate very similar power levels.  The data sheets for each FET
>> indicate that both brands are rated at 300-400 watts, support similar
>> mismatches and run at similar voltage maximums.  They have very
>> similar specs all together.
>>
>> Perhaps our amplifier gurus could weigh in here.  Much appreciated.
>>
>> 73,
>> Jim Robbins
>> N1JR
>>
>> ______________________________________________________________
>> 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
>
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>
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Re: Elecraft KPA500 vs Tokyo Hy-Power 1.1Kfx

David Christ
I think I was not clear and am possibly being misunderstood.  First,
I own a KPA500 and couldn't be happier.  Second, in no way am I
saying there is anything wrong with the KPA500 design.  The question
was if the power levels are the same and the individual device
capabilities are similar, why would one use 2 or 4 devices.  I merely
reported what one experienced designer told me would cause him to use
4 devices.  Was he right or wrong?  Probably neither.  As I indicated
he was used to designing for a different market with a different
cost/reliability model.  If you are cost driven you will run closer
to device maximums.  If you wish to go for long life and a lower
chance of failure you derate devices.



David K0LUM

At 8:10 PM -0400 8/17/12, Joe Subich, W4TV wrote:

>  > With only two of these devices he says you either have to run the
>>  voltage too high or have the current density too high in order to get
>>  500 watts.
>
>Since the VRF2933 is *designed* for the current necessary to produce
>300 W each with proper cooling, one can not say the current density
>is "too high".  The THP design with its four ST2933 is effectively
>the old Granberg 4xMRF150 amplifier and no different than an Ameritron
>ALS-600 with more expensive FETs that are not being used to their full
>capability.
>
>  > He was designing military/aircraft gear and had to allow a big safety
>  > margin.
>
>The military can afford to pay for redundancy - particularly in mission
>critical applications - but such overkill is wasteful in commercial and
>amateur applications.
>
>73,
>
>     ... Joe, W4TV
>
>
>On 8/17/2012 7:31 PM, David Christ wrote:
>>  I myself am not qualified to judge the designs, but a friend of mine
>>  with decades of design experience at Rockwell Collins has been saying
>>  from the first revealing of the KPA500 design that he would have used
>>  4 devices not two.  If I understand his comments it relates to
>>  current density and voltage.  With only two of these devices he says
>>  you either have to run the voltage too high or have the current
>>  density too high in order to get 500 watts.  He does agree that the
>>  KPA500 is a nice amp but that he would have made different choices.
>>  He was designing military/aircraft gear and had to allow a big safety
>>  margin.
>>
>>  Hopefully a real engineer can tell me if this makes any sense.
>>
>>  David K0LUM
>>
>>  At 6:20 PM -0400 8/17/12, Robbins, James wrote:
>>>  I am wondering if anyone has an explanation for why the Elecraft
>>>  KPA500 amplifier (500 watts) employs 2 VRF2933 FETs (Microsemi) in
>>>  the final PA where the THP uses 4 ST2933 FETs (STMicroelectronics) to
>>>  generate very similar power levels.  The data sheets for each FET
>>>  indicate that both brands are rated at 300-400 watts, support similar
>>>  mismatches and run at similar voltage maximums.  They have very
>>>  similar specs all together.
>>>
>>>  Perhaps our amplifier gurus could weigh in here.  Much appreciated.
>>>
>>>  73,
>>>  Jim Robbins
>>>  N1JR
>>>
>>>  ______________________________________________________________
>>>  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
>>
>>  ______________________________________________________________
>>  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
>>
>______________________________________________________________
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Re: Elecraft KPA500 vs Tokyo Hy-Power 1.1Kfx

Joe Subich, W4TV-4

> The question was if the power levels are the same and the individual
> device capabilities are similar, why would one use 2 or 4 devices.

Using four devices instead of two makes cooling system design somewhat
less critical.  On the other hand, four FETs instead of two makes the
biasing much more critical (current balance), makes transformer design
more difficult due to the higher capacitance involved and makes the
amplifier marginally less stable.

73,

    ... Joe, W4TV


On 8/17/2012 10:18 PM, David Christ wrote:

> I think I was not clear and am possibly being misunderstood.  First,
> I own a KPA500 and couldn't be happier.  Second, in no way am I
> saying there is anything wrong with the KPA500 design.  The question
> was if the power levels are the same and the individual device
> capabilities are similar, why would one use 2 or 4 devices.  I merely
> reported what one experienced designer told me would cause him to use
> 4 devices.  Was he right or wrong?  Probably neither.  As I indicated
> he was used to designing for a different market with a different
> cost/reliability model.  If you are cost driven you will run closer
> to device maximums.  If you wish to go for long life and a lower
> chance of failure you derate devices.
>
>
>
> David K0LUM
>
> At 8:10 PM -0400 8/17/12, Joe Subich, W4TV wrote:
>>   > With only two of these devices he says you either have to run the
>>>   voltage too high or have the current density too high in order to get
>>>   500 watts.
>>
>> Since the VRF2933 is *designed* for the current necessary to produce
>> 300 W each with proper cooling, one can not say the current density
>> is "too high".  The THP design with its four ST2933 is effectively
>> the old Granberg 4xMRF150 amplifier and no different than an Ameritron
>> ALS-600 with more expensive FETs that are not being used to their full
>> capability.
>>
>>   > He was designing military/aircraft gear and had to allow a big safety
>>   > margin.
>>
>> The military can afford to pay for redundancy - particularly in mission
>> critical applications - but such overkill is wasteful in commercial and
>> amateur applications.
>>
>> 73,
>>
>>      ... Joe, W4TV
>>
>>
>> On 8/17/2012 7:31 PM, David Christ wrote:
>>>   I myself am not qualified to judge the designs, but a friend of mine
>>>   with decades of design experience at Rockwell Collins has been saying
>>>   from the first revealing of the KPA500 design that he would have used
>>>   4 devices not two.  If I understand his comments it relates to
>>>   current density and voltage.  With only two of these devices he says
>>>   you either have to run the voltage too high or have the current
>>>   density too high in order to get 500 watts.  He does agree that the
>>>   KPA500 is a nice amp but that he would have made different choices.
>>>   He was designing military/aircraft gear and had to allow a big safety
>>>   margin.
>>>
>>>   Hopefully a real engineer can tell me if this makes any sense.
>>>
>>>   David K0LUM
>>>
>>>   At 6:20 PM -0400 8/17/12, Robbins, James wrote:
>>>>   I am wondering if anyone has an explanation for why the Elecraft
>>>>   KPA500 amplifier (500 watts) employs 2 VRF2933 FETs (Microsemi) in
>>>>   the final PA where the THP uses 4 ST2933 FETs (STMicroelectronics) to
>>>>   generate very similar power levels.  The data sheets for each FET
>>>>   indicate that both brands are rated at 300-400 watts, support similar
>>>>   mismatches and run at similar voltage maximums.  They have very
>>>>   similar specs all together.
>>>>
>>>>   Perhaps our amplifier gurus could weigh in here.  Much appreciated.
>>>>
>>>>   73,
>>>>   Jim Robbins
>>>>   N1JR
>>>>
>>>>   ______________________________________________________________
>>>>   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
>>>
>>>   ______________________________________________________________
>>>   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
>>>
>> ______________________________________________________________
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>> 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
>
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>
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>
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Re: Elecraft KPA500 vs Tokyo Hy-Power 1.1Kfx

Bob Henderson-2
In reply to this post by jsrobbins
Jim

The ST SD2933 and Microsemi VRF2933 are only superficially similar.

The key differentiator is drain source breakdown voltage, which for the
SD2933 is 130V but for the VRF2933 is typically 180V.

The THP 550fx was designed using SD2933 devices but failures were high.  I
have met several dead HL550fx amps on my trips to the Pacific.  The
THP1.1kfx is essentially the same amp.  THP now use devices marked
THP2933.  I can't say with absolute certainty but I believe these to be
VRF2933.

Running the VRF2933 from a 60V supply is a good idea.  Doing the same with
SD2933 isn't such a good one.

73 Bob, 5B4AGN



Date: Fri, 17 Aug 2012 18:20:39 -0400
From: "Robbins, James" <[hidden email]>
Subject: [Elecraft] Elecraft KPA500 vs Tokyo Hy-Power 1.1Kfx
To: [hidden email]
Message-ID: <[hidden email]>
Content-Type: text/plain; charset=US-ASCII; delsp=yes; format=flowed

I am wondering if anyone has an explanation for why the Elecraft
KPA500 amplifier (500 watts) employs 2 VRF2933 FETs (Microsemi) in
the final PA where the THP uses 4 ST2933 FETs (STMicroelectronics) to
generate very similar power levels.  The data sheets for each FET
indicate that both brands are rated at 300-400 watts, support similar
mismatches and run at similar voltage maximums.  They have very
similar specs all together.

Perhaps our amplifier gurus could weigh in here.  Much appreciated.

73,
Jim Robbins
N1JR
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Re: Elecraft KPA500 vs Tokyo Hy-Power 1.1Kfx

K9TWO
This post has NOT been accepted by the mailing list yet.
In reply to this post by jsrobbins
I promise you this, if Elecraft designed it, it will be right. They are in business to make good products
At a fair price. Failures would pur them out of business. I would have no reservations on buying any of their products.,I own a KPA500 amp and a P3 Panadapter which beats the pants off any others and requires no external computer. Can't go wrong with Elecraft.

73 Don Ferrill since 1959

P.s.  The KPA 500 has a linear power supply, not one of those cheap pink/white noise generating switching common mode supplies. Why do you think they have those large RF Chokes built inside? I have proven they make random noises that wipe out even strong signals. My FT-897D is unusable on 2 meters because of the build in switching supplies. They are trash, period..... I use two Yaesu Linear supplies to power my rigs.
Wish Elecraft would start making linear supplies also. You get what you pay for.

73 Don Ferrill.  K9TWO since 1959
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