http://elecraft.85.s1.nabble.com/Elecraft-KPA500-vs-Tokyo-Hy-Power-1-1Kfx-tp7561226p7561241.html
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
capabilities are similar, why would one use 2 or 4 devices. I merely
4 devices. Was he right or wrong? Probably neither. As I indicated
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
> > 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
>>>
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