http://elecraft.85.s1.nabble.com/Elecraft-KPA500-vs-Tokyo-Hy-Power-1-1Kfx-tp7561226p7561243.html
less critical. On the other hand, four FETs instead of two makes the
... Joe, W4TV
> 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
>>>>
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