[Elecraft] KPA 1500 efficiency

[Dave]

I would be concerned about reducing voltage for SSB and TX IMD. The NXP 1K50H devices are only biased at 1 amp each which is a bit low for optimal IMD as it is. SSB IMD could be improved by increasing bias to 2 amps per device. Since the bias is only present during TX the waste heat increase would be negligible. 

The FLex Power Genius XL uses same RF devices and they use 2 amps per device @ 52 volts on SSB.  IMD at that spec on PG. L is very acceptable. 

I am sure there is a reason I am overlooking for the Elecraft engineers to adjust bias to 1 amp per device. 

Dave wo2x


Sent from my waxed string and tin cans. 

> On Nov 13, 2020, at 10:28 AM, Roy <k6xk at ncn.net> wrote:
> 
> Yes, I read the same. Lowering the PA voltage might be a bit difficult...
> 
> 73,   Roy    K6XK
> 
>> On 11/13/2020 8:27 AM, Howard Sherer wrote:
>> Reading the display on the KPA 1500 at various RF output levels shows an
>> efficiency as follows on 40M into a dummyload:
>> 
>> 
>> 300W   23%
>> 500W   27%
>> 1000W  42%
>> 1300W  48%
>> 1500W  52%
>> 1600W  54%
>> 
>> Have other owners seen results like this? Do you think a firmware and menu
>> item could be developed to increase the amps efficiency at lower power
>> levels by lowering the voltage to the PA?
>> ______________________________________________________________
>> 
> 
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