[Elecraft] KPA1500 Solution to the efficiency problem?

[N4ZR]

There also seems to be some real-world question.  I've been operating 
the WW Digi contest this morning, and find that running at 500 watts out 
vs 1500 watts out,with similar sequences of transmissions there is about 
a 10-degree difference in temperature as reported by the amp.

73, Pete N4ZR
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On 8/31/2019 10:15 AM, Roger D Johnson wrote:
> I think I've discovered a fly in my ointment! The efficiency
> that the amp displays is based on it's determination of the
> output power. If the amp is looking into a higher Z load,
> the indicated power is greater than normal resulting in a
> higher efficiency reading.
>
> Oh well, back to the drawing board!
>
> 73, Roger
>
>
> On 8/31/2019 9:32 AM, Roger D Johnson wrote:
>> It occurred to me that the KPA1500's built in tuner might be of
>> some help.
>>
>> Here's my reasoning. If we decrease the drive power to lessen
>> the output power but keep the same voltage, the amplifier wants
>> to see a higher load impedance.
>>
>> Here are the results of some quick tests:
>>
>> Base line is the amp set for 1000 watts output and eff is 44%
>>
>> I the set the tuner so the amp "sees" a load of 60 Ohms (actually)
>> 58 Ohms with the values of L and C available. Eff went up to 53%!
>>
>> I then set the tuner to present a 70 Ohm load (actually 68 Ohms).
>> Eff went up to 59%!
>>
>> This was into a dummy load. I realize that, if you're using the tuner
>> to match an antenna, this could be very complicated.
>>
>> If Elecraft could figure some way to give us a choice of voltages
>> for differing power levels, this problem would go away.
>>
>> 73, Roger
>>
>>
>>
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