Re: KPA-1500 on digital modes

Posted by Nr4c on Aug 30, 2019; 9:43am
URL: http://elecraft.85.s1.nabble.com/KPA-1500-on-digital-modes-tp7654828p7654863.html

Yes. It has been mentioned on this list that the KPA500 is designed to be most efficient at 500 Watts and running at lower power does not mean saving the amp.

Sent from my iPhone
...nr4c. bill

> On Aug 29, 2019, at 3:11 PM, Bob McGraw K4TAX <[hidden email]> wrote:
>
> My KPA500 runs from a low of 35% to a high of 55% depending on power.   Lower power is least efficient.   Thus I always run close or at maximum rated power.    Also the load impedance will affect efficiency.
>
> 73
>
> Bob, K4TAX
>
>> On 8/29/2019 2:04 PM, John Simmons wrote:
>> No one has mentioned amplifier efficiency at differing power levels.
>>
>> -John NI0K
>>
>> Andy Durbin wrote:
>>> "They bias the LDMOS devices at 1 amp each. That is minimal in overall heat when you are pulling over 40 amps at high power."
>>>
>>> You beat me to it.  My KPA500,  keyed but with no RF input, showed 0.5 A at 76.7 V.  That's only 38 W which is a small part of the 400 W plus PA dissipation seen in some operating conditions.
>>>
>>> All my measurements of PA dissipation take PA DC input and subtract RF output so my data include dissipation in the LPF. It would be interesting to separate  the dissipation in the finals from the dissipation in the LPF but I don't know how to do that without modifying the amplifier.
>>>
>>> 73,
>>> Andy, k3wyc
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