http://elecraft.85.s1.nabble.com/KPA-1500-on-digital-modes-tp7654828p7654847.html
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.
Sent from my waxed string and tin cans.
> On Aug 29, 2019, at 1:29 PM, David Gilbert <
[hidden email]> wrote:
>
>
> This was discussed here not long ago, and it is normal for any linear amplifier. It needs to be biased up to be linear, and that bias energy ends up as heat even if you don't use it.
>
> I worked as a component engineer at Collins Radio in Cedar Rapids when I first got out of college. One of the low level RF stages (or IF stage, I don't remember for sure) in several of their receivers used a stud-mounted RF power transistor biased up hard enough to discolor them.
>
> 73,
> Dave AB7E
>
>
>> On 8/29/2019 6:03 AM, Roger D Johnson wrote:
>> It's interesting that the heat that has to be dissipated is pretty close
>> to 1000 watts in all these scenarios! Running the amp at less than full
>> power buys you nothing.
>>
>> 73, Roger
>>
>>
>>> On 8/29/2019 8:38 AM, Larry (K8UT) wrote:
>>> Pete,
>>>
>>> I don't run my amp at full legal limit on digital modes, but typically set the input power for about 1000 watts output. One of the interesting characteristics of the amp is increased efficiency as power increases. At 600 watts efficiency is only 38%, whereas at 1000 efficiency increases to 50% and at 1500 watts to 60%.
>>>
>>> (see screenshots)
>>>
>>> -larry (K8UT)
>
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