Posted by
Doug Turnbull on
Aug 29, 2019; 9:53pm
URL: http://elecraft.85.s1.nabble.com/KPA-1500-on-digital-modes-tp7654828p7654857.html
Dear OMs and YLs,
Remember that a small reduction in power, current or voltage for most
electronic components gives a manifold increase in reliability. Not only
is it better for other users but I will bet the KPA1500 is a lot happier
(more reliable) for a 20% drop in output power which is memory serves me
right is about 1 dB drop in signal strength.
73 Doug EI2CN
-----Original Message-----
From:
[hidden email]
[mailto:
[hidden email]] On Behalf Of Dave
Sent: 29 August 2019 18:13
To: David Gilbert
Cc:
[hidden email]
Subject: Re: [Elecraft] KPA-1500 on digital modes
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.
Dave wo2x
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%.
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