[Elecraft] [KX3][2M] Over heat question

[Chris Johnson]

OK Good to know.   I could not get all the way through a single radiogram on Olivia 1000/32 with an average transmit time of 2.5 minutes without it shutting down a hair after 2 minutes in.   I just installed all the SideKick panels and Fred's heatsink on my newest KX3 and will retry tonight.

Is there a reason why you chose 50mhz instead of 28mhz for the IF?   The KX3 is very inefficient on 6M it seems.

On Sep 16, 2014, at 7:50 AM, Wayne Burdick <n6kr at elecraft.com> wrote:

> On 2 meters, heating is divided between the HF power amplifier and the 2-meter power amplifier. I.F. drive for the 2-meter module is generated by the HF PA, which must still be biased class AB to ensure low distortion. While the HF PA is not putting out much power, it is reasonably heavily biased and will eventually heat up. This should take quite awhile, but it is not rated for key-down "forever," even in this instance.
> 
> 73,
> Wayne
> N6KR
> 
> On Sep 16, 2014, at 12:15 AM, Chris Johnson <elecraft at ozy.us> wrote:
> 
>> I participated in a local ARES net with my KX3/2M combo and a mirage B-310-G and B-34-G amps.  We were using Olivia 1000/32 using 2M verticals to pass traffic around the valley and Tucson testing various power levels.
>> 
>> Long story short,  these mirage amps work well but the 310 consumes 9 amps even when driven with .3 watts in / 30w out from the KX3-2M, and the B-34 uses a more field-use reasonable 3.9 amps when driven with 3 Watts In/ 20 watts out from the KX3.  The net current usage is more optimal with the KX3 + B34G, but using this combination the KX3 over heats and shuts off.   Here's where my confusion comes in.
>> 
>> The back of the KX3 where the primary FETs are were hot.   I was under the impression that the KX3 used a 50Mhz IF to drive the 2M module and the 2M FET on the side would be where the heat is generated, ultimately being the part that would overheat if driven too long.   But it seemed that the rear FETs were where the max heat was generated, ultimately resulting in a self protection shutdown.   Can I get some clarification on why this happened and what the drive level of the IF is?
>> 
>> I have a heat sink to install but have not done it yet.  I have two KX3's, and will likely make one my digital high-duty cycle KX3 if this is unavoidable at even 3W.  I have a 2M module in both KX3s.
>> 
>> https://www.flickr.com/photos/ozy311/15255424125/sizes/h/
>> 
>> Thank you ahead of time!
>> 
>> Chris
>> K6OZY
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