My K2/100 is up and running, first go :)

[James Cutler]

Just a quick note to say that I have built the KPA100 and installed and
aligned it, and it is working fine on all bands. When I built my K2 at
the beginning of the year, it also worked fine, and still is. I have to
say that over all, I am happy with the radio, and it's performance.

I have one query though, I am wondering why Elecraft have opted to use
thermal pads on the PA transistors in the KPA100 as opposed to heat
paste? (A lot of linear amplifiers that I have seen over the years use
thermal paste on the PA transistors without apparent problems.) I just
suspect that the thermal resistance of a thermal transfer pad may be
higher than that of thermal paste......please advise me if I am way off
on this point.

Cheers and 73 to all......

James Cutler,
VK2TIM

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[Matthew D. Pitts]

James,

My feeling is that since they were using that for the base K2, they felt
that it would be good enough for the KPA100; and it seems to have been true,
since I don't know of any failures that can be attributed to the thermal
pads. Just my two cents(US)

Matthew Pitts
N8OHU
K2 #5956

----- Original Message -----
From: "James Cutler" <[hidden email]>
To: <[hidden email]>
Sent: Thursday, July 26, 2007 7:41 PM
Subject: [Elecraft] My K2/100 is up and running, first go :)

> Just a quick note to say that I have built the KPA100 and installed and
> aligned it, and it is working fine on all bands. When I built my K2 at the
> beginning of the year, it also worked fine, and still is. I have to say
> that over all, I am happy with the radio, and it's performance.
>
> I have one query though, I am wondering why Elecraft have opted to use
> thermal pads on the PA transistors in the KPA100 as opposed to heat paste?
> (A lot of linear amplifiers that I have seen over the years use thermal
> paste on the PA transistors without apparent problems.) I just suspect
> that the thermal resistance of a thermal transfer pad may be higher than
> that of thermal paste......please advise me if I am way off on this point.
>
> Cheers and 73 to all......
>
> James Cutler,
> VK2TIM
>
> _______________________________________________
> Elecraft mailing list
> Post to: [hidden email]
> You must be a subscriber to post to the list.
> Subscriber Info (Addr. Change, sub, unsub etc.):
> http://mailman.qth.net/mailman/listinfo/elecraft
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> Elecraft web page: http://www.elecraft.com
>

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[Don Wilhelm-3]

James,

 From what I have read, it all depends on the kind of thermal compound
that is used.  If you rate them in terms of thermal conductivity only,
some are slightly better than the thermal pads and some are worse.
OTOH, if you rate thermal paste in terms of 'messiness', it is far, far
worse than the thermal pads.  With thermal paste there are several
variables - how thick a coating?, how much pressure on the mounting
screws? - yes with the thermal pads it is necessary to go back after 10
to 20 hours of operating at high power to snug the mounting screws down
again, but IMHO, that is a small price to pay for the 'neatness' and
repeatability of the thermal pads.

73,
Don W3FPR

James Cutler wrote:

> Just a quick note to say that I have built the KPA100 and installed and
> aligned it, and it is working fine on all bands. When I built my K2 at
> the beginning of the year, it also worked fine, and still is. I have to
> say that over all, I am happy with the radio, and it's performance.
>
> I have one query though, I am wondering why Elecraft have opted to use
> thermal pads on the PA transistors in the KPA100 as opposed to heat
> paste? (A lot of linear amplifiers that I have seen over the years use
> thermal paste on the PA transistors without apparent problems.) I just
> suspect that the thermal resistance of a thermal transfer pad may be
> higher than that of thermal paste......please advise me if I am way off
> on this point.

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