[hpsdr] Fwd: Re: Munin - Heat Spreader under Final Transistors...

[n3evl]

-------- Original Message --------
Subject: 	Re: [hpsdr] Munin - Heat Spreader under Final Transistors...
Date: 	Sat, 28 Jul 2012 12:33:47 -0400
From: 	n3evl <n3evl at townisp.com>
To: 	Kjell Karlsen <la2ni at online.no>



Thanks for all the responses.  It looks like there are a variety of
techniques that have been employed for the various Munin boards that
have been built so far - I think this is due to the fact that there are
different heat sink designs being used.

I have one of the heat sinks provided by Tim O'Rourke, W4YN.  This style
has the milled area that allows the pair of driver transistors to sit
lower while allowing the PA transistors to mate directly to the surface
of the aluminum thus giving good heat transfer so I don' t think a heat
spreader is needed with this design.

Pete, N3EVL




On 7/28/2012 3:10 AM, Kjell Karlsen wrote:
> Hi Pete.
>
> I agree with Bob about the heat transfer with the copper bar.
>
> Another reason to use ta 3-4 mm thick bar is to lift the PCB so that the
> leads of the PA transistors are leveled with the top of the PCB. The
> driver transistor now can be installed so that the PCB is parallel
> with the sink.
>
> I am at my summer house at the moment working with the antenna park.
> My plan is to have a HPSDR transceiver here and control it remotely
> from home. The noise level is up to 20 dB better than in town,
> especially on 160 and 80 meter.
>
> 73, Kjell
>
>
> På Fri, 27 Jul 2012 23:54:22 +0200, skrev Bob G Mahrenholz
> <bobm at edge.net>:
>
>> ***** High Performance Software Defined Radio Discussion List *****
>>
>> Hi Pete,
>>
>> I bought a 4" piece of 1/8" x 1-1/4" copper bar from Speedy Metals LLC
>> to put under the output transistors to conduct to my heat sink. It works
>
>> great! The transistors really run cool to the touch but the heat sink
>> gets quite warm. This was their CA 110 copper bar which they sell by
>> the inch.
>>
>> I got one of Communication Concepts 12" heat sinks so I wouldn't have to
>
>> listen to a fan and it works.
>>
>> I used RadioShack's 28-1099 Thermal Compound between the transistors and
>
>> the copper bar and between the copper bar and the heatsink.
>>
>> The piece of copper bar was only $4.60 but the freight cost me $17.30!
>> I don't have Speedy Metals LLC webb address right off hand but their
>> E-mail is joe_f at speedymetals.com and their phone is 262-784-4140.
>>
>> 73,
>> Bob, K4QQK
>>
>> -----Original Message-----
>>> From: n3evl <n3evl at townisp.com>
>>> Sent: Jul 27, 2012 1:08 PM
>>> To: HPSDR list <hpsdr at lists.openhpsdr.org>
>>> Subject: [hpsdr] Munin - Heat Spreader under Final Transistors...
>>>
>>> ***** High Performance Software Defined Radio Discussion List *****
>>>
>>> I'm nearing completion of my Munin amp and recall reading some postings
>
>>> about the possible need for a copper heat spreader between the
>>> bottom of
>>> the finals and the aluminum heat sink.  My question is - how essential
>>> is it to place something here?
>>>
>>> I have some sheet copper in my junk box that is ~1mm thick so I could
>
>>> cut a piece to sit under the finals and attach it to the heat sink
>>> if it
>>> is thought to be necessary.  Maybe this sheet stock is too thin to make
>
>>> much difference.
>>>
>>> Any thoughts/ideas appreciated.
>>>
>>> 73, Pete, N3EVL
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>
>




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