[sdiy] Heat Paste/Compound

[Happy Harry]

Hi Terry:

I (semi) disagree...

The thermal mass of the big block of epoxy does two
things...

It shields you from air drafts, a BIG problem...

It makes the rate of temperature change very slow.
You don't heat of cool the large mass at a high rate..

so not only are you protected from the wind... even
when you do drift it will have to be slowly.

NOW OTOH: I notice that my Aries had the SCHEMATIC
of the potted block section removed. Now THAT IS
trying to protect the design.

H^) harry


>From: Terry Michaels <104065.2340 at compuserve.com>
>To: "INTERNET:djblue at graffiti.net" <djblue at graffiti.net>,   synth 
><synth-diy at node12b53.a2000.nl>
>Subject: [sdiy] Heat Paste/Compound
>Date: Wed, 14 Mar 2001 08:02:12 -0500
>
>Message text written by INTERNET:djblue at graffiti.net
> >and... what would people recommend... I'm
>pasting a tempco to a tranny-pair...
>
>thanks.
>-ben.<
>
>Hi Ben:
>
>IMHO, any type of heat sink compound will do the job.  The tempco resistor
>compensates the expo transistor scale factor, and the compensation will be
>less than perfect if the tempco and the expo transistors are at different
>temperatures, however the heat dissipated in these devices is very small,
>probably in the microwatt range, so the temperature differential will be
>very small with the use of almost any type of heat sink compound.   It
>should take only a small amount of thermal conductance to equalize the
>temperatures.
>
>You could make a good case for using a dab of epoxy between the devices to
>create a permanent mechanical bond between them.  After all, silicone
>grease could dry out and fall away after a long time, so you might
>eventually lose some thermal conductance.
>
>This is quite a different situation than putting a power transistor on a
>heat sink and running a hundred or so watts into it, in that case you want
>the best possible heat transfer to minimize the temperature rise in the
>power transistor.
>
>ARP used to put their VCO's and other circuits in blocks of epoxy
>supposedly for better heat transfer, but that was way overkill.  I'm sure
>they did it only to prevent people like us from reverse engineering their
>circuitry.
>
>Terry Michaels

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