1PW "OneNpOeSnPuAtMwhistle att a0l dot calm" wrote in message
...
Ian Jackson wrote:
In message , Baron
writes
snip...snip
The question is "Is the thermal conductivity reduced when the grease
dries out?"
Some 30 years ago, in the lab where I worked, we did some comparative
tests on the effectiveness of thermal compound. We did the tests on a
TO3 transistor bolted to a large heat sink, with a variety of
interfaces.
With or without a mica washer, thermal compound seemed to make very
little difference. Surprisingly, the best conductivity seemed to be with
a thin piece of Izal toilet paper (no mica). However, although we
concluded that thermal compound was probably a very viscous form of
snake oil, it didn't seem to be consistently worse than when it wasn't
used, so we continued to use it in production.
Hello Ian:
The Izal toilet paper you refer to isn't readily available on all
continents. However, might we deduce that almost any toilet paper
might have done comparably?
In all seriousness, does the possibility exist that thermal compounds,
in the mid-1970s, were very inferior to todays offerings?
What you have stated is /very/ interesting.
Thank you.
--
1PW
And my little experiment into modern day snake oil sales, no patent revenue
stream on the use of mica compared to new doobries.
From one of my repair brief files
Kustom KPM6160A mixer amp from 1997
....
The heatsink insulating pads had shrunk,
probably excessive heat, leaving a crumpling
on the uncompressed areas, but all in working order as a pa.
Replaced with mica washers.
Previously took 50 minutes to stabilise at 33 deg C
above ambient pumping 9Vac of 400Hz continuous sine
into 4 ohms.
With mica replacements, down to 30 minutes and you
could keep your fingers on the body of the trannies,
too hot previously.
The pads may have chemically failed , but even then ,
mica does not degrade over 10 years.
....
--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/