Andrew, do you know what the thermal conductivity of beeswax is?
Alan

http://www.fao.org/docrep/w0076e/w0076e12.htm
Bruno
Thanks (or is it Danke)
Very informative.
Alan

In article ,
Alan Peake wrote:

Andrew, do you know what the thermal conductivity of beeswax is?
Alan


Nope. Is it remotely relevant to this application?

Andrew VK3BFA

It could be. One problem with temperature compensation is that the
various components of an oscillator have differing thermal masses,
thermal conductivities and hence thermal time constants. So it helps to
have everything thermally connected so all component values change at
the same rate.
If beeswax conducts heat well, then potting the oscillator with it would
assist temperature stability.
Alan



The beeswax also stabilizes the components so they don't vibrate for
whatever reason. Vibrations can induce changes in values for susceptible
components resulting in modulation of the output frequency.

Al

Yukio YANO wrote:
Andrew Mitz wrote:

"Larry Gagnon" wrote in message
newsan.2004.12.15.21.21.27.858623@fakeuniserve .com...


I gather the beeswax is to ensure rigid components to maintain
stability of the oscillator? Any other reasons for it? Is it
necessary for me to remelt the old wax and spread it around as
before, or can I get away with just reshielding the VCO?

Any suggestions appreciated.

Larry VE7EA


I have repaired a number of Epoxy Potted VCO modules by simply resoldering ALL of the PCB board connections !
The source of the problem is difference in the Coefficient of Expansion
between the Epoxy potting compound and the PCB and the solder
connections. Close inspection (under a microscope) will show that the
joints in question have been fractured by repeated thermal cycling. Hand
resoldering, rather than the original Wave-Soldering will produce a
much stronger bond between the component leads and the PC board and
reduce the problem.

Yukio YANO VE5YS

Thats a good point, Yukio - BUT...... its usually a major job to get to
the bottom of the vco module anyway - (it was in the 480R I did) - to
just resolder, then re-assemble into the board would have been easier,
but it would also have meant another load of massive thermal stress on
everything if it DIDNT work, or failed again. Thats why I did the
chisel out and replace job.

I did manage to establish (by using a steel probe and poking) it was
one of the epoxy potted on board transistors - I wonder if the two
epoxy mixes were pulling and pushing each other apart?

Interesting speculation - I just fix the things based on 20 years of
stuffing around, burning fingers, and cursing pig ignorant engineers
who design radios without thought of serviceability!

And if you have the right iron (a big one) and can solder well, its not
really a problem to do - just tedious, but worth it for a long term
fix.

Andrew VK3BFA.

Andrew, do you know what the thermal conductivity of beeswax is?

http://www.fao.org/docrep/w0076e/w0076e12.htm

Very informative.

http://www.kayelaby.npl.co.uk/genera...2_3/2_3_7.html is also
interesting, especially if you follow the link to the polymers page at
http://www.kayelaby.npl.co.uk/chemis..._1.html#3_11_1

It looks as if beeswax and paraffin both have thermal conductivities
of about 0.25 ( when measured in W / (m K) ), and that epoxy cast
resins are in the range of 0.17 - 0.21.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

Alan Peake wrote:

It could be. One problem with temperature compensation is that the
various components of an oscillator have differing thermal masses,
thermal conductivities and hence thermal time constants. . .

This is one of several reasons that the best approach in designing an
oscillator -- or any other temperature sensitive circuit -- is to use
components that each have as small a temperature coefficient as
possible. That is, first minimize the inherent drift. Then, if you must,
compensate what drift remains.

Roy Lewallen