In a message dated 11/03/2005, charles.r.patton@........ writes:

Hi-stability oscillators use proportional oven control techniques such  as a=
=20
copper container that has a heater coil and sensing. Then the ckt is  inside=
=20
with some insulation. A cheaper variation would be to use aluminum pipe  rat=
her=20
than copper =E2=80=93 not as good in the thermal mass dept., but still prett=
y  good=20
thermal conductivity.
Hi Charles,
=20
    The thermal mass per unit volume shows much less  variation than one=20
might expect - 2.6 for Al and 3.5 for Cu. However, the  thermal conductivity=
 may=20
be quite a bit lower for alloys than for pure  metals. A lot of metal sold a=
s=20
'Aluminum' is actually an Al + Silicon  alloy.

A very  simple way to reduce air current variation is to put your circuit in=
=20
a small,  open-top box and pour in clean, dry, sand. I like #30 silica sand=20
(the fine,  white sand you see in hotel lobby ash-tray cans), about $4 for a=
 50=20
lb. sack  at Home Depot. Also helps with microphonics =E2=80=93 if you have=20=
them. Just=20
pour out  the sand to work on the circuit.
    Do check to see that the sand is washed free of any  salts. The circuit=20
board may be protected with a coat of single pack  polyurethane varnish. Thi=
s=20
melts under a soldering iron, so the circuit can  be repaired if necessary.=20
Putting the board inside a thin polythene bag is an  alternative to to varni=
shing=20
and keeps sand out of any connectors, IC  sockets.



Another method is to fill the container with melted  paraffin wax - at about=
=20
58 C. This will make the circuit water proof and allows  reasonably good=20
thermal contact. A mixture of half and half candle wax and bee's  wax may al=
so be=20
used, giving less shrinkage. =20
=20
    Regards,
=20
    Chris Chapman





In a message dated 11/03/2005, charles.r.patton@........ writes:
<=
FONT=20
  style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000=20
  size=3D2>Hi-stability oscillators use proportional oven control techniques=
 such=20
  as a copper container that has a heater coil and sensing. Then the ckt is=20
  inside with some insulation. A cheaper variation would be to use aluminum=20=
pipe=20
  rather than copper =E2=80=93 not as good in the thermal mass dept., but st=
ill pretty=20
  good thermal conductivity.
Hi Charles,
 
    The thermal mass per unit volume shows much les=
s=20
variation than one might expect - 2.6 for Al and 3.5 for Cu. However, the=20
thermal conductivity may be quite a bit lower for alloys than for pure=20
metals. A lot of metal sold as 'Aluminum' is actually an Al + Silicon=20
alloy.
<=
FONT=20
  style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size=
=3D2>A very=20
  simple way to reduce air current variation is to put your circuit in a sma=
ll,=20
  open-top box and pour in clean, dry, sand. I like #30 silica sand (the fin=
e,=20
  white sand you see in hotel lobby ash-tray cans), about $4 for a 50 lb. sa=
ck=20
  at Home Depot. Also helps with microphonics =E2=80=93 if you have them. Ju=
st pour out=20
  the sand to work on the circuit.
    Do check to see that the sand is washed free of=
 any=20
salts. The circuit board may be protected with a coat of single pack=20
polyurethane varnish. This melts under a soldering iron, so the circuit=
 can=20
be repaired if necessary. Putting the board inside a thin polythene bag is a=
n=20
alternative to to varnishing and keeps sand out of any connectors, IC=20
sockets.

 

    Another method is to fill the container with me=
lted=20
paraffin wax - at about 58 C. This will make the circuit water proof and all=
ows=20
reasonably good thermal contact. A mixture of half and half candle wax and b=
ee's=20
wax may also be used, giving less shrinkage.  
 
    Regards,
 
    Chris Chapman