AB9GO wrote:

On Nov 23, 3:43 pm, Eeyore
wrote:
Peter Elem wrote:
AS with $5 vacuum tubes, $150 audio vacuum tubes sometimes fail at an early
age.........One culls them out and often very old tubes just keep on going
fine. 12AX7's have become "fools gold" in this inflated acoustic
psycho-babble golden ear but tin brain market...........

Do their brains suffer from tin pest ?http://en.wikipedia.org/wiki/Tin_pes...try.php?id=310

Graham

That's funny! I buy all of the old 60/40 solder I can find because if
the tin dendrite issue that will be comming in the future. Tin
dendrites have been known to grown to over 10mm in length. That is
why NASA and critical biomed devices (pacemakers and ICD's etc) will
continue to use lead in their solder, and so will I for as long as I
have a supply.

Likewise.

You can still get it legally even in the EU for repair of pre PB-free equipment.


Randy AB9GO

Current carrying capacity of dendrites
Bjorndahl, W.D.; Lau, J.C.
Aerospace Applications Conference, 1994. Proceedings., 1994 IEEE
Volume , Issue , 5-12 Feb 1994 Page(s):399 - 405
Digital Object Identifier 10.1109/AERO.1994.291179
Summaryendrites are sometimes found on electronic hardware during
failure analysis or trouble shooting activities. Problems due to
dendrite formation can vary from catastrophic failure to occasional
electronic glitches. If a dendrite is thought of as a fuse in a
circuit, then it is apparent that it can have, depending on size, a
wide range of current carrying capability. Mathematical modeling and
experimental analyses were conducted to determine the reasons for the
wide range of observed behavior. Mathematical modeling indicates that
the resistivity of the dendrite and the thermophysical characteristics
of the substrate on which it is grown determine its current carrying
capacity. More specifically, the modeling indicates that maximum
dendrite size and time to failure are determined by the power loss
within the dendrite and the rate at which heat can be transferred away
from the dendrite. Small dendrites are stable and can grow until they
reach a size at which internal heat generation cannot be accommodated
by the heat loss due to conduction through the substrate. Dendrites in
low voltage applications on substrates with high thermal diffusivity
are more likely to lead to failures with high power loss, whereas
dendrites in high voltage applications on low thermal diffusivity
substrates (e.g. tin on glass/epoxy circuit board material) are more
likely to lead to high resistance shorts. Experimental results and
failure analysis observations agree qualitatively and semi-
quantitatively with the results of the idealized dendrite model

Do you have a link for that ? I heard somewhere a typical tin whisker can support 30mA.

Graham