[R-390] New owner with (probably dumb) questions

[blw]

Barry,

Yup, that's the nasty stuff. I use the accordian/pleated ones. More surface
contact vs cooling spaces. I just happened to have enough of those types. I
also have a  few cardboard tube shields with aluminum foil that I've taken
out of cheap plastic radios.


Barry


> The nasty metal is beryllium copper.  Like the meters, it's OK to handle,
> but not to eat.  Seriously though, don't  grind/sand it or cause to become
> airborne dust.
> 
> There are two main aspects of the IERC shields -- black surfaces to reduce
> reflection and heat sinking.  The shields themselves are coated with
> something special or black anodized.  Even so, you'll notice that the lower
> 1/2 inch is shiny/uncoated on the inside, so as to make a good thermal
> connection to the socket mount.  The tube mostly "sees" the heat sink insert
> which is blackened.  It's actually better if the inside of the shield itself
> is bare to maintain good thermal coupling to the insert. It should not be
> heavily coated.
> 
> I've seed 3 major styles of heat sink inserts -- simple 5-or 6-sided
> cylinders, the "finger stock" style with lots of springy contacts stamped
> into the insert, and the pleated type, which is a kind of accordion fold.
> I'd imagine these vary in terms of effectiveness of heat-sinking vs.
> ventilation, with a trade-off.  The simplest 5-sided ones allow maximum
> direct cooling -- vertical airflow, but minimize the area contact between
> the glass and the heat sink.  The finger-type improve on the thermal
> coupling and still allow for a lot of convection.  The accordion pleated
> type maximizes the glass to heatsink area, but might limit direct convection
> cooling from the glass. However, the pleats run vertically and there's
> probably a good deal of convection through the insert as well as heat
> conducted away through the metal to the shield.
> 
> There's a another variation on the design of the shields themselves.  Most
> shiny shields have a substantial flange which retains the spring at the top.
> This reduce the top opening and probably affecting convection cooling
> somewhat.  The IERC's usually don't have springs and there is typically a
> minimum kerf on the top so it maintains it's shape and the insert has
> something to back up against.  I've seen some without the kerf, with small
> stampings to retain the insert.
> 
> Lately, I've come across quite a few shiny shields with the pleated type of
> insert.  I would imagine that performance is nearly the same as an IERC
> type.  So, look inside before you cast them aside.  I don't know if they
> were originally equipped that way or upgraded after the fact.
> 
> As for painting -- particularly with barbeque or engine paint -- I don't
> think that's a good idea.  Regular coatings serve as a thermal insulator, so
> the whole shield would tend to retain more heat inside.  At minimum, mask
> off the bottom inside surface.  Best to use some other blackening method,
> like gun bluing.  Anyone ever try that?
> 
> Barry