On 12/25/2010 9:18 PM, Ron Youvan wrote:
>>> I have an obviously commercially made 4-1000 chimney that is aluminum,
>>> so that could be fashioned. Shame to imprison a beauty such as a 4-1000.
>>> Using a metal chimney might bring some comments out of the woodwork,
>>> though, after all the discussion on heat and reflections. At least it
>>> might be easier to fabricate.
With the metal chimney I'd be more concerned about stray capacity than
absorption or cooling.
>>> Remember, I am just reporting - not advocating, although I do plan it
>>> use it in my unfinished 4-1000 amp.
> Several commercial cavities that I worked on had a very thin "fiber glass
> + epoxy" cylinder that
> dropped down around the fins, it was a sheet that was glued into a cylinder
> with a white cement I
> was once told it was done with "dental cement." ??? They were 1/32" thick or
> thinner.
> G-10 has been known to support combustion, most of the fiber glass + epoxy
> that I have found near
> high Voltage was made with a white hard glue that looked like white epoxy,
> but obviously is different.
There are many ways of making or repairing chimneys. I was not joking
when I mentioned earlier about a ceramics class. A non conductive
chimney made of fired clay would be quite practical and with a bit of
reinforcement quite strong. Another is the chimney made of silicone
rubber wrapped and glued using silactic RTV (TM). These chimneys are
durable, long lasting, and rugged. Fiberglass and resin OTOH are not at
all rugged when heat is taken into consideration. it depends on the
resin used as to the "critical temp", or softening point. Vinyl Ester
which has a much lower viscosity (is thinner or more runny) allows for a
thicker cloth or more dense weave making a much stronger layup as well
as having a notably higher critical temps. Dow Derakane is one of these.
None these make a really good replacement for a glass chimney for what
should be obvious reasons. The glass transmits radiant energy freely.
Silicone rubber and fiberglass both absorb this energy almost as
readily. That means they need a wider spacing from the tube envelope and
more air to keep the new chimney cool. How well the forced air cools
the chimney remains to be seen, but fiberglass, silastic rubber (TM) and
even ceramic used on a glass tube is an entirely different proposition
compared to using them on external anode/metal tubes.
I think the earlier suggestion make by some one to use cut large glass
jars such as pickle jars is probably both the best and cheapest approach
although it does take a bit of practice to make a good one. Done with
care you can get the straight sides and slight curve in at the top to
cool the anode seal..
73
Roger (K8RI)
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