[Amps] Cracked Chimney

[Jeff Blaine]

I would be worried about using a plastic around this tube where the HDT (heat deformation temp) is unknown - the "problem" with the 
glass tubes is that a good amount of their disipation is by radiation rather than conduction - which means, no matter how fierce are 
the cooling winds that are blowing, the plastic is going to be bombed with a ton of IR from the tube.

The cooling fan flow will help to keep the surface of the plastic facing the tube from melting in the worst case, but I have got to 
wonder what the long term prospect would be for the plastic surround material.  The more transparent it is, the less the problem 
would be (because it will absorb less heat) - but what's transparent to visible light does not necessary mean IR transparency.  And 
in the event the fan were to fail, you would have your own melt-down of that envelope even if it's made from PC (HDT 125c?).  What a 
mess it could be in the wost case...

A glass envelope of some kind seems the way to go for this application - and it has the advantage of letting the sweet glow out into 
the shack if there were to be a suitable window into the RF cage.

73, Jeff ACØC
www.ac0c.com

-----Original Message----- 
From: Ron Youvan
Sent: Saturday, December 25, 2010 8:18 PM
To: amps
Subject: Re: [Amps] Cracked Chimney

>> 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.

>> 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.
-- 
    Ron KA4INM - I'm proud to be Chuck's pop!
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