[R-390] Heat Death

[Les Locklear]

The original tube for the FCU (frequency control unit) was a metal tube, a 
6AC7, later versions used a 6AH6 7 pin miniature glass tube.

Les

-----Original Message----- 
From: Todd, KA1KAQ
Sent: Monday, December 03, 2012 8:08 PM
To: R-390-List
Subject: Re: [R-390] Heat Death

On Mon, Dec 3, 2012 at 5:32 PM, Barry <n4buq at knology.net> wrote:

> > Interestingly there is one application where I found the IERC tubes
> > were a
> > very bad idea. On the Hammarlund SP-600, any of the JX models that
> > have the
> > crystal deck, there is a tube on the backside of that module. It is
> > sideways mounted. IERC shields make that tube run almost hot enough
> > to melt
> > solder (it will definitely melt the skin off of your finger).
>
> I would think that's to be expected since the chimney effect of the shield
> can't work that way.
>

That's exactly right, and why the later IERC shields with the open/tabbed
tops work best, and why you don't want to use a short shield on a tall tube.

But I'm a bit confused as to the original post. Wasn't that particular tube
on the SP-600 crystal module a metal octal based tube anyhow, not a 7 or
9-pin miniature? Even if IERC shields for that type of tube were available,
it would seem redundant even in vertical service.

de Todd/'Boomer'  KA1KAQ/4
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