[Hammarlund] purpose of tube shields

[Les Locklear]

Removing the tube shields completely cools even better. I have IERC shields 
on a couple of receivers,
the others have none. Unless you are transmitting close by and don't want
to spring for the pricey IERC shields, simply remove them.

Les

-----Original Message----- 
From: Kenneth G. Gordon
Sent: Friday, September 26, 2014 11:07 AM
To: Hammarlund Mail List
Subject: Re: [Hammarlund] purpose of tube shields

On 25 Sep 2014 at 21:03, Bob Camp wrote:

> As mentioned in other replies, the main reasons are for shielding and 
> physically
> locking the tube in place. Sometimes you see "hollowed out" tube shields 
> that
> are just a skeleton to keep the tube in place (hold down but no shield).

Yes. I have a whole box of those in various sizes. They are not particularly
useful to me...

> If you want to really dissipate heat, there are shields made for that 
> purpose.
> They are dead black well into IR wavelengths. They also have an 
> arrangement to
> make the shield directly contact the tube envelope. Usually that´s with an
> accordion pleated aluminum insert, there are other approaches. The contact 
> and
> black on the inside get the heat off the envelope and out of the inside. 
> The
> black on the outside helps it radiate heat better.

Yes. Those are the so-called IERC tube shields I mentioned earlier. Some
were made by manufacturers other than IERC, but that is their common
name.

> Do they work - sure. Are they
> expensive - yup.

Are they very hard to find? YUP! :-(

According to a link someone posted here, those reduce the heat in the tube
by between 25% and 38%.

According to my experiment, painting the tube shields with flat black paint
reduces the heat by 17% on average, and it is a lot cheaper.

Ken W7EKB
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