[Hammarlund] purpose of tube shields

[Kenneth G. Gordon]

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