[Hammarlund] purpose of tube shields

[Bob Camp]

Hi

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).

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

Bob

On Sep 25, 2014, at 2:06 PM, Robert Sauvan <rsauvan at beyondbb.com> wrote:

> Hi all,
> Can someone please explain to me what exactly is the purpose of tube shields? Are they for rf shielding? It seems to me that a major complaint about old tube radios is that they run so hot. As I have been working on my various radios, lately of course my HQ-180, I have spent a lot of time trying to swap tubes to find the "best" one for the radio. Or, even one that works. Of course, you let it warm up for a while to see if it works any better than the last tube you had in there, but, man they are hot! When I leave a shield off for testing purposes, the tube cools off really fast. Seems to me if the tube ran cooler, it might last longer. Im just plain curious!
> 
> Thanks-Bob-W0YBS
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