[Hammarlund] purpose of tube shields

[Arthur Delibert]

I think they were meant for RF shielding, like the metal-envelope tubes one sees on WW II era receivers. (Researchers discovered during the war that enemy forces could locate our forces by detecting low-power emissions from the internal oscillators of superhet receivers.)  I think it's common practice among boat-anchor hobbyists today to use black shields on oscillator tubes to limit their emissions, and to remove the shields from other tubes.

> 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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