[Hammarlund] purpose of tube shields

[Robert Sauvan]

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