[Hammarlund] purpose of tube shields

[W2HX]

You have received many responses to this question. I will add one.  I believe there is also the property of adding thermal mass to a tube. This thermal mass should make the tube more temperature stable. For oscillator tubes and other that change characteristics with temperature can benefit from this thermal mass helping to maintain the temperature.

73 Eugene W2HX


-----Original Message-----
From: Hammarlund [mailto:hammarlund-bounces at mailman.qth.net] On Behalf Of Robert Sauvan
Sent: Thursday, September 25, 2014 2:07 PM
To: Hammarlund Mail List
Subject: [Hammarlund] purpose of tube shields

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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