[Hammarlund] purpose of tube shields

[Howard Weeks]

In military tactical radios, a major purpose of the shields is to keep 
the tubes from falling out of the sockets (or loosening). A tactical 
vehicle, tracked or wheeled, could easily shake a tube or any other 
component that was plugged in out of the socket.

Howard in GA

On 9/25/2014 6:43 PM, Robert Sauvan wrote:
> Well,
> This has been very interesting for sure, but I will have to say, and you
> all know quite well, that I am not an electronics guru by any means
> whatsoever. It seems to me, after reading the numerous replies, why
> would a shield be put over something that needs to dissipate heat
> outwards. That just doesnt really make a whole lot of sense to me. Take
> the HQ-180 I am working on right now. The case around all of the tubes
> is huge in cubic area compared to what is housed in it. Seems to me, the
> tubes have plenty of room to let out steam inside the box and then out
> the top which is completely filled with venting holes. I would think
> because those shields are very tight to most tubes, this would just get
> hotter because of the metal, instead of the tube just venting if you
> were to not have the shield on it. The black paint idea kinda helps the
> heat dissipation argument though. Hummm. I kinda have to lean more
> toward an issue of helping keep rf in check.I remember reading
> somewhere, and I think it was an article about an HX-50, the guy was
> having trouble with some self oscillation issue and someone else pointed
> out that he needed to be sure his tube shields were tight and making
> good contact. So, now that I know both sides of the story, I might just
> see what happens if I leave the tube shields off for a bit and maybe do
> some experimenting with temperatures just for the grins and see what
> happens. But, how can one doubt the technology that has been around for
> 50 years and more. We are still playing with these old radios and they
> work purdy darn good I would say!! You guys are great and thanks for the
> info.
>
> 73-Bob-W0YBS
>
>
>
> On 9/25/2014 1:51 PM, Arthur Delibert wrote:
>> 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
>>> ______________________________________________________________
>>> Hammarlund mailing list
>>> Home: http://mailman.qth.net/mailman/listinfo/hammarlund
>>> Help: http://mailman.qth.net/mmfaq.htm
>>> Post: mailto:Hammarlund at mailman.qth.net
>>>
>>> List Administrator: Duane Fischer, W8DBF
>>> ** For Assistance: dfischer at usol.com **
>>>
>>>
>>> This list hosted by: http://www.qsl.net
>>> Please help support this email list: http://www.qsl.net/donate.html
>>>
>
> ______________________________________________________________
> Hammarlund mailing list
> Home: http://mailman.qth.net/mailman/listinfo/hammarlund
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Hammarlund at mailman.qth.net
>
> List Administrator: Duane Fischer, W8DBF
> ** For Assistance: dfischer at usol.com **
>
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>