[Boatanchors] Tube shields CORRECTION

[rbethman]

Jim,

You are so right!

The vast majority of these old BAs would do much better with removing 
these shields that do NOT have RF issues and installing a muffin fan to 
take the heat out.

Either computer CPU fans with a 12VDC rating at VERY low current draw, 
or a 120VAC one with a large sand resistor that drops the RPM so that 
noise doesn't become an issue.

Bob - N0DGN

On 5/26/2014 12:19 PM, Jim Wilhite wrote:
> Correct me if I am wrong, but I don't think the purpose of those shiny 
> shields was to aid heat transfer.  My recollection is they are to 
> prevent the tubes from emitting a signal of any sort and came into 
> being because of WW2.  Moral receivers on shipboard require 
> extraordinary shielding to prevent submarines from hearing the 
> oscillator and mixer signals so the shields were developed for 
> miniature tubes following the metal tube of WW2.
>
> Those metal tubes with the octal base are nothing more than miniature 
> tubes in the can with (usually) pin 1 grounded to prevent radiation.  
> I would surmise that following the war manufacturers continued with 
> various shields should subsequent wars break out like Korea which they 
> thought might flare up to a world conflict.
>
> Jim
> W5JO
>
> -----Original Message-----
> There are a number of people who have tried painting the "shiny" 
> shields with flat black paint, both inside and outside, that have 
> found a reduced tube temperature.  Over the years, I have tried this a 
> few times and the temperature of the tubes did seem to be lower.  
> However, I never actually measured the temperature and, as such, the 
> reduction in temperature is more anecdotal than scientific.
>
> ______________________________________________________________
> Boatanchors mailing list
> Home: http://mailman.qth.net/mailman/listinfo/boatanchors
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Boatanchors 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
>