[Boatanchors] Tube shields CORRECTION

[hwhall at compuserve.com]

or a 120VAC one with a large sand resistor that drops the RPM so that 
noise doesn't become an issue.

 
I've also seen suggestions to use 240vac fans to get lower run noise, and no resistor to heat up. They can probably be bought cheaper than 120vac versions since they are less desirable to most folks.
  

 Wayne

 WB4OGM


-----Original Message-----
From: rbethman <rbethman at comcast.net>
To: boatanchors <boatanchors at mailman.qth.net>
Sent: Mon, May 26, 2014 10:40 am
Subject: Re: [Boatanchors] Tube shields CORRECTION


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.
>
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