[Boatanchors] Tube shields CORRECTION

[rbethman]

The only reason I suggested the 120VAC high RPM types is that there is 
an abundance of them from Computer racks, and a BIG surplus of them from 
old S-100 Bus computers.

I have a large number of them from such sources.  We used to replace the 
S-100 ones whenever owners complained about vibration.

I managed to replace them as instructed, then open the bushing cover and 
oil them.

They last for a very long time.  One bank of six came off an AT&T data 
comm box.

They upgraded the box and left the bank of them behind.  Serves well 
when in the kitchen, placed in the window while baking.

Bob - N0DGN

On 5/26/2014 1:59 PM, hwhall at compuserve.com wrote:
>
> 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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