tube shields

[Patrick]

For what is worth...I have measured the temperature of tubes with black tube 
shields (Military) and shiny ones and the difference is minimal, between 1 
to 3%, depending on tube type.On the other hand, painting the shiny tubes 
with ultra flat black paint obtained the same results. The measurement was 
done using one of these new laser temperature gadgets and the paint used was 
Americas Finest by Rust-Oleum HD2876 ultra blat black..
From: "Kenneth G. Gordon" <kgordon2006 at VERIZON.NET>
To: <HEATH at LISTSERV.TEMPE.GOV>
Sent: Tuesday, November 13, 2007 3:24 PM
Subject: Re: [HEATH-TEMPE] tube shields


> On 13 Nov 2007 at 13:45, EP Swynar wrote:
>
>> Hi Dean,
>>
>> An interesting aside re. tube shields...
>>
>> There was a piece awhile back ("Electric Radio" magazine...?) where
>> some analysis was done on the longevity of common tubes with specific
>> shields attached to them...
>
> Although ER may have reprinted that data, it goes WAAAAAY
> back.
>>
>> If I recall correctly, the ONLY shield that did not reduce tube life
>> due to over-heating was the black-metal military type...
>
> also called the IERC tube shield. These are difficult to get, but can
> be found. I think Fair Radio Sales has some sizes, but not many.
>
>> the common
>> bayonet-attached / internal spring jobbies were death to tubes,
>> relatively-speaking.
>
> Yes. The reason being that they are very shiny inside and out, and
> thus reflect the heat back INTO the tube.
>
>> I'm sure someone with a memory better than mine can enlighten us all
>> further on this...but I guess the bottom line is, for maximum tube
>> life, if you don't require a tube shield in your circuit(s), DON'T USE
>> ONE.
>
> Well, don't use the shiny ones, at least.
>
> The Heathkit shields I have used in the SB/HW transceivers are a
> corrugated metal which has been anodized black inside and out.
> Those do radiate a LOT of excess heat away.
>
> In point of fact, the data you mention was gathered by the military
> some time ago. That particular report, if I remember correctly, also
> stated that simply painting the tube shields with black liquid shoe
> polish, inside (especially), but also outside made a HUGE
> difference in the tube heat.
>
> That data was one reason that Heathkit also changed the final
> amplifier cages in their parallel 6146 rigs from a shiny unpainted
> aluminum to a black-anodized material. Radiates heat away much
> better.
>
> I routinely paint the sides of shields which I install around tube
> compartments with black liquid shoe polish, or with flat black
> enamel.
>
> BTW, the temperature difference between black SHINY paint vs
> black FLAT paint was also significant according to that military
> report.
>
> You want to suck the heat OUT of the tube, not reflect it back INTO
> the tube.
>
> Ken Gordon W7EKB
>
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