tube shields

[Garey Barrell]

Consider that what we are interested in is the  _efficiency_  of the 
shield to transfer heat to the air surrounding it, NOT the actual 
temperature of the shield itself.  A black surface absorbs AND radiates 
heat more effectively than a white or shiny surface.

73, Garey - K4OAH
Glen Allen, VA

Drake 2-B, 4-B & C-Line Service Supplement CDs
<www.k4oah.com>



Patrick wrote:
> 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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>
>

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