[Hammarlund] Re: [R-390] Re: Tube shields? We don’t need any stinking tube shields!

[Les Locklear]

 "In many cases, these inserts were
retro-fitted to shields that were not necessarily made for them -- i.e.
no crimp stop near the top of the shield to keep the insert from riding
up too high when the shield is installed."

Exactly the case with the ones tested, the tube shields tested were 
retrofitted with the "accordion" type (better description than waveform) 
beryllium inserts.

Les Locklear
Gulfport, Ms.
DX'ing Since '57
http://www.hammarlund.info/


----- Original Message ----- 
From: "Barry Hauser" <barry at hausernet.com>
To: "Les Locklear" <leslocklear at cableone.net>
Cc: "rbethman" <rbethman at comcast.net>; <r-390 at mailman.qth.net>; 
<Hammarlund at mailman.qth.net>
Sent: Monday, December 03, 2007 5:44 PM
Subject: [R-390] Re: Tube shields? We don’t need any stinking tube shields!


> Originally, it was my impression that the "finger" style inserts were 
> best, but I later thought that the pleated type -- which I suspect you 
> call  the "waveform" style should be theoretically better.  To be clear, 
> these are sort of accordion folded sheet beryllium copper. The are formed 
> such that they make nearly 100% contact with the glass -- OK, maybe nearly 
> 90% and maybe 80% with the inside surface of the shield.
>
> A variable that may be important with this type in particular -- any 
> perforations at the base of the shield and, maybe more important -- the 
> flange, if any at the top of the shield.
> Ideally, these would provide maximum thermal physical contact between the 
> two, while, at the same time, allow for maximum convection cooling --  
> vertical "chimney" effect -- from the base of the tube and shield out the 
> top of the shield.
>
> Best Laid Plans of Mice & Men Dept.:  If combined with a shield with a 
> large top flange AND the insert located high up, might well block the 
> airflow, resulting in heat buildup.  In many cases, these inserts were 
> retro-fitted to shields that were not necessarily made for them -- i.e. no 
> crimp stop near the top of the shield to keep the insert from riding up 
> too high when the shield is installed.
>
> Another factor, that would be more important with the pleated type -- 
> actual quality of the heat sinking to the glass and the inside of the 
> shield.  While it provides for maximum insert to glass contact, it is 
> susceptible to dirt or painted labeling on the glass.  If there is raised 
> painted labeling, that could keep quite a bit of it lifted.  To maximize, 
> the paint should be removed with solvent.
>
> The shields vary in how they mesh with the shield mounts on the chassis. 
> A standard bayonet mount makes maximum contact, but also closes off 
> venting.
> I suspect the finger type are better all around because the fingers either 
> cut through the paint, get around it, etc., and sort of hedge all bets. 
> The pleated type makes greater contact but is essentially double or triple 
> ply and there may be a blanketing/insulation effect with them.  However, 
> if the tube is clean, and they are used in a shield that has little or no 
> flange at the top, I suspect they should be comparable to the finger type. 
> Some of the IERC shields have a very narrow lip at the top and some have 
> none at all.
> I have one of those gun thermometers -- same brand, but lower model 
> without the laser aiming.
> Bottom line though -- if electrical/signal shielding isn't needed (to 
> avoid spurious effects, whatever), the best bet is no shields -- with some 
> form of forced air cooling -- like well-positioned muffin fans.
>
> Also, the convection model is a bit upset for all those tubes that are 
> upside down ;-)
>
> Well, I've run out of time.  I have to go calibrate my fly-spec-ometer so 
> I can check out some ground condiments, which are suspect due to the 
> country of origin.
>
> Barry
>
>
>
>
>
>
> Les Locklear wrote:
>> If I had a bunch of the "Real" IERC shields, I would use them, but I'm 
>> not about to pay the price they seem to sell for these days. No shields 
>> seems to work for me.
>>
>> Les
>> ----- Original Message ----- From: "rbethman" <rbethman at comcast.net>
>> To: "Les Locklear" <leslocklear at cableone.net>
>> Cc: <r-390 at mailman.qth.net>; <Hammarlund at mailman.qth.net>
>> Sent: Monday, December 03, 2007 4:40 PM
>> Subject: Re: Tube shields? We don’t need any stinking tube shields!
>>
>>
>>> Les,
>>>
>>> While I do not have the sophisticated temperature measuring 
>>> capabilities, I have long suspected that the results you've posted was 
>>> the case.
>>>
>>> I long done away with those pesky shields, both in R-390As and SP-600s.
>>>
>>> They DO seem to run cooler!
>>>
>>> Bob - N0DGN
>>>
>>> Les Locklear wrote:
>>>> Groups,
>>>>
>>>> This test was done using a Raytek laser digital thermometer. 
>>>> Temperatures were taken from a 6BZ6 1st RF amp tube on a John R. Leary 
>>>> SP-600JX no suffix number, serial number 1262. Ambient room temperature 
>>>> was 75°F. I’m not a scientist nor should this be misconstrued as a 
>>>> scientific test. I have always been curious as to whether the IERC tube 
>>>> shields “actually” prolong tube life. As noted there were several 
>>>> different tube shields used in this “test.” Also note there are several 
>>>> different types of inserts inside these tube shields.
>>>>
>>>> The “Real McCoy” IERC Tube Shields have a finger grip type of insert 
>>>> that acts as a heat sink and the test results show that the temperature 
>>>> difference between the shield and the tube itself is little. That 
>>>> should tell us that that type of shield is the “Standard.” For your 
>>>> information, I don’t use tube shields and my tubes seem to last a long 
>>>> time.
>>>>
>>>> Take this information as it’s meant to be, strictly informational.
>>>>
>>>>  1.. Shiny metal Eby tube shield no insert. 94°, bare tube 124°F.
>>>>
>>>>
>>>>  2.. Shiny metal Eby tube shield with seven-sided black aluminum 
>>>> insert. 96°F, bare tube 127°F.
>>>>
>>>>
>>>>  3.. Dull metal Elco tube shield no insert.108°F, bare tube 135°F.
>>>>
>>>>
>>>>  4.. Black heat resistant painted Eby tube shield no insert. 104°F, 
>>>> 126°F bare tube.
>>>>
>>>>
>>>>  5.. Black anodized Eby tube shield with “waveform, nine ridges” 
>>>> aluminum black heat shield insert. 107°F, bare tube 127°F.
>>>>
>>>>
>>>>  6.. Collins black anodized tube shield with “waveform, nine ridges” 
>>>> aluminum black heat shield. 100°F, bare tube 122°F.
>>>>
>>>>
>>>>  7.. W.P.M. tube shield with five-sided aluminum insert. 106°F, bare 
>>>> tube 118°F.
>>>>
>>>>
>>>>  8.. IERC tube shield with “finger grip” type beryllium insert. “The 
>>>> Standard.” 102°F, bare tube 104°F. ( has to be the insert)
>>>>
>>>>
>>>>  9.. Bare tube, no shield. 6BZ6 114°F.
>>>>
>
>
>
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