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

[Barry Hauser]

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.
>>>