[R-390] Tube shields

[Barry Hauser]

I've seen quite a few shiny shields with the accordion pleat type of 
beryllium copper insert in them.  Not sure if they were retro-fit or not. 
Same for the flat, hex-type.  I don't recall seeing any with the fingerstock 
style of insert.  The retrofitted ones usually reveal theselves when you 
remove them and the insert stays on the tube.  Of course, there could have 
been an arbor jig where they made those indentations after the fact.

My take is that the "silver" shields with the inserts -- preferably finger 
or accordion - -should be fairly close to full IERC shields in dissipation. 
However, other factors -- the stock shields have a rather large flange which 
can block the air channels and generally impede airflow -- and the IERC 
shield are made of aluminum or some similar alloy which may have better 
heatsinking characteristics than plated steel.  But, I think the insert is 
most of the benefit and they also provide the black/nonreflective surface, 
nearly the same as the inside of an IERC shield in that respect.  BTW - even 
the IERC's vary in terms of inserts and flange size.  Some have no lip on 
the top at all -- just a piece of rolled up aluminum.

We may be overdue to dig up the ol' tube shield pony and start whippin' it 
again.  Been a while.  Keeps 'em from spoilin'.

Barry
----- Original Message ----- 
From: <odyslim at comcast.net>
To: "Cecil Acuff" <chacuff at cableone.net>; "R390list" <r-390 at mailman.qth.net>
Sent: Monday, May 02, 2005 7:45 AM
Subject: Re: [R-390] Tube shields


> I have a radio that is loaded with them. It is a Collins R390-A
> from the first run, #43.
>
> Scott
>
> -------------- Original message -------------- 
>
>> Hey Folks,
>>
>> Found something interesting this evening while working on an R-390
>> restoration. Found two ELCO tube shields...the silver twist lock kind 
>> with
>> the IERC finger style contacts between the shell and the spring. I 
>> thought
>> at first some wise guy had shoved it up in there to make a somewhat 
>> hybrid
>> IERC tube shield. Upon closer investigation it appears to be factory.
>> There are two folded indentations in the shell that catch the bottom of 
>> the
>> finger contact piece to keep it from sliding out when the shield is 
>> pulled
>> off the tube.
>>
>> Interesting....
>>
>> Is this a new find or are these shields pretty common? First I have seen!
>> Not sure they are any better than the silver variety as far as 
>> dissipation.
>>
>> Cecil....
>>