[Hammarlund] purpose of tube shields

[Bob Young]

Yes tube shields are and were originally made for RF isolation, they have been in radios since the 20's maybe even earlier. RCA started making metal tubes for the same purpose in the mid 30's. IERC shields were (I think) made for the government for the high tube count receivers. I have most of the tube shields off in my R-390A and SP-600 except for a few crucial ones which need the shielding. I have never seen them in any commercial home receiver.

Bob
KB1OKL

> From: leslocklear at hotmail.com
> To: kgordon2006 at frontier.com; hammarlund at mailman.qth.net
> Date: Fri, 26 Sep 2014 11:16:25 -0500
> Subject: Re: [Hammarlund] purpose of tube shields
> 
> Removing the tube shields completely cools even better. I have IERC shields 
> on a couple of receivers,
> the others have none. Unless you are transmitting close by and don't want
> to spring for the pricey IERC shields, simply remove them.
> 
> Les
> 
> -----Original Message----- 
> From: Kenneth G. Gordon
> Sent: Friday, September 26, 2014 11:07 AM
> To: Hammarlund Mail List
> Subject: Re: [Hammarlund] purpose of tube shields
> 
> On 25 Sep 2014 at 21:03, Bob Camp wrote:
> 
> > As mentioned in other replies, the main reasons are for shielding and 
> > physically
> > locking the tube in place. Sometimes you see "hollowed out" tube shields 
> > that
> > are just a skeleton to keep the tube in place (hold down but no shield).
> 
> Yes. I have a whole box of those in various sizes. They are not particularly
> useful to me...
> 
> > If you want to really dissipate heat, there are shields made for that 
> > purpose.
> > They are dead black well into IR wavelengths. They also have an 
> > arrangement to
> > make the shield directly contact the tube envelope. Usually that´s with an
> > accordion pleated aluminum insert, there are other approaches. The contact 
> > and
> > black on the inside get the heat off the envelope and out of the inside. 
> > The
> > black on the outside helps it radiate heat better.
> 
> Yes. Those are the so-called IERC tube shields I mentioned earlier. Some
> were made by manufacturers other than IERC, but that is their common
> name.
> 
> > Do they work - sure. Are they
> > expensive - yup.
> 
> Are they very hard to find? YUP! :-(
> 
> According to a link someone posted here, those reduce the heat in the tube
> by between 25% and 38%.
> 
> According to my experiment, painting the tube shields with flat black paint
> reduces the heat by 17% on average, and it is a lot cheaper.
> 
> Ken W7EKB
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