[R-390] New owner with (probably dumb) questions

[G4GJL]

I agree about the ridiculous priced IERC tube shields are going for these
days.Witness Ebay from time to time as a (high end) price guide.
 I have two remedies for this situation which may arouse some thought
amongst the group:

Thought 1
There are many items of none-radio-interest electronic equipment which turn
up from time to time at boot sales, industry sales, rallies (hamfests west
of here) and other suchlike sources.
 I have found that whilst this sort of kit is of no use to us in a pure
radio sense, it will often yield high quality components such as
transformers, chokes, switches, fuse holders, knobs, tubes and , yes tube
screening cans.
 Better quality equipment will often have black high performance tube
shields which can be put to good use in our, shall I say, more desirable
equipment.
Personally I build a lot of my own gear any way, so the source of components
I mentioned is a very valuable one to me. I appreciate this is not everyones
cup of tea, though.

Thought 2
Higher performance in tube shields  is gained mainly by virtue of them being
black. So many plain metal shields have the close fitting spring inserts to
conduct heat away from the tube and will benefit from the following . These
shields can be enhanced simply by painting or spraying them black.
Personally I use a USA product for this, which is a high temperature flat
black spray aerosol paint, intended for renovation of barbecue equipment. It
will easily withstand the tube heat.
 I dismantle the shields and spray all surfaces, inside and out. bulk
spraying will improve your yield per can. Let them dry well, or oven them if
the domestic situation permits, before they are put into use..

73 and peace to you all this Easter

Stingy Pete
G4GJL

----- Original Message -----
From: "blw" <ba.williams@charter.net>
To: "R-390 List" <r-390@mailman.qth.net>
Sent: Monday, April 21, 2003 3:27 AM
Subject: Re: [R-390] New owner with (probably dumb) questions


>
> > Almost all of the R-390's had silver tube shields on them. The IERC's
are a
> > rare item. You can get a set of them but it will significantly increase
your
> > investment in the radio. I am not convinced that they are worth the
money
> > they are selling for these days. Tubes are still pretty cheap ...
> >
> > Enjoy!
> >
> > Bob Camp
> > KB8TQ
>
>
>
> I think that if you are going to spend the money on the black IERC
shields,
> then get the best shields. I used to have a detailed report of lab tests
> that somebody sent the list a few years ago, probably Dr. Jerry. Anyway,
> without finding the specs of the tests, the shiny shields do damage to
tube
> life by reflecting heat back to the tubes. There are 2 types of IERC tube
> shields. The type that doesn't do the job as well are the type with only 3
> or 4 large finger tabs on the inside to contact the tube glass. The good
> shields are the ones with a lot of small, mini fingers to grab the glass.
> Those dissipate the heat more efficiently.  That report had temps from the
> different combinations, etc.
>
> There are only a few tubes that should be shielded. Chuck has those listed
> on his website, or he used to have it up there the last time I looked.
> http://www.R390A.com/. I only shield those that he suggests.
>
>
> Barry
>
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