[R-390] Re: [R-390]IERC shields (was New owner with...)

[Todd Bigelow - PS]

blw wrote:

>Found that older reference to tube shields. This was a long thread in 1999
>and 2000. Maybe someone has the info on the pros/cons of cutting on the tube
>shields??? Wasn't that about berylium, or some other nasty metal?  I need
>more coffee before I finish beating horses.
>
>Barry
>  
>
Barry and group -

To the best of my knowledge, the nasty part is the insert itself, not 
the shield. Don't hold me to that though, because I didn't build 'em! 
The thinking on shiney shields is that they weren't really intended as 
shields so much as holders to keep the tube in place for gear used in 
harsh environments (like on a battleship with 16 in guns firing). Makes 
sense when you look at the bayonet base and spring in the top to keep 
downward pressure on the tube. Whatever the case, it sure doesn't look 
like removing heat was a consideration.

Here's my view of cutting them (IERC): Don't. They are designed a 
certain way to perform a certain way. Altering the shape could 
potentially mess this mechanism up and defeat the purpose. Now, having 
said that, here are some other thoughts:

-Use the correct size shield for the correct tube size. Or, don't use a 
shield designed for a short 9-pin on a 6U8A (slightly taller, 
medium-height 9-pin). I've seen this recently on an SP-600 listed via 
ePay. If you look at the tubes, you'll see that the shorter shield is 
snug to the top of the tube. This defeats the chimney or convection of 
heat being sinked away from the tube and passing up and out of the 
shield. You get the false security of having an IERC shield 'protecting' 
your tube, yet in reality it's just keeping heat in. Looks fancy, but 
doesn't work. One exception would be the later IERC types with the open 
sides. I've never seen these in the shorter 9-pin configuration, though. 
Still, the inner fingers have to align properly with the tube. If you 
tried using a tall 7-pin on a stubby 6AL5 for example, it wouldn't work 
worth a damn. Best thing to do is to take the different sizes and 
inspect them side-by-each. You'll quickly see the difference.

-WPM sockets work well also, just not as well as the IERC types. WPM are 
more along the lines of the ELCO/EBY/CINCH bayonet-base shiney shield, 
except they are black with inserts. I have a bunch of these in older 
equipment, I'm thinking of enlarging the top opening just a bit with a 
reamer to allow better airflow up through the inserts. There's a reason 
the IERCs have a wider mouth at the top.

-Some of the shiney shields actually have great inserts in them. I've 
always wondered how a shield with a shiney exterior and black interior 
with an insert would fair. Shiney exterior = reflects external heat 
floating around inside the radio instead of absorbing it. I have to 
guess that the engineers who came up with the IERC designs knew what 
they were doing, so I've never pursued it.

- Heatsinks/inserts for bases are important also. Somewhere between the 
shiney shields and the IERC types, these were used to pull heat away 
from the pin bases were too much heat can cause the seals to fail 
accompanied by loss of vacuum and the associated darkness within the 
tube. I've seen only a few IERC bases made to work with the IERC 
shields, and therefore conclude that the more standard IERCs were 
perhaps made to replace older types (or work with existing designs) and 
offer an improvement in cooling.

- Prices are only as bad as you're willing to pay. Sure, they appear on 
ePay for big $$ and if you want the convenience of not having to look 
around and can afford the price, it's a deal made for you. If your 
budget won't permit or you're a packrat at heart though, there are 
always the usual sources: old avionics, defunct test equipment, etc 
often yeild these nice, black tube shields. It involves being patient as 
well as looking around at surplus outlets, under tables at hamfests, or 
even dumpster diving. Where do you think the dealers who sell them 
online are getting them? Just remember when cannabilizing an old piece 
of gear to also retreive the little 'band of fingers' from the tube 
socket bases, if they're in the unit. Always check!

Now, a couple years back a few of us put together a deal on here which 
yeilded a lot of these shields. I'm fairly well set myself for now, 
although I could use a few of the taller 9-pin types. IIRC, there where 
3 of us - Bill Cotter, myself, and one other person whose identity 
escapes me. We mainly traded with other list members, with trading being 
the preferred method, selling being the second choice (Bill sold a 
bunch, though). If there's enough interest and enough people have at 
least some amount of surplus they'd like to trade for sizes they need, 
we could try it again. Sizes are(from memory, don't yell if I'm wrong):

5015 - short 7-pin (6AL5/5654 etc)
5020 - medium 7-pin (6BA6)
5025 - tall 7-pin (6AQ5 etc)

6015 - short 9-pin (6AK6?)
6020 - medium 9-pin (6U8A, 12AX7 etc)
6025 - tall 9-pin (12BA7, 3TF7, etc)

So....any interest?

de Todd/'Boomer'  KA1KAQ