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

[Gene Beckwith]

Gents,

In spite of Fest scrounging....if a list effort to make some shields 
available....count me in on the effort...still looking for them...

73,

Gene
W8KXR


Todd Bigelow - PS wrote:

> 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
>
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