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

[blw]

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


>Bill, KD0HG wrote:
> 
> I've received several inquiries regarding my post here concerning
> IERC tube shields and in response, here's a quick elaboration.
> In ER #66 for October, '94, I described the results of a 1954 ARINC
> [Aeronautical Radio, Inc] and GE tube life studies that were done using over
> 150,000 tubes of 20 different types.
> I provided summaries and graphs of tube life vs. envelope temperature
> for several representative tube types- here are a couple:
> 
> 5654/6AK5W, 200 tube random lots
> The 80% survival of this type was
> 750 hours @ 192 C
> 1500 hours @ 125 C
> 2000 hours @ 100 C
> 
> 6005/6AQ5W
> Over 95% of the 6AQ5 survived 5000 hours of operation
> at an envelope temperature of 220 C, but at only 17 degrees
> hotter fewer than 70% survived even 2500 hours.
> 
> Another chart in the article shows the measured envelope
> temperature of a 12BY7A dissipating 10 watts [including heater].
> Under still air conditions, at room temperature, worst to best,
> >220 C inside a shiny JAN tube shield
> 190 C inside a black anodized JAN tube shield
> 165 C inside a black JAN shield with ventilation slots
> 150 C  bare bulb, no shield
>  82 C  inside an IERC T6-1025H shield/cooler
> 
> The results of these life tests indicate a bare bulb is the way
> to go for reliability's sake, unless one uses the IERC coolers.
> Of course, electrical considerations often mandate
> the electrical isolation of a shield.
> 
> I once read a reference that around 1960, the shiny tube
> shields were removed from the military's QPL listings as a
> consequence of these earlier studies. This does not agree
> with my observation that many pieces of military gear from
> around that time are full of the shiny type of shields, so I don't
> know if this is really true.
> 
> As of the article's press date in '94, IERC was still in
> business and making tube shields and coolers. I don't know about
> today.
> IERC
> 135 W. Magnolia Blvd.
> Burbank, CA 91507
> 
> Best,
> 
> -BK
> Berthoud, Colo.